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JOURNAL 

OF  THE  SOCIETY  OF 

MOTION  PICTURE  ENGINEERS 

Volume  XXXI  JULY,  1938  Number  1 

CONTENTS 

Page 

A  Criticism  of  the  Proposed  Standards  for  16-Mm.  Sound-Film 

J.  A.  MAURER  AND  W.  H.  OFFENHAUSER        3 

The  Shrinkage  of  Acetate-Base  Motion  Picture  Films 

J.  A.  MAURER  AND  W.  BACH       15 

Processing  of  Ultraviolet  Recordings  on  Panchromatic  Films 

J.  O.  BAKER      28 

An  Optical  System  for  the  Reproduction  of  Sound  from  35-Mm. 
Film J.  H.  McLEOD  AND  F.  E.  ALTMAN      36 

Push-Pull  Recording  with  the  Light- Valve 

J.  G.  FRAYNE  AND  H.  C.  SILENT      46 

Report  of  the  Standards  Committee 65 

The  Influence  of  pR  on  Washing  Films  after  Processing 

S.  E.  SHEPPARD  AND  R.  C.  HOUCK      67 

Problems   Involved  in   Full-Color  Reproduction  of  Growing 
Chick  Embryo E.  S.  PHILLIPS      75 

Documentary  Film  Study — a  Supplementary  Aid   to    Public 
Relations A.  A.  MERCEY      82 

New  Motion  Picture  Apparatus 

An  Ultraviolet  Push-Pull  Recording  Optical  System  for  News- 
reel  Cameras G.  L.  DIMMICK  AND  L.  T.  SACHTLEBEN      87 

Overload  Limiters  for  the  Protection  of  Modulating  Devices 

R.  R.  SCOVILLE       93 

Current  Literature 99 

Fall,  1938,  Convention  at  Detroit,  Mich.;  Oct.  31st-Nov.  3rd, 
Incl 102 

Society  Announcements 105 


JOURNAL 

OF  THE  SOCIETY  OF 

MOTION  PICTURE  ENGINEERS 


SYLVAN  HARRIS,  EDITOR 

Board  of  Editors 
J.  I.  CRABTREB,  Chairman 

A.  N.  GOLDSMITH  L.  A.  JONES  H.  G.  KNOX 

A.  C.  HARDY  E.  W.  KELLOGG  G.  E.  MATTHEWS 


Subscription  to  non-members,  $8.00  per  annum;  to  members,  $5.00  per  annum, 
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Order  from  the  Society  of  Motion  Picture  Engineers,  Inc.,  20th  and  Northampton 
Sts.,  Easton,  Pa.,  or  Hotel  Pennsylvania,  New  York,  N.  Y. 
Published  monthly  at  Easton,  Pa.,  by  the  Society  of  Motion  Picture  Engineers. 

Publication  Office,  20th  &  Northampton  Sts.,  Easton,  Pa. 
General  and  Editorial  Office,  Hotel  Pennsylvania,  New  York,  N.  Y. 

West-Coast  Office,  Suite  226,  Equitable  Bldg.,  Hollywood,  Calif. 
Entered  as  second  class  matter  January  15,  1930,  at  the  Post  Office  at  Easton, 
Pa.,  under  the  Act  of  March  3,  1879.     Copyrighted,  1938,  by  the  Society  of 
Motion  Picture  Engineers,  Inc. 

Papers  appearing  in  this  Journal  may  be  reprinted,  abstracted,  or  abridged 
provided  credit  is  given  to  the  Journal  of  the  Society  of  Motion  Picture  Engineers 
and  to  the  author,  or  authors,  of  the  papers  in  question.  Exact  reference  as  to 
the  volume,  number,  and  page  of  the  Journal  must  be  given.  The  Society  is 
not  responsible  for  statements  made  by  authors. 


OFFICERS  OF  THE  SOCIETY 

'President:    S.  K.  WOLF,  RKO  Building,  Rockefeller  Center,  New  York,  N.  Y. 
'Past-President:    H.  G.  TASKER,  Universal  City,  Calif. 
'Executive   Vice-President:    K.  F.  MORGAN,  6601  Romaine  St.,  Los  Angeles, 

Calif. 

"Engineering   Vice-President:    L.  A.  JONES,  Kodak  Park,  Rochester,  N.  Y. 
'Editorial  Vice-President:    J.  I.  CRABTREE,  Kodak  Park,  Rochester,  N.  Y. 
"Financial  Vice-President:    E.  A.  WILLIFORD,  30  E.  42nd  St.,  New  York,  N.  Y. 
'Convention    Vice-President:    W.   C.   KUNZMANN,   Box  6087,   Cleveland,  Ohio. 
'Secretary:    J.  FRANK,  JR.,  90  Gold  St.,  New  York,  N.  Y. 
'Treasurer:    L.  W.  DAVEE,  250  W.  57th  St.,  New  York,  N.  Y. 

GOVERNORS 

•J.  O.  AALBERG,  157  S.  Martel  St.,  Los  Angeles,  Calif. 
*M.  C.  BATSEL,  Front  and  Market  Sts.,  Camden,  N.  J. 
**R.  E.  FARNHAM,  Nela  Park,  Cleveland,  Ohio. 
*G.  FRIEDL,  JR.,  90  Gold  St.,  New  York  N.  Y. 
*A.  N.  GOLDSMITH,  444  Madison  Ave.,  New  York  N.  Y. 
**H.  GRIFFIN,  90  Gold  St.,  New  York,  N.  Y. 

**A.  C.  HARDY,  Massachusetts  Institute  of  Technology,  Cambridge,  Mass. 
*S.  A.  LUKES,  6145  Glenwood  Ave.,  Chicago,  111. 
*Term  expires  December  31,  1938. 
**Term  expires  December  31,  1939. 


A  CRITICISM  OF  THE  PROPOSED  STANDARDS  FOR 
16-MM.  SOUND-FILM* 


J.  A.  MAURER  AND  W.  H.  OFFENHAUSER** 

Summary. — It  has  been  proposed  that  the  standard  dimensions  of  16-mm.  sound- 
prints  be  changed,  principally  by  widening  the  sound  record  and  scanned  areas.  The 
question  is  reviewed  from  the  standpoint  of  the  cumulative  effects  of  film  shrinkages 
and  mechanical  inaccuracies  in  the  steps  leading  to  the  final  sound-print  and  in  the 
projection  of  that  print,  following  the  method  described  by  R.  P.  May  in  the  April, 
1932,  Journal. 

A  film  having  sound  records  of  various  widths  supports  the  contention  that  in- 
creased width  of  sound-track  is  not  needed,  and  that  if  any  change  from  the  present 
standard  is  to  be  made,  it  should  be  in  the  direction  of  a  narrower  track  to  provide  a 
wider  margin  outside  the  sound-track  and  a  wider  safety  area  between  the  sound- 
track and  the  picture. 

The  present  dimensional  standards  of  sound-film,  both  35-mm.  and 
16-mm.,  reflect  the  fact  that  sound  was  added  to  the  motion  picture 
long  after  these  two  film  sizes  had  been  standardized  for  silent  pic- 
tures. The  silent  film  standards  necessarily  limited  the  amount  of 
space  on  the  film  that  could  be  made  available  for  the  sound.  How 
much  more  space  the  sound  engineers  would  have  liked  to  have  can 
be  seen  by  comparing  our  present  standards  with  the  wide  films 
of  1929  and  1930,  in  which  the  sound-track  was  approximately  three 
times  as  wide  as  the  ones  we  use  today. 

Because  the  space  that  could  be  taken  for  the  sound  record  was 
thus  limited,  a  second  conflict  of  interests  necessarily  arose  between 
two  classes  of  sound  engineers.  What  might  be  called  the  optico- 
photographic  group  naturally  wished  to  use  as  much  of  the  available 
space  as  possible  for  the  sound-track.  At  the  same  time  the  mechani- 
cal engineer  designing  the  sound  equipment  logically  demanded  a 
certain  amount  of  space  for  mechanical  handling  of  the  film  and  for 
providing  tolerances  against  inaccuracies  in  guiding. 

The  compromise  between  the  two  requirements  was  bound  to  prove 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;     received 
May  4,  1938. 

**  The  Berndt-Maurer  Corp.,  New  York,  N.  Y. 

3 


4  J.  A.  MAURER  AND  W.  H.  OFFENHAUSER   [J.  S.  M.  p.  E. 

unstable  in  a  rapidly  advancing  art.  Every  improvement  in  mechani- 
cal accuracy  naturally  encouraged  those  who  wished  to  enlarge  the 
sound-track  at  the  expense  of  the  safety  areas.  Conversely,  every 
improvement  in  film  stock  or  in  recording  or  processing  technic  that 
increases  the  volume  range  attainable  from  the  track  might  serve  as 
an  excuse  for  the  mechanical  designer  to  call  for  a  relaxation  of  the 
narrow  dimensional  limits  that  hold  him,  as  it  were,  in  a  strait- 
jacket.  If  he  does  not  protest,  it  is  because  the  mechanical  engineer 
rarely  lays  claim  to  any  very  complete  knowledge  of  photographic 
and  optical  requirements  in  recording  and  reproduction.  Not  feeling 
sure  of  his  ground,  it  is  only  when  he  is  pushed  too  far  that  he  rebels 
against  the  tendency  to  increase  the  width  of  the  track  at  the  expense 
of  the  safety  areas. 

In  the  JOURNAL  of  the  Society  for  March,  1938,  there  appeared  a 
report  of  the  Standards  Committee1  in  which  a  considerable  number 
of  revisions  in  the  standards  are  proposed  for  adoption  by  the  Society. 
So  far  as  these  revisions  relate  to  sound,  they  consist  mostly  of  in- 
creases in  the  width  of  the  sound-track  areas,  with  corresponding  re- 
ductions in  the  width  of  what  we  have  been  calling  the  safety  areas. 

The  authors  have  studied  with  particular  care  the  proposals  relating 
to  16-mm.  sound-films.  Briefly,  they  feel  that  these  new  proposals 
seriously  unbalance  a  situation  that  was  already  unfavorable  for  the 
mechanical  designer,  and  that  they  do  so  without  gaining  any  per- 
ceptible advantage  in  the  way  of  better  sound  reproduction.  There- 
fore, in  response  to  the  published  invitation2  to  discuss  the  proposed 
revision  of  the  standards,  this  analysis  of  the  problem  is  presented  by 
the  authors  as  they  see  it. 

A  brief  historical  review  may  serve  to  illuminate  several  of  the 
points  at  issue.  The  present  system  of  16-mm.  sound-film  standards 
originated  in  the  proposal  made  by  R.  P.  May3  at  the  Swampscott 
meeting  of  the  Society  in  the  Fall  of  1931.  The  standard  that  Mr. 
May  proposed  was  based  upon  a  careful  study  of  the  various  errors 
in  track  location  that  were  likely  to  occur  in  going  from  a  35-mm. 
original  sound-track  through  the  steps  of  re-recording  on  16-mm.  film 
and  contact-printing  the  resulting  sound  negative,  followed  by  run- 
ning the  print  on  a  projector.  A  study  was  made  also  of  the  case  in 
which  the  sound-track  was  directly  re-recorded  to  the  print.  Adding 
up  the  possible  errors,  Mr.  May  arrived  at  the  interesting  conclusion 
that  a  film  0.660  inch  wide  (instead  of  the  standard  0.630  inch)  would 
be  required  to  accommodate  what  he  believed  to  be  a  sufficiently 


July,  1938]        CRITICISM  OF  PROPOSED  16-MM.  STANDARDS  5 

wide  track,  plus  full  provision  for  overlap  of  the  scanning  beam,  and 
safety  areas  wide  enough  to  provide  for  proper  mechanical  support. 
But,  on  the  assumption  that  all  the  possible  errors  would  hardly  ever 
accumulate  in  one  direction,  it  was  believed  possible  to  arrive  at  a 
workable  standard  within  the  limits  of  the  0.630-inch  film.  The 
standard  that  was  proposed  had  substantially  the  same  track  width 
as  the  one  that  was  adopted  in  1934,  but  placed  the  track  center-line 
0.045  inch  from  the  edge  of  the  film  instead  of  at  the  present  standard 
distance  of  0.058  inch.  A  safety  area  0.0284  inch  wide  was  provided 
between  the  printed  area  of  the  sound  and  the  printed  area  of  the 
picture. 

The  standard  that  was  set  up  in  November,  1934, 4  is  shown  drawn 
accurately  to  scale  in  the  top  half  of  Fig.  1.  It  will  be  noticed  that 
the  safety  area  between  the  picture  frame  and  the  space  allotted  to 
variable-density  sound-track  was  reduced  to  0.012  inch.  On  the 
other  side  of  the  track  was  provided  a  fairly  comfortable  space  of 
0.018  inch  between  the  variable-density  track  and  the  edge  of  the  film. 
But  the  principal  objection  to  this  standard  was  the  small  allowance 
for  sound-track  weave.  The  variable- width  track  was  set  at  0.060 
inch ;  the  scanned  area  was  only  0.065  inch  wide ;  therefore,  the  al- 
lowance for  weave  was  only  0.0025  inch  in  each  direction,  which  is 
insufficient.  So  far  as  the  authors  are  aware,  no  manufacturer  of 
projection  equipment  followed  the  standard  in  this  respect.  Scanning- 
beam  lengths  used  in  practice  varied  from  0.070  inch  to  0.080  inch 
with  different  manufacturers. 

After  1934,  the  process  of  optically  reducing  the  sound-track  from 
35-mm.  negative  to  16-mm.  print  became  the  most  widely  used 
method  of  producing  16-mm.  sound-films.  Certainly  the  excellence 
of  the  results  that  were  attained  justified  the  widespread  adoption 
of  the  method.  But  this  brought  with  it  a  complication  of  the  stand- 
ards problem.  Optical  printers  were  designed  to  reduce  the  0.071- 
inch  variable-width  track  on  the  35-mm.  film  to  a  width  of  0.060 
inch  on  16-mm.  film.  This  ratio  of  60  to  71  gave  a  reduced  variable- 
density  track  having  a  width  of  0.0845  inch  instead  of  the  0.080-inch 
width  called  for  by  the  1934  standard. 

Eventually  the  35-mm.  standard  was  changed  to  specify  a  track 
space  0.076  inch  wide  in  variable-width  recording.  This  track,  on 
the  optical  reduction  printer,  gave  a  16-mm.  print  having  a  track 
width  of  0.0642  inch. 

These  two  dimensions — 0.0845  inch  for  the  variable-density  track, 


J.  A.  MAURER  AND  W.  H.  OFFENHAUSER   [j.  S  M  P.  E. 


.018 


1934 
STANDARD. 


1938 
STANDARD. 


.0155 


012 


.0095 


FIG.  1.     SMPE  standard. 


FIG.  2.     One  form  of  idler  construction. 


July,  1938]       CRITICISM  OF  PROPOSED  16-MM.  STANDARDS  7 

and  0.0642  inch  for  the  variable- width  track — are  substantially  those 
called  for  by  the  1938  specification.  As  was  logical,  the  width  of  the 
scanned  area  has  been  set  at  0.074  inch,  a  value  providing  equal 
tolerances  for  weave  on  the  two  types  of  track. 

Thus,  while  the  1938  proposed  standard  follows  present  commercial 
practice,  it  seems  to  have  been  arrived  at  by  a  process  of  commercial 
evolution  rather  than  by  any  process  of  careful  analysis.  Standards 
arrived  at  in  this  way  are  likely  to  contain  defects  that  will  sooner 
or  later  lead  to  a  desire  for  modification. 

Before  drawing  definite  conclusions,  however,  let  us  analyze  the 
new  standard  step  by  step.  In  the  first  place,  does  it  provide  suitable 
allowance  for  side  motion  of  the  film  and  for  accumulated  inaccura- 
cies in  the  location  of  the  sound-track?  The  method  of  study  de- 
scribed by  Mr.  May  should  give  the  answer. 

The  two  processes  in  use  today — optical  reduction  and  direct  re- 
cording— give  about  equal  opportunities  for  mislocating  the  track. 
Let  us  study  the  optical  reduction  method. 

We  have  35-mm.  film  carrying  a  sound-track  that  is  officially  per- 
mitted5 to  be  0.003  inch  out  of  position,  in  the  direction  toward  the 
picture.  This  film  must  be  guided  through  one  side  of  the  optical 
printer.  If  the  guiding  is  done  by  the  best  available  means,  it  can  be 
made  accurate  to  about  0.001  inch,  but  hardly  better  than  that. 
Thus,  up  to  the  point  where  the  printing  light-beam  passes  through 
the  negative  film,  there  is  a  possible  error  of  0.004  inch  in  the  location 
of  the  35-mm.  track.  Reduced  through  the  optical  system,  this  be- 
comes 0.0034  inch. 

The  16-mm.  film  must  be  guided  also  on  the  optical  printer.  Allow- 
ing again  an  error  of  0.001  inch  in  guiding  the  film,  the  total  possible 
error  in  track  location  on  the  16-mm.  film  becomes  0.0044  inch. 

This  film  must  be  run  on  the  16-mm.  projector.  At  the  sound 
translation  point  it  must  again  be  guided.  But  at  the  sound  transla- 
tion point  the  film  needs  to  be  left  as  free  as  possible  to  move  with 
uniform  speed,  and  this  condition  is  not  compatible  with  extreme  ac- 
curacy of  guiding.  The  method  that  most  projector  manufacturers 
have  adopted  is  to  pass  the  film  between  guide  rollers  or  flanges  placed 
a  fixed  distance  apart.  If  the  film  is  fresh,  this  method  will  guide  it 
within  0.002  inch,  but  when  shrinkage  has  reached  a  value  of  around 
one-half  of  one  per  cent,*  the  film  is  0.003  inch  narrower,  and  the 

*  As  set  forth  in  a  corollary  paper  "The  Shrinkage  of  Acetate-Base  Motion 
Picture  Films,"  by  J.  A.  Maurer  and  W.  Bach  (see  page  15  of  this  issue), 


8  J.  A.  MAURER  AND  W.  H.  OFFENHAUSER   [J.  S.  M.  P.  E, 

error  in  guiding  is  more  likely  to  be  0.005  inch.  Adding  this  to  the 
error  of  location  that  may  occur  in  printing,  we  find  that  the  sound- 
track may  in  some  cases  be  as  much  as  0.009  inch  out  of  central 
location  with  respect  to  the  scanning  beam. 

The  1938  standard  allows  a  tolerance  of  0.005  inch  before  any  part 
of  the  track  misses  the  scanning  beam.  This  is  defensible  on  the  basis 
that  most  of  the  time  the  errors  enumerated  above  will  partly  cancel 
each  other  instead  of  adding,  and  therefore  in  most  cases  the  total 
error  will  be  less  than  0.005  inch. 

Referring  now  to  the  picture  standards,  we  find  that  the  standard 
camera  aperture  is  0.030  inch  wider  than  the  standard  projector 
aperture.  This  permits  a  weave  of  0.015  inch  toward  either  side  of  the 
picture  gate,  which  is  three  times  as  much  as  is  allowed  for  the  sound- 
track. 

This  difference  becomes  significant  when  we  turn  our  attention  to 
the  matter  of  the  safety  areas.  As  shown  in  the  lower  half  of  Fig.  1, 
the  safety  area  between  the  picture  and  the  variable-density  sound- 
track (or  printed  area)  has  now  been  reduced  to  0.0095  inch.  The 
safety  area  at  the  edge  of  the  film  has  a  width  of  0.0155  inch.  In  these 
two  narrow  spaces  the  projector  manufacturer  must  locate  his  sup- 
porting strips  for  handling  the  sound-track  edge  of  the  film  where 
it  passes  around  sprockets  and  rollers  and  where  it  is  fed  through 
the  picture  gate. 

Fig.  2  shows  the  type  of  idler  construction  that  one  prominent  pro- 
jector manufacturer  has  been  forced  to  adopt  in  the  attempt  to  cope 
with  this  situation.  If  the  observer  remembers  that  the  idler  roller 
in  this  illustration  is  only  J/4  inch  in  diameter,  he  will  realize  how  very 
tiny  these  two  rounded  ridges  are.  Yet  they,  and  others  like  them  on 
the  sprocket  drums  and  in  the  picture  gate,  are  all  the  support  it  is 
possible  to  give  to  the  sound-track  edge  of  the  film  in  its  passage 
through  the  projector. 

It  is  the  writers'  opinion,  based  to  a  considerable  extent  upon  ob- 
servation of  what  has  happened  to  sound-prints  in  the  field,  that  no 

the  shrinkages  to  be  found  in  current  films  in  use  measurably  exceed  the  0.5 
per  cent  assumed  in  this  discussion.  For  example,  it  has  been  not  unusual  to 
find  in  film  libraries  film  that  has  shrunk  considerably  more  than  1  per  cent. 
Recently  it  has  been  observed  that  there  seems  to  have  been  a  change  in  the  base 
of  this  particular  stock,  which  change  indicates  that  0.5  per  cent  will  be  a  reason- 
able figure  for  the  future.  The  stocks  of  other  manufacturers  point  to  the  same 
possibility.  The  film  manufacturers  are  to  be  commended  for  their  progress  in 
thus  contributing  to  the  solution  of  our  knotty  standards  problem. 


July,  1938]        CRITICISM  OF  PROPOSED  16-MM.  STANDARDS  9 

type  of  metal,  no  method  of  plating,  and  no  technic  of  polishing, 
can  prevent  the  scratching  of  the  film  by  a  supporting  strip  as  narrow 
as  is  required  by  this  1938  standard  proposal.  The  pressure  per  unit 
area  on  the  film  is  too  great.  Clean  new  films  will  go  through  a  clean 
projector  without  perceptible  scratching,  but  as  soon  as  the  film  ac- 
cumulates a  little  dust  and  grit,  the  scratches  appear.  And,  more 
often  than  not,  they  find  their  way  into  the  scanned  area,  because 
weave  in  the  picture  gate  and  at  the  sprockets  and  idlers  can  not  be 
reduced  to  zero. 

These  remarks  are  not  intended  in  any  way  as  a  criticism  of  the 
projector  manufacturers  or  their  products.  The  authors  feel  that  the 
manufacturers  have  accomplished  all  that  is  mechanically  possible 
within  the  limits  imposed  by  the  standard.  But  it  is  also  felt  that 
much  better  mechanical  design  would  be  possible  if  larger  safety 
areas  could  be  provided  on  the  film. 

In  order  to  provide  larger  safety  areas  we  must  either  (a)  reduce 
the  width  of  the  sound-track  and  scanned  area  or  (b)  reduce  the  al- 
lowance for  picture  weave.  We  suggest  doing  both,  in  moderation. 

The  objectiqn  will  immediately  be  raised  that  any  reduction  of  the 
width  of  the  sound-track  means  a  reduction  of  the  available  volume 
range.  We  propose  to  demonstrate  that  this  loss  is  much  less  serious 
than  it  is  commonly  believed  to  be. 

Suppose  that  the  modulated  track-width  of  a  record  is  reduced  from 
0.064  to  0.060  inch.  The  difference  in  reproduction  level  is  0.54  deci- 
bel. A  change  of  this  magnitude  is  inaudible.  If  the  track-width 
is  reduced  from  0.064  inch  to  0.057  inch,  the  difference  in  reproduc- 
tion level  is  one  decibel.  This  is  about  the  smallest  difference  in  level 
that  can  be  detected.  Volume  controls  on  monitoring  loud  speakers 
and  the  like  are  commonly  made  with  steps  of  two  decibels. 

When  the  width  of  a  sound-track  is  reduced,  the  background  noise 
level  diminishes  almost,  though  not  quite,  as  fast  as  the  overall  level, 
and  the  result  is  that  the  volume  range  is  reduced  much  less  than  the 
volume  level.  Therefore,  alterations  in  track-width  that  produce  in- 
audible or  barely  audible  changes  in  volume  level,  produce  wholly 
negligible  changes  in  volume  range. 

(In  order  to  permit  the  Society  to  judge  these  effects,  the  authors  had  prepared 
a  number  of  recordings  of  a  given  musical  selection,  using  different  maximum 
track-widths.  This  film  was  played  at  the  close  of  this  presentation,  to  support 
the  contention  that  no  harm  is  done  by  moderately  reducing  the  track-width.) 

To  accomplish  this  reduction  requires,  of  course,  a  modification  of 


10  J.  A.  MAURER  AND  W.  H.  OFFENHAUSER   [J.  S.  M.  p.  E. 

existing  optical  reduction  printers.  Such  modification  is  not  difficult. 
In  many  of  the  machines  in  use  at  the  present  time,  a  pair  of  cylin- 
drical lenses  is  used  to  obtain  unequal  magnification  in  forming  the 
image  longitudinally  and  laterally  with  respect  to  the  sound-track.  In 
most  cases  a  slight  change  of  the  positions  of  these  cylindrical  lenses 
in  the  system  is  all  that  is  required  to  give  the  necessary  slight  change 
in  the  lateral  reduction  ratio. 

Any  change  of  standards  must  be  made  with  caution  in  order  to 
avoid  impairing  the  performance  of  the  large  number  of  16-mm. 
sound  projectors  now  in  use.  In  view  of  this  consideration,  we  sug- 
gest that  it  is  proper  to  retain  the  track- widths  of  the  1934  standard, 
which  we  know  reproduce  satisfactorily  on  existing  projectors. 

These  track-widths  were  0.080  inch  for  the  variable-density  record, 
and  0.060  inch  for  the  variable- width  record.  The  present  standards 
for  35-mm.  film  are  0.100  inch  and  0.076  inch.  If  we  adopt  an  optical 
reduction  ratio  of  0.8  instead  of  the  present  ratio  of  0.85,  we  shall  ob- 
tain track-widths  of  0.080  and  0.0608  inch,  respectively,  for  the  vari- 
able-density and  variable-width  records.  This  is  close  enough  to  the 
1934  standards.  The  width  of  the  scanned  area  can  logically  be  made 
0.070  inch,  which  will  give  substantially  the  same  tolerance  for  weave 
as  the  1938  standard  proposal. 

In  case  35-mm.  negatives  having  the  old  track-width  of  0.071  inch 
are  reduced  on  optical  printers  having  an  0.8  ratio,  a  16-mm.  track- 
width  of  0.0568  inch  will  be  obtained.  As  has  been  pointed  out,  a 
track  of  this  width  is  only  one  decibel  lower  in  level  of  reproduction 
than  the  0.064-inch  track  called  for  by  the  1938  standard.  Therefore, 
no  perceptible  sacrifice  of  performance  is  involved. 

The  change  of  track-widths  just  discussed  would  gain  0.0025  inch 
for  each  of  the  two  safety  areas  on  the  film.  In  order  to  gain  addi- 
tional space  for  the  safety  area  between  the  sound-track  and  the  pic- 
ture, we  suggest  a  slight  change  in  the  width  of  the  standard  camera 
aperture. 

This  is  by  no  means  as  revolutionary  a  suggestion  as  it  may  at  first 
appear.  A  situation  has  existed  ever  since  the  introduction  of  optical 
reduction  printing  that  has  made  it  impracticable  to  conform  exactly 
to  the  official  standard.  This  situation  came  about  because  the  ratio 
of  height  to  width  of  the  35-mm.  projector  aperture  as  standardized 
after  the  introduction  of  sound  is  not  quite  the  same  as  the  ratio  of 
height  to  width  of  the  standard  16-mm.  projector  aperture.  It  is 
not  easy  to  decide  whether  to  reduce  the  picture  in  the  ratio  of  the 


July,  1 938  ]        CRITICISM  OF  PROPOSED  1 6-MM .  STANDARDS  1 1 

heights  or  in  the  ratio  of  the  widths.  It  has  been  suggested  by  the 
Standards  Committee  that  the  Society  ought  to  establish  a  standard 
reduction  ratio  for  printing  picture  on  16-mm.  film  from  35-mm.  nega- 
tives, but  no  final  decision  has  been  taken. 

This  ratio  problem  has  been  subjected  to  thorough  analysis  by  G. 
Friedl,  Jr.,6  with  whose  conclusions  we  are  in  general  agreement. 
Mr.  Friedl  recommends  that  the  ratio  of  reduction  be  established  as  the 
ratio  of  the  widths  of  the  35-mm.  and  16-mm.  projector  apertures,  that 
is  to  say,  the  ratio  0.825  to  0.380.  If  this  is  done  the  reduced  image 
of  the  35-mm.  camera  aperture  is  0.400  inch  wide.  We  suggest  that 
this  be  made  the  standard  width  of  the  16-mm.  camera  aperture,  the 
projector  aperture  standard  remaining  unchanged.  This  will  give 
a  standard  to  which  16-mm.  optical  reduction  prints  can  conform. 

In  one  particular  we  wish  to  suggest  a  deviation  from  the  recom- 
mendations of  Mr.  Friedl.  In  the  35-mm.  standards  there  is  a  displace- 
ment of  0.006  inch  between  the  center-line  of  the  camera  aperture  and 
the  center-line  of  the  projector  aperture.  This  is  provided  as  an 
allowance  for  shrinkage.  Mr.  Friedl  has  recommended  that  the 
optical  reduction  printer  be  adjusted  so  as  to  place  the  center-line  of 
the  image  of  the  area  covered  by  the  35-mm.  projector  aperture  on 
the  common  center-line  of  the  16-mm.  camera  and  projector  aper- 
tures. This  gives  an  image  of  the  35-mm.  camera  aperture  that  is  off 
center  a  trifle  less  than  0.003  inch,  in  the  direction  of  the  sound-track 
edge  of  the  film.  As  Mr.  Friedl  has  mentioned  in  his  paper,  this  dis- 
placement is  in  the  wrong  direction  to  serve  as  a  shrinkage  allowance, 
since  the  16-mm.  standard  assumes  that  the  film  is  to  be  guided  by 
the  sound-track  edge. 

The  authors  suggest  that  the  center-line  of  the  image  of  the  35-mm. 
camera  aperture,  not  the  projector  aperture,  be  made  to  coincide 
with  the  center-line  of  the  16-mm.  film,  which  is  the  same  as  the 
center-line  of  the  16-mm.  camera  and  projector  apertures.  This  will 
give  a  margin  of  0.010  inch  of  picture  on  each  side  of  the  16-mm.  pro- 
jector aperture.  The  shrinkage  that  occurs  during  the  first  few  pro- 
jections of  the  print  will  then  move  the  center-line  in  the  proper 
direction  to  make  the  16-mm.  projected  area  identical  with  that  pro- 
jected from  the  35-mm.  film. 

No  harm  will  be  done  by  changing  the  16-mm.  camera  aperture 
standard  to  a  width  of  0.400  inch,  since  an  allowance  of  0.010  inch 
for  picture  weave  will  remain.  This  is  sufficient  for  the  modern  pro- 
jector, as  is  proved  by  the  successful  projection  of  optical  reduction 


12 


J,  A.  MAURER  AND  W.  H.  OFFENHAUSER   [J.  s.  M.  P.  E. 


prints  in  the  past.    At  the  same  time  a  space  of  0.005  inch  will  have 
been  added  to  the  safety  area  between  picture  and  sound. 

A  suggested  set  of  specifications  embodying  these  two  changes  is 
shown  in  an  enlarged  true-to-scale  drawing  in  Fig.  3.  It  will  be  noted 
that  the  safety  area  between  the  picture  and  the  sound-track  is  now 
0.017  inch  wide  instead  of  0.0095  inch;  that  the  two  safety  areas  are 
of  nearly  equal  width,  the  one  of  the  edge  of  the  film  being  0.018  inch 


.115 


-.017 
Proposed  specifications. 


wide;   and  that  the  allowances  for  weave  of  picture  and  sound  have 
been  brought  more  nearly  into  agreement. 

We  believe  that  this  set  of  specifications,  if  put  into  use,  would 
cause  substantially  no  difficulty  during  the  period  of  transition,  since 
films  made  in  accordance  with  it  would  reproduce  satisfactorily  on 
existing  projectors,  while  projectors  built  in  accordance  with  this  set 
of  specifications  would  give  satisfactory  results  with  film  made  on 
existing  optical  reduction  equipment.  At  the  same  time  the  changes 
are  not  trivial,  since  they  result  in  nearly  doubling  the  space  available 
to  the  projector  manufacturer  for  the  placement  of  his  film  supports, 


July,  1938]       CRITICISM  OF  PROPOSED  16-MM.  STANDARDS  13 

and  thus  make  possible  longer  life  and  better  performance  on  the  part 
of  both  projector  and  film. 

The  philosophy  that  is  the  basis  of  this  entire  discussion  can  be 
stated  very  briefly.  We  believe  that  better  and  more  uniform  sound 
can  be  reproduced  from  an  undamaged  track  of  moderate  width  than 
from  a  wide  track  that  has  been  mutilated  by  scratching.  Further, 
we  believe  that  improved  overall  performance  can  be  achieved  under  a 
set  of  specifications  that  provides  for  the  customary  machine-shop 
tolerances  in  making  the  parts  that  touch  or  support  the  film  in  the 
projector. 

We  recognize  that  certain  assumptions  have  been  made  through- 
out this  discussion  that  may  not  be  in  agreement  with  the  opinions  of 
others.  Further  discussion  seems  desirable.  We  suggest,  therefore, 
that  action  upon  the  proposed  standards  for  16-mm.  sound-film  be 
postponed  until  a  more  complete  consensus  can  be  obtained. 

REFERENCES 

1  "Revision  of  SMPE  Standards  Proposed  for  Adoption  by  the  Society,"  J. 
Soc.  Mot.  Pict.  Eng.,  XXX  (Mar.,  1938),  No.  3,  p.  249. 
8  Ibid,  p.  249. 

3  MAY,  R.  P.:    "Sixteen-Mm.  Sound-Film  Dimensions,"  /.  Soc.  Mot.  Pict.  Eng., 
XVIH  (Apr.,  1932),  No.  4,  p.  488. 

4  "Standards  Adopted  by  the  Society  of  Motion  Picture  Engineers,"  J.  Soc. 
Mot.  Pict.  Ewg.,  XXIII  (Nov.,  1934),  No.  5,  p.  247. 

6  C/ref.  1,  p.  267. 

6  FRIEDL,  G.,  JR.:  "Data  Regarding  Dimensions  of  the  Picture  Image  in 
16-Mm.  Reduction  Printing,"  /.  Soc.  Mot.  Pict.  Eng.,  XXVIII  (June,  1937),  No. 
6,  p.  585. 

DISCUSSION 

MR.  CARVER:  I  should  like  to  compliment  Mr.  Maurer  for  what  seems  to  me 
to  be  the  best  criticism  of  a  standard  that  I  have  ever  heard  at  one  of  these  meet- 
ings. It  is  to  get  such  opinions  as  this  that  we  publish  the  drawings  as  proposals, 
before  validation  by  the  Board  of  Governors.  During  the  Committee's  dis- 
cussions of  the  drawings  the  dimensions  were  changed  several  times,  mainly  to 
keep  up  with  changes  that  the  manufacturers  were  making  during  the  time. 
None  of  them  seemed  very  satisfactory  and  we  felt  that  it  would  be  best  to  pub- 
lish the  drawings  for  wider  criticism.  The  two  drawings  DS35-7-1  and  DS 
16s-7-l,  showing  the  35-mm.  and  16-mm.  sound-tracks,  were  not  validated  as 
SMPE  standards  at  the  Board  meeting  on  April  24th,  and  as  a  consequence  are 
up  for  further  study  and  alteration,  if  advisable.  We  hope,  with  the  aid  of  your 
analysis,  to  arrive  at  a  satisfactory  answer. 

MR.  OFFENHAUSER:  Mr.  Maurer  and  I  were  not  associated  with  the  Stand- 
ards Committee,  and  became  aware  of  the  nature  of  the  Committee's  deliberations 


14  J.  A.  MAURER  AND  W.  H.  OFFENHAUSER 

only  when  we  received  our  copies  of  the  JOURNAL  for  March,  of  this  year,  in  which 
the  proposed  standards  were  printed. 

While  we  have  been  interested  in  standards  for  a  number  of  years,  it  was  only 
about  six  months  ago,  and  for  entirely  different  reasons,  that  we  began  making 
shrinkage  and  other  measurements,  the  results  of  which  are  applicable  to  this 
problem.  Our  direct  preparation  for  this  paper  began  when  the  proposed  stand- 
ards were  published,  and  only  at  that  time  did  we  begin  to  collect  data  related 
specifically  to  the  problem.  It  takes  time  to  collect  data.  I  believe  that  this 
procedure  has  to  be  followed  in  practically  every  instance  where  comment  is 
made  from  outside  the  Society's  Committees,  in  order  that  those  offering  the 
comment  may  be  sure  of  their  ground.  We  felt  that  a  communication  at  this 
time  was  proper,  inasmuch  as  the  Standards  Committee  published  an  invitation 
to  discussion  in  connection  with  the  new  standards  proposal. 

MR.  TOWNSLEY:  I  hope  that  the  Standards  Committee  will  give  some  thought 
to  arranging  the  final  dimensions  so  that  the  lateral  reduction  ratio  for  optical 
reduction  printing  will  be  the  same  for  variable-density  and  variable-width 
track. 

MR.  KELLOGG:  We  want  to  make  sure  that  any  step  we  take  will  be  toward 
higher  standards  of  performance,  even  if  it  should  make  certain  jobs  a  little  more 
difficult  today,  provided  we  do  not  make  them  excessively  expensive. 

Sometimes  changing  a  standard  in  one  direction  may  be  a  very  simple  matter 
while  changing  it  in  the  other  direction  may  mean  serious  difficulty.  Regardless 
of  the  dimensions  of  the  sound-track  as  now  proposed,  I  do  not  see  why  the  length 
of  the  scanning-beam  in  a  projector  should  not  be  about  as  long  as  one  can  make 
it  without  getting  over  into  the  edge  that  needs  the  support,  and  coming  danger- 
ously close  to  the  picture  frame  line.  If  many  projectors  are  built  with  shorter 
scanning-beams,  it  will  be  practically  out  of  the  question  to  adopt  a  wider  track 
later. 


THE  SHRINKAGE  OF  ACETATE-BASE  MOTION  PICTURE 

FILMS* 

J.  A.  MAURER  AND  W.  BACH** 

Summary. — A  simple  direct-reading  film-shrinkage  gauge  has  been  constructed 
with  which  shrinkage  readings  may  be  made  in  a  few  seconds.  The  accuracy  of  the 
instrument  is  such  that  the  maximum  variation  in  a  series  of  readings  made  upon  a 
particular  film  will  not  be  more  than  0.02  per  cent  of  the  predetermined  length  mea- 
sured. Readings  have  been  taken  systematically  with  this  instrument  over  a  period 
of  five  months  to  determine  the  shrinkage  behavior  of  acetate-base  films  under  various 
conditions  of  storage  and  use. 

The  results  indicate  that  the  safety-base  film  made  by  each  of  the  three  American 
manufacturers  has  a  characteristic  value  of  shrinkage  that  is  ordinarily  reached  within 
a  few  days  after  processing.  Subsequent  shrinkage  is  slow  but  continuous  over  a  long 
period  of  time.  The  ultimate  shrinkage  is  of  the  order  of  1.25  per  cent  except  in  the 
case  of  films  that  have  been  projected  many  times  on  projectors  using  high-wattage 
lamps.  The  bearing  of  this  shrinkage  information  upon  equipment  design  is  dis- 
cussed briefly. 

Ever  since  motion  picture  films  were  first  made,  it  has  been  recog- 
nized that  they  shrink  as  a  result  of  exposure  to  the  air  and  to  the 
various  chemical  baths  used  in  the  film  laboratory.  It  has  also  been 
recognized  for  a  long  time  that  the  shrinkage  of  acetate-base,  or  safety, 
films  is  greater  than  that  of  nitrate-base  films,  and,  in  fact,  this  is 
one  of  the  principal  reasons  for  the  continued  use  by  the  industry  of 
inflammable  films  in  preference  to  safety  films.  The  literature  of  the 
art  contains  numerous  references  to  the  fact  of  shrinkage  but  very 
little  quantitative  information  about  it.  This  is  unfortunate,  inas- 
much as  it  is  hardly  possible  to  arrive  at  a  comprehensive  design  of  any 
part  of  a  motion  picture  machine  having  to  do  with  the  handling  of 
film  without  at  least  making  some  assumptions  as  to  the  range  of  film 
dimensions  within  which  the  machine  will  be  required  to  operate. 

With  regard  to  nitrate-base  film  it  is  possible  to  gain  at  least  a  fair 
idea  of  these  limits  by  studying  the  published  material  on  sprocket 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;    received 
April  15,  1938. 

**  Berndt-Maurer  Corp.,  New  York,  N.  Y. 

15 


16  J.  A.  MAURER  AND  W.  BACH  [J.  S.  M.  P.  E. 

design.  With  respect  to  acetate  base,  however,  a  careful  search  of 
the  past  publications  of  the  Society  has  indicated  that  they  contain 
no  information  of  any  appreciable  value  about  the  shrinkage  of  this 
basic  raw  material  of  the-16-mm.  industry. 

As  a  first  step  toward  the  accumulation  of  a  body  of  facts  as  to  the 
shrinkage  of  safety-base  films,  the  authors  constructed  the  shrinkage 
gauge  shown  in  Fig.  1.  This  gauge  operates  upon  the  simple  principle 
of  magnifying  by  a  lever  the  differences  in  length  occurring  over  39 
sprocket-holes  of  the  16-mm.  film.  One  sprocket-hole  is  placed  over 
a  fixed  pin  at  the  left  side  of  the  gauge.  The  39th  sprocket-hole  to  the 


FIG.  1.     The  shrinkage  gauge  in  use. 

right  of  this  is  placed  over  a  pin  on  the  short  end  of  the  lever.  Be- 
tween these  two  points  the  film  lies  in  a  channel  between  two  parallel 
plates  of  metal  separated  by  twice  the  thickness  of  the  film.  The  up- 
per of  these  plates  is  a  flap  which  is  closed  down  after  the  film  has 
been  laid  in  place.  This  arrangement  serves  to  assure  that  the  film 
will  lie  straight  without  kinks  between  the  two  measuring  points.  A 
light  coiled  spring  attached  to  the  pointer  applies  enough  tension  to 
overcome  any  tendency  of  the  fulcrum  bearing  to  stick,  and  to  take 
up  any  possible  looseness  in  this  bearing,  but  does  not  apply  enough 
pressure  to  cause  the  pin  on  the  end  of  the  lever  to  distort  the  edge 
of  the  sprocket-hole  at  which  the  reading  is  being  taken. 

The  distance  corresponding  to  39  sprocket-holes  was  chosen  as  the 


July,  1938] 


SHRINKAGE  OF  ACETATE-BASE  FILMS 


17 


length  of  film  to  be  measured  because  this  length  leaves  no  uncer- 
tainty as  to  which  sprocket-hole  is  the  one  to  be  placed  over  the  pin 
on  the  end  of  the  lever,  and  thus  it  is  not  necessary  for  the  person  us- 
ing the  gauge  to  count  the  number  of  sprocket-holes  in  the  length  he 
is  measuring.  Thirty-nine  holes  were  chosen,  instead  of  the  round 
number  of  40,  because  this  permits  calibrating  the  gauge  by  the  aid  of 
an  ordinary  12-inch  machinist's  vernier  caliper.  The  scale  was  cali- 
brated so  that  each  division  corresponds  to  0.1  per  cent  of  the  stand- 
ard perforation  length  for  39  sprocket-holes,  plus  the  height  of  one 
sprocket-hole,  which  must  be  added  because  the  two  pins  on  the  gauge 
are  in  contact  with  opposite  sides  of  the  sprocket-holes  in  which  they 
are  placed.  This  is  11.750  inches.  Without  introducing  doubt  as  to 
which  sprocket-hole  was  the  cor- 
rect one  on  which  to  measure,  it 
was  found  possible  to  make  the 
scale  read  all  lengths  from  1.0 
per  cent  longer  than  standard 
pitch  to  2.0  per  cent  shorter 
than  standard  pitch,  as  shown 
in  Fig.  2.  Since  we  were  think- 
ing of  shrinkage  as  a  positive 


FIG.  2.     The  scale  on  which  shrinkage 
readings  are  indicated. 


quantity,  the  points  on  the  scale 

corresponding  to  lengths  of  film 

greater  than  the  standard  were 

marked  as  "negative"  shrinkages, 

and  points  corresponding  to  lengths  of  film  less  than  the  standard 

were  marked  as  "positive."    Thus,  when  the  pointer  stands  at,  for 

example,  the  line  marked  .5,  this  signifies  that  the  film  being  measured 

is  one-half  of  one  per  cent  shorter  than  the  standard  pitch. 

The  pointer  of  this  instrument  is  relatively  long  and  fragile,  and  it 
was  considered  possible  that  it  might  be  bent  by  accident,  which  would 
result  in  false  readings.  To  provide  an  easy  means  of  checking  the 
accuracy  of  the  gauge  we  constructed  the  master  test-bar  shown  in  the 
upper  left-hand  part  of  Fig.  1  and  in  use  on  the  shrinkage  gauge  in 
Fig.  3.  The  space  between  the  stops  at  the  ends  of  this  bar  was  made 
11.750  inches  plus  or  minus  0.001  inch.  By  placing  this  test-bar  upon 
the  gauge,  as  shown  in  Fig.  3,  and  noting  whether  or  not  the  pointer 
reads  exactly  zero,  one  can  check  the  accuracy  of  the  instrument  in  a 
very  few  seconds. 

With  this  gauge  on  a  rewind  table  a  series  of  readings  giving  the 


18  J.  A.  MAURER  AND  W.  BACH  [j.  S.  M.  P.  E. 

state  of  shrinkage  throughout  a  reel  of  film  can  be  made  in  a  few 
minutes.  The  time  required  to  take  an  individual  reading  is  no  longer 
than  the  time  required  to  write  out  the  result  in  a  notebook.  The 
readings  are  reproducible  to  about  two-tenths  of  the  distance  between 
adjacent  divisions  on  the  scale,  or  within  about  0.02  per  cent,  without 
exercising  any  unusual  care  in  handling  the  gauge. 

We  began  using  this  gauge  in  October,  1937,  taking  readings  on  such 
pieces  of  film  as  passed  through  our  hands  in  the  course  of  regular 
work,  and  noting  the  results  in  a  small  book  which  was  kept  with  the 
shrinkage  gauge.  In  the  course  of  a  few  days  we  noticed  so  many  in- 


FIG.  3.    Checking  the  gauge  by  means  of  the  test-bar. 

teresting  facts  that  we  were  impelled  to  begin  making  a  systematic 
series  of  readings  on  two  pieces  of  film  that  happened  to  have  been 
processed  under  identical  conditions  on  the  same  day.  For.  con- 
venience we  shall  refer  to  the  manufacturers  of  these  two  pieces  of 
film  as  manufacturer  No.  1  and  manufacturer  No.  2. 

The  two  films  were  kept  on  separate  reels  and  were  stored  in  an 
ordinary  filing  cabinet  in  two  identical  400-foot  cans  of  the  type  used 
for  packing  film  for  use  in  laboratories.  Both  the  films  were  of  the 
"positive"  type  used  for  making  sound  and  picture  prints.  The  cans 
were  kept  closed  when  the  film  was  not  being  handled,  but  were  not 
sealed  with  tape.  The  lids  fitted  closely,  but  not  closely  enough  to 
exclude  air  and  moisture.  In  short,  conditions  of  storage  corresponded 
roughly  with  the  conditions  under  which  sound  or  picture  nega 


July,  1938] 


SHRINKAGE  OF  ACETATE-BASE  FILMS 


19 


lives  are  commonly  stored.  The  air  of  the  building  was  not  condi- 
tioned, and  therefore  the  humidity  varied  according  to  the  general 
state  of  the  weather.  Each  day  for  a  period  of  a  little  more  than  five 
months,  except  on  Sundays  and  holidays,  each  of  these  films  was  re- 
wound, and  during  the  rewinding  the  shrinkage  was  measured  at  six 
points  throughout  its  length,  these  points  being  identified  by  punch 
marks  in  the  film  outside  the  length  being  measured. 

The  behavior  of  the  two  films  during  this  five  months'  period  is 
shown  in  Fig.  4.  Each  point  plotted  on  these  curves  is  the  average 
of  the  six  readings  taken  on  the  particular  day  in  question,  these  six 
readings  invariably  agreeing  within  0.05  per  cent.  Therefore  we  are 


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OCT.     NOVEMBER.  DECEMBER.  JANUARY.  FEBRUARY.  MARCH.  APRIL. 

FIG.  4.    Shrinkage  of  two  samples  of  acetate-base  film  measured  daily  over  a 
five-month  period. 

confident  in  stating  that  the  apparently  erratic  variations  in  length 
indicated  on  these  graphs  are  real  variations  and  not  the  result  of 
inaccuracy  in  the  shrinkage  gauge.  Each  vertical  line  on  the  graph 
represents  a  period  of  one  week ;  the  months  are  shown  at  the  bottom 
of  the  figure. 

It  will  be  noted  that  the  two  films  on  the  day  they  were  processed 
both  showed  a  shrinkage  of  0.2  per  cent.  Two  days  later  when  the 
next  reading  was  taken,  these  shrinkages  had  increased  to  0.4  per 
cent  for  the  film  of  manufacturer  No.  1,  shown  in  the  upper  curve, 
and  0.29  per  cent  for  the  film  of  manufacturer  No.  2,  shown  in  the 
lower  curve.  Two  days  later  still,  the  values  were  0.45  and  0.31  per 
cent,  respectively.  These  values  are  generally  representative  of 


20 


J.  A.  MAURER  AND  W.  BACH 


[J.  S.  M.  P.  E. 


what  we  have  observed  in  other  samples  of  film  of  the  same  manu- 
facturers. It  will  be  noted  that  the  shrinkage  that  occurred  during  the 
first  two  days  after  processing  was  as  great  as  the  further  shrinkage 
that  occurred  during  the  next  two  weeks.  It  will  be  noted  also  that, 
disregarding  erratic  variations,  which  we  will  endeavor  to  explain 
later,  the  shrinkage  after  the  first  two  days  occurred  at  a  practically 
uniform  rate  over  the  following  six  weeks.  After  that,  the  rate  of 
shrinking  decreased  gradually  until  after  three  months  the  curves 
seem  to  indicate  that  a  condition  of  stability  has  been  reached. 

It  will  be  noted  that  the  apparently  erratic  variations  above  and 
below  the  general  trend  of  the  curves  show  a  definite  correspondence 


©  cuou 


MARCH 


APRIL 


FIG.  5.     Enlargement  of  a  section  of  Fig.  4  to  show  cor- 
relation between  shrinkage  and  weather  conditions. 


in  the  two  curves.  This  is  especially  easy  to  see  during  the  two  weeks 
following  the  start  of  the  series  of  measurements  and  over  the  part  of 
the  curve  after  a  condition  of  approximate  stability  has  been  reached . 
We  noticed  as  the  series  of  measurements  proceeded  that  these  varia- 
tions above  and  below  the  general  trend  could  be  correlated  with  the 
changes  in  weather  conditions,  and  therefore  with  the  general  hu- 
midity of  the  air.  Fig.  5  has  been  plotted  to  show  this  correlation  more 
clearly.  In  this  figure  the  character  of  the  circle  drawn  around  each 
point  observed  shows  the  weather  prevailing  at  the  time  the  measure- 
ment was  made.  An  open  circle  indicates  fair  weather  with  the  sun 
shining.  A  circle  containing  a  cross  indicates  cloudy  weather.  A 
circle  completely  filled  in  indicates  rain.  It  can  be  seen  from  Fig.  5 
that  the  film,  even  though  kept  in  a  closed  metal  can  and  exposed 
directly  to  the  air  for  only  a  few  minutes  each  day,  is  able  to  absorb 


July,  1938] 


SHRINKAGE  OF  ACETATE-BASE  FILMS 


21 


enough  moisture  during  periods  of  high  humidity  to  expand  by  as 
much,  in  some  instances,  as  0.04  per  cent,  and  that  on  the  other  hand 
it  loses  this  moisture  during  periods  of  lower  humidity  within  as 
short  a  period  as  two  days  during  which  it  is  not  handled  at  all.  Ap- 
preciable absorption  or  loss  of  moisture  does  not  occur  during  the  time 
required  to  take  the  readings,  as  is  proved  by  the  fact  that  the  read- 
ings on  any  given  day  are  consistent  from  one  end  of  the  film  to  the 
other. 

While  the  film  is  able  to  take  up  and  lose  moisture  in  this  way  if 
it  is  kept  in  an  unsealed  can,  we  have  found  that  a  strip  of  ordinary 


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FIG.  6. 


0  1E345G78 

HOURS     EXPOSED  TO   AIR. 

Shrinkage  of  three  samples  of  fresh  raw  stock  freely  exposed  to  air. 


adhesive  tape  around  the  joint  of  the  can  seals  it  very  effectively.  A 
roll  of  processed  film  placed  in  the  ordinary  400-foot  can  and  sealed 
in  this  way  will  shrink  less  than  0.1  per  cent  over  several  weeks.  The 
same  conclusion  may  be  drawn  from  the  behavior  of  raw  stock,  which, 
as  we  shall  show,  shrinks  very  rapidly  when  freely  exposed  to  the  air, 
but  shows  not  more  than  0.15  per  cent  change  in  length  even  when 
kept  in  storage  for  several  months. 

Fig.  6  shows  what  happens  when  strips  of  raw  stock  freshly  taken 
from  the  original  package  are  hung  up  so  as  to  be  exposed  to  the  air 
on  both  sides.  The  vertical  lines  in  this  figure  represent  half -hour  in- 
tervals, the  entire  experiment  extending  over  eight  hours.  The  films 
of  manufacturer  No.  1  and  manufacturer  No.  2  were  from  fresh 
stock,  and  showed  a  shrinkage  value  of  the  order  of  0.05  per  cent 


22 


J.  A.  MAURER  AND  W.  BACH 


[J.  S.  M.  P.  E. 


when  first  taken  from  their  cans.  The  strips  were  not  taken  from  the 
very  outside  of  the  roll  but  from  a  point  about  one-quarter  of  an  inch 
in.  The  sample  from  manufacturer  No.  3  had  been  in  stock  for  about 
two  months,  and  therefore  it  is  perhaps  not  fair  to  compare  it  with  the 
other  two  samples,  though  the  results  are  in  accord  with  our  other 
observations  in  connection  with  the  stock  of  manufacturer  No.  3.  It 
will  be  noted  that  each  of  the  samples  underwent  a  shrinkage  of  the 


0-9 


0.5 


MAN  ffiMTi  Wll  MO.  3 


FIG.  7.     Shrinl^age  of  three  samples  of  film  as  affected 
by  use  on  a  projector. 

general  order  of  0.2  per  cent  within  the  first  hour  and  a  half,  and  that 
thereafter  the  shrinkage  is  much  slower.  The  day  on  which  this  ex- 
periment was  made  was  rather  humid,  and  for  that  reason  the  total 
shrinkage  in  the  curves  of  the  8-hour  period  is  not  as  great  as  we 
should  ordinarily  expect  on  the  basis  of  other  observations. 

Thus  far  our  experiments  were  directed  principally  toward  deter- 
mining what  may  be  expected  to  happen  to  negative  films  under  the 
conditions  of  storage  and  use  for  printing  in  film  laboratories.  When 
we  decided  to  present  this  material  in  the  form  of  a  paper  before  the 
Society  it  seemed  desirable  to  acquire  some  information  about  the 


July,  1938]  SHRINKAGE  OF  ACETATE-BASE  FILMS  23 

behavior  of  prints  as  used  on  projectors.  For  that  purpose  we  made 
up  a  reel  consisting  of  three  prints  of  the  same  subject  on  the  three 
types  of  raw  stock,  all  the  prints  being  processed  at  the  same  time. 
Immediately  after  processing  we  measured  the  shrinkages  at  several 
points  in  each  section  of  the  film,  and  thereafter  for  a  period  of  two 
weeks  we  projected  the  film  twice  daily  on  a  projector  having  a 
1000- watt  lamp  operated  at  95  per  cent  of  its  rated  voltage.  The 
series  of  measurements  was  repeated  before  and  after  each  running 
of  the  film  on  the  projector.  The  results  are  shown  in  Fig.  7,  in  which 
the  broken  lines  pass  through  the  points  measured  before  running 
the  film  through  the  projector  and  the  solid  lines  pass  through  the 
points  measured  after  projection.  It  may  be  noted  that  the  film 
shrinks  unmistakably  during  each  projection  and  in  most  cases  does 
not  reabsorb  enough  moisture  to  regain  its  earlier  length  before  the 
next  time  it  is  projected.  However,  these  curves  do  display  in  a 
striking  fashion  the  effect  of  three  successive  days  of  heavy  fog  and 
drizzling  rain,  which  occurred  late  in  March.  The  moisture  in  this 
case  was  absorbed  by  the  film  in  some  instances  so  rapidly  as  to  can- 
cel the  ordinary  drying  effect  of  the  heat  of  the  projector  lamp. 

In  the  test  shown  in  Fig.  7  the  films  of  manufacturer  No.  2  and 
manufacturer  No.  3  behaved  as  would  have  been  expected  from  our 
previous  observations,  but  the  film  of  manufacturer  No.  1  shows  a 
radical  departure  from  its  previously  observed  performance.  On  the 
basis  of  all  previous  observations  we  should  have  expected  the  curve 
for  manufacturer  No.  1  to  lie  between  the  curves  for  manufacturer 
No.  2  and  manufacturer  No  3,  but  on  the  contrary  we  find  that  the 
film  of  manufacturer  No.  1  here  shows  a  much  lower  value  of  shrink- 
age, and  even  after  repeated  passages  through  the  projector  has 
reached  a  shrinkage  of  only  0.3  per  cent,  a  value  comparable  to  the 
shrinkages  observed  in  nitrate-base  films  and  one  that  would  ordinar- 
ily be  reached  within  a  few  hours  after  processing.  We  do  not  know 
whether  to  attribute  this  to  some  factor  that  escaped  our  attention 
in  the  handling  of  the  three  films  or  to  a  change  in  the  nature  of  the 
film-base  itself,  but  we  have  not  at  any  other  time  observed  a  sample 
that  showed  as  low  a  shrinkage  value  as  this  particular  sample.  If 
the  change  in  behavior  is  due  to  a  change  in  the  nature  of  the  stock, 
it  is  to  be  hoped  that  this  manufacturer  will  continue  to  supply  stock 
having  these  characteristics. 

In  addition  to  these  more  or  less  systematic  studies  of  the  be- 
havior of  films  under  specified  conditions,  we  have  made  many  ran- 


24  J.  A.  MAURER  AND  W.  BACH  [j.  s.  M.  p.  E. 

dom  measurements  of  films  processed  at  various  times  and  handled 
under  various  conditions.  These  measurements  serve  only  to  call 
attention  to  the  great  complexity  of  the  problem  presented  by  film 
shrinkage.  We  have  been  unable  to  arrive  at  any  general  conclusions 
as  to  the  effect  of  processing  conditions,  since  films  processed  in  differ- 
ent laboratories — some  by  the  rack-and-tank  method  and  some  by 
automatic  machine — all  measure  about  the  same  length  after  they 
have  been  in  storage  for  several  months.  Films  that  have  been 
stored  in  unsealed  tin  cans  show  no  markedly  less  shrinkage  than  films 
stored  in  cardboard  containers.  At  one  tune  we  felt  that  we  were 
justified  in  assigning  a  characteristic  value  of  shrinkage  of  0.5  per  cent 
to  the  film  of  manufacturer  No.  2,  0.7  per  cent  to  the  film  of  manu- 
facturer No.  1,  and  0.9  per  cent  to  the  film  of  manufacturer  No.  3 
under  the  conditions  of  our  observations.  Recent  behavior  of  these 
film  stocks,  however,  does  not  justify  our  making  these  generaliza- 
tions. 

The  value  of  ultimate  shrinkage  is  of  considerable  importance,  since 
it  affects  the  design  of  sprockets  wherever  used.  The  bearing  surface 
diameter  of  a  hold-back  sprocket  is  directly  determined  by  the  maxi- 
mum shrinkage  to  be  accommodated,  and  the  thickness  necessary 
at  the  base  of  the  tooth  of  any  sprocket  is  determined  by  the  maximum 
shrinkage,  the  minimum  shrinkage,  and  the  number  of  teeth  in  mesh. 
In  our  stock  of  old  films,  some  of  which  are  as  old  as  six  years,  we 
have  found  only  one  film  that  was  shrunk  more  than  1.25  per  cent. 
That  was  on  the  stock  of  manufacturer  No.  1  and  showed  a  shrink- 
age of  1.4  per  cent.  It  was  about  five  years  old.  On  the  other  hand, 
films  belonging  to  film  libraries  on  which  we  have  been  able  to  take 
measurements  sometimes  showed  shrinkages  as  high  as  1.6  per  cent. 

It  is  possible  that  all  our  measurements  are  profoundly  influenced 
by  the  fact  that  they  were  made  in  New  York  City,  where  the  average 
humidity  is  considerably  greater  than  it  is  in  other  parts  of  the  United 
States.  In  view  of  the  direct  evidence  that  we  have  presented,  that 
moisture  absorption  can  cause  an  actual  lengthening  of  the  stock,  we 
feel  that  our  results  as  to  the  ultimate  degree  of  shrinkage  are  of  little 
value  except  as  applying  strictly  to  New  York  City  conditions. 

It  is  clear  that  we  have  only  scratched  the  surface  of  a  very  large 
and  complicated  problem.  The  most  casual  reflection  will  suggest  a 
large  number  of  experiments  that  might  be  tried  to  determine  the 
influence  of  such  factors  as  humidity,  surface  treatment  of  the  film  (as 
by  anti-scratch  processes),  temperature  of  storage,  etc. 


July,  1938]  SHRINKAGE  OF  ACETATE-BASE  FILMS  25 

One  fact  we  feel  has  been  definitely  revealed  by  these  studies. 
Acetate  film  base  is  not  a  definite  product  having  definite  physical 
constants;  its  properties  can  be  made  to  vary  over  a  wide  range  by 
different  methods  of  manufacture.  We  feel  that  with  further  ex- 
perimentation on  the  part  of  the  manufacturers  there  is  a  possibility 
that  safety  films  may  be  produced,  at  least  for  record  purposes  and 
in  general  for  all  applications  where  permanence  is  desired,  having 
shrinkage  properties  comparable  to  those  of  nitrate-base  film. 

We  have  made  no  comparisons  of  different  film  stocks  on  the  basis 
of  strength,  flexibility,  or  any  physical  properties  other  than  shrink- 
age. Such  comparisons  as  we  have  made  between  the  stocks  of 
different  manufacturers  relate  only  to  the  one  point  of  shrinkage  be- 
havior. We  hope  that  the  results  that  have  been  presented  here  will 
prove  sufficiently  interesting  to  stimulate  others  to  undertake  similar 
studies  and  to  publish  their  results. 

DISCUSSION 

MR.  BRADLEY:  The  subject  of  this  paper  is  of  great  interest  to  the  National 
Archives  and  the  National  Bureau  of  Standards.  There  is  a  project  at  the  Bureau 
of  Standards  that  has  been  going  on  for  about  three  years  under  the  general  title 
of  "Reproduction  of  Records,"  but  actually  it  has  turned  out  to  be  a  considera- 
tion of  preservation  of  records,  and  one  of  the  items  considered  was  the  shrinkage 
of  film. 

Mr.  Maurer's  device  for  measuring  the  shrinkage  is  a  distinct  contribution. 
The  results  of  our  own  studies,  in  which  shrinkage  was  observed  under  controlled 
predetermined  humidity,  were  published  in  the  December,  1937,  Journal  of  Re- 
search of  the  National  Bureau  of  Standards.  We  found  that  the  film  shrinks 
very  rapidly  in  the  first  ten  days  in  ovens  where  the  humidity  is  under  control. 
We  are  now  trying  to  determine  the  percentage  of  shrinkage  in  aerial-mapping 
film,  where  the  accuracy  must  be  very  great  to  prevent  ground  distortion.  A 
very  small  shrinkage  of  an  aerial  map  may  produce  distortion  equivalent  to  as 
much  as  sixteen  feet  on  the  ground,  depending  upon  the  elevation  of  the  camera 
at  the  time  the  exposure  was  made. 

Mr.  Maurer  stated  that  on  three  rainy  days  the  moisture  content  of  the  film 
rose  very  rapidly.  Did  the  studies  include  measurement  of  the  restoration  of 
moisture  to  the  film? 

MR.  MAURER:  No,  they  did  not.  We  only  infer  that  moisture  was  taken  up 
because  of  the  very  definite  correlation  between  shrinkage  and  state  of  the 
weather. 

MR.  BRADLEY:     Would  it  be  an  advantage  to  measure  it? 

MR.  MAURER:  I  believe  that  it  would.  However,  we  do  not  have  facilities 
for  making  such  measurements. 

MR.  BRADLEY:  We  have  developed  a  technic  for  restoring  the  moisture  con- 
tent in  film.  It  consists  in  rewinding  the  film  slowly,  through  what  we  call  a  re- 
humidifier,  and  blowing  moisture  across  the  surface  of  the  film.  If  the  film  is 


26  J.  A.  MAURER  AND  W.  BACH  [J.  s.  M.  p.  E. 

closely  wound  in  rolls,  as  many  as  six  months  may  be  required  for  the  moisture  to 
penetrate  to  the  interior  of  the  roll. 

MR.  KELLOGG:  I  do  not  suppose  that  you  have  made  measurements  of  film 
from  which  the  gelatin  has  been  removed.  The  question  does  not  enter,  so  far  as 
I  can  see,  into  the  practical  problem  that  you  are  investigating,  but  it  might  be 
of  interest  to  be  able  to  separate  the  effect  of  moisture  upon  the  gelatin  from  the 
effect  upon  the  base.  There  are  some  problems  in  connection  with  which  we  are 
interested  in  the  action  of  moisture  on  the  base  alone. 

MR.  MAURER:  No  measurements  of  that  sort  have  been  made.  However, 
in  the  piece  of  film  that  was  projected  at  regular  intervals  we  provided  areas  that 
were  transparent  and  other  areas  were  exposed  to  complete  opacity  so  far  as  was 
possible,  and  care  was  taken  in  making  the  measurements  to  include  both  the 
transparent  and  the  completely  opaque  areas.  We  found  no  consistent  difference 
between  the  shrinkage  behaviors  of  these  two  sections  of  the  film.  We  expected 
to  find  such  a  difference,  because  the  black  film  would  presumably  absorb  heat 
during  projection  more  completely  than  the  transparent  film,  but  to  our  surprise 
we  found  no  difference. 

MR.  FRIEDL:  Several  years  ago  some  shrinkage  measurements  were  made  in 
an  exchange  in  New  York  on  35-mm.  film,  checking  the  films  as  they  went  out  and 
as  they  were  returned  after  being  shown  in  several  theaters,  plotting  the  shrinkage 
against  age  and  use,  and  keeping  records  of  the  weather  during  that  period. 
Our  observations,  I  should  say,  were  very  similar  to  Mr.  Maurer's  with  respect  to 
the  stretching  of  the  film  on  wet  days. 

MR.  GRIFFIN:  I  noticed  that  your  shrinkage  measurements  were  longitudinal 
shrinkages.  In  such  measurements  as  I  have  made,  on  35-mm.  nitrate-base 
stock,  I  have  found  that  the  lateral  shrinkage  is  far  greater  than  the  longitudinal. 
I  am  wondering  whether  that  is  so  in  the  case  of  acetate-base  stock,  and  whether 
you  used  the  longitudinal  shrinkage  figures  in  computing  the  figures  you  gave  for 
the  placement  of  the  sound-track. 

MR.  MAURER:  The  answer  is  yes.  We  used  the  longitudinal  shrinkage 
figures.  We  have  not  made  direct  measurements  of  the  lateral  shrinkage  of  16- 
mm.  film.  A  number  of  years  ago  I  had  occasion  to  do  a  piece  of  work  that  ex- 
tended over  about  a  year,  that  showed  at  that  time  very  accurate  agreement  be- 
tween longitudinal  and  lateral  shrinkage  of,  as  it  happened,  acetate-base  films. 
However,  those  films  were  not  subjected  to  the  conditions  encountered  when  a 
film  is  projected,  and  therefore  the  result  arrived  at  then,  that  the  longitudinal 
and  lateral  shrinkages  were  the  same,  is  not  valid  as  applying  to  the  conditions 
of  actual  use  of  16-mm.  films.  Mr.  Griffin  has  raised  a  very  important  question 
and  one  on  which  we  shall  endeavor  to  throw  some  light  if  we  can  devise  a  satis- 
factory method  of  making  the  measurements. 

MR.  MITCHELL:  Has  anybody  investigated  what  might  be  described  as  the 
"warping"  of  16-mm.  sound-film,  caused  by  the  film  having  sprocket-holes  on 
one  side  and  not  on  the  other?  It  is  found  more  particularly  in  8-mm.  film,  but 
also  in  16-mm.,  that  the  shrinkage  is  not  the  same  along  the  two  sides.  Greater 
shoe  service  between  the  picture  and  the  sound  area  takes  care  of  any  very  slight 
wrinkling  that  may  occur  that  would  affect  the  sound  quality,  and  would  help  to 
keep  the  film  down  and  within  the  depth  of  focus  of  the  scanning  lens. 

MR.  DEPUE:     I  had  occasion  to  try  to  make  some  reduction  prints  from  a  60- 


July,  1938]  SHRINKAGE  OF  ACETATE-BASE  FILMS  27 

mm.  film  that  I  had  in  1897,  and  I  had  a  sprocket-wheel  that  fitted  the  film  at 
that  time.  When  I  came  to  make  the  reduction  I  looked  up  the  old  sprocket- 
wheel  and  found  that  the  shrinkage  sidewise  at  the  perforations  was  more  than 
VM  inch,  not  by  accurate  measurement,  but  rough  observation.  Longitudinally 
the  sprockets  seemed  to  fit  all  right  over  the  four  or  five  teeth  the  film  engaged. 
The  film  was  a  nitrate  negative  film,  kept  in  ordinary  storage. 

MR.  IVES:  V.  B.  Sease  in  a  paper  published  in  the  Transactions  of  the  Society 
("Moisture  in  Motion  Picture  Film,"  12,  No.  34,  p.  390,  April,  1928)  showed 
some  interesting  effects  of  fluctuating  moisture  content  upon  the  dimensions  of 
cellulosic  films.  More  recently,  Weber  and  Hill  ("The  Care  of  Slide-Films  and 
Motion  Picture  Films  in  Libraries,"  J.  Soc.  Mot.  Pict.  Eng.,  XXVII,  Dec.,  1936, 
p.  691)  studied  the  interrelations  of  shrinkage,  moisture  content  of  film,  and 
humidity  of  surrounding  atmosphere  for  the  safety  type  of  film.  In  another 
paper  published  about  the  same  time  by  the  same  authors  ("Stability  of  Motion 
Picture  Films  as  Determined  by  Accelerated  Aging,"  /.  Soc.  Mot.  Pict.  Eng., 
XXVII,  Dec.,  1936,  p.  677)  safety-film  was  reported  to  be  stable  and  lasting  in 
accelerated  aging  tests.  While  their  judgments  were  based  upon  tests  of  chemical 
and  mechanical  properties,  their  conclusions  are  of  interest  in  connection  with  the 
topics  under  discussion.  Davis  and  Stovall  ("Dimensional  Changes  in  Aerial 
Photographic  Films  and  Papers,"  Research  Paper  1051,  J.  of  Research  Nat.  Bur. 
of  Standards,  19,  Dec.,  1937,  p.  613)  have  commented  favorably  upon  the  shrink- 
age characteristics  of  some  samples  of  acetate  film  tested  in  comparison  with 
films  of  the  type  used  for  aerial  mapping. 


PROCESSING  OF  ULTRAVIOLET  RECORDINGS 
ON  PANCHROMATIC  FILMS* 


J.  O.  BAKER** 


Summary. — The  necessity  in  newsreel  work  of  making  the  original  sound  re- 
cording on  panchromatic  film  has  always  meant  a  serious  sacrifice  in  quality  and 
ground-noise  ratio,  as  compared  with  results  that  can  be  attained  when  sound  is 
recorded  on  a  separate  film.  While  ultraviolet  recording  materially  increases  fidelity 
of  response,  with  panchromatic  as  well  as  with  standard  sound  negative  film,  the 
low  contrast  and  high  base  fog  of  panchromatic  film  processed  for  negative  picture 
development  produce  noise  and  considerable  reduction  in  volume  range. 

The  track  density  on  the  panchromatic  film  is  rather  low,  of  the  order  of  1.0  to  1.2, 
when  recorded  with  a  practical  optical  system  for  a  single- film  system.  When  this 
track  is  printed  on  commercial  release  print  stock  the  dense  portion  of  the  negative 
track  will  print  through,  producing  a  fog  density  in  the  clear  portion  of  the  printed 
track.  This  fog  in  the  clear  portion  tends  to  produce  noise  and  reduces  the  volume 
range.  When  the  panchromatic  negative  and  print  are  processed  in  accordance 
with  commercial  practice,  the  reduction  in  volume  range  is  of  the  order  of  6  db. 

Printing  panchromatic  negative  upon  a  high-contrast  emulsion  improves  both 
the  noise  and  volume  range.  Since  the  release  prints  must  be  on  standard  picture 
positive  stock  and  not  on  high-contrast  film,  it  is  proposed  to  make  a  master  positive 
on  high-contrast  emulsion  and  to  re-record  from  this  to  a  standard  sound  negative, 
which  would  be  used  in  the  ordinary  way  to  make  the  release  prints.  An  improve- 
ment in  release  print  ground-noise  of  8  to  12  db.  is  obtained  by  this  method,  and  the 
volume  range  is  increased  by  6  db.  Briefly,  the  proposed  method  is  a  means  for 
increasing  the  density  contrast  of  the  final  release  print  track  when  the  original  is 
recorded  on  panchromatic  film. 

It  has  long  been  known  that  emulsions  with  fine  grain  and  high 
contrast  gave  superior  results  for  variable-width  sound  recording. 
The  investigations  made  by  Hoxie  of  the  General  Electric  Company 
in  1921  led  to  the  adoption  of  positive  types  of  emulsion  for  this  pur- 
pose; however,  in  single-film  systems,  where  the  picture  and  sound 
are  recorded  simultaneously  on  the  same  film,  the  sound  must  be 
subordinated  to  the  picture.  The  coarse  grain  of  panchromatic 
emulsion  together  with  the  method  of  picture  processing  for  an  over- 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,   B.C.;  received 
April  15,  1938. 

**  RCA  Manufacturing  Co.,  Camden,  N.  J. 
28 


ULTRAVIOLET  RECORDINGS  ON  FILMS 


29 


all  gamma  of  unity  produces  sound-tracks  of   poorer   quality  than 
can  be  obtained  with  fine-grain  recording  emulsions. 

This  paper  describes  the  results  that  can  be  obtained  when  vari- 
able-width sound-tracks  are  recorded  with  ultraviolet  light  on  pan- 
chromatic film  and  printed  with  ultraviolet  light  on  motion  picture 
positive  film  and  processed  in  accordance  with  the  commercial  tech- 
nic  for  motion  pictures,  as  well  as  the  employment  of  a  high-contrast 
emulsion  for  use  as  a  master  positive.  Image  definition  of  panchro- 
matic emulsion  is  somewhat  poorer  than  that  of  positive  emulsions. 


FIG.  1.  Sensitometric  characteristics  for  sound 
recording:  Panchromatic  in  D76,  8Vz  min.,  60°F; 
motion  picture  positive  in  D16,  4J/2  min.,  65°F;  high- 
contrast  positive  in  "Dev.  A,"  13 Va  min.,  65 °F. 


.e  ultraviolet  filter  is  used  in  the  recording  to  reduce  the  image 
spread  and  to  improve  the  response  at  the  higher  frequencies.  This 
permits  recording  at  a  higher  track  density,  but  limits  the  maximum 
density  attainable  due  to  the  restriction  of  the  recorder  light  to  a 
narrow  spectral  band. 

With  white-light  recording  on  panchromatic  film,  the  best  results 
were  attained  with  equal  negative  and  print  densities,  of  approxi- 
mately 0.80.  These  were  the  conditions  that  most  nearly  fitted  the 
requirements  for  minimum  image  distortion  in  motion  picture  posi- 


30 


J.  O.  BAKER 


[J.  S.  M.  P.  E. 


tives.     Ultraviolet  recording  reduces  the  image  spread  in  the  nega- 
tive thereby  permitting  a  higher  density  in  the  recorder  track. 

The  base  or  fog  density  of  panchromatic  film  is  approximately 
0.34,  and  with  a  recorded  track  density  of  1  or  greater,  the  difference 
in  transmission  through  the  dense  and  clear  portions  of  the  track  is 
considerably  reduced.  The  printer  light  will,  therefore,  penetrate 
the  clear  portion  and  produce  an  exposure  on  the  print  which  for  a 


1000~High-Contraat  Print 


Made  from  UV  Panchromatic  Nagatlva 
Track  Density   1.0 
Fog  Dentlty    0.34 


FIG.     2  (A).     Panchromatic     sound     recording:      cross- 
modulation  characteristics. 


perfect  track  should  be  unexposed.  This  exposure  or  fogging  of  the 
clear  portion  of  the  positive  track  results  in  reduced  output  as  well 
as  increased  noise. 

By  the  use  of  a  high-contrast  emulsion  for  printing  a  master  posi- 
tive for  use  in  re-recording,  the  fog  density  in  the  clear  portion  will  be 
materially  reduced.  A  more  complete  explanation  will  be  given  later 
in  this  paper. 

Use  is  made  here  of  "densitometric  level"  for  the  purpose  of  com- 


July,  1938] 


ULTRAVIOLET  RECORDINGS  ON  FILMS 


31 


paring  the  results  obtained  in  the  two  methods  of  printing.  The 
zero  reference  of  densitometric  level  is  chosen  as  that  of  an  ideal  film 
in  which  the  clear  portions  are  completely  transparent,  the  dense 
portions  completely  opaque,  and  the  recorded  track  is  equal  in  width 
to  the  scanning  slit.  A  perfect  sound-track  with  the  present  stand- 
ardized dimensions  for  width  of  recorded  track  and  scanning-slit 
width  would  have  a  densitometric  level  of  —0.9  db. 

The  procedure  for  determining  the  processing  conditions  has  been 
described  previously  in  the  JOURNAL.1 

Procedure. — Modulated  recordings  were  made  on  panchromatic 
film,  using  the  standard  ultraviolet  optical  system  on  an  R-4  type  of 


O-O  I.O 

Print  D»nsity--Sound-Track 


FIG.    2(B).     Panchromatic   sound   recording:     fogging 
of  positive  track. 


recorder,  but  substituting  a  2-mm.  No.  597  Corning  filter,  for  the  30- 
mil  No.  584  filter. 

The  recordings  consisted  of  1000-,  6000-,  and  6000-cycles  modu- 
lated with  400-cycles,  each  of  sufficient  length  for  making  output 
measurements.  A  frequency  of  6000  cycles  was  used  in  this  case 
since  this  is  the  cut-off  frequency  of  most  single-film  systems  for 
newsreel  work.  The  film  was  then  processed  for  picture  technic  by 
developing  the  panchromatic  film  in  D-76  for  S1/^  minutes  at  62 °F. 
producing  a  gamma  of  0.58.  The  negative  was  then  printed  on 
the  non-slip  printer  upon  motion  picture  positive  and  processed  for 
picture  technic  by  developing  in  D-16  for  4:/2  minutes  at  65°F,  giv- 
ing a  gamma  of  2.10. 

The  high-contrast  prints  were  also  made  on  the  non-slip  printer 
using  a  high-contrast  emulsion  and  developing  in  a  high-contrast 


32  J.  O.  BAKER  [J.  S.  M.  P.  E. 

developer,  Developer  A,2  for  I3l/z  minutes  at  65°F,  producing  a 
gamma  of  3.95. 

A  frequency  recording  ranging  from  1  to  10,000  cycles  was  made 
also  on  the  panchromatic  film  and  printed  upon  both  the  motion 
picture  positive  and  high-contrast  positive  with  their  respective 
processings  for  determining  the  high-frequency  loss. 

An  unmodulated  track  of  various  widths  ranging  from  5  to  36  mils 
was  recorded  on  panchromatic  film  and  printed  upon  both  types  of 
positives  for  the  purpose  of  making  the  ground-noise  measurements. 

All  output  measurements  were  made  on  a  calibrated  film  phono- 
graph and  were  corrected  for  amplifier  and  reproducer  slit  losses. 
All  measurements  are  expressed  in  terms  of  the  densitometric  level. 


-8 


-12 


5   OT  tt.P.  PosltlT*  Print  (Dpr  1.5)  from  UV  sound  Recording  N«gatlY«  (Dn 


High-Contrt 


UT  II. P.  PoaltiT*  Print  (D  s  1.15)  tram  DT  Panohromatle  Nesa^ 

-/*r  • 

-/I 


/OO  ,0*0 

FIG.  3.     Panchromatic  sound  recording:  film  loss  characteristics. 

Panchromatic  Negative. — While  a  number  of  negative  densities  were 
recorded,  the  one  with  a  track  density  of  1.0  was  chosen  for  showing 
the  relative  levels  and  image-spread  cancellation,  since  this  density 
will  probably  be  the  average  that  can  be  obtained  in  practice. 

For  the  film-loss  characteristics  and  ground-noise  measurements, 
slightly  higher  densities  were  used.  The  sensitometric  curve  is 
shown  in  Fig.  1. 

Motion  Picture  Positive. — The  motion  picture  positive  stock  was 
printed  to  various  densities  for  determining  the  image-spread  can- 
cellation and  relative  outputs. 

The  sensitometric  curve  for  the  motion  picture  positive  is  shown  in 
Fig.  1  and  the  1000-  and  6000-cycle  output  measurements  together 
with  the  400-cycle  output  are  shown  in  Fig.  2(A).  Fig.  2(B)  shows 
how  the  fogging  of  the  clear  portion  of  the  printed  track  varies  with 
the  printed  track  density. 


July,  1938] 


ULTRAVIOLET  RECORDINGS  ON  FILMS 


33 


The  print  of  film-loss  characteristics  was  made  at  a  density  of 
1.11,  and  the  results  are  shown  in  Fig.  3.  The  print  for  the  ground- 
noise  characteristics  was  made  at  a  density  of  1.23,  and  results  are 
shown  in  Fig.  4. 

In  the  latter  two  cases,  the  print  density  was  made  to  equal  that 
of  the  negative  density  as  nearly  as  possible.  All  motion  picture 
positive  prints  were  made  with  an  ultraviolet  filter  in  the  printer. 

High-Contrast  Positive. — The  high-contrast  positives  were  printed 
on  the  non-slip  printer  with  white  light  and  the  various  results  ob- 
tained are  shown  in  the  corresponding  figures  mentioned  above  for  the 
motion  picture  positive. 


FIG.   4.     Panchromatic    sound    recording:    ground-noise 
characteristics. 

Discussion. — In  Fig.  2  the  motion  picture  positive  print  for  a  den- 
sity of  1  is  approximately  Ql/2  db.  below  the  output  of  a  print  made 
from  an  ultraviolet  recording  on  sound  recording  positive  while  the 
output  of  the  high-contrast  emulsion  is  only  lv/z  db.  lower  than  that 
attainable  with  a  print  made  from  a  negative  recorded  on  standard 
sound  recording  positive  emulsion.  The  fog  density  for  the  motion 
picture  positive  at  a  track  density  of  1  is  0.35,  while  that  of  the  high- 
contrast  positive  is  only  0.08. 

Cancellation  of  image  spread  occurs  over  a  rather  wide  range  for 
the  high-contrast  emulsion,  ranging  from  approximately  0.09  to  1.2, 
while  that  of  the  motion  picture  positive  ranges  from  a  print  density 
of  1.0  downward. 


34 


J.  O.  BAKER 


[J.S.M.P.E.] 


The  film-loss  characteristic  of  Fig.  3  shows  a  low-frequency  output 
for  the  motion  picture  positive  print  of  only  —  12  db.  while  the  high- 
contrast  low-frequency  level  is  —5  db.  The  10,000-cycle  output  for 
the  motion  picture  positive  is  2  db.  less  than  that  for  the  standard 
sound  recording,  while  the  output  for  the  high-contrast  positive  at 
10,000  cycles  is  only  l/%  db.  less.  The  ground-noise  for  the  high-con- 
trast is  considerably  lower  than  that  for  the  motion  picture  positive, 
being  — 19  db.  lower  for  low  values  of  modulation. 

The  use  of  an  inverted  mask  in  the  recorder  optical  system  for  re- 
cording a  positive  sound-track  provides  a  negative  sound-track  when 


Negatlv*  Track  Density 


FIG.  5.  Panchromatic  sound  recording:  differential 
exposure  through  track  and  fog  densities  of  negative 
(fog  density  =  0.34). 

printed  upon  the  high-contrast  emulsion,  which  could  then  be  used 
as  a  negative  for  printing  directly  to  the  motion  picture  prints. 

Fig.  5  provides  a  ready  means  for  determining  the  track  fog 
density  of  a  print  for  any  value  of  recorded  track  density.  The  dif- 
ferential exposure  when  applied  to  the  base  line  of  the  sensitometric 
curves  will  spread  between  the  print  track  density  (which  should  be 
the  same  as  the  negative  track  density)  and  the  track  fog  density. 

Conclusions. — Since  the  fog  density  of  panchromatic  film  is  approxi- 
mately 0.34  and  the  maximum  negative  track  density  attainable  is  of 
the  order  of  0.8  to  1.1,  the  difference  in  transmission  through  the  dense 
and  clear  portions  of  the  track  is  quite  small.  Printing  this  track 
upon  positive  film  results  in  fogging  the  clear  portion  of  the  printed 


July,  1938]  ULTRAVIOLET  RECORDINGS  ON  FILMS  35 

track,  thereby  introducing  noise  and  reducing  volume  range.  The 
higher  the  negative  density,  the  less  will  be  the  ground-noise  and  the 
reduction  in  volume  range. 

When  the  negative  and  positive  sound-tracks  are  processed  in  ac- 
cordance with  picture  technic,  the  print  density  should  be  equal  to 
the  negative  density  or  slightly  less.  With  a  negative  track  density 
of  1.0  on  the  panchromatic  film  and  a  print  density  of  1.0  on  motion 
picture  positive,  the  density  of  the  clear  portion  of  the  printed  track 
is  approximately  0.35,  resulting  in  a  densitometric  level  for  1000  cycles 
of  —12  db.  and  a  ground-noise  level  of  —28  db.  for  zero  signal  and 
-38  db.  for  a  100-per  cent  signal. 

Printing  this  same  negative  on  a  high-contrast  emulsion  for  the 
purpose  of  making  a  dupe  negative  or  master  positive  for  re-recording, 
the  density  of  the  clear  portion  of  the  track  is  0.08,  giving  a  densito- 
metric level  of  —7  db.  and  a  ground-noise  level  of  —37  db.  for  zero 
signal,  and  —50  db.  for  a  100-per  cent  signal. 

While  satisfactory  results  can  be  obtained  from  an  ultraviolet  re- 
cording on  panchromatic  film  and  printing  directly  to  motion  picture 
positive,  they  are  far  from  ideal.  The  use  of  a  high-contrast  emulsion 
as  an  intermediate  step  provides  means  for  obtaining  greater  volume 
range  and  lower  ground-noise.  The  final  release  print  in  either  case 
can  not,  of  course,  be  as  good  as  recordings  made  on  the  finer-grained 
emulsions. 

REFERENCES 

1  BAKER,  J.  O.,  AND   ROBINSON,  D.    H.:     "Modulated   High-Frequency   Re- 
cording as  a  Means  of  Determining  Conditions  for  Optimal  Processing,"  /.  Soc. 
Mot.  Pict.  Eng.,  XXX  (Jan.,  1938),  No.  1,  p.  3. 

2  BAKER,  J.  O.:     "Recording  Tests  on  Some  Recent  High-Resolution  Experi- 
mental Emulsions,"  /.  Soc.  Mot.  Pict.  Eng.,  XXX  (Jan.,  1938),  No.  1,  p.  18. 


DISCUSSION 

MR.  FRAYNE:  Why  was  the  change  made  from  the  584  to  the  597  filter,  which 
has  more  blue-violet? 

MR.  SACHTLEBEN  :  For  the  reason  that  the  584  transmitted  more  red  light  than 
the  597.  Of  course  the  red  could  be  reduced  somewhat  by  increasing  the  thickness 
of  the  584,  but  we  should  have  to  go  up  quite  a  way  and  suffer  a  loss  in  the  ultra- 
violet. We  chose  the  597  to  get  rid  of  the  red  without  such  loss. 

MR.  RICHTER:    What  is  the  thickness  of  the  niters? 

MR.  SACHTLEBEN:  The  597  used  in  the  newsreel  system  is  2  mm.  thick.  That 
was  the  minimum  thickness  we  could  use  and  still  eliminate  the  red. 


v 


AN  OPTICAL  SYSTEM  FOR  THE  REPRODUCTION 
OF  SOUND  FROM  35-MM.  FILM* 


J.  H.  McLEOD  AND  F.  E.  ALTMAN** 


Summary. — An  optical  system  has  been  designed  and  tested  for  use  in  35-mm. 
sound  reproducers.  It  is  the  slitless  type,  and  gives  a  scanning  image  that  is  0.001 
inch  wide  when  used  with  an  exciter  lamp  having  a  coil  diameter  of  0.055  inch.  A 
tone  lens  is  used  to  form  a  curved-line  image  of  the  filament  of  the  lamp.  This  curved 
image  is  then  re-imaged  by  a  highly  corrected  objective  lens  of  numerical  aperture 
0.28.  The  objective  lens  has  inherent  curvature  of  field,  but  this  curvature  is  compen- 
sated by  the  curvature  of  the  line-image  formed  by  the  toric  lens  so  that  the  final  image 
is  flat.  The  toric  lens  also  acts  as  a  condenser  lens  to  throw  an  image  of  the 
filament  into  the  objective  lens.  Careful  tests  of  samples  show  that  the  final  image  is 
flat,  straight,  and  of  uniform  width  and  intensity. 

The  purpose  of  the  optical  system  in  a  sound  reproducer  for  sound 
on  film  is  to  provide  a  narrow  bright  line  of  light,  usually  0.084  inch 
long  and  0.001  inch  wide,  on  the  sound-track  of  the  film. 

Some  of  the  requirements  of  the  system  may  be  stated  briefly  as 
follows : 

(1)  The  line  image  must  be  of  the  proper  dimensions. 

(2)  The  image  must  be  as  bright  as  possible. 

(3)  No  light  other  than  the  light  in  the  image  should  strike  the  film. 

(4)  The  image  must  be  straight. 

(5)  The  image  must  be  fiat,  so  as  to  be  in  focus  in  the  plane  of  the  film  along  the 
entire  length  of  the  image. 

(6)  The  image  should  be  of  uniform  width  and  of  uniform  intensity  along  its 
length. 

(7)  In  the  plane  of  the  film,  the  image  must  be  at  right  angles  to  the  direction 
of  motion  of  the  film. 

(8)  Small  displacements  of  the  source  should  not  produce  changes  in  the  in- 
tensity or  dimensions  of  the  image. 

A  great  variety  of  optical  systems  have  been  designed  from  time  to 
time.  In  general,  they  fall  into  three  classes:  (1)  The  slit  type,  in 
which  an  image  of  the  filament  of  the  exciter  lamp  is  formed  upon  a 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;    received 
April  22,  1938;    Communication  No.  670  from  the  Kodak  Research  Laboratories. 

**  Eastman  Kodak  Co.,  Rochester,  N.  Y. 
36 


OPTICAL  REPRODUCTION  OF  SOUND 


37 


narrow  physical  slit  and  the  slit  is  then  re-imaged  by  an  objective 
lens  upon  the  sound-track  on  the  film;  (2)  the  condenser  projection 
system,  similar  to  a  lantern-slide  projector,  in  which  an  objective  lens 
forms  an  image  of  the  condenser  (and  anything  placed  over  the  con- 
denser) upon  the  film :  a  physical  slit  is  accordingly  placed  over  the 
condenser  lens;  (3)  the  slitless  type  or  so-called  apertureless  system, 
in  which  an  image  of  the  filament  itself  is  formed  upon  the  film  by  one 
or  more  lenses. 

Of  these  classes,  the  first  has  two  serious  faults :  (a)  If  a  coiled  fila- 
ment is  used,  the  illumination  along  the  slit  will  not  be  uniform  be- 
cause of  the  individual  turns  of  the  coil ;  (b)  the  filament  must  be  lo- 
cated very  accurately,  relatively  to  the  optical  system,  in  order  to 


FIG.  1.     Idealized  perspective  view  of  the  optical  system. 


place  the  image  of  the  filament  exactly  upon  the  slit ;  otherwise,  loss 
of  illumination  and  microphonics  will  result. 

The  second  class  of  optical  system  may  be  subject  to  microphonics 
resulting  from  movement  of  the  image  of  the  filament  across  the  ob- 
jective lens.  On  the  other  hand,  this  class  should  give  very  uniform 
illumination  along  the  length  of  the  scanning  image. 

The  slitless  type  of  optics  is  superior  in  its  freedom  from  micro - 
phonics.  The  width  of  the  scanning  line,  however,  is  not  fixed  by  the 
optical  system  alone,  but  depends  upon  the  size  of  the  source  and  the 
distance  of  the  source  from  the  lens. 

An  important  problem  in  the  design  of  high-quality  sound  optics 
is  to  obtain  a  flat  scanning  image  upon  the  film.  This  problem 
arises  from  the  fact  that  the  simpler  types  of  spherical  objective 
lenses  have  the  defect  of  curvature  of  field.  This  defect  is  in  some  sys- 


38 


J.  H.  McLEOD  AND  F.  E.  ALTMAN         [J.  s.  M.  p.  E. 


terns  compensated  for  by  curved  slits  or  by  curved  virtual  images  of 
slits  to  make  the  final  image  flat. 

One  of  the  features  of  the  system  herein  described  is  the  unique 
method  used  to  obtain  a  flat  field.  Another  aspect  of  the  system  is 
that  it  does  not  belong  to  any  one  of  the  three  main  classes  mentioned, 
but  is  a  mixture  of  (2)  and  (3). 

Fig.  1  illustrates  the  general  idea  of  the  system  and  Fig.  2  shows 
elevation  and  plan  views  of  it.  Fig.  2(B)  illustrates  the  projection 
type  of  sound  optics;  the  elevation  view,  Fig.  2(^4),  the  slitless  type. 
Let  us  look  at  the  elevation,  Fig.  2  (A).  The  small  cylindrical  lens  in 


IMAGE   OF    FILAMENT 
S     O.OOi" 


FILAMENT 
0.055" 


o=--r:L 


OBJECTIVE 


APERTURES 


IMAGE  OF   FILAMENT 
ON   FILM    O  OOl" 


K 


DOTTED   LINE    SHOWS 

CURVED  ASPECT   OF  IMAGE 

OF   FILAMENT 


IMAGE    OF   O    AND  OF 
CURVED    IMAGE 


FIG.  2.     Sound  optics  for  35-mm.  reproducers:    (.4)  elevation  view, 
(5)  plan  view. 


the  condenser  unit  images  the  filament  into  a  line  at  a  reduction  of 
18.3  times  in  the  short  dimension.  This  line  is  re-imaged  upon  the 
film  at  a  reduction  of  3:1  by  a  high-quality  spherical  objective.  If 
the  diameter  of  the  filament  coil  is  0.055  inch,  the  final  image  is  there- 
fore 0.001  inch  thick. 

A  mask  covers  all  of  the  condenser  unit  except  a  narrow  strip  along 
the  small  cylinder.  The  width  of  the  strip  is  such  as  to  provide  a 
relative  aperture  about  twice  as  large  as  is  necessary  to  fill  the  objec- 
tive lens.  This  allows  for  a  vertical  displacement  of  the  filament  of 
about  half  its  diameter,  up  or  down,  without  affecting  the  intensity 
of  the  light  that  passes  through  the  objective.  Microphonics  are  thus 
almost  completely  eliminated. 

Fig.  2(B)  is  a  plan  view  of  the  optical  system.    The  unique  design 


July,  1938] 


OPTICAL  REPRODUCTION  OF  SOUND 


39 


of  the  condenser  unit  now  becomes  apparent.  It  is  seen  that  the 
small  cylinder,  shown  in  cross-section  in  Fig.  2(A),  has  a  curved  axis. 
In  this  way  a  toric  lens  is  produced.  Its  minor  radius  appears  in  Fig. 
2(A)  and  its  major  radius  in  Fig.  2(B). 

The  major  radius  of  the  toric  lens  has  two  very  important  pur- 
poses: It  acts  in  conjunction  with  a  special  window  as  a  condenser 
lens  to  throw  an  enlarged  image  of  the  filament  into  the  objective 
lens;  and  in  addition,  it  produces  a  curved  line  image  of  the  filament 
within  the  glass  of  the  condenser  unit.  This  curvature  of  the  image 
is  for  the  purpose  of  matching  the  curvature  in  the  object  space  of 
the  objective  lens  so  that  the  final  image  will  lie  flat  upon  the  film. 
It  so  happened  that  the  curvature  required  for  the  condenser  and  for 
correcting  the  curvature  of  field  were  practically  identical. 


FIG.  3.     Path  of  a  ray  through  a  toric  lens. 

A  circular  aperture  D  was  placed  over  the  condenser  unit,  as  shown 
in  Fig.  2(B),  to  define  the  length  of  the  scanning  image. 

A  window  was  placed  over  the  condenser  unit  to  keep  dirt  away 
from  the  surface  of  the  toric  lens.  In  addition,  the  window  is  an 
aspheric  lens  whose  inner  surface  is  shaped  to  compensate  for  "spheri- 
cal" aberration  in  the  condenser  aspect  of  the  toric  lens. 

The  objective  lens  consists  of  three  simple  achromatic  doublets. 
The  doublet  on  the  object  side  collimates  the  light;  the  other  two 
then  bring  the  parallel  beam  to  a  focus  upon  the  film.  The  lens  is 
very  highly  corrected,  and  therefore  gives  excellent  definition  in  spite 
of  the  high  working  aperture  of  //1. 8,  or  the  numerical  aperture  of 
0.28.  Incidentally,  the  working  aperture  could  be  increased  to //1. 5, 
if  desired. 


40  J.  H.  MCLEOD  AND  F.  E.  ALTMAN         [J.  S.  M.  p.  E. 

In  order  to  test  the  general  idea  of  the  optics  as  outlined  above,  a 
toric  lens  as  described  was  made  up.  The  system  gave  a  very  well 
defined  image  of  great  intensity  and  it  lay  flat  in  the  plane  of  the 
film.  One  expected  defect,  however,  was  apparent,  i.  e.,  the  width 
of  the  image  was  less  at  the  ends  than  at  the  center.  An  examination 
of  the  first  curved  image  formed  directly  by  the  toric  lens  showed 
that  it,  too,  suffered  from  a  falling  off  in  width  at  the  ends. 

The  reason  for  the  decrease  in  width  of  the  line  image  at  its  ends 
was  that  rays  from  the  lamp  that  struck  the  toric  lens  at  points  off 
the  axis  of  the  lens  system  did  so  at  an  angle  6,  rather  than  normally 
(Fig.  3).  These  rays,  therefore,  encountered  a  sharper  curve  and 
were  brought  to  a  focus  at  a  shorter  distance  and,  therefore,  formed 
a  smaller  image. 


X  \ 

1      J 


FIG.  4.     Section  of  a  cylinder  cut  by  a  plane  at  the 
angle  6. 


The  magnitude  of  the  defect  can  be  calculated  as  follows:  The 
section  of  a  complete  cylinder  cut  by  a  plane  is  an  ellipse  (Fig.  4).  Let 
the  radius  of  the  cylinder  be  r.  Then  the  minor  axis  of  the  ellipse  will 
be  r.  Let  the  major  axis  of  the  ellipse  be  a.  Then  a  =  r/cos  6.  We 
are  interested  in  the  radius  of  curvature  of  the  ellipse  at  the  end  of 
the  major  axis  because  that  is  the  curvature  that  determines  the 
power  of  the  cylindrical  lens  for  rays  hitting  it  at  the  angle  6.  It 
can  be  shown  from  geometry  that  the  radius  of  curvature  R  at  the 
end  of  the  major  axis  of  an  ellipse  equals  rz/a.  Substituting  for  a,  we 
get  R  =  r  cos  6.  Thus,  the  effective  radius  of  the  toric  lens  decreases 
as  cos  6,  and,  therefore,  the  size  of  the  image  formed  will  be  propor- 
tional to  cos  6.  This  was  found  to  be  true  experimentally  in  the  case 
of  the  toric  lens  mentioned  above. 

A  new  toric  lens  was  then  designed  in  which  the  minor  axis  was 


July,  1938] 


OPTICAL  REPRODUCTION  OF  SOUND 


41 


made  greater  in  the  proportion  I/cos  0  at  points  off  the  axis  of  the 
system.    Fig.  5  shows  the  appearance  of  the  finished  lens. 

Three  of  these  completed  lenses  were  mounted  in  three  finished 
optical  systems  and  were  given  very  careful  tests. 


///// 


\  '.  \  \\\\% 


FIG.  5.     The  toric  lens. 


The  optical  system  being  tested  was  mounted  in  a  jig  along  with  a 
10-volt,  5-ampere  exciter  lamp  placed  at  the  proper  position  relative 
to  the  optics.  The  jig  was  then  placed  upon  a  travelling  microscope, 
and  the  microscope  was  focused  upon  the  scanning  image.  The 


FIG.  6.     Enlarged  plot  of  scanning  image. 

microscope  had  a  4-mm.  objective  in  it  so  that  a  magnification  of 
about  400X  was  produced.  A  micrometer  eye-piece  was  used  in  the 
microscope  to  measure  the  position  of  the  edges  of  the  image  and 
hence  the  width  of  the  scanning  line.  The  microscope  could  be  moved 
sidewise  to  bring  into  view  any  desired  part  of  the  scanning  image. 

The  image  was  found  to  be  flat  to  such  a  high  degree  that  it  was 
scarcely  possible  to  detect  any  loss  of  sharpness  as  the  microscope  was 


42 


J.  H.  McLEOD  AND  F.  E.  ALTMAN         [J.  S.  M.  P.  E. 


moved  from  end  to  end  of  the  image.  With  the  micrometer  eye-piece 
measurements  were  made  of  the  positions  of  the  two  edges  of  the 
image,  at  twenty-two  positions  distributed  equally  along  the  length 
of  the  image.  Fig.  6  is  a  plot  of  these  measurements  taken  of  one  of 
the  systems;  the  straight  lines  were  drawn  0.001  inch  apart.  Inspec- 
tion of  Fig.  6  shows  that  the  image  was  straight  and  of  uniform  width 
to  a  high  degree  of  accuracy.  The  other  two  systems  had  images  sub- 
stantially the  same  as  that  given  in  Fig.  6.  The  average  widths  of 
the  images  formed  by  the  three  systems  were  0.00107  inch,  0.00104 
inch,  and  0.00107  inch,  respectively,  and  the  lengths  were  0.0847 
inch,  0.0852  inch,  and  0.0847  inch.  The  correct  length  is  0.084  ± 


FIG.  7.  Microdensitometer  traces  of  intensities  along 
the  scanning  images  produced  by  sound  optical  systems. 
The  curves  marked  1,  2,  and  3  are  for  three  sample 
systems  of  the  type  described.  The  one  marked  STD 
is  for  a  well  known  system  in  general  use. 

0.001  inch.  The  width  of  the  image  can,  of  course,  be  adjusted  by 
placing  the  filament  of  the  lamp  closer  to  or  farther  from  the  optical 
system.  For  example,  if  the  filament  were  moved  1  mm.  farther  from 
the  optics,  the  size  of  the  final  image  would  be  reduced  by  about  7  per 
cent.  A  microdensitometer  trace  showed  that  the  uniformity  of  il- 
lumination remained  the  same  when  this  change  was  made. 

The  final  test  was  to  place  the  jig  containing  the  optical  system  in 
a  microdensitometer  so  that  an  enlarged  image  of  the  scanning  image 
was  thrown  across  the  slit  of  the  microdensitometer.  When  the  stage 
of  the  microdensitometer  was  moved,  it  carried  the  optical  system 
with  it,  and  the  image  moved  across  the  slit,  and  thus  a  record  could 
be  made  of  the  intensity  of  the  scanning  image  from  one  end  of  the 
scanning  image  to  the  other.  A  standard  optical  system  of  a  well 
known  make  was  tested  in  a  similar  way.  An  8-mm.  objective  was 


July,  1938]  OPTICAL  REPRODUCTION  OF  SOUND  43 

used  in  the  microdensitometer  instead  of  the  usual  16-mm.  one  so  as 
to  be  certain  that  all  of  the  cone  of  light  from  a  point  of  the  scanning 
image  would  be  transmitted  to  the  photocell. 

The  curves  of  Fig.  7  give  the  results.  It  will  be  noted  that  the  new 
systems  give  about  35  per  cent  more  light  than  the  standard  system, 
as  indicated  by  the  average  heights  of  the  curves.  Of  this  amount, 
23.5  per  cent  would  be  accounted  for  by  the  use  of  an//1.8  objective 
instead  of  the  //2.0  objective  used  in  the  standard  optics.  Another 
6  per  cent  would  result  from  the  fact  that  the  width  of  the  scanning 
images  is  0.00106  inch  wide  instead  of  0.0010  inch.  In  addition,  it 
was  noticed  that  the  objectives  in  the  three  new  optics  were  almost 
completely  filled  with  light  because  of  the  nature  of  the  design, 
whereas  in  the  standard  the  objective  was  not  completely  filled. 

The  other  factor  to  be  noticed  is  the  variation  in  the  height  of  the 
curves  from  one  end  to  the  other.  Measurements  give  a  variation  of 
=*=  11,  ±  13,  and  ±9  per  cent  for  the  three  new  systems,  and  ±17  per 
cent  for  the  standard  one. 

To  sum  up,  we  now  list  the  following  advantages  for  the  new 
optics :  (a)  Considerable  tolerance  in  the  position  of  the  filament  of 
the  exciter  lamp  is  permissible,  e.  £.,  ±0.020  inch  in  any  direction; 
(b)  freedom  from  microphonics ;  (c)  excellent  definition;  (d)  an  ex- 
tremely flat  and  straight  image ;  (e)  good  uniformity  of  light-intensity 
along  the  length  of  the  image  and  a  high  total  intensity ;  and  (/)  com- 
paratively low  cost. 

DISCUSSION 

MR.  ALBERSHEIM:  I  should  like  to  warn  against  being  too  optimistic  with 
regard  to  lamp  filament  vibrations  in  such  a  system.  While  vertical  vibration  of 
the  filament  in  this  type  of  optic  will  not  produce  microphonic  noise,  it  will  shift 
the  scanning-beam  image  up  and  down  in  a  direction  opposite  to  the  filament 
vibration  and  therefore  will  modulate  the  signal  frequency,  producing  flutter. 
Therefore,  it  is  better  to  watch  for  good  cushioning  of  the  lamp  despite  the  ab- 
sence of  direct  microphonics. 

MR.  ALTMAN:  It  is  true  that  there  would  be  a  slight  motion  of  the  scanning- 
beam  in  the  film-gate  with  an  extreme  vertical  vibration  of  the  filament.  How- 
ever, since  the  total  optical  reduction  is  about  fifty  to  one,  such  motion  should 
not  be  serious. 

MR.  CARLSON:  Mr.  Altman  mentioned  the  fact  that  the  height  of  the  scan- 
ning-beam could  be  reduced  by  moving  the  source  either  nearer  to  or  farther  from 
the  collecting  lens.  It  might  be  well  to  add  that  the  height  of  the  scanning-beam 
can  be  varied  also  by  selecting  a  lamp  having  a  coil  diameter  different  from  the 
one  referred  to  in  the  paper. 

MR.  ALTMAN:     Mr.  McLeod  examined  the  uniformity  of  intensity  with  some 


44  J.  H.  McLEOD  AND  F.  E.  ALTMAN         [J.  S.  M.  P.  E. 

longitudinal  motion  of  the  source.  He  moved  the  source  enough  to  produce  a 
6  to  8  per  cent  change  in  the  height  of  the  scanning  image.  No  appreciable  change 
in  the  uniformity  of  illumination  was  noted. 

MR.  KELLOGG:  Have  you  any  figures,  either  calculated  or  measured,  that 
show  the  tolerance  of  filament  height,  as  limited  by  the  tendency  to  produce  a 
curved  image  on  a  film  if  it  gets  much  below  a  normal  level? 

MR.  ALTMAN:  We  had  not  anticipated  a  departure  from  the  ideal  axial  posi- 
tion, which  I  imagine  is  what  you  mean  would  cause  a  curvature.  There  was  a 
suggestion  of  slight  curvature  in  the  findings  of  Mr.  McLeod.  Whether  or  not 
that  was  due  to  a  slight  defect  in  the  pressing  or  caused  by  some  displacement  I 
would  not  know. 

MR.  COOK:     How  do  you  form  a  lens  as  complicated  as  that? 

MR.  ALTMAN:  It  is  a  molded  lens.  The  die  is  polished  so  that  an  optical  sur- 
face results.  The  making  of  the  die  can  be  visualized  by  imagining  a  piano  wire 
wrapped  around  a  small  cylinder,  and  this  used  as  a  pattern  for  the  die.  It  was 
found  necessary  to  vary  the  diameter  of  the  piano  wire  along  its  length  to  secure 
uniform  width  of  image  of  the  filament. 

MR.  FRIEDL:  Do  you  find  in  this  system  any  secondary  images,  caused  by 
reflection  within  the  glass  of  the  exciter  lamp? 

MR.  ALTMAN:  There  is  in  the  system  a  mask.  The  focal  length  of  the  ana- 
morphote  in  its  strong  meridian  is  about  0.8  mm.,  and  since  we  wish  to  flood  the 
imaging  objective  with  light  at  about  //5.4,  you  would  have  to  have  an  aperture 
in  that  meridian  of  only  0.8/5.4,  which  would  be  about  0.15  mm.  That  does  re- 
quire, then,  a  small  mask  with  a  slit  0.15  or  0.20  mm.  along  the  strong  meridian 
of  the  pressing.  The  diffraction,  or  scattered  light,  from  the  edges  of  the  mask 
might  cause  some  secondary  image. 

MR.  MCLEOD:  If  the  axis  of  the  exciter  lamp  is  perpendicular  to  the  axis  of 
the  optical  system,  as  it  is  in  practice,  the  reflected  image  in  the  glass  is  directly 
behind  the  filament  and  is  hidden  by  the  filament.  However,  it  has  been  found 
that  if  the  lamp  is  displaced  a  considerable  distance  above  or  below  its  proper 
position,  a  weak  image  is  formed  above  or  below  the  main  image.  The  displace- 
ment to  produce  this,  however,  has  to  be  greater  than  is  normally  encountered. 

MR.  FRIEDL:  Do  you  find  that  so-called  azimuth  variation  is  more  critical  in 
this  type  of  system?  In  the  system  with  the  mechanical  slit,  the  slit  is  held 
in  fixed  relation  with  respect  to  the  optical  scanning  beam,  and  that  determines 
the  azimuth  with  respect  to  the  position  of  the  filament;  whereas  in  this  case, 
I  am  wondering  whether  or  not  the  tilt  of  the  filament  axis  may  not  introduce  an 
azimuth  loss  or  scanning  loss,  as  a  function  of  the  tilt. 

MR.  ALTMAN:  Each  and  every  point  on  the  filament  is  imaged  as  a  line  on  the 
film,  and  the  azimuth  of  the  line  is  determined  solely  by  the  azimuth  of  the  press- 
ing or  cylinder.  The  total  image  on  the  film  is  the  net  effect  of  all  the  lines  imaged 
from  all  the  points  on  the  filament. 

If  the  filament  is  tilted  it  will  not  change  in  the  slightest  degree  the  azimuth  of 
the  final  image  but  will  increase  somewhat  the  height  of  the  image. 

MR.  FRIEDL  :  That  is  the  same  effect  as  is  due  to  misalignment  in  a  mechani- 
cal system.  The  effect  of  the  azimuth  is  the  same  as  having  a  slit  as  wide  as  the 
two  corners. 

MR.  ALTMAN:     That  is  true. 


July,  1938]  OPTICAL  REPRODUCTION  OF  SOUND  45 

MR.  FRIEDL:     And  the  filament  sag  would  cause  a  very  similar  effect. 

MR.  ALTMAN:  That  is  right.  The  particular  lamp  we  have  suggested  is  well 
suited  because  it  has  a  rather  large  diameter  of  filament  and  a  rather  short  length. 
A  given  angular  tip  therefore  produces  less  spread  of  the  image  than  would  a  simi- 
lar angular  tip  with  a  long  slender  filament. 

MR.  KELLOGG  :  I  believe  that  I  see  the  answer  to  the  question  I  asked  a  few 
minutes  ago  in  reference  to  the  effect  of  changing  the  lamp  height ;  the  conditions 
of  focal  length  and  focus  position  that  give  you  a  beam  of  uniform  width  are 
identical  with  the  conditions  for  relative  immunity  to  curvature  resulting  from 
change  in  lamp  height. 

MR.  MCLEOD:  We  agree  that  Mr.  Kellogg's  remark  is  an  exact  statement  of 
the  truth  regarding  the  absence  of  curvature  when  the  height  of  the  lamp  is 
changed.  The  toric  lens  is  designed  to  give  a  line  image  of  uniform  width.  That 
means  that  the  magnification  is  the  same  at  the  center  as  at  the  ends  of  the  line. 
Since  the  magnification  is  the  same,  a  given  displacement  of  the  source  up  or  down 
will  cause  a  displacement  of  the  line  up  or  down  that  will  be  the  same  at  the  cen- 
ter as  at  the  ends.  In  other  words,  the  plane  of  the  curved  image  (which  is  hori- 
zontal) will  remain  parallel  to  itself  if  the  source  is  moved  up  or  down.  It  is  true 
that  as  viewed  from  the  objective  the  curved  line  will  appear  straight  when  the 
plane  of  the  curve  passes  through  the  center  of  the  objective,  but  when  the  plane 
moves  above  or  below  the  center  of  the  objective  lens  the  curved  line  will  appear 
to  be  slightly  curved.  A  slightly  curved  image  would  be  produced.  However, 
since  the  vertical  displacement  of  the  curved  image  is  Vis  the  displacement  of  the 
source,  and  this  in  turn  is  reduced  to  Va  size,  the  curvature  in  the  final  image  on 
the  film  would  be  too  small  to  measure. 


PUSH-PULL  RECORDING  WITH  THE  LIGHT- VALVE* 
J.  G.  FRAYNE  AND  H.  C.  SILENT** 

Summary. — Push-pull  recording  on  film  is  accomplished  by  means  of  a  double 
light-valve  having  four  ribbons.  Distortions  introduced  by  the  recording  medium  that 
are  represented  by  second-order  harmonics  balance  out  in  reproducing,  as  do  also  the 
frequencies  introduced  by  the  action  of  the  noise-reduction  system.  As  a  result,  push- 
pull  recording  not  only  eliminates  certain  defects  of  conventional  recording,  but  per- 
mits the  application  of  new  technics  that  allow  further  extension  of  the  volume  range 
and  improvement  in  the  naturalness  in  the  final  product. 

The  use  of  the  push-pull  principle  in  transmission  systems  is  well 
known  as  a  means  by  which  certain  distortions  introduced  by  the 
transmitting  devices  are  balanced  out.  These  are  distortions  caused 
by  the  introduction  of  second-order  harmonics  and  effects  that  occur 
simultaneously  in  both  sides  of  the  push-pull  system,  but  not  in  push- 
pull  relationship.  This  principle  has  been  applied  to  recording  sound 
on  film  by  recording  two  adjacent  tracks  180  degrees  out  of  phase 
with  each  other. x  The  two  tracks  are  scanned  in  reproducing  so  that 
the  light  transmitted  through  the  individual  tracks  falls  separately 
upon  two  photoelectric  surfaces  connected  to  amplifiers  in  such 
manner  that  the  resultant  voltage  developed  is  proportional  to  the 
difference  in  transmission  of  the  two  tracks.  In  this  manner  the 
push-pull  principle  is  employed  to  balance  out  certain  distortions 
that  otherwise  would  be  reproduced.  These  are  referred  to  in  the 
following  as  "unwanted  components." 

In  order  to  understand  better  the  value  of  push-pull  recording,  we 
shall  classify  here  the  various  sources  of  distortion  ordinarily  en- 
countered in  conventional  recording.  The  exposure  characteristics 
of  the  light- valve  have  already  been  pointed  out,2  and  it  was  shown 
that  pure  sine-wave  modulation  by  the  light-valve  does  not  always 
result  in  a  pure  sine-wave  on  the  film,  but  rather,  a  complex  wave 
with  considerable  second  harmonic  in  the  higher  frequencies.  This 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;    received 
April  20,  1938. 

**  Electrical  Research  Products,  Inc.,  Los  Angeles,  Calif. 
46 


PUSH-PULL  RECORDING  47 

is  the  direct  result  of  the  velocity  with  which  the  film  moves.  Ref- 
erence to  Appendix  A  illustrates  how  the  unwanted  components  thus 
introduced  are  eliminated  in  push-pull  recording.  A  second  effect  of 
the  film  velocity  is  intermodulation  between  the  high  and  low  fre- 
quencies. When  the  modulation  is  sufficiently  high  that  overload 
occurs,  both  even  and  odd  harmonics  are  impressed  upon  the  film 
along  with  other  products  of  the  overload  that  are  of  such  nature  as 
to  be  largely  eliminated  by  the  push-pull  arrangement. 

Another  source  of  distortion  may  be  introduced  in  the  development 
and  printing  process.  It  will  be  recalled3  that  if  the  modulation  of  the 
negative  is  entirely  confined  to  the  straight-line  portion  of  the  nega- 
tive H&D  curve,  and  the  printer  point  is  selected  to  confine  the 
modulation  on  the  print  to  a  similar  part  of  the  print  characteristic, 
the  true  overall  gamma  being  kept  at  unity,  no  unwanted  components 
are  introduced  by  the  processing.  However,  if  the  gamma  is  per- 
mitted to  depart  from  unity  harmonics  are  introduced ;  or,  the  gamma 
being  held  at  unity,  an  improper  selection  of  negative  or  print  density 
will  result  similarly  in  the  introduction  of  harmonics,  as  shown  by 
reference  to  Appendix  B.  The  cancellation  of  harmonics  in  this 
case  by  the  push-pull  process  is  identical  to  that  brought  about  by  the 
use  of  the  push-pull  stage  in  amplifiers  where  the  unwanted  com- 
ponents are  introduced  by  the  curvature  of  the  operating  character- 
istic of  the  vacuum  tubes. 

Another  form  of  unwanted  component  is  introduced  in  film  record- 
ing by  the  process  of  noise  reduction.4  In  this  case,  in  addition  to 
the  signal  recorded  upon  the  film,  some  low-frequency  rectified  com- 
ponents transmitted  through  the  noise-reduction  filter  are  intro- 
duced also,  the  effect  being  sometimes  known  as  "shutter  bump." 
The  existence  of  this  effect  has  restricted  the  application  of  noise- 
reduction  principles.  In  push-pull  recording,  while  the  signal  is 
recorded  on  the  two  tracks  180  degrees  out  of  phase,  the  noise-reduc- 
tion modulation  is  in  phase  on  the  two  tracks.  Thus,  these  unwanted 
noise-reduction  components  being  recorded  in  phase,  are  cancelled 
out  when  the  tracks  are  reproduced  in  push-pull.  This  makes  pos- 
sible a  much  faster-operating  noise-reduction  mechanism  which,  in 
turn,  permits  greater  noise  reduction.  The  faster  type  of  noise  re- 
duction makes  possible  the  use  of  a  much  smaller  "margin"  which,  in 
turn,  tends  to  reduce  the  "hush-hush"  effect  that  is  quite  noticeable 
in  single-track  recordings  of  some  types  of  recorded  sounds.  While 
push-pull  recording  is  instrumental  in  largely  reducing  the  types  of 


48  J.  G.  FRAYNE  AND  H.  C.  SILENT          [j.  s.  M.  p.  E. 

distortion  listed  in  previous  classifications,  perhaps  its  most  spec- 
tacular use  has  been  in  permitting  much  more  effective  use  of  noise 
reduction  or  what  amounts  to  a  much  greater  signal-to-noise  ratio 
of  the  recording  medium. 

Reference  has  been  made  to  the  intermodulation  effects  due  to  film 
velocity.  This  intermodulation  results  in  amplitude  variations  of 
a  high  frequency  recorded  simultaneously  with  a  low  frequency,  the 
amplitude  of  the  high  frequency  being  reduced  when  the  light-valve 
ribbons  open  under  the  action  of  the  low  frequency.  Since  in  push- 
pull  recording  one  half  of  the  valve  is  at  its  maximum  opening  when 
the  other  half  is  at  its  minimum  opening,  the  amplitude  variations  of 
the  high  frequency  are  opposite  on  the  two  halves  of  the  push-pull 
track.  Thus  they  tend  to  offset  each  other  when  the  track  is  repro- 
duced. Variations  that  might  be  as  great  as  20  per  cent  on  a  single 
track  are  reduced  to  only  1  x/4  per  cent  on  the  push-pull  track. 

Under  certain  conditions  of  processing  the  transmission-exposure 
characteristic  may  depart  from  a  straight  line.  If  the  departure  is  at 
one  end  only,  it  introduces  second-order  harmonics  which  are  balanced 
out  in  the  reproduction  of  push-pull  records.  This  form  of  depar- 
ture also  results  in  volume  distortion  and  intermodulation  which  are, 
in  turn,  considerably  reduced  in  push-pull.  When  the  departure  of 
the  transmission-exposure  characteristic  occurs  at  both  ends,  i.  e.,  is 
essentially  symmetrical,  odd-order  harmonics  are  introduced  which 
can  not  be  balanced  out,  and  the  volume  distortion  and  intermodula- 
tion also  are  not  reduced  by  push-pull.  Since  the  "delta  db."  test 
reveals  the  nature  of  the  departure  of  the  transmission -exposure 
characteristic,5  it  provides  a  means  for  readily  checking  the  value  of 
push-pull  recording  in  reducing  this  type  of  distortion,  and  for  de- 
termining the  amount  of  noise  reduction  that  may  safely  be  applied. 
The  latter  is  usually  about  14  db.  in  good  commercial  processing. 

An  incidental  advantage  of  push-pull  recording  is  its  adaptability 
to  certain  forms  of  pre-  and  post-equalization  recently  proposed  by 
Douglas  Shearer  of  the  Metro -Goldwyn-Mayer  Studios.  Since  the 
noise-reduction  action  is  recorded  in  phase  on  both  halves  of  the 
push-pull  track,  any  low-frequency  components  of  this  action  balance 
out  and  are  not  reproduced  as  sound.  Even  when  considerable  over- 
emphasis of  the  low  frequencies  is  given  ih  reproduction  by  means  of 
equalization  the  noise-reduction  action  or  "shutter  bump"  is  still 
inaudible.  Therefore,  by  attenuating  the  low  frequencies  in  re- 
cording and  introducing  an  equivalent  gain  in  reproducing,  several 


July,  1938] 


PUSH-PULL  RECORDING 


49 


incidental  improvements  are  obtained  without  any  sacrifice  in  qual- 
ity. The  reduced  amplitude  of  recorded  low  frequencies  reduces 
still  further  the  intermodulation  between  high  and  low  frequencies. 
There  is  also  a  reduction  of  modulation  of  the  ground-noise  by  low 


FIG.  1.     Four-ribbon  push-pull  light-valve. 


frequencies  of  high  amplitude,  since  their  amplitude  is  kept  low  at  all 
times.  This  results  in  a  greatly  improved  tonal  quality  or  purity  in 
this  register.  Since  the  low  frequencies  are  reproduced  through  an 
equalizer  that  reestablishes  their  relative  levels,  the  high  frequencies 


FIG.  2.     Light-valve  monitoring  by  means  of  quartz  rods. 


of  the  signal  and  of  the  ground-noise  are  reproduced  through  some 
attenuation.  The  result  is  a  reduction  in  apparent  ground-noise, 
with  an  improvement  in  usable  volume  range  of  at  least  5  db.  and  a 
complete  elimination  of  "hush-hush"  on  even  the  most  difficult  re- 
cording material. 


50 


J.  G.  FRAYNE  AND  H.  C.  SILENT          [j.  S.  M.  P.  E. 

PUSH-PULL  RECORDING  EQUIPMENT 


(a)  Recording  Channel. — The  microphone,  recording  amplifier,  and 
mixing  equipment  for  push-pull  recording  are  the  same  as  for  standard 
recording.     The  noise-reduction  unit  is  provided  with  a  special  ad- 
justment producing  a  faster  time  of  operation  (of  the  order  of  6 
milliseconds).     The  noise-reduction  current  is  fed  to  the  light-valve 
through  a  potentiometer  to  balance  the  current  in  each  half  of  the 
light- valve,  thus  insuring  the  same  noise  reduction  on  each  track. 

(b)  Push-Pull   Light-Valve. — The   light-valve   for    push-pull   re- 
cording is  essentially  two  valves,  being  equipped  with  four  ribbons 
instead  of  the  customary  two.     A  valve  with  similar   modulating 


TO  LOUD  SPEAKER 


OQUPU   ELEMENT  PHQTQ-CEIL 

BEAM  SPLITTER  LENS 


LIGHT  VALVE 
PARTIAL    REFLECTOR 


FIG.  3. 


Light-valve  monitoring  by  means  of  partial  re- 
flector plate. 


structure  is  described  in  a  paper  by  E.  C.  Manderfeld.6     A  photograph 
of  the  electromagnet  type  of  valve  is  shown  in  Fig.  1. 

The  normal  spacing  of  the  light-valve  without  bias  is  1.4  mils.  In 
order  to  achieve  the  maximum  noise  reduction  possible,  a  high  ratio 
of  maximum  to  minimum  light-valve  spacing,  under  the  control  of 
the  noise-reduction  circuit,  is  desirable.  Accordingly,  the  noise- 
reduction  device  has  been  designed  to  provide  a  reverse  bias  on  very 
loud  signals,  thereby  causing  the  light-valve  to  open  to  2.0  mils. 
Noise-reduction  settings  of  14  db.  are  entirely  satisfactory,  and  under 
very  carefully  controlled  conditions  excellent  recordings  have  been 
obtained  with  as  much  as  20  db.  of  noise  reduction.  Because  of  the 
fast  operation  of  the  noise-reduction  system  made  feasible  by  push- 
pull  recording,  considerably  reduced  margin  settings  are  possible,  as 


July,  1938] 


PUSH- PULL  RECORDING 


51 


little  as  1  to  2  db.  being  commonly  used.     This  results  in  reduced 
"breathing"  of  the  ground-noise  or  "hush-hush." 

(c)  Push-Pull  Photoelectric  Cell  Monitoring. — Fig.  2  shows  the 
arrangement  of  the  valve  to  provide  photoelectric  cell  monitoring. 
It  will  also  be  noted  that  two  small  rods  extend  from  each  side  of  the 
valve  and  pass  underneath  each  pair  of  ribbons.  These  are  quartz 
rods  which  deflect  a  small  fraction  of  the  modulated  light  from  each 
side  of  the  valve.  At  the  same  time  the  mount  for  these  rods  serves 


CD 
O 

CD 


0  \ 

a 

a 

j—\  . 

100  MIL 

| 

•/^ 
% 

u 

f\(\A" 

'                       " 

i 

,-:,. 

y. 

f\f.A" 

a 

AAC" 

\ 

1 

1 

I 

a 

1                            - 

i 

/: 

fU7«i 

^ 

i  —  i  . 

200  MIL 


i 


O 


-.025' 
-.125 


-.010' 


.095' 
-.095" 


FIG.  4.     Dimensions  of  push-pull  positive  sound- 
tracks. 


provide  a  septum  between  the  two  tracks.     Fig.  2  shows  also  how 
le  light  transmitted  through  the  rods  is  deflected  in  turn  to  individ- 
ial  photoelectric  cells,  the  output  of  the  cells  being  connected  in 
push-pull  to  the  monitoring  amplifier.     Another  monitoring  arrange- 
ment recently  developed  is  shown  in  £ig.  3.     This  consists  of  a  thin 
unsilvered  flat  glass  plate  mounted  at  45  degrees  to  the  recording 
beam,  and  deflecting  a  small  portion  of  the  entire  modulated  light 
through  a  suitable  lens  system,  which  in  turn  produces  upon  the 


52  J.  G.  PRAYNE  AND  H.  C.  SlLENT  [J.  S.  M.  P.  E. 

cathodes  of  a  double-anode  photoelectric  cell  two  enlarged  images  of 
the  recording  slits.  The  monitoring  system  may  be  used  for  standard 
or  push-pull  recording  without  any  change  other  than  operating  a  key. 
(d)  Optical  System. — The  optical  system  used  in  push-pull  record- 
ing is  essentially  the  same  as  that  used  previously  with  standard  re- 
cording. Because  of  the  double  light-valve,  it  is  necessary  to  use  a 
slightly  longer  filament  in  the  exciting  lamp.  The  objective  lens  is 
of  the  type  previously  described,7  but  has  been  specially  designed  to 
give  a  4 : 1  reduction  of  the  light-valve  aperture  at  the  film  plane. 
This  results  in  the  standard  track  width  of  100  mils,  the  center  of  the 


LAMP 

......          OBJECTIVE  SLIT        PEC 

LENS 

3E 

A-USING  DOUBLE  CATHODE  PHOTO-ELECTRIC  CELL 

P£C*I 

OBJECTIVE  SLIT 

LAMP 

'  PRISM 


PEC*2 


B-USING  TWO  PHOTO-ELECTRIC  CELLS 
FIG.  5.     Push-pull  reproducer  optical  systems. 

track  being  54  mils  from  the  inside  edge  of  the  sprocket-holes.  The 
use  of  the  4:1  reduction  makes  it  possible  to  use  a  mean  light-valve 
spacing  up  to  2  mils  without  exceeding  the  V2-mil  image  height  which 
has  been  standard  practice  with  1-mil  light-valves  and  2:1  lens  re- 
duction. The  dimensions  of  the  track  are  shown  in  Fig.  4.  For  origi- 
nal recording  from  which  to  re-record,  and  where  no  interference 
between  sound  and  picture  is  involved,  the  Metro -Goldwyn-Mayer 
Studios  have  produced  push-pull  sound-tracks  through  the  original 
2 :1  lens.  This  results  in  a  track  200  mils  wide,  having  a  signal-to- 
noise  ratio  3  db.  higher  than  that  of  the  100-mil  track.  The  dimen- 
sions of  this  track  are  shown  also  in  Fig.  4. 


July,  1938] 


PUSH-PULL  RECORDING 
FILM  PROCESSING 


53 


In  general,  the  film-processing  practices  and  controls  that  are  used 
in  processing  standard  variable-density  track  are  followed  for  push- 
pull  track.  Because  of  the  balancing  out  of  certain  distortion  com- 
ponents it  is  possible  to  permit  deviations  from  the  customary  prac- 
tices without  having  to  sacrifice  the  standard  of  quality.  However, 
it  is  not  possible  to  obtain  all  of  the  other  benefits  of  push-pull  re- 


P.P. 


USING  TWO    PHOTO-ELECTRIC 
CELLS    RESISTANCE  COUPLED. 


DOUBLE   CATHODE  PEC 


90V. 


USING    DOUBLE  CATHODE 
PHOTO-ELECTRIC  CELL 
TRANSFORMER  COUPLED 


FIG.  6. 


Schematic    diagrams  of  circuits  for 
push-pull  reproducing. 


cording  when  these  deviations  are  permitted.  Thus,  if  no  more  than 
the  usual  amount  of  noise  reduction  is  used,  say,  8  db.,  there  exists 
considerable  latitude  in  print  density  and  overall  gamma  over  which 
a  satisfactory  product  is  obtainable.  If,  on  the  other  hand,  full 
benefit  is  taken  of  the  higher  noise  reduction  possible,  then  film 
processing  is  no  less  critical  than  formerly.  Under  this  condition  devi- 
ations in  overall  gamma  result  in  volume  distortion  of  the  reproduced 
sound,  and  incorrect  print  density  frequently  produces  both  volume 
distortion  and  intermodulation  of  the  recorded 'sounds,  both  of  which 
may  be  practically  non-existent  at  lower  values  of  noise  reduction. 


54  J.  G.  FRAYNE  AND  H.  C.  SILENT  [j.  s.  M.  P.  E. 

PUSH-PULL  REPRODUCTION 

In  order  to  reproduce  two  push-pull  sound-tracks  it  is  necessary 
to  provide  either  two  individual  photocells  or  a  special  photocell 
having  two  cathode  surfaces  and  a  double  anode,  which  amounts  to 
placing  two  individual  photocell  units  within  one  envelope.  An  op- 
tical system  must  be  provided  to  collect  the  light  from  each  sound- 
track onto  the  proper  cathode  surface.  The  image-scanning  method 
of  reproduction  lends  itself  very  readily  to  push-pull  reproduction  and 
has  been  used  quite  extensively  in  re-recording  and  in  theater  repro- 
ducers. Such  an  optical  system  combined  with  a  double  photocell 
and  also  with  the  special  double  anode  photocell  is  shown  in  Fig.  5. 
In  Fig.  6  is  shown  the  method  whereby  either  system  is  coupled 
through  resistance  or  transformer  to  the  amplifier.  The  key  shown 
in  the  figure  is  used  to  switch  the  system  from  push-pull  reproduction 
to  standard  single-track  reproduction,  this  being  the  only  change 
necessary  to  play  either  type  of  track  interchangeably.  Where  a 
push-pull  track  width  of  200  mils  is  used,  it  is  necessary  to  provide 
additional  means  of  switching  from  push-pull  to  standard,  since  the 
center-lines  of  the  two  tracks  are  different. 

Considerable  study  has  been  necessary  to  determine  the  effects  of 
unbalance  between  the  two  halves  of  the  push-pull  tracks.  One  of 
the  factors  contributing  to  this  unbalance  is  weave.  By  proper 
assignment  of  tolerances  at  various  steps  in  the  overall  system,  it 
appears  possible  to  permit  a  weave  of  approximately  =*=  5  mils  in  the 
reproduced  sound-track  without  encountering  appreciable  degrada- 
tion. In  order  to  arrive  at  this  permissible  value  of  weave,  studies 
of  movement  of  film  in  recorders,  printers,  and  projectors  were  made. 
It  was  found  that  the  weave  in  the  recorder  could  be  held  to  ±  1  mil 
by  the  addition  of  a  guide-roller  above  the  main  recording  sprocket 
in  the  standard  Western  Electric  film  recorder.  The  printer  weave 
that  might  be  designated  more  properly  as  displacement  of  track 
position  was  found  to  be  approximately  ±2  mils  from  the  mean 
position.  This  may  be  attributed  to  the  fact  that  in  the  regular 
printer  the  film  at  present  is  guided  by  one  set  of  sprocket  teeth  and 
the  width  of  the  sprocket  tooth  at  the  base  is  4  mils  less  than  the 
sprocket-hole  dimension.  It  was  not  possible  to  study  the  amount 
of  weave  that  may  be  present  in  all  types  of  projectors,  but  it  was 
found  that  in  certain  well  maintained  machines  the  weave  intro- 
duced was  of  the  order  of  =«=2  mils.  Since  in  all  probability  these  in- 
dividual weaves  will  rarely  be  all  in  the  same  direction  at  the  same 


July,  1938]  PUSH-PULL  RECORDING  55 

time,  the  resultant  weave  will  seldom  amount  to  the  =±=5-mil  toler- 
ance permitted  by  the  scanning  system. 

(a)  Track  Balance. — The  improvement  to  be  obtained  from  push- 
pull  recording  by  the  cancellation  of  distortion  may  be  realized  fully 
only  when  the  outputs  from  the  individual  photocells  in  the  repro- 
ducer are  equal,  i.  e.,  in  balance.  Differences  in  sensitivity  of  the 
translating  devices  or  in  the  modulation  of  the  two  tracks  will  neces- 
sarily mean  that  instead  of  complete  cancellation  of  unwanted  com- 
ponents, residuals  of  these  components  will  be  present  to  some  extent. 
In  considering  the  various  elements  that  contribute  to  an  overall 
balance  of  the  two  push-pull  tracks,  the  following  factors  may  be 
listed: 

(1)  Uniformity  of  illumination  of  the  exposing  beam  in  recording, 

(2)  Equal  sensitivity  of  the  two  component  valves. 

(3)  Uniformity  of  illumination  of  the  printer  light. 

(4)  Uniformity  of  illumination  of  the  reproducer  scanning  beam. 

(5)  Equality  of  sensitivity  of  cells  and  associated  coupling  circuits  in  repro- 
duction. 

Contrary  to  the  general  impression,  the  balance  of  the  tracks  is  not 
affected  by  changes  that  may  occur  in  valve  spacing  so  long  as  the 
valve  sensitivity  remains  unchanged.  This  assumes  that  such 
change  of  spacing  does  not  cause  one-half  of  the  track  to  assume  a  non- 
linearity  of  characteristic  not  already  present.  This  is  best  under- 
stood by  reference  to  Appendix  C. 

With  regard  to  the  first  three  items  mentioned  above,  the  illumi- 
nation of  the  exposing  beam  can  be  kept  within  close  limits  by  cor- 
rect adjustment  of  the  exciting  lamp  with  respect  to  the  light-valve 
apertures.  It  has  been  found  that  the  coiled  filament  type  of  lamp 
generally  used  is  very  uniform  in  illumination  across  the  useful 
length  of  the  filament.  The  sensitivity  of  the  two  valves  can  easily 
be  adjusted  within  x/2  db.,  and  will  continue  to  remain  balanced  to 
this  extent  unless  severely  abused  in  the  recording  process.  A  study 
made  of  several  printers  indicated  that  the  variation  of  illumination 
across  the  printer  aperture  in  a  commercial  printer  probably  intro- 
duces the  greatest  possibility  of  unbalance  between  the  tracks.  The 
net  unbalance  in  output  resulting  from  variations  in  negative  and 
positive  density,  from  inequality  in  light-valve  sensitivity,  and  from 
variation  in  printer  illumination,  has  been  found  to  amount  to  a 
maximum  of  about  2.5  db. 


56 


J.  G.  FRAYNE  AND  H.  C.  SILENT  [J.  S.  M.  P.  E. 


In  reproducing  circuits  involving  the  use  of  two  individual  photo- 
electric cells,  these  may  be  selected  having  a  sensitivity  unbalance  of 
not  more  than  1  db.,  and  it  has  been  found  possible  to  produce  a 
double  photocell  having  an  inherent  unbalance  of  the  same  order  of 
magnitude.  Thus  a  maximum  of  about  3.5  db.  is  the  most  that  may 
be  expected  in  the  unbalance  of  two  push-pull  tracks  when  due  pre- 
cautions have  been  taken  to  see  that  the  various  elements  are  lined 
up  with  the  degree  of  accuracy  found  feasible  under  studio  conditions. 


20 


24 


28 


SENSITIVITY  RATIO   OB. 


-  8 


-12 


-16 


-20 


-24 


CURVE  A    LOSS  IN  FUNDAMENTAL 

CURVE  B    SUPPRESSION  OF   2ND  HARMONIC 


VARIOUS  DEGREES  OF  UNBALANCE  IN   P.E.C 


CIRCUITS 


FIG.  7. 


Effect  of  unbalance  between  sides  in  push- 
pull  system. 


In  order  to  appreciate  what  the  effect  of  unbalance  between  the  two 
tracks  means  to  the  suppression  of  unwanted  components,  the  mathe- 
matical analysis  shown  in  Appendix  D  has  been  made,  the  graphical 
results  of  which  are  shown  in  Fig.  7.  The  curves  show  that  a  differ- 
ence in  sensitivity  of  3  db.  results  in  the  reduction  of  the  wanted  com- 
ponents by  about  1.5  db.,  but  suppresses  the  second-order  distortion 
components  by  about  17  db. ;  this  amount  of  suppression  to  be  added, 
of  course,  to  the  amount  by  which  they  are  already  attenuated  in  the 
film  modulation.  It  has  been  shown1  that  in  single-track  light- valve 
recording  in  which  the  image  height  is  0.5  mil,  the  second  harmonic 


July,  1938]  PUSH-PULL  RECORDING  57 

at  4000  cycles  is  19.5  db.  below  the  fundamental.  Additional  sup- 
pression of  only  15.5  db.  would  reduce  this  to  a  total  of  35  db.,  corre- 
sponding to  1.8  per  cent  of  second  harmonic.  Since  the  third  har- 
monic has  been  shown  to  be  negligible  in  the  recording  range,  we  thus 
see  that  the  push-pull  recording  essentially  eliminates  the  unwanted 
components  that  are  present  in  standard  light-valve  recording.  It 
will  be  recalled  that  in  this  process  a  maximum  spacing  of  2  mils  is 
permitted,  but  when  this  is  associated  with  the  4 : 1  lens  reduction,  the 
image  height  is  still  retained  at  the  0.5-mil  value  which  has  been  more 
or  less  the  practice  in  standard  recording.  The  next  principal  source 
of  harmonics  is  introduced  in  the  film  processing,  and  experience  has 
shown  that  if  the  overall  gamma  is  not  permitted  to  vary  more  than 
20  per  cent  from  the  mean  value  of  unity,  the  second  harmonic  will 
not  exceed  more  than  5.0  per  cent  of  the  fundamental.  If  we  add 
this  to  the  ribbon-velocity  components  and  assume  the  15.5-db.  sup- 
pression, we  arrive  at  a  total  suppression  at  4000  cycles  of  31.5  db. 

EXTERNAL  BALANCING  OF  PHOTOCELL  OUTPUT 

In  the  preceding  discussion  on  the  degree  of  balance  to  be  expected 
in  push-pull  recording,  it  has  been  assumed  that  no  special  means  was 
to  be  used  to  achieve  better  balance  than  could  be  accomplished  by 
carefully  lining  up  the  equipment  and  taking  all  necessary  precautions 
in  recording  and  reproducing  to  see  that  no  unnecessary  unbalance 
is  introduced.  However,  it  is  quite  possible  to  balance  the  output 
of  the  two  photoelectric  cells  either  by  reducing  the  light-flux  of  the 
scanning  beam  on  the  cell  showing  the  greatest  output,  or  by  altering 
the  potential  of  the  cell  anodes  in  such  manner  as  to  balance  their 
outputs  more  effectively.  With  either  of  these  methods  it  has  been 
found  possible  to  suppress  the  unwanted  components  as  much  as 
30  db.,  which  is  considerably  more  than  is  necessary. 

TRACK  ALIGNMENT 

A  cause  of  unbalance  that  has  not  been  discussed  hitherto  is  mis- 
alignment of  the  images  on  the  two  tracks.  It  will  be  recalled  that 
the  two  apertures  in  the  light-valve  pole-piece  are  separated  by  a 
considerable  distance  and  that  the  two  recording  beams  passing 
through  these  apertures  are  brought  into  line  by  the  use  of  refractor 
plates.  An  analysis  has  been  made  to  determine  what  the  effect  of 
alignment  is  upon  the  passage  of  the  wanted  and  the  suppression  of 
the  unwanted  components.  The  mathematical  analysis  is  indicated 


58 


J.  G.  FRAYNE  AND  H.  C.  SILENT          [J.  s.  M.  P.  E. 


<M  O 

CJ  <VJ 


July,  1938] 


PUSH-PULL  RECORDING 


59 


in  Appendix  E,  while  in  Fig.  8  is  shown  the  loss  of  wanted  signal  for 
frequencies  up  to  9000  cycles,  and  in  Fig.  9  is  shown  the  degree  of  sup- 
pression of  the  unwanted  components  for  misalignment  values  vary- 
ing from  0.2  mil  to  1  mil.  It  will  be  noted  that  the  effects  are  neg- 
ligible for  misalignment  at  the  film  of  less  than  0.2  mil.  Due  to  the 
use  of  the  4 : 1  reducing  lens,  misalignment  of  that  amount  corresponds 
to  effective  misalignment  of  0.8  mil  at  the  light-valve.  In  practice 
it  has  been  found  quite  feasible  to  make  alignment  adjustments 
within  a  very  small  fraction  of  this  requirement. 

CONCLUSION 

It  has  been  shown  that  the  principal  distortions  in  light-valve 
recording,  such  as  result  from  ribbon  velocity  effect,  light-valve 


^ 

—•s^ 

s 

»n 

*%   -30 

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4% 

V 

^ 

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3% 

5      35 

__. 

-- 

__. 

-X 

— 

— 

•/• 

__. 

___ 



2% 

1 

\ 

/ 

SIN 

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TRAC 

K 

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.30  .40  .50  .60  .70  .80  .90 

PRINT  DENSITIES- VISUAL 

FIG.  10.     Comparison  of  second-harmonic  distortion : 
single  track  vs.  push-pull  track. 

overload,  and  errors  in  film  processing,  have  been  materially  reduced 
by  the  push-pull  method.  In  addition,  the  low-frequency  noise- 
reduction  components  and  certain  other  extraneous  components  of 
accidental  overload  of  the  light-valve  in  regular  recording  are  elimi- 
nated in  the  push-pull  process,  since  they  are  recorded  in  phase  upon 
the  two  component  tracks.  This  makes  possible  the  use  of  increased 
noise  reduction,  up  to  14  db.  being  regarded  as  commercially  prac- 
ticable. In  reproduction  no  trouble  has  been  experienced  from  nor- 
mal weaving  of  the  sound-tracks.  It  has  been  shown  that  the  degree 
of  unbalance  that  may  be  introduced  in  the  output  of  the  two  tracks 
arising  from  errors  of  operation  and  other  discrepancies  introduced 


60  J.  G.  FRAYNE  AND  H.  C.  SILENT  [J.  S.  M.  p.  E. 

in  the  overall  process  is  sufficient  to  suppress  the  unwanted  com- 
ponents more  than  the  15  db.  believed  to  be  sufficient.  Further 
improvement  has  been  made  possible  by  balancing  devices  in 
the  reproducing  mechanism,  where  the  utmost  is  required  for  re- 
recording  purposes.  Additional  advantages  can  be  obtained  by  com- 
bining pre-  and  post-equalization  with  push-pull,  thereby  achieving 
greater  signal-to-noise  ratio,  better  tonal  quality  of  the  low  fre- 
quencies, and  complete  elimination  of  "hush-hush." 

In  the  practical  operation  of  push-pull  systems  in  the  studios,  the 
two  qualities  that  appeal  most  to  the  recording  engineer  are  the  ad- 
ditional noise  reduction  made  possible  by  the  method  and  the  elimi- 
nation of  the  harsh  quality  that  has  hitherto  been  characteristic  of 
light-valve  overload.  The  method  also  permits  considerable  reduc- 
tion in  the  modulation  of  the  light-valve  for  low  input  sounds  which  in 
the  past  would  have  been  masked  by  the  background  noise.  This 
permits  more  natural  recording  of  the  volume  range  without  raising 
the  low  signal  or  depressing  the  high  signals;  in  fact,  for  the  great 
bulk  of  recorded  material,  such  as  dialog,  little  mixing  is  necessary 
with  the  push-pull  method  outlined  here. 

At  the  present  time  the  use  of  push-pull  recording  is  limited  to  origi- 
nal recording,  since  comparatively  few  theaters  are  as  yet  equipped 
to  play  push-pull  track.  However,  a  definite  gain  is  obtained  in 
recording  from  this  type  of  track  to  the  standard  single  track,  com- 
pared to  re-recording  from  standard  to  standard  track. 

REFERENCES 

1  MILLIARD,  J.  K.:     "Push-Pull  Recording,"  /.   Soc.  Mot.  Pict.  Eng.,  XXX 
(Feb.,  1938),  No.  2,  p.  156. 

CBCCARINI,  O.  O. :     "Theoretical  Notes  on  the  Push-Pull  Method  of  Record 
ing  Sound,"  /.  Soc.  Mot.  Pict.  Eng.,  XXX  (Feb.,  1938),  No.  2,  p.  162. 

2  SHEA,  T.  E.,  HERRIOTT,  W.,  AND  GOEHNER,  W.  R.:     "The  Principles  of  the 
Light-Valve,"  J.  Soc.  Mot.  Pict.  Eng.,  XVIII  (June,  1932),  No.  6,  p.  697. 

3  MACKENZIE,  D.:     "Straight  Line  and  Toe  Records  with  the  Light- Valve," 
/.  Soc.  Mot.  Pict.  Eng.,  XVII  (Aug.,  1931),  No.  2,  p.  172. 

4  FRAYNE,  J.  G.,  AND  SILENT,  H.  C.:     "Western  Electric  Noiseless  Recording," 
/.  Soc.  Mot.  Pict.  Eng.,  XVIII  (May,  1932),  No.  5,  p.  551. 

6  ALBIN,  F.  G.:  "A  Dynamic  Check  on  the  Processing  of  Film  for  Sound 
Records,"  J.  Soc.  Mot.  Pict. •  Eng.,  XXV  (Aug.,  1935),  No.  2,  p.  161. 

6  MANDERFELD,   E.   C.:     "Permanent-Magnet  Four-Ribbon  Light-Valve  for 
Portable  Push-Pull  Recording,"  presented  at  the  Spring,  1938,  Meeting  at  Wash- 
ington, D.  C.;  to  be  published  in  a  forthcoming  issue. 

7  HERRIOTT,  W.:     "A  Method  of  Measuring  Axial  Chromatic  Aberration  in  an 
Objective  Lens,"  /.  Soc.  Mot.  Pict.  Eng.,  XX  (April,  1933),  No.  4,  p.  323. 


July,  1938]  PUSH-PULL  RECORDING  61 


FOSTER,  L.  V.,  AND  HERRIOTT,  W. :  "Recent  Optical  Improvements  in 
Sound-Film  Recording  Equipment,"  /.  Soc.  Mot.  Pict.  Eng.,  XXIII  (Sept.,  1934), 
No.  3,  p.  167. 


APPENDIX  A 


The  exposure  impressed  upon  moving  film  by  a  two-ribbon  valve  is  given  by  the 
equation  : 

,   4v  r  •  fbw\         aw   .  ,    i/.  /2bw\    .    2aw        _  ... 

d  =  2a  +  —  I  ji  ^—  j  cos  —  sin  wt  +  lAj*  ^—  J  sm  —  cos  2  wt  +  l/tfi- 

/3fcw\        3aw   .  "I 

-  )  cos  -  sm  3  wt  +  .  .  .  (7) 

V    v  /  r  J 

This  may  be  written  as  : 

e}  =  A  +  5  sin  wt  +  Ccos  2  wt  +  £>  sin  3  wt  +  .  .  .  (2) 

where  ^4,5,  C,  D  correspond  to  the  coefficients  of  the  time  function  above.  If 
eq.  2  represents  the  wave-form  on  one  track,  the  wave-form  on  the  track  180  de- 
grees out  of  phase  is 

e2  =  A  4-  B  sin  (wt  -  180)  +  Ccos  2(wt  -  180)  +  D  sin  3(wt  -  180)        (3) 

On  the  print,  for  correct  development,  the  transmission  wave-forms  will  corre- 
spond to  the  above.  Hence  we  may  express  the  resultant  wave-form,  when  the 
two  tracks  are  correctly  reproduced  in  push-pull,  as  the  difference  of  the  above. 
Thus  the  output 

e  =  ei  —  e-i  =  2  B  sin  wt  +  2  D  sin  3  wt  +  .  .  .  (4) 

all  even  harmonics  cancelling  out. 

APPENDIX  B 

The  relation  between  print  transmission  and  negative  exposure  for  film  process- 
ing where  the  gamma  is  other  than  unity  is: 

Ti  =  K(l  +  b  sin  w>/)7  -o) 

Where  T  =  print  transmission. 

K  =  a  constant. 

b  =  film  modulation. 

7  =  overall  gamma  of  developing  process. 

Thus 


This  reduces  to 


cos  2  wt  _  7  -  2)  63  sin  3 


62  J.  G.  FRAYNE  AND  H.  C.  SILENT          [j.  s.  M.  p.  E. 

which  may  be  written  as 

T}  =  K[a  +  bsmwt  —  c  cos  2  wt  —  d  sin  3  wt] 

As  in  appendix  A\  a  similar  wave-form  180  degrees  out  of  phase  on  the  second 
push-pull  track  will  result  in  complete  cancellation  of  the  second-harmonic  term. 
An  illustration  of  the  measured  cancellation  of  second  harmonics  over  a  wide 
range  of  prints  density  is  shown  in  Fig.  10. 

APPENDIX  C 

The  sample  equation  of  exposure  for  the  light-valve  is  : 

e\  =•  a  -\-  c  sin  wt 
where  a  =  normal  spacing  of  ribbons  and  c  =  amplitude  of  ribbon  movement. 

Assume  that  the  second  valve  in  a  four-ribbon  valve  is  spaced  ma  units,  and 
that  its  sensitivity  is  the  same  as  first  valve.  Then  the  exposure  through  valve 
No.  2  is  e2  =  ma  +  c  sin  wt. 

Now  on  the  print  the  transmission  of  track  No.  1  is  TI  =•  k(a  -\-  c  sin  wt)  and 
that  of  track  No.  2  is  !T2  =  k(ma  +  c  sin  wt}.  The  voltage  developed  by  each 
track  is  thus  kc  sin  wt  and  is  independent  of  m.  This  assumes  that  m  is  of  such 
value  that  the  resultant  exposure  in  valve  No.  2  does  not  bring  out  a  photographic 
unbalance  in  the  modulation  of  the  two  tracks. 

APPENDIX  D 

Assuming  that  equal  sinusoidal  signals  are  recorded  on  both  tracks,  the  voltage 
impressed  upon  the  grid  of  the  first  amplifier  tube  derived  from  track  No.  1  is: 

EI  =  b  sin  wt  +  c  sin  2  wt 
Similarly  for  track  No.  2 

EI  =  nb  sin  wt  —  nc  sin  2  w 

where  n  is  the  sensitivity  ratio  of  the  translating  device.     The  resultant  voltage  is: 
E  =  b(  1  +  n)  sin  wt  +  c  (  1  -  w)  sin  2  wt 

The  output  of  a  push-pull  reproducing  device  thus  unbalanced  relatively  to  that 
of  a  balanced  system  is: 


db.  =  20  log 


The  corresponding  function  for  the  second  harmonic  represents  suppression  of 
that  component,  and  is  expressed  as: 


db.  =  20  log 


The  output  of  second  harmonic  relative  to  the  fundamental  for  any  degree 
of  unbalance  of  the  translating  devices  is  : 


db.  =  20  log   -^-2  +  20  log  c. 
1  ~\~  n  o 


July,  1938  J  PUSH-PULL  RECORDING  63 

APPENDIX  E 

Track  Misalignment. — Assume  k  =  linear  displacement  on  the  film  between 
corresponding  points  of  the  signals,  and  v  the  speed  of  the  film  in  reproduction. 
The  voltages  impressed  on  the  grid  from  tracks  No.  1  and  No.  2  are,  respectively, 

E\  =  a  sin  wt 
E2  =  a  sin  (  wt J 

wk  .    wk 

=  a  sm  wt  cos a  cos  wt  sin  — 

V  V 


E  =  EI  -f  E-2  =  a  1 1  +  cos  —  )  sin  wt  —a  s'n —  cos  wt 

\  V     /  V 

This  reduces  to 

E    =  2a  cos  -  sin  (wt  —  0) 

where 

/        .    wk      \ 
/       sin  —        \ 

0  =  tan-1  a  I  _ 


wk  I 

\  1+  COST/ 

The  loss  of  wanted  signal  is 

db.    =   -20  log  -^  cos  0/2 

=   -20  log  cos  0/2 

The  voltages  of  the  unwanted  signal  from  each  track  are  similar  to  the  above. 
Their  resultant,  however,  is  the  difference  rather  than  the  sum  of  the  individual 
voltages. 

The  amplitude  of  the  unwanted  signal  becomes  E  —  2a  sin  0/2.  The  suppres- 
sion is  db.  =  —20  log  sin  0/2. 

DISCUSSION 

MR.  DAY:  Is  this  suppression  of  noise  or  "hush-hush"  considered  a  novelty? 
I  demonstrated  this  principle  in  1930  and  1931. 

MR.  FRAYNE:  Post-equalization  is  well  known.  It  has  been  used  com- 
mercially in  hill-and-dale  recording  for  about  seven  or  eight  years  and  experi- 
mentally for  a  considerably  longer  period.  It  is  possible  to  find  many  things 
that  have  been  done  in  years  gone  by  that  have  not  been  followed  up,  or  did  not 
originally  work  well  because  of  some  difficulties  at  the  time. 

The  form  of  equalization  used  here  is  not  that  used  in  the  hill-and-dale  method. 
This  particular  type  was  developed  by  Douglas  Shearer,  of  M.  G.  M.,  and  is  a 
peculiar  form  of  equalization  which  reduces  not  only  the  film  noise  but  also  the 
"breathing"  or  "hush-hush"  effects. 


64  J.  G.  FRAYNE  AND  H.  C.  SILENT 

MR.  DAY:  I  believe  my  organization  put  out  the  first  sound-on-film  16-mm. 
projector,  and,  perhaps  foolishly,  we  used  the  light  from  the  projection  lamp  for 
exciting  the  photoelectric  cell.  Naturally  we  had  a  great  deal  of  noise,  so  we  used 
the  same  arrangement  that  you  showed  today,  with  two  photoelectric  cells  buck- 
ing each  other.  Into  the  one  cell  we  put  a  beam  of  light  that  had  only  noise  in  it, 
and  into  the  other  a  beam  modulated  by  both  noise  and  sound.  We  had  very 
satisfactory  sound  by  that  arrangement,  and  found  that  neutralizing  by  two  cells 
worked  very  well,  but  we  had  quite  a  little  difficulty  in  magnetic  elimination 
through  transformer  coils. 

MR.  KELLOGG:  I  did  not  quite  understand  why  the  push-pull  system  makes 
it  possible  to  get  better  results  out  of  pre-equalization  than  you  could  anyhow. 
Am  I  correct  in  assuming  that  the  pre-equalization  is  essentially  what  is  shown 
in  Mr.  Friedl's  paper?  If  so,  why  was  that  particular  form  chosen? 

MR.  FRAYNE:  The  reason  why  push-pull  is  desirable  is  that  the  noise-reduc- 
tion frequencies,  which  I  spoke  of  as  unwanted  components,  being  in  phase  on 
both  sides  of  the  track,  are  relatively  low-frequency  effects.  When  you  raise  the 
low  frequencies  12  db.  to  bring  up  the  low  end  in  the  post-equalization  charac- 
teristic, you  bring  up  the  unwanted  components  by  12  db. ;  to  a  point  where,  in 
some  kinds  of  recording,  especially  of  pianos  or  drums,  they  would  be  above  the 
desirable  level.  The  cancellation  that  the  push-pull  system  offers  is  very  desir- 
able in  getting  rid  of  those  frequencies. 

The  particular  curve  was  arrived  at  by  considering  the  energy  distribution  in 
both  speech  and  music,  film  noise,  and  ear  sensitivity,  and  interrelating  these  in 
such  a  manner  as  to  obtain  the  best  possible  signal-to-noise  ratio.  This  results 
in  practically  eliminating  the  "hush-hush"  and  other  effects  resulting  from  high- 
amplitude  low  frequencies. 

MR.  KELLOGG:  In  other  words,  the  equalization  is  more  or  less  complemen- 
tary to  your  observed  or  experienced  spectral  distribution. 

MR.  FRAYNE  :     More  or  less. 


REPORT  OF  THE  STANDARDS  COMMITTEE* 

The  recent  publication1  of  the  "Revision  of  SMPE  Standards  Pro- 
posed for  Adoption  by  the  Society"  summarizes  the  activities  of  the 
Standards  Committee  for  the  past  two  or  three  years.  These  drawings 
have  all  received  initial  approval  and  final  approval  by  the  Com- 
mittee and  are  referred  to  the  Board  of  Governors  of  the  Society  for 
approval. 

Unfavorable  comments  have  been  received  in  regard  to  the  sound- 
track dimensions  both  for  35-mm.  and  16-mm.  film.  In  the  opinion 
of  the  Chairman  of  the  Committee  these  comments  justify  withhold- 
ing adoption  of  these  two  standards  until  further  study  is  undertaken. 

There  have  been  very  few  comments  on  any  other  drawings  and  it  is 
recommended  that  all  other  drawings  be  adopted  by  the  Society.** 

The  uncompleted  items  at  present  under  consideration  are  as  follows  : 

(1}  A  study  of  the  best  dimensions  for  standard  cores  for  cine  film,  being 
made  by  P.  H.  Arnold. 

(2)  Further  consideration  of  all  the  dimensions  for  35-mm.  and  16-mm. 
sound-tracks. 

(5)  Drawings  for  sprockets  for  16-mm.  sound-film.  These  may  depend,  to  a 
certain  extent,  upon  possible  modifications  of  the  sound-track  dimensions. 

(4)  Revision  of  the  standard  release  print  to  correspond  with  the  revisions 
made  by  the  Academy. 

(5)  Review  and  possible  revision  of  the  glossary  of  technical  terms. 

(6)  Carrying  out  of  actual  tests  of  the  new  sprocket  perforation  of  35-mm. 
film,  which,  it  is  hoped,  will  displace  the  old  Bell  &  Howell  perforation. 

Two  punches  and  dies  have  been  constructed  in  accordance  with  the 
specifications  originally  outlined  by  Howell  and  Dubray,2  and  another 
punch  has  been  constructed  by  the  Agfa  Ansco  Corporation  using  the 
same  radius  at  the  corner  as  the  present  SMPE  perforation.  Tests 
have  been  made,  and  further  tests  are  under  way,  comparing  these 
two  types  of  perforation  both  for  breakdown  in  the  projection  ma- 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;  received 
April  22,  1938. 

**  Subsequently  to  the  preparation  of  this  report,  action  on  the  proposed  re- 
vision of  the  standards  was  taken  by  the  Board  of  Governors  (April  24,  1938), 
all  the  proposals  being  validated  as  SMPE  Standards  with  the  exception  of 
DS35-7-1  and  DSsl6-7-l,  relating  to  35-mm.  and  16-mm.  sound-tracks. 


66 


STANDARDS  COMMITTEE  REPORT 


chine  and  for  steadiness  in  various  types  of  cameras.  Preliminary 
tests  give  some  indication  that  the  Howell  and  Dubray  perforation 
is  not  quite  as  good  as  the  SMPE  perforation  for  durability  in  pro- 
jection, although  it  is  considerably  better  than  the  Bell  &  Howell 
perforation.  Tests  also  indicate  that  in  some  cameras  the  positioning 
of  the  new  perforation  is  exactly  as  good  as  with  the  Bell  &  Howell 
perforation,  but  that  in  other  cameras  it  is  not  quite  as  good.  These 
two  points  will  have  to  be  established  definitely  before  a  decision 
can  be  made. 

REFERENCES 

1  "Revision  of  SMPE  Standards  Proposed  for  Adoption  by  the  Society," 
/.  Soc.  Mot.  Pict.  Eng.,  XXX  (March,  1938),  No.  3,  p.  249. 

2  Report  of  the  Sub-Committee  on  Perforation  Standards,  J.  Soc.  Mot.  Pict. 
Eng.,  XXIX  (Oct.,  1937),  No.  4,  p.  376. 


P.  H.  ARNOLD 
F.  C.  BADGLBY 
M.  C.  BATSEL 
L.  N.  BUSCH 
A.  COTTET 
L.  W.  DAVEE 
A.  C.  DOWNES 
J.  A.  DUBRAY 
P.  H.  EVANS 
R.  E.  FARNHAM 


E.  K.  CARVER,  Chairman 
C.  L.  FARRAND 
G.  FRIEDL,  JR. 
H.  GRIFFIN 
A.  C.  HARDY 
L.  B.  HOFFMAN 
R.  C.  HUBBARD 
E.  HUSE 
C.  L.  LOOTENS 
K.  F.  MORGAN 


T.  NAGASE 
N.  F.  OAKLEY 
G.  F.  RACKETT 
W.  B.  RAYTON 
C.  N.  REIFSTECK 
H.  RUBIN 

0.  SANDVIK 
J.  L.  SPENCE 

J.  VAN  BREUKELEN 

1.  D.  WRATTEN 


THE  INFLUENCE  OF  pH  ON  WASHING  FILMS 
AFTER  PROCESSING* 

S.  E.  SHEPPARD  AND  R.  C.  HOUCK** 


Summary. — Advantages  stated  to  be  obtained  by  adjusting  foxing  baths  and  wash- 
water  to  the  isoelectric  point  of  gelatin  have  been  claimed.  The  advantages  are  said 
to  be  shorter  washing  time,  less  swelling  and  retention  of  water,  with  consequent  im- 
provement in  the  jelly  strength  of  the  wet  emulsion,  and  reduced  drying  time.  In 
the  present  investigation  the  conditions  as  to  pH  of  the  solutions,  and  wash-water, 
rate  of  flow  of  water,  residual  thiosulfate,  etc.,  were  controlled  accurately.  The  re- 
sults indicate  that  with  a  regular  acid  fixing  and  hardening  bath  ( F-25)  there  is  no 
advantage,  but  rather  a  disadvantage  in  washing  at  the  isoelectric  point  (ca.  pH  4.9} 
rather  than  at  pH  7  to  8,  since  the  time  required  to  remove  hypo  to  the  same  degree  is 
increased,  nor  is  less  water  retained.  In  a  non-hardening  acid  fixing  bath,  there  was 
little  difference  in  washing  time,  but  some  gain  in  drying  time  for  the  isoelectric  wash 
because  of  reduced  water  absorption. 


The  principal  object  of  washing  processed  film  is  to  remove  as 
completely  as  possible  the  salts  of  the  fixing  bath,  and  particularly 
thiosulfate,  otherwise  "hypo."  The  retention  of  relatively  very 
small  amounts  of  hypo  makes  the  image  liable  to  discoloration  and 
deterioration.1  The  investigations  of  Hickman  and  Spencer2  have 
demonstrated  that  with  efficient  mechanical  conditions  hypo  can  be 
washed  out  of  a  photographic  (plate)  layer  of  normal  thickness  in 
quite  a  short  time;  they  estimated  the  permissible  residue  in  terms 
of  the  lowest  density  it  was  desired  to  conserve  (against  sulfiding  or 
sulfating) — then  assuming  a  safety  factor  of  10,  suggested  0.00016 
gram  per  sq.  decimeter,  or  about  0.008  mg.  per  sq.  inch.  However, 
in  their  investigations  no  particular  attention  was  paid  to  £H  con- 
ditions as  effecting  the  efficiency  of  washing. 

Recently  this  factor  has  been  considered  by  D.  K.  Allison,3  who 
claims  that  washing  should  be  done  with  water  adjusted  to  the 
isoelectric  point  of  the  gelatin  used  in  the  emulsion.  He  states  that 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;    received 
April  21,  1938.     Communication  No.  666  from  the  Kodak  Research  Laboratories. 
**  Eastman  Kodak  Company,  Rochester,  N.  Y. 

' 


68  S.  E.  SHEPPARD  AND  R.  C.  HOUCK         [j.  s.  M.  P.  E. 

washing  is  accomplished  in  shorter  time  with  consequent  smaller 
water  absorption  by  the  gelatin,  hence  also  less  water  consumption 
and  shorter  drying  time.  In  his  U.  S.  Patent  1,954,512  (1934)  he 
proposes  to  have  the  pH  of  both  fixing  bath  and  wash  water  adjusted 
to  the  same  value.  In  discussion  of  this  proposal3  it  is  stated  that 
"At  pH  values  other  than  the  narrow  range  of  maximum  efficiency, 
the  salts  such  as  hypo  and  alum  are  chemically  combined  with  the 
gelatin  and  can  not  be  entirely  removed."  (Italics  in  original.)  This 
statement  is  not  precisely  correct.  In  general,  gelatin  as  an  am- 
photeric  electrolyte  does  not  combine  with  salts,  but  with  ions;  at 
pH  values  lower  than  the  isoelectric  point,  the  gelatin  becomes  more 
negatively  charged  and  has  a  greater  attraction  (electrostatic)  for 
anions,  while  the  converse  is  the  case  for  pH  values  greater  than  the 
isoelectric  point,  when  the  attraction  for  anions  diminishes,  but  in- 
creases for  cations.  These  facts  are  currently  employed  in  processes 
of  de-ashing  gelatin,4  the  removal  of  anions  (SO4,  PO4,  Cl,  etc.)  being 
effected  by  washing  with  alkaline  water — pH.  8—10,  then  the  com- 
bined cations  are  removed  by  washing  in  weak  acid  (dilute  acetic, 
pH  ca.  4),  finally  with  distilled  water,  pH  5.5,  which  removes  excess 
acetic  until  the  pH  approaches  the  isoelectric  point,  ca.  pH  5.  The 
isoelectric  point  of  gelatins  used  in  photographic  emulsions  may  vary 
from  about  pH  4.7  to  pH  5.2.  As  the  pH  of  wash  water  is  lowered 
from  about  7.5  or  8  (service  water)  to  5  or  lower,  the  attraction  for 
SzOz  (thiosulfate)  and  SO  3  (sulfite)  ions  is  increased,  and  their  re- 
moval is  not  facilitated,  but  hindered.  In  the  paper  and  patent  of 
D.  K.  Allison,  no  criterion  is  given  of  completeness  of  washing  in 
respect  of  removal  of  hypo,  nor  is  the  washing  procedure  described 
in  any  precise  fashion.  In  view  of  the  facts  and  claims  cited  it 
seems  desirable  to  study  the  effect  of  pH  upon  washing,  using  a 
mechanically  reproducible  procedure,  and  an  efficient  test  for  re- 
moval of  hypo. 

EXPERIMENTAL 

All  the  experiments  were  made  at  18°C  (64.4°F).  The  emul- 
sion used  was  Eastman  motion  picture  positive.  The  solutions  used 
during  processing  are  outlined  below : 

(1)  The  developer  was  D-16  without  the  developing  agent.  The 
developing  agent  was  omitted  to  facilitate  the  test  used  to  determine 
satisfactory  washing.  This  will  be  described  separately.  The  time 
of  development  in  all  cases  was  5  minutes. 


July,  1938] 


INFLUENCE  OF  pH  ON  WASHING  FILMS 


69 


(2)  A  rinse  water  of  15  seconds  was  inserted  between  the  de- 
veloper and  fixing  bath.     This  rinse  water  was  the  same  as  the  final 
wash  water. 

(3)  Various  fixing  baths  were  used.     The  first  tests  were  made 
with  F-25,  an  acid  hardening  fixing  bath  recommended  for  use  with 
Eastman  motion  picture  positive  film.     The  pH  was  varied  from  4.1 
as  received  to  pH  4.8,  depending  upon  the  test. 

Other  experiments  were  made  with  non-hardening  fixing  baths. 
The  pH  was  varied  in  these  cases  from  pH  4.1  to  4.8.  The  time  of 
fixation  in  all  cases  was  5  minutes.  The  results  with  hardening  and 
non-hardening  fixing  baths  will  be  described  separately. 

(4)  The  wash  water  used  was  tap  water  with  a  pH,  as  taken, 


TO   VACUUM 


TO  DRAIN  •* — 


ADJUSTABLE: 

KODAK  FILM 
TANK  REEL. 


•* WASH   WATER 


FIG.  1.     Diagram  of  washing  apparatus. 

varying  from  7.8  to  8.0.  In  part  of  the  experiments  the  pH  of  the 
tap  water  was  reduced  to  pH  4.8  by  addition  of  acetic  acid. 

The  rate  of  flow  of  water  through  the  washing  apparatus  was  275 
cc.  of  water  per  minute.  This  was  checked  during  each  experiment. 

The  film  to  be  washed  was  wound  onto  a  reel  from  an  adjustable 
Kodak  film  tank.  This  reel  gives  a  continuous  Vs-inch  separation 
of  the  film  throughout  its  entire  length  of  5  feet.  The  reel  fits  nicely 
into  1500-cc.  beakers,  which  were  used  in  the  processing.  After 
developing,  rinsing,  and  fixing,  the  reel  was  connected  to  the  shaft  of 
a  Cenco  Motsinger  vacuum  stirrer  and  lowered  into  the  washing 
vessel.  This  stirrer  is  operated  either  by  water  suction  or  vacuum 
pump,  and  gives  an  up-and-down  movement  of  69  times  per  minute. 
The  wash  water  was  siphoned  from  the  container  in  the  thermostat 
at  the  rate  of  275  cc.  per  minute.  The  washing  set-up  is  shown 
diagrammatically  by  Fig.  1. 


70 


S.  E,  SHEPPARD  AND  R.  C.  HOUCK         [j.  s.  M.  P.  E. 


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INFLUENCE  OF  pH  ON  WASHING  FILMS 


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S.  E.  SHEPPARD  AND  R.  C.  HOUCK         [J.  s.  M.  p.  E. 


Washing  was  continued  until  a  negative  azide  test  on  the  fixed 
emulsion  itself  was  obtained.  The  azide  test  used  was  that  de- 
scribed by  Jelley  and  Clark.5  The  solutions  were  made  as  described 
and  recommended  by  them.  The  test  was  made  on  the  gelatin 
surface  instead  of  the  wash  water.  A  definite  amount  of  the  test 
solution  0.05  c.  c.  was  placed  upon  the  gelatin  surface  after  removing  ex- 
wash  water  by  blotting.  This  solution  was  spread  over  a  square- 
inch  of  surface.  If  the  blue  color  persisted  after  one  minute,  the  film 
was  considered  washed.  The  time  in  minutes  to  reach  this  point 
was  taken  as  the  washing^time,  tests  being  made  every  two  minutes. 
The  test  was  facilitated  by  using  D-16  without  developing  agent, 
the  change  from  blue  to  colorless  being  easy  to  see. 

Percentage  gains  in  weight,  drying  rates,  and  drying  times  were 
determined  on  the  washed  film.  The  drying  rate  and  drying  time 
were  determined  by  removing  the  excess  water  from  the  washed  film 
by  blotting  off  with  filter  paper,,  then  placing  this  film  in  a  drying 
atmosphere.  The  drying  was  done  at  75°F  with  air  at  47  per  cent 
relative  humidity  moving  over  the  film  at  the  rate  of  60  feet  per 
minute.  Weighings  were  made  every  two  minutes  until  approxi- 
mately constant  weight  was  obtained.  The  time  for  the  emulsion 
to  be  dry  to  the  touch  was  also  determined.  This  is  given  as  the 
drying  time  in  all  the  tables  of  data.  Actually  the  emulsion  con- 
tinued to  lose  weight  for  several  minutes  after  the  "dry-to-the- 
touch"  point  was  obtained.  The  emulsion  then  was  dried  further 
over  phosphorous  pentoxide.  The  weight  of  the  sample  was  deter- 
mined by  washing  off  the  dried  gelatin  and  weighing  the  base.  From 
the  data  obtained,  the  percentage  gain  in  weight  was  calculated. 

The  results  obtained  with  hardening  and  non-hardening  fixing 
baths  will  be  described  separately. 

Acid  Hardening  Fixing  Baths. — Typical  results  obtained  using  the 
acid  hardening  fixing  bath,  F-25,  at  />H  4. 1  are  given  in  Table  I.  The 
drying  curves  are  given  in  Fig.  2. 

TABLE  I 

Effect  of  pH  of  Wash  Water  on  the  Washing  and  Drying  of  Motion  Picture  Film 
Processed  with  Acid  Hardening  Fixing  Bath  at  pH  4.1 


£H 
Fixing     Fixing 
Bath        Bath 

Wash 
Water 

*>H 
Wash 
Water 

Time             « 
to' 
Wash 

Time  to 
"Dry  to 
Touch" 

%  Gain 
in 
Weight 

F-25       4.1 
F-25       4.1 

Tap  water 
Tap   water    + 
AcOH 

7.8 

4.75 

13-15  min. 
>45  min. 

18  min. 
18-19  min. 

440 
446 

July,  1938] 


INFLUENCE  OF  pH  ON  WASHING  FILMS 


73 


As  can  be  seen  from  the  data  and  curves,  lowering  the  pH  of  the 
wash  water  from  pH  7.8  to  4.75  has  not  resulted  in  a  shorter  washing 
time  but,  on  the  contrary,  has  increased  the  washing  time  consider- 
ably. The  drying  times  are  about  the  same,  a  fact  that  one  would 
expect  since  the  percentage  gains  in  weight  are  practically  the  same. 
Agreement  in  the  drying  times  is  further  checked  by  the  drying 
curves.  These  coincide  almost  exactly. 

TABLE  II 

Effect  of  pH  of  Wash  Water  on  the  Washing  and  Drying  of  Motion  Picture  Film 
Processed  with  Acid  Hardening  Fixing  Bath  at  pH  4.74 


Fixing 
Bath 

PH 
Fixing 
Bath 

Wash                  Wash 
Water                Water 

Time 
to 
Wash 

Time  to 
"Dry  to 
Touch" 

%  Gain 
in 
Weight 

F-25 
F-25 

4.74 

4.74 

Tap  water          7  .  8 
Tap  water  +  AcOH  4.74 

10-11  min. 
25-26  min. 

18  min. 
16  min. 

458 
448 

Data  obtained  similarly,  but  with  the  />H  of  the  fixing  bath  in- 
creased to  pH.  4.74,  are  given  in  Table  II  and  Fig.  3.  Again,  lower- 
ing the  pH  of  the  wash  water  from  pH  7.8  to  4.74  has  not  decreased 
but  has  increased  the  washing  time. 

Comparing  the  case  claimed  by  Allison  as  giving  the  greatest  gain, 
that  in  which  the  fixing  bath  and  the  wash  water  are  at  the  £H  of  the 
isoelectric  point  of  the  gelatin,  with  the  one  in  which  the  fixing  bath 
is  at  pH  4.1  and  the  wash  water  at  />H  7.8,  it  is  seen  from  data  in 
Table  III  that  again  the  time  to  wash  is  increased  at  pYL  4.74,  with  an 
insignificant  gain  in  drying  This  is  shown  in  Fig.  4. 

TABLE  III 

Comparison  of  Film  Processed  Normally  and  Film  Processed  with  All  Solutions 
except  Developer  at  pH  of  Isoelectric  Point  of  Gelatin 


Toyr 

Process 

PH 
Fixing    Fixing 
Bath        Bath 

PH 
Wash           Wash 
Water         Water 

Time 
to 
Wash 

Time  to 
"Dry  to 
Touch" 

%  Gain 
in 
Weight 

Normal 
"Iso" 

F-15     4.1 
F-25     4.74 

Tap  water     7  .  8 
Tap  water 
+  AcOH      4.74 

13-15  min. 
25-26  min. 

18  min. 
16  min. 

440 

448 

In  the  case  of  an  acid  hardening  and  fixing  bath,  when  the  criterion 
of  hypo  removal  was  the  azide  test,  isoelectric  washing  increased  the 
time  required  for  washing,  and  showed  no  appreciable  gain  in  drying. 
The  azide  test,  in  the  presence  of  gelatin,  detects  definitely  between 
0.05  to  0.01  mg.  per  sq.  inch,  which  tends  to  the  same  order  as  the 
safety  factor  suggested  by  Hickman  and  Spencer. 


74 


S.  E.  SHEPPARD  AND  R.  C.  HOUCK 


Non-Hardening  Fixing  Baths. — Similar  studies  were  made  with 
non-hardening  fixing  baths,  the  fixing  bath  used  being  F-25  without 
hardening  agent.  In  this  case  the  pR  of  the  fixing  bath  was  raised 
to  £H  4.72  in  all  the  experiments. 

Typical  results  obtained  are  given  in  Table  IV  and  Fig.  5. 

TABLE  IV 

Effect  of  pH  of  Wash  Water  on  the  Washing  and  Drying  of  Motion  Picture  Film 
Processed  with  Non-Hardening  Fixing  Bath  F-22  without  Alum 


pn 

Fixing 
Bath 

Wash 
Water 

PH 
Wash 
Water 

Time 
to 
Wash 

Time 
to  Dry 

%  Gain 
Weight 

4.72 

Tap  water 

7.8 

13  min. 

29-30  min. 

608 

4.72 

Tap  water  +  AcOH 

4.69 

13-15  min. 

20-21  min. 

461 

4.72 

Same 

4.59 

17-19  min. 

23  min. 

510 

4.72 

Same 

4.41 

21-24  min. 

28-29  min. 

557 

As  seen  from  the  data  in  the  table,  there  is  no  shortening  of  the 
washing  time  on  lowering  the  pH  of  the  wash  water  from  7.8  to  pH 
4.69.  Less  water  is  taken  up  by  the  gelatin,  and  this  accounts  for 
the  shorter  and  faster  drying.  This  decreased  drying  time  checks 
the  results  obtained  by  Allison  but,  on  the  other  hand,  the  time  to 
wash  is  not  materially  reduced.  If  the  pH  is  decreased  to  pH  4.41, 
the  time  to  wash,  per  cent  gain  in  weight,  and  drying  time  increase. 

It  is  concluded  from  the  results  obtained  that  washing  of  an  emul- 
sion that  has  been  processed  with  non-hardening  fixing  baths  is  im- 
proved by  the  use  of  wash  water  at  the  isoelectric  point  of  gelatin 
only  in  that  the  amount  of  wash  water  taken  up  is  decreased.  This 
results  in  a  decreased  drying  time. 

Our  thanks  are  due  to  Mr.  C.  Dittmar,  who  carried  through  a 
large  number  of  the  experiments  described  in  this  paper. 

REFERENCES 

1  Cf.  LUMIERE,  A.,  LUMIERE,  L.,  AND  SsYEWETZ,  A.:     "The  Fading  of  Positive 
Photographic  Prints  Printed  on  Chlorocitrate  of  Silver  Paper,  Toned  and  Fixed 
in  One  Operation,"  Phot.  J.,  42  (Nov.,  1902),  No.  10,  p.  225. 

2  HICKMAN,  K.  C.  D.,  AND  SPENCER,  D.  A.:     "The  Washing  of  Photographic 
Products,"  Phot.  J.,  62  (May,  1922),  p.  225. 

3  ALLISON,  D.  K.:     "Accurate  Lab.  Control.      Pt.  3.      £H  in  Processing,"  In- 
ternal.   Phot.,  9  (June,  1937),  No.  5,  p.  35. 

4  NORTHROP,    J.    H.,    AND    KUNITZ,    M.:     "Preparation   of    Electrolyte-Free 
Gelatin,"  /.  Gen.  Physiol.,  11  (May  20, 1928),  No.  5,  p.  477. 

8  JELLEY,  E.  E.,  AND  CLARK,  W.:  "A  Sensitive  Test  for  Thiosulfates,"  Phot. 
J.,  70  (May,  1930),  p.  234. 


PROBLEMS  INVOLVED  IN  FULL-COLOR  REPRODUCTION 
OF  GROWING  CHICK  EMBRYO* 


E.  S.  PHILLIPS** 

Summary. — Attempts  to  record  on  16-mm.  color-film  the  structural  changes  taking 
place  during  the  21-day  incubation  period  of  the  hen's  egg  present  problems  varying 
with  each  day's  growth.  Because  the  authors  were  working  with  living  subjects  that 
required  strict  adherence  to  narrow  tolerances  in  order  to  maintain  normal  embryo- 
logical  development  and  even  life  itself,  it  was  necessary  to  adapt  photography  to  the 
problem — not  the  reverse,  as  is  often  possible. 

Development  of  the  embryo  is  shown  in  three  different  ways,  i.  e.,  by  transmitted 
light,  with  shell  entire;  removal  of  part  of  the  shell  and  subsequent  photography  by 
reflected  light;  removing  the  entire  shell  and  placing  the  embryo  in  a  watch  crystal, 
thus  showing  all  parts  in  relative  sizes. 

In  all  three  methods,  temperature,  humidity,  and  light  control  constituted  the  major 
problems.  Special  equipment  devised  to  meet  the  requirements  of  both  normal  incuba- 
tion and  photography  had  to  be  built,  and  the  use  of  mineral  oil  to  obtain  a  transparent 
plane  surface  over  the  opaque,  irregular.,  inner  membrane  of  the  egg's  air-cell  was 
evolved. 

Color  motion  pictures  have  provided  a  distinct  contribution  in  reproducing  accu- 
rately the  structural  changes  occurring  during  the  incubation  period. 

The  recent  introduction  of  easily  manipulated  color-film  has  now 
made  possible  the  recording  of  biological  phenomena  that  hitherto 
have  been  unsuccessfully  reproduced  on  black-and-white  film.  This 
results  because  of  the  distinct  limitations  of  black-and-white  film  in 
recording  brightness  differences  that  become  immediately  obvious 
when  portrayed  in  color. 

A  biological  occurrence  of  this  kind  has  recently  been  solved  by 
Professor  Alexis  Romanoff,  of  the  Poultry  Department  of  Cornell  Uni- 
versity, and  the  author.  The  problem  was  to  show  the  process  of 
development  that  takes  place  during  the  21 -day  incubation  period  of 
a  hen's  egg.  Inasmuch  as  the  authors  were  dealing  with  problems  so 
close  to  the  creation  of  life,  namely,  the  formation  of  a  living  animal 
as  it  progresses  through  the  delicate  changes  preceding  hatching,  and 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;    received 
April  19,  1938. 

**  Cornell  University,  Ithaca,  N.  Y. 

75 


76  E.  S.  PHILLIPS  [J.  s.  M.  p.  E. 

final  independence  as  an  individual,  photographic  methods  had  to 
be  limited  to  the  narrow  tolerances  vital  to  maintaining  normal 
development  and  even  life  itself. 

The  Motion  Picture, — Very  few  persons  have  witnessed  the  miracu- 
lous transformations  that  take  place  within  the  protective  shell  of  an 
egg  as  a  new  living  creature  develops.  In  the  short  period  of  three 
weeks  a  seemingly  inert  object  assumes  definite  form,  emerges  from 
its  confining  walls,  and  independent  life  begins.  To  portray  this 
miracle  adequately,  the  authors  and  Mr.  Meade  Summers  of  the 
Ralston  Purina  Company,  sponsors  of  the  project,  determined  to 
show  development  in  three  ways.  The  first  series  of  pictures  depicts 
growth  as  seen  through  the  shell  wall  by  means  of  transmitted  light. 
The  second  series  was  made  by  cutting  a  hole  about  one  inch  in  di- 
ameter at  the  blunt  end  of  the  egg.  With  the  proper  lighting  align- 
ment it  was  possible  to  see  clearly  within  the  egg  itself.  In  the  third 
series  the  entire  contents  of  the  shell  were  emptied  into  a  large  watch- 
crystal.  As  a  grand  finale  an  egg  actually  hatches  before  the  camera 
lens. 

Problems  Involved. — The  problems  involved  in  filming  this  sequence 
of  events  were  the  same  as  those  in  controlling  normal  incubation  con- 
ditions. The  temperature  of  the  egg  had  to  be  maintained  at  99l/2°  F. 
Humidity,  although  not  so  critical  as  temperature  control,  never- 
theless had  to  be  kept  as  near  the  optimum  value  as  possible.  Since 
normal  development  was  shown  three  different  ways,  these  conditions 
varied  slightly  in  each  case. 

Photographic  Equipment. — The  photographic  equipment  consti- 
tuded  a  16-mm.  Eastman  Special  camera  with  a  1-inch //1. 9  lens,  a 
3-inch //4.5  lens,  and  a  4-inch  f/2. 7  lens.  The  time-lapse  mechanism 
made  expressly  for  the  Eastman  Special  was  used  for  all  pictures  taken 
by  transmitted  light. 

Pictures  by  Transmitted  Light. — Commercial  hatcherymen  normally 
view  incubating  eggs  by  candling;  that  is,  by  placing  the  unbroken 
egg  before  a  light-source  and  viewing  the  contents  by  transmitted 
light.  To  duplicate  this  practice  a  special  incubator  box  and  lamp- 
housing  were  designed,  shown  in  Fig.  1 .  Light  from  a  No.  4  photo  flood 
lamp  passed  through  a  water-cell  which  removed  heat  radiating  from 
the  bulb.  Slightly  above  the  water-cell  a  condensing  lens  focused 
the  light  upon  the  egg.  The  egg  was  supported  by  an  opaque,  velvet- 
covered  mat  with  a  hole  the  exact  shape  but  slightly  smaller  than  the 
minimum  egg  size.  The  entire  mat  was  held  in  a  glass-  covered  incuba- 


July,  1938] 


REPRODUCTION  OF  CHICK  EMBRYO 


77 


tor  box.  A  velvet-lined  tube  extended  from  the  plate-glass  covering 
of  the  incubator  box  to  the  camera  lens,  to  protect  the  egg  from  any 
possible  extraneous  light.  Heat  within  the  box  was  supplied  by 
ordinary  resistance  wire,  controlled  by  a  thermostat  to  within  0.2 °F. 
To  guard  against  short  periods  of  overheating,  a  water  cooling-coil 
was  installed.  Conduction  of  heat  from  the  lamp-housing  was  re- 
duced by  forced  ventilation.  The  same  incubator  box  was  used  with 


FIG.  1.      Incubator  box  and  lamp  house. 

but  slight  modification  for  all  the  pictures  portraying  embryonic  de- 
velopment by  other  methods. 

The  f/2.7  4-inch  lens  was  used  in  making  all  pictures  by  trans- 
mitted light.  Exposures  varied  on  Type  A  Kodachrome  film  from  l/30 
second  per  frame  for  a  fresh  egg  to  6  seconds  per  frame  for  the  20-day- 
old  embryo.  This  wide  range  was  caused  by  the  increasing  opacity 
of  the  growing  embryo. 

Embryo  Viewed  through  Aperture  in  Egg-Shell. — The  second  series 
in  the  motion  picture  shows  the  development  of  the  embryo  as  seen 
from  the  blunt  end  of  the  egg.  Preparing  specimens  for  this  series 
was  extremely  difficult,  particularly  from  the  5th  to  the  13th  day  of 


78 


E.  S.  PHILLIPS 


[J.  S.  M.  p.  E. 


Mineral  Oil 


Inner 

Membrane 

Shell 


incubation.  Professor  Romanoff  skillfully  removed  both  the  shell 
and  the  shell-membranes  at  the  large  end  of  the  egg.  When  that  was 
done  it  was  possible  to  look  within  the  shell  and  clearly  see  the  de- 
veloping embryo.  This  procedure  was  followed  until  the  embryo  was 
13  days  old,  at  which  time  removal  of  the  inner  membrane  became  so 
difficult  (because  hemorrhages  were  invariably  produced)  that  a  new 
method  had  to  be  employed.  In  its  normal  state  this  membrane  is 
white  and  practically  opaque.  After  considerable  experimentation 
the  authors  evolved  a  technic — old  in  principle  but  new,  it  is  believed, 
in  application.  When  painted  with  an  oily  substance  the  membrane 
became  transparent.  But  to  complicate  the  photographic  problem 

the  membrane  wrinkled  and  pro- 
duced innumerable  highlights 
which  precluded  any  possibility 
of  a  clear-cut  picture.  Any 
movement  on  the  part  of  the 
embryo  changed  the  surface 
structure  and  accentuated  the 
undesirable  effect.  Mineral  oil 
floated  upon  the  invaginated 
inner  shell  membrane  (at  the 
air-cell  space)  provided  the  most 
satisfactory  solution  (Fig.  2). 
In  addition  to  making  the  mem- 
brane transparent  the  oil  formed 
a  plane  surface  through  which  it 
was  possible  to  photograph  clearly.  By  building  the  oil  surface  con- 
siderably higher  than  the  membrane,  embryonic  movement  pro- 
ceeded without  inducing  any  photographic  difficulties. 

In  Fig.  3  is  shown  the  incubator  box,  with  the  egg  placed  vertically 
on  a  black-velvet-covered  base.  This  support  was  made  slightly 
smaller  than  the  sides  of  the  box  to  allow  free  air  circulation.  The 
cover  was  plate  glass.  Two  lights  with  reflectors  were  placed  approxi- 
mately 32  inches  apart;  one,  a  No.  2  photoflood,  was  17  inches  from 
the  egg;  and  the  other,  a  No.  1  photoflood,  was  15  inches  from  the 
egg.  The  two  lights  and  the  egg  were  aligned  on  the  same  axis  at  a 
30-degree  angle  to  the  glass  top.  This  eliminated  direct  reflection 
from  the  oil  surface,  cast  enough  shadow  to  emphasize  delicate  struc- 
tural details,  and  gave  an  illusion  of  depth. 

The  greatest  difficulty  encountered  in  filming  these  activities  was 


FIG.  2.  Mineral  oil  placed  upon  the 
inner  membrane  to  produce  trans- 
parency. 


July,  1938] 


REPRODUCTION  OF  CHICK  EMBRYO 


79 


to  maintain  strict  temperature  control.  If  the  temperature  became 
too  high,  embryonic  movement  was  accelerated,  and  the  converse  was 
true  with  temperatures  lower  than  normal.  The  reason  is  obvious 
when  we  consider  the  high  radiant  energy  emitted  from  the  two  light- 
sources.  Although  it  is  true  that  this  entire  series  of  pictures  was 
made  without  controlling  radiant  energy,  if  the  work  were  to  be 
duplicated,  either  water-cells  or  heat-absorbing  glass  would  be  used. 
Determining  the  exact  exposure  was  exceedingly  difficult  because 
the  reflectivity  of  the  embryo  changed  from  day  to  day  as  it  under- 
went structural  changes.  In  general,  it  may  be  said  that  the  first  few 
days  of  development  required  less  exposure  than  the  intermediate 
stages,  and  the  last  few  days  of  growth  the  least  exposure  because  of 


••t«r 

3t«t 

• 

f=~\ 

-     c 

-  —  i  ) 

V«lT«t 

x^/ 

-  EMtlBM 

Coll 

£ 

FIG.  3. 


Incubator  box,  with  egg  placed  vertically  on  velvet- 
covered  base. 


the  formation  of  down  and  its  high  reflecting  value.  The  lens  used 
for  these  pictures  was  the  4-inch //2. 7,  and  the  exposure  was  approxi- 
mately 1/80  second  at  f/8. 

"Close-ups"  of  the  heart  presented  an  interesting  problem  in  focus- 
ing. Since  the  working  distance  between  the  lens  and  the  subject 
was  very  short,  focusing  had  to  be  very  critical.  However,  it  is  well 
known  that  when  an  egg's  contents  are  placed  upon  an  approximately 
flat  surface  sagging  of  the  yolk  occurs.  Thus,  it  is  obvious  that  as  the 
yolk  slowly  receded,  the  embryo,  which  was  on  the  top  surface  of  the 
yolk,  moved  away  from  the  lens,  thus  throwing  the  picture  out  of 
focus. 

Pictures  with  Embryo  in  Watch- Crystal. — The  third  series,  showing 
the  egg's  contents  emptied  into  a  watch-crystal,  presented  approxi- 
mately the  same  difficulties  as  did  the  preceding  pictures,  with  two 
exceptions — humidity  and  radiant  energy.  With  much  of  the  egg 


80  E.  S.  PHILLIPS  [J.  s.  M.  P.  E. 

content  exposed  to  the  air,  both  evaporation  and  absorption  of  radiant 
heat  were  increased,  thus  accentuating  the  effects  noted  in  the  pre- 
vious series. 

Hatching  Pictures. — The  most  tedious  series  of  exposures  were 
those  made  at  the  hatching  period.  Relative  humidity  had  to  be 
maintained  at  65-70  per  cent  to  insure  a  normal  hatch.  Because 
of  the  high  humidity,  condensation  upon  the  glass  cover  of  the  incu- 
bator box  made  photography  difficult.  Also,  the  emerging  chick 
was  extremely  conscious  of  visible  light  and  often  ceased  all  activity 
as  the  exposure  was  made.  However,  the  greatest  difficulty  arose 
because  of  extreme  variations  in  the  hatching  time  for  each  individual, 
for  some  chicks  emerged  in  ten  minutes  and  some  in  three  hours. 

General. — So  far  as  general  comments  are  concerned  the  motion  pic- 
ture Where  Chick  Life  Begins  took  three  months  to  produce,  more 
than  2000  eggs  were  used,  and  five  separate  originals  were  made  at 
the  same  time.  It  should  also  be  said  that,  with  the  exception  of  cer- 
tain scenes  incorrectly  exposed,  the  fidelity  of  color  reproduction  is 
excellent.  At  the  present  writing  more  than  40,000  persons  in  all  sec- 
tions of  this  country  and  parts  of  Canada  have  seen  the  picture,  and 
more  than  500  written  requests  (from  all  over  the  nation)  for  its  use 
have  been  refused. 

It  is  this  author's  opinion  that  if  we  exclude  the  interest  inherent 
in  the  subject  itself,  the  enthusiastic  reception  that  this  picture  has 
received  is  due  more  to  its  reproduction  in  color  than  to  any  other 
technic  involved.  Furthermore,  if  the  picture  may  be  regarded  as  a 
fair  example  of  what  can  be  done  in  the  biological  sciences,  the  latent 
possibilities  for  similar  projects  are  enormous  in  variety  and  number. 

DISCUSSION 

MR.  KELLOGG:    How  much  film  footage  was  used? 

MR.  PHILLIPS:  That  is  difficult  to  say,  because  in  addition  to  the  three  months 
for  making  the  picture,  there  was  about  a  month  of  experimental  work,  during 
which  we  used  probably  400  or  500  feet  of  film  to  determine  the  exposure  ex- 
perimentally. We  often  had  pictures  that  did  not  show  what  we  wanted  to  show, 
from  an  embryological  point  of  view,  so  we  had  to  discard  them.  So  far  as 
exposure  is  concerned,  we  lost  about  500  or  600  feet  and  used  approximately,  as 
a  grand  total,  about  8000  feet  of  film. 

The  film  has  been  shown  in  a  great  many  schools  throughout  the  country.  The 
Purina  Company  received  four  copies  and  the  University  one,  and  Professor 
Romanoff  has  shown  the  film  extensively  in  schools  of  higher  education. 

MR.  ROGER:  I  wish  to  congratulate  the  makers  of  this  film,  Professor  Romanoff 
and  Mr.  Phillips,  for  the  excellent  material  we  have  had  the  opportunity  of  seeing. 


July,  1938]  REPRODUCTION  OF  CHICK  EMBRYO  81 

I  have  produced  a  lot  of  such  material  myself,  not  only  on  embryos  but  also  on 
living  tissue  and  blood  cells,  and  I  realize  how  difficult  it  was  to  get  the  material 
together  and  make  the  picture.  As  Mr.  Phillips  has  indicated,  temperature  and 
conditions  of  light,  heat,  and  so  on  have  much  to  do  with  the  success  of  the  film. 

MR.  TUTTLE:  What  was  the  relative  humidity  during  the  incubation  period; 
and  how  long  do  the  embryos  live? 

MR.  PHILLIPS:  The  relative  humidity  was  approximately  70  per  cent,  slightly 
above  the  value  for  normal  incubation. 

The  eggs  with  the  shell  opened  at  one  end  may  be  capable  of  hatching,  but  in 
our  work  we  used  mineral  oil  at  the  opening,  which  caused  suffocation  of  the 
embryo  in  a  relatively  short  period  of  time.  The  embryos  broken  into  the 
watch  crystal  did  not  live  more  than  a  few  minutes,  or  at  the  most  several  hours. 

MR.  KELLY:  The  chick's  supply  of  oxygen  depends  upon  a  continuous  supply 
through  the  shell,  does  it  not? 

MR.  PHILLIPS:  Yes.  The  shell  is  permeable,  as  is  also  the  membrane.  This 
allows  for  interchange  of  gases. 

MR.  KELLOGG  :  How  do  you  dispose  of  waste  products,  or  render  them  harm- 
less? 

MR.  PHILLIPS:  Aside  from  carbon  dioxide,  the  waste  is  not  a  large  item;  it  is 
usually  left  in  the  alantoic  sac,  as  it  is  called,  at  hatching. 


DOCUMENTARY  FILM  STUDY  -A  SUPPLEMENTARY  AID 
TO  PUBLIC  RELATIONS* 


A.  A.  MERCEY** 

Summary. — The  success  of  two  U.  S.  documentary  films,  "The  Plow  That 
Broke  the  Plains"  and  "The  River,"  written  and  directed  by  Pare  Lorentz,  has  focused 
new  attention  upon  this  type  of  film.  The  school  of  Public  Affairs  of  American 
University  conducts  a  film  course  of  eight  weeks,  with  screenings,  film  analyses,  and 
discussions  conducted  by  visiting  experts  in  film-making  and  film  use.  The  subjects 
covered  are:  the  newsreel  as  contemporary  historian;  the  "March  of  Time"  as  a  docu- 
ment; federal,  educational,  and  scientific  films;  U.  S.  Government  documentary 
films;  documentary  aspects  of  Hollywood  films;  foreign  documentaries;  industrial, 
sales,  and  domestic  propaganda  films.  Technical  aspects  with  reference  to  advances 
in  film  production  were  discussed. 

In  addition  to  regular  discussion  and  study,  a  number  of  reports  were  made  on  docu- 
mentary film  activities.  Among  the  most  important  was  a  complete  survey  of  all  U.  S. 
government  films. 

The  emergence  of  the  documentary  film  as  a  medium  of  social 
expression  is  a  significant  development  in  the  evolution  of  the  modern 
motion  picture.  Without  seeking  a  definition  of  this  new  film  form, 
producers  have  gone  forward  and  made  films  of  extraordinary  social 
value.  The  documentary  form  has  developed  with  amazing  speed 
and  success.  While  film  experts  indulge  in  "streamlined"  scholasti- 
cism trying  to  define  the  word  "documentary,"  films  have  evolved  in 
many  parts  of  the  world  that  transcend  the  temporary  values  of  the 
entertainment  film,  and  are  making  their  own  definition  of  the  term. 

This  new  form  has  had  a  surprising  growth  abroad  both  on  the 
Continent  and  in  Great  Britain.  Its  most  representative  exponent 
in  this  country  is  Pare  Lorentz,  who  made  The  Plow  That  Broke  the 
Plains  and  The  River  for  the  United  States  Government.  The  atten- 
tion attracted  to  the  new  form,  particularly  to  the  Lorentz  films,  has 
given  impetus  to  the  study  and  production  of  the  documentary  form. 

Definitions   of   varying  refinement,  charges,  and  countercharges 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C. ;    received 
April  15,  1938. 

**  School  of  Public  Affairs,  American  University,  Washington,  D.  C. 

82 


DOCUMENTARY  FILM  STUDY  83 

hurled  at  the  documentary  film  have  stimulated  the  curiosity  of  those 
working  with  human  equations,  especially  those  engaged  directly  or 
indirectly  in  educational  or  public  relations  work. 

The  course,  "Documentary  Films  Today,"  was  instituted  at  Ameri- 
can University,  School  of  Public  Affairs,  to  round  out  a  constantly 
expanding  curriculum  encompassing  the  various-  technics  used  in 
public  relations.  The  School  of  Public  Affairs'  "in-service"  training 
school  for  government  employees  is  taught  by  recognized  experts 
in  the  government.  It  was  for  this  group  that  the  course  was  inaugu- 
rated. 

"Documentary  Films  Today"  was  offered  for  the  purpose  of  giving 
some  direction  and  guidance  along  the  lines  of  contemporary  docu- 
mentary production.  It  was  not  offered  as  a  technical  or  production 
course,  but  rather  as  a  survey  course  that  would  include  discussions  of 
technical  changes  in  motion  picture  production. 

Given  for  a  period  of  eight  weeks,  the  study  necessarily  had  to  be 
both  intensive  and  flexible.  In  order  to  dissipate  some  of  the  con- 
fusion created  by  pat  definitions  of  the  documentary  film  by  the 
critics,  the  students  were  shown  films  recognized  as  documentary  or 
as  having  documentary  aspects.  Nearly  sixty  reels,  including 
twenty-one  different  subjects,  were  screened,  while  five  guest  speakers, 
acknowledged  experts  in  their  field,  supplemented  the  lecture  mate- 
rial. By  going  to  the  material  contained  in  various  documentary 
films,  it  was  felt  that  a  truer  definition  of  the  new  film  form  could  be 
gained.  The  general  scheme  of  the  course  ran  along  the  following 
lines : 

The  rise  and  growth  of  the  documentary  film. 

The  newsreel  as  contemporary  historian. 

The  March  of  Time  as  a  document. 

Federal,  educational,  scientific,  documentary,  and  action  program  films. 

Documentary  aspects  of  the  Hollywood  film. 

Foreign  documentary  films. 

Industrial,  sales,  and  propaganda  films. 

The  film  for  the  future  historian. 

The  opening  lecture  pointed  out  by  specific  example  the  general 
distinctions  between  a  Hollywood  story  film,  the  regular  educational 
or  scientific  film,  and  the  documentary  film.  The  general  survey  was 
followed  by  a  showing  of  governmental,  educational,  scientific,  and 
action  program  films. 

Mr.  Fanning  Hearon,  Director  of  Motion  Pictures  of  the  Depart- 
ment of  the  Interior,  spoke  to  the  class  before  the  showing.  He  out- 


84  A.  A.  MERCEY  [j.  s.  M.  P.  E. 

lined  various  methods  of  making  government  films;  and  following  his 
lecture,  conducted  the  class  through  the  film  laboratories  of  the  De- 
partment of  the  Interior.  Hands  by  the  WPA,  and  In  the  Beginning  by 
the  U.  S.  Department  of  Agriculture  were  outstanding  subjects  on 
this  program.  Other  films  included  those  from  the  Department  of 
the  Interior,  The  Social  Security  Board,  The  Federal  Housing  Ad- 
ministration, and  the  U.  S.  Army. 

Both  The  Plow  That  Broke  the  Plains  and  The  River  were  screened 
after  a  lecture  explaining  problems  of  production,  administration,  and 
distribution.  A  general  outline  under  the  general  title,  "From  Script 
to  Screen,"  answered  questions  previously  raised  by  members  of  the 
class. 

The  Adventures  of  Chico,  produced  by  Stacy  and  Horace  Woodard, 
was  given  a  pre-release  screening  for  the  class  in  the  discussion  of 
documentary  aspects  of  the  entertainment  film. 

Two  outstanding  modern  films  were  included  in  the  section  devoted 
to  foreign  documentaries :  Housing  Problems,  a  British  film,  by  Arthur 
Elton  and  Edgar  Anspey,  and  Triumph  of  the  Will,  a  German  film 
of  the  Nazi  festival  at  Nuremburg,  filmed  by  Leni  Riefenstahl. 

The  Birth  of  a  Nation,  D.  W.  Griffith's  classic,  and  Sergi  Eisen- 
stein's  Potemkin  illustrated  the  documentary  aspects  of  the  historical 
film. 

A  program  of  industrial  and  propaganda  films  gave  the  class  a 
general  idea  of  the  progress  being  made  in  these  fields.  Progress  on 
Parade  and  Where  Mileage  Begins,  both  General  Motors'  pictures  and 
Voices  in  the  Air  and  Getting  Together,  Bell  Telephone  productions, 
were  screened. 

H.  S.  Fitz,  assistant  in  customer  relations  of  the  Chesapeake  & 
Potomac  Telephone  company,  gave  the  point  of  view  of  the  industrial- 
ist who  uses  films  for  winning  public  favor.  Floyd  Brooker,  now  as- 
sociated with  the  film  project  of  the  American  Council  on  Education, 
and  an  accomplished  script  writer,  presented  the  problems  of  the 
educator  in  regard  to  new  industrial  and  propaganda  films. 

The  American  Way,  sponsored  by  the  National  Defenders,  and 
Death  to  the  Open  Shop,  made  by  the  United  Automobile  Workers  of 
the  CIO,  illustrated  a  sharp  contrast  in  objectives  in  the  propaganda 
field. 

J.  G.  Bradley,  Chief  of  the  Division  of  Motion  Pictures  and  Sound 
Recordings  of  the  National  Archives,  described  to  the  class  the  most 


July,  1938]  DOCUMENTARY  FILM  STUDY  85 

modern  methods  yet  devised  to  preserve  films  for  the  future  historian. 
He  escorted  the  class  through  the  motion  picture  division  and  ex- 
plained the  facilities  for  screening,  classifying,  and  preserving  films 
for  tjie  Archives.  The  students  also  heard  Pare  Lorentz  speak  at  a 
Washington  forum  on  the  difficulties  affecting  production  of  the  docu- 
mentary film. 

Since  the  time  of  the  course  was  so  limited,  many  important  phases 
of  film  making  of  direct  and  indirect  value  to  documentaries  had  neces- 
sarily to  be  omitted.  Supplemental  material  given  the  students, 
however,  included:  preliminary  and  extensive  bibliography  of  film 
writings;  glossary  of  film  terms;  condensation  of  lecture  notes; 
folders,  lithographs,  and  scripts  of  The  Plow  and  The  River;  program 
notes  on  the  industrial,  foreign  documentary,  propaganda,  and  histori- 
cal films;  and  lists  of  outstanding  newsreels  and  best  films  of  the 
year. 

A  word  about  the  personnel  of  the  class  might  be  of  interest. 
The  course  included  one  person  who  had  written  a  dozen  books,  one 
who  was  formerly  instructor  of  English  at  the  University  of  Wisconsin, 
a  chief  of  exhibits  of  one  bureau,  a  film  chief  of  another,  the  wife  of  a 
high  bureau  official,  and  editors  and  publicity  experts  from  other 
bureaus.  The  class  was  of  rather  exceptional  caliber. 

Reports  were  prepared  by  the  students  in  lieu  of  the  examinations 
customarily  given  in  the  School  of  Public  Affairs.  Included  in  these 
reports  was  a  Federal  film  survey,  the  first  of  its  kind  ever  done. 
This  survey  includes  history,  administrative  description,  and  the 
work  of  various  Federal  film  units.  This  report  has  long  been  needed 
and  answers  a  demand  by  educators  and  industry  for  authentic  and 
complete  data  on  the  Government's  motion  picture  activity.  It  is 
now  being  edited  for  final  presentation  in  a  form  to  be  announced 
later. 

The  course  proved  unequivocally  that  a  definite  need  exists  for 
film  courses  of  this  kind,  which  give  direction  and  guidance  to  stu- 
dents, especially  those  of  adult-education  groups,  who  are  working 
with  publicity,  educational,  or  training  groups. 

The  Society  of  Motion  Picture  Engineers  might  well  perform  a  ser- 
vice to  the  schools  by  articulating  a  course  giving  a  definite  approach 
to  film  study.  The  need  exists  for  such  a  course,  and  the  Society 
would  make  a  real  contribution  to  contemporary  thought,  if  it  ful- 
filled such  a  mission. 


86  A.  A.  MERCEY 

DISCUSSION 

MR.  WOLF:   Did  you  limit  your  work  to  documentary  and  propaganda  film? 

MR.  MERCEY:  Since  the  course  was  only  eight  weeks  long  we  could  take  up 
very  little  else.  We  did  give  some  attention  to  documentary  aspects  of  entertain- 
ment films,  but  there  has  been  so  much  confused  discussion  about  documentary 
films  that  we  tried  to  give  what  we  could  to  eliminate  some  of  the  haze.  The 
course  was  a  part  of  a  series  of  courses  in  public  relations,  so  we  had  to  gear  the 
film  course  to  its  influence  upon  public  relations,  not  educational  primarily,  not 
entertainment,  but  the  course  for  which  it  was  designed. 

MR.  WOLF:   Do  The  Plow  and  The  River  represent  all  the  government  pictures? 

MR.  MERCEY:  No.  I  mentioned  those  two  because  it  happened  that  I  was 
identified  with  the  production  and  distribution  of  them.  I  would  advise  those 
who  are  interested  to  obtain  a  complete  list  from  the  National  Emergency  Council, 
which  has  a  complete  list  of  film  units  and  film  sources.  Many  of  the  films  listed 
are  documentary;  some  are  educational,  some  are  scientific. 

MR.  WOLF:  Are  all  these  films  produced  in  the  government  departments — 
photography,  laboratory  and  studio  work,  and  so  forth? 

MR.  MERCEY:  No,  the  Department  of  Agriculture  and  the  Department  of  the 
Interior  both  produce  films  in  their  own  laboratories  from  the  time  the  script  is 
written  until  the  film  is  shown.  The  films  we  made  were  not  so  produced.  We 
hired  cameramen  on  a  per  diem  basis  and  worked  in  commercial  studios.  Our 
work  was  done  in  New  York  commercial  laboratories,  and  some  work  in  Holly- 
wood. There  are  three  ways  of  making  government  films :  One  is  through  govern- 
ment laboratories  such  as  the  Interior  and  Agriculture  Departments  have;  another 
by  engaging  per  diem  employees,  and  the  third,  through  the  contract  method, 
which  has  been  used  by  the  Social  Security  and  Federal  Housing  and  other 
agencies. 


NEW  MOTION  PICTURE  APPARATUS 


During  the  Conventions  of  the  Society,  symposiums  on  new  motion  picture  appara- 
tus are  held,  in  which  various  manufacturers  of  equipment  describe  and  demonstrate 
their  new  products  and  developments.  Some  of  this  equipment  is  described  in  the 
following  pages;  the  remainder  will  be  published  in  subsequent  issues  of  the  Journal. 

AN  ULTRAVIOLET  PUSH-PULL  RECORDING  OPTICAL  SYSTEM  FOR 
NEWSREEL  CAMERAS* 

G.  L.  DIMMICK  AND  L.  T.  SACHTLEBEN** 


A  very  compact  and  light-weight  variable-width  recording  optical  system  has 
been  designed  for  newsreel  cameras.  Fig.  1  shows  the  system  as  it  appears 
mounted  upon  a  camera  and  ready  for  use.  It  is  6  inches  long,  4  inches  wide  and 
37/g  inches  high,  and  weighs  about  3l/4  pounds  complete  and  ready  to  record. 
The  mounted  system  shown  in  the  figure  extends  about  5  inches  back  from  the 
supporting  camera  wall.  Advanced  performance  and  new  design  features  char- 
acterize the  system,  as  it  is  really  a  studio  recording  system1  compressed  to  news- 
reel  proportions,  embodying  the  more  important  recent  advances  in  studio 
recording  optical  system  design. 

Sound  negatives  made  on  panchromatic  film  by  this  system  are  freer  of  distor- 
tion and  ground-noise  than  has  hitherto  been  possible  with  panchromatic  film. 
By  exposing  the  track  with  ultraviolet  light  (in  the  range  of  3000  to  4300  A) 
irradiation  within  the  emulsion  and  attendant  spread  of  the  developed  image  are 
reduced.  An  improvement  is  thus  obtained  in  frequency  response  and  wave- 
form, similar  to  that  resulting  from  recording  with  ultraviolet  light2  on  the  special 
sound  recording  emulsions  used  in  studios.  The  aperture  plate  or  mask  of  the 
system  is  designed  to  produce  the  Class  B  push-pull  form  of  the  variable-width 
sound-track.3  As  a  result,  a  very  substantial  reduction  in  ground-noise  is  effected 
without  the  employment  of  a  ground -noise  reduction -amplifier  and  ground - 
noise  shutter  equipment.  In  addition  to  this  "free"  ground-noise  reduction,  the 
push-pull  form  of  the  track  contributes  to  improved  fidelity  by  effectively  sup- 
pressing the  distortion  that  occurs  with  amplitude-modulated  high  frequencies, 
such  as  sibilants,  when  the  normal  spread  of  the  negative  image  is  not  com- 
pensated for  in  printing.  Prints  from  a  single  negative  having  a  wide  range  of 
density  are  equal  in  fidelity  and  differ  only  in  respect  to  surface-noise  and  overall 


*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;    received 
April  15,  1938. 

**  RCA  Manufacturing  Co.,  Camden,  N.  J. 

87 


88 


NEW  MOTION  PICTURE  APPARATUS        [J.  s.  M.  P.  E. 


FIG.  1.     Optical  system  as  it  appears  on  the  camera. 


FIG.  2.  Enlargements  from  panchromatic 
negative  tracks  made  with  the  system:  (top] 
overshot  ultraviolet  Class  B  push-pull; 
(center)  white-light  bilateral  and  ultraviolet 
bilateral,  6000  cps. ;  (bottom)  normally  modu- 
lated ultraviolet  Class  B  push-pull  panchro- 
matic. 


July,  1938  J 


NEW  MOTION  PICTURE  APPARATUS 


•89 


output.  This  is  important  in  a  single-film  system  where  negative  development 
is  determined  by  the  character  of  the  picture  and  its  exposure  and  the  sound- 
track has  to  come  out  as  best  it  can.  Fig.  2  shows  two  speech-waves  made  by 
the  new  system  with  ultraviolet  light,  and  two  comparison  tracks,  at  6000  cps., 
made  with  ultraviolet  light  and  with  white  light.  The  tone  tracks  were  pur- 
posely made  in  the  bilateral  form  to  facilitate  comparison  and  measurement. 
The  fully  modulated  Class  B  push-pull  track  has  the  standard  width  of  0.076  inch 
with  a  0.006  septum  separating  its  two  portions  to  assure  against  overlapping  in 
reproduction.  The  zero  lines  connecting  the  modulation  segments  are  each 
0.001  inch  wide.  The  Class  B  push-pull  prints  from  ultraviolet  panchromatic 
negatives  have  a  ground-noise  level  50  db.  below  100  per  cent  modulation,  which  is 
12  db.  below  the  ground-noise  level  of  a  print  from  a  comparable  standard  track 
ultraviolet  negative  having  no  ground -noise  reduction. 

The  curves  of  Fig.  3  show  the  frequency-response  of  tracks  made  with  the  new 
system.  The  upper  curve  is  for  negatives  made  with  ultraviolet  light,  and  the 
lower  for  those  made  with  white  light.  Both  are  printed  with  ultraviolet 
light.  At  full  lamp  current  (4.3  amperes)  the  ultraviolet  negative  has  a  density 
between  1.0  and  1.2,  depending  upon  development,  and  it  is  recommended  that 


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FIG.  3.  Frequency-response  of  ultraviolet  prints  from 
panchromatic  ultraviolet  and  white-light  negatives  made 
with  the  system. 

the  print  density  be  made  equal  to  the  negative  density,  although  that  is  not 
absolutely  essential.  When  recording  with  white  light,  this  range  of  density  is 
obtained  with  a  lamp  current  of  about  3  amperes. 

Although  the  new  system  is  extremely  compact,  it  is  complete  in  all  details. 
All  the  usual  adjustments  of  lamp,  galvanometer,  focus,  track  location,  etc.,  are 
provided.  Some  of  these  features  are  shown  in  Fig.  4.  The  lamp  is  mounted  in 
a  cavity  or  "lamp  house"  at  one  corner  of  the  system  and  may  be  adjusted  in  all 
three  planes  and  firmly  locked  in  its  required  position.  At  full  current,  21  watts 
of  power  are  dissipated  in  the  lamp.  Cooling  fins  are  provided  on  the  main  part 
of  the  casting  to  aid  the  escape  of  the  heat.  It  is  found,  however,  that  the  large 
mass  and  surface  of  the  camera  to  which  the  system  is  secured  prevent  an  ap- 
preciable temperature  rise  from  this  source  even  when  the  lamp  is  operated  for 


90 


NEW  MOTION  PICTURE  APPARATUS        [J.  S.  M.  P.  E. 


considerable  periods  of  time.  In  practice  the  lamp  is  interlocked  with  the  camera 
motor  switch  and  is  turned  on  only  while  the  camera  operates.  The  lamp  in- 
stantly comes  to  full  brilliance.  The  galvanometer  can  be  rotated  about  its 
vertical  axis  and  locked  in  the  required  adjustment  by  the  two  opposing  screws 
at  the  back  of  the  system.  A  thumb-nut,  accessible  underneath  the  system  and 
protected  by  a  guard,  adjusts  the  galvanometer  about  its  horizontal  axis.  A 
focus  adjustment  knob  is  graduated  in  thousandths  of  an  inch  to  permit  accurate 
adjustment  of  the  distance  from  the  objective  lens  to  the  film,  and  may  be  easily 
reset  to  care  for  any  change  in  thickness  of  film  stock.  (The  objective  moves 
independently  of  the  slit  which  is  fastened  to  the  main  casting.)  A  lock-screw  at 
the  side  of  the  system  secures  this  adjustment  after  it  has  been  made.  The 
ultraviolet  filter  is  specially  mounted  so  that  it  may  be  turned  easily  to  one  side 


FOCUS  ADJUSTMENT 
JAM   SCREW  \_ 

LIGHT  FILTER  LEVER 
VERTICAL -ULTRA  VIOLET 
HORIZONTAL-  WHITE    ~~-~~- 


FOCUS  ADJUSTMENT 
^  KNOB 


SLIT  PLATE 
\ 

\     MIRROR  FOR  VIEWING 
\    LAMr»  IMAGE   ON 
GALVANOMETER 

MIRROR  FOR 
,     VIEWING 

\  I  APERTURE  PLATE 

IMAGE 


FIG.  4.     Optical  system  with  covers  and  galvanometer  removed. 


to  permit  recording  with  white  light,  a  clear  glass  plate  taking  its  place  to  provide 
the  required  optical  compensation.  The  provision  for  white-light  recording  allows 
the  demand  upon  the  power  supply  to  be  reduced  in  cases  of  necessity  as  the  lamp 
then  operates  at  reduced  current.  The  entire  system  is  mounted  upon  a  special 
plate,  a  groove  in  the  casting  cooperating  with  a  tongue  on  the  plate  for  azimuth 
adjustment.  The  tongued  plate  is  in  turn  secured  to  the  camera  by  screws  and 
dowels.  Three  screws  hold  the  optical  system  to  the  plate,  by  loosening  which 
the  system  may  be  moved  sidewise  for  adjusting  the  track  location.  A  vernier 
scale  on  the  system  cooperates  with  another  on  the  tongued  plate  to  aid  in  making 
lateral  adjustments  of  the  system.  The  azimuth  of  both  the  push-pull  aperture 


July,  1938] 


NEW  MOTION  PICTURE  APPARATUS 


91 


plate  and  the  slit  are  adjusted  and  dowelled  at  the  factory.  A  small  auxiliary 
mirror  permits  the  galvanometer  mirror  to  be  seen  when  lamp  adjustments  are 
being  made,  and  an  auxiliary  lens  and  mirror  system  permit  a  magnified  view  of 


LATERAL    INDEX    LINES 


MODULATING 
IMAGES 


FIG.  5.  Diagram  showing  correct  adjustment  of 
aperture  plate  image  on  slit  (Note:  lines  shown  heavy 
are  engraved  on  slit  face). 

the  slit  face  when  adjusting  the  galvanometer  and  judging  modulation.  Fig.  5 
shows  the  appearance  of  the  correctly  adjusted  Class  B  push-pull  aperture  image 
as  seen  upon  the  slit  face  when  looking  through  the  peep  lens.  The  lines  marked 
50%  and  100%  enable  the  operator  to  judge  modulation  amplitude  and  set  the 
volume  indicator  meter  on  his  amplifier  accordingly. 


ULTRA-VIOLET  CLASS-B    PUSH  PULL  RECORpING   SYSTEM  FOR  NEWS   REEL  CAMERAS 

FIG.  6.     Schematic  diagram  of  the  optics. 

The  optical  system  proper  is  of  the  same  general  design  as  the  variable-width 
studio  system1  but  incorporates  certain  new  design  features  made  necessary  by 
its  small  size.  The  optical  arrangement  is  shown  schematically  in  Fig.  6.  A 


92 


NEW  MOTION  PICTURE  APPARATUS        [J.  S.  M.  P.  E. 


new  lamp  of  4.9  volts,  4.3  amperes  rating  (21  watts)  is  used  in  an  S-S  bulb.  The 
condenser  is  somewhat  faster  than  those  in  the  studio  systems,  having  a  speed  of 
about  //I,  and  is  of  two  elements  designed  for  minimum  spherical  aberration. 
It  is  made  of  crystal  quartz  to  insure  against  transmission  loss  in  the  near-ultra- 
violet. The  aperture  plate  is  in  a  dust-proof  mounting  between  the  condenser 
and  a  quartz  dust  window.  The  very  limited  space  requirements  make  it  impos- 
sible to  image  the  aperture  plate  upon  the  slit  by  means  of  a  lens  mounted  axially 
either  preceding  or  following  the  galvanometer  mirror,  and  this  function  is  per- 
formed by  a  galvanometer  window  lens  through  which  the  light  passes  obliquely 
both  before  and  after  reflection  from  the  mirror.  This  lens  is  of  crown  glass  and 
so  shaped  and  placed  with  respect  to  the  mirror  as  to  perform  its  function  properly. 
The  condenser  at  the  slit  is  again  of  crystal  quartz  and  serves  to  image  the  galvan- 
ometer mirror  upon  the  objective  lens.  The  objective  lens  consists  of  four  air- 
spaced  elements,  corrected  chromatically  for  3650  and  5460  A,  and  having  an 
equivalent  focal  length  of  7.6  mm.  and  a  speed  of //2.  The  image  of  the  slit  that 


FIG.  7.     Frequency  characteristic  of  the  galvanometer. 

it  forms  on  the  film  is  0.076  inch  long  and  0.0005  inch  wide.  The  filter  between 
the  slit  and  objective  is  of  Corning  597,  Red  Purple  Ultra  glass  of  2-mm.  thick- 
ness, and  very  effectively  restricts  exposure  to  the  region  from  3000  to  4300  A. 

The  galvanometer2  incorporates  some  recent  improvements.  Nicaloi  is  used 
for  both  pole-pieces  and  armature  to  prevent  corrosion  and  further  reduce  dis- 
tortion. The  mirror  pivot  plate  has  approximately  the  same  coefficient  of  thermal 
expansion  as  glass.  It  is  a  stainless  nickel  iron  alloy,  and  is  soldered  to  the  ribbon. 
The  curve  of  Fig.  7  shows  the  frequency-response  characteristic  of  the  galvanom- 
eter. The  rise  in  high-frequency  response  approximately  compensates  for  film 
loss  to  5500  cps.  The  required  power  input  at  100  per  cent  deflection  is  about  60 
milliwatts.  Each  galvanometer  is  supplied  with  a  matched  capacitor  that  adjusts 
the  characteristic  to  the  form. shown.3 

Negatives  made  on  the  system  are  printed  and  re-recorded  to  the  bilateral  track 
form  with  noise  reduction  for  theater  release.  The  system  can  easily  be  con- 
verted to  produce  a  bilateral  track  directly  simply  by  exchanging  aperture  plates. 

Acknowledgment  is  due  the  Bausch  &  Lomb  Optical  Company  for  developing 
the  short-focus,  wide-field  objective  used  on  the  system,  and  further  acknowledg- 


July,  1938]  NEW  MOTION  PICTURE  APPARATUS  93 

ment  is  due  R.  F.  Brady  and  F.  E.  Runge  for  the  excellent  mechanical  design  of 
the  system. 

REFERENCES 

1  SACHTLEBEN,  L.  T.:  "Characteristics  of  the  Photophone  Light-Modulating 
System,"  /.  Soc.  Mot.  Pict.  Eng.,  XXV  (Aug.,  1935),  No.  2,  p.  175. 

8  DIMMICK,  G.  L. :  "Improved  Resolution  in  Sound  Recording  and  Printing 
by  the  Use  of  Ultraviolet  Light,"  /.  Soc.  Mot.  Pict.  Eng.,  XXVII  (Aug.,  1936), 
No.  2,  p.  168. 

8  DIMMICK,  G.  L.:  "The  RCA  Recording  System  and  Its  Adaptation  to  Vari- 
ous Types  of  Sound-Track,"  J.  Soc.  Mot.  Pict.  Eng.,  XXIX  (Sept.,  1937),  No.  3, 
p.  258. 


OVERLOAD  LIMITERS  FOR  THE  PROTECTION  OF  MODULATING 

DEVICES* 


IR.  R.  SCOVILLE** 
In  order  to  assure  the  high  quality  essential  to  sound  recording  and  reproducing, 
it  is  very  desirable  to  avoid  overloads,  particularly  of  the  recording  device.  On 
the  other  hand,  the  requirement  for  maintaining  a  high  signal-to-noise  ratio  in- 
duces operation  as  near  the  overload  point  as  possible.  With  even  the  most  care- 
ful monitoring  occasional  overloading  is  unavoidable.  The  effects  of  overload 
may  be  either  degradation  of  quality  or  actual  injury  to  the  recording  device. 
Several  forms  of  devices  for  the  prevention  of  these  have  been  developed.  Their 
application  to  the  field  of  sound  recording  is,  however,  fairly  recent. 

One  type  of  amplitude  Jimiter  that  is  now  being  extensively  used  in  the  radio 
broadcast  field1  prevents  excessive  amplitudes  by  automatically  changing  the  loss 
through  a  network  by  an  amount  that  is  a  function  of  the  amplitude  of  the  signal 
envelope.  Since  the  loss  of  the  system  can  not  be  changed  instantly  without 
noticeable  distortion,  a  time  delay  'of  the  order  of  10  to  20  milliseconds  between 
the  occurrence  of  the  peak  and  the  correcting  action  of  the  system  is  used.  A 
time  delay  of  approximately  125  to  250  milliseconds  is  used  to  restore  the  system 
to  its  normal  gain  so  that  the  changes  are  gradual  rather  than  abrupt.  Since  all 
portions  of  a  wave  are  attenuated  to  nearly  the  same  extent  over  a  given  small 
interval  of  time,  no  apparent  harmonics  are  generated  to  degrade  the  quality. 
This  kind  of  limiter  will  subsequently  be  referred  to  as  a  "peak  limiter."  A  de- 
tailed description  of  such  a  device  is  to  be  found  elsewhere  in  the  literature.2 

A  second  type  of  amplitude  limiter  to  be  described  herein  limits  peak  signal  am- 
plitudes to  a  predetermined  value  and  is  without  time  delay.  It  has  no  effect 
upon  signals  of  lesser  amplitude  than  the  critical  value  and  generates  harmonics  of 
odd  order  when  "limiting."  This  will  be  called  a  "peak  chopper." 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;    received 
April  29,  1938. 

**  Electrical  Research  Products,  Inc.,  Hollywood,  Calif. 


94 


NEW  MOTION  PICTURE  APPARATUS        [J.  S.  M.  p.  E. 


Comparison  of  Volume-Limiting  Methods. — Volume  limiting  has  not  up  to  the 
present  time  played  as  active  a  role  in  motion  picture  recording  as  it  has  in  radio 
broadcasting.  Motion  picture  scenes  are  generally  well  rehearsed  as  to  volume 
range,  and  several  "takes"  are  made.  If  overload  occurs  on  some  takes,  others 
may  usually  be  made  that  are  satisfactory ;  whereas  in  radio  work  it  is  not  always 
possible  to  foresee  what  volumes  will  arise;  and,  once  "on  the  air,"  no  retakes  are 
possible.  As  a  result,  amplitude  limiters  have  not  been  used  in  the  majority  of 
motion  picture  recording  sequences.  However,  there  are  many  cases  wherein 
unusual  and  unpredictable  volume  relationships  occur  when  the  use  of  a  limiter 
is  definitely  valuable.  Whether  the  peak  limiter  or  the  peak  chopper  type  of 
equipment  is  most  suitable  depends  upon  the  type  of  material  involved  and  upon 
the  limitations  of  the  recording  medium. 

In  speech  and  in  certain  types  of  music  a  small  percentage  of  the  peaks  may 
reach  amplitudes  15  to  20  db.  higher  than  the  average  signal  amplitude.  With 

many  of  the  recording  systems 
used  today,  and  particularly  with 
variable-density  systems,  the  aver- 
age recording  volume  is  set  ap- 
proximately 10  db.  below  the 
modulator  overload  point.  It  is 
apparent  that  if  a  peak  limiter 
that  acts  upon  the  signal  envelope 
is  used  under  these  conditions,  an 
appreciable  reduction  of  the  under- 
lying signal  strength  will  result, 
which  occurs  when  the  peak  causes 
the  gain  through  the  device  to 
change.  Compression  of  the  signal 
in  this  manner  results  in  no  un- 
pleasant effects  provided  the  com- 
pression does  not  exceed  3  db. 
.When  greater  compression  is  used 

the  loss  of  volume  range  may  in  some  cases  cause  a  loss  of  dramatic  expression, 
or  "punch."  Thus,  instead  of  this  kind  of  limiting,  which  is  harmonic-free,  it 
may  at  times  be  preferable  to  allow  considerable  "overload"  to  obtain  the  maxi- 
mum volume.  Examples  of  this  sort  are  gunshots,  crashes,  hurricanes,  battles, 
or  other  scenes  featuring  excitement  and  commotion.  Here  the  peak  chopper 
proves  most  suitable,  since  it  prevents  damage  to  equipment  and  at  the  same 
time  permits  the  maximum  volume  of  which  the  modulating  device  is  capable. 
On  the  other  hand,  in  dialog  scenes  of  an  emotional  nature  the  harmonics  pro- 
duced by  a  peak  chopper  during  overload  sequences  may  be  objectionable.  Here 
the  peak  limiter,  which  automatically  reduces  gain  without  incurring  harmonics, 
proves  valuable. 

Amplitude  limiters  should  be  used  in  a  manner  adapted  to  the  recording 
method  employed.  With  the  variable-width  system,  for  example,  the  harmonics 
generated  with  signals  exceeding  the  modulator  overload  point  are  somewhat 
more  severe  than  is  the  case  with  the  variable-density  method.  This  is  because 


FIG.  1.     Peak  chopper  circuit. 


July,  1938] 


NEW  MOTION  PICTURE  APPARATUS 


95 


the  space  limitations  of  the  sound-track  effect  a  sharp  cut-off  of  both  positive  and 
negative  peaks  in  the  variable-width  system,  whereas  in  the  variable-density 
system  the  signal  is  not  so  sharply  cut  off  at  the  overload  point.  There  is  a  con- 
siderable range  available  on  the  film,  even  though  non-linear,  which  is  of  value 
in  reducing  the  severity  of  overloads.  Owing  to  this  difference,  the  usual  practice 
has  been  to  operate  variable-density  recorders  with  a  percentage  modulation 
from  4  to  6  db.  greater  than  in  the  case  of  variable- width  recorders.  Use  of  the 
peak  limiter  with  the  variable-density  system  entails  the  disadvantage  that  if 
the  limiter  operates  at  the  overload  point  of  the  valve,  a  small  percentage  of  the 
peaks  will  cause  a  compression  greater  than  the  permissible  3  db.,  giving  a  notice- 
able "pumping"  effect  and  also  a  loss  in  the  upper  volume  range.  This  effect 
may  be  avoided  by  reducing  the  average  volume,  but  owing  to  background  noise 
this  is  not  generally  desirable.  Another  alternative  is  to  adjust  the  peak  limiter 


THRESHOLD  VOLTAGE 


FIG.  2.     Showing  effect  of  peak  chopper  on  signal. 

to  operate  at  a  point  2  to  4  db.  above  the  modulator  overload.  But  in  this  case 
the  harmonic-free  result  is  largely  lost.  Still  another  alternative  is  to  permit  a 
certain  amount  of  overload  for  the  sake  of  the  volume  range  and  guard  against 
damaging  signals  by  using  a  limiter  of  the  peak  chopper  type  set  to  operate  for 
signal  amplitudes  4  to  6  db.  above  modulator  overload.  However,  for  variable- 
width  recording  systems  or  for  radio  broadcasting  wherein  the  overload  point  is 
sharply  defined  and  may  not  be  exceeded  appreciably,  the  peak  limiter  or  variable- 
gain  type  provides  a  useful  function  for  certain  types  of  speech  or  music. 

A  Peak  Chopper  Equipment. — A  peak  chopper  that  cuts  off  excessive  ampli- 
tudes without  time  delay  is  shown  schematically  in  Fig.  1.  Its  operation  is  as 
follows:  A  copper-oxide  rectifier,  or  varistor,  of  suitable  design  has  its  a-c. 
terminals  connected  across  the  line  and  the  d-c.  terminals  connected  to  a  battery 
having  the  same  polarity  as  the  normal  output  of  the  rectifier.  Current  will  flow 
from  the  line  through  the  rectifier  only  when  the  peak  voltage  exceeds  the  battery 
voltage.  During  such  periods  the  device  acts  very  much  as  a  short-circuit,  so 
that  the  line  voltage  is  held  down  to  the  predetermined  value.  For  signal  vol- 


96 


NEW  MOTION  PICTURE  APPARATUS 


[J.  S.  M.  P.  E. 


NI  Miundnv  xvid  indino 
I I I I 


July,  1938] 


NEW  MOTION  PICTURE  APPARATUS 


97 


tages  lower  than  this  value  the  device  has  no  appreciable  effect.  Fig.  2  shows  the 
manner  in  which  a  sine-wave  signal  is  limited,  and  Fig.  3  shows  the  relation  of 
output  amplitude  to  input  amplitude.  Here  a  10-db.  increase  in  input  signal 
above  the  threshold  results  in  a  2-db.  increase  in  output  amplitude.  As  the 
threshold  value  is  passed  odd  harmonics  are  progressively  generated.  Even  har- 
monics are  not  produced  in  the  device.  When  a  peak  chopper  of  this  type  is 
used  with  a  modulating  device  having  resonance  in  the  upper  audible  range,  it  is 
advisable  to  employ  a  low-pass  filter  following  the  limiter.  This  filter  should 
have  its  cut-off  frequency  just  below  the  resonance  frequency  of  the  modulator. 
Third  harmonics  generated  by  the  limiter  and  having  values  in  the  neighborhood 
of  modulator  resonance  will  thus  be  incapable  of  causing  trouble. 

Fig.  4  shows  the  third  harmonics  introduced  by  the  chopper  for  signals  greater 
than  the  threshold  value.  These  are  of  somewhat  greater  magnitude  than  those 
introduced  by  the  film  under  corresponding  conditions.  However,  by  setting  the 
peak  chopper  to  operate  at  approximately  4  db.  above  the  modulator  overload 
point,  when  working  with  variable-density  recording,  the  harmonic  generation 


FIG.  5.     Peak  chopper  unit. 

is  held  down  practically  to  that  contributed  by  the  film,  and  at  the  same  time 
protection  is  afforded  to  the  modulator  against  further  damaging  peaks. 

With  variable-width  recording  devices  the  threshold  may  be  set  at  or  slightly 
above  the  modulator  overload  point,  since  any  harmonic  generated  will  be  about 
the  same  whether  generated  by  the  limiter  or  by  the  system. 

Fig.  5  shows  the  appearance  of  a  peak  chopper  of  the  type  described.  A  low- 
pass  filter  is  incorporated  within  the  unit  for  the  purpose  previously  mentioned. 
A  six-position  switch  shown  on  the  right  side  of  the  instrument  connects  the  de- 
sired threshold  voltage,  which  is  indicated  by  pressing  the  push-button  shown  on 
the  left  of  the  meter.  The  meter  reads  voltage  on  one  scale,  and  overload  point 
in  decibels  relative  to  0.006  watt  across  500  ohms  on  the  second  scale.  As  con- 
structed, the  threshold  may  be  set  so  that  limiting  begins  at  a  value  as  low  as 
-f-6  db.  or  as  high  as  +18  db.  relative  to  0.006  watt.  During  operation  the  meter 
acts  as  a  milliammeter  in  the  resistor  circuit  indicating  when  overload  occurs. 
The  degree  of  overloading  obtained  is  a  function  of  the  meter  reading  (except  as 
modified  by  the  lag  of  the  movement)  and  may  be  determined  by  reference  to 
calibration  curves  furnished  with  the  unit. 


98  NEW  MOTION  PICTURE  APPARATUS 

Prior  to  the  use  of  this  equipment  with  light-valve  systems,  considerable  in- 
convenience was  experienced  in  ribbon  breakage  and  changes  in  adjustment. 
After  installation  of  the  peak  chopper  practically  no  trouble  of  this  kind  that  may 
be  attributed  to  overloads  was  experienced. 

This  paper  has  endeavored  to  show  wherein  amplitude  limiters  have  a  useful 
function  in  sound  recording.  Of  the  two  types  of  limiters  discussed,  one  com- 
presses the  envelope  for  excessive  amplitudes  without  harmonic  generation  but 
with  a  time  delay;  whereas  the  other  type  chops  off  excessive  peaks  instantane- 
ously, with  generation  of  harmonics.  It  is  felt  that  the  first  type  is  most  useful 
for  systems  wherein  a  critical  overload  point  may  not  be  exceeded  to  any  appreci- 
able extent  and  where  such  volume  compression  as  results  will  not  be  objection- 
able. For  other  conditions  the  peak  chopper  is  found  useful  for  the  protection  of 
equipment  against  damaging  overloads. 

REFERENCES 

1  HOVGAARD,  O.  M.:  "A  Volume  Limiting  Amplifier,"  Bell  Laboratories  Record, 
XVI  (Jan.,  1938)  No.  5,  p.  179. 

2  DOBA,  S.:     "Higher  Volumes  without  Overloading,"  Bell  Laboratories  Rec- 
ord, XVI  (Jan.,  1938)  No.  5,  p.  174. 

3  HOVGAARD,  O.  M.,  AND  DOBA,  S.:    "Higher  Program  Level  without  Circuit 
Overloading"  (Presented  before  the  Institute  of  Radio  Engineers,   May,  1937; 
not  yet  published). 


CURRENT   LITERATURE   OF   INTEREST   TO   THE   MOTION   PICTURE 

ENGINEER 

The  editors  present  for  convenient  reference  a  list  of  articles  dealing  with  subjects 
cognate  to  motion  picture  engineering  published  in  a  number  of  selected  journals. 
Photostatic  copies  may  be  obtained  from  the  Library  of  Congress,  Washington,  D.  C., 
or  from  the  New  York  Public  Library,  New  York,  N.  Y.  Micro  copies  of  articles 
in  magazines  that  are  available  may  be  obtained  from  the  Bibliofilm  Service,  Depart- 
ment of  Agriculture,  Washington,  D.  C. 

American  Cinematographer 

19  (Apr.,  1938),  No.  4 
Low  Key  Lighting  May  Be  as  Easy  in  Color  as  It  Is 

in  Monochrome  (pp.  146-151)  W.  H.  GREENE 

Agfa  Issues  Its  35-Mm.  Supreme  in  Spools,  Press  in 

Rolls  and  Packs  (p.  150) 

Color  in  Broadcasting  Studied  by  New  Hollywood  Tele- 
vision Group  (pp.  160-161).  W.  L.  PRAGER 
Micro  Movies  Most  Efficient  Research  Tool  (pp.  162- 

164).  P.  A.  ZAHL 

European  Product  Eumig  C4  8-Mm.  Camera  Enters 

American  Market  (pp.  166-168). 

19  (May,  1938),  No.  5 
Arnold  Devises  Semi-Automatic  Follow-Focus  Finder 

for  Camera  (pp.  188-189).  W.  STULL 

Cine  Kodak  Secures  Added  Range  in  New  Eastman 

Focusing  Finder  (p.  205). 
Bell    &    Howell   Announces    16-Mm.   Projector    with 

Powerful  Arc  (pp.  206-207). 
National  Archives  Will  Preserve  Motion  Pictures  for 

Generations  (pp.  217-219).  J.  G.  BRADLEY 

Cinematographie  Francaise 

20  (Mar.  25,  1938),  No.' 1012 

Le  Nouveau  Super-Equipement  Sonore  de  laKlangfilm- 
Tobis  (New  Super  Sound  Equipment  of  Klangfilm- 
Tobis)  (p.  IX). 

Spectrometre  Electro- Acoustique  Siemens  (Siemens 
Electroacoustic  Spectrometer)  (p.  X). 

Electronics 

11  (Apr.,  1938),  No.  4 

Television  Receivers,  (pp.  29-31,  63-66).  E.  W.  ENGSTROM  AND 

R.  S.  HOLMES 

99 


100  CURRENT  LITERATURE  [].  s.  M.  p.  E. 

International  Photographer 

10  (Apr.,  1938),  No.  3 

Hollywood's  Service  Army  (pp.  11-13). 

Photography  Back  on  Top — New  cameras  (pp.  15-16, 
20-25). 

Rear  Projection  Big  Advance  (pp.  30-33). 

Sound  Problems  Overcome  (pp.  39-42).  J.  N.  A.  HAWKINS 

Lighting — Pan  and  Sound  Put  Inkies  on  Top  (pp.  43- 
48). 

Laboratory — Science  Supersedes  Guesswork  (Develop- 
ing Machines)  (pp.  50-52)  D.  K.  ALLISON 

Light-Sources  Big  Improvement  (pp.  55-58).  P.  R.  CRAMYR 

International  Projectionist 

13  (Apr.,  1938),  No.  4 

The  Geneva  Intermittent  Movement:  Its  Construc- 
tion and  Action  (pp.  7-9)  (II).  A.  C.  SCHROEDER 

Chaotic  Status  of  Laws  Anent  Projection  Technic, 
Equipment,  Rooms  Revealed  by  Nation- Wide 
Survey  (Bureau  of  Labor  Statistics,  U.  S.  Dept.  of 
Labor)  (pp.  15-16)  (II). 

Technical  Data  on  New  Simplex  Sound  System  (pp. 
17,  26). 

Analyses  of  Modern  Theater  Sound  Reproducing  Units 

(pp.  20-22).  A.  NADELL 

Kinotechnik 

20  (Apr.,  1938),  No.  4 
Physiologische    Untersuchungen    zur    Kinoprojektion 

(Physiological  Experiments  on  Motion  Picture  Pro-  H.  FRIESER  AND 
jection)  (pp.  85-92).  W.  MUNCH 

Die  Lichtverteilung  hn  Filmspaltbild  als  Quelle  nicht- 
linearer  Verzerrungen  (Light  Distribution  in  Image 
of  the  Aperture  as  a  Source  of  Non- Linear  Distortion) 
(pp.  93-96)  A.  NARATH 

Motion  Picture  Herald  (Better  Theaters  Section) 

131  (Apr.  30,  1938),  No.  5 
Perfection  of   Mercury  Vapor  Lamp  to   Bring  New 

Lighting  Technique  (p.  5). 

A  New  Sound  System  Designed  by  a  Projection  Organi- 
zation (pp.  27-28). 

Photographische  Industrie 

36  (Mar.  30,  1938),  No.  13 

Die  deutsche  Photo-  und  Kino-Fruhjahrsmesse  1938 
(Photographic  and  Motion  Picture  Spring  Exhibi- 
tion) (pp.  394-406). 

Neue  Richtlinien  fur  Schul-Stehbildwerfer  (New 
Standards  for  School  Lantern  Slides)  (pp.  415-417). 

- 


July  1938]  CURRENT  LITERATURE  101 

RCA  Review 

2  (Apr.,  1938),  No.  4 

Equipment   and   Methods    Developed   for    Broadcast 

Facsimile  Service  (pp.  379-395).  C.  J.  YOUNG 

The  Monoscope  (pp.  414-420).  C.  E.  BURNETT 

Some  Notes  on  Video-Amplifier  Design  (pp.  421-432).   A.  PREISMAN 

Effect  of  the  Receiving  Antenna  on  Television  Recep- 
tion Fidelity  (pp.  433-441).  S.  W.  SEELEY 

A  200-Kilowatt  Radiotelegraph  Transmitter  (pp.  442-  C.    W.    HANSELL   AND 
458).  G  L.  USSELMAN 


FALL,  1938,  CONVENTION 


DETROIT,  MICHIGAN 

HOTEL  STATLER 
OCTOBER  31,  NOVEMBER  1-3,  INCLUSIVE 


Officers  and  Committees  in  Charge 

W.  C.  KUNZMANN,  Convention  Vice-P resident 
J.  I.  CRABTREE,  Editorial  Vice-President 
G.  E.  MATTHEWS,  Chairman,  Papers  Committee 
H.  GRIFFIN,  Chairman,  Projection  Committee 
E.  R.  GEIB,  Chairman,  Membership  Committee 
J.  HABER,  Chairman,  Publicity  Committee 


G.  AVIL 
A.  J.  BRADFORD 
F.  C.  DICKELY 
E.  H.  FORBES 
W.  M.  HARRIS 


E.  R.  GEIB 


Local  Arrangements 

K.  BRENKERT,  Chairman 
G.  A.  MCARTHUR 

E.  J.  McGLINNEN 

R.  R.  McMATH 
H.  S.  NORTON 
R.  L.  RUBEN 


G.  J.  SKIMIN 
J.  F.  STRICKLER 
H.  H.  STRONG 
W.  J.  TURNBULL 
E.  F.  ZATORSKY 


Registration  and  Information 

W.  C.  KUNZMANN,  Chairman 


S.  HARRIS 


G.  J.  SKIMIN 


Hotel  and  Transportation  Committee 

A.  J.  BRADFORD,  Chairman 

H.  ANDERS  L.  A.  FIFERLIK  W.  C.  KUNZMANN 

A.  B.  CHERTON  G.  J.  JARRETT  P.  M.  MOLS 

M.  DUDELSON  K.  KALLMAN  E.  J.  SCHAEFBR 


A.  J.  BRADFORD 
K.  BRENKERT 
F.  C.  DICKELY 
E.  H.  FORBES 


Projection 

H.  GRIFFIN,  Chairman 
W.  M.  HARRIS 

F.  MOLES 

H.  S.  MORTON 

G.  A.  MCARTHUR 


E.  J.  McGLINNEN 

R.  L.  RUBEN 
H.  H.  STRONG 
W.  J.  TURNBULL 


Officers  and  Members  of  Detroit  Projectionists  Local  No.  199 


A.  J.  BRADFORD 
K.  BRENKERT 
H.  GRIFFIN 

102 


Banquet 

J.  F.  STRICKLER,  Chairman 
S.  HARRIS 
G.  J.  JARRETT 
W.  C.  KUNZMANN 


R.  R.  MCMATH 
H.  H.  STRONG 
E.  F.  ZATORSKY 


FALL  CONVENTION  103 

Publicity 

J.  HABER,  Chairman 

J.  R.  CAMERON  S.  HARRIS  P.  A.  McGuiRE 

J.  J.  FINN  G.  E.  MATTHEWS  F.  H.  RICHARDSON 

Ladies1  Reception  Committee 

MRS.  J.  F.  STRICKLER,  Hostess 

assisted  by 

MRS.  G.  AVIL  MRS.  F.  C.  DICKELY  MRS.  G.  A.  MCARTHUR 

MRS.  A.  J.  BRADFORD  MRS.  E.  H.  FORBES  MRS.  R.  L.  RUBEN 

MRS.  K.  BRENKERT  MRS.  W.  M.  HARRIS  MRS.  G.  J.  SKIMIN 

Headquarters 

The  Headquarters  of  the  Convention  will  be  at  the  Hotel  Statler,  where  excellent 
accommodations'  are  assured.  A  reception  suite  will  be  provided  for  the  Ladies' 
Committee,  who  are  now  engaged  in  preparing  an  excellent  program  of  entertain- 
ment for  the  ladies  attending  the  Convention. 

Special  hotel  rates  guaranteed  to  SMPE  delegates  and  friends,  European  plan, 
will  be  as  follows : 

One  person,  room  and  bath  $3.00  to  $6.00 

Two  persons,  room  and  bath  5.00  to    8.00 

Two  persons  (twin  beds),  room  and  bath  5.50  to    9.00 

Three  persons,  room  and  bath  7.50  to  10.50 

Parlor  suite  and  bath,  for  one  8.50  to  11.00 

Parlor  suite  and  bath,  for  two  12.00  to  14.00 

Room  reservation  cards  will  be  mailed  to  the  membership  of  the  Society  in  the 
near  future,  and  everyone  who  plans  to  attend  the  Convention  should  return  his 
card  to  the  Hotel  promptly  in  order  to  be  assured  of  satisfactory  accommodations. 
Registrations  will  be  made  in  the  order  in  which  the  cards  are  received.  Local 
railroad  ticket  agents  should  be  consulted  as  regards  train  schedules,  and  rates  to 
Detroit  and  return. 

The  following  special  rates  have  been  arranged  for  SMPE  delegates  who  motor 
to  the  Convention,  at  the  National-Detroit  Fireproof  Garage  (the  Hotel  Statler's 
official  garage),  Clifford  and  Elizabeth  Streets,  Detroit:  Self-delivery  and  pick-up, 
12  hours,  $0.60;  24  hours,  $1.00;  Hotel-delivery  and  pick-up,  24  hours,  $1.25. 
Special  weekly  rates  will  be  available. 

Technical  Sessions 

An  attractive  and  interesting  program  of  technical  papers  and  presentations  is 
being  assembled  by  the  Papers  Committee.  All  technical  sessions,  apparatus 
symposiums,  and  film  programs  will  be  held  in  the  Large  Banquet  Room  of  the 
Hotel. 

Registration  and  Information 

Registration  headquarters  will  be  located  at  the  entrance  of  the  Large  Banquet 
Room,  where  members  of  the  Society  and  guests  are  expected  to  register  and  re- 
ceive their  badges  and  identification  cards  for  admittance  to  the  sessions  and  film 


104  FALL  CONVENTION 

programs.     These  cards  will  be  honored  also  at  several  motion  picture  theaters 
in  the  neighborhood  of  the  Hotel,  during  the  days  of  the  Convention. 

Informal  Luncheon  and  Semi- Annual  Banquet 

The  usual  Informal  Luncheon  will  be  held  at  noon  of  the  opening  day  of  the 
Convention,  October  31st,  in  the  Michigan  Room  of  the  Hotel.  On  the  evening  of 
Wednesday,  November  2nd,  the  Semi-Annual  Banquet  of  the  Society  will  be  held 
in  the  Grand  Ballroom  of  the  Hotel  at  8  P.M.  Addresses  will  be  delivered  by 
prominent  members  of  the  industry,  followed  by  dancing  and  other  entertainment. 

Points  of  Interest 

In  addition  to  being  a  great  industrial  center,  Detroit  is  also  well  known  for  the 
beauty  of  its  parkways  and  buildings,  and  its  many  artistic  and  cultural  activities. 
Among  the  important  buildings  that  one  may  well  visit  are  the  Detroit  Institute 
of  Arts;  the  Detroit  Historical  Society  Museum;  the  Russell  A.  Alger  House,  a 
branch  of  the  Detroit  Institute  of  Arts;  the  Cranbrook  Institutions;  the  Shrine 
of  the  Little  Flower;  and  the  Penobscot  Building. 

At  Greenfield  Village,  Dearborn,  are  grouped  hundreds  of  interesting  relics  of 
early  American  life,  and  there  also  is  located  the  Edison  Institute,  established  by 
Henry  Ford  in  memory  of  Thomas  A.  Edison. 

On  the  way  to  Greenfield  Village  is  the  Ford  Rotunda,  a  reception  hall  for  visi- 
tors to  the  Ford  Rouge  Plant.  Here  are  complete  reproductions  and  displays  of 
motorcar  design,  and  representations  of  the  famous  highways  of  the  world,  from 
Roman  days  to  modern,  are  on  the  grounds  surrounding  the  building. 

The  General  Motors  Research  Building  and  Laboratory,  located  on  Milwaukee 
Avenue,  will  be  of  particular  interest  to  engineers  visiting  the  City. 

Various  trips  may  be  taken  from  Detroit  as  a  center — to  Canada,  by  either  the 
Ambassador  Bridge  or  the  Fleetway  Tunnel;  to  Bloomfield  Hills,  a  region  of 
lakes;  Canadian  Lake  Erie  trip  from  Windsor,  Ontario;  to  Flint,  Michigan, 
another  center  of  the  automotive  industry;  to  Milford,  General  Motors'  Proving 
Grounds;  and  to  the  Thumb  of  Michigan  Resort  Beaches.  The  City  contains 
also  a  number  of  beautiful  parks  and  golf  courses. 


SOCIETY  ANNOUNCEMENTS 


ADMISSIONS  COMMITTEE 

At  a  recent  meeting  of  the  Admissions  Committee,  at  the  General  Office  of 
the  Society,  the  following  applicants  for  membership  were  admitted  to  the 
Associate  grade: 


CHICKAMOTO,  T. 
Makaweli, 

Kanai,  T.  H. 
DICKELY,  F.  C. 
Altec  Service  Co., 

2111  Woodward  Ave., 

Detroit,  Mich. 
FORBES,  E.  H. 
210  W.  Montcalm  St., 

Detroit,  Mich. 
GROB,  E.  F. 

3  Chesterton  Flats, 

Manion  Ave., 

Rose  Bay, 

Sydney,  Australia. 
HARRIS,  W.  M. 

United  Detroit  Theater  Corp., 
1600  Stroh  Building, 

Detroit,  Mich. 
JUDSON,  F. 

134  North  Hobart  Blvd., 

Los  Angeles,  Calif. 
KAPILA,  P.  N. 

RCA  Photophone  (India)  Ltd., 
Prospect  Chambers, 
Hornby  Rd., 

Bombay,  India. 
KRULISH,  J.  A. 

63-01  Alderton  St., 

Elmhurst,  Long  Island, 
New  York. 

McGLINNEN,  E.  J. 

19303  Pennington  Dr., 
Detroit,  Mich. 


MALHERBE,  E.  G. 

National  Bureau  of  Educational  and 

Social  Research, 
Union  Buildings, 

Pretoria,  South  Africa. 

MATTHEWS,  J.  G. 

10845  Wellworth  Ave., 
West  Los  Angeles,  Calif. 

MILGROVE,  J.  D. 
17  Kambala  Rd., 
Bellevue  Hill, 

Sydney,  Australia. 

MlNTERN,  M. 

SS  Manhattan 

U.  S.  Lines,  1  Broadway, 
New  York,  N.  Y. 

MORTENSEN,  A. 

316  M.  &  M.  Bldg., 
Houston,  Texas. 

PANCHOLI,  R.  M. 

Empire  Talkie  Distributors, 
Heera  House, 
Sandhurst  Rd., 
Bombay  4,  India. 

SIMMONS,  E.  E.  JR. 

California  Institute  of  Technology, 
Pasadena,  Calif. 

SINGH,  U. 

Empire  Talkie  Distributors, 
Chandani  Chowak, 
Delhi,  India. 

105 


106  SOCIETY  ANNOUNCEMENTS 

SMITH,  M.  A.  THOMPSON,  C.  J.  P. 

Box  68,  Balboa  Heights,  Mariners,  Christchurch  Rd. 

Canal  Zone.  Virginia  Water, 

STRALEY,  W.  Surrey,  England. 

3725  Warwick  Blvd.  VAVRINA,  E. 

Kansas  City,  Mo.  Prague  V, 

TRECELLAS,  L.  K.  Czechoslovakia. 
57  Pollman  Court, 
Streatham  Hill, 

London  S.  W.  2.,  England. 


In  addition,  the  following  applicants  have  been  admitted  by  vote  of  the  Board 
of  Governors  to  the  Active  grade : 

BRADBURY,  H.  D.  BURNS,  R.  P. 

411  Fifth  Ave.,  3034  Leland  Ave., 

New  York,  N.  Y.  Chicago,  111. 

BREITENSTEIN,  S.  COOK,  A.  W. 

198  Johnson  Ave.,  34  Hayes  St., 

Teaneck,  N.  J.  Binghamton,  N.  Y. 

BROWN,  R.  C.  PESCE,  J.  S. 

1540  Broadway,  RCA  Manufacturing  Co. 

New  York,  N.  Y.  Camden,  N.  J. 

STRONG,  L.  D, 

908  S.  Wabash  Ave., 
Chicago,  111. 


JOURNAL 

OF  THE  SOCIETY  OF 

MOTION  PICTURE  ENGINEERS 

Volume  XXXI  AUGUST,  1938  Number  2 

CONTENTS 

Page 

Progress  in  the  Motion  Picture  Industry — Report  of  the  Prog- 
ress Committee 109 

The  Multiplane  Camera  Crane  for  Animation  Photography .  .  . 

W.  E.  GARITY  AND  W.  C.  MCFADDEN     144 

Distortion  in  Sound  Reproduction  from  Phonograph  Records 

J.  A.  PIERCE  AND  F.  V.  HUNT     157 

A  Higher-Efficiency  Condensing  System  for  Picture  Projectors 

F.  E.  CARLSON     187 

A  Color  Densitometer  for  Subtractive  Processes.  . R.  M.  EVANS  194 

Report  of  the  Papers  Committee ' 202 

Current  Literature 212 

Detroit  Convention 214 

Society  Announcements 217 


JOURNAL 

OF  THE  SOCIETY  OF 

MOTION  PICTURE  ENGINEERS 


SYLVAN  HARRIS,  EDITOR 

Board  of  Editors 
J.  I.  CRABTREE,  Chairman 

A.  N.  GOLDSMITH  L.  A.  JONES  H.  G.  KNOX 

A.  C.  HARDY  E.  W.  KELLOGG  G.  E.  MATTHEWS 


Subscription  to  non-members,  $8.00  per  annum;  to  members,  $5.00  per  annum, 
included  in  their  annual  membership  dues;  single  copies,  $1.00.  A  discount 
on  subscriptions  or  single  copies  of  15  per  cent  is  allowed  to  accredited  agencies. 
Order  from  the  Society  of  Motion  Picture  Engineers,  Inc.,  20th  and  Northampton 
Sts.,  Easton,  Pa.,  or  Hotel  Pennsylvania,  New  York,  N.  Y. 
Published  monthly  at  Easton,  Pa.,  by  the  Society  of  Motion  Picture  Engineers. 

Publication  Office,  20th  &  Northampton  Sts.,  Easton,  Pa. 
General  and  Editorial  Office,  Hotel  Pennsylvania,  New  York,  N.  Y. 

West-Coast  Office,  Suite  226,  Equitable  Bldg.,  Hollywood,  Calif. 
Entered  as  second  class  matter  January  15,  1930,  at  the  Post  Office  at  Easton, 
Pa.,  under  the  Act  of  March  3,  1879.     Copyrighted,  1938,  by  the  Society  of 
Motion  Picture  Engineers,  Inc. 

Papers  appearing  in  this  Journal  may  be  reprinted,  abstracted,  or  abridged 
provided  credit  is  given  to  the  Journal  of  the  Society  of  Motion  Picture  Engineers 
and  to  the  author,  or  authors,  of  the  papers  in  question.  Exact  reference  as  to 
the  volume,  number,  and  page  of  the  Journal  must  be  given.  The  Society  is 
not  responsible  for  statements  made  by  authors. 


OFFICERS  OF  THE  SOCIETY 

^President:     S.  K.  WOLF,  RKO  Building,  Rockefeller  Center,  New  York,  N.  Y. 
*Past-President:    H.  G.  TASKER,  Universal  City,  Calif. 
*Executive   Vice-President:    K.  F.  MORGAN,  6601  Romaine  St.,  Los  Angeles, 

Calif. 

** Engineering    Vice-President:    L.  A.  JONES,  Kodak  Park,  Rochester,  N.  Y. 
^Editorial  Vice-President:    J.  I.  CRABTREE,  Kodak  Park,  Rochester,  N.  Y. 
** Financial  Vice-President:    E.  A.  WILLIFORD,  30  E.  42nd  St.,  New  York,  N.  Y. 
* 'Convention    Vice-President:    W.   C.   KUNZMANN,   Box  6087,   Cleveland,  Ohio. 
^Secretary:    J.  FRANK,  JR.,  90  Gold  St.,  New  York,  N.  Y. 
^Treasurer:    L.  W.  DAVEE,  250  W.  57th  St.,  New  York,  N.  Y. 

GOVERNORS 

*J.  O.  AALBERG,  157  S.  Martel  St.,  Los  Angeles,  Calif. 

*M.  C.  BATSEL,  Front  and  Market  Sts.,  Camden,  N.  J. 

**R.  E.  FARNHAM,  Nela  Park,  Cleveland,  Ohio. 

*G.  FRIEDL,  JR.,  90  Gold  St.,  New  York  N.  Y. 

*A.  N.  GOLDSMITH,  444  Madison  Ave.,  New  York,  N.  Y. 

**H.  GRIFFIN,  90  Gold  St.,  New  York,  N.  Y. 

**A.  C.  HARDY,  Massachusetts  Institute  of  Technology,  Cambridge,  Mass. 

*S.  A.  LUKES.  6145  Glenwood  Ave.,  Chicago,  111. 

*Tenn  expires  December  31,  1938. 

**Term  expires  December  31,  1939. 


PROGRESS  IN  THE  MOTION  PICTURE  INDUSTRY* 
REPORT  OF  THE  PROGRESS  COMMITTEE 


immary.—This  report  of  the  Progress  Committee  covers  the  year  1937.     The 
advances  in  the  cinematographic  art  are  classified  as  follows: 

(I)  Cinematography:  (A}  Professional  and  (B)  Substandard;  (II)  Sound  Re- 
cording; (III)  Sound  and  Picture  Reproduction;  (IV)  Publications  and  New 
Books;  (Appendix)  The  Japanese  Motion  Picture  Industry;  Progress  in  Germany; 
Progress  in  Great  Britain. 

The  most  notable  advances  recorded  during  the  past  year  appear 
to  have  been  in  the  production  of  new  panchromatic  emulsions  for 
professional  cimematography.  One  emulsion  has  resulted  in  addi- 
tional negative  speed  without  any  consequent  increase  of  grain  size. 
Another  new  emulsion,  intended  for  newsreel  use  and  work  under  ad- 
verse lighting,  has  from  three  to  four  times  greater  speed  than  stand- 
ard super-sensitive  panchromatic  films. 

In  the  field  of  substandard  cinematography  the  popularization  of 
color  has  advanced  rapidly  coincidentally  with  improvement  in  proc- 
essing of  color-films. 

In  the  field  of  sound  recording  there  is  little  to  report  in  the  way  of 
advances  in  equipment,  the  year's  activities  being  largely  confined  to 
the  consolidation  of  advances  previously  reported  for  1936. 

The  modernization  of  theaters  has  progressed  satisfactorily,  es- 
pecially in  the  matter  of  installation  of  the  newer  two-way  horn  sys- 
tems announced  in  last  year's  report. 

In  the  projection  field  there  is  little  to  report  in  the  way  of  new 
equipment,  either  for  sound  or  picture  projection.  The  Committee 
is  including  for  the  first  time  this  year  material  describing  theater 
lighting  and  marquee  illumination. 

The  Committee  wishes  to  thank  the  following  companies  for  supply- 
ing materials  and  photographs  for  the  report :  Ampro  Corporation ; 
Bell  &  Howell  Co.;  Eastman  Kodak  Co.;  Electrical  Research 
Products,  Inc.;  General  Electric  Co.;  General  Service  Studios,  Inc.; 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;  received 
April  15,  1938. 

109 


110  PROGRESS  IN  MOTION  PICTURE  INDUSTRY  [j.  s.  M.  p.  E. 

General  Radio   Co.;    Mole-Richardson   Co.;    Paramount   Pictures 
Corp.;  Victor  Animatograph  Corp. 

J.  G.  FRAYNE,  Chairman 

W.  H.  BAHLER  J.  L.  FORREST 

L.  N.  BUSCH  F.  L.  HOPPER 

R.  E.  FARNHAM  G.  E.  MATTHEWS 

V.  E.  MILLER 

SUBJECT  CLASSIFICATION 

(I)  Cinematography 
(A}  Professional 

(1)  Emulsions 

(2)  Cameras  and  accessories 

(3)  Stage  illumination 

(B)  Substandard 

(1)  Films 

(2)  Cameras 

(3)  Projectors 

(4)  Miscellaneous 

(II)  Sound  Recording 

(1)  General 

(2)  Equipment 

(3)  Accessories 

(4)  Films 

(III)  Sound  and  Picture  Reproduction 

(1)  Motion  picture  theater  lighting 

(2)  Theater  lighting  equipment 

(3)  Accessories 

(IV)  Publications  and  New  Books 
Appendix  A 

The  Japanese  Motion  Picture  Industry — 1937 
Appendix  B 

Progress  in  Germany 
Appendix  C 

Progress  of  the  Motion  Picture  Industry  in  Great  Britain 

(I)   CINEMATOGRAPHY 
(A)  Professional 

The  year  1937  has  seen  some  very  definite  progress  in  the  field 
professional  motion  picture  photography. 


Aug.,  1938]       PROGRESS  IN  MOTION  PICTURE  INDUSTRY  111 

(1)  Emulsions. — Perhaps  the  outstanding  advance  for  the  year 
has  been  made  by  the  Agfa  Ansco  Corporation,  who  developed  and 
marketed  two  new  and  very  fast  panchromatic  negatives  that  have 
proved  almost  revolutionary,  in  that  they  have  "de-axiomized"  the 
old  belief  that  added  negative  speed  always  meant  increased  grain 
size.  Conversely,  their  new  negatives,  with  a  very  great  increase  in 
speed,  have  maintained  and  even  lessened  the  grain  size.  The 
Agfa  Supreme  is  a  new  product  having  twice  the  speed  of  standard 
supersensitive  panchromatic  emulsions.  It  retains  to  the  full  extent 


FIG.  1.     Dual  screen  transparency  camera. 

such  essential  qualities  as  keeping  stability,  color  balance,  and  ex- 
tremely fine  grain  which,  heretofore,  were  impaired  by  increased 
speed.  It  provides  the  production  cameraman  with  a  means  of  re- 
ducing working  camera  apertures,  with  a  consequent  increase  of  defi- 
nition and  better  photographic  quality.  It  minimizes  the  problem 
of  character  grouping  which,  in  the  past,  has  been  restricted  by 
shallow  focus.  It  increases  the  efficiency,  realism,  and  scope  of  proc- 
ess projection  work,  thereby  enabling  economy  to  producers.  In 
general,  it  represents  a  major  achievement  in  research  and  emulsion 
manufacture  by  providing  the  industry  with  a  medium  of  increased 
latitude  and  quality. 


112  PROGRESS  IN  MOTION  PICTURE  INDUSTRY  [j.  s.  M.  p.  E. 

The  Agfa  Ultra-Speed  Pan  is  intended  for  newsreels  and  adverse 
light  conditions.  It  has  from  three  to  four  times  greater  speed  than 
standard  supersensitive  panchromatic  material.  It  possesses  full 
keeping  stability  and  provides  the  industry  with  a  means  of  obtaining 
photographic  results  under  adverse  conditions  heretofore  impossible. 
It  is  of  particular  value  for  night  scenes  photographed  under  ordi- 
nary artificial  illumination  and  for  night  scenes  of  large  area  with 
special  artificial  illumination.  It  increases  economy  in  production 
by  permitting  work  in  poor  light  thereby  increasing  the  working  day. 
It  provides  newsreels  with  an  efficient  material  under  conditions  out- 
lined above. 

The  Eastman  Kodak  Company  brought  out  two  fine-grain  dupli- 
cating films,1  negative  and  positive,  that  are  well  worthy  of  note  in 
that  they  bring  duplication  quality  much  closer  to  the  original. 
Since  speed  is  not  especially  essential  in  duplication,  the  Eastman 
Company  have  concentrated  upon  grain  reduction,  resulting  in  an 
extremely  fine  grain  so  necessary  for  ideal  results.  Duplicate  nega- 
tives from  lavender  positives,  using  this  new  fine-grain  stock,  are 
almost  exact  replicas  of  the  original,  retaining  their  texture  and 
quality.  These  new  stocks  have  proved  highly  adaptable  to  pro- 
jection work,  because  of  their  lack  of  grain  and  great  latitude. 

(2)  Cameras  and  A  ccessories. — No  new  cameras  have  been  developed 
during  the  year,  but  the  Twentieth  Century-Fox  Camera,  described 
last  year  in  the  JOURNAL,  having  successfully  photographed  eighteen 
productions  since  its  inception,  still  leads  the  field.  It  is  of  interest  to 
note  that  ten  similar  cameras  are  now  in  course  of  construction  for 
Twentieth  Century-Fox,  the  first  to  be  delivered  in  April.  Since  this 
camera  will  be  made  available  to  other  studios,  its  use  by  the  studio 
of  origin  will  be  under  careful  scrutiny  during  the  coming  year. 

The  semi-automatic  follow-focus  finder,  as  used  more  or  less  on  all 
blimped  cameras,  has  been  carried  to  a  high  degree  of  completion  at 
MGM  Studios,  where  every  camera  is  so  equipped.  Paramount  also 
has  several  of  similar  design,  as  no  doubt  have  other  studios,  but 
MGM,  through  their  chief  cinematographer,  John  Arnold,  have 
stressed  the  importance  of  this  tool.  The  improved  finder  is  void  of 
lost  motion,  exactly  correlating  the  focus  and  fields  of  the  camera  and 
finder  lenses,  respectively,  greatly  facilitating  the  speed  and  acH 
curacy  of  the  camera  crew. 

A  rather  unique  set-up  is  the  dual  screen  transparency  camera,! 
devised  by  Farciot  Edouart  and  the  Transparency  Department  of| 


Aug.,  1938]       PROGRESS  IN  MOTION  PICTURE  INDUSTRY  113 

Paramount  Studio  (Fig.  1).  It  augments  projection  background 
work  by  doubly  widening  the  process  background,  and  permitting 
its  use  by  simultaneous  projection  on  two  screens  of  this  doubled 
area.  Twin  cameras  are  mounted  in  such  a  way  that  they  photo- 
graph a  background  of  double  the  ordinary  width  as  reflected  on  sur- 
face reflectors  adjusted  to  simulate  a  single  background.  This  makes 
possible,  for  instance,  continuity  of  action  across  two  screens  (or  a 
screen  of  double  width) ;  the  exact  alignment  of  horizon  levels  on  the 
two  screens;  no  lap-overs  at  their  junction;  and  the  maintenance  of 
the  size  of  actors  or  objects  found  in  the  single  screen. 

Although  designed  for  and  adapted  to  Technicolor  and  cartoon 
work,  the  new  Disney  multiplane  camera  is  an  outstanding  achieve- 
ment, with  possibilities  in  the  black-and-white  field,  particularly  in 
title  work.  The  camera,  specially  designed,  is  mounted  to  shoot 
vertically  downward  from  the  top  of  a  chassis  carrying  several  planes 
on  which  the  action  is  depicted,  each  supplementing  the  others  as 
desired.  The  machine  is  of  extreme  accuracy;  each  of  the  planes 
may  be  moved  separately  or  jointly,  with  vernier  calibrations  assur- 
ing exactness  of  duplication  when  necessary.  Since  each  plane  may 
be  lighted  separately,  or  moved  closer  to  or  further  from  the  shooting 
lens,  or  at  different  speeds,  some  of  its  possibilities  are  evident.  It 
does  the  work  in  the  Disney  Studio  of  a  Special  Effects  Department 
in  the  Major  Studios,  plus  a  speeding  up  of  production  due  to  the 
photographing  of  the  several  planes  simultaneously.  Because  of  the 
various  planes,  truer  perspective  may  be  achieved  as  the  camera 
"dollies"  up  to  or  away  from  the  "key"  plane,  while  "atmosphere" 
is  varied  at  will  by  altering  the  focal  distances  of  the  planes.  Another 
of  its  manifold  uses  is  the  substitution  of  a  "projection"  background 
for  one  of  the  planes,  enabling  the  operator  to  double  in  effects 
(shimmer,  ripples,  heat  waves,  etc.)  in  conjunction  with  the  other 
planes.  The  Old  Mill  and  Snow  White  contain  examples  of  this  multi- 
plane work. 

(3)  Stage  Illumination. — The  two  Mazda  lamp  manufacturers 
announced  as  of  March  1st  two  new  photoflash  lamps,  the  No.  7, 
which  incorporates  a  fine  aluminum  wire  and  a  small  amount  of  foil 
in  the  A-15  bulb;  and  the  No.  15,  which  employs  special  heat-treated 
foil  in  the  A-19  bulb.  The  No.  7  has  a  total  light  output  of  22,500 
lumen-seconds  and  the  No.  15,  30,000  lumen-seconds.  Because  of 
the  aluminum  wire  and  the  specially  treated  foil  the  light-output  vs. 
time  relation  is  much  broader  than  the  older,  regular  foil  lamps.  The 


114  PROGRESS  IN  MOTION  PICTURE  INDUSTRY  [j.  s.  M.  p.  E. 

advantage  of  this  broader  peak  characteristic  is  to  improve  the  re- 
liability of  obtaining  pictures  when  the  lamps  are  used  with  syn- 
chronizing equipment.  The  broader  flash  also  affords  more  prac- 
tical synchronism  with  focal-plane  type  shutters.  The  No.  7  lamp, 
being  in  the  A-15  bulb,  has  also  the  advantage  of  greater  compact- 
ness. 

The  Libbey-Owens-Ford  Glass  Company  of  Toledo,  through  coop- 
eration with  the  Nela  Park  Engineering  Department  of  the  General 
Electric  Company  and  with  the  Technicolor  Motion  Picture  Corpora- 
tion, has  made  available  a  special  blue  glass  filter  which,  when  used 
with  incandescent  lamps  of  the  CP  type,  corrects  their  light  so  as  to 
give  correct  color  with  the  Technicolor  process.  The  light  emitted  by 
incandescent  lighting  equipment  employing  the  CP  lamps  and  these 
niters  is  such  a  close  duplication  of  daylight  that  subjects  can  be  il- 
luminated with  a  mixture  of  this  filtered  light  and  daylight  or  arc 
light  and  no  difference  in  the  color  can  be  detected .  The  filters  con- 
sist of  a  base  of  medium-blue  glass  upon  which  has  been  sprayed  a 
magenta-blue  enamel,  which  is  subsequently  fired  into  the  glass. 
This  process  has  the  advantage  also  of  greatly  strengthening  the 
glass  so  that  the  likelihood  of  breakage  is  extremely  remote.  These 
filters  had  their  first  general  introduction  in  the  photography  of 
The  Goldwyn  Follies  and  are  being  used  in  subsequent  productions. 

(B)  Substandard 

Keeping  step  with  the  pace  set  in  immediately  preceding  years 
1937  has  actively  contributed  to  advancements  in  the  substandard 
field  of  cinematography.  Much  new  equipment  of  improved  design 
has  made  its  appearance,  both  of  domestic  and  European  manufac- 
ture. Both  8-mm.  and  16-mm.  equipment  retain  their  popularity  in 
America,  while  in  addition  to  these  sizes  the  9.5-mm.  equipment  con- 
tinues its  popularity  abroad ;  although  it  is  not  favorably  received  in 
this  country.  Sixteen-mm.  sound  equipment  of  improved  and  sim- 
plified design  has  done  much  to  popularize  16-mm.  film  in  the  educa- 
tional, entertainment,  and  advertisement  fields.  Sound  projection 
equipment  of  satisfactory  quality,  while  still  somewhat  too  expensive 
to  find  favor  with  the  average  amateur,  is  being  slowly  reduced  in 
price  and  is  now  beginning  to  attract  the  attention  of  the  advanced 
amateurs. 

For  commercial  entertainment  16-mm.  film  has  not  found  exten- 


Aug.,  1938]       PROGRESS  IN  MOTION  PICTURE  INDUSTRY 


115 


sive  use  in  America  as  yet;  abroad  in  England  and  the  Continent 
numerous  theaters  operate  regularly  with  16-mm.  film.  Gaumont 
British  are  currently  releasing  productions  on  both  35-mm.  and  16- 
mm.  widths.  Except  for  the  late  productions  of  a  few  major  pro- 
ducers, 16-mm.  library  films  are  restricted  to  old  pictures  of  indepen- 
dent producers. 

Improvements  in  sound  recording  technic,  advancements  in  the 
art  of  animation,  refinements,  and  simplification  of  projection  mecha- 
nisms have  contributed  in  popularizing  16-mm.  film  for  educational 
purposes.  The  field  of  visual  education  has  grown  so  rapidly  that 
producers  of  educational  films  have  not  been  able  to  keep  up  with  the 
demand  for  them.  In  science,  in 
medicine,  in  industry,  and  in  sport 
this  substandard  film  medium  is 
proving  more  and  more  important. 

(1)  Films. — Superpan     Negative, 
new     type,     replaced     the     former 
Superpan  manufactured  by  the  Agfa 
Ansco  Corporation.     The  new  film  is 
approximately  twice  as  fast  as  the 
former  Superpan.     The  film  has  the 
same   type   of   color-sensitivity   and 
latitude,  and  the  grain  size  has  not 
been  increased. 

Dufaycolor  film  has  been  im- 
proved. The  reseau  has  been  made 
finer,  resulting  in  a  decided  improve- 
ment in  appearance  of  the  screen 
pattern  and  assuring  sharper  definition.  Dufaycolor  has  been  made 
available  abroad  for  9.5-mm.  cameras.  The  film  is  supplied  in  maga- 
zines in  30-ft.  lengths. 

(2)  Cameras. — The  new  Cine  Kodak  model  E  was  brought  out  by 
the  Eastman  Kodak  Company.     It  is  a  moderately  priced  camera 
equipped  with //3. 5  lens  and  variable  speeds  of  16,  32,  and  64  frames 
per  second.     It  takes  either  50-ft.  or  100-ft.  rolls  of  film. 

Bell  &  Howell  Co.  introduced  a  new  "streamlined"  8-mm.  camera 
(Fig.  2),  differing  from  former  models  in  the  design  of  the  exposure 
dial  and  in  the  shutter  release  mechanism.  The  new  models  incor- 
porate single-frame  exposure  devices  as  standard  equipment. 

Agfa  abroad  introduced  the  8-mm.  Movex.     The  camera  is  of  the 


FIG.  2.     Bell  &  Howell  8-mm. 
camera. 


116 


PROGRESS  IN  MOTION  PICTURE  INDUSTRY  [j.  s.  M.  p.  E. 


It  is 


magazine  type,  each  magazine  holding  33  ft.  of  8-mm.  film, 
equipped  with  an//2.8  fixed-focus  lens. 

The  model  F  16-mm.  Siemens  camera,  introduced  by  Siemens- 
Halske,  is  of  the  magazine  type  and  follows  the  well  established  line 
of  Siemens  equipment.  It  has  interchangeable  lenses  and  the  lenses 
are  provided  with  focal  lengths  from  20  to  200  mm.  The  camera  has 


FIG.  3.     Victor  model  38. 

four  speeds,  8,  16,  24,  and  64,  and  is  equipped  with  a  single-frame 
device  for  making  still  pictures.  This  camera  is  being  imported  for 
the  American  market.  Siemens  also  introduced  an  8-mm.  camera 
taking  25-ft.  spools  of  double-^  film.  The  speed  control  is  coupled 
with  the  aperture.  Four  speeds  have  been  provided.  The  camera 
is  also  equipped  with  a  single-picture  device. 

Zeiss  Ikon  abroad  brought  out  the  Movikon  8.  The  camera  is 
equipped  with  an  //2  Zeiss  lens.  Features  of  the  camera  are  inter- 
changeable lenses  and  film  speeds  of  8,  16,  and  64  frames  a  second. 


1938]       PROGRESS  IN  MOTION  PICTURE  INDUSTRY 


117 


This  camera  is  said  to  be  the  first  precision-built  camera  to  accommo- 
date both  single  8-mm.  and  double-^  film. 

Ditmar,  a  9.5-mm.  camera  made  in  Austria,  was  announced  to  the 
European  trade.  The  camera  is  equipped  with  an//2.9  Cassar  lens, 
has  an  interchangeable  lens  mount  and  two  speeds.  This  Company 
also  introduced  a  new  8-mm.  camera. 

Pathe  abroad  introduced  a  new  9.5-mm.  camera,  equipped  with  a 
fixed-focus //2. 5  lens.  The  camera  is  claimed  to  be  unusually  silent 
and  is  said  to  be  the  smallest  movie  camera  made. 


FIG.  4.     Victor  model  33. 

(3)  Projectors. — The  Animatophone  model  38  (Fig.  3),  a  16-mm. 
sound  projector,  was  introduced  by  the  Victor  Animatograph  Cor- 
poration. It  is  regularly  equipped  with  two  12-inch  magnetic  type 
speakers  and  delivers  30  watts  of  undistorted  output.  The  use  of 
permanent-magnet  speakers  makes  it  possible  to  use  four  speaker 
units  when  desired  to  insure  better  sound  distribution.  The  equip- 
ment is  suitable  for  large  auditoriums.  In  addition,  a  mixing  panel 
has  been  provided  for  educational  purposes  and  classroom  use,  which 
permits  the  instructor  to  add  his  own  comments  by  eliminating  the 
sound  without  having  to  readjust  the  volume  or  tone  of  the  amplifier. 
Victor  Animatograph  Corp.  also  brought  out  a  model  33  Animato- 
phone (Fig.  4),  a  small,  compact,  low-priced  16-mm.  sound  projector. 


118 


PROGRESS  IN  MOTION  PICTURE  INDUSTRY  [j.  s.  M.  p.  E. 


The  speaker  and  projector  are  combined  in  one  unit  for  portability. 
A  5-watt  output  amplifier  is  provided.  The  lamp  house  has  spira- 
draft  ventilation  and  is  adaptable  to  all  standard  prefocus  projec- 
tion lamps. 


FIG.  5. 


Sound   Kodascope   Special;   set  up  with 
1600-ft.  reels. 


The  sound  Kodascope  Special  (Fig.  5)  was  introduced  by  the 
Eastman  Kodak  Company.  This  instrument  represents  years  of 
research  in  the  development  of  16-mm.  sound  equipment  and  is  a 
radical  departure  from  the  usual  16-mm.  sound  projection  apparatus. 
Operation  of  the  equipment  is  extremely  simple.  An  automatic 
loop-forming  mechanism  assures  synchronism.  The  scanning-drum 
shaft  carries  a  flywheel  and  is  driven  by  viscous  coupling.  In  this 


Aug.,  1938]       PROGRESS  IN  MOTION  PICTURE  INDUSTRY  119 

way  any  possibility  of  high-  or  low-frequency  modulation  is  avoided. 
The  pull-down  is  of  the  single-claw  type,  and  is  designed  to  have  low 
acceleration  at  both  ends  of  the  stroke.  The  entire  mechanism  is 
enclosed  in  an  oil-bath  which  insures  long  mechanical  quietness. 
Films  may  be  projected  at  24  or  16  frames  per  second.  An  //1. 6 
2-inch  lens  is  supplied  as  standard  equipment,  and  a  4-inch //1. 6  lens 
is  also  available.  Reel  arms  are  provided  for  1600-ft.  reels.  A  lever 
changes  the  focus  of  the  high  aperture  scanning-beam  so  that  re- 


FIG.  6.     The  138-  J  Filmosound  and  the  138-  J  with  booster  amplifier. 

versible  films,  positive  prints,  or  reversible  duplicates  may  be  pro- 
jected without  loss  of  frequency  response.  The  pre-amplifier  is  in- 
stalled in  the  base  of  the  Kodascope  and  the  power  amplifier  is  con- 
tained in  the  speaker  assembly. 

The  Filmosound  model  138,  manufactured  by  Bell  &  Ho  well,  has 
been  much  improved.  A  reversing  switch  has  been  provided  as  well 
as  a  still-picture  clutch.  In  addition  to  the  single-case  machine,  a 
two-case  model  is  now  offered,  one  of  the  cases  being  the  projector 
blimp  and  the  other  housing  the  loud  speaker.  For  installations  where 
volume  greater  than  can  be  provided  by  the  1 38  model  is  necessary, 


120 


PROGRESS  IN  MOTION  PICTURE  INDUSTRY  [j.  s.  M.  p.  E. 


a  special  speaker  case  housing  a  power  amplifier  is  available  (Fig.  6) . 
With  this  arrangement  sufficient  volume  can  be  obtained  for  large 
auditoriums.  The  model  120  Filmosound  is  also  now  equipped  with 
a  reverse  switch  and  still-picture  clutch.  A  new  amplifier  for  the 
equipment  has  been  designed  which  provides  25  watts  of  undistorted 
output.  High-fidelity  permanent-magnet  dynamic  speakers  are 
now  furnished  with  this  equipment.  The  power  output  of  the 
Filmosound  model  130  (Fig.  7)  has  been  increased  to  an  output  of 


FIG.  7.     Model  130- D  Filmosound. 


50  Watts  when  two  speakers  are  used.  The  volume  is  said  to  be  more 
than  sufficient  for  average  auditorium  use. 

The  Ampro  Corporation  brought  out  a  new  16-mm.  sound  pro- 
jector, model  L  (Fig.  8).  The  projector  is  equipped  with  a  barrel 
type  of  shutter  and  a  750- watt  lamp.  It  provides  sufficient  illumina- 
tion for  auditorium  projection.  The  amplifier  output  is  40  watts 
undistorted  power  to  two  speakers. 

Standard  Projectors,  Inc.,  introduced  anew  16-mm.,  750-watt  pro- 
jector employing  a  barrel  type  of  shutter  and  an //1. 6  lens.  An  in- 
teresting novelty  is  the  adjustable  gate  tension  which  makes  it 
possible  to  project  any  type  of  film  with  safety. 


Aug.,  1938]       PROGRESS  IN  MOTION  PICTURE  INDUSTRY 


121 


Eastman  Kodak  Co.  introduced  an  8-mm.  Kodascope  model  50. 
This  is  a  projector  in  the  medium-price  range. 

S.  P.  Equipment,  Ltd.,  brought  out  a  new  16-mm.  sound  projector 
making  use  of  an  intermittent  sprocket  instead  of  the  customary 
claw  for  moving  the  16-mm.  film.  The  film  is  moved  over  a  6-tooth 
sprocket  which  insures  smooth  film  operation  even  with  damaged 
perforations. 


FIG.  8.     Ampro  model  L  sound  projector  (16-mm, 
watt). 


750- 


Abroad,  Paillard-Bolex  improved  their  line  of  universal  projection 
equipment  for  projecting  interchangeably  8,  9.5,  and  16-mm.  films  by 
introducing  the  interchangeable  condensers  so  that  maximum  il- 
lumination would  be  obtained  with  whatever  width  of  film  was  being 
used. 

Agfa  abroad  introduced  the  Movector  8.  A  200-watt  lamp  with 
specially  designed  condensers  is  claimed  to  give  excellent  illumination. 

(4)  Miscellaneous. — A  cine  exposure  meter  was  brought  out  by 
Weston.  The  meter  has  a  viewing  angle  of  25  degrees,  which  is  ap- 
proximately that  of  a  1-inch  lens. 


122 


PROGRESS  IN  MOTION  PICTURE  INDUSTRY  [j.  s.  M.  p.  E. 


A  new  wide-angle  lens  for  all  16-mm.  Cine  Kodaks  was  made  avail- 
able by  the  Eastman  Kodak  Company  (Fig.  9).  The  lens  has  a  focal 
length  of  15  mm.  and  an//2.7  lens  in  a  focusing  mount.  The  focus- 
ing scale  is  graduated  down  to  6  inches  which  makes  the  lens  especially 
useful  for  close-up  cinematography. 

A  new  auxiliary  condenser  to  be  used  on  all  current  model  Bell  & 
Howell  projectors,  except  the  model  130,  was  brought  out  by  Bell 
and  Howell  (Fig.  10).  This  condenser  is  inserted  in  a  slot  provided 
in  the  rear  of  the  regular  condenser  in  the  equipment.  Its  use  is  said 
to  increase  the  illumination  as  much  as  56  per  cent  when  wide-angle 
lenses  or  lenses  of  wide  aperture  are  being  used. 

A  new  exposure  guide  for 
Kodachrome  film  was  brought 
out  by  the  Eastman  Kodak 
Company  (Fig.  11)  to  assist  users 
of  this  film  in  obtaining  correct 
exposures. 

(II)   SOUND  RECORDING 

(1)  General. — The  trend  toward 
mobile  recording  equipment  has 
been  brought  about  by  a  desire 
to  use  equipment  interchange- 
ably for  stage  and  location  work, 
and  by  the  advantages  of  having 
channel-operating  personnel  more 
intimately  associated  with  stage  production.  It  is  further  em- 
phasized by  the  new  sound-stage  construction  that  makes  de- 
centralization of  the  recording  plant  more  necessary.  Twentieth 
Century-Fox  have  added  a  number  of  channels  employing  trucks  in 
which  the  recording  equipment  is  located.  A  portable  mixer  is 
carried  to  the  set,  and  connects  to  the  truck  for  recording. 
Metro-Goldwyn-Mayer  have  added  stage  units,  dolly-mounted, 
which  contain  complete  channels  from  mixer  to  recorder.  These  are 
operated  on  the  stage  adjacent  to  the  set,  and  require  only  connection 
to  the  110-volt  a-c.  lines  for  power.  General  Service  Studios  mount 
their  recording  equipment  in  trailers  (Fig.  12),  and  carry  a  portable 
mixer  unit  to  the  set.  In  addition,  they  have  trailer-mounted  re- 
recording  machines  that  may  be  used  in  conjunction  with  either  fixed 
or  mobile  recording  channels  for  re-recording.  Such  a  set-up  usually 


FIG.  9.     Kodak  15-mm.  f/2.7  lens. 


Aug.,  1938]       PROGRESS  IN  MOTION  PICTURE  INDUSTRY  123 


,„ 


•olves  the  use  of  a  review  room  or  small  stage  for  monitoring  and 
projection  facilities.  Paramount  employs  stage  units  or  "teawagons" 
on  the  set,  connected  to  a  central  recording  building  housing  the  re- 
corders and  associated  equipment.2 

Increased  emphasis  has  been  placed  upon  recording  methods  pro- 
viding improved  quality  and  greater  volume  range.  Methods  in- 
clude: non-slip  printing;  intercutting  of  variable-width  and  vari- 
able-density sound-tracks;  the  use  of  track-squeezing  devices  with 
variable-density  recordings;  and  the  application  of  a  new  form  of 
pre-  and  post-equalization  to  variable-density  push-pull  records. 
The  latter  method  was  introduced  by  Metro-Goldwyn-Mayer,  and 


FIG.  10.     Magnilite  condenser. 

results  in  additional  noise  reduction,  decreased  intermodulation,  and 
elimination  of  background  noise  modulation  or  "hush-hush." 

Multichannel  recording  for  musical  scoring  is  an  interesting  varia- 
tion of  the  usual  scoring  technic.  Separate  channels  are  used  for  the 
soloist,  orchestra,  or  chorus.  As  much  acoustic  separation  as  possible 
is  employed  between  the  different  microphones.  This  method 
makes  it  possible  to  record  all  parts  simultaneously,  effecting  some 
recording  economies.  The  separate  tracks  are  then  available  for 
re-recording  in  the  usual  way.  In  exceptional  circumstances,  notably 
in  Universal's  100  Men  and  a  Girl,  separate  channels  were  used  to 
record  different  instrumental  groups  of  an  orchestra. 

(2)  Equipment. — A  number  of  novel  devices  based  upon  advanced 
engineering  principles  have  been  announced  during  the  past  year. 
Electrical  Research  Products,  Inc.,  have  developed  a  negative  play- 
back amplifier  suitable  for  reproducing  directly  from  film  negatives3 


124 


PROGRESS  IN  MOTION  PICTURE  INDUSTRY  [J.  s.  M.  p.  E. 


(Fig.  13).  Applications  include  editing  and  re-recording  newsreels, 
and  studio  facilities  for  reproducing  from  negatives  when  it  is  desired 
to  compare  sound  quality  from  negatives  and  prints. 


KODACHROME   EXPOSURE   GUIDE 
TYPE  "A"  FILM-PHOTOFLOOD  LIGHT 

16  MM.  8  MM. 


^*>"^ 


LAMPS 
NUMBER  OF  PHOTOFLOOb  LAMPS  USED 


FIG.  11.     Kodachrome  exposure  guide  for  type  A  film 
in  photoflood  light. 


A  new  type  of  hill-and-dale  recorder  utilizing  reverse  feedback  was 
announced  by  Bell  Telephone  Laboratories.4  In  addition  to  im- 
proved quality  for  processed  recording  materials,  it  provides  ex- 
cellent recordings  on  direct  materials  for  immediate  playback.  It 
has  wide  application  for  scoring  for  playback  work. 

RCA  has  developed  a  new  modulator  system  capable  of  recording 


Aug.,  1938]       PROGRESS  IN  MOTION  PICTURE  INDUSTRY 


125 


variable-width  or  variable-density  tracks,  either  standard  or  push- 
pull.5 

A  large  number  of  RCA  recorders  of  both  studio  and  portable 
types  manufactured  and  in  service  before  the  advent  of  ultraviolet 
recording  and  the  bilateral  shutter6  were  equipped  to  include  these 
recent  developments. 

The  non-slip7  printer  developed  by  RCA  has  come  into  more  gen- 


FIG.  12.     Trailer  recording  unit. 


eral  use  during  the  past  year.  Printers  utilizing  the  principle  are 
being  produced  commercially  and  the  industry  has  come  to  use  non- 
slip  prints  as  the  standard  of  comparison.  A  motor-driven  blooping 
shutter  has  been  added  to  a  number  of  RCA  printers  with  very  satis- 
factory results. 

Class  A  push-pull  recording8  was  demonstrated  very  successfully 
in  a  series  of  tests.  Due  to  its  numerous  advantages,  such  as  can- 
cellation of  even-harmonic  distortion,  elimination  of  splice  noises, 
speeding  up  of  noise-reduction  shutter  action,  and  elimination  of 
shutter  thump  usually  resulting  from  this  increased  speed  of  action, 


126 


PROGRESS  IN  MOTION  PICTURE  INDUSTRY  [j.  s.  M.  p.  E. 


etc.,  a  number  of  recordings  have  been  made  under  routine  studio 
conditions. 

The  development  of  the  modulated-carrier  oscillator9  has  provided 
an  excellent  means  for  determining  the  optimal  processing  conditions 
for  variable- width  recordings.  Continued  use  of  this  oscillator  in 
making  recordings  for  a  number  of  processing  laboratories  during  the 
past  eighteen  months  has  demonstrated  the  value  of  this  instrument. 


FIG.  13.     Negative  playback  unit. 


A  newsreel  type  of  recording  equipment  was  introduced  by  RCA. 
This  equipment  provides  class  B  push-pull  recording  with  ultraviolet 
light  on  the  identical  film  upon  which  the  picture  is  photographed. 
The  recording  optical  system  is  mounted  on  the  rear  of  the  motion 
picture  camera.  Although  light  in  weight  and  simple  to  operate, 
this  equipment  includes  features  heretofore  obtained  only  in  studio 
type  apparatus,  and  produces  results  that  compare  favorably  with 
studio  recordings. 


Aug.,  1938]       PROGRESS  IN  MOTION  PICTURE  INDUSTRY  127 

(3)  Accessories. — The  General  Radio  Company  brought  out  a  new 
power-level  indicator,  a  vacuum-tube  type  rather  than  copper-oxide, 
which  they  had  previously  manufactured  (Fig.  14).  This  instru- 
ment has  a  high-speed  meter  with  a  delay  circuit  so  that  sudden  peaks 
are  not  lost  but  are  indicated  quite  faithfully.  A  delay  circuit  makes 
the  return  swing  much  slower  than  that  provided  by  the  meter  move- 
ment itself,  with  the  result  that  the  indication  seems  to  float  on  peaks 
and  gives  an  accurate  monitoring  indication  without  the  erratic 
motion  characteristic  of  high-speed  instruments. 

The  Mole-Richardson  Co.  has  developed  the  type  103-B  microphone 
boom  and  type  126-B  microphone  boom  perambulator  (Fig.  15). 
The  wide  use  of  the  new  light-weight  microphones  indicated  that  it 
was  advisable  to  use  duralumin  and  light-weight  aluminum  alloys  in 


FIG.  14.     Type  686-A  power-level  indicator. 

the  construction  of  the  new  boom  head.  In  analyzing  the  causes 
of  noise  in  boom  operation  it  was  decided  to  eliminate  the  use  of 
stranded -wire  cable,  to  put  all  moving  parts  on  rolling  rather  than 
sliding  contact  surfaces,  and  as  the  design  was  developed  a  means 
was  worked  out  of  supporting  the  telescoping  tubes  on  rubber  rollers. 
Incorporated  in  the  design  as  an  integral  part  is  the  complete  gunning 
device  which  rotates  the  microphone  through  280  degrees.  The 
weights  of  the  various  components  are  indicated  in  the  specifications. 
The  microphone  boom  perambulator  is  of  the  three-wheel  type, 
which  facilitates  maneuvering,  and  is  designed  so  that  the  wheel 
tread  can  be  narrowed  to  pass  the  perambulator  through  a  30-inch 
door  and  can  be  widened  to  provide  a  substantial  working  base.  The 
column  and  supporting  platform  for  the  operator  are  simultaneously 
elevated  or  lowered  by  means  of  a  screw-operated  lifting  system. 
Careful  attention  has  been  given  in  the  design  of  the  perambulator  to 
the  elimination  of  all  extraneous  noise. 


128 


PROGRESS  IN  MOTION  PICTURE  INDUSTRY    [j.  s.  M.  p.  E. 


Other  equipment  introduced  during  the  past  year  that  tends  to 
improve  or  facilitate  recording  includes  the  miniature  condenser 
transmitter,  high-quality  moving-coil  head-sets  for  monitoring  on  the 
set,  and  various  forms  of  the  peak  volume  indicator.10'11  All  these 
devices  require  some  change  in  studio  operating  technic  to  realize 
their  full  advantages. 

Routine  transmission  testing  has  been  greatly  facilitated  by  the 
use  of  recording  types  of  gain-measuring  apparatus.12  This  method 
gives  records  that  are  useful  for  immediate  inspection  and  subse- 
quent filing,  and  minimizes  maintenance  costs. 


FIG.  15. 


Type  103-B  microphone  boom  and  type  126-B  microphone  boom 
perambulator. 


A  new  method  of  determining  correct  negative  and  print  densities 
utilizing  a  modulated  high-frequency  oscillator  has  been  described 
by  RCA.13 

The  Academy  of  Motion  Picture  Arts  &  Sciences  has  continued 
with  its  program  of  standardization,  and  has  recommended  a  number 
of  standards  for  theater  electrical  characteristics,  dividing  networks, 
filters,  and  other  allied  subjects. 

(4)  Films. — The  Eastman  Kodak  Company  announced  a  new 
fine-grain,  high-contrast  film,  designated  as  E.K.  1360,  for  variable- 
width  recording.  It  is  claimed  that  white  light  may  be  used  with 
this  emulsion  with  results  as  good  as  or  superior  to  that  obtained  with 


Aug.,  1938]       PROGRESS  IN  MOTION  PICTURE  INDUSTRY 


129 


ultraviolet  light  and  standard  positive  emulsions.  It  is  also  claimed 
that  this  film  is  very  quiet  in  projection  and  has  high  resolving  power. 
The  Dupont  Film  Manufacturing  Corporation  announced  two  new 
sound  recording  films  during  1937,  types  214  and  215,  which  replace 
the  former  201  and  202  types.  The  new  films  retain  the  desirable 


TWO  FEATURES 

LAST  TRAIN  FROM 

M  AOR1D"&  "WiNlCS 

OVER  HO MO LULU" 


FIG.  16. 


Glass  blocks  with  lights  of  various  colors 
behind  them. 


emulsion  characteristics  of  the  former  types  and  differ  only  in  that 
they  are  manufactured  by  a  newly  perfected  technic  that  eliminates 
the  periodic  density  fluctuations  characteristic  of  all  films  manufac- 
tured in  the  conventional  manner.  This  results  in  a  more  steady 
ouput,  especially  from  variable-density  films,  as  is  easily  observed 
in  the  reproduction  of  constant-frequency  films. 


130 


PROGRESS  IN  MOTION  PICTURE  INDUSTRY  [j.  s.  M.  p.  E. 

(in)   SOUND  AND  PICTURE  REPRODUCTION 


The  past  year  has  been  peculiarly  barren  in  the  production  of  new 
types  of  sound-picture  projection  equipment.  Many  theaters  have 
been  modernized  with  the  various  equipments  described  in  last  year's 
report.  The  Academy  of  Motion  Picture  Arts  &  Sciences  has  labored 


FIG.   17.     Changeable-letter  sign  with   extended    back- 
ground to  allow  use  of  letters  of  a  variety  of  sizes. 


hard  to  effect  standardization  of  reproducer  characteristics  and  has 
issued  information  on  the  subject  during  the  year.14 

(1)  Motion  Picture  Theater  Lighting. — In  view  of  the  many  interest- 
ing advances  in  theater  lighting  equipment  and  technic  the  Committee 
is  including  in  this  report  for  the  first  time  information  on  this  topic. 

Two  important  developments  have  occurred  during  the  past  year 
to  make  it  possible  to  lift  the  shroud  of  darkness  that  has  covered 


Aug.,  1938]       PROGRESS  IN  MOTION  PICTURE  INDUSTRY  131 

motion  picture  theater  audiences:  (1)  The  efforts  of  the  National 
Carbon  Co.  to  increase  the  prevailing  levels  of  screen  illumination 
through  the  use  of  the  newer  carbons,  thus  making  possible  moderate 
increases  in  the  general  level  of  the  auditorium  illumination.  This 
was  done  by  conducting  a  campaign  throughout  the  industry  for 
greater  screen  brightness.  (2)  More  important  still,  the  widespread 
use  of  down  lights  mounted  above  the  ceiling  of  the  auditorium  and 
projecting  a  well  defined  beam  of  light  through  a  2-inch  hole  toward 
the  front  of  the  auditorium.  Thus  is  provided  ample  general  audi- 
torium illumination  for  patrons  to  move  about  and  read  their  pro- 
grams ;  and  at  the  same  time  the  decorative  colored  lighting,  which  is 
often  of  a  low  order  of  brightness,  as  well  as  the  contrasts  on  the 
screen,  is  not  destroyed. 

Considerable  progress  has  been  made  also  in  the  use  of  polished 
fluted  metal  reflectors  for  both  decorative  and  exterior  lighting. 
These  reflectors  may  employ  either  individual  incandescent  lamps  or 
neon  tubes.  They  have  the  effect  in  many  instances  of  apparently 
creating  many  more  sources  than  are  actually  present. 

There  has  been  a  more  widespread  use  of  the  luminous  treatment 
of  theater  fronts  and  marquees.  These  comprise  the  use  of  glass 
blocks  as  well  as  luminous  panels  and  polished  metal  illuminated  by 
projected  light.  The  use  of  these  developments  is  shown  in  the  photo- 
graphs of  the  Cine  Theater  (Fig.  16).  The  changeable-letter  sil- 
houette sign,  previously  reported,  has  been  expanded  to  permit  the 
use  of  a  variety  of  letter  sizes  and  thus  obtain  greater  emphasis. 
The  illustration  showing  the  Rhodes  Theater  (Lost  Horizon)  demon- 
strates this  feature  (Fig.  17). 

Theater  interiors  are  receiving  the  same  general  treatment  as  the 
outside  in  that  there  is  more  general  use  of  luminous  panels  and  deco- 
rated glass  blocks,  behind  which  lamps  of  various  colors  are  placed. 

(2)  Theater  Lighting  Equipment. — For  theater  use  there  has  re- 
cently been  made  available  a  500- watt,  115-volt,  T-14  bulb,  biplane- 
filament,  medium-bipost  base  lamp  for  elliptical  spots  and  down- 
lights.  This  lamp  is  unusual  in  that  the  highly  concentrated  light- 
source  is  placed  relatively  near  the  end  of  the  bulb  and  the  lamp  is 
intended  for  base-up  operation.  This  design  results  in  a  minimum  of 
obstruction  of  the  light  from  the  reflector  by  the  lamp  bulb. 

Two  stage-lighting  equipment  manufacturers  have  developed  a 
Fresnel-lens  spot  somewhat  similar  to  those  introduced  a  few  years 
ago  for  motion  picture  set  lighting.  These  are  to  be  used  for  theater 


132 


PROGRESS  IN  MOTION  PICTURE  INDUSTRY  [j.  s.  M.  p.  E. 


spots  and  general  stage  lights.  Another  equipment  manufacturer 
has  placed  upon  the  market  an  end -seat  lighting  unit,  which  consists 
of  a  decorated  luminous  panel  to  provide  aisle  illumination. 

(3)  Accessories. — About  two  years  ago  the  Mazda  lamp  manu- 
facturers introduced  a  general  service  lamp  having  an  anti-blackening 
screen  mounted  above  the  filament,  upon  which  the  tungsten  evapo- 
rated from  the  filament  was  deposited.     During  the  past  year  there 
_  has  been  made  available  a  1000-watt,  T-12  bulb, 

concentrated-filament  projection  lamp  incorporat- 
ing a  similar  anti-blackening  screen  (Fig.  18). 
The  amount  of  blackening  reaching  the  bulb  is 
thus  reduced  to  the  extent  of  improving  the  candle- 
power  maintenance  during  life  30  per  cent  over  that 
of  a  lamp  not  equipped  with  this  device. 

(IV)    PUBLICATIONS  AND  NEW  BOOKS 

The  growing  interest  in  the  use  of  motion  pic- 
tures in  education  was  shown  by  the  introduction 
of  a  new  publication,  Motion  Pictures  of  the  World. 
This  is  a  quarterly  publication  issued  by  Inter- 
national Educational  Pictures,  Inc.,  Boston,  and 
is  stated  to  contain  a  list  of  all  new  pictures 
released  in  the  preceding  three  months.  World 
Film  News  (Cinema  Contact,  Ltd.,  London)  made 
its  de"but  during  1937.  Current  pictures  are  re- 
viewed, studio  activities  discussed,  progress  in  the 
documentary  film  treated,  and  television  develop- 
ments noted.  It  is  a  pleasure  to  note  that  the 
British  Kinematograph  Society  has  been  able  to 
replace  their  Proceedings  by  a  Journal,  of  which 
the  first  number  made  its  appearance  in 

December,  1937. 

Since  the  last  report  of  the  Committee  in  May,  1937,  the  following 

books  of  noteworthy  interest  have  appeared: 

(1)  Motion  Picture  Sound  Engineering  (chapters  by  various  authors),  Academy 
of  Motion  Picture  Arts  &  Sciences,  Hollywood,  Calif. 

(2)  Sound  Recording  for  Films;  W.  F.  Elliott,  Pitman  &  Sons,  Ltd.,  London. 
(5)  Talking  Pictures;  B.  C.  Kiesling,  Johnson  Publishing  Co.,  New  York,  N.  Y. 
(4)  Sound  Motion  Pictures  and  Servicing  Sound  Equipment;   J.  R.  Cameron, 

Cameron  Publishing  Co.,  Woodmont,  Conn. 


FIG.  18.  1000- 
watt  standard- 
voltage,  T-12 
bulb  projection 
lamp  with  col- 
lector grids. 


Aug.,  1938]       PROGRESS  IN  MOTION  PICTURE  INDUSTRY  133 

(5)  Entwicklung  der  Kinotechnik  (Development  of  Motion  Picture  Technic); 
R.  Thun,  VDI  Verlag,  Berlin. 

(6)  Amateur  Movies  and  How  to  Make  Them;    A.  Strasser,  Studio,  Ltd., 
London. 

(7)  How  to  Write  a  Movie;  A.  L.  Gale,  Brick  Row  Book  Shop,  New  York,  N.  Y. 

(8)  Film  and  School;  H.  Rand  and  R.  Lewis,  Appleton  Century  Co.,  New  York, 
Y. 

(9)  Motion  Pictures  in  Education;   Compiled  by  E.  Dale,  F.  W.  Dunn,  C.  F. 
L,  Jr.,  and  E.  Schneider;    The  H.  W.  Wilson  Co.,  New  York,  N.  Y. 

Camera  Lenses  and  Shutters;   R.  M.  Fanstone,  British  Periodicals,  Ltd., 
mdon. 

(11)  Camera  Lenses,  2nd  Edition;  A.  Lockett,  revised  by  H.  W.  Lee,  Pitman 
publishing  Corp.,  New  York,  N.  Y. 

(12)  Home  Movie  Gadgets;   W.  J.  Shannon,  Moor  field  &  Shannon,  Nutley, 
N.J. 

(13)  Exposing  Cine  Film;    P.  C.  Smethurst,  Link  House  Publications,  Ltd., 
London. 

(14)  The  Secrets  of  Trick  Photography;    O.  R.  Croy,  translated  by  P.  C. 
Smethhurst,  American  Photographic  Publishing  Co.,  Boston,  Mass. 

(15)  Film  Making  from  Script  to  Screen;  A.  Buchanan,  Faber  and  Faber,  Ltd., 
London. 

(16)  Titeltechnik  (Title  Technic) ;   F.  Lullack,  W.  Knapp,  Halle,  Germany. 

(17)  Mein  Weg  mit  dem  Film  (My  Experience  with  the  Film);    O.  Messter, 
M.  Hess,  Berlin-Schonberg. 

(18)  Technique  of  Color  Photography,  2nd  Edition;   F.  R.  Newens,  Blackie  & 
Son,  Ltd.,  London. 

(19)  Picturing  Miracles  of  Plant  and  Animal  Life;  A.  C.  Pillsbury,  Lippincott 
Co.,  Philadelphia,  Pa. 

(20)  Photography — Theory  and  Practice,  2nd  English  Edition;    Pitman  Pub- 
lishing Co.,  New  York,  N.  Y. 

(21)  Lichtspieltheater,  Anlage  und  Einrichtung  (Planning  and  Equipping  a 
Motion  Picture  Theater);   Bauwelt-Encyclopedia  Vol.  9,  Bauwelt-Verlag,  Berlin. 

(22)  We  Make  the  Movies,  edited  by  Nancy  Naumberg,  W.  W.  Norton  &  Co., 
Ind.,  New  York,  N.  Y. 

Yearbooks  were  issued  by  the  following  publishers: 

(1)  Quigley  Publishing  Co.,  New  York,  N.  Y. 

(2)  Film  Daily,  New  York,  N.  Y. 

(3)  Kinematograph  Publications,  Ltd.,  London. 

(4)  Photokino- Verlag,  Berlin. 

(5)  M.  Hess,  Berlin-Schonberg. 

Abridgments  and  collections  of  original  papers  were  published  as 
follows : 

Abridged  Scientific  Publications  of  the  Kodak  Research  Laboratories,  17 
(1935),  Eastman  Kodak  Co.,  Rochester,  N.  Y. 

Veroffentlichungen  des  wissenschaftlichen  Zentral-Laboratoriums  der  Photo- 
Ateilung  Agfa  (Publications  of  the  Afga  Central  Photographic  Research 
Laboratories),  5,  Hirzel,  Leipzig. 


134  PROGRESS  IN  MOTION  PICTURE  INDUSTRY  [j.  s.  M.  p.  E. 

REFERENCES 
(All  references  are  to  J.  Soc.  Mot.  Pict.  Eng.  unless  otherwise  noted) 

1  IVES,  C.  E.,  AND  CRABTREE,  J.  I. :  "Two  New  Films  for  Duplicating  Work," 
XXIX  (Sept.,  1937),  No.  3,  p.  317. 

*GRIGNON,  L.  D.:  "Light- Weight  Stage  Pick-Up  Equipment,"  XXIX  (Aug., 
1937),  No.  2,  p.  191. 

'ALBERSHEIM,  W.  J.:  "A  Device  for  Direct  Reproduction  from  Variable- 
Density  Sound  Negatives,"  XXIX  (Sept.,  1937),  No.  3,  p.  274. 

4  VEITH,  L.,  AND  WIEBUSCH,  C.  F.:    "Recent  Developments  in  Hill-and-Dale 
Recorders,"    XXX  (Jan.,  1938),  No.  1,  p.  96. 

5  DIMMICK,  G.  L.:    "The  RCA  System  and  Its  Application  to  Various  Types 
of  Sound-Track,"  XXIX  (Sept.,  1937),  No.  3,  p.  258. 

6  HASBROUCK,  H.  J.,  BAKER,  J.  O.,  AND  BATSEL,  C.  N.:     "Improved  Noise- 
Reduction  System  for  High-Fidelity  Recording,"  XXIX   (Sept.,    1937),   No.  3, 
p.  310. 

7  BATSEL,  C.  N.:    "A  Non-Slip  Sound  Printer,"  XXIII  (Aug.,   1934),  No.  2, 
p.  100. 

8  Cf.  ref.  5. 

9  BAKER,  J.  O.,  AND  ROBINSON,  D.  H.:    "Modulated  High-Frequency  Record- 
ing as  a  Means  of  Determining  Conditions  for  Optimal  Processing,"  XXX  (Jan., 
1938),  No.  1,  p.  3. 

10  HOPPER,  F.  L.:  "Power  Level  Indicators  for  Sound  Recording,"  XXDI 
(Aug.,  1937),  No.  2,  p.  184. 

UALBIN,  F.  G.:  "A  Linear  Decibel-Scale  Volume  Indicator,"  XXK  (Nov., 
1937),  No.  5,  489. 

12  Symposium  on  Transmission  Meters  (Spring,  1937,  Convention): 
LINDSAY,  W.  W.:     "A  Transmission  Measuring  System  Utilizing  a  Graphic 

Recording  Meter,"    XXIX  (July,  1937),  No.  1,  p.  68. 

MACLEOD,  A.  D.:  "An  Automatic  Audio-Frequency  Graphic  Recorder," 
XXIX  (Dec.,  1937),  No.  6,  p.  663. 

HILLIARD,  J.  K.,  AND  SpRAGUE,  G.  M.:  "A  Continuous  Level  Recorder  for 
Routine  Studio  and  Theater  Measurements,"  XXIX  (Dec.,  1937),  No.  6,  p.  645. 

AICHOLTZ,  L.  A.:  "A  Curve-Plotting  Transmission  Meter,"  XXIX  (Dec., 
1937),  No.  6,  p.  655. 

GRIGNON,  L.  D.:  "A  Curve-Plotting  Transmission  Meter,"  XXIX  (Dec., 
1937),  No.  6,  p.  660. 

13  Cf.  ref.  9. 

14  "Standard  Electric  Characteristic  for  Two- Way  Reproducing  Systems  in 
Theaters,"  Bulletin,  Academy  of  Motion  Picture  Arts  &•  Sciences,  June  8,  1937; 
Hollywood,  Calif. 

APPENDIX  A 

THE  JAPANESE  MOTION  PICTURE  INDUSTRY 

The  year  1937,  while  not  during  its  course  regarded  as  an  eventful 
year  for  the  motion  picture  industry  of  Japan,  will  be  remembered 
because  it  witnessed  the  enactment  of  several  governmental  regula- 


Aug.,  1938]       PROGRESS  IN  MOTION  PICTURE  INDUSTRY  135 

tions  that  will  have  increasing  effect  upon  the  industry  during  en- 
suing years.  Early  in  the  year  Japan  found  it  necessary  to  overcome 
her  unfavorable  balance  of  trade  by  an  exchange  control  measure 
that  has  steadily  become  more  stringent.  Japan's  deficiency  in 
natural  resources  made  the  application  of  this  measure  the  more  re- 
strictive when  the  China  "Incident"  made  the  purchase  of  war  mate- 
rials a  vital  necessity.  It  was  only  natural  then  that  certain  im- 
portations would  be  classified  as  nonessential  in  the  face  of  the  na- 
tional emergency.  Unfortunately,  motion  picture  raw  film  and 
foreign  motion  pictures  fell  into  this  category.  Notwithstanding 
the  fact  that  certain  governmental  groups  consider  Japanese-made 
motion  pictures  and  newsreels  a  valuable  vehicle  for  the  internal  dif- 
fusion of  propaganda  pertaining  to  the  Incident,  the  supply  of  im- 
ported raw  stocks  has  been  cut  drastically;  in  fact,  to  a  point  where 
it  is  questionable  whether  the  local  manufacturers  can  supply  the 
demand. 

As  mentioned  above,  the  importation  of  foreign  pictures  suffered 
under  these  exchange  control  measures.  This  fact,  however,  except 
for  a  few  newspaper  and  magazine  articles,  did  not  come  to  the 
public's  attention  because  foreign  distributors  began  during  the  au- 
tumn to  distribute  their  supplies  of  previously  imported  but  unre- 
leased  pictures.  This  procedure  made  possible  the  distribution  of 
practically  the  same  number  of  foreign  pictures  in  1937  as  during 
the  previous  year,  but  it  certainly  did  not  allow  the  year  to  fulfill 
financially  its  earlier  promises.  Approximately  300  foreign  pictures 
were  released  in  Japan  during  1937,  of  which  about  25  per  cent  com- 
prised pictures  from  European  studios.  It  will  be  noticed  that  Euro- 
pean productions  seem  to  be  steadily  gaining  ground  against  Ameri- 
can pictures,  but  this  does  not  necessarily  imply  they  are  gaining 
popularity.  Pictures  produced  under  the  social  and  political  re- 
straint peculiar  to  European  countries  are  much  more  likely  to  find 
favor  in  the  eyes  of  the  Japanese  censors,  especially  in  view  of  govern- 
mental amity.  Also  it  must  be  borne  in  mind  that  the  exhibitor  is 
able  to  make  more  favorable  terms  for  these  pictures  than  for  the 
American  pictures.  The  average  American  picture,  however,  is  still 
the  better  box-office  success,  especially  in  the  large  city  theaters  that 
make  a  specialty  of  showing  foreign  films. 

It  is  estimated  that  in  1937  about  600  Japanese-made  pictures  of 
the  entertainment  type  were  released.  This  includes  features,  come- 
dies, and  shorts.  There  is  still  an  appreciable  number  of  silent  pic- 


136  PROGRESS  IN  MOTION  PICTURE  INDUSTRY  [j.  s.  M.  p.  E. 

tures  made  expressly  for  the  small  country  theaters  not  equipped  for 
sound.  Incidentally,  these  theaters  still  employ  the  benshi  (narrator) 
to  explain  the  action  of  the  picture  to  the  audience.  These  unscored 
pictures  average  only  about  5  or  6  prints  per  picture  as  compared  to 
the  10  to  12  prints  made  for  each  sound  picture.  On  the  basis  of 
released  footage  there  were  better  than  4  feet  of  sound-film  released 
to  every  foot  of  silent  film.  The  writer  believes  the  total  released 
footage  approximated  50  million  feet  in  1937.  About  50  per  cent  of 
the  productions  are  still  of  the  historical  type.  A  possible  reason  for 
the  sustained  popularity  of  these  classical  plays  is  the  fact  that 
foreign  releases  provide  the  modern  style  picture  on  a  scale  upon 
which  it  is  difficult  for  the  local  producers  to  compete. 

There  was  considerable  activity  in  the  production  of  documentary 
and  educational  films.  Governmental  agencies,  newspapers,  uni- 
versities, and  cultural  societies  as  well  as  the  motion  picture  com- 
panies participated  in  making  some  250  such  pictures.  Since,  how- 
ever, these  films  were  made  primarily  for  private  distribution,  figures 
as  to  the  lengths  and  subjects  are  difficult  to  obtain.  The  following 
classifications,  however,  will  cover  probably  80  per  cent  of  these 
films:  tourist,  industrial,  propaganda,  educational,  sport,  and 
military. 

The  China  Incident  introduced  into  Japan  an  unprecedented  in- 
terest in  news  films.  Almost  overnight  newsreel  theaters  sprang  into 
existence  in  the  large  cities.  These  theaters  are  small,  accommodat- 
ing only  200  or  300  persons  and  offer  a  1  to  1  V2-hour  program  made 
up  primarily  of  newsreels  with  one  or  two  shorts.  News  of  the  In- 
cident monopolizes  the  screen  to  such  an  extent  that  at  this  early 
date  when  the  spectacular  Chinese  news  is  diminishing  in  volume 
consternation  is  already  arising  as  to  just  what  to  do  with  many  of 
these  theaters  after  the  Incident  is  closed. 

The  construction  of  many  new  theaters  was  completed  last  year. 
Two  large  first-class  theaters,  one  in  Tokyo  (the  Kokusai  Gekijo)  and 
one  in  Osaka  (the  Umeda  Gekijo)  were  built  by  the  Shochiku  interests 
and  Toho  interests,  respectively.  Both  theaters  are  equipped  with 
Western  Electric  sound  reproducing  equipment.  The  Kokusai 
Gekijo  is  without  doubt  the  largest  theater  in  Japan  and  perhaps  one 
of  the  largest  in  the  world.  It  has  a  total  seating  capacity  of  about 
3000.  The  new  theaters  are  being  built  with  the  proper  acoustical 
considerations  incorporated  in  the  design  and  construction  materials, 
a  matter  that  previously  had  been  given  little  thought. 


Aug.,  1938]       PROGRESS  IN  MOTION  PICTURE  INDUSTRY  137 

At  this  point  it  may  be  interesting  to  point  out  a  few  pertinent 
facts  about  theaters  and  attendance.  In  point  of  view  of  attendance, 
last  year  set  a  record,  with  a  figure  approaching  300,000,000  paid 
admissions.  There  are  about  1400  theaters  in  Japan,  1100  of  which 
show  Japanese  films  exclusively,  the  remainder  having  mixed  or  all- 
foreign  programs.  Needless  to  say,  the  latter  group  are  concentrated 
in  the  large  cities.  About  85  per  cent  of  the  theaters  are  equipped 
for  sound,  but  only  the  larger  theaters  have  invested  in  imported 
equipment;  Western  Electric  leads  with  more  than  130  theater  in- 
stallations. It  can  be  seen  from  the  above  figures  that  by  far  the 
major  portion  of  the  sound  reproducing  equipments  is  manufactured 
locally. 

Several  of  the  studios  in  Japan  are  equipped  to  process  their  own 
films  by  machines:  notably,  J.  O.  Studio  Co.,  P.C.L.,  Shochiku 
(Tokyo)  and  Nikkatsu  (Tokyo).  There  are  also  several  companies 
that  make  a  business  of  processing  film,  i.  e.,  local  negatives  and  posi- 
tive as  well  as  duplicates  of  foreign  productions.  Of  these  the  largest 
is  the  Far  East  Laboratory,  with  eight  positive  and  four  negative 
machines  of  the  Debrie  type.  Others  in  this  field  are  J.  O.  Studio 
Co.,  P.C.L.,  K.  S.  Talkie,  and  Yokohama  Cinema.  The  latter  two 
employ  machines  of  the  Art  Reeves  type,  and  process  largely  Japanese 
newsreels.  The  majority  of  these  machines  have  positive  processing 
speeds  of  20  to  40  feet  per  minute  and  a  negative  processing  speed  of 
5  to  10  feet  per  minute.  For  financial  reasons,  however,  many  studios 
are  still  processing  their  negative  and  positive  films  by  the  rack-and- 
tank  systems,  though  at  present  that  is  true  only  of  those  interested 
in  the  production  of  silent  pictures. 

The  motion  picture  laboratories  in  Japan  have,  in  the  past  few 
years,  become  conscious  of  the  advantages  to  be  gained  from  close 
sensitometric  control  of  their  processing.  This  is  especially  true  of 
the  laboratories  employing  machines,  where  the  processing  of  sound 
negative  has  made  development  control  a  vital  necessity.  The  East- 
man type  116  sensitometer  has  been  universally  accepted  as  the 
standard  instrument  for  this  control  work. 

The  Fuji  Photo  Film  Company  has  expanded  its  manufacturing 
facilities  in  an  effort  to  supply  the  raw  film  necessary  for  the  local 
market,  now  that  imported  stocks  are  so  severely  restricted.  Their 
products  include  a  clear  base  panchromatic  negative  film,  a  positive 
film  and  a  newly  introduced  sound  recording  film. 


APPENDIX  B 

PROGRESS  IN  GERMANY 


As  a  result  of  experience  with  the  magnetic  oscillograph  introduced 
four  years  ago  for  variable- width  recording,  this  system  has  now  been 


FIG.  19.     Minicord  modulator. 


FIG.  20.     Minicord  sound  mechanism. 


developed  in  very  small  dimensions.  Including  the  optics  the  os- 
cillograph measures  only  3  X  4.5  X  8  cm. ;  the  weight  is  approxi- 
mately 200  grams;  the  power  consumption  of  the  lamp  is  3.5  watts; 
5  milliamperes  are  required  to  operate  the  mirror.  Fig.  19  illustrates 
138 


Aug.,  1938]       PROGRESS  IN  MOTION  PICTURE  INDUSTRY 


139 


the  recorder  known  as  the  "Minicord"  sound  recorder.  Variable- 
width  recording  may  be  done  with  this  instrument  without  lowering 
the  noise  level.  The  amplifier  and  other  electrical  equipment  have 
been  reduced  to  a  minimum  of  weight  and  space.  The  amplifier  and 
batteries  of  10-hour  capacity  are  built  into  a  case  measuring  450  X 
130  X  390  cm.  and  weighing  15  kg.  Fig.  20  shows  the  35-mm.  sound 
mechanism  in  comparison  with  a  60- watt  lamp.  The  results  at- 
tained with  this  apparatus  may  be  regarded  as  very  satisfactory. 
The  small  size  of  the  apparatus  makes  its  use  possible  not  only  in 
combination  with  standard  film 
cameras  forming  a  single  unit, 
but  also  in  combination  with  sub- 
standard film  cameras. 

In  the  field  of  reproduction  the 
new  sound  apparatus  for  very 
large  theaters,  made  by  the  Klang- 
film  Gesellschaft  and  called  "Eu- 
ronor,"  is  remarkable,  especially 
for  its  very  large  compound  loud 
speaker.  The  size  of  the  latter 
is  determined  primarily  by  the 
labyrinth  system  which  consists 
of  a  large  membrane  50  cm.  in 
diameter,  a  horn  having  a  length 
of  2.6  meters,  and  an  opening  of 
4  square-meters.  The  efficiency 
of  this  labyrinth  system  and  its 
capacity  are  so  great  that  about 
12  watts  of  undistorted  output 
may  be  obtained  at  50  Hertz. 
Four  upper  cones  1.6  meters  in 
length  are  provided  for  the 
medium  and  higher  frequencies. 
Fig.  21  shows  the  loud  speaker. 
Experience  with  this  apparatus  has  proved  that  the  extension  of  the 
frequency  range  at  the  lower  end  represents  a  considerable  step 
toward  more  natural  reproduction.  The  possibility  of  reproducing 
special  effects  (explosions,  earthquakes,  etc.)  is,  of  course,  con- 
siderably greater  due  to  the  high  acoustical  efficiency  at  the  low 
frequencies. 


FIG.    21. 


Klangfilm    loud 
system. 


speaker 


APPENDIX    C 

GENERAL  FIELD  OF  PROGRESS  OF  THE  MOTION  PICTURE 
INDUSTRY  IN  GREAT  BRITAIN  * 

Although  there  has  been  considerable  improvement  in  the  techni- 
cal and  artistic  standards  of  British  pictures,  the  year  1937  has  been 
an  unsatisfactory  one  for  the  industry.  Financial  interests  showed  a 
desire  for  severe  retrenchment  largely  owing  to  disappointing  returns 
from  the  1936  program  and  there  was  a  rapid  falling  off  in  the  num- 
ber of  pictures  in  active  production. 

Another  reason  for  the  decline  has  been  the  general  uncertainty  as 
to  the  final  results  of  the  Government's  new  Films  Bill,  designed  to 
replace  the  expiring  Act  of  1927.  The  main  object  of  the  bill  is, 
of  course,  to  foster  the  production  of  British  films,  and  the  Govern- 
ment, starting  with  the  Moyne  Report  as  a  basis,  has  considered 
the  views  of  all  sections  of  the  industry.  Unfortunately  a  funda- 
mental conflict  of  interests  has  been  revealed  and  the  bill  will  require 
considerable  modification  before  a  compromise  can  be  reached. 

An  important  function  of  new  legislation,  and  one  that  is  generally 
agreed  to  be  desirable,  would  be  not  only  to  regulate  the  proportion 
of  British  films  exhibited  but  also  to  set  a  minimum  standard  of 
entertainment  quality  and  so  eliminate  the.  damage  to  prestige 
caused  by  "quota  quickies,"  a  type  of  picture  made  more  with  the 
object  of  complying  with  the  law  than  as  entertainment.  The 
means  of  achieving  this  quality  standard  is  still  under  discussion  but 
it  seems  likely  that  a  minimum  cost  figure  will  be  established  with  the 
provision  that  a  fixed  proportion  will  be  spent  on  labor. 

With  the  American  product  available  as  a  standard  of  comparison 
no  act  can  guarantee  that  competitive  films  are  produced,  but  it  is 
felt  that  the  studio  facilities  available  in  this  country  are  ample  and 
that  if  a  reasonable  compromise  bill  can  be  passed  and  future  con- 
ditions stabilized  a  return  of  confidence  will  produce  increased  ac- 
tivity in  the  coming  year. 

Studios. — Amalgamated  Studios,  Elstree,  were  completed  in  the 
early  part  of  this  year.  These  studios  comprise  four  large  stages, 
each  equipped  with  its  own  dressing  rooms,  cutting  theater,  and  sound 

*  Received  June  21,  1938,  from  R.  J.  Engler. 
140 


PROGRESS  IN  MOTION  PICTURE  INDUSTRY  141 


recording  and  monitoring  facilities.  Two  large  theaters  are  available 
for  the  combined  purposes  of  dubbing,  scoring,  and  reviewing.  The 
sound  equipment  is  Western  Electric.  Owing  to  the  depressed  state 
of  the  industry  the  studios  have  not  yet  started  production. 

The  Warner  Brothers  Studios  at  Teddington  have  been  equipped 
with  RCA  variable-width  recording  facilities,  which  are  to  be  con- 
verted for  class  A  push-pull  operation  in  the  near  future. 

In  order  to  eliminate  price-cutting,  an  agreement  was  reached  be- 
tween the  major  service  studios  on  standardizing  charges  to  producers, 
and  during  the  year  various  means,  such  as  the  making  of  pictures 
on  a  cooperative  basis,  have  been  tried  to  keep  the  studios  in  pro- 
duction. 

Laboratories. — Generally  the  laboratories  have  had  a  quiet  year, 
although  improvements  in  technic  have  occurred  in  some  instances, 
particularly  in  the  use  of  sensitometric  methods  of  development  con- 
trol and  an  increased  use  of  turbulation  of  the  developing  solutions. 
Efforts  to  improve  the  quality  of  duplicates  have  led  to  the  use  of 
two  new  film  products,  Eastman  fine-grain  duplicating  positive  and 
Eastman  fine-grain  duplicating  negative,  both  extensively  used  in  the 
U.S.A.  These  new  films  differ  materially  from  the  normal  duplicat- 
ing product,  and  require  considerable  modification  of  the  printing 
equipment  set  aside  for  this  work.  A  certain  amount  of  tinting  and 
toning  of  release  prints  was  undertaken  although  the  quantity  of  this 
kind  of  work  does  not  seem  to  be  increasing.  Several  laboratories 
are  adding  35-mm.  to  16-mm.  sound  and  picture  reduction  printers, 
and  there  was  an  increase  in  the  use  of  16-mm.  prints,  mainly  for 
industrial  purposes. 

The  new  Technicolor  Laboratories  at  Harmonds worth  started 
commercial  operations  early  in  1937.  By  the  end  of  the  year 
they  were  working  at  full  single-shift  capacity  and  were  manufactur- 
ing all  British  release  print  requirements  as  well  as  a  number  of 
foreign-language  versions  of  all  current  Technicolor  pictures  pro- 
duced in  England  and  the  United  States. 

Denham  Laboratories,  situated  near  London  Film  Production 
Studios,  are  now  in  operation  and  are  equipped  with  the  latest  type 
of  processing  apparatus.  Five  DeBrie  daylight  developers  are  avail- 
able with  seven  DeBrie  Duplex  printers,  one  Bell  &  Howell  type 
printer  as  well  as  an  optical  printer  for  special  effects.  A  35-mm.  to 
16-mm.  optical  reduction  printer  is  also  installed. 

Twelve  non-slip  sound  printers  are  now  installed  in  London  Labo- 


142  PROGRESS  IN  MOTION  PICTURE  INDUSTRY  [J.  s.  M.  p.  E. 

ratories  and  are  proving  valuable  for  re-recording  copies  and  duplicat- 
ing work. 

Newsreels. — The  major  event  in  the  newsreel  sphere  was  the  re- 
cording of  the  coronation  ceremony,  particularly  as  permission  was 
obtained  from  the  authorities  to  take  photographs  within  West 
minster  Abbey.  The  conditions  were,  however,  very  difficult  and  the 
results  obtained,  which  included  several  colored  versions,  must  bt 
regarded  as  remarkably  successful. 

British  Movietonews  have  moved  to  enlarged  premises  in  Sohc 
Square  and  Kay  Film  Laboratories  have  established  a  plant  adjacenl 
so  as  to  give  an  improved  service. 

Technical  Advance. — Messrs.  W.  Vinten,  Ltd.,  have  developed  £ 
step-wedge  printing  machine  for  making  rising  density  test  prim 
strips  of  negatives  and  also  density  strips  for  taking  the  speed  or  ex 
haustion  of  developing  baths.  This  machine  prints  eleven  frame* 
with  one  pull  of  a  handle,  and  can  be  operated  in  daylight.  A  syn 
chronous  generator  ensures  steadiness  of  the  voltage  on  the  light 
source  from  day  to  day  and  a  special  photocell  is  used  to  check  th< 
color  constancy  of  the  lamp. 

The  same  firm  has  also  produced  a  complete  portable  daylighi 
processing  unit  which  can  be  mounted,  complete  with  air-condition 
ing,  in  a  moderately  sized  lorry.  A  camera  taking  250  pictures  t 
second  and  equipped  with  a  special  view-finder  has  also  been  de 
veloped  to  supplement  the  existing  high-speed  type.  This  camen 
is  equipped  with  a  400-ft.  magazine  and  is  very  light  in  weight. 

A  new  type  of  multiple  printer  is  being  developed  capable  of  taking 
four  16-mm.  prints  from  one  negative  at  the  same  time.  It  is  pro 
vided  with  four  double-8-mm.  heads  interchangeable  with  th< 
16-mm  heads.  The  machine  can  also  be  arranged  to  use  four  nega 
tives  and  take  four  positives  when  a  special  light  control  is  providec 
for  with  separate  control  of  each  of  the  four  printing  lights. 

A  35-mm.  to  16-mm.  sound  reduction  printer  is  available  operating 
on  a  dual  track  method  with  a  unique  system  of  mechanical  syn 
chronization  between  35-mm.  and  16-mm.  films. 

Exhibition. — Despite  the  decline  in  the  production  side  of  the  in 
dustry  1937  was  an  improved  year  for  exhibitors.  Extensive 
new  building  continues,  although  a  campaign  against  overbuilding 
has  been  started  and  attempts  made  to  include  provisions  against  il 
in  the  New  Films  Bill.  There  has,  however,  been  a  halt  in  the 
building  of  news  theaters  and  it  is  felt  that  the  trade  will  eventuall} 


Aug.,  1938]       PROGRESS  IN  MOTION  PICTURE  INDUSTRY  143 

regulate  new  building  in  cooperation  with  the  renters  by  refusing  to 
supply  films  to  unrecognized  cinemas. 

Technical  developments  have  been  in  the  direction  of  the  increased 
use  of  two-way  horn  systems  with  multicellular  high-frequency 
units,  the  Western  Electric  Mirrophonic  system  having  been  demon- 
strated early  in  the  year. 

Broadcasting  and  Television. — The  broadcasting  of  advertising 
programs  intended  for  British  listeners  from  certain  continental 
stations  continues  despite  proposed  international  legislation  to  limit 
it.  The  programs  are  generally  recorded  either  on  disks  or  by  means 
of  the  Philips-Miller  system. 

Television  has  made  some  progress  in  the  home  entertainment 
field  and  several  successful  outside  broadcasts  have  been  made, 
notably  those  of  the  coronation  ceremony  and  several  from  film 
studios.  The  Gaumont  British  and  British  Movietonews  reels  con- 
tinue to  be  a  regular  part  of  the  programs. 

As  yet,  however,  the  number  of  sets  is  estimated  as  only  2000,  so 
that  no  effect  is  likely  to  be  felt  by  the  cinemas  for  a  considerable 
time.  Factors  limiting  a  substantial  increase  in  these  numbers  are 
the  limit  of  coverage  of  the  London  area,  the  restricted  hours  of 
transmission,  and  the  high  cost  of  receiving  sets. 

However,  recent  demonstrations  of  large-screen  television  by  the 
Scophony  and  Baird  systems  have  proved  encouraging  and  its  use  in 
cinemas  is  being  considered.  Both  the  companies  demonstrating 
are  associated  with  large  theater  circuits  so  that  the  systems  will 
probably  be  exploited  as  soon  as  technical  development  is  sufficiently 
advanced.  The  future  of  television  in  motion  picture  theaters  will 
depend  upon  several  factors  that  are  at  present  doubtful.  Among 
these  are  the  questions  of  the  copyright  of  the  B.B.C.  television 
transmission  and  the  possibility  of  providing  programs,  suitable  for 
showing  in  cinemas,  either  by  the  B.B.C.  or  some  separate  organiza- 
tion. The  latter  would,  of  course,  entail  the  erection  of  special 
radio  transmitting  stations  or  the  provision  of  suitable  cable  distribu- 
tion networks. 


THE  MULTIPLANE  CAMERA  CRANE  FOR  ANIMATION 
PHOTOGRAPHY* 


W.  E.  GARITY  AND  W.  C.  McFADDEN' 


Summary. — In  connection  with  the  general  improvement  in  cartoon  technic, 
it  was  recognized  that  several  developments  could  be  undertaken  that  would  add  much, 
if  successfully  adapted,  to  the  power  and  charm  of  animated  motion  pictures.  By 
confining  cartoon  photography  to  a  single  plane  in  front  of  the  camera,  the  expense 
and  difficulty  of  creating  a  convincing  illusion  of  depth  and  a  real-life  appearance 
by  camera  movement  made  the  consideration  of  a  multiplane  technic  imperative. 
The  out-of-focus  diffusion  and  the  differential  movement  of  foreground  and  back- 
ground of  scenes  can  be  achieved  most  easily  by  separating  the  elements  on  different 
planes  in  front  of  the  camera.  The  problem  resolved  itself  into  the  adaptation  of 
glass-shot  technic  to  cartoon  production.  In  separating  the  scene  elements  into 
several  planes,  many  other  advantages  were  gained,  such  as  lighting  control  of  single- 
scene  elements,  ease  of  using  special  effects  equipment,  and  possibility  of  using  back- 
light and  process  backgrounds. 

The  answer  to  the  problem  was  the  multiplane  camera,  built  with  the  view  of  ac- 
curacy of  control,  complete  flexibility  of  scene  set-up,  and  ease  of  operation.  This 
required  plane  elements  that  could  be  quickly  and  accurately  assembled  and  disas- 
sembled; separate  lights  for  each  plane;  a  quick-reading  and  accurate  indicating 
system;  and  an  interlocked  system  of  controls. 

Because  the  light  level  on  each  plane  is  an  important  part  of  every  set-up,  a  special 
light-measuring  system  had  to  be  devised.  The  number  of  machine  adjustments 
involved  was  so  large  that  a  master  control  sheet  was  laid  out,  giving  complete  opera- 
tion information  for  each  frame  of  film.  As  a  final  check  before  exposure,  a  peri- 
scope type  of  finder  was  devised  so  that  the  chief  operator  could  check  the  set-up  visu- 
ally before  each  exposure.  To  write  out  the  master  control  sheets,  it  was  necessary  to 
develop  a  scene-planning  group  of  artists  and  technicians  to  control  and  plan  the 
use  of  the  machine  in  creating  the  desired  illusions. 

The  results  in  enhancing  the  effectiveness  of  animated  motion  pictures  have  been 
very  satisfactory.  The  multiplane  technic  has  proved  so  flexible  that  its  complete 
possibilities  will  be  realized  only  with  experience. 

The  usual  cartoon  technic  is  to  photograph  both  character  and 
background  on  one  plane  in  sharp  focus.  The  multiplane  technic  is 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;    received 
April  14,  1938. 

**  Walt  Disney  Productions,  Inc.,  Hollywood,  Calif. 
144 


THE  MULTIPLANE  CAMERA  CRANE  145 

the  separation  of  scenes  into  their  several  foreground  and  background 
elements,  and  designing  them  to  be  photographed  at  different  dis- 
tances in  front  of  the  camera.  The  camera  photographs  through 
these  elements,  which  are  painted  on  glass.  On  one  or  more  of  the 
elements  the  usual  animated  characters  are  held  in  register  to  the 
action  level  part  of  the  scene. 

The  advantages  of  using  a  multiple-plane  technic  in  cartoon 
photography  are  manifold.  An  evaluation  of  these  advantages,  an 
analysis  of  the  means  of  getting  them,  and  the  adaptation  of  these 
means  into  the  established  technic  of  animation,  comprised  the  back- 
ground for  the  design  of  the  multiplane  crane. 

The  primary  problem  leading  to  the  multiplane  idea  was  to  increase 
the  illusion  of  depth  in  animated  motion  pictures.  To  do  this,  there 
are  several  things,  short  of  true  stereoscopic  photography,  that  can 
be  done.  Careful  handling  of  color  and  painting  technic  will  add 
much  to  the  illusion  of  depth.  However,  the  artistic  problem  of 
getting  and  controlling  the  out-of-focus  diffusion  of  foreground  and 
background  scene  elements  is  very  difficult  when  whole  scenes  are 
shot  on  one  plane  in  sharp  focus.  Controlling  this  diffusion  by  using 
several  plane  scenes  and  adjusting  the  depth  of  focus  as  desired  gives 
a  more  convincing  result.  But  the  most  important  part  of  the  ap- 
pearance of  depth  comes  from  camera  movements. 

Pan  shots,  in  cartoon  parlance,  refer  to  scenes  in  which  the  camera 
appears  to  travel  parallel  to  the  background.  It  is  in  pan  shots  that 
the  real-life  movement  between  foreground  and  background  elements 
can  best  be  portrayed.  As  the  scene  elements  are  moved  rather  than 
the  camera  in  photographing  the  cartoon,  the  speed  of  the  elements 
can  be  controlled  as  they  pass  in  front  of  the  camera.  In  the  pan 
shot,  therefore,  the  sky,  the  middle  distance,  and  the  foreground  can 
be  separated  and  moved  at  speeds  that  will  maintain  the  correct 
perspective  relations  of  the  scene  as  originally  conceived  by  the 
artists.  While  it  might  seem  possible  to  paint  all  the  elements  on 
separate  transparencies  to  be  shot  on  one  plane  and  still  control  the 
perspective  by  different  movements,  it  is  not  practicable  because  the 
pile-up  of  transparencies  will  cause  noticeable  shadows  of  the  top 
characters  upon  the  bottom  characters  if  the  pile-up  is  more  than 
0.040  inch  thick. 

In  a  so-called  truck  shot,  in  which  the  camera  appears  to  move 
toward  or  away  from  an  object,  a  depth  effect  can  be  accomplished 
only  by  the  use  of  a  multiplane  scene.  In  moving  the  camera  along 


146  W.  E.  GARITY  AND  W.  C.  MCFADDEN      [j.  S.  M.  p.  E. 

the  lens  axis,  it  is  easily  shown  that  the  photographed  fields  nearest 
the  camera  are  changed  in  size  at  a  proportionally  greater  rate  than 
those  farther  away.  The  proportional  change  varies  inversely  with 
the  field  size,  which  is  exactly  the  condition  found  in  real-life  ob- 
servation. In  multiplane  scenes,  it  is  possible  to  keep  the  very 
distant  background  and  sky  elements  from  changing  in  size  during 
camera  trucks  by  keeping  them  at  the  same  distance  from  the  camera 
while  the  latter  is  moving  with  respect  to  the  characters  and  fore- 
ground. 

Overall  light  changes  showing  transitions,  such  as  dawn  to  full 
daylight  in  the  same  scene,  can  be  done  in  cartoon  work  with  fades 
or  filters.  But  when  only  part  of  the  scene  requires  a  lighting 
change,  in  standard  cartoon  photography  such  a  change  can  be  done 
only  by  double  exposures.  In  multiplane  photography,  the  lighting 
changes  can  be  achieved  easily  by  filtering  or  otherwise  controlling 
the  light  on  the  element  to  be  changed.  A  large  range  of  light  level 
can  be  attained  by  using  bulbs  of  diiferent  wattages  in  the  lamp- 
boxes.  For  smaller  variations  in  light,  a  range  of  voltage  from  normal 
to  20  volts  above  normal  can  be  used.  This  over-voltage  range  is 
necessarily  small  because  of  the  usual  limitation  due  to  variation  of 
the  color  of  tungsten  lamps  with  voltage.  In  practice  it  has  been 
found  that  this  voltage  range  is  consistent  with  reasonable  bulb  life 
and  color  quality.  At  times  the  color  variation  of  tungsten  lamps  is 
used  to  advantage  by  running  them  under  voltage  for  certain  effects. 

Because  of  the  separation  of  scene  elements,  the  possibilities  of 
special  effects  are  greatly  increased.  Distortion  and  diffusion  glasses 
for  a  single  background  element  can  be  used  without  affecting  the 
rest  of  the  scene  or  characters.  The  use  of  mirrors  and  other  optical 
equipment  is  greatly  facilitated  in  multiplane  scenes.  By  careful 
planning,  almost  any  scene  can  be  broken  down  in  such  a  way  that 
control  of  lighting,  color,  and  optics  is  achieved  over  any  part  or  all 
of  the  scene.  This  control  would  not  be  at  all  practicable  if  the  tech- 
nic  were  confined  to  a  single  plane.  While  animation  effects  are  ap- 
parently unlimited,  there  are  certain  weaknesses  that  special-effects 
equipment  circumvents.  It  is  impracticable  to  paint  gradual  changes 
of  light  level  or  color,  or  to  animate  the  slow  distortion  of  backgrounds 
or  reflections. 

As  the  multiplane  idea  necessitated  transparent  backing  for  car- 
toon characters,  the  door  was  opened  to  a  large  range  of  effects  with 
back-lighting  such  as  the  glow  around  lamps,  sparkles,  sunsets 


Aug.,  1938] 


THE  MULTIPLANE  CAMERA  CRANE 


147 


through  dark  clouds,  etc.     Although  process  backgrounds  have  not 
been  used,  they  are  quite  possible  with  the  multiplane  crane. 

From  the  experimental  work  on  the  multiplane  idea,  the  necessary 
requirements  for  a  successful  camera  crane  were  set  up  (Fig.  1). 
Two  general  types  of  supports  for  the  scene  elements  were  required. 


FIG.  1.     General  view  of  multiplane  crane. 


One  was  the  contact  plane,  which  would  handle  both  glass  back- 
grounds and  animation;  and  the  other  was  the  background  plane, 
which  would  support  only  the  glass  backgrounds.  However,  the 
desire  for  freedom  from  limitations  in  breaking  down  scenes  made  it 
imperative  that  it  be  possible  to  arrange  the  various  planes  in  front 
of  the  camera  in  any  order.  That  meant  that  the  planes  would  have 
to  be  quickly  and  easily  demountable  from  the  structure  and  light 
enough  in  weight  to  be  handled  easily.  It  meant  that  each  plane 


148 


W.  E.  GARITY  AND  W.  C.  MCFADDEN      [J.  S.  M.  P.  E. 


would  have  to  carry  its  own  light-boxes.  Because  of  the  large 
number  of  background  separations  desired,  the  overall  height  of  the 
plane  and  light-boxes  had  to  be  kept  to  a  minimum :  it  was  possible 
to  keep  it  under  14  inches.  The  contact  planes  had  to  carry  all  the 


FIG.  2.     Multiplane  camera,  front  elevation. 

usual  cartoon  facilities  for  handling  animation,  such  as  peg  bars, 
platen,  etc.,  in  addition  to  the  background  support. 

The  desire  for  controlling  depth  of  focus  over  a  large  range  made 
many  revisions  necessary  in  the  usual  cartoon  camera  set-up.  Analy- 
sis of  lenses  of  various  focal  lengths,  focusing  close  to  the  camera, 
showed  that  the  depth  "of  focus  was  practically  independent  of  focal 
length  for  the  same  photographed  field  size.  It  remained  for  us  to 
choose  a  lens  with  an  angle  that  would  give  us  a  convenient  range  of 
field  sizes  within  the  limits  of  our  structure.  For  a  large  enough 


Aug.,  1938]  THE  MULTIPLANE  CAMERA  CRANE  149 

depth  of  focus,  it  was  necessary  to  stop  the  lens  down  as  small  as 
//32.  In  making  three-color  separation  negatives,  the  small  lens 
aperture  raised  the  light  requirements  far  in  excess  of  those  of  the 
usual  cartoon  system.  As  we  use  stop-motion  photography  to  make 
the  successive  color  separations,  we  were  able  to  reduce  the  light  to 
about  500  foot-candles  by  increasing  the  exposure  time.  We  es- 
tablished, for  our  purposes,  exposure  times  varying  from  0.9  to  9 
seconds  per  exposure. 


FIG.  3.  Top  view  of  camera  carriage  showing  camera 
drive  and  "East- West,  North-South"  and  rotational 
mounts. 

In  mounting  the  camera,  the  usual  small  horizontal  movements  in 
two  directions  as  well  as  the  vertical  movement  were  required.  A 
rotational  movement  about  the  lens  axis  was  also  required  for  angle 
shots  and  airplane  spin  effects,  etc.  By  a  combination  of  horizontal 
and  rotational  movements,  any  type  of  angular  or  rotational  move 
was  possible.  It  was  found  necessary  to  equip  each  of  the  planes 
with  a  vertical  truck  movement,  so  that  the  photographed  size  of 
any  scene  element  could  be  controlled  individually. 

In  lighting  the  photographed  field,  it  was  found  feasible  to  paint 
for  the  effect  desired  and  to  use  as  flat  a  light  as  possible.  However, 
provision  was  made  for  filters  and  special-effects  masks  over  each 
light-box.  The  one  most  difficult  problem  was  spill  light.  It  was 
finally  necessary  to  develop  special  light-boxes  that  would  simul- 


150 


W.  E.  GARITY  AND  W.  C.  MCFADDEN      [J.  S.  M.  P.  E. 


taneously  light  the  field  flatly,  have  a  high  efficiency,  keep  spill  light 
off  the  planes  immediately  above  and  below,  and  have  an  overall 
height  limited  to  10  inches.  Heat  from  high-intensity  light  was 
serious  and  necessitated  an  exhaust  system  for  all  light-boxes  (Fig.  2) . 
Because  the  operation  of  the  machine  was  to  be  such  that  it  could 
be  tied  into  regular  production,  a  planning  group  of  technicians  and 
artists  had  to  be  developed  to  prepare  the  necessary  camera  instruc- 
tions. 

To  minimize  operation  errors,  an  interlocked  control  system  had 
to  be  developed  that  would  keep  the  numerous  machine  adjust- 
ments coordinated.  The  regular 
cartoon  system  of  scene  set-up  and 
exposure  sheets  had  to  be  expanded 
to  include  the  new  elements  and 
movements  of  the  multiplane  crane. 
The  crane  itself  is  a  vertical  four- 
post  structure  to  which  the  various 
planes  are  movably  attached.  The 
four  posts  are  rigidly  held  in  rec- 
tangular top  and  base  castings  40 
X  60  inches  in  size.  The  posts 
are  unsupported  except  at  the  ends, 
and  are  ground  steel  tubes  47/8  inches 
outside  diameter,  with  y4-inch  walls, 
and  are  11  feet  4  inches  long.  Each 
tube  has  a  gear  rack  bolted  on  along 
its  entire  length.  The  rack  teeth 
are  matched  so  as  to  provide  very 
accurate  control  of  the  height.  In  the  control  system,  the  optical 
axis  and  the  floor  form  the  origin.  The  rack  teeth  are  numbered  in 
inches,  reading  from  the  floor,  to  serve  as  height  indicator  for  all 
equipment  on  the  crane.  The  tubes  are  the  guides  and  the  gear 
racks  are  the  supports  for  all  the  equipment.  As  can  be  seen  from 
the  general  view  of  the  crane  (Fig.  1),  the  camera  is  at  the  top  and 
photographs  vertically  down  through  the  various  planes. 

The  camera  carriage  is  a  rigid  platform  guided  by  bushings  and  sup- 
ported by  worm-driven  rack  gears  (Fig.  3).  The  carriage  is  counter- 
weighted  at  each  corner  by  weights  hanging  inside  the  tubes.  On 
the  camera  carriage  is  an  "east- west"  dovetail  slider  which  carries 
a  "north-south"  dovetail  slider.  On  the  north-south  slider  is  a  large 


FIG.  4.     Service  gutter  for  power 
feed  to  planes. 


Aug.,  1938]  THE  MULTIPLANE  CAMERA  CRANE  151 

ball-bearing  ring  which  supports  the  camera  and  drive  and  allows  them 
to  rotate  through  an  arc  of  360  degrees.  The  camera  is  mounted  so 
that  the  optical  axis  coincides  with  the  center  of  rotation  of  the 
mount.  Every  movement  has  calibrations  correlated  to  the  pro- 
duction technic  so  that  camera  movements  can  be  laid  out  and 
calculated,  prior  to  photographing,  with  a  high  degree  of  accuracy, 
and,  by  the  same  means,  any  given  set  of  conditions  may  be  repeated 
at  any  time.  Due  to  the  requirement  of  variable  exposure  time, 
the  camera  is  driven  by  a  synchronous  motor  through  a  variable- 
speed  transmission  and  stop-motion  clutch.  A  selsyn  motor  is  also 


FIG.  5.     Adjusting  reflectors  with  the  special  photometer. 

tied  into  the  stop-motion  shaft  to  drive  the  operation  control  mecha- 
nism and  film  counter. 

The  most  complicated  of  the  scene  element  supports  are  the  action 
levels  or  contact  planes.  The  contact  planes  contain  all  the  features 
of  a  standard  cartoon  photographing  table,  plus  the  background  sup- 
port. The  plane  carries  its  own  light-boxes.  The  power  control 
circuits  and  compressed  air  are  fed  to  the  planes  from  a  special 
gutter  having  a  series  of  plugs  and  valves  arranged  along  its  length 
(Fig.  4).  This  gutter  is  mounted  vertically  and  parallel  to  the  rear 
left  post  of  the  crane.  The  background  planes  are  fitted  to  carry 
transparent  backgrounds  of  various  widths  in  a  movable  east- west 
slide,  each  carrying  its  own  light-boxes  and  control  circuits.  All 
the  movements  are  fitted  with  calibrations  referred  to  the  optical 
axis  as  center,  so  that  all  planes  have  indications  that  are  mutually 


152 


FW.  E.  GARITY  AND  W.  C.  MCFADDEN      [j.  s.  M.  p.  E. 


Aug.,  1938]  THE  MULTIPLANE  CAMERA  CRANE  153 

consistent.  All  planes  are  fitted  with  rack  gear  vertical  supports 
and  movements  similar  to  those  of  the  camera  carriage. 

The  lamp-boxes  are  of  the  adjustable  facet  reflector  type,  designed 
to  fit  a  multitude  of  stringent  conditions  (Fig.  5).  The  reflectors  are 
individually  adjusted  with  the  use  of  a  caesium  cell  photometer  de- 
signed especially  for  the  purpose.  The  adjustments  control  flatness 
of  the  lighting  as  well  as  the  intensity  of  illumination. 

Due  to  the  fact  that  in  the  normal  operation  of  this  camera  the 
services  of  one  to  six  operators  may  be  required,  and  their  efforts 
must  all  be  coordinated  and  the  possibility  of  human  error  eliminated, 
all  the  indices  have  been  provided  with  special  illuminating  lamps. 
While  the  operator  of  one  plane  is  preparing  his  various  controls  for 
photography,  these  lamps  permit  him  to  read  the  indices.  When 
he  has  set  all  the  controls,  he  pushes  a  button,  conveniently  located 
on  his  particular  plane,  which  turns  out  these  lights,  making  it  im- 
possible for  him  to  read  his  control  setting.  When  he  pushes  the 
button  he  trips  a  specially  designed  relay  which  cuts  out  the  illumi- 
nation of  his  indices  and  places  the  electrical  circuit  in  such  condition 
that  when  all  the  planes  have  thus  functioned,  then  and  only  then,  can 
the  chief  operator  trip  the  camera.  These  relays  are  connected  by  a 
series  method  so  that  all  the  relays  from  the  various  planes  in  opera- 
tion must  be  closed  before  the  chief  operator  can  energize  the  elec- 
trical mechanism  that  trips  the  camera.  When  the  exposure  is  com- 
pleted to  the  chief  operator's  satisfaction,  he  pushes  a  button  that 
releases  all  the  planes  simultaneously  so  that  the  individual  opera- 
tors may  proceed  with  establishing  the  settings  for  the  next  exposure. 

To  correlate  the  detailed  manipulation,  it  was  found  necessary  to 
produce  a  master  control  sheet  showing  on  it  the  settings  of  each 
plane  for  each  successive  operation.  This  master  control  sheet  is 
made  out  in  duplicate.  The  duplicate  sheet  is  split  up  and  the  por- 
tion carrying  the  camera  carriage  instruction  is  given  to  the  camera 
operator;  the  portion  carrying  the  instruction  covering  plane  A  is 
given  to  the  operator  of  plane  A;  and  so  on;  and  the  original  master 
is  placed  on  a  master  control  board  immediately  in  front  of  the  chief 
operator  (Fig.  6). 

To  eliminate  errors  on  the  part  of  the  chief  operator  in  knowing  at 
just  what  frame  he  is  working,  a  selsyn  interlocked  motor  has  been 
incorporated  in  the  camera  mechanism.  A  second  selsyn  motor  is 
incorporated  in  the  master  control  board  and  operates  a  glass  ruler 
device  that  indicates  to  the  chief  operator  exactly  upon  which  frame 


154  W.  E.  GARITY  AND  W.  C.  MCFADDEN      [J  s.  M.  P.  E. 

he  is  working.  In  other  words,  when  a  new  control  sheet  is  placed 
on  the  board,  the  glass  ruler  is  returned  to  the  first  exposure,  the 
interlocking  motors  are  energized  and  the  master  ruler  driven  by 
the  camera,  regardless  of  whether  the  camera  moves  forward  or 
backward.  There  is  therefore  no  opportunity,  except  in  the  case  of 
electrical  failure,  for  the  chief  operator  to  make  an  error. 

In  view  of  the  fact  that  projection  type  lamps  are  used,  and  for 
the  technicolor  process  it  is  required  that  they  operate  a  voltage 
higher  than  rated,  their  lives  are  necessarily  short.  To  circumvent 
this  condition,  an  electrical  circuit  has  been  arranged  to  introduce  a 
resistance  into  the  main  current  supply  line  so  as  to  reduce  the  volt- 
age on  the  lamps  to  about  85  or  90  volts  during  the  time  when  changes 
and  camera  set-ups  are  being  made.  A  special  relay  is  provided  in 
the  circuit  so  that  it  is  impossible  for  the  chief  operator  to  make  an 
exposure  while  the  protective  resistance  is  in  circuit. 

To  increase  the  life  of  the  bulbs  further,  as  well  as  to  reduce  the 
heat  in  the  camera  area,  it  was  necessary  to  incorporate  an  exhaust 
system  in  the  lamp-boxes  (Fig.  2) .  This  equipment  was  designed  to 
provide  one  change  of  air  per  second  in  the  lamp-box,  and  has  been 
quite  successful  in  increasing  the  useful  life  of  the  lamp  besides  pre- 
venting practically  all  heat  conduction  through  the  lamp-box. 

In  the  development  and  design  of  the  light-sources  used  with  the 
camera,  it  was  necessary  to  develop  special  photometric  equipment 
due  to  the  acute  angle  of  the  light-source  to  the  photographed  area, 
which  averages  about  27  degrees.  None  of  the  commercial  photo- 
metric devices  was  satisfactory.  The  device  developed  for  this 
particular  function  contained  a  caesium  photoelectric  cell  in  a  vac- 
uum-tube voltmeter  circuit  (Fig.  5) .  The  photocell  was  mounted  so 
that  its  cathode  scanned  a  small  disk  of  heavy  ground-glass  suspended 
about  5  inches  below  the  photocell.  This  glass  disk  is  held  in  position 
by  means  of  a  piece  of  glass  tubing  about  2  inches  long,  the  disk  being 
centered  at  the  bottom  of  the  tube.  The  glass  tube  is  suspended  in 
a  piece  of  brass  tubing  about  3  inches  long,  and  the  interior  of  the 
brass  tube  is  entirely  opaqued  and  rendered  non-reflecting. 

The  photocell  and  tube  are  suspended  by  means  of  a  double 
trunnion  of  a  design  similar  to  that  used  to  suspend  a  ship's  compass. 
The  outer  pair  of  trunnions  is  established  in  a  ring,  and  in  the  ring 
are  set  three  posts  so  that  the  ground-glass  disk  is  suspended  about 
y4  inch  above  the  illuminated  surface  to  be  measured,  and  the  three 
supporting  legs  are  positioned  so  as  not  to  cast  a  shadow  upon  the 


Aug.,  1938]  THE  MULTIPLANE  CAMERA  CRANE  155 

ground-glass  disk.  The  instrument  measures  very  accurately  the 
perpendicular  light,  which  is  the  useful  photographic  light.  A  de- 
vice of  this  type  is  necessary  so  that  the  reflection  surface  remain 
absolutely  parallel  at  all  times;  a  slight  deviation  from  the  level 
would  cause  a  wide  discrepancy  in  our  measurements.  This  ap- 
paratus is  useful  only  in  leveling  the  overall  illumination,  and  is 
impracticable  for  establishing  the  light  levels  for  the  photography. 
The  scene-planning  group  of  artists  and  technicians  was  developed 
to  control  the  use  of  the  multiplane  crane  in  creating  the  desired 
illusions.  In  breaking  down  a  scene  the  group  works  with  a  pencil 


FIG.    7.     Multiplane    set-up    on   crane   showing   four 
levels,  with  water  and  reflections. 


perspective  layout  of  the  scene  as  originally  conceived  by  the  layout 
department.  After  due  allowance  has  been  made  for  any  special 
set-up  for  some  particular  effect,  the  scene  is  broken  into  its  fore- 
ground, action,  and  background  elements  and  these  elements  are 
indicated  on  the  original  layout  (Fig.  7).  As  the  original  layout  is 
already  drawn  to  action-level  size,  every  change  in  size  for  the  sepa- 
rations is  referred  to  the  action  level  as  a  base.  Field  sizes  are  then 
chosen  for  each  of  the  separated  backgrounds  and  the  separations 
are  photostatically  enlarged  or  reduced,  depending  upon  their  posi- 
tions above  or  below  the  action  level.  In  order  to  get  correct  per- 
spective speeds  in  pan  shots,  the  real-life  distance  from  the  action 
level  to  each  separation  is  estimated  by  measuring  the  drawn  size  of 
similar  objects  in  the  original  layout.  The  speed  of  motion  for  any 


156  W.  E.  GARITY  AND  W.  C.  MCFADDEN 

plane  is  the  contact-level  speed  multiplied  by  the  ratio  of  the  separa- 
tion-field size  to  the  contact-level  field  size;  and  by  the  ratio  of  the 
drawn  size  of  an  object,  in  the  original  layout  at  the  real-life  dis- 
tance of  the  separation  to  the  drawn  size  of  the  same  object  at  the 
real-life  distance  of  the  contact  level. 

To  control  the  out-of -focus  diffusion,  a  depth-of -focus  chart  is 
used.  After  a  circle  of  confusion  for  a  particular  separation  is 
chosen,  and  using  the  lens  aperture  that  will  give  enough  depth  of 
focus,  the  field  size  of  the  separation  can  be  set  by  using  the  dis- 
tance from  the  focal  plane  or  contact  level  that  will  have  the  diffusion 
desired.  In  making  finished  backgrounds,  photostats  are  traced 
upon  the  transparency  to  indicate  to  the  artists  the  size  and  com- 
position. Then  specially  trained  artists  paint  the  elements.  The 
artist  must  develop  a  high  degree  of  skill  to  handle  the  color  harmony 
from  plane  to  plane  in  such  a  way  that  the  planned  effect  of  depth 
will  be  maintained. 

To  lay  out  the  master  control  sheets,  the  technicians  keep  records 
of  all  the  decisions,  as  to  the  effects  desired,  upon  a  multiplane  scene 
script.  When  the  scene  is  completed  for  photography,  it  is  checked 
for  both  artistry  and  mechanics,  and  then  the  master  control  sheets 
are  laid  out  by  the  technicians  who  give  the  complete  operating  in- 
structions for  each  frame  of  film. 

The  multiplane  technic  was  first  used  and  developed  on  the  "Silly 
Symphony"  entitled  The  Old  Mill  and  was  used  extensively  in  the 
feature  production  Snow  White  and  the  Sewn  Dwarfs.  Following 
the  latter,  the  Silly  Symphony  Wynken,  Blynken  and  Nod  was  pro- 
duced in  which  the  multiplane  technic  was  also  employed.  The 
technic  has  definitely  improved  the  photographic  quality  of  the  prod- 
uct and  we  are  convinced  that  its  possibilities  are  unlimited  and 
that  the  results  justify  the  increased  cost  of  operation. 


DISTORTION  IN  SOUND  REPRODUCTION  FROM 
PHONOGRAPH  RECORDS* 


J.  A.  PIERCE  AND  F.  V.  HUNT' 


Summary. — When  the  spherical  tip  of  an  ideal  reproducer  stylus  slides  over  a 
warped  groove  surface  having  a  sinusoidal  profile,  the  traced  curve  is  not  exactly 
sinusoidal.  An  analysis  of  the  harmonic  content  of  the  traced  curve,  similar  to  that 
given  by  DiToro  (J.  Soc.  Mot.  Pict.  Eng.,  Nov.,  1937)  but  avoiding  his  approxima- 
tions, is  directly  applicable  to  reproduction  from  vertical-cut  records.  These  results 
may  be  applied  to  reproduction  from  lateral-cut  records  by  taking  the  original  groove 
surface  as  inclined  approximately  45  degrees  from  the  horizontal,  projecting  the 
traced  curve  upon  the  horizontal  and  vertical  planes,  and  adding  in  proper  phase 
the  guidance  of  the  stylus  tip  by  both  sidewalk.  It  is  shown  that  there  is  a  residual 
vertical  component  of  stylus  motion  ("pinch"  effect)  and  complete  cancellation  of  all 
even  harmonics  in  the  tracing  distortion.  Computation  of  the  remaining  odd  har- 
monics indicates  that,  when  the  ideal  lateral-cut  reproducer  characteristics  include 
ideal  "following"  for  vertical  motion  at  signal  frequency,  a  lateral-cut  record  may  be 
reproduced  with  one-fourth  to  one-tenth  the  rms.  distortion  of  a  similarly  recorded 
vertical-cut  record.  These  results  are  displayed  for  convenient  reference  by  contours 
of  constant  distortion  upon  a  universal  chart,  the  dimensionless  coordinates  of  which 
characterize  any  recording  condition  and  allow  immediate  specification  of  the 
maximum  permissible  recorded  amplitude,  maximum  predistortion  of  the  frequency 
characteristic,  and  the  required  clearance  angle  of  the  recording  stylus . 

In  the  complicated  process  of  recording  and  reproducing  a  phono- 
graph record  there  are  many  ways  in  which  non-linear  or  harmonic 
distortion  may  enter  the  system.  If  one  assumes  that  the  electro- 
mechanical conversion  is  perfect  in  both  recording  and  reproduction 
there  still  remain  two  geometric  factors  introducing  harmonic  dis- 
tortion which  may  not  be  reduced  except  by  altering  the  dimensions 
of  the  apparatus.  The  first  of  these  is  "tracking  error,"  and  may  be 
defined  as  the  angle  between  the  vertical  plane  containing  the  vibra- 
tion axis  of  the  mechanical  system  of  the  reproducer  and  a  vertical 
plane  containing  the  tangent  to  the  record  groove.  Such  an  angle 
arises  from  the  convenient  mechanical  device  of  pivoting  the  re- 
producer tone-arm  from  a  fixed  point.  If  the  vibration  axis  of  the 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;    received 
April  15,  1938.     Published  also  in  /.  Acoust.  Soc.  Amer.  (July,  1938). 
**  Cruft  Laboratory,  Harvard  University,  Cambridge,  Mass. 

157 


158  J.  A.  PIERCE  AND  F.  V.  HUNT  [j.  s  M.  P.  E. 

reproducer,  extended,  passes  through  the  tone-arm  pivot,  it  may 
readily  be  shown  that  the  vibration  axis  can  never  be  truly  tangent 
to  the  record  groove  at  more  than  one  value  of  the  radius.  On  the 
other  hand,  if  the  vibration  axis  of  the  reproducer  system  is  set  at  an 
appropriate  angle  with  the  line  connecting  the  stylus  tip  and  the  tone- 
arm  pivot,  and  if  the  length  of  the  tone-arm  is  properly  adjusted  to 
the  distance  between  the  tone-arm  pivot  and  the  record  axis,  then 
the  tracking  error  may  be  held  to  a  few  degrees.  In  the  case  of  re- 
production of  vertical-cut  records  this  tracking  error  does  not  intro- 
duce distortion  and  the  tone-arm  may  therefore  be  made  quite  short. 
On  the  other  hand,  in  the  reproduction  of  lateral-cut  records  a  sinus- 
oidal groove  is  not  traced  sinusoidally  by  the  reproducer  stylus  tip 
if  the  tracking  error  is  considerable.  Olney1  has  discussed  this  effect 
and  has  given  numerical  examples  of  the  harmonic  distortion  intro- 
duced under  practical  recording  conditions.  He  shows,  for  example, 
that  even  with  so  large  a  tracking  error  as  15  degrees  (as  large  as  is 
usually  met  in  practice)  the  maximum  distortion  to  be  expected  from 
this  source  is  approximately  4  per  cent.  On  the  other  hand,  it  is 
readily  possible  to  offset  the  vibration  axis  in  such  a  manner  that  the 
tracking  error  does  not  exceed  ±6  degrees,  and  under  these  condi- 
tions the  harmonic  distortion  introduced  by  tracking  error  can  be 
neglected  in  comparison  with  other  distortions  met  with  in  a  practical 
recording  system. 

A  very  much  more  serious  source  of  harmonic  distortion  arises 
from  the  fact  that  the  tip  of  the  reproducer  stylus  has  finite  size. 
The  curve  traced  by  the  center  of  the  tip  (which  we  shall  assume  to 
be  spherical)  of  a  reproducer  stylus  sliding  over  a  sinusoidal  groove 
surface  is  not,  unfortunately,  sinusoidal,  and  it  is  embarrassing  that 
the  only  way  to  reduce  the  distortion  due  to  this  effect  is  to  reduce  the 
size  of  the  needle  tip.  Such  reduction  can  be  carried  only  so  far, 
with  the  practical  result  that  this  distortion,  herein  called  tracing 
distortion,  currently  remains  the  most  serious  limitation  in  the  at- 
tainable fidelity  of  phonograph  reproduction.  DiToro2  has  dis- 
cussed this  type  of  distortion  with  an  analysis  based  upon  an  approxi- 
mate sine  curve  composed  of  parabolic  and  straight-line  sections,  and 
has  given  results  that  are  applicable  to  reproduction  from  vertical- 
cut  records.  These  results  are  satisfactory  for  high  values  of  dis- 
tortion, but  are  in  some  error  at  the  lower  and  more  interesting  values. 
It  is  the  purpose  of  this  paper  to  present  an  extension  of  this  work, 
based  upon  a  method  of  computation  that  avoids  DiToro's  approxi- 


Aug.,  1938]          DISTORTION  IN  SOUND  REPRODUCTION  159 

mations,  and  to  apply  the  results  to  an  evaluation  of  the  tracing  dis- 
tortion arising  in  the  reproduction  of  both  vertical  and  lateral-cut 
records. 

HARMONIC  ANALYSIS  OF  THE  TRACED  CURVE 

The  first  step  in  the  solution  of  this  problem  lies  in  the  harmonic 
analysis  of  the  curve  traced  by  the  center  of  a  circle  that  slides  or 
rolls  along  a  sine  curve.  These  results  will  give  directly  the  com- 
ponents of  motion  of  a  spherical  needle  tip  tracing  a  vertically 
modulated  record  groove,  and  the  application  of  the  results  to  the 
analogous  motion  of  a  needle  tip  tracing  a  laterally  modulated  groove 
will  be  discussed  later.  Fig.  1  represents  such  a  circle  sliding  along 
a  cosine  curve.  It  will  be  noted  that  the  traced  curve  (shown  dotted) 
is  not  mathematically  simple.  It  is,  however,  so  simple  physically 
that  it  seems  as  though  it  should  be  numbered  among  the  curves  that 
are  dignified  by  titles,  and  for  want  of  a  better  name  we  have 
dubbed  this  curve  the  poid  and  shall  so  designate  it  in  this  discussion. 

The  coordinates  of  the  center  of  the  tracing  circle,  £,  77  (which  are 
the  coordinates  of  a  point  on  the  poid),  may  be  expressed  in  terms  of 
the  corresponding  coordinates  of  the  point  of  contact  of  the  circle 
with  the  cosine  curve,  as  follows:  Let  axes  be  established  as  indi- 
cated in  Fig.  1  so  that  the  cosine  curve  is  defined  by 

n     „ 

y  =  a  cos  — -  =  a  cos  kx  (1) 

A 

where 

k    =    27T/X 

Now 

£  =  x  +  r  sin  0 

but,  — tan  8  is  the  slope  of  the  cosine  curve  at  the  point  (x,  y),  or 

—  tan  0  =   —  ka  sin  kx 
Hence 

ka  sin  kx 

sm  0  = 

and 


VI  +  k*a*  sin*  kx 
Similarly, 

77  =  y  +  r  cos  0 
=  a  cos  kx  +  -7====L===  (5) 


160  J.  A.  PIERCE  AND  F.  V.  HUNT  [j.  s.  M.  p.  E. 

These  parametric  equations  for  the  poid  have  involved  no  approxi- 
mations. Unfortunately  the  elimination  of  x  between  them  and  the 
expansion  of  17  in  a  Fourier  series  in  £  is  extremely  difficult,  each  coef- 
ficient involving  the  term-by-term  integration  of  the  product  of 
three  infinite  series,  none  of  which  converges  rapidly  for  the  range  of 
values  in  which  we  are  interested. 

An  alternative  method  of  solution  was  therefore  sought.  Chaffee3 
has  described  a  simplified  form  of  schedule  analysis,  applicable  to 
even  functions,  which  is  capable  of  considerable  accuracy  and  re- 
quires a  knowledge  of  the  coordinates  of  only  a  limited  number  of 
points.  The  poid  is  an  even  function,  as  indicated  by  its  symmetry 
about  either  a  maximum  or  a  minimum  point,  so  that,  with  the  co- 
ordinates of  only  seven  points  in  a  half -wavelength,  the  amplitudes 
of  the  second  and  third  harmonics  may  be  determined  within  one  or 
two  per  cent,  and  reasonably  accurate  values  may  be  calculated  for 
harmonics  up  to  the  sixth.  This  precision  was  deemed  adequate  for 
our  purpose. 

It  was  required,  then,  to  determine  values  of  t]  corresponding  to 
the  values  of  k£  prescribed  by  the  harmonic  analysis  schedule.  The 
values  of  x  corresponding  to  these  prescribed  values  of  k£  were  first 
obtained  by  successive  approximations,  assumed  values  of  x  being 
inserted  in  equation  2  until  k%  was  established  with  sufficient  ac- 
curacy. These  values  of  x  for  each  prescribed  point  were  successively 
inserted  in  equation  3  and  the  resulting  values  of  ?j  used  to  enter  the 
harmonic  analysis  schedule.  The  relative  amplitudes  of  the  six 
harmonics  were  then  obtained  by  simple  arithmetic. 

This  method  of  computation,  while  laborious,  requires  no  ap- 
proximations except  those  inherent  in  the  schedule  analysis  and  these 
may  be  made  as  small  as  desired  by  computing  a  sufficiently  large 
number  of  points.  By  making  check  calculations  using  as  many  as 
thirteen  points  for  a  half -cycle  it  was  found  that  the  "seven -point" 
analysis  was  indeed  sufficiently  accurate. 

On  reference  to  Fig.  1  it  may  be  noted  that  the  size  and  shape  of 
the  poid,  and  therefore  the  amplitude  of  each  harmonic  constituent 
of  the  poid,  is  given  by  three  linear  dimensions,  a,  r,  and  X.  On  the 
other  hand,  the  shape  of  the  poid  and  the  relative  amplitudes  of  its 
harmonic  constituents  are  determined  by  the  two  dimensionless 
ratios,  a/\  and  r/X.  Our  subsequent  discussion  will  be  simplified 
if  we  take  these  ratios  as  2ira/\  and  2irr/\  (i.  e.,  as  ka  and  kr),  and  we 
may  then  say  that  the  relative  harmonic  structure  of  the  poid  is  a 


Aug.,  1938]          DISTORTION  IN  SOUND  REPRODUCTION  161 

function  of  the  two  independent  variables  ka  and  kr.  It  is  necessary 
now  only  to  calculate  the  distortion  corresponding  to  all  possible 
values  of  these  two  variables  —  a  straightforward  but  tedious  process. 

The  values  of  harmonic  distortion  so  calculated  might  be  plotted 
vertically  over  the  ka-kr  plane  and  constitute  a  characteristic  surface 
whose  distance  above  the  horizontal  plane  is  a  measure  of  the  har- 
monic distortion  for  the  condition  corresponding  to  the  coordinates 
ka  and  kr.  It  is  frequently  convenient  to  represent  such  a  warped 
surface  by  projecting  onto  the  horizontal  ka-kr  plane  contours  of 
selected  constant  values  of  harmonic  distortion.  It  is  thus  possible 
to  represent  on  a  single  chart  the  entire  range  of  tracing  distortion 
met  under  all  recording  conditions.  The  computational  labor  in- 
volved in  obtaining  such  a  set  of  contours  is  reduced  by  the  prepara- 
tion of  a  family  of  intermediate  curves,  each  showing  harmonic  dis- 
tortion plotted  against  the  variable  kr  with  selected  values  of  ka  held 
constant  for  each  of  the  intermediate  curves.  If  horizontal  lines  are 
now  drawn  at  the  chosen  values  of  the  total  harmonic  distortion,  they 
will  cut  the  family  of  intermediate  curves  in  a  series  of  points  which 
establish  the  pairs  of  coordinates  for  the  points  lying  along  the  con- 
stant-distortion contour  curve.  These  points  are  then  transferred  to 
the  ka-kr  plane  and  the  contours  drawn  as  exhibited  by  the  dashed 
lines  of  Fig.  4.  By  this  method  the  harmonic  analysis  of  some  thirty 
poids  is  sufficient  to  establish  the  contour  set  covering  the  entire 
useful  range  of  the  independent  variables  ka  and  kr. 

It  may  be  pointed  out  that  the  harmonic  analysis  schedule  yields 
the  amplitudes  of  the  various  harmonics.  Inasmuch  as  reproducing 
systems  are  almost  invariably  velocity-responsive  (either  intrinsically, 
as  in  the  electromagnetic,  or  through  equalization,  as  in  the  piezo- 
electric) each  harmonic  amplitude  is  multiplied  by  its  harmonic 
number  before  comparison  with  the  amplitude  of  the  fundamental, 
and  the  contour  chart  of  Fig.  4  is  then  drawn  in  terms  of  the  total 
root-mean-square  harmonic  velocity  distortion.* 

As  suggested  above,  the  dashed-line  contours  of  Fig.  4  are  directly 
applicable  to  reproduction  from  vertical-cut  records,  and  their  in- 
terpretation under  specific  recording  conditions  will  be  given  in  a 
later  section.  Before  applying  these  results  to  the  reproduction  of 

*  If  v\t  i>2,  Vs,  •  •  •  •  are  the  harmonic  velocity  components  the  total  rms.  distor- 
tion is  defined  as 


H.D. 


162  J.  A.  PIERCE  AND  F.  V.  HUNT  [j.  s.  M.  p.  E. 

lateral-cut  records  we  must  consider  in  greater  detail  the  geometrical 
relation  between  a  laterally  modulated  groove  and  the  stylus  tip. 
Fig.  2  is  a  plan  view  and  two  typical  cross-sections  of  a  laterally 
modulated  record  groove.  This  groove  is  generated  by  a  plane  cut- 
ting surface  which  is  always  perpendicular  to  the  axis  of  the  un- 
modulated groove.  There  arises,  consequently,  a  constriction  in 
the  width  of  the  groove,  measured  perpendicular  to  its  instantaneous 
direction,  whenever  the  cutting  needle  is  moving  at  an  angle  to  the 
direction  of  the  unmodulated  groove.  This  is  illustrated  by  the 
sectional  views  of  the  groove  given  at  the  bottom  of  Fig.  2.  If  such 
a  groove  be  traced  by  a  stylus  that  bears  at  least  partially  upon  the 
groove  sidewalls,  it  will  be  seen  at  once  that  the  stylus  must  rise  and 
fall  twice  during  the  tracing  of  each  fundamental  wavelength.  This 
phenomenon  appears  to  have  been  ignored  or  neglected  in  previous 
discussions  of  the  so-called  "pinch  effect,"  but  it  leads  to  the  neces- 
sary conclusion  that  an  ideal  reproducer  for  lateral-cut  records  must 
embody  sufficient  vertical  flexibility  to  enable  the  stylus  to  execute  this 
motion  faithfully.  This  requirement  appears  even  more  severe  when 
it  is  remembered  that  this  vertical  motion  must  be  executed  at  twice 
the  frequency  of  the  fundamental  groove  modulation.  In  typical 
commercial  reproducers  for  lateral-cut  records  there  is  no  provision 
for  vertical  motion  of  the  stylus  relative  to  the  tone-arm,  with  the 
result  that  the  stylus  must  ride  at  some  intermediate  elevation  above 
its  normal  position  in  the  unmodulated  groove.  Since  the  mass  of 
the  reproducer  head  and  arm  is  too  large  to  be  vibrated  at  signal 
frequencies,  the  stylus  is  driven  into  the  groove  in  the  "pinched" 
sections.  This  gouges  out  the  groove  walls,  producing  additional 
surface  noise  and  altering  the  original  groove  shape.  When  the 
groove  section  is  not  "pinched"  the  stylus  floats  above  the  groove 
and  is  free  to  "rattle"  since  it  is  not  necessarily  in  contact  with  either 
wall.  With  conventional  reproducing  apparatus  this  process  con- 
tinues until  the  pinched  sections  of  the  groove  have  been  enlarged 
(involving  the  erasure  of  any  small  amplitude  high-frequency  modu- 
lation that  may  be  superimposed),  or  the  needle  has  been  worn. 
The  needle  tip  then  rides  at  some  constant  level  but  is  never  there- 
after positively  driven  by  more  than  one  groove  wall  at  a  time. 
Olney1  has  pointed  out  that  distortions  may  arise  from  this  con- 
dition. On  the  other  hand,  if  the  stylus  point  is  sufficiently  sharp  to 
reach  the  rounded  bottom  of  the  "standard  groove"  the  result  is 
equally  bad;  while  the  tendency  to  vertical  motion  is  minimized  or 


Aug.,  1938]          DISTORTION  IN  SOUND  REPRODUCTION 


163 


FIG.  1.  Coordinates  and  nomenclature  for  the  harmonic  analy- 
sis of  the  curve  ("poid")  traced  by  the  center  of  a  circle  sliding  or 
rolling  along  a  cosine  curve. 


SECTION    A-A 


SECTION    B-B 


FIG.  2.     Plan  and  sectional  views  of  the  assumed  stylus  bearing 
relations  in  a  typical  laterally  modulated  groove. 


164 


J.  A.  PIERCE  AND  F.  V.  HUNT 


[J.  S.  M.  P.  E. 


removed,  the  stylus  is  never  positively  driven  by  the  groove.  It  is 
not  possible  to  make  an  accurate  quantitative  analysis  of  the  dis- 
tortion introduced  by  the  uncontrolled  rattling  of  a  stylus  tip  in  a 
record  groove,  but  it  seems  reasonable  to  assume  that  the  distortion 
under  such  conditions  will  be  at  least  as  large  as  would  be  generated 
if  the  stylus  were  in  continuous  contact  with  the  groove  walls.  More- 


FIG.  3.  Section  and  projected  plan 
views  illustrating  the  stylus  displacement 
components  during  the  tracing  of  a  later- 
ally modulated  record  groove. 


over,  the  distortion  generated  by  rattling  would  be  inharmonic,  and 
as  this  would  contribute  noise  as  well  as  signal  distortion,  we  may  con- 
dude  that  an  ideal  reproducer  whose  stylus  is  positively  driven  by  the 
groove  walls  will  yield  a  lower  background  noise  level. 

It  seems,  therefore,  that  it  is  highly  desirable  in  practice,  and  neces- 
sary for  a  mathematical  analysis,  to  endow  our  assumed  ideal  lateral 
reproducer  with  such  characteristics  that  it  can  execute  the  pre- 
scribed vertical  motion  faithfully,  and  we  further  assume  and  hold 


Aug.,  1938]          DISTORTION  IN  SOUND  REPRODUCTION  165 

as  desirable  that  the  stylus  should  be  supported  by  the  sidewalls  of 
the  groove.  With  a  spherical  stylus  tip  this  does  not  lead  to  a  large 
increase  in  needle  bearing  pressure  in  practice,  and  we  assume  here 
and  throughout  this  discussion  that  no  account  need  be  taken  of  the 
distortion  of  the  groove  surface  by  the  needle  bearing  pressure. 
When  these  conditions  are  satisfied  we  may  discuss  the  components 
of  stylus  motion  with  the  assistance  of  Fig.  3. 

Consider  that  BC  and  B'C'  are  the  projections  onto  the  plane  of 
the  paper  of  the  two  extreme  positions  of  a  radial  section  of  one  wall 
of  a  groove  that  is  modulated  laterally  with  an  amplitude  a.  As  the 
record  rotates,  this  groove  wall  is  generated  as  a  wavy  surface  having  a 
sinusoidal  profile.  The  curve  traced  by  the  center  of  a  ball  sliding 
upon  this  surface,  if  projected  upon  a  plane  perpendicular  to  BC,  as 
indicated  by  DG,  will  be  a  poid  which  will  have  a  maximum  and  a 
minimum  at  G  and  F,  respectively.  In  this  plane  through  DG,  per- 
pendicular to  the  paper,  the  amplitude  of  the  sine  wave  is  a  sin  a, 
and  the  poid  may  be  represented  by 

17'  =«=  a\  sin  a  cos  k%  +  a-2  sin  a  cos  2k%  +  #3  sin  a.  cos  3k!;  +  .  .  .         (6) 

This  poid  may  be  projected  upon  a  plane  parallel  to  AB,  such  as  the 
one  through  HJ,  by  dividing  equation  6  by 

cos  (x/2  —  2a)  =  sin  2a  =  2  sin  a  cos  a 
Its  equation  now  becomes, 


cos  *£  +         —  cos  2**  +  =--  cos  3k*  +  .          (7) 


2  cos  a  '    2  cos  a  '2  COS  a 

This  equation  expresses  the  motion  of  the  sphere  caused  by  the 
change  in  position  of  the  sidewall  represented  by  BC  and  B'C',  and 
since  the  motion  is  projected  upon  a  plane  parallel  to  the  opposite 
sidewall  it  may  be  divided  into  components,  in  both  the  vertical  and 
horizontal  planes,  which  are  independent  of  any  simultaneous  mo- 
tions of  the  opposite  sidewall.  For  example,  the  horizontal  com- 
ponent of  the  motion  is  given  by 

n'H  =  |cos^  +  |2cos2^  +  |  cos  3**  +  ...  (<?) 

The  corresponding  equation  for  the  component  of  motion  induced 
by  the  opposite  sidewall  is  identical  except  for  direction  and  a  phase 
difference  between  the  two  poids.  It  is  to  be  noted  that  there  is  a 
phase  displacement  of  180  degrees  in  the  equation  of  the  motion  due 
to  the  sidewall  indicated  by  AB;  that  is,  the  maximum  of  one  poid 


166  J.  A.  PIERCE  AND  F.  V.  HUNT  [j.  s.  M.  p.  E. 

occurs  simultaneously  with  the  minimum  of  the  other.  This  is  in- 
dicated by  the  plan  view,  shown  in  the  upper  part  of  Fig.  3,  which 
represents  the  projection  onto  the  horizontal  plane  of  the  sine  curve 
profile  of  the  groove  walls  and  the  poids  generated  in  the  planes 
through  HJ  and  HJ'.  The  horizontal  projection  of  the  poid  gener- 
ated by  the  wall  AB  is  directed  oppositely  to  that  generated  by  the 
wall  BC,  as  viewed,  say,  from  the  center  of  the  record,  because  the 
sphere  is  being  pushed  away  from  the  center  of  the  record  in  one  case 
and  toward  it  in  the  other.  The  expression  for  the  horizontal  com- 
ponents of  motion  generated  by  the  second  poid  is  given,  therefore, 

by, 

,'H  =  -  I'  COS  (TT  +  *{)  -  |  COS  2(ir  +  ftf)  -  |'  COS  3(7r  +  *{)  -  .  .  . 
=  |  cos  *£  -  |  cos  2k£  +  I  cos  3*{  -  .  .  .  (9) 

As  shown  by  the  directed  arrows  in  Fig.  3,  when  the  displacement  of 
the  groove  is  away  from  the  center  of  the  record  the  stylus  is  forced 
to  move  part  way  in  this  direction  by  the  displacement  of  the  inner 
groove  wall,  and  allowed  to  slide  the  remainder  of  the  way  by  the 
retreat  of  the  other  wall. 

The  total  lateral  motion  of  the  stylus  is,  therefore,  the  sum  of 
the  motions  induced  by  both  sidewalls,  or 

T;H  =  a\  cos  k£  +  o3  cos  3k£  -f-  .  .  .  (10) 

This  yields  at  once  the  important  result  that  the  even  harmonics  of 
the  fundamental  frequency  are  cancelled  out  of  the  lateral  motion 
of  the  reproducer  stylus.  Returning  to  equation  7  and  projecting 
the  poid  on  the  vertical  plane  through  H  by  multiplying  the  equation 
by  sin  a,  we  find  for  the  component  of  vertical  motion  induced  by  the 
sidewall  BC, 

.    a\  tan  a    .   .  a?,  tan  a    _.  ,  .  .  0,3  tan  a    _  ,        /  -  -  \ 
TI'  =  -L~  -  cos  k£  +  ==-  -  cos  2k£  +  —  —  cos  3k£  +  .  .  .  (11) 


For  the  component  of  motion  induced  by  the  opposite  sidewall  we 
have  still  the  180-degree  displacement  in  phase,  but  the  direction  of 
the  displacement  represented  by  the  poid  is  in  this  case  the  same, 
that  is,  upward.  Hence,  for  the  wall  AB, 


„        a\  tan  a        ,      .    ,  fcN    ,  a2  tan  a        n, 
il'y  =  — g cos  ^  +  k®  ^ 2 —  °°S    ^  + 


cos  3(,r 


Aug.,  1938]          DISTORTION  IN  SOUND  REPRODUCTION  167 

..  (M) 

As  before,  the  resultant  vertical  motion  is  given  by  the  sum  of  the 
components  of  motion  induced  by  the  two  sidewalls  and  is 

i)v  =  az  tan  a  cos  2k£  +  .  .  .  (13) 

We  may,  therefore,  extend  the  conclusion  stated  above  as  follows: 
the  lateral  motion  of  a  stylus  tracing  the  groove  of  a  lateral-cut  record  is 
determined  by  the  fundamental  and  odd  harmonics  only  of  the  poid 
characterized  by  the  groove  amplitude,  the  wavelength,  and  the  needle 
radius;  the  even  harmonics  of  the  poid  appear  as  vertical  motion  and 
constitute  the  "pinch"  effect. 

It  may  be  pointed  out  for  contrast  that  in  the  corresponding  case 
of  a  vertical-cut  record  the  motion  of  the  two  sidewalls  is  in  phase, 
the  maxima  of  the  two  poids  occur  simultaneously,  the  lateral  mo- 
tion is  completely  cancelled  out,  and  all  the  harmonic  constituents  of 
the  poid  enter  into  the  expression  for  the  total  vertical  motion. 

The  difference  in  the  distortions  arising  in  the  reproduction  of 
these  two  types  of  groove  modulation  is  emphasized  by  the  observa- 
tion that  positive  drive  of  the  stylus  tip  by  both  sidewalls  of  the  groove 
yields  the  usual  advantages  of  a  push-pull  system,  with  the  result 
that  a  large  part  of  the  distortion  inherent  in  the  reproduction  of  vertical- 
cut  records  is  entirely  absent  in  the  reproduction  of  lateral-cut  records 
when  a  satisfactory  lateral  reproducer  is  employed.  The  latter  qualifi- 
cation is  added  to  indicate  that  the  specifications  of  the  ideal  lateral 
reproducer  here  assumed  are  somewhat  unconventional,  and  these 
reduced  distortion  levels  are  not  to  be  expected  generally  with  the 
present  types  of  conventional  lateral  reproducers. 

On  this  basis  we  may  return  to  the  original  data  upon  which  the 
dashed  contours  of  Fig.  4  were  based  and  compute  the  root-mean- 
square  value  of  the  odd  harmonics,  prepare  a  set  of  intermediate 
curves,  and  establish  the  solid-line  contours  as  characteristic  of  the 
distortion  generated  in  the  reproduction  of  a  lateral-cut  record. 

CHARACTERISTICS  OF  THE  *a-*r  CHART 

We  turn  now  to  a  more  detailed  discussion  of  the  chart  upon  which 
contours  of  constant  distortion  are  represented.  A  choice  of  loga- 
rithmic scales  for  the  two  coordinate  axes  endows  the  contour 
chart  with  the  interesting  property  that  almost  all  the  characteristic 
quantities,  in  terms  of  which  the  performance  of  a  phonograph  system 


168  J.  A.  PIERCE  AND  F.  V.  HUNT  [j.  s.  M.  p.  E. 

is  analyzed,  are  represented  on  the  chart  by  straight  lines  which  are 
horizontal,  vertical,  or  inclined  at  45  degrees  to  the  principal  axes. 

(A)  The  ordinate  scale,  ka,  gives  directly  the  ratio  of  the  maxi- 
mum cyclic  stylus  velocity  to  the  tangential  groove  velocity,  so  that, 
other  factors  being  held  constant,  a  vertical  line  on  the  chart  repre- 
sents a  change  in  the  recorded  velocity  amplitude.     Since  the  or- 
dinate scale  is  logarithmic,  a  uniform  scale,  as  appended  to  the  right- 
hand  margin  of  the  chart,  may  yield  the  velocity  amplitude  in  deci- 
bels referred  to  the  tangential  groove  velocity  as  zero  level.     Such 
a  scale  is  convenient  for  estimating  changes  in  the  recorded  level. 

The  maximum  radial  velocity  of  the  stylus  occurs  as  the  center-line 
of  the  groove  crosses  the  line  of  the  unmodulated  groove,  and  the 
cutting  angle  is  therefore  a  maximum  at  that  time.  The  tangent  of 
this  angle  is  given  directly  by  ka  so  that  a  subsidiary  scale  may  be 
appended  to  the  upper  right-hand  corner  of  the  contour  chart  es- 
tablishing the  minimum  value  of  the  clearance  angle  of  the  cutting 
stylus  required  in  order  that  the  groove  be  cut  without  interference 
from  the  trailing  edge. 

(B)  A  45-degree  line  on  the  contour  chart  extending  from  the 
lower  left  to  the  upper  right  is  a  line  corresponding  to  a  constant  ratio 
of  the  amplitude  of  groove  modulation  to  the  stylus  tip  radius. 
Along  such  a  sloping  line,  drawn  for  a  given  ratio,  a/r,  one  may  plot 
frequency  increasing  upward  to  the  right  or  tangential  groove  ve- 
locity increasing  downward  to  the  left,  according  as  one  or  the  other 
variable  is  assumed  constant. 

(C)  As  indicated  under  A,  a  horizontal  line  on  the  contour  chart 
is  a  line  of  constant  velocity  amplitude.     Inasmuch  as  this  represents 
the  usual  ideal  recording  situation  it  represents  an  important  locus, 
and,  in  general,  frequency  increases  toward  the  right  along  such  a 
horizontal  line.     There  will  always  be,  for  any  assumed  standard 
conditions  of  record  speed,  maximum  amplitude,  and  stylus  radius, 
some  record  radius  for  which  a  horizontal  line  would  allow  frequency 
to  be  read  directly  from  the  scale  of  abscissa,  in  kilocycles.     This 
record  radius  is  frequently  an  unusable  one,  but  the  reference  line  so 
denned  is  convenient  in  that  a  frequency  may  be  located  on  this  line 
and  a  projection  made  along  a  45-degree  line  downward  to  the  left 
to  the  record  radius  desired. 

(D)  A  45-degree  line  extending  from  the  lower  right  to  the  upper 
left  is  a  line  for  which  the  product  of  ka  and  kr  is  constant.     It  can  be 
shown  that  along  such  a  line  the  ratio  of  the  radius  of  the  needle  tip 


Aug.,  1938]          DISTORTION  IN  SOUND  REPRODUCTION  169 

to  the  minimum  radius  of  curvature  of  the  record  groove  is  constant. 
For  example,  a  line  having  this  slope  and  passing  through  the  (1,1) 
point  is  the  line  for  which  the  ratio  of  these  curvatures  is  unity.  All 
traced  curves  represented  by  points  lying  above  and  to  the  right  of 
this  line  are  poids  having  a  cusp. 

APPROXIMATE  GENERALIZATION  OF  THE  DISTORTION  DATA 

One  striking  characteristic  of  the  constant-distortion  contours 
exhibited  in  Fig.  4  is  the  fact  that,  except  in  the  upper  portion  cor- 
responding to  extreme  values  of  velocity  amplitude,  the  contours 
are  straight  lines  inclined  at  45  degrees  to  the  principal  axes.  So  far 
as  this  is  an  accurate  description  of  the  contours,  we  may  derive  cer- 
tain general  relationships  by  examining  the  distortion  as  this  family 
of  45-degree  lines  is  cut  by  other  lines  representing  loci  of  constant 
parameters  of  the  recording  conditions. 

(1)  As  suggested  above  under  D,  a  45-degree  line  having  the  orien- 
tation of  the  contours  is  a  line  along  which  the  ratio  of  the  needle  tip 
radius  to  the  minimum  radius  of  groove  curvature  is  constant.  Ex- 
amination of  the  contours  indicates  that  for  vertical  reproduction 
the  total  distortion  varies  linearly  with  the  ratio  of  these  radii.  For 
lateral  reproduction  the  total  distortion  is  smaller  and  varies  as  the 
square  of  this  ratio.  It  may  be  pointed  out  that  if  the  frequency,  the 
groove  speed,  and  the  needle  tip  radius  are  constant,  then  the  ratio 
of  the  groove  and  needle  tip  curvatures,  and  hence  the  total  distortion 
for  vertical  reproduction,  is  a  linear  function  of  the  recorded  ampli- 
tude. For  lateral  reproduction  the  corresponding  total  distortion  is 
proportional  to  the  square  of  the  recorded  amplitude.  The  ratio  of 
the  radii  of  curvature  has  frequently  been  offered  as  a  criterion  of  the 
upper  limit  of  frequency  that  could  be  reproduced  satisfactorily. 
Our  study  indicates  that  this  is  indeed  a  satisfactory  rough  criterion 
of  distortion,  and  it  may  be  seen  from  the  chart  that  equality  in  these 
radii  corresponds  to  approximately  40  per  cent  total  distortion  for 
vertical  reproduction  and  20  per  cent  total  distortion  for  lateral  re- 
production. If  one  selects  10  per  cent  total  distortion  as  a  tolerable 
limit,  the  required  ratios  are  approximately  3/6  for  lateral  and  1/6  for 
vertical. 

The  velocity  amplitude  of  any  harmonic  component,  relative  to 
the  fundamental  component,  may  be  determined  by  the  simple  em- 
pirical relationship, 

(kakr}n~l 
Hn  =  (KaKT)  (14} 


170 


J.  A.  PIERCE  AND  F.  V.  HUNT 


[J.  S.  M.  p.  E. 


*\ 

VERTICAL 


A° 


\ 


60- 

I50" 
^40- 

H 


*t 

riii 


\ 


CONTOURS  Of  CONSTANT   PERCENTAGE    R.M  S.    HARMONIC    DISTORTION 

FIG.  4.  Universal  chart,  for  velocity-responsive  systems,  dis- 
playing contours  of  constant  rms.  total  harmonic  distortion,  for 
both  vertical-  and  lateral-cut  records,  plotted  against  the  di- 
mensionless  independent  variables  ka  and  kr. 


R/DIUU 


TS 


1  1 


\ 


47T 


CONTOIJRS   OF  CONSTANT    PERCENTAGE    R.MS.    HARMONIC    DISTORTION. 

FIG.  5.  Recording  loci  superimposed  upon  the  ka-kr  chart. 
Along  the  heavy  reference  line  for  V  =  4?r  in. /sec.  the  frequency 
may  be  read  directly  in  kilocycles  from  the  abscissa  scale. 


Aug.,  1938]          DISTORTION  IN  SOUND  REPRODUCTION  171 

where  n  is  the  number  of  the  harmonic.  Comparison  of  this  relation 
with  the  preceding  approximate  statements  about  the  variation  of 
the  total  harmonic  distortion  confirms  the  fact  that  the  principal 
component  of  distortion  for  vertical  reproduction  is  a  second  har- 
monic, while  the  principal  distortion  component  for  lateral  reproduc- 
tion is  a  third  harmonic. 

(2)  A  horizontal  line,  as  discussed  under  C  above,  is  a  line  of  con- 
stant velocity  amplitude,  along  which  frequency  increases  toward 
the  right.     Examination  of  the  chart  reveals  that  total  distortion 
varies  directly  with  the  frequency  for  vertical  reproduction  and  as 
the  square  of  the  frequency  for  lateral  reproduction.     On  the  other 
hand,  if  the  frequency  and  other  reproducing  conditions  remain  con- 
stant, then  points  corresponding  to  a  variation  in  needle  tip  radius 
will  lie  along  the  horizontal  line,  and  the  total  distortion  will  increase 
linearly  with  the  needle  tip  radius  for  vertical  and  as  the  square  of 
the  needle  tip  radius  for  lateral. 

(3)  If  both  the  recorded  velocity  amplitude  and  the  needle  tip 
radius  be  held  constant  as  either  the  record  radius  or  the  record  speed 
is  varied,  the  values  of  both  ka  and  kr  change  simultaneously,  so  that 
the  contour  curves  are  crossed  along  a  45-degree  line  extending  from 
lower  left  to  upper  right.     Examination  of  the  chart  then  indicates 
that,  for  vertical  reproduction,  the  total  distortion  varies  inversely 
as  the  square  of  either  the  record  radius  or  the  record  speed,  accord- 
ing as  one  or  the  other  of  the  two  variables  is  held  constant.     For 
lateral  reproduction  the  total  distortion  increases  inversely  as  the 
record  radius  or  record  speed  raised  to  the  fourth  power. 

Summarizing  these  approximate  relations,  we  may  say  that  in 
general  the  distortion  obtained  in  lateral  reproduction  is  always  lower 
than  in  vertical  but  that  it  varies  more  rapidly  with  the  parameter 
introducing  the  distortion.  Two  additional  characteristics  of  the 
contour  chart  may  be  pointed  out  in  this  connection.  The  total  dis- 
tortion for  either  lateral  or  vertical  shows  a  distinct  "saturation"  as 
the  distortion  approaches  some  high  value.  In  the  case  of  lateral 
this  saturation  value  is  approximately  48  per  cent;  for  vertical  the 
saturation  value  is  nearly  80  per  cent.  It  will  be  noted  that  no  con- 
tours have  been  drawn  on  the  chart  indicating  the  reduction  in  the 
amplitude  of  the  fundamental  component  as  the  distortion  increases. 
This  omission  was  made  in  the  interests  of  avoiding  confusion  in  the 
contour  chart.  The  data  indicate  that  the  contour  lines  correspond- 
ing to  20  per  cent  distortion  for  lateral  or  40  per  cent  distortion  for 


172  J.  A.  PIERCE  AND  F.  V.  HUNT  [j.  s.  M.  P.  E. 

vertical  correspond  roughly  to  a  reduction  in  fundamental  amplitude 
of  approximately  0.7  db.  in  either  case.  It  is  obvious  therefore  that 
the  total  harmonic  distortion  will  have  reached  intolerable  propor- 
tions before  there  is  any  significant  reduction  in  fundamental  ampli- 
tude. It  follows  that  an  appreciable  "quality"  difference  between 
the  inside  and  outside  radii  of  a  recording,  detectable  as  a  loss  in  high 
frequencies,  must  inevitably  be  accompanied  by  a  serious  increase  in 
harmonic  distortion  and  should  never  be  tolerated  in  a  high-fidelity 
system.  The  provision  of  variable  equalization  for  recording  at  the 
inside  of  a  record ,  which  has  been  seriously  proposed,  appears  to  be 
defensible  only  as  a  partial  corrective  for  the  characteristics  of  a  re- 
corder that  relies  principally  upon  the  recording  medium  for  damping. 

DISTORTION  ANALYSIS  FOR  TYPICAL  RECORDING  CONDITIONS 

We  shall  now  illustrate  the  application  of  the  contour  chart  to  an 
evaluation  of  the  distortion  arising  under  typical  recording  condi- 
tions. We  shall  assume  for  this  purpose  that  the  record  is  cut  with 
100  grooves  per  inch,  each  groove  being  6  mils  wide  at  the  surface  of 
the  record,  2.5  mils  deep,  with  an  included  angle  of  90  degrees,  and 
having  a  bottom  surface  rounded  to  a  radius  of  curvature  of  approxi- 
mately 1.25  mils.  Under  these  conditions  the  assumptions  regarding 
support  of  the  stylus  tip  by  the  sidewalls  of  the  groove  may  be  satis- 
fied by  a  stylus  having  a  tip  radius  of  2  mils.  The  maximum  al- 
lowable amplitude  of  modulation,  determined  by  the  groove  spacing, 
will  also  be  2  mils.  If  the  record  is  vertical-cut,  only  the  assumed 
values  of  a  and  r  are  material.  For  the  standard  recording  condi- 
tions we  shall  assume  that  the  amplitude  of  the  cut  is  constant  for 
frequencies  up  to  300  cycles,  and  that  the  velocity  amplitude  is  main- 
tained constant  at  all  higher  frequencies.  The  constant-amplitude 
portion  of  this  recording  locus  is  represented  by  the  left-hand  margin 
of  the  parallelogram  superimposed  upon  a  ka-kr  chart  in  Fig.  5. 
Frequency  increases  upward  along  the  left-hand  border  of  the  paral- 
lelogram, and  the  frequency  300  cycles,  at  which  the  recording  locus 
breaks  into  a  horizontal  line,  occurs  at  some  point  dependent  upon 
the  tangential  groove  velocity.  Four  such  horizontal  lines  are  il- 
lustrated, corresponding  to  the  inside  and  outside  radii  of  typical 
33  and  78  rpm.  recordings.  For  the  assumed  stylus  tip  radius  the 
reference  line  along  which  frequency  may  be  read  directly  from  the 
scale  of  abscissas  occurs  at  a  groove  velocity  of  4ir  inches  per  second. 
A  45-degree  system  of  projection  coordinates  is  based  upon  this  ref- 


Aug.,  1938] 


DISTORTION  IN  SOUND  REPRODUCTION 


173 


erence  line  and  allows  any  frequency,  established  along  the  reference 
line,  to  be  referred  to  the  appropriate  record  radius.  For  example,  if 
it  is  desired  to  determine  the  distortion  at  5000  cycles,  2-inch  radius, 
78  rpm.,  the  procedure  is  as  follows:  follow  the  ordinate  kr  =  5 
upward  to  the  standard  reference  line,  trace  downward  along  the  45- 
degree  line  to  its  intersection  with  the  horizontal  corresponding  to 
78  rpm.,  2-inch  radius,  interpolate  between  the  contours  to  determine 


REC 

ORD     1 

1 

/ 

/ 

33  '/3  R.P.M. 

RADIUS    T 

1 

1 

/       y 

STYLUS    TIP    RA 

DIUS 

o.c 
oc 

02 

11 

y  ' 

^ 

*/ 

/ 

/ 

AMPLITUDE  -  0.002" 

/ 

/ 

/ 

/ 

M/ 

L 

/ 

I/ 

' 

^ 

s 

/ 

, 

X 

R  = 

8" 

|    < 

/ 

^ 

'' 

-' 

A 

^' 

' 

\ 

._ 

-  —  ' 

^s**^*^ 



^ 

• 

1 

100  200 


500  1000  2000  5000  10000         20000 

FREQUENCY    IN    CYCLES 


FIG.  6.     Total  distortion  plotted  as  a  function  of  frequency  for  con- 
stant velocity  amplitude  and  typical  recording  conditions. 


the  total  (lateral)  harmonic  distortion  as  22  per  cent.  Following 
this  procedure  we  may  derive  the  data  exhibited  in  Fig.  6,  showing  the 
rms.  total  distortion  at  typical  inside  and  outside  radii  for  33-  and 
78-rpm.  recordings,  both  lateral-  and  vertical-cut.  These  curves 
exhibit  clearly  the  marked  superiority  of  lateral-cut  over  vertical-cut 
with  regard  to  distortion,  and  indicate  also  the  more  rapid  increase  in 
distortion  for  lateral-cut  as  the  frequency  increases.  One  may  be 
pardoned  for  wondering,  on  examination  of  the  curves  of  Fig.  6,  how 
it  can  be  that  records  sound  as  well  as  they  do  in  view  of  these  serious 


174 


J.  A.  PIERCE  AND  F.  V.  HUNT 


fj.  S.  M.  P.  E. 


distortions.  The  explanation  of  this  anomaly  lies  in  the  fact  that 
speech  and  music  by  no  means  present  the  recording  medium  with 
the  necessity  of  recording  a  constant  velocity  amplitude  at  all  fre- 
quencies. The  valuable  data  of  Sivian,  Dunn,  and  White4  on  the 
intensity  distributions  in  speech  and  music  are  available  for  an  eval- 
uation of  this  situation.  We  present  our  interpretation  of  these  data 
in  Fig.  7  in  order  to  avoid  any  ambiguity  about  the  application  of 
this  correction.  The  two  curves  for  speech  and  music  are  arbitrarily 
shifted  vertically  to  have  the  same  peak  amplitude  inasmuch  as  an 
adequate  volume  indicator  should  indicate  these  peaks  and  provide 
a  common  basis  for  level  control.  The  manner  of  applying  these 
correction  data  to  the  distortion  contours  consists  in  locating  fre- 


S 

rMPHONIC/'  , 

MUSIC,  ^y/ 

^ 

--' 

>< 

^ 

^ 

^^ 

>s 

"X 

/ 
~ 

'Y  / 

^ 

^ 

x 

/ 

/ 

/   /^-SPEE 

M 

\ 

"• 

^ 

» 

. 

/ 

/,' 

\ 

7 

\ 

0                                ICO                           300                              1000                         3000 
FREQUENCY     IN    CYCLES 

0000 

FIG.  7.  Peak  power  as  a  function  of  frequency  (from  the  data 
of  Sivian,  Dunn,  and  White)  used  to  evaluate  the  distortion  in  re- 
corded speech  or  music. 

quencies  along  the  broken-straight-line  recording  locus  as  before, 
but  interpolating  between  the  contours  for  a  point  shifted  vertically 
downward  by  the  number  of  decibels  plotted  for  the  corresponding 
frequency  in  Fig.  7.  These  corrected  values  of  distortion  might  be 
shown  along  with  the  curves  of  Fig.  6  for  constant  velocity  ampli- 
tude, but  for  the  illustration  of  an  alternative  method  of  exhibiting 
these  data,  we  have  prepared  the  curves  of  Fig.  8.  These  show  the 
minimum  value  of  record  radius  that  will  allow  the  music  spectrum 
of  Fig.  7  to  be  recorded  with  a  total  distortion  not  exceeding  10  per 
cent,  plotted  as  a  function  of  the  frequency.  The  corresponding 
correction  for  speech  would  yield  similar  curves  but  without  further 
rise  beyond  2500  cycles.  The  nearly  horizontal  portions  of  the 
curves  of  Fig.  8  indicate  that  the  present  accepted  standard  inside 
radii  for  lateral-cut  transcription  and  commercial  pressings  are  ac- 


Aug.,  1938]          DISTORTION  IN  SOUND  REPRODUCTION  175 

ceptable  for  the  satisfaction  of  the  10-per  cent  distortion  limit,  but 
that,  for  the  assumed  amplitude  of  groove  modulation,  the  33-rpm. 
vertical  transcription  record  is  not  capable  of  meeting  the  10-per  cent 
distortion  specification  without  a  reduction  in  needle  tip  radius. 

EXPERIMENTAL  CONFIRMATION  OF  THE  DISTORTION  DATA 

In  connection  with  his  study  of  vertical  reproduction,  DiToro2 
has  measured  the  relative  amplitude  of  the  second  harmonic  for  values 
of  ka  and  kr  lying  in  the  lower  right-hand  corner  of  our  contour  dia- 
gram. The  agreement  between  his  experimental  observations  and 
our  calculations  is  quite  good  for  this  type  of  measurement,  and  may 
be  considered  adequate  to  confirm  the  dotted  contours  of  Fig.  4. 

In  view  of  the  significantly  lower  distortion  revealed  by  this  study 
to  be  characteristic  of  lateral  reproduction,  it  seems  worth  while  to 
present  some  experimental  data  confirming  these  predictions.  A 
direct-reading  distortion  meter  operating  at  400  cycles  was  used,  and 
in  order  to  simulate  the  conditions  that  would  occur  at  a  higher  fre- 
quency at  normal  groove  velocities,  records  were  made  and  played 
back  at  speeds  of  9  and  13  rpm.  By  thus  shortening  the  wavelength, 
values  of  ka  as  high  as  0.7  were  obtained  with  kr  no  greater  than  2,  so 
that  we  were  able  to  investigate  the  most  useful  part  of  the  ka-kr 
diagram.  A  new  type  of  lateral  reproducer5  satisfying  the  conditions 
assumed  in  the  distortion  analysis  was  employed. 

The  test  grooves  were  cut  on  lacquer-coated  records.  The  cutting 
head  used  relies  to  some  extent  upon  the  record  material  for  damping 
and  so  did  not  yield  a  constant  amplitude  at  all  groove  speeds.  This 
was  taken  into  account  in  constructing  the  solid  "calculated"  curves 
of  Fig.  9,  the  larger  amplitudes  being  measured  optically  while  the 
smaller  were  found  by  measuring  the  relative  reproducer  outputs  at 
the  fundamental  frequency.  Measurements  were  made  at  various 
record  radii  for  two  record  speeds  and  for  three  different  recording 
levels.  The  results  are  shown  in  Fig.  9  and  seem  to  provide  a  wholly 
satisfactory  verification  of  the  mathematical  analysis. 

The  residual  distortion  levels  of  2,  5,  and  10  per  cent,  shown  at  the 
right-hand  side  of  Fig.  9,  may  be  attributed  to  the  recording  equip- 
ment, and  principally  to  the  recording  head  itself.  It  is,  however, 
obvious  that  for  the  smaller  values  of  tangential  groove  velocity 
tracing  distortion  is  the  predominant  factor,  and  that  its  magnitude 
has  the  calculated  value.  It  may  also  be  concluded  that  not  only 
were  the  reproducer  specifications  satisfactorily  met,  but  that  the 


176 


J.  A.  PIERCE  AND  F.  V.  HUNT 


[J.  S.  M.  p.  E. 


1000         .  3000 

FREQUENCY    IN    CYCLES 


FIG.  8.  Distortion  data  for  the  music  spectrum  (solid  lines),  ex- 
hibited by  plotting  the  minimum  groove  radius  for  which  the  dis- 
tortion will  never  exceed  10  per  cent.  The  dashed  curves  corre- 
spond to  constant  recorded  velocity  amplitude. 


456 
TANGENTIAL    GROOVE    VELOCITY   IN    INCHES    PER    SECOND 

FIG.  9.     Experimental  data  verifying  the  calculated  distortion  for 
lateral  reproduction. 


Aug.,  1938]          DISTORTION  IN  SOUND  REPRODUCTION  177 

assumption  made  in  the  analysis  regarding  the  negligibility  of  mo- 
mentary deformations  of  the  groove  sidewalls  was  justified. 

CONCLUSIONS   AND    RECOMMENDATIONS 

A  method  of  reducing  the  effective  surface  noise  level  has  been  sug- 
gested, and  in  some  cases  utilized,  that  consists  in  predistorting  the 
recording  frequency  characteristic  in  such  a  way  that  high-frequency 
components  are  recorded  at  an  increased  level.  Complementary 
equalization  in  the  reproducing  system  restores  the  original  balance 
and  at  the  same  time  suppresses  a  portion  of  the  surface  noise  gener- 
ated in  reproduction.  The  distortion  contour  chart  provides  a 
method  of  evaluating  the  effect  upon  harmonic  distortion  of  this  type 
of  alteration  of  the  frequency  response  of  the  recording  system.  We 
have  indicated  above  that  in  vertical -cut  records  the  total  distortion 
is  a  linear  function  of  the  recorded  amplitude  so  that  it  would  appear 
at  first  sight  that  it  would  be  permissible  to  enhance  the  high  fre- 
quencies in  recording,  allowing  the  distortion  to  increase  linearly, 
and  in  the  complementary  equalization  not  only  restore  the  original 
tonal  balance  but  also  return  the  relative  harmonic  distortion  to  the 
original  value  it  would  have  had  without  modification.  This  is  in- 
deed a  useful  method  of  reducing  effective  surface  noise  so  long  as  its 
use  does  not  increase  the  distortion  beyond  the  range  for  which  the 
second  harmonic,  which  is  the  component  varying  linearly  with  am- 
plitude, is  the  principal  distortion  factor.  If  significant  distortion 
terms  higher  than  the  second  occur,  not  only  will  they  increase  more 
rapidly,  and  hence  not  be  proportionately  removed  by  the  reproduc- 
ing equalization,  but  the  higher  terms  will  also  contribute  cross- 
modulation  products  which  would  not  have  been  present  at  the 
original  distortion  level.  Inasmuch  as  the  distortion  level  is  already 
high  for  vertical  reproduction  under  typical  conditions  of  groove 
amplitude  and  stylus  radius,  it  appears  that  the  gain  to  be  derived 
from  a  predistorting  technic  is  rather  limited.  On  the  other  hand,  in 
the  case  of  lateral  groove  modulation,  the  total  distortion  increases 
with  the  square  of  the  recorded  amplitude,  so  that  an  increase  in 
distortion  introduced  by  modification  of  the  recording  frequency 
characteristic  would  not  be  compensated  by  complementary  equali- 
zation in  the  reproducing  system.  It  appears,  therefore,  that  in  this 
case  the  predistorting  technic  can  never  be  employed  unless  the  needle 
tip  radius  can  be  reduced  to  such  an  extent  that  tracing  distortion  is 
a  negligible  factor  in  the  overall  distortion  of  the  system. 


178  J.  A.  PIERCE  AND  F.  V.  HUNT  [j.  s.  M.  p.  E. 

The  effect  of  cross-modulation  mentioned  above  should  be  em- 
phasized in  connection  with  the  curves  of  Figs.  6  and  8.  It  is  probable 
that  we  are  seldom  if  ever  interested  in  the  harmonic  distortion  com- 
ponents accompanying  fundamental  frequencies  higher  than  4000 
to  6000  cycles.  On  the  other  hand,  the  cross-modulation  products 
that  accompany  such  distortion  are  of  considerable  interest,  and,  al- 
though difficult  to  analyze  accurately,  are  approximately  of  the  same 
magnitude  as  the  harmonic  components  themselves.  Thus,  all  the 
distortion  data  presented  above  for  frequencies  higher  than  about 
5000  cycles  are  to  be  interpreted  as  indicative  of  the  magnitude  of 
the  cross-modulation  components.  These  components  are  observed 
aurally  in  wide-range  systems  as  a  "burr"  accompanying  loud  pas- 
sages. The  sum  and  difference  tones,  being  inharmonic,  are  more 
objectionable  than  comparable  harmonic  overtones.  Thus,  even 
though  the  overtones  of  these  high  frequencies  may  be  outside  the 
transmission  band  of  the  reproducing  channel,  the  distortion  limits 
that  should  be  imposed  upon  a  high-fidelity  system  are  more  severe 
than  for  the  lower  frequencies.  These  considerations  indicate  that 
the  10-per  cent  distortion  limit  assumed  for  the  curves  of  Fig.  8  is 
too  high  to  be  acceptable  if  the  overall  system  response  is  to  extend 
significantly  above  5000  cycles. 

A  second  conclusion  can  be  drawn  from  the  foregoing  exhibition 
of  the  distortion  performance  of  typical  vertical  and  lateral  recording 
conditions,  based  upon  the  broken-straight-line  envelope  of  the  peak- 
power  correction  curve  shown  in  Fig.  7.  It  may  be  seen  from  this 
curve  that  the  low-frequency  peak  amplitude  falls  off  by  slightly 
more  than  6  db.  per  octave  for  frequencies  below  250.  On  the  other 
hand,  this  is  exactly  the  reduction  in  velocity  amplitude  that  one 
seeks  to  gain  by  altering  the  standard  cut  from  constant  velocity  to 
constant  amplitude  for  frequencies  below  250-300  cycles.  The  con- 
clusion is  that  there  is  no  real  necessity  for  altering  the  character  of 
the  cut  from  constant  velocity  to  constant  amplitudes  at  this  low 
frequency.  If  the  "standard"  cut  is  maintained  at  constant  velocity 
amplitude  for  the  entire  spectrum  the  greatest  danger  of  "over- 
cutting"  would  still  occur  in  the  neighborhood  of  300  cycles,  just  as 
under  the  present  "standard"  conditions,  but  it  would  then  become 
unnecessary  to  provide  electrical  equalization  for  the  range  below 
300  cycles,  as  is  at  present  required  with  high-fidelity  recording  and 
reproducing  equipment. 

A  third  conclusion  and  recommendation  may  be  based  upon  a  pos- 


Aug.,  1938] 


DISTORTION  IN  SOUND  REPRODUCTION 


179 


sible  modification  of  the  ''standard"  groove  cross-sectional  shape 
used  in  lateral  recording.  It  seems  almost  certain  that  a  lateral 
reproducer  having  the  necessary  vertical  mobility  assumed  in  the 
foregoing  analysis  can  be  designed  to  exert  extremely  light  forces 
upon  the  groove  wall.  If  this  feature  of  the  design  can  be  carried  far 
enough  there  is  no  reason  why  the  needle  tip  radius  may  not  be  re- 
duced to  less  than  1  mil.  If  these  conditions  are  satisfied  there  is 
then  no  necessity  for  (a)  a  total  groove  depth  of  2.5  mils,  or  (b)  such 
a  large  rounded  bottom  portion  of  the  groove.  For  example,  a  sharp 
bottomed  (or  very  slightly  rounded)  groove  2  mils  wide  should  be 
adequate  to  provide  tracking  for  a  reproducer  capable  of  operating 
satisfactorily  with  a  stylus  tip  radius  of  0.75  mil.  If  the  desired 
maximum  amplitude  of  groove  modulation  be  retained  at  2  mils, 
there  would  be  a  net  saving  of  some  40  per  cent  of  the  available  rec- 
ord surface,  so  that  a  groove  pitch  of  175  per  inch  could  be  used. 

TABLE  I 

Playing  Time  in  Minutes 


Size  and 
Speed  of 
Record 

r  =  2  Mils 
100  Grooves/ 
Inch 

r  =  0.75  Mil 
175  Grooves/ 
Inch 

r  =  2  Mils 
100  Grooves/ 
Inch 

r  =  0.75  Mil 
175  Grooves/ 
Inch 

10-per  cent  distortion 

5-per  cent  distortion 

10"—  78  rpm. 

4.2 

8.8 

3.8 

8.3 

12"  —  78  rpm. 

5.5 

11.0 

5.1 

10.5 

16"  —  78  rpm. 

8.1 

15.5 

7.7 

15.0 

12"—  33  rpm. 

6.9 

19.2 

4.8 

16.8 

16"—  33  rpm. 

12.9 

29.7 

10.8 

27.3 

Such  groove  spacing  would  allow  as  much  as  30  minutes  of  recording 
on  each  side  of  a  16-inch,  33  rpm.  transcription  record,  with  no  sacri- 
fice in  the  present  available  recorded  levels,  and  with  a  material  re- 
duction in  total  harmonic  and  cross-modulation  distortion  compared 
with  present  transcription  records.  For  a  12-inch,  78-rpm.  record 
suitable  for  home  use  a  total  of  11  minutes  of  recording  would  be 
available  with  a  similar  reduction  in  total  distortion  as  compared 
with  current  practice.  These  reductions  in  harmonic  distortion  and 
the  gain  in  length  of  playing  time  stem  principally  from  the  reduction 
in  radius  of  the  needle  tip  and  the  consequent  desirability  of  reducing 
the  width  of  the  recorded  groove  at  the  record  surface.  Table  I 
exhibits  a  comparison  of  the  playing  times  available  with  a  10-per 
cent  and  a  5-per  cent  distortion  limit,  for  lateral-cut  records. 


180  J.  A.  PIERCE  AND  F.  V.  HUNT  [j.  s.  M.  P.  E. 

The  gain  in  playing  time  and  usefulness  of  the  convenient  12-inch, 
33-rpm.  record  is  worthy  of  note,  as  is  the  fact  that  the  lower  the 
permissible  distortion  the  greater  is  the  advantage  of  the  proposed 
narrow  groove  and  small  stylus  tip. 

To  achieve  comparable  reductions  in  distortion  for  the  present  type 
of  standard,  round-bottomed,  lateral-cut  groove,  Mr.  Olney  has  sug- 
gested to  us  the  possibility  of  using  a  needle  tip  having  either  an 
elliptical  cross-section  presenting  a  small  radius  of  curvature  to  the 
groove  wall,  or,  alternatively,  a  needle  tip  section  consisting  of  a  flat 
circular  disk  perpendicular  to  the  groove  axis  with  the  edges  rounded 
to  a  small  radius. 

Because  this  study  has  enabled  us  to  predict  the  conditions  neces- 
sary to  its  success,  we  wish  to  call  attention  here  to  the  system  of 
controlled  volume  expansion  illustrated  in  Fig.  10.  This  method  has 
been  proposed  before  as  a  means  of  avoiding  volume  distortion,  but 
it  does  not  appear  to  have  made  its  way  into  the  art  as  yet. 

As  the  figure  indicates,  the  only  modification  necessary  in  the 
recording  technic  is  the  introduction  of  a  constant  tone  at  a  point 
in  the  system  preceding  the  gain  control  which  is  used  to  compress 
the  program  material.  This  pilot  tone  must  be  of  such  a  frequency 
that  it  is  within  the  pass-band  of  the  recorder  and  reproducer,  but 
outside  of  the  desired  program  band.  In  the  diagram  we  suggest  a 
12-kc.  pilot  tone,  to  be  used  with  a  10-kc.  program  channel.  No 
other  change  need  be  made  in  the  recording  technic. 

When  such  a  record  is  reproduced  with  conventional  equipment 
not  responsive  to  the  high-frequency  pilot  tone  the  performance  is 
entirely  normal  and  the  user  need  not  be  aware  that  the  record  is  in 
any  way  unusual.  This  seems  to  be  an  important  feature  since  the 
pilot  tone  could  be  introduced  in  commercial  records  without  impair- 
ing their  value  for  use  with  existing  phonographs.  On  the  other  hand, 
if  the  user  wishes  to  take  advantage  of  the  enhanced  volume  range  it 
is  necessary  only  to  employ  a  reproducer  capable  of  responding  to 
frequencies  as  high  as  that  of  the  pilot  tone,  to  segregate  the  pilot 
tone  with  a  filter,  rectify  it,  and  apply  it  to  the  automatic  volume 
control  circuit  of  an  amplifier  similar  to  those  ordinarily  used  in  radio 
receivers.  This  automatic  volume  control  operates  to  maintain  a 
constant  level  of  the  pilot  tone  at  the  amplifier  output.  Since  this 
condition  is  that  which  obtained  during  recording,  the  original  volume 
range  will  have  been  restored.  That  this  is  possible  may  be  made 
clearer  by  consideration  of  the  fact  that  we  now  have  two  independent 


Aug.,  1938] 


DISTORTION  IN  SOUND  REPRODUCTION 


181 


recorded  and  reproduced  channels,  operating  in  synchronism.  By 
proper  use  of  these  two  channels  we  are  able  to  add  their  volume 
ranges  while  listening  to  the  program  material  carried  by  one  of  them. 
The  ka-kr  chart  of  Fig.  4  indicates  that  the  high-frequency  pilot 
tone  will  be  subject  to  considerable  distortion  (and  cross-modulation 
with  the  program  material)  unless  it  is  recorded  at  a  level  substanti- 
ally less  than  that  of  the  program.  In  spite  of  this  restriction  the 
effective  signal-to-noise  ratio  for  the  pilot  channel  may  be  as  high  as 
for  the  program  channel  if  the  control-tone  is  separated  out  with  a 
filter  whose  pass-band  is  no  wider  than  necessary  to  guard  against 


RECORDING 


REPRODUCER 

to  AU 

VOLUM 

• 

AMPLIf 

ER 

""~~ 

FREQUENCY 
DIVIDING 
NETWORK 

1- 

LOUDSPEAKER 

"TOMATIC 
C    «ONTROL 
"CUT 

i. 

RECTIFIER 

REPRODUCTION 

FIG.  10.  Diagram  illustrating  system  for  controlled 
volume  expansion,  capable  of  restoring  full  dynamic 
range  of  original  program  material. 

variations  in  turntable  speed,  and  if  the  time-constant  of  the  auto- 
matic volume  control  circuit  is  large  enough  to  smooth  out  the  irregu- 
larities of  surface  noise. 

In  brief,  such  a  system  of  controlled  volume  expansion  can  fur- 
nish an  accurate  complement  to  the  compression  necessary  in  record- 
ing, and  provide  for  the  re-creation  of  the  desired  program  in  its  full 
dynamic  range.  At  the  same  time,  it  should  be  emphasized  that  such 
records  would  remain  as  satisfactory  as  any  of  those  in  common  use 
when  reproducing  facilities  for  expansion  are  not  available. 

As  an  alternative  method  of  utilizing  a  second  recorded  channel, 
it  may  be  pointed  out  that  if  it  is  undesirable  to  re-create  the  full 
dynamic  range  of  the  original  material  the  control  channel  may  be 
used  to  provide  volume  inflection  while  the  program  is  recorded  well 


182  J.  A.  PIERCE  AND  F.  V.  HUNT  [j.  s.  M.  P.  E. 

above  noise  level  at  all  times.  While  such  records  could  be  used  only 
with  reproducing  equipment  designed  especially  for  them,  they  would 
provide  phonographic  reproductions  entirely  free  from  the  audible 
effects  of  surface  noise. 

In  conclusion  it  may  be  said  that  a  principal  result  of  this  study 
has  been  the  recognition  and  analysis  of  a  large  latent  advantage, 
with  regard  to  distortion,  inherent  in  the  lateral  type  of  groove  modu- 
lation. While  not  all  these  indicated  gains  are  realized  by  the  pres- 
ent conventional  lateral-cut  technic,  we  hope  that  new  reproducer 
designs  and  a  study  of  these  geometrical  relations  will  furnish  some 
guidance  for  significant  improvements  in  the  fidelity  and  usefulness  of 
disk  records. 

REFERENCES 

1  OLNEY,  B.:    Electronics  (Nov.,  1937),  p.  19. 

2  DiToRO,  M.  J.:     "Distortion  in  the  Reproduction  of  Hill-and-Dale  Record- 
ings," /.  Soc.  Mot.  Pict.  Eng.,  XXIX  (Nov.,  1937),  No.  5,  p.  493. 

3  CHAFFBE,  E.  L.:  Rev.  Sci.  Instr.,  7  (1936),  p.  384. 

4  SIVIAN,  DUNN,  AND  WHITE:    /.  Acoust.  Soc.  Amer.,  2  (1931),  p.  330. 
FLETCHER,  H.:     Bell  Syst.  Tech.  J.,  3  (1931),  p.  349;    Rev.  Mod.  Phys.,  3 

(1931),  p.  258;   J.  Acoust.  Soc.  Amer.,  3  (1931),  Supp.,  p.  1. 

5  HUNT,  F.  V.,  AND  PIERCE,  J.  A:    Electronics,  11  (1938),  p.  9. 

DISCUSSION 

MR.  MACNAIR:  The  kind  of  distortion  on  hill-and-dale  records  that  was 
analyzed  in  the  paper  was  discussed  qualitatively  at  the  Fall,  1931,  Meeting  of 
the  Society  (/.  Soc.  Mot.  Pic.  Eng.,  Feb.,  1932,  p.  143).  A  quantitative  analysis 
of  it  appeared  last  year,  and  again  we  have  a  beautiful  analysis  of  the  subject 
presented  to  us  this  morning. 

In  Fig.  1  the  lower  curve  is  a  sine  wave,  showing  the  shape  of  the  bottom  of  a 
groove  cut  in  a  hill-and-dale  record.  When  a  stylus  of  finite  radius  traces  the  sine 
curve,  there  appears  in  the  electrical  output  of  the  reproducer  a  signal  correspond- 
ing to  the  upper  curve  having  the  characteristics  that  were  mentioned  by  Mr. 
Pierce,  namely,  broad  on  the  top  and  sharp  at  the  bottom.  It  is  therefore  not 
a  sine  wave,  and  contains  certain  distortion  products  that  were  not  in  the  original 
cut  record. 

There  are  several  possible  ways  to  correct  for  this  kind  of  distortion.  One  is 
simply  to  dubb  with  the  circuits  poled  properly.  If  one  records  the  signal  picked 
up  from  the  reproducer,  this  upper  shaped  wave  is  recorded  in  the  wax.  But  in 
doing  this  the  circuit  should  be  properly  poled  so  as  to  cut  the  signal  in  the  wax 
as  illustrated  by  turning  Fig.  1  upside  down.  If  the  last  record  is  now  traced  with 
a  stylus  of  the  same  size,  the  signal  reproduced  will  be  the  original  sine  wave. 

What  has  been  done,  then,  is,  when  playing  the  record,  to  get  from  the  re- 
producer a  signal  that  is,  so  far  as  this  kind  of  distortion  is  concerned,  exactly  the 
sine  wave  with  which  you  started,  a  true  picture  of  the  originally  recorded  signal. 


Aug.,  1938]          DISTORTION  IN  SOUND  REPRODUCTION  183 

There  are  other  possible  ways  to  take  care  of  this  distortion,  but  the  way  de- 
scribed, namely,  a  dubbing  process  with  the  circuits  properly  poled,  is  the  easiest 
to  present  here.  Whether  the  distortions  are  of  an  objectionable  magnitude  de- 
pends, as  the  author  pointed  out,  upon  the  recording,  the  level,  and  other  con- 
ditions of  the  process,  and  also  upon  the  purposes  for  which  the  recorded  material 
is  to  be  used.  This  method  of  greatly  reducing  this  form  of  distortion  has  been 
available  for  some  years. 

MR.  PIERCE:  In  order  properly  to  reverse  the  poid  this  way  it  is,  of  course, 
necessary  to  have  a  transmission  band  that  will  pass  all  the  harmonics  generated 
in  the  original  poid.  In  the  extremely  high-frequency  cases,  5000-10,000  cycles, 
it  may  well  require  fourth  and  fifth  harmonics  in  order  to  do  this,  which  calls  for 
a  recording  technic  of  rather  remarkable  excellence  to  do  it  properly. 

A  rather  worse  objection  is  that  cross-modulation  products,  sum  and  difference 
tones  (particularly  difference  tones),  appear  in  the  output  through  this  phenome- 
non. They  are  rather  difficult  to  analyze,  but  may  be  taken  as  more  or  less  of  the 
order  of  magnitude  of  the  harmonic  distortion.  However,  it  is  impossible  to  re- 
produce these  cross-modulation  products  accurately  the  second  time  by  this  dub- 
bing procedure,  which  is  very  unfortunate  because  they  are  the  worst  offenders  so 
far  as  hearing  is  concerned.  Ten  to  15  per  cent  of  pure  harmonic  content  is  toler- 
able, but  when  signals  having  those  energies  appear  at  random  frequencies  not 
associated  with  the  material  being  reproduced,  the  effect  upon  the  ear  is  a  familiar 
burring,  an  unpleasant  form  of  distortion  that  is  heard  when  a  commercial  record 
is  played  through  a  10,000-cycle  channel,  a  way  it  is  not  originally  intended  to  be 
used. 

MR.  COOK:  Have  you  investigated  the  magnitude  of  the  distortion  which 
might  result  from  a  lack  of  needle  tangency  to  the  record  groove? 

MR.  PIERCE:  Not  very  much,  except  to  investigate  it  experimentally.  We 
found  it  was  not  a  very  serious  subject  on  play-back,  but  did  make  quite  a  bit  of 
difference  in  recording.  Mr.  Olney  has  made  a  rather  good  analysis  of  the  subject, 
published,  I  think,  in  Electronics  last  year,  which  indicates  that  with  reasonable 
precaution  it  can  be  kept  down  so  well  as  to  be  practically  out  of  the  picture. 

MR.  COOK:  I  assume  you  refer  to  the  use  of  an  offset  pick-up  head  placed  at 
an  angle  to  the  tone-arm.  It  is  interesting  to  note  that  both  these  expedients 
were  employed  by  the  Brunswick,  Balke,  Collender  Co.  who,  it  is  believed,  first 
proposed  and  used  them  in  their  first  commercial  electrical  phonographs. 

MR.  PIERCE:  That  form  of  correction  is  entirely  applicable.  I  might  point 
out  one  other  thing  that  Mr.  Olney  has  suggested,  which  is  the  use  of  stylus  tips  of 
non-spherical  shape,  so  that  they  present  to  the  edge  of  the  groove  a  smaller 
radius  than  they  have  in  other  dimensions. 

MR.  COOK:  I  was  interested  in  your  recommendation  for  the  use  of  a  control 
tone.  My  first  acquaintance  with  it  was  while  with  the  RCA.  The  results  they 
obtained  were  impressive  and,  as  Mr.  Pierce  has  reported,  it  represents  a  desir- 
able improvement.  Their  work  with  it  was  mentioned  at  the  1935  Spring  Con- 
vention in  Hollywood  in  a  paper  entitled  "A  Consideration  of  Some  Special 
Methods  for  Re-Recording,"  J.  Soc.  Mot.  Pict.  Eng.,  XXV  (Dec.,  1935),  No.  6, 
p.  523. 

MR.  PIERCE:  It  can  be  added  to  present  technics  so  simply  that  it  is  worth 
thinking  about. 


184  J.  A.  PIERCE  AND  F.  V.  HUNT  [j.  s.  M.  P.  E. 

MR.  DAVEE:  For  the  past  two  and  one-half  years  or  so  I  have  been  connected 
with  the  World  Broadcasting  Company.  You  probably  have  heard  their  tran- 
scribed records  over  the  radio,  probably  the  program  of  Chevrolet  with  Graham 
MacNamee.  I  did  not  appreciate  that  this  burring  sound  you  are  discussing 
was  there.  In  all  program  work  of  that  kind  a  certain  amount  of  re-recording  and 
dubbing  has  to  be  done,  as  in  motion  picture  work,  and  as  a  result  we  have  been 
using  this  poled  dubbing  scheme  regularly. 

MR.  KELLOGG:  The  correction  obtainable  by  correctly  poled  dubbing,  or  by 
any  method  that  attempts  to  precompensate  and  give  back  the  desired  wave, 
involves  some  extreme  difficulties,  and  while  I  would  not  for  a  moment  deny  that 
with  reasonably  good  channels  it  would  always  be  helpful,  I  had  not,  until  this 
morning,  realized  that  it  has  ever  been  practically  applied,  unless  the  dubbing 
were  necessary  for  other  purposes.  It  involves,  for  example,  such  difficulties  as 
providing  (when  you  reach  the  limiting  curvature)  infinite  acceleration  of  the 
cutting  stylus. 

In  lateral  recording  it  appears  that  an  analysis  based  upon  purely  geometrical 
relations  leaves  out  so  many  important  factors  that  its  predictions  can  not  be  veri- 
fied by  tests. 

MR.  HASBROUCK:  In  Fig.  2  I  noticed  that  the  stylus  was  shown  as  not  reaching 
the  bottom  of  the  groove.  The  groove  that  we  use,  and  which  is  generally  used 
for  transcription  work,  has  a  radius  at  the  bottom.  The  straight  sides  are  rather 
short  compared  with  the  radius,  and  we  attempt  to  contact  the  spherical  portion 
of  the  stylus  completely  on  the  bottom.  In  that  way  we  distribute  the  weight 
most  uniformly  and  reduce  wear  and  so  forth. 

I  wonder  whether  any  improvement  is  found  in  riding  the  straight  sides  of  the 
groove,  and  whether  it  would  not  increase  the  wear  on  the  record  as  well  as  dis- 
tortion. The  question  of  cold  flow  of  the  record  material  was  not  mentioned. 
It  is  quite  pronounced;  so  much  so,  in  fact,  that  a  pick-up  that  has  one  frequency 
characteristic  on  one  record  material  will  have  another  frequency  characteristic 
on  another  record  material,  depending  upon  the  hardness.  On  these  new  in- 
stantaneous records,  with  fairly  soft  material,  we  have  found  it  very  annoying. 

Also,  as  regards  the  high-frequency  losses,  a  small  playing  diameter  increases 
them  very  greatly,  particularly  with  soft  record  material.  That  would  seem  to 
interfere  with  the  control  tone  idea  to  some  extent.  We  have  measured  losses  at 
10,000  cycles  on  nitrate  lacquer  amounting  to  some  28  db.,  playing  from  an 
8-inch  diameter  to  a  16-inch  diameter.  While  that  could  be  compensated  for  to 
some  extent  in  recording,  I  wonder  whether  it  would  not  make  the  control  tone 
idea  more  complicated. 

MR.  MACNAIR:  This  discussion  may  have  given  the  impression  that  correcting 
distortion  of  this  type  is  very  complicated.  Many  of  you  do  something  similar 
in  the  motion  picture  business  every  day.  If  the  harmonic  content  of  a  variable- 
density  negative  is  analyzed,  harmonics  and  cross-modulation  products  will  be 
found  in  abundance.  These  are  eliminated  by  the  simple  process  of  printing, 
and  certainly  we  do  not  claim  to  print  40,000  cycles  very  well.  There  are  two  ways 
of  looking  at  these  problems.  The  analysis  into  harmonic  components  is  the  more 
appropriate  one  for  some  problems,  and  the  simple  consideration  of  returning  the 
wave  shape  to  its  original  is  another  way  of  looking  at  it. 

The  micromatics  of  harmonic  analysis  for  this  problem  leads  to  great  complica- 


Aug.,  1938]          DISTORTION  IN  SOUND  REPRODUCTION  185 

tion,  and  it  happens  that  the  other  way  of  looking  at  it  is  the  simple  way. 

MR.  PIERCE:  Mr.  Davee's  remarks  point  out  admirably  the  fact  that  our 
established  amplitudes  of  cut,  frequency  response,  record  speed,  stylus  tip  radius, 
and  so  on,  are  all  so  interrelated  as  to  give  a  pleasing  result.  The  types  of  distor- 
tion with  which  we  are  particularly  concerned  here  are  most  readily  observable 
when  standard  commercial  records  are  played  through  a  really  high-fidelity 
system.  In  case  Mr.  Davee  is  really  anxious  to  observe  the  distortions,  we  sug- 
gest that  he  try  listening  only  to  the  frequency  band  between  5000  and  10,000  or 
12,000  cycles. 

I  think  that  Mr.  Kellogg  has  answered  Mr.  MacNair  more  aptly  than  I  was 
able  to  do.  The  effect  of  compensating  by  properly  poled  dubbing  seems  to  put 
the  system  in  push-pull  with  the  pull  appearing  as  a  separate  episode  from  the 
push.  It  is  obvious  that  this  is  a  difficult  technic  to  handle  and  it  is  hard  to  see 
how  the  final  result  can  be  better  than  it  is  in  the  case  where  we  have  a  truly  push- 
pull  system.  We  are  under  the  impression  that  this  poled  dubbing  technic  is  not 
used  as  standard  practice,  so  that  many  vertical-cut  records  are  released  without 
its  advantages.  Mr.  Kellogg's  concluding  remarks  about  the  inadequacy  of 
geometrical  analysis  seems  to  be  effectively  answered  by  the  data  exhibited  in 
our  Fig.  9.  It  is  true  that  other  factors  may  become  important  unless  the  re- 
producer meets  the  requirements  we  have  discussed  in  the  paper. 

The  condition  that  troubles  Mr.  Hasbrouck  has  been  chosen  deliberately,  and 
the  illustration  to  which  he  refers  is  a  fairly  accurate  representation  of  the  geomet- 
rical conditions  obtaining  in  our  equipment.  As  we  have  explained,  this  is  done  to 
prevent  distortion  due  to  "rattling"  of  the  stylus;  in  other  words,  to  provide  posi- 
tive drive  for  the  stylus  which  is  following  a  laterally  modulated  groove.  It  is 
true  that  the  pressures  at  the  points  of  contact  are  greater  than  they  would  be  if 
the  stylus  rested  in  the  bottom  of  the  groove,  but  it  is  possible  to  build  a  reproducer 
that  will  not  deform  the  record  material  even  when  such  a  condition  exists.  As 
we  have  pointed  out,  this  is  necessary  in  order  to  permit  us  to  calculate  distor- 
tion. We  believe  that  the  distortion  so  calculated  will  be  at  least  no  greater  than 
that  caused  by  allowing  the  needle  tip  to  trace  a  random  course  that  we  can  not 
examine  analytically.  The  necessary  requirement  in  this  case  is  that  the  stylus 
must  execute  a  vertical  motion  without  generating  a  corresponding  electrical 
output. 

We  have  been  able  to  show  experimentally  that  instantaneous  cold  flow  of  the 
record  material  is  not  an  important  factor  when  a  sufficiently  light  reproducer  is 
used.  A  simple  and  adequate  way  of  checking  this  fact  is  by  making  a  frequency- 
response  record  and  playing  it  at  more  than  one  speed,  such  at  an  33  Vs  and  78 
rpm.  When  the  record  speed  is  varied  in  this  way  the  output  at  all  corresponding 
frequencies  should  change  by  a  constant  factor.  When  this  is  the  case  it  indicates 
that  the  reproducer  stylus  is  not  deforming  the  record  material  either  temporarily 
or  permanently. 

Variations  in  hardness  of  the  record  material  can  affect  the  frequency  character- 
istic only  because  many  cutting  heads  depend  upon  the  record  material  for  at 
least  part  of  their  damping.  Thus  the  amplitude  of  the  cut  is  a  function  of  fre- 
quency, record  hardness,  and  linear  groove  speed,  instead  of  frequency  alone.  In 
the  best  cutting  heads,  this  effect  is  practically  negligible.  As  we  have  shown  in 
the  paper,  any  variation  in  frequency  response  over  the  record  surface  is  an  indica- 


186  J.  A.  PIERCE  AND  F.  V.  HUNT 

tion  either  of  a  poor  cutting  head  or  of  too  great  cutting  levels.  Variations  in 
amplitude  upon  playback,  of  28  db.,  corresponding  to  only  a  2:1  variation  in 
linear  groove  speed  seem  startling  to  us  and  are  a  strong  indication  of  some  serious 
condition  that  should  be  corrected. 

Mr.  MacNair's  final  argument  is  beautifully  expressed  and  seems  plausible 
but  will  not  bear  close  inspection.  Regardless  of  the  argument  used,  it  is  im- 
possible to  change  the  physical  fact  that  transmission  of  the  complete  band  cor- 
responding to  the  original  poids,  that  is,  all  high  harmonics  and  cross-modulation 
products,  is  so  difficult  as  to  be  practically  impossible.  Mr.  MacNair  will  agree, 
I  am  sure,  that,  if  we  can  reproduce  only  a  difference  tone  because  the  sum  of  two 
high  frequencies  lies  outside  the  transmission  band,  it  is  impossible  to  restore  the 
original  two  tones  by  his  poled  dubbing  technic  without  leaving  distortion  in  the 
final  product.  We  realize  that  correction  of  this  sort  for  vertically  cut  records  is 
decidedly  beneficial  and  may  even,  if  properly  executed,  produce  a  final  result 
comparable  to  that  which  is  easily  obtained  with  lateral  groove  modulation.  Al- 
though the  technic  has  certain  apparent  disadvantages,  we  regret  that  it  is  not 
used  more  consistently  in  commercial  practice. 


A  HIGHER-EFFICIENCY  CONDENSING  SYSTEM 
FOR  PICTURE  PROJECTORS* 

F.  E.  CARLSON** 

Summary. — In  motion  picture  projection  optical  systems  for  tungsten-filament 
sources,  the  condenser  design  is  such  that  the  source  is  imaged  well  ahead  of  the  picture 
aperture.  This  position  is  dictated  by  considerations  of  uniformity  of  screen  bright- 
ness. It  is  not  the  optimal  position  from  the  standpoint  of  utilization  of  light,  for  it 
entails  losses  at  the  aperture.  At  the  best  position  for  efficiency,  the  degree  of  brightness 
uniformity  is  inacceptable  because  of  the  non-uniform  brightness  of  the  source.  The 
paper  describes  a  method  for  reducing  such  losses  without  sacrificing  picture  quality. 

The  design  requirements  of  optical  systems  for  picture  projection 
have  been  well  defined  in  technical  papers  presented  before  the 
Society  over  the  years.  It  is  well  known,  for  example,  that  to  achieve 
uniformity  of  lighting  of  the  screen  the  condenser  diameter  and  con- 
denser-aperture spacing  must  be  such  that  upon  looking  backward 
through  the  projection  system  from  all  points  on  the  screen  one  will 
see  equal  are£s  of  uniform  brightness.  In  practice  that  is  not  com- 
pletely realized  at  the  margins  because  of  vignetting  by  the  projection 
lens  tube. 

Given  a  source  of  uniform  brightness,  uniform  illumination  of  the 
screen  is  achieved  with  greatest  efficiency  in  light  utilization  if  the 
image  of  the  source  formed  by  the  condensing  lens  lies  slightly  ahead 
of  the  aperture.  When,  as  in  Fig.  I  (A),  the  image  is  formed  at  the 
aperture,  the  light  lost  at  this  gate  is  at  a  minimum.  However,  the 
divergence  of  the  beam  is  then  so  great  that  much  of  the  light  is  not 
intercepted  and  transmitted  by  the  projection  lens.  As  the  source 
image  is  moved  farther  ahead,  Fig.  1  (J5),  aperture  losses  increase  but 
a  greater  proportion  of  the  remaining  light  is  transmitted  by  the 
projection  lens.  It  is  apparent  that  for  any  given  combination  of 
condenser-aperture  spacing,  aperture  size,  and  projection  lens,  there 
is  an  optimal  position  where  the  sum  of  the  two  losses  is  at  a  minimum. 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;    received 
April  15,  1938. 

**  General  Electric  Co.,  Cleveland,  Ohio. 

187 


188 


F.  E.  CARLSON 


[J.  S.  M.  P.  E. 


If  the  source  be  non-uniform  in  brightness,  the  image  formed  by  the 
condensing  lens  will  also  be  non-uniform.  It  is  the  degree  of  uniformity 
across  the  beam  at  the  picture  aperture  that  determines  whether  the 
screen  is  acceptably  illuminated;  and  this  uniformity  increases  as 
the  position  of  the  image  is  moved  forward  from  the  aperture.  In 
practice  the  image  has,  accordingly,  been  placed  a  considerable  dis- 
tance from  the  point  of  optimal  utilization  of  light.  This  paper  deals 
with  means  for  minimizing  the  losses  that  have  heretofore  been  thus 
incurred. 

In  order  to  determine  the  effect  of  image  position  upon  net  output 
of  projectors,  tests  were  made  with  five  typical  optical  systems  of 


0    SOURCE    IMAGED    AT  APERTURE 


(I)    SOURCE     IMAGED    IN    PROJECTION  UMS 

FIG.  1.     Effect  of  position  of  source  image  upon  light  losses  at  pic- 
ture aperture  and  at  projection  lens. 

the  16-mm.  size.  The  condensers  employed  included  the  usual  spheric 
types  as  well  as  aspheric  combinations.  The  light-source  was  an 
incandescent  filament  lamp  of  the  conventional  biplane  construction, 
and  of  such  size  as  to  insure  that  the  system  was  always  completely 
filled. 

Various  image  positions  along  the  optical  axis  were  attained  by 
changing  the  focal  length  of  the  condensers.  In  the  case  of  the  spheric 
combinations,  and  in  the  aspheric  systems  combining  all  corrections 
in  one  lens,  this  was  accomplished  simply  by  substitution  in  the 
element  nearest  the  aperture.  In  one  system,  in  which  both  elements 
are  aspheric,  the  focal  length  of  the  combination  was  changed  by 
introducing  a  third  element  of  appropriate  focal  length  mounted 
close  to  the  lens  nearest  the  aperture. 


Aug.,  1938]          CONDENSING  SYSTEM  FOR  PROJECTORS 


189 


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SCREEN  ILLUMINATION 

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RESP 

MAGE    POSITION 

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20 
10 

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0         10         O          10         20         30        40         50        60         70        00        90       101 

IMAGE    POSITION   —  MM.  FROM  APERTURE 

FIG.  2.  Relation  of  position  of  source  image  to  screen 
illumination  for  16-mm.  projection  systems  with  aspheric 
condensers. 


60        00 
IMAGE    POSITION—    MM.  FROM  APERTURE 


FIG.  3.  Relation  of  position  of  source  image  to  level 
of  screen  illumination  for  16-mm.  projection  systems  with 
spheric  condensers. 


190  F.  E.  CARLSON  [j.  s.  M.  P.  E. 

The  results  of  these  tests  are  shown  graphically  in  Figs.  2  and  3. 
While  the  data  apply  only  to  the  five  optical  systems  tested,  they 
indicate  the  order  of  the  penalty  imposed  by  non-uniformity  of  source 
in  projectors  generally,  whether  of  the  8-mm.,  16-mm.,  or  35-mm. 
size.  The  standard  position  of  the  source  image  for  each  of  the  equip- 
ments tested  is  noted  on  the  curves.  It  will  be  observed  that  in  the 
aspheric  systems  the  net  output  actually  utilized  is  16  to  25  per  cent 
below  the  maximum  possible,  and  that  for  spheric  condensers  it  runs 
to  nearly  40  per  cent  below. 

Fig.  4  shows,  in  A  and  B,  respectively,  the  approximate  appearance 
of  the  screen  when  the  image  is  focused  at  the  point  of  maximum 


FIG.  4.     Appearance  of  screen  when  source  is  imaged  (.4)  at  point  of  maxi- 
mum light  output,  and  (B)  at  standard  positions  indicated  in  Figs.  2  and  3. 

light  output  and  at  the  positions  actually  used  in  practice.  It  will  be 
seen  that  the  lack  of  uniformity  is  evidenced  crosswise  of  the  screen, 
not  vertically.  In  other  words,  so  far  as  uniformity  of  brightness 
from  top  to  bottom  of  screen  is  concerned,  the  source  could  be  imaged 
close  to  the  position  of  maximum  output. 

It  has  been  standard  practice  to  focus  both  dimensions  of  the  source 
in  the  same  plane.  It  is  not  necessary  that  that  be  done.  A  more 
rational  procedure  would  be  to  incorporate  a  cylindrical  or  toric 
surface  in  the  condensing  system  to  provide  a  differential  in  the  dis- 
tance at  which  the  vertical  and  horizontal  dimensions  of  the  source 
are  focused.  Such  structures  are  commercially  feasible.  Cylindrical 
surfaces  have,  for  example,  been  used  to  give  the  beam  from  a  cir- 
cular source  an  approximately  elliptical  cross-section  in  order  to  fit 
it  more  nearly  to  the  dimensions  of  a  particular  aperture.  If,  now, 


Aug.,  1938]          CONDENSING  SYSTEM  FOR  PROJECTORS 


191 


CONVEX    CYLINDRICAL   SURFACE 


CONCAVE  CYLINDRICAL  SURFACE 


CONVEX    CYLINDRICAL  SURFACES 


FIG.  5.  A  few  of  the  methods  available  for  incorporating  cylindrical  or 
toric  surfaces  in  typical  condensing  systems  for  differential  focusing  of  width 
and  height  of  source. 


192  F.  E.  CARLSON  fj.  s.  M.  P.  E. 

the  structure  is  instead  adapted  to  focus  one  dimension  of  a  rec- 
tangular source  in  the  plane  of  maximum  output  and  the  other  di- 
mension in  the  nearest  plane  for  which  uniform  illumination  results 
at  the  aperture,  considerable  gain  in  output  can  be  achieved  at  the 
same  time  that  uniformity  of  screen  brightness  is  preserved. 

Fig.  5  illustrates  three  of  a  number  of  possible  modifications  of 
representative  types  of  condensing  systems  to  accomplish  the  differ- 


25% 

INCREASE 


FIG.  6.  Increase  in  light  output  obtained  by  incor- 
porating cylindrical  or  toric  surface  in  condenser. 

The  height  of  the  column  represents,  for  each  of  three 
equipments,  the  net  light  output  with  source  imaged  at 
position  for  maximum  light  utilization,  disregarding 
uniformity  of  screen.  The  black  portion  represents  the 
part  of  the  possible  output  realized  in  equipment  as  now 
made.  The  shaded  blocks  show  the  gain  when  con- 
densers are  modified  as  described. 

The  three  columns  are  not  to  the  same  scale  and 
therefore  are  not  to  be  compared  with  each  other  as  to 
absolute  values. 


ential  focusing.  A  shows  the  simple  case  of  substituting  a  cylindrical 
for  a  plane  surface  of  a  combination,  thus  producing  a  lens  of  shorter 
focal  length  in  the  meridian  corresponding  to  the  length  of  the  coils 
of  the  lamp.  In  B  the  cylinder  is  concave  instead  of  convex  in  order 
to  increase  the  focal  length  of  the  meridian  corresponding  to  the 
position  at  right  angles  to  the  coils  of  the  lamp.  If  all  the  surfaces 
of  the  combination  were  spheric  or  aspheric  one  would  provide,  in 
place  of  the  cylindrical  surfaces  illustrated,  corresponding  convex 
and  concave  toric  surfaces.  In  C,  two  cylindrical  (or  toric)  surfaces 


Aug..  1938]          CONDENSING  SYSTEM  FOR  PROJECTORS  193 

with  their  axes  90  degrees  to  each  other  are  uc  1  produce  a  differ- 
ential in  strength  or  focal  length  in  these  two  meridians. 

Lenses  were  made  incorporating  these  p  .pies,  but  otherwise 
identical  with  those  employed  in  the  above  tests  of  conventional 
systems.  They  were  tested  in  three  of  the  equipments,  all  representa- 
tive of  the  high-quality  group  of  16-mm.  projectors,  with  results  as 
charted  in  Fig.  6.  The  increase  in  net  output  of  the  projectors  varied 
from  a  minimum  of  12  per  cent  for  an  aspheric,  to  25  per  cent  for  a 
spheric  system.  Factors  affecting  the  realizable  gain  in  efficiency 
include  the  angle  of  acceptance  and  the  relative  aperture  and  focal 
length  of  the  projection  lens,  as  well  as  the  condenser-aperture  spacing. 

DISCUSSION 

MR.  KELLOGG:  Your  analysis  and  estimate  of  gain  are  based  upon  the  sup- 
position that  you  have  a  large  enough  projection  lens  to  collect  all  the  light  that 
gets  through  the  aperture;  in  other  words,  that  you  fill  the  lens  with  the  filament 
image  at  all  times? 

MR.  CARLSON:  The  gains  shown  are  measurements  and  not  e,<  ^d  values, 

and  there  has  been  no  change  in  any  of  the  optical  systems  other  an  in  the  focal 
length  of  the  condensing  lens.  That  is,  the  projection  lens  was  r  »t  changed  nor 
was  its  position  changed. 

I  doubt  that  projection  lenses,  even  when  used  with  conde  iv^ng  systems  de- 
signed in  accordance  with  present  practice,  collect  and  redirect  to  the  screen  all 
the  light  that  gets  through  the  aperture.  Ignoring  surface  losses,  there  is  usually 
some  obstruction  to  marginal  rays,  varying  in  amount  with  the  angle  these  rays 
bear  to  the  optical  axis.  The  reason  we  obtain  a  gain  in  screen  illumination  is 
that  we  are  working  at  the  point  where  the  sum  of  the  losses  at  the  projection 
lens  and  at  the  aperture  is  reduced. 

MR.  KELLOGG:  Would  not  your  story  be  changed  if  you  assumed  a  smaller 
projection  lens?  You  are  assuming,  are  you  not,  about  as  fast  a  projection  lens 
as  is  practically  available? 

MR.  CARLSON:  Not  necessarily.  The  data  for  each  optical  system  tested 
were  not  included  in  the  charts  shown,  but  there  were  also  tested  in  the  course 
of  the  earlier  experiments  optical  systems  incorporating  f/2  projection  lenses  in- 
stead of //1. 65,  and  the  same  relative  gains  seem  to  apply. 


A  COLOR  DENSITOMETER  FOR  SUBTRACTIVE 
PROCESSES* 


R.  M.  EVANS** 

Summary. — In  subtractive  color  processes  it  is  desirable  to  have  some  type  of  sensi- 
tometry  to  tell  how  the  process  departs  from  correct  rendering  of  neutral  gray  scales. 
Reading  the  density  of  a  color  deposit  through  an  arbitrary  filter  does  not  give  rise  to 
a  useful  value  in  terms  of  the  final  color  process.  For  practical  use  the  "effective  den- 
sity'' of  a  color  is  defined  as  the  visual  density  produced  by  adding  sufficient  of  the 
other  colors  of  the  process  to  produce  gray.  An  instrument  is  described  that  reads 
such  values  directly.  This  instrument  is  capable  also  of  analyzing  the  amounts  of 
each  of  two  or  more  colors  when  present  simultaneously  and  permits  the  analysis  of  a 
sensitometric  exposure  into  the  corresponding  deposits  of  each  color.  Complete 
sensitometric  curves  may  be  drawn  for  all  the  records  from  the  readings  of  a  single 
strip. 

In  all  processes  of  subtractive  color  photography,  the  problem  of 
so  "balancing"  the  individual  color  records  that  the  requirements  of 
best  tone  reproduction  are  realized  is  rather  difficult.  A  large  part 
of  the  difficulty  arises  from  the  lack  of  suitable  means  for  measuring 
and  specifying  the  actual  amounts  of  image-forming  material  in  each 
record  individually.  Once  these  amounts  are  measured,  however, 
there  still  remains  the  problem  of  determining  the  relationships  be- 
tween them  that  will  produce  the  required  results. 

The  conventional  methods  of  colorimetry  may  always  be  applied 
to  any  color  process,  either  for  each  layer  or  for  the  process  as  a  whole. 
Such  methods,  however,  are  concerned  primarily  with  the  later  stages 
in  which  the  final  colors  may  be  compared  to  the  original  subject. 
For  this  purpose,  no  substitute  is  known  or  needed  and  the  subject 
need  not  here  be  discussed  further. 

In  the  earlier  stages  when  any  color  process  is  being  worked  out  or 
being  brought  under  control,  there  usually  exists  a  need  for  the 
equivalent  in  colors  of  black-and-white  sensitometry.  It  is  a  usually 
accepted  axiom  of  color  photography  that  the  colors  used  and  the 

*Received  June  6,  1938.    Communication  No.  676  from  the  Kodak  Research 
Laboratories. 

**  Eastman  Kodak  Co.,  Rochester,  N.  Y. 

194 


COLOR  DENSITOMETER  195 


mode  of  operation  of  any  process  must  make  it  possible  to  reproduce 
a  scale  of  neutral  grays  as  such,  unless  a  fourth  record  in  gray  is  to 
be  added  to  the  image.  Even  in  this  case  a  close  approximation  to 
this  condition  is  necessary. 

The  methods  of  sensitometry  apply  directly  to  such  a  gray  scale 
and  the  reproduction  of  such  a  scale  is  usually  considered  to  define 
the  tone  or  brightness  reproduction  possibilities  of  the  process.  In 
other  words,  the  brightness  reproduction  scale  of  the  process  is  as- 
sumed to  be  denned  by  the  brightness  reproduction  of  a  scale  of 
neutral  grays.  In  reality,  such  an  assumption  is  not  justified  for  any 
part  of  the  reproduction  except  that  of  gray  scales,  and  it  obviously 
has  nothing  to  say  about  the  reproduction  of  hue  or  saturation  of 
colors.  That  that  is  true  is  obvious  from  the  fact  that  three  colors 
that  are  each  very  similar  to  gray  might  be  used  and  the  reproduction 
of  a  scale  of  grays  made  practically  perfect  without  aiming  at  a  color 
process  worthy  of  the  name. 

The  present  paper  is  concerned  with  subtractive  color  processes  in 
which  the  individual  colors  used  for  the  part  images  are  considered 
satisfactory  in  themselves.  Consideration  will  be  given  only  to  the 
measurement  of  each  color  record  in  such  a  way  that  it  is  directly 
apparent  how  much  of  each  is  necessary  to  form  a  gray  of  the  re- 
quired density. 

The  statement  is  found  frequently  in  the  literature  of  color  photog- 
raphy that  one  of  the  important  requirements  of  a  subtractive  color 
process  is  that  the  contrast  or  "gamma"  of  all  the  color  records 
shall  be  the  same.  In  general  principle,  this  requirement  is  obvious 
enough,  but  further  consideration  shows  that  it  is  a  rather  vague  con- 
cept unless  new  definitions  are  made  for  density  and  gamma. 

In  the  sensitometry  of  ordinary  silver  processes  in  which  the  images 
are  essentially  gray,  the  term  "density"  is  defined  as  the  logarithm 
of  the  reciprocal  of  the  transmissions  of  the  deposit.  It  is  usually 
assumed  that  the  transmission  is  measured  visually,  but  that  is  not 
entirely  necessary  since  the  deposit  is  usually  so  uniform  in  its  trans- 
mission of  light  of  all  colors  that  the  sensitivity  of  the  eye  to  color 
does  not  come  into  the  problem  as  a  large  variable.  "Gamma"  is 
then  defined  as  the  slope  of  the  line  in  a  plot  of  density  against  the 
logarithm  of  the  exposure  that  caused  it.  In  other  words,  it  is  the 
ratio  of  cause  to  effect,  and  as  such  is  an  extremely  useful  concept. 
The  requirement  stated  above  for  color  processes,  then,  is  that 
the  ratio  of  cause  to  effect  shall  be  the  same  for  each  color  record. 


196 


R.  M.  EVANS 


[J.  S.  M.  P.  E. 


The  three  colors  are  assumed,  whether  correctly  or  not,  to  give  gray 
when  present  in  equal  amounts.  This  latter  assumption  is  not  true 
in  the  case  of  most  practical  processes.  What  is  wanted,  then,  is  a 
method  of  measuring  the  color  deposits  constituting  each  color  record, 
in  such  a  way  that  the  quantity  of  each  color  appears  equal  when  the 
colors  superimposed  give  a  visual  gray.  If  each  record  could  be  read 
in  terms  of  "density,"  then,  when  the  density  of  each  of  the  color 
records  was  the  same,  the  result  of  superimposing  the  colors  would 
be  gray.  The  "gamma"  of  each  record,  defined  in  terms  of  these 
densities,  would  then  each  be  the  same  when  the  process  was  repro- 
ducing a  gray  scale.  This  result  may  be  accomplished  by  defining  a 
new  kind  of  density  which  might  be  called  the  "equivalent  density" 


500  600 

WAVELENGTH 


FIG.    1.     Effect   of   impurities   upon  combined 
density. 

of  a  color.  We  may  define  this  as  follows:  The  "equivalent  density" 
of  a  color  in  any  subtractive  color  process  is  the  visual  density  it  would 
have  if  it  were  converted  to  a  neutral  gray  by  superimposing  the  just- 
required  amounts  of  the  fundamental  colors  of  the  process.  The  defini- 
tion appears  as  if  it  might  be  extended  to  any  color  independent  of 
a  color  process  and  defined  as  the  density  that  a  color  would  have  if 
it  were  subtractively  combined  with  its  exact  physical  complementary. 
Such  an  extension  of  the  definition,  however,  does  not  lead  to  the 
same  result.  This  may  be  demonstrated  by  an  example. 

If  three  practical  dyes  are  chosen  which  in  a  certain  ratio  give 
neutral  gray,  the  visual  density  of  this  gray  is  greater  than  the  maxi- 
mum absorption  density  of  any  one  of  the  dyes  at  any  wavelength. 
This  is  due  to  the  so-called  "impurity"  of  the  colors,  and  is  illustrated 
by  the  arbitrarily  drawn  curves  of  Fig  1.  In  this  figure  the  density 
of  each  dye  at  each  wavelength  of  light  in  the  spectrum  is  plotted 


Aug.,  1938]  COLOR  DENSITOMETER  197 

separately,  the  density  at  each  wavelength  being  defined  as  in  the 
case  of  silver  images.  (This  is  possible  because  the  relative  sensitivity 
of  the  eye  to  different  wavelengths  does  not  enter.)  The  density  at 
each  wavelength  for  the  three  dyes  combined  may  then  be  obtained 
by  adding  the  three  curves  at  each  wavelength,  just  as  neutral  densi- 
ties may  be  added.  Since  the  three  dyes  have  been  chosen  to  give 
a  neutral  gray  when  mixed,  the  point-by-point  addition  of  the  curves 
gives  rise  to  a  fourth  curve  which  is  at  essentially  the  same  density 
at  all  wavelengths.  Being  the  same  at  all  wavelengths,  this  density 
is  the  value  that  would  be  read  by  white  light  on  a  densitometer. 
Note,  however,  that  since  each  of  the  dyes  had  a  definite  density  at 
every  wavelength,  the  final  neutral  density  is  higher  than  any  point 
in  any  of  the  curves.  If  the  exact  physical  complementary  for  any  of 
the  dyes  were  added  to  that  dye,  nothing  would  have  been  added  to 
its  maximum  density  and  the  final  neutral  density  would  have  been 
less  in  such  a  case  than  in  the  case  of  the  three  actual  dyes. 

Furthermore,  the  term  "complementary"  color  as  used  here  could 
apply  only  to  a  given  dye  at  a  given  concentration,  and  would  require 
to  be  changed  if  the  concentration  of  the  dye  in  question  were  changed. 
It  is  for  these  reasons  that  the  density  of  a  dye  deposit  as  determined 
by  reading  it  through  an  arbitrary  filter  on  a  visual  densitometer 
does  not  lead  to  density  readings  that  are  directly  significant  for  a 
process  in  which  the  dye  is  used. 

It  is  apparent  from  what  has  been  said  above  that  the  density 
curve  for  any  individual  color  record  in  a  subtractive  process  may  be 
obtained  readily  by  determining  the  densities  formed  when  sufficient 
amounts  of  the  other  two  colors  are  superimposed  on  each  step  to 
form  a  neutral  gray.  The  densities  so  determined  have  the  property 
that  when  equal  densities  of  all  the  colors  are  superimposed  the  result 
is  a  neutral  gray  whose  density  is  equal  to  that  of  each  record.  In 
other  words,  if  the  densities  are  so  determined,  the  sensitometric 
curves  for  each  record  must  have  the  same  slope  or  gamma  and  must 
lie  in  the  same  position  with  respect  to  the  exposure  axis  in  order 
that  the  process  shall  reproduce  a  scale  of  neutrals  as  a  scale  of 
neutrals. 

A  simple  instrument  has  been  devised  for  the  purpose  of  measuring 
densities  according  to  the  above  definition.  In  principle  it  is  similar 
to  that  of  the  Capstaff-Purdy  densitometer1  now  widely  used  in  the 
motion  picture  industry.  In  this  well  known  instrument  the  image 
whose  density  it  is  desired  to  determine  is  placed  in  a  beam  of  light 


198 


R.  M.  EVANS 


[J.  S.  M.  P.  E. 


in  series  with  a  circular  neutral  gray  wedge  whose  densities  are 
known  at  every  point.  By  another  path,  light  from  the  same  source 
is  brought  around  the  wedge  and  both  beams  of  light  enter  an  eyepiece 
in  such  a  way  that  comparison  of  the  brightnesses  of  the  two  may  be 
made  to  high  precision.  The  brightness  of  the  unimpeded  beam,  due 
to  the  length  of  its  path,  is  made  less  than  that  of  the  wedge  beam  in 


FIG.  2.     Schematic  arrangement  of  color  densitometer. 


a  known  ratio.  In  other  words,  it  requires  a  definite  density  of,  say, 
3.4  in  the  path  of  the  light  through  the  wedge  to  make  it  equal  to 
brightness  of  the  comparison  beam.  The  density  of  the  unknown 
sample  may  be  determined  by  moving  the  wedge  until  the  two  beams 
match.  At  this  point  it  is  known  that  the  sum  of  the  density  of  the 
wedge  and  the  unknown  equals  3.4,  and  the  instrument  may  be  cali- 
brated to  read  the  difference  between  this  and  the  actual  wedge  den- 
sity, or  the  density  of  the  unknown.  The  great  advantage  of  this 


Aug.,  1938]  COLOR  DENSITOMETER  199 

type  of  instrument,  aside  from  its  simplicity,  lies  in  the  fact  that  the 
actual  brightness  of  the  field  when  the  two  beams  are  matched  is 
always  the  same. 

The  present  instrument  retains  this  feature  and  has,  as  well,  the 
important  feature  for  visual  color  work  that  both  fields  are  neutral 
at  the  balance  point. 

The  design  of  the  instrument  is  as  follows :  In  a  densitometer  with 
an  optical  system  similar  to  that  of  the  Capstaff-Purdy  instrument 
there  is  placed  in  the  beam  of  light  passing  through  the  wedge  a  color 
wedge  for  each  color  of  the  process  formed  by  the  color  process  for  which 
the  instrument  is  to  be  used.  If  it  is  a  three-color  process  there  will 
be  three  color  wedges  in  addition  to  the  gray  wedge  of  the  usual  in- 
strument. Fig.  2  shows  the  instrument  diagrammatically. 

To  measure  the  density  of  a  color  deposit  the  film  carrying  the  color 
is  placed  in  the  beam  C  with  all  wedges  set  at  maximum  transmission. 
The  brightnesses  of  the  two  halves  of  the  field  are  then  roughly 
matched  by  rotating  the  neutral  wedge.  Considering  for  the  moment 
that  the  color  being  measured  is  that  of  one  of  the  color  records  only, 
each  of  the  other  two  wedges  is  rotated  until  the  transmitted  light  is 
gray.  The  brightnesses  of  the  two  halves  of  the  field  are  then  matched 
and  the  exact  density  is  then  read  from  the  scale  of  the  neutral  wedge. 
In  actual  practice  the  balancing  operation  is  only  slightly  more 
difficult  than  in  the  case  of  the  single- wedge  instruments. 

If  the  color  is  not  a  deposit  of  one  color  record  alone  but  is  a  mix- 
ture of  two  or  of  all  the  records,  the  density  may  still  be  determined 
and  is  of  equal  validity  to  that  read  from  a  deposit  of  a  single  color 
if  care  is  taken  to  add  in  only  those  colors  in  which  the  original  is 
deficient.  Where  the  density  corresponding  to  one  color  record  is  all 
that  is  desired  there  is  no  need  for  calibration  of  any  of  the  color 
wedges.  It  is  within  the  capacities  of  the  instrument,  however,  to 
calibrate  itself,  and  when  this  is  done  it  becomes  possible  to  de- 
termine the  equivalent  density  of  each  of  the  colors  in  any  mixture. 
This  makes  it  possible  to  determine  the  curves  for  each  color  record 
from  a  single  photograph  of  a  neutral  scale  or,  more  conveniently, 
from  a  single  exposure  to  white  light  in  a  sensitometer  of  the  con- 
ventional type. 

The  calibration  and  application  of  the  instrument  for  this  purpose 
are  carried  out  as  follows :  Arbitrary  scales  are  attached  to  each  of 
the  color  wedges.  If  wedge  C  is  to  be  calibrated,  it  is  set  at  the  first 
division  of  its  arbitrary  scale,  say,  ten  degrees  from  the  point  at  which 


200 


R.  M.  EVANS 


[J.  S.  M.  P.  E. 


the  wedge  has  no  color.  The  other  two  wedges  are  then  rotated  until 
the  light  passing  through  is  gray,  the  brightness  of  the  beam  is 
matched  to  that  of  the  comparison  beam,  and  the  "equivalent 
density"  read  from  the  neutral  wedge  is  applied  to  the  wedge  being 
measured.  In  other  words,  each  wedge  at  successive  points  is  con- 
sidered as  a  sample  to  be  measured,  and  in  this  way  each  is  calibrated. 
Any  color  may  now  be  specified  in  terms  of  the  equivalent  densities 
of  each  of  its  components.  To  do  this  the  sample  is  placed  in  the 
beam  as  usual ;  the  wedge  corresponding  in  color  to  the  predominant 
color  of  the  sample  is  left  at  zero,  and  sufficient  of  each  of  the  other 


FIG.  3.     Color  density  curves  of  a  sensitometric  strip. 

colors  is  added  by  means  of  the  wedges  to  give  a  neutral  which  is  then 
balanced  with  the  neutral  wedge.  The  neutral  wedge  now  reads  the 
equivalent  density  of  the  color  present  in  the  greatest  amount,  and 
the  densities  on  the  other  two  wedges,  subtracted  from  this  value, 
give  the  equivalent  density  of  each  of  the  other  colors  present  in  the 
sample. 

If  a  sensitometer  strip  is  exposed  by  white  light  and  the  resulting 
steps  are  read  on  the  instrument,  the  curves  of  each  color  may  be 
plotted  independently.  Such  curves,  read  on  an  instrument  built 
according  to  the  above  scheme  are  shown  in  Fig.  3.  They  are  chosen 
deliberately  to  show  a  color  process  not  balanced  for  reproduction  in 
gray  of  a  neutral  scale.  The  strip  appeared  neutral  on  step  A ,  red 
at  step  B,  and  green  at  step  C. 


Aug.,  1938]  COLOR  DENSITOMETER  201 

A  slight  modification  of  the  instrument  may  be  necessary  in  the 
case  of  some  processes,  particularly  if  the  deposits  for  each  color  are 
highly  diffusing.  In  this  case  the  addition  of  spherical  lenses  between 
the  color  wedges  as  shown  in  Fig.  2  may  be  necessary.  In  any  case 
the  addition  of  such  lenses  will  increase  the  light  transmission  of  the 
instrument.  The  instrument  depends  for  its  successful  operation, 
particularly  if  the  color  wedges  are  to  be  calibrated,  upon  the  inter- 
changeability  of  any  color  at  the  wedge  and  at  the  position  of  the 
sample.  This  is  readily  tested  by  reading  a  series  of  color  deposits 
separately  and  then  superimposed.  An  actual  instrument  built  in 
the  Kodak  Research  Laboratories  for  a  process  employing  dye 
images  has  been  highly  successful  and  meets  the  requirement  of 
additivity  well  within  the  required  precision.  Finally,  it  must  be 
emphasized  that  such  an  instrument  must  be  fitted  to  each  particular 
process,  the  wedges  being  made  by  the  process,  and  the  interchange- 
ability  of  colors  at  the  wedge  and  sample  positions  must  be  checked 
over  a  sufficient  range  before  the  results  can  be  expected  to  yield 
useful  information  in  the  control  and  adjustment  of  the  process. 

The  author  acknowledges  his  thanks  to  his  colleagues,  Mr.  George 
Silberstein  and  Dr.  W.  T.  Hanson,  Jr.,  the  former  for  his  painstaking 
construction  of  the  first  instrument  and  the  latter  for  the  additivity 
test  necessary  to  determine  the  reliability  of  the  instrument. 

REFERENCE 

1  CAPSTAFF,  J.  G.,  AND  PURDY,  R.  A.:  "A  Compact  Motion  Picture  Densitom- 
eter,"  Trans.  Soc.  Mot.  Pict.  Eng.,  XI  (1927),  No.  31,  p.  607. 


REPORT  OF  THE  PAPERS  COMMITTEE* 

Summary. — The  plan  of  work  followed  by  the  Papers  Committee  during  the  past 
couple  of  years  is  discussed,  together  with  the  results  achieved  by  following  the  plan. 
The  Report  concludes  with  regulations  of  the  Society  with  regard  to  the  preparation  of 
papers  for  presentation  and  publication,  and  detailed  instructions  concerning  edi- 
torial style  and  typographical  arrangement. 

The  functions  of  the  Papers  Committee  are  two-fold:  (1)  to  ar- 
range and  supervise  an  appropriate  program  of  papers  for  our  semi- 
annual meetings ;  (2)  to  secure  an  adequate  number  of  papers  to  fill 
twelve  issues  of  our  JOURNAL  during  each  year.  Nearly  1400  mem- 
bers depend  upon  the  Committee  for  the  latter  function;  about  250 
for  the  former. 

There  were  96  papers  and  13  reports  published  in  the  JOURNAL 
during  1937.  Out  of  this  total  of  109,  only  8  were  submitted  di- 
rectly to  the  Editorial  Board  for  publication ;  5  were  reprinted  from 
other  publications,  and  1  was  read  before  a  Local  Section  meeting. 
These  14  papers  represent  less  than  13  per  cent  of  the  total,  and 
should  impress  upon  us  the  importance  of  having  an  adequate  num- 
ber of  papers  at  each  semi-annual  meeting  to  provide  material  for  six 
issues  of  the  JOURNAL.  It  indicates  also  that  the  majority  of  our 
membership  are  stimulated  primarily  to  write  papers  when  they  plan 
to  attend  Conventions  and  not  at  other  times. 

Two  years  ago,  a  plan  was  suggested  by  this  Committee  for  the 
organization  of  its  work.  It  consisted  of  the  following  steps:  (1) 
publication  of  a  request  for  papers  in  each  issue  of  the  JOURNAL  for 
four  months  before  the  meeting,  offering  preferred  positions  on  the 
program,  with  ample  time  for  presentation  and  discussion,  to  those 
who  turn  in  their  manuscripts  six  weeks  before  the  meeting;  (2) 
personal  solicitation  of  papers  by  members  of  the  Committee;  (3) 
publication  of  abstracts  in  the  issue  of  the  JOURNAL  appearing  im- 
mediately before  the  meeting;  (4)  request  for  manuscript  copies  10 
days  before  the  meeting.  It  has,  in  addition,  been  customary  to  cir- 
culate a  Tentative  Program  about  3  weeks  before  the  meeting  as  well 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;    received 
May  25,  1938. 
202 


REPORT  OF  PAPERS  COMMITTEE 


203 


as  to  publish  this  Program  in  the  number  of  the  JOURNAL  immedi- 
ately preceding  the  meeting. 

This  plan  has  proved  quite  effective,  as  shown  by  the  quality  and 
number  of  papers  presented  at  the  last  four  meetings.  Much 
work  is  necessary,  however,  to  secure  abstracts  and  manuscripts 
on  time,  but  authors  appear  to  have  become  more  appreciative  of  the 
requirements  and  are  making  greater  efforts  to  comply  with  the  regu- 
lations. Some  lack  of  understanding  of  the  meaning  of  the  term 
abstract  has  been  found  among  a  few  authors ;  others  have  said  that  it 
was  unfair  to  request  manuscript  delivery  before  the  meeting. 

An  "abstract"  may  be  defined  as  a  digest  of  a  paper,  which  states  in 
clear,  concise  sentences  the  significant  material  discussed  in  the  paper. 
Examples  of  good  abstracts  are  included  in  the  Special  Bulletin  of  this 
Committee,  supplementing  this  report.  This  Bulletin  was  drawn 
up  two  years  ago  and  has  been  revised  from  time  to  time.  It  contains 
a  summary  of  the  administrative  practices  of  the  Society  regarding  ac- 
ceptance and  preparation  and  oral  delivery  of  manuscripts.  It  has 
been  distributed  to  the  majority  of  authors  during  the  past  two  years 
and  has  proved  of  service  to  the  authors  as  well  as  the  editorial  office. 
Several  papers  are  received  for  each  meeting,  however,  that  do  not 
comply  with  our  regulations,  and  it  is  evident  that  the  authors  have 
not  read  or,  perhaps,  have  not  been  aware,  of  the  regulations,  espe- 
cially those  related  to  bibliography  and  footnote  style,  illustrations, 
and  drawings.  It  is  suggested,  therefore,  that  wider  distribution 
should  be  made  of  this  Bulletin  by  publishing  it  in  the  JOURNAL  as  a 
supplement  to  this  report.  Reprints  could  then  be  obtained  for  cir- 
culation to  authors  who  are  not  members  of  the  Society. 

It  has  been  customary  to  print  the  Preliminary  Program  both  in  the 
JOURNAL  issued  before  the  meeting  and  in  leaflet  form  for  distribution 
to  all  members  and  authors.  A  final,  corrected  program  is  also 
printed  in  the  JOURNAL  a  month  after  the  meeting.  It  seemed  an 
unnecessary  duplication  to  distribute  the  Preliminary  Program  twice, 
and  with  the  approval  of  the  Board  of  Governors,  the  Preliminary 
Program  was  omitted  from  the  April,  1938,  issue  of  the  JOURNAL. 
Abstracts  have  been  published,  however,  to  facilitate  discussion  at 
the  meeting  and  to  provide  a  source  of  reference  until  the  paper  has 
been  published. 

It  is  important  that  the  Papers  Committee  should  cooperate  closely 
with  the  Publicity  Committee,  especially  during  the  period  just  prior 
to  and  during  the  semi-annual  meetings.  Copies  of  all  abstracts  of 


204  REPORT  OF  PAPERS  COMMITTEE  [j.  s.  M.  P.  E. 

papers  are  turned  over  to  the  Publicity  Committee  several  weeks 
before  the  meeting,  as  well  as  details  concerning  special  demonstra- 
tions or  prominent  speakers  on  our  programs. 

Two  years  ago  we  began  the  practice  of  supplying  the  Chairman  of 
the  Publicity  Committee  with  a  copy  of  all  available  manuscripts  for 
his  use  during  the  period  of  the  Convention.  This  plan  proved 
very  effective,  but  imposed  a  handicap  upon  the  Committee  because 
it  had  been  customary  to  obtain  only  one  copy  of  each  author's 
manuscript,  and  occasionally  it  was  necessary  for  both  Committee 
Chairmen  to  refer  to  a  manuscript  simultaneously. 

Accordingly,  it  was  decided  that  our  request  for  manuscripts  before 
the  meeting  should  specify  two  copies  so  that  the  Publicity  Committee 
could  have  the  exclusive  use  of  one  set.  It  is  always  possible,  of 
course,  for  an  author  to  make  the  reservation,  when  turning  in  his 
copies,  that  further  corrections  may  be  necessary  on  the  manuscript 
and  that  the  Committee  is  not  to  release  the  copy  submitted,  for 
publication  in  the  JOURNAL,  until  these  corrections  are  supplied. 
If  the  manuscript  is  essentially  correct  (even  though  some  or  all  of 
the  figures  may  be  missing),  it  is  usually  satisfactory  for  publicity 
purposes. 

A  request  for  a  finished  manuscript  10  days  before  the  meeting  is 
not  believed  to  be  too  severe,  and  past  experience  has  shown  that  the 
majority  of  authors  are  able  to  meet  these  requirements  satisfactorily. 

It  may  be  of  interest,  in  conclusion,  to  present  a  rough  classification 
of  the  information  that  has  been  presented  to  the  membership  at  our 
last  four  meetings.  Your  comments  and  suggestions  are  requested. 
The  number  and  type  of  papers  may  be  divided  broadly  as  follows : 

Acoustics  4  Optics 

Apparatus  28  Lighting          [•      34 

Color  9  Projection      J 

Education  ]  Sound  30 

Historical  >  11  Stereoscopy  1 

Industrial  j  Stereophony  J 

General  Engineering  Practice  8  Television               3 

Laboratory      }  2g 
Photographic  J 

This  summary  indicates  that  emphasis  has  been  placed  about 
equally  on  papers  dealing  with  apparatus,  laboratory  and  photo- 
graphic problems,  optics,  lighting,  and  projection.  The  papers  on 
sound  have  dealt  with  many  aspects  of  this  subject,  and  the  total 


Aug.,  1938]  REPORT  OF  PAPERS  COMMITTEE  205 

number  of  papers  in  the  class  is  about  the  same  as  the  total  in  each  of 
the  other  classes.  These  figures  show  that  no  single  subject  of  these 
fundamental  classes  has  been  emphasized  at  our  meetings  to  the  ex- 
clusion of  others. 

The  usual  effort  has  been  made  to  obtain  papers  for  the  1938  spring 
meeting.  The  results  have  been  most  encouraging.  Approximately 
69  papers  have  been  offered  and  only  3  were  withdrawn.  There  are 
15  papers  scheduled  on  the  program,  the  authors  of  which  will  not  be 
present.  These  will  be  restricted  to  10  minutes  or  may  be  read  by 
title  if  time  is  limited.  There  are  15  papers  dealing  with  apparatus 
and  these  are  limited  to  10  minutes  for  presentation.  A  total  of  36 
papers  remain,  therefore,  for  which  a  longer  reading  time  has  been 
allowed. 

It  is  particularly  gratifying  to  note  the  number  of  papers  on  the 
program  by  technicians  on  the  West  Coast,  and  the  Committee  wishes 
to  acknowledge  the  excellent  cooperation  shown  by  the  Research 
Council  of  the  Academy  of  Motion  Picture  Arts  &  Sciences  in  con- 
nection with  the  preparation  of  the  program. 

The  generous  response  to  our  request  for  papers  indicates  that  we 
may  yet  achieve  the  goal  of  every  technical  society — a  selected  papers 
program  and  a  large  enough  volume  of  paper  material  to  permit  the 
editorial  board  to  publish  a  selected  group  of  high-quality  papers  in 
each  number  of  our  JOURNAL. 

G.  E.  MATTHEWS,  Chairman 

P.  ARNOLD  C.  FLANNAGAN  F.  H.  RICHARDSON 

L.  N.  BUSCH  E.  W.  KELLOGG  P.  R.  VON  SCHROTT 

A.  A.  COOK  R.  F.  MITCHELL  C.  K.  WILSON 

L.  J.  J.  DIDIEE  I.  D.  WRATTEN 

(West  Coast) 

L.  A.  AICHOLTZ,  Chairman 

C.  N.  BATSEL  L.  D.  GRIGNON  H.  C.  SILENT 

O.  O.  CECCARINI  W.  A.  MUELLER  H.  G.  TASKER 

Supplement 

REGULATIONS  OF  THE  SOCIETY  OF  MOTION  PICTURE  ENGINEERS  RELATED  TO 
THE  PREPARATION  OF  PAPERS  FOR  PRESENTATION  AND  PUBLICATION 

This  bulletin  contains  details  regarding  the  preparation  of  material  for  papers, 
both  for  presentation  and  for  publication,  and  also  includes  information  on  the 
Administrative  Practices  of  this  Society  relative  to  the  responsibility  it  assumes 
regarding  the  acceptance  of  papers  for  publication.  Please  read  the  information 
carefully. 


206          REPORT  OF  PAPERS  COMMITTEE     [j.  s.  M.  p.  E. 

Sect.  8,  Div.  4  Administrative  Practices  reads  as  follows: 

Instructions  to  Authors. — Papers  may  be  submitted  for  presentation  at  the  Semi- 
Annual  Conventions,  for  publication  in  the  JOURNAL  of  the  Society  without  presen- 
tation at  Conventions,  or  for  presentation  at  Local  Section  meetings. 

Papers  will  not  be  accepted  for  presentation  at  Semi-Annual  Conventions  unless 
their  quality  is  regarded  by  the  Board  of  Editors  to  be  such  as  to  merit  publication 
In  many  cases,  however,  it  is  impossible  for  the  authors  to  submit  manuscripts 
sufficiently  in  advance  of  a  Semi-Annual  Convention  to  permit  careful  examination 
by  the  Board  of  Editors.  The  Board  of  Editors,  therefore,  shall  reserve  the  right 
to  decline  to  publish  any  paper  not  submitted  at  least  one  month  prior  to  a  Semi- 
Annual  Convention  and  approved,  even  though  it  be  accepted  by  the  Papers  Com- 
mittee of  the  Society  and  presented  at  a  Semi-Annual  Convention.  Papers 
presented  at  Local  Section  meetings  are  subject  to  these  same  regulations. 

Papers  accepted  for  publication  but  not  presented  at  Conventions  or  other 
Society  meetings  will  be  published  as  early  as  possible,  but  do  not  have  priority 
over  those  already  in  the  hands  of  the  Editorial  Staff. 

The  subject  matter  of  papers  should  be  such  as  to  be  of  interest  to  the  motion 
picture  engineer,  the  term  "engineer"  being  regarded  in  a  very  broad  sense  as 
"anyone  who  contributes  to  the  building  of  the  motion  picture." 

Prior  Right  of  Publication. — Papers  presented  at  Conventions  or  other  meetings 
of  the  Society  or  submitted  only  for  publication  in  the  JOURNAL  shall  be  regarded 
as  the  confidential  property  of  the  Society  unless  withdrawn  by  the  author,  and 
shall  not  be  published  elsewhere  (except  upon  the  approval  of  the  Editorial  Vice- 
President)  until  they  have  either  been  published  in  the  JOURNAL  or  have  been 
returned  to  the  author.  Prior  publication  to  the  extent  of  30  per  cent  of  the  ver- 
bal length  of  any  paper,  with  due  acknowledgment  of  the  source,  is  permitted. 

Right  to  Reprint. — After  its  date  of  appearance  in  the  JOURNAL,  an  article  may 
be  published  in  other  publications  provided  complete  credit  is  given  to  the  JOUR- 
NAL of  the  Society  of  Motion  Picture  Engineers  and  to  the  author  of  the  article  in 
question.  The  citation  should  appear  preferably  after  the  title  of  the  article  or 
as  a  footnote  to  the  article  on  the  first  page  and  should  read  as  follows:  Re- 
printed from  Journal  of  the  Society  of  Motion  Picture  Engineers,  Volume,  Page, 
Month,  Year. 

Prior  Publicity  of  Convention  Papers. — Publicity  incident  to  the  presentation  of 
papers  at  conventions  is  the  responsibility  of  the  Papers  and  Publicity  Committees 
of  the  Society  and  should  not  be  undertaken  by  the  authors  or  their  representa- 
tives, except  in  collaboration  with  these  Committees. 

An  abstract  or  abridgment  for  publicity  purposes  about  200  words  long  should 
be  supplied  about  six  weeks  before  the  meeting  at  which  the  paper  is  to  be  read. 
Examples  of  satisfactory  abstracts  are  the  following: 

"High-Speed  Motion  Picture  Photography  Applied  to  Design  of  Telephone 
Apparatus";  W.  Herriott,  Bell  Telephone  Laboratories,  Inc.,  New  York,  N.  Y. 

High-speed  motion  pictures  are  employed  at  Bell  Telephone  Laboratories  as  a 
visual  aid  in  the  study  of  problems  associated  with  the  design,  manufacture,  and 
testing  of  telephone  apparatus.  A  new  high-speed  camera  of  the  optical  compen- 
sator type  operating  at  4000  pictures  per  second  is  described,  and  its  application 
to  the  study  of  problems  associated  with  telephone  apparatus  is  discussed. 


.Aug.,  1938]  REPORT  OF  PAPERS  COMMITTEE  207 

"A  Modern  Motion  Picture  Laboratory";  C.  L.  Lootens,  Republic  Productions, 
Inc.,  North  Hollywood,  Calif. 

A  complete  description  of  the  new  laboratory  of  the  Consolidated  Film  Indus- 
tries, Inc.,  which  was  completed  during  the  winter  1936-37.  Included  are  layouts 
and  pictures  of  equipment  in  the  basement,  first,  and  second  floors.  The  de- 
scription of  the  laboratory  and  equipment  follows  the  sequence  of  operation  of 
negative  development,  "dailies,"  master  and  release  printing,  together  with  a 
description  of  the  special  printers,  processing  units,  chemical  system,  silver  re- 
covery system,  and  other  mechanical  items  of  interest. 

"Reduction  of  Loop-Length  Variations  in  Non-Slip  Printers";  E.  W.  Kellogg, 
RCA  Manufacturing  Co.,  Inc.,  Camden,  N.  J. 

Compensation  for  varying  degrees  of  film  shrinkage  is  accomplished  in  the 
Bedford  non-slip  printer  by  changes  in  the  length  of  a  loop  of  film  between  a 
sprocket  and  the  printing  point.  This  involves  uncertainty  of  synchronism  by 
the  amount  that  the  loop,  as  first  threaded,  differs  in  length  from  the  final  running 
loop.  For  most  purposes,  the  present  designs  do  not  cause  more  change  in  loop- 
length  than  may  readily  be  tolerated. 

For  certain  purposes,  especially  if  this  type  of  printer  is  to  be  employed  for  16- 
mm.  films,  there  may  be  too  much  departure  for  synchronism.  A  guide-roller 
arrangement  is  described  by  which  the  necessary  change  of  angle  of  approach  of 
the  raw  stock  to  the  printing  point  is  attained  with  comparatively  small  change 
in  loop-length. 

Several  possible  arrangements  are  considered  and  some  other  features  of  the 
non-slip  printer  are  discussed. 

Order  of  Publication. — The  order  of  publication  of  material  presented  at  con- 
ventions or  submitted  only  for  publication  in  the  JOURNAL  is  at  the  discretion  of 
the  Board  of  Editors  and  is  determined  in  general  by  the  chronological  order  in 
which  the  papers  are  received,  the  timeliness  of  the  material,  the  technical  quality 
of  the  papers,  and  their  editorial  completeness.  The  Board  of  Editors  will  give 
due  and  proper  consideration  to  requests  for  special  and  early  publication. 

The  Complete  Manuscript. — The  complete  manuscript,  from  the  editorial  point 
of  view,  consists  of  the  following  items: 

(a)  Title. 

(6)  Name  of  author. 

(c)  Company  affiliation  (as  a  footnote  on  the  first  page). 

(d)  Summary  of  paper  (not  to  exceed  500  words). 

(e)  The  paper  proper. 

(/)     A  complete  list  of  references  or  citations. 

(g)     A  complete  set  of  illustrations  suitable  for  making  engravings,  with  a  cap- 
tion for  each  illustration. 

Text. — Papers  should  be  typewritten,  double  spaced,  upon  only  one  side  of  the 
paper.  It  is  desirable  to  send  for  publication  the  original  (ribbon  copy) — a  car- 
bon copy  is  easily  erased  and  may  become  illegible. 

Illustrations. — Each  drawing  or  photograph  should  occupy  a  separate  sheet 
and  be  capable  of  good  reproduction.  Blueprints,  photostats,  or  sepia  prints  will 
not  be  accepted.  Tracings  or  line-drawings  should  be  made  with  black  india  ink 


208 


REPORT  OF  PAPERS  COMMITTEE 


[J.  S.  M.  P.  E. 


upon  white  paper  or  tracing  cloth.  Closely  spaced  coordinate  lines  on  curves 
should  be  avoided. 

The  minimum  amount  of  reading  matter  should  be  included  upon  the  illustra- 
tions. Necessary  information  can  better  be  set  in  type  in  the  caption  accompany- 
ing the  illustration. 

The  maximum  width  of  a  JOURNAL  cut  is  4  inches  and  the  maximum  height  is 
6V4  inches.  Illustrations  or  drawings  should  preferably  be  larger  and  not  smaller 
than  these  size  requirements.  It  is  important  that  the  necessary  reduction  of  an 
illustration  will  not  make  the  height  of  letters  contained  in  reading  matter  on  the 


BAKELITE 
WASHERS 


-TEMPERATURE 
CONTROL  COtL 


FIG.  1.     Good  example  of  a  drawing. 


illustration  less  than  l/32  inch.  All  inscriptions  on  graphs  or  illustrations  should  be 
lettered  and  not  typewritten. 

When  preparing  illustrations,  the  style  of  lettering  should  be  so  chosen  and  the 
lettering  so  placed  upon  the  illustrations  as  to  be  easily  read  when  projected  as 
lantern-slides  before  an  audience  of  several  hundred  persons.  Slides  are  usually 
reproduced  about  ten  or  more  feet  wide,  and  should  be  readable  at  a  distance  of 
fifty  feet.  Examples  of  satisfactory  illustrations  are  shown  in  Figs.  1  and  2. 

Listing  Captions. — Captions  for  figures  and  tables  should  be  listed  upon  sepa- 
rate sheets  accompanying  the  manuscript. 


Aug.,  1938] 


REPORT  OF  PAPERS  COMMITTEE 


209 


Address. — It  is  important  that  the  author's  business  affiliation  and  mailing 
address  be  written  upon  the  first  page  of  the  manuscript. 

PRINTING   STYLE   (HEADINGS) 


The  value  and  clarity  of  a  paper  are  undoubtedly  increased  by  dividing  it  into 
sections.  The  author  can  assist  the  editorial  office  by  specifying  the  type  of 
heading  or  sub -heading  desired  in  each  instance.  The  headings  conforming 
to  JOURNAL  style,  in  descending  order  of  importance,  are  as  follows. 


.3     .4  .5  A     .8    1.0  2 

INCHES  OF   WATER 


3     456     8    10 


FIG.  2.     Good  example  of  a  graph. 


CENTERHEAD 

Italic  Centerhead 
Italic  Sidehead. — These  sideheads  are  run  into  the  text  of  the  paragraph. 

BIBLIOGRAPHY  AND  FOOTNOTES 

References  to  literature  should  be  accurate  and  complete.     References 
periodical  literature  should  contain  the  following  items  in  the  given  order: 


to 


(1)  The  reference  number,  corresponding  to  the  number  in  the  text. 

(2)  The  name  of  the  author  of  the  paper;   correctly  spelled  and  with  initials. 
(5)  The  name  of  the  article,  in  quotation  marks. 

(4)  The  name  of  the  periodical  (unless  the  periodical  is  well  known  its  title 

should  not  be  abbreviated). 

(5)  The  volume  number. 

(6)  The  date,  month,  and  year,  in  parentheses. 


210  REPORT  OF  PAPERS  COMMITTEE     [j.  s.  M.  p.  E. 

(7)  The  serial  number,  preceded  by  the  abbreviation  "No." 

(8)  The  page  number,  preceded  by  the  letter  "p." 

Example:  l  McCov,  J.  L.:  "A  Light-Intensity  Meter,"  /.  Soc.  Mot.  Pict. 
Eng.,  XIV  (March,  1930),  No.  3,  p.  357. 

Reference  to  books  should  be  made  as  follows: 

(1}  Author's  name. 

(2)  Name  of  book,  in  quotation  marks. 

(5)  Edition. 

(4)  Publisher. 

(5)  Place  of  publication. 

(6)  Date  of  publication,  in  parentheses. 

(7)  Page,  preceded  by  letter  "p." 

Example:  FRANKLIN,  H.  B.:  "Sound  Motion  Pictures."  1st  Ed.  Doubleday, 
Doran  &  Co.,  Garden  City,  L.  I.,  N.  Y.  (1929),  p.  101. 

Reprints. — Reprints  of  articles  published  in  the  JOURNAL  may  be  obtained  from 
the  Society's  headquarters  office,  Pennsylvania  Hotel,  New  York,  N.  Y.  These 
reprints  are  most  economically  obtainable  currently  with  the  publication  of  the 
issue  of  the  JOURNAL  in  which  they  appear.  Prices  in  the  quantity  desired  may 
be  obtained  by  communicating  with  the  Society's  headquarters  office. 

REGULATIONS  ON  DELIVERY  OF  MANUSCRIPTS  PRIOR  TO  A  CONVENTION 

(2)  Two  copies  of  each  manuscript  must  be  delivered  to  the  Chairman  of  the 
Papers  Committee  at  least  one  month  before  the  meeting  date  in  order  that  the 
paper  be  presented  at  the  meeting.  Papers  arriving  less  than  one  month  before 
the  meeting  date  may,  at  the  discretion  of  the  Papers  Committee,  be  scheduled  on 
the  program  to  be  read  by  title  or  substituted  for  other  papers  in  the  event  of 
cancellations. 

(2)  Two  copies  are  needed  in  order  that  one  set  may  be  made  available  for  the 
Publicity  Committee  and  one  for  the  Papers  Committee  during  the  period  of  the 
Convention. 

(3)  Final  and  complete  copies  ready  for  publication  are  desired.     In  the  event 
that  such  are  not  possible,  preliminary  copies  requiring  further  slight  alterations 
in  text  or  completion  of  illustrations  (as  per  regulations  regarding  preparation  for 
publication)  before  final  release  by  the  author  will  be  accepted.     These  changes 
should  be  made,  however,  within  one  week  after  the  meeting. 

(4)  Authors  are  urged  to  study  carefully  the  regulations  on  the  preparation  of 
illustrations,  and  to  give  consideration  to  the  legibility  of  the  figures  (I)  as  lan- 
tern-slides when  the  paper  is  read  at  the  meeting,  and  (2)  as  printed  cuts  in  the 
JOURNAL. 

SUGGESTIONS  ON  PAPER  PRESENTATION  AT  THE  CONVENTION 

The  attention  of  all  authors  is  directed  especially  to  the  following  sugges- 
tions regarding  oral  delivery  of  their  papers  at  Conventions.  Valuable  time  of 
the  delegates  and  other  authors  will  be  conserved  if  each  author  on  the  program 
follows  these  suggestions: 


Aug.,  1938]  REPORT  OF  PAPERS  COMMITTEE  211 

(1)  Arrangement   of  Material. — Manuscripts   prepared    for   publication   are 
seldom  suitable  for  oral  presentation.     The  paper  should  convey  clearly  to  the 
hearer:    (a)  the  purpose  of  the  work;    (6)  the  experimental  method;    (c)  the  re- 
sults obtained;    and  (d)  conclusions.     The  nature  of  the  material  and  the  time 
available  for  presentation  will  determine  the  degree  of  emphasis  to  be  placed 
upon  each  subdivision.     The  author  should  make  certain  by  trial  against  his 
watch  that  the  essential  points  can  be  presented  adequately  in  the  time  allotted 
to  the  paper. 

(2)  Statement  of  Purpose. — Orient  the  audience  clearly  as  to  the  nature  and 
purpose  of  the  work.     A  lengthy  historical  review  is  generally  out  of  place. 

(3}  Technic. — Describe  the  experimental  method  employed  so  as  to  indicate 
the  principles  involved.  Omit  details  of  apparatus  or  procedure  unless  there  is 
some  particularly  novel  development.  Such  data  may  belong  in  the  published 
paper  but  will  bore  your  audience. 

(4)  Statement  of  Results. — Present  the  results  graphically,  preferably  with  dia- 
grams.    Lantern-slides  are  more  clearly  seen  than  hand-drawn  charts.     These 
slides  should  be  of  standard  size  (3.25  X  4  inches)  and  should  project  clearly  on 
the  screen.     Lettering  should  be  kept  to  a  minimum,  consistent  with  clarity,  and 
should  be  of  such  size  that  when  the  illustration  is  reduced  for  publication  in  the 
JOURNAL,  the  reduced  lettering  will  not  be  smaller  than  1/32  inch  in  height. 
Usually  it  is  not  satisfactory  to  typewrite  legends  on  drawings,  especially  if  the 
typewriter  type  is  small.     Regardless  of  who  has  made  the  charts  or  slides,  try 
them  from  the  point  of  view  of  the  audience  before  presenting  them  at  the  meet- 
ing.    Do  not  read  tables,  a  procedure  that  wastes  time  and  destroys  interest, 
but  point  out  the  general  trend  of  the  data.     Whenever  possible,  the  results  of 
research  should  be  shown  by  means  of  motion  pictures,  for  which  adequate  pro- 
jection facilities  will  be  available. 

(5)  Conclusions. — Summarize  the  evidence  and  discuss  the  importance  of  the 
results  or  conclusions  to  the  particular  field  of  research  involved. 

(6}  Manner  of  Presentation. — Do  not  read  from  a  manuscript  verbatim,  unless 
the  material  has  been  written  expressly  for  oral  presentation.  Talk  directly  to 
your  audience  in  a  clear,  loud  voice.  Do  not  face  blackboard  or  screen  while 
speaking.  Articulate  distinctly. 

(7)  Demonstrations. — Details  of  demonstrations  should  be  checked  carefully 
before  the  opening  of  the  session  during  which  the  demonstration  is  to  be  given. 
This  will  insure  a  smoother  demonstration  and  avoid  using  up  valuable  time  during 
the  technical  session. 

Many  exceptions  to,  and  modifications  of,  the  above  suggestions  will  apply  in 
particular  instances.  Nevertheless,  general  adherence  to  the  points  brought  out 
will  go  far  toward  eliminating  the  valid  criticisms  that  have  been  aimed  at  our 
programs. 

Acknowledgment  is  made  to  the  Society  of  American  Bacteriologists  and  the 
American  Chemical  Society  for  many  of  the  ideas  incorporated  in  these  sugges- 
tions. 


CURRENT  LITERATURE   OF  INTEREST   TO   THE   MOTION   PICTURE 

ENGINEER 


The  editors  present  for  convenient  reference  a  list  of  articles  dealing  with  subjects 
cognate  to  motion  picture  engineering  published  in  a  number  of  selected  journals. 
Photostatic  copies  may  be  obtained  from  the  Library  of  Congress,  Washington,  D.  C., 
or  from  the  New  York  Public  Library,  New  York,  N.  Y.  Micro  copies  of  articles 
in  magazines  that  are  available  may  be  obtained  from  the  Bibliofilm  Service,  Depart- 
ment of  Agriculture,  Washington,  D.  C. 

Communications 

18  (May,  1938),  No.  5 

Home  Newspapers  by  Radio  (pp.  7-9, 35)  F.  C.  EHLERT 

General-Purpose  Audio  Amplifier  (pp.  1 1-13, 26, 30)          A.  PREISMAN 
Measuring  the  Recording  System  with  Limited  Equip- 
ment (pp.  14-15,  36-37)  A.  W.  NIEMANN 

Electronics 

11  (May,  1938),  No.  5 

Wideband  Television  Amplifiers — II  (pp.  24-27) 
Reverberation  Control  in  Broadcasting  (pp.  28-29)          H.  A.  CHINN 
A  Method  of  Periodical  Sound  Reproduction  (pp.  38, 40)   T.  KORN 
Multiplying  the  Range  of  the  Vacuum  Tube  Voltmeter 

(pp.  42,  44,  46)  G.  R.  CHINSKI 

Theater  Sound  Reproducing  System  Standards  (pp.  46, 

48,  50)  J.  K.  HILLIARD 

International  Photographer 

10  (May,  1938),  No.  4 

Tradewinds — News  of  New  Products  (pp.  5-8) 
Electrometric  Titration  Method  (pp.  22-24)  D.  K.  ALLISON 

International  Projectionist 

13  (May,  1938),  No.  5 
The  Geneva  Intermittent  Movement :  Its  Construction 

and  Action.    Ill  (pp.  7-11)  A.  C.  SCHROEDER 

Notes  on  Audio  Amplification  (pp.  12,  15-16)  L.  P.  WORK 

Measuring  Projected  Light  and  Screen  Brilliancy  (pp. 

17-19)  J.  A.  COOK 

Analyses  of  Modern  Theater  Sound  Reproducing  Units 

(pp.  20-23,  32)  A.  NADELL 

Enlarging  the  Visual  Field  of  the  Motion  Picture  (pp. 

24-25,  31,  32)  R.  SCHLANGER 

A  New  Arc  Aligning  Method :  The  Bantau  "Theaomai" 

(pp.  26-27,  30-31)  K.  NUNAN 

212 


CURRENT  LITERATURE 


213 


Kinotechnik 

20  (May,  1938),  No.  5 
Zur  Theorie  des  Rauschens  (Ground-Noise  Theory) 

(pp.  116-118) 
Das  Farbfilmverfahren  von  Prof.  Roux  (Prof.  Roux's 

Color-Film  Process)  (p.  119) 
Das  Problem  des  plastischen  Tones  im  Film  (Problem 

of  Stereoscopic.  Effects  on  Film)  (pp.  120-125) 
Bemerkungen  zur  Anwendung  des  Raumton-Effektes 

im  Tonnlm  (Remarks  on  the  Use  of  Stereo-Sound 

Effects  on  Sound-Film)  (pp.  125-126) 

Photographische  Industrie 

36  (May  4,  1938),  No.  18 

Neue  Tonfilm-Kamera  fur  16-Mm.  Schmalfilm  (New 
16-Mm.  Sound  Camera)  (p.  537) 

36  (May  25,  1938),  No.  21 

Die  optischen  Grundlagen  fur  die  Form  des  Linsenras- 
terfilms  in  der  Farbenphotographie  (Optical  Basis 
for  the  Form  of  Lenticular  Screens  for  Color  Photog- 
raphy) (pp. 610-612) 

Proceedings  of  the  Institute  of  Radio  Engineers 

26  (May,  1938),  No.  5 
The  Fine  Structure  of  Television  Images  (pp.  540-575) 


A.  NARATH 


C.  BECKER 


H.  WARNCKE 


A.  KLUGHARDT 


H.  A.  WHEELER  AND 
A.  V.  LOUGHREN 


FALL,  1938,  CONVENTION 


DETROIT,  MICHIGAN 

HOTEL  STATLER 
OCTOBER  31,  NOVEMBER  1-2,  INCLUSIVE 


Officers  and  Committees  in  Charge 

W.  C.  KUNZMANN,  Convention  Vice-President 
J.  I.  CRABTREB,  Editorial  Vice-P resident 
G.  E.  MATTHEWS,  Chairman,  Papers  Committee 
H.  GRIFFIN,  Chairman,  Projection  Committee 
E.  R.  GEIB,  Chairman,  Membership  Committee 
J.  HABER,  Chairman,  Publicity  Committee 


G.  AVIL 

A.  J.  BRADFORD 
F.  C.  DICKELY 
E.  H.  FORBES 
W.  M.  HARRIS 


E.  R.  GEIB 


Local  Arrangements 

K.  BRENKERT,  Chairman 

G.  A.  McARTHUR 
E.  J.  McGLlNNEN 

R.  R.  McMATH 
H.  S.  NORTON 
R.  L.  RUBEN 


G.  J.  SKIMIN 
J.  F.  STRICKLER 
H.  H.  STRONG 
W.  J.  TURNBULL 
E.  F.  ZATORSKY 


Registration  and  Information 

W.  C.  KUNZMANN,  Chairman 


S.  HARRIS 


G.  J.  SKIMIN 


Hotel  and  Transportation  Committee 

A.  J.  BRADFORD,  Chairman 

H.  ANDERS  L.  A.  FIFERLIK  W.  C.  KUNZMANN 

A.  B.  CHERTON  G.  J.  JARRETT  P.  M.  MOLS 

M.  DUDELSON  K.  KALLMAN  E.  J.  SCHAEFER 


A.  J.  BRADFORD 
K.  BRENKERT 
F.  C.  DICKELY 
E.  H.  FORBES 


Projection 

H.  GRIFFIN,  Chairman 
W.  M.  HARRIS 

F.  MOLES 

H.  S.  MORTON 

G.  A.  MCARTHUR 


E.  J.  McGLlNNEN 

R.  L.  RUBEN 
H.  H.  STRONG 
W.  J.  TURNBULL 


Officers  and  Members  of  Detroit  Projectionists  Local  No.  199 


A.  J.  BRADFORD 
K.  BRENKERT 
H.  GRIFFIN 
214 


Banquet 

J.  F.  STRICKLER,  Chairman 
S.  HARRIS 
G.  J.  JARRETT 
W.  C.  KUNZMANN 


R.  R.  MCMATH 
H.  H.  STRONG 
E.  F.  ZATORSKY 


FALL  CONVENTION  215 

Publicity 

J.  HABER,  Chairman 

J.  R.  CAMERON  S.  HARRIS  P.  A.  McGuiRE 

J.  J.  FINN  G.  E.  MATTHEWS  F.  H.  RICHARDSON 

Ladies'  Reception  Committee 

MRS.  J.  F.  STRICKLER,  Hostess 

assisted  by 

MRS.  G.  AVIL  MRS.  F.  C.  DICKELY  MRS.  G.  A.  MCARTHUR 

MRS.  A.  J.  BRADFORD  MRS.  E.  H.  FORBES  MRS.  R.  L.  RUBEN 

MRS.  K.  BRENKERT  MRS.  W.  M.  HARRIS  MRS.  G.  J.  SKIMIN 

Headquarters 

The  Headquarters  of  the  Convention  will  be  at  the  Hotel  Statler,  where  excellent 
accommodations  are  assured.  A  reception  suite  will  be  provided  for  the  Ladies' 
Committee,  who  are  now  engaged  in  preparing  an  excellent  program  of  entertain- 
ment for  the  ladies  attending  the  Convention. 

Special  hotel  rates  guaranteed  to  SMPE  delegates  and  friends,  European  plan, 
will  be  as  follows: 

One  person,  room  and  bath  $3.00  to  $6.00 

Two  persons,  room  jand  bath  5.00  to    8.00 

Two  persons  (twin  beds),  room  and  bath  5.50  to    9.00 

Three  persons,  room  and  bath  7.50  to  10.50 

Parlor  suite  and  bath,  for  one  8.50  to  11.00 

Parlor  suite  and  bath,  for  two  12.00  to  14.00 

Room  reservation  cards  will  be  mailed  to  the  membership  of  the  Society  in  the 
near  future,  and  everyone  who  plans  to  attend  the  Convention  should  return  his 
card  to  the  Hotel  promptly  in  order  to  be  assured  of  satisfactory  accommodations. 
Registrations  will  be  made  in  the  order  in  which  the  cards  are  received.  Local 
railroad  ticket  agents  should  be  consulted  as  regards  train  schedules,  and  rates  to 
Detroit  and  return. 

The  following  special  rates  have  been  arranged  for  SMPE  delegates  who  motor 
to  the  Convention,  at  the  National-Detroit  Fireproof  Garage  (the  Hotel  Statler's 
official  garage),  Clifford  and  Elizabeth  Streets,  Detroit:  Self -delivery  and  pick-up, 
12  hours,  $0.60;  24  hours,  $1.00;  Hotel-delivery  and  pick-up,  24  hours,  $1.25. 
Special  weekly  rates  will  be  available. 

Technical  Sessions 

An  attractive  and  interesting  program  of  technical  papers  and  presentations  is 
being  assembled  by  the  Papers  Committee.  All  technical  sessions,  apparatus 
symposiums,  and  film  programs  will  be  held  in  the  Large  Banquet  Room  of  the 
Hotel. 

Registration  and  Information 

Registration  headquarters  will  be  located  at  the  entrance  of  the  Large  Banquet 
Room,  where  members  of  the  Society  and  guests  are  expected  to  register  and  re- 
ceive their  badges  and  identification  cards  for  admittance  to  the  sessions  and  film 


216  FALL  CONVENTION 

programs.     These  cards  will  be  honored  also  at  several  motion  picture  theaters 
in  the  neighborhood  of  the  Hotel,  during  the  days  of  the  Convention. 

Informal  Luncheon  and  Semi-Annual  Banquet 

The  usual  Informal  Luncheon  will  be  held  at  noon  of  the  opening  day  of  the 
Convention,  October  31st,  in  the  Michigan  Room  of  the  Hotel.  On  the  evening  of 
Wednesday,  November  2nd,  the  Semi- Annual  Banquet  of  the  Society  will  be  held 
in  the  Grand  Ballroom  of  the  Hotel  at  8  P.M.  Addresses  will  be  delivered  by 
prominent  members  of  the  industry,  followed  by  dancing  and  other  entertainment. 

Points  of  Interest 

In  addition  to  being  a  great  industrial  center,  Detroit  is  also  well  known  for  the 
beauty  of  its  parkways  and  buildings,  and  its  many  artistic  and  cultural  activities. 
Among  the  important  buildings  that  one  may  well  visit  are  the  Detroit  Institute 
of  Arts;  the  Detroit  Historical  Society  Museum;  the  Russell  A.  Alger  House,  a 
branch  of  the  Detroit  Institute  of  Arts;  the  Cranbrook  Institutions;  the  Shrine 
of  the  Little  Flower;  and  the  Penobscot  Building. 

At  Greenfield  Village,  Dearborn,  are  grouped  hundreds  of  interesting  relics  of 
early  American  life,  and  there  also  is  located  the  Edison  Institute,  established  by 
Henry  Ford  in  memory  of  Thomas  A.  Edison. 

On  the  way  to  Greenfield  Village  is  the  Ford  Rotunda,  a  reception  hall  for  visi- 
tors to  the  Ford  Rouge  Plant.  Here  are  complete  reproductions  and  displays  of 
motorcar  design,  and  representations  of  the  famous  highways  of  the  world,  from 
Roman  days  to  modern,  are  on  the  grounds  surrounding  the  building. 

The  General  Motors  Research  Building  and  Laboratory,  located  on  Milwaukee 
Avenue,  will  be  of  particular  interest  to  engineers  visiting  the  City. 

Various  trips  may  be  taken  from  Detroit  as  a  center — to  Canada,  by  either  the 
Ambassador  Bridge  or  the  Fleetway  Tunnel;  to  Bloomfield  Hills,  a  region  of 
lakes;  Canadian  Lake  Erie  trip  from  Windsor,  Ontario;  to  Flint,  Michigan, 
another  center  of  the  automotive  industry;  to  Milford,  General  Motors'  Proving 
Grounds;  and  to  the  Thumb  of  Michigan  Resort  Beaches.  The  City  contains 
also  a  number  of  beautiful  parks  and  golf  courses. 


SOCIETY  ANNOUNCEMENTS 


STANDARD  COMMITTEE 

At  a  meeting  of  the  Committee  held  on  July  8th,  the  question  of  film  cores  was 
considered  and  tentative  dimensions  were  proposed  by  Mr.  P.  Arnold,  Chairman 
of  the  Sub-Committee  dealing  with  the  subject.  Drawings  are  being  prepared 
and  a  ballot  of  the  Standards  Committee  will  be  taken  very  shortly. 

Further  study  was  given  to  the  question  of  35-mm.  sound-track  dimensions 
by  the  Sub-Committee  under  the  Chairmanship  of  L.  W.  Davee,  and  J.  A.  Maurer 
reported  for  his  Committee  on  Optical  Reduction  Ratio  that  a  definite  report 
and  recommendation  will  be  forthcoming  at  the  next  meeting,  as  soon  as  opinions 
have  been  received  from  all  manufacturers  and  laboratories  concerned  with  re- 
duction printing. 

The  specifications  for  safety-film  proposed  by  the  French  Standards  Association 
for  the  meeting  of  Committee  36  of  the  ISA  at  Berlin  during  July  were  considered 
by  the  Committee.  Final  action  on  these  specifications  will  be  taken  in  the  near 
future,  as  soon  as  the  opinions  of  the  Underwriters  Laboratories  have  been  ob- 
tained. 

PROJECTION  PRACTICE   COMMITTEE 

The  last  meeting  of  the  season  was  held  on  June  23rd  at  the  Paramount  Build- 
ing, New  York,  under  the  Chairmanship  of  Harry  Rubin.  Unfinished  business 
was  completed  and  preparations  made  for  resuming  the  activities  of  the  Committee 
in  the  fall,  the  date  of  the  next  meeting  being  scheduled  for  September  15th.  In 
the  meantime,  several  meetings  of  the  Sub-Committees  on  Projection  Room  Plans, 
under  the  Chairmanship  of  S.  Harris,  and  on  Projector  Tools  and  Tolerances, 
under  the  Chairmanship  of  P.  Larsen,  have  been  held,  and  it  is  expected  that  com- 
plete reports  will  be  available  from  these  Sub-Committees  by  the  end  of  the 
summer. 

The  proposed  revision  of  the  NFPA  "Regulations  for  Handling  Nitrocellulose 
Film"  has  been  completed  and  copies  of  the  revision  have  been  transmitted  to  a 
special  committee  established  by  the  NFPA  to  consider  it.  It  is  expected  that 
the  revision  will  be  in  proper  shape  for  publication  in  the  fall.  The  SMPE  is 
represented  on  the  NFPA  Committee  by  S.  Harris,  Chairman  of  the  Sub-Com- 
mittee on  Projection  Room  Fire  Regulations,  of  the  Projection  Practice  Com- 
mittee. 

PACIFIC  COAST  SECTION 

At  a  meeting  of  the  Pacific  Coast  Section  held  at  the  Filmarte  Theater  in  Holly- 
wood on  June  29th,  two  papers  presented  at  the  Washington  Convention  last 
May  were  re-presented,  namely,  "The  Transmission  of  Motion  Pictures  over  a 
Coaxial  Cable,"  by  H.  E.  Ives  of  the  Bell  Telephone  Laboratories;  and  "The  In- 

217 


218  SOCIETY  ANNOUNCEMENTS 

fluence  of  />H  on  Washing  Films  after  Processing,"  by  S.  E.  Sheppard  and  R.  C. 
Houck  of  the  Eastman  Kodak  Company,  Rochester.  The  former  paper  was] 
presented  by  L.  F.  Brown  of  Electrical  Research  Products,  Inc.,  and  the  latter  byl 
R.  B.  Atkinson.  A  resume  of  the  proceedings  of  the  Washington  Convention  was 
presented  by  J.  G.  Frayne. 

ERRATUM 

RESEARCH  COUNCIL  STANDARD  NOMENCLATURE  FOR  RELEASE   PRINT 
SOUND-TRACKS 

In  the  June,  1938  issue  of  the  JOURNAL,  beginning  on  page  656,  appeared  the 
above-entitled  article  by  John  K.  Hilliard,  describing  the  Academy  Standard 
sound-track  nomenclature  approved  by  the  Research  Council  of  the  Academy 
of  Motion  Picture  Arts  and  Sciences  and  published  in  the  Academy  Research 
Council  Technical  Bulletin  of  November  24,  1937. 

As  reprinted  in  the  JOURNAL,  the  article  employed  the  term  "variable-width" 
throughout,  instead  of  the  term  "variable-area"  as  approved  by  the  Research 
Council  in  the  original  publication. 

The  entire  Standard  Nomenclature  is  now  under  consideration  by  the  Sec- 
tional Committee  on  Motion  Pictures  of  the  American  Standards  Association, 
and  if  adopted  these  terms  will  hereafter  be  used  throughout  the  industry  to 
designate  the  various  indicated  types  of  sound-track. 

In  particular,  the  term  "variable-area"  has  been  approved  by  the  studios  and 
by  the  equipment  companies  involved  to  designate  that  type  track,  throughout 
the  industry. 

Readers  of  the  JOURNAL  should,  therefore,  in  the  above-mentioned  article  sub- 
stitute the  term  "variable-area"  whenever  designating  that  type  of  track,  instead 
of  the  term  "variable- width." 


JOURNAL 

OF  THE  SOCIETY  OF 

MOTION  PICTURE  ENGINEERS 

Volume  XXXI  SEPTEMBER,  1938  Number  3 


CONTENTS 

Page 

A  Water-Cooled  Quartz  Mercury  Arc 

E.  B.  NOEL  AND  R.  E.  FARNHAM     221 

Negative-Positive  Technic  with  the  Dufaycolor  Process 

T.  T.  BAKER     240 

Application  of  Non-Linear  Volume  Characteristics  to  Dialog 
Recording J.  O.  AALBERG  AND  J.  G.  STEWART    248 

The  Transmission  of  Motion  Pictures  over  a  Coaxial  Cable.  . 

HERBERT  E.  IVES     256 

Maintenance  of  a  Developer  by  Continuous  Replenishment.  . 

R.  M.  EVANS    273 

Sound-Stages  and  Their  Relation  to  Air-Conditioning 

C.  M.  WERT  AND  L.  L.  LEWIS    287 

New  Motion  Picture  Apparatus 

Problems  in  the  Use  of  Ultra-Speed  Negative  Film 

P.  H.  ARNOLD    307 

Permanent-Magnet  Four-Ribbon  Light- Valve  for  Portable 
Push-Pull  Recording E.  C.  MANDERFELD    315 

A  Basically  New  Framing  Device  for  35-Mm.  Projectors .  .  . 

H.  A.  DEVRY    319 

Current  Literature 322 

Book  Review 324 

Detroit  Convention .  .  325 


JOURNAL 

OF  THE  SOCIETY  OF 

MOTION  PICTURE  ENGINEERS 


SYLVAN  HARRIS,  EDITOR 

Board  of  Editors 
J.  I.  CRABTREE,  Chairman 

A.  N.  GOLDSMITH  L.  A.  JONES  H.  G.  KNOX 

A.  C.  HARDY  E.  W.  KELLOGG  G.  E.  MATTHEWS 


Subscription  to  non-members,  $8.00  per  annum ;  to  members,  $5.00  per  annum, 
included  in  their  annual  membership  dues;  single  copies,  $1.00.  A  discount 
on  subscriptions  or  single  copies  of  15  per  cent  is  allowed  to  accredited  agencies. 
Order  from  the  Society  of  Motion  Picture  Engineers,  Inc.,  20th  and  Northampton 
Sts.,  Easton,  Pa.,  or  Hotel  Pennsylvania,  New  York,  N.  Y. 
Published  monthly  at  Easton,  Pa.,  by  the  Society  of  Motion  Picture  Engineers. 

Publication  Office,  20th  &  Northampton  Sts.,  Easton,  Pa. 
General  and  Editorial  Office,  Hotel  Pennsylvania,  New  York,  N.  Y. 

West-Coast  Office,  Suite  226,  Equitable  Bldg.,  Hollywood,  Calif. 
Entered  as  second  class  matter  January  15,  1930,  at  the  Post  Office  at  Easton, 
Pa.,  under  the  Act  of  March  3,  1879.     Copyrighted,  1938,  by  the  Society  of 
Motion  Picture  Engineers,  Inc. 

Papers  appearing  in  this  Journal  may  be  reprinted,  abstracted,  or  abridged 
provided  credit  is  given  to  the  Journal  of  the  Society  of  Motion  Picture  Engineers 
and  to  the  author,  or  authors,  of  the  papers  in  question.  Exact  reference  as  to 
the  volume,  number,  and  page  of  the  Journal  must  be  given.  The  Society  is 
not  responsible  for  statements  made  by  authors. 


OFFICERS  OF  THE  SOCIETY 

"President:     S.  K.  WOLF,  RKO  Building,  Rockefeller  Center,  New  York,  N.  Y. 
"Past-President:     H.  G.  TASKER,  Universal  City,  Calif. 
"Executive    Vice-P resident:     K.  F.   MORGAN,  6601   Romaine  St.,   Los  Angeles, 

Calif. 

""Engineering    Vice-President:    L.  A.  JONES,  Kodak  Park,   Rochester,  N.   Y. 
*Editorial   Vice-President:    J.  I.  CRABTREE,  Kodak  Park,  Rochester,  N.  Y. 
**  Financial  Vice-President:    E.  A.  WILLIFORD,  30  E.  42nd  St.,  New  York,  N.  Y. 
*  Convention    Vice-President:    W.   C.   KUNZMANN,   Box  6087,   Cleveland,  Ohio. 
"Secretary:    J.  FRANK,  JR.,  90  Gold  St.,  New  York,  N.  Y. 
"Treasurer:    L.  W.  DAVEE,  250  W.  57th  St.,  New  York,  N.  Y. 

GOVERNORS 

*J.  O.  AALBERG,  157  S.  Martel  St.,  Los  Angeles,  Calif. 

*M.  C.  BATSEL,  Front  and  Market  Sts.,  Camden,  N.  J. 

**R.  E.  FARNHAM,  Nela  Park,  Cleveland,  Ohio. 

*G.  FRIEDL,  JR.,  90  Gold  St.,  New  York  N.  Y. 

*A.  N.  GOLDSMITH,  444  Madison  Ave.,  New  York,  N.  Y. 

**H.  GRIFFIN,  90  Gold  St.,  New  York,  N.  Y. 

**A.  C.  HARDY,  Massachusetts  Institute  of  Technology,  Cambridge,  Mass. 

*S.  A.  LUKES.  6145  Glenwood  Ave..  Chicago,  111. 

*Term  expires  December  31,  1938. 

**Term  expires  December  31,  1939. 


A  WATER-COOLED  QUARTZ  MERCURY  ARC* 
E.  B.  NOEL  AND  R.  E.  FARNHAM** 

Summary. — The  structure  of  the  water-cooled  quartz  mercury  lamp,  its  operation, 
quality  of  radiation,  brightness,  and  source  size  limitations  are  first  described,  followed 
by  a  discussion  of  the  power-supply  equipment,  both  a-c.  and  d-c.  Applications  oj 
the  lamp  are  as  follows: 

(1)  Motion  picture  projection,  with  single  lamps  and  with  several  sources. 

(2)  Motion  picture  photography,  both  black-and-white  and  color,  and  the  ap 
plication  to  very  high-speed  motion  picture  photography.    For  black-and-white  photog  • 
raphy  the  lamp  is  quite  satisfactory.    For  color  work  the  relatively  limited  red  radia 
tion  may  call  for  external  methods,  either  in  the  use  of  fluorescent  reflectors  or  a  highly 
red-sensitive  emulsion,  to  make  up  for  this  deficiency. 

(3}  Film  printing.  Because  of  the  relatively  high  output  in  the  blue-violet  and 
ultraviolet  regions  this  lamp  may  prove  a  very  satisfactory  source,  especially  where 
advantage  is  taken  of  the  ultraviolet  radiation. 

The  following  additional  applications,  of  secondary  interest  to  the  motion  picture 
industry,  are  also  discussed:  photo-enlarging,  photoengraving,  and  searchlights. 

Within  the  past  few  years  a  number  of  new  mercury-vapor  light- 
sources  have  made  their  appearance.1  New  materals  and  technics 
have  made  possible  operation  at  temperatures  and  pressures  far 
above  previous  values  and  at  which  the  characteristics  of  the  light 
emitted  differ  greatly  from  those  of  the  older  type  of  mercury  source 
It  is  the  purpose  of  this  paper  to  discuss  the  work  done  at  Nela  Park 
on  one  of  the  newest  developments — a  water-cooled  quartz  mercury 
lamp  operating  at  a  pressure  of  about  1100  pounds  per  square-inch — 
and  some  of  its  possible  applications  in  the  motion  picture  industry 

Construction  of  the  Lamp. — A  1000-watt  lamp  of  this  type  is  shown 
in  Fig.  104).  It  consists  of  a  quartz  tube  about  40  mm.  long  having 
an  outside  diameter  of  6  mm.  and  a  bore  of  2  mm.  Sealed  into  each 
end  by  means  of  a  special  glass  are  tungsten  wires  which  are  both  the 
leads  and  the  electrodes.  The  tips  of  the  wires  project  just  through 
the  surface  of  a  small  quantity  of  mercury  located  in  each  end  of  the 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;  received 
April  20,  1938. 

**  General  Electric  Co.,  Cleveland,  Ohio. 

221 


222  E.  B.  NOEL  AND  R.  E.  FARNHAM          [J.  S.  M.  P.  E. 

lamp.     In  order  to  aid  in  starting,  the  lamp  is  filled  with  argon  gas 
at  50  mm.  pressure.     Other  characteristics  are  listed  in  Table  I. 

When  not  lighted,  the  internal  pressure  is  that  of  the  argon  gas, 
namely,  Vi&  of  an  atmosphere.  However,  when  lighted,  the  heat 
from  the  arc  vaporizes  some  of  the  mercury  in  the  pools  around  the 
electrodes,  building  up  a  pressure  of  the  order  of  75  atmospheres,  the 
exact  value  being  determined  by  the  wattage  input  and  the  distance 
by  which  the  electrodes  project  from  the  surfaces  of  the  mercury. 

TABLE  I 

Characteristics  of  1000- Watt  Water- Cooled  Quartz  Mercury  Lamp 

Arc  Length  25  mm. 

Inside  Diameter  2  mm. 

Outside  Diameter  6  mm. 

Operating  Pressure  75  atm. 

Watts  1000 

Operating  Volts  840 

Operating  Amperes  (a-c.)  1.4 

Lumens  per  Watt  65 

Lumens  65,000 

Max.  Surface  Brightness  (initial)  30,000  candles/cm2. 

Burning  Position  Horizontal 

In  order  to  be  able  to  dissipate  1000  watts  within  such  a  small 
volume  the  lamp  must  be  cooled  very  effectively.  It  is  not  sufficient 
merely  to  place  the  lamp  in  a  bath  of  water;  the  water  must  be  passed 
over  the  lamp  with  enough  velocity  to  prevent  the  formation  of 
steam  bubbles  on  the  surface  of  the  quartz.  Placed  around  the  lamp 
is  a  "velocity  tube"  having  a  radial  clearance  from  the  lamp  of  about 
1  mm.,  through  which  the  water  must  flow.  Because  of  this  restricted 
cross-section,  more  than  ample  water  velocity  is  attained  to  prevent 
the  formation  of  steam  with  a  water  flow  of  about  three  liters  per 
minute.  In  passing  over  the  lamp  the  increase  in  water  temperature 
is  only  a  few  degrees  Centigrade. 

One  type  of  cooling  jacket  is  shown  in  Fig.  1(B).  Water  enters  at 
one  end  and  leaves  at  the  other,  while  electrical  connections  are  made 
at  each  end  of  the  jacket  on  the  brass  rings.  A  socket  for  this  type 
of  jacket  is  shown  in  Fig.  2,  while  Fig.  3  shows  one  designed  to  take 
two  such  lamps. 

Since  both  leads  to  the  lamp  are  in  contact  with  the  water,  the  arc 
operates  in  parallel  with  a  water  resistance.  Where  the  water  sur- 
rounding the  lamp  has  a  large  cross-section  the  resistance  is  low 


Sept.,  1938]        WATER-COOLED  QUARTZ  MERCURY  ARC 


223 


enough  to  interfere  with  the  operation  of  the  lamp.  With  a  "velocity 
tube"  around  the  lamp,  however,  the  cross-section  of  the  water  is 
small  enough  so  that  the  current  through  the  water  is  only  10  to  25 
milliamperes. 

Spectral  Distribution  of  the  Discharge. — Incandescent  sources,  such 
as  tungsten  and  the  crater  of  a  carbon  arc,  emit  a  continuous  spec- 
trum; that  is,  all  colors  of  light  are  given  out.  Luminous  vapors 
and  gases,  however,  emit  only  certain 
colors  which  are  characteristic  of  the 
substance.  Fig.  4  shows  the  spectra  of 
a  number  of  commercial  mercury- vapor 
sources  and  the  spectra  of  a  water- 
cooled  quartz  mercury  lamp  operating 
at  various  pressures.  The  spectrum  of 
the  Cooper-Hewitt  lamp  operating  at 
0.0003  atmosphere  shows  only  a  few 
distinct  lines.  That  of  the  H-l  operat- 
ing at  1.4  atmospheres  appears  to  be 
little  different.  The  H-4  lamp  spec- 
trum at  8  atmospheres  shows  the  pres- 
ence of  a  very  weak  "background 
radiation" — the  colors  between  the 
mercury  lines  are  beginning  to  fill  in. 
At  25  atmospheres  (the  H-3  lamp),  the 
background  is  somewhat  stronger;  and, 
in  addition,  it  will  be  noticed  that  the 
main  spectral  lines  are  no  longer  sharp, 
the  blurring  being  more  pronounced  on 
the  long-wave  side. 

With  the  water-cooled  lamp  the  cur- 
rent densities  and  pressures  are  so 
much  greater  that  the  lines  are  even 
more  blurred  and  the  continuous  back- 


U)  W 

FIG.  1.  1000-watt  water- 
cooled  quartz  mercury  lamp: 
04)  the  lamp  proper;  (B) 
the  lamp  in  place  in  its  water 
jacket. 


ground  forms  a  very  appreciable  portion  of  the  radiation.*  The 
spectral  distribution  curves  of  Figs.  5  and  6  may  show  this  even 
better.  At  the  highest  loading,  shown  in  Fig.  6(D),  the  lamp  life 
is  quite  short,  but  if  a  better  material  than  quartz  becomes  available 
lamps  operating  at  this  pressure  may  be  practicable.**  The  emitted 


*  Pressures  are  calculated  from  the  formula2  Patm 
**  Cf.  footnote  p.  9. 


(Gradient  -  100)/3. 


224 


E.  B.  NOEL  AND  R.  E.  FARNHAM 


[J.  S.  M.  P.  E 


light  contains  appreciable  red,  as  shown  by  Table  II.4   The  effect  of 
this  upon  the  rendition  of  skin  tones  is  quite  noticeable. 

As  the  pressure  is  increased  still  further,  the  lines  merge  more  and 
more  into  the  background  until  they  disappear  completely.  Mr. 
Cornelias  Bol,  who  did  the  original  work  on  these  lamps  at  The  Philips 
Co.  in  Holland,  and  who  is  now  associated  with  our  Company,  has 


FIG.  2.     Single-unit  socket  with  lamp 
and  jacket  in  position. 


FIG.  3.  Socket  for  two  lamps.  The 
cap  is  hollow,  to  allow  the  water  to 
flow  up  through  one  lamp  and  down 
through  the  other. 


been  experimenting  with  mercury  discharges  at  extremely  high  pres- 
sures at  Stanford  University.  By  enclosing  a  lamp  in  a  bomb-like 
vessel  and  subjecting  it  to  an  external  pressure  of  10,000  pounds  per 
square-inch  to  prevent  it  from  bursting  he  obtained  the  spectrogram 
of  Fig.  7,  which  at  the  highest  voltage  per  centimeter  and  pressure 
shows  complete  absence  of  lines.  It  shows  also  that  as  the  pressure  is 
increased,  there  is  less  and  less  short-wave  ultraviolet  emitted. 


»pt.,  1938]        WATER-COOLED  QUARTZ  MERCURY  ARC 


225 


2  Q  0 

4J   LO  |>» 

J0    ^H  ^^ 

CO  (M 


00 
^O        CO 


"-O         00        TH        O 


08Z9 


6SI8 


I-   - 


w  O         O        O 

TS  O         O        ^f 

O     T-l  Oi  b- 


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fiq    O 


226 


E.  B.  NOEL  AND  R.  E.  FARNHAM          [j.  s.  M.  p.  E. 


FIG.  5.  Spectral  energy  distribution  curves 
for  water-cooled  lamp  (top)  and  two  air-cooled 
lamps  (below).  The  ordinates  are  milliwatts 
per  100  Angstrom  units  per  steradian  per  watt 
input. 


A-55    ATMOSPHERES 


B- 75  ATMOSPHERES 


f] 


fl 


, 


A 


700048000 


•C-  125  ATMOSPHERES 


0-225  ATMOSFVERES 


t; 


t 


FIG.  6.  Spectral  energy  distribution  curves  for  a  water-cooled 
quartz  mercury  lamp  operating  at  different  pressures.  The  ordi- 
nates are  milliwatts  per  100  Angstrom  units  per  steradian  per  watt 
input. 


Sept.,  1938]        WATER-COOLED  QUARTZ  MERCURY  ARC 


227 


The  alteration  in  the  spectral  distribution  as  the  pressure  is  in- 
creased is  such  that  the  color  of  the  light  is  materially  changed.  In 
air-cooled  lamps  at  very  low  pressures  the  discharge  is  distinctly 
greenish,  but  as  the  pressure  is  raised,  the  color  becomes  more  and 
more  white.  These  changes  are  plotted  in  Fig.  8  on  the  standard 
I.C.I,  color-chart.  On  this  chart  the  points  for  pure  spectral  colors 
lie  on  the  large  boundary  curve  as  marked,  while  those  for  unsatu- 
rated  colors  lie  inside.  The  dominant  hue  is  determined  by  the  direc- 


Volts 

1160 
1860 
2300 


FIG.  7.  Spectrogram  by  C.  Bol  at  Stanford  University:  quartz  mercury  arc 
with  gap  of  10  mm.  and  bore  of  1  mm.  operating  in  steel  container  with  the  circu- 
lating water  under  a  pressure  of  10,000  Ibs.  per  square-inch. 


tion,  and  the  saturation  by  the  distance  from  the  daylight  point.  It 
may  be  seen,  as  the  pressure  of  mercury  is  increased  in  the  series  of 
lamps  tested,  that  while  the  hue  changes  from  green  to  yellow-green 


TABLE  IP 


Percentage  of  Total  Light  from  Mercury  Arcs  Operating  at  Various  Pressures,  from 
Sun,  from  a  Tungsten  Lamp,  of  Wavelength  6000-7600 A 


Source 

Cooper-Hewitt 

H-l  Lamp 

H-4  Lamp 

H-3  Lamp 

Water-Cooled  Capillary  'Arc 

Sun 

500- Watt,  11 5- Volt  Tungsten 


Mercury 
Pressure 

in 
Atm. 

0.0003 
1.4 
8 
29 
110 


Per  Cent 

of  Light 

6000  „ 

-7600A 

0 

1.0 
1.7 
1.9 

7.0 
20.0 
27.0 


to  blue,  the  light  actually  becomes  very  nearly  white  as  shown  by 
the  closeness  with  which  the  points  for  high-pressure  operation  ap- 
proach the  daylight  point. 

Brightness  of  the  Discharge. — Even  more  unique  than  the  fact  that 
these  lamps  have  appreciable  continuous  radiation  is  their  intrinsic 
brightness.  Fig.  9  shows  the  brightness  of  water-cooled  lamps  oper- 


228 


E.  B.  NOEL  AND  R.  E.  FARNHAM          [j.  s.  M.  p.  E. 


COLOR  DIAGRAM 
1931    i.c.i.  SYSTEM- 


FIG.  8.     Color  coordinates  of  mercury  lamps  operating 
at  various  pressures. 


MAXKLM 

BRIGHTNE. 

SS    OF   2 

VM.  I.D. 

^ 

I40000 

^f>~ 

^^ 

—  - 

^^* 

$30000 

^ 

^^ 

^*^ 

i 

1- 

X 

/ 

3 

*: 

« 

80 

1 
tfPMC 

»          ia 

KMkIC      PI 

>                   M 
ItSSUC     M 

ATMOtftC 

Ss          " 

0                20 

0                 Z 

FIG.  9.  Maximum  brightness  of  water-cooled  mer- 
cury arcs  operating  at  various  pressures  in  tubes  of 
2-mm.  inside  diameter. 


Sept.,  1938]        WATER-COOLED  QUARTZ  MERCURY  ARC  229 

ated  at  various  pressures.*  These  figures  should  be  compared  with 
the  brightness  of  a  1000- watt  projection  lamp,  which  is  3100  candles 
per  square-centimeter  and  that  of  a  crater  of  a  carbon  arc,  which 
ranges  from  14,000  candles  per  square-centimeter  for  the  regular 
type  to  50,000  to  86,000  candles  per  square-centimeter  for  the  high- 
intensity  type.  The  brightness  of  the  quartz  lamp  is  essentially 
constant  along  the  length  of  the  arc,  but  across  the  arc  stream  it 
varies  as  shown  in  Fig.  10.  Since  it  is  a  line  source  of  light,  for  some 
applications,  several  must  be  used  side  by  side,  or  the  more  usual 
type  of  optical  systems  must  be  modified  for  use  with  a  source  of  this 
shape. 

TABLE  III 

Comparison  of  Energy  Radiated  in  the  Ultraviolet,  Visible,  and  Infrared  Portions  of 

the  Spectrum  by  a  1000-Watt  Quartz  Water-Cooled  Mercury  Lamp  and  a  1000- 

Watt  High-Efficiency  Biplane- Filament  Lamp.    (For  the  Tungsten  Lamp  the  Figures 

Are  for  Energy  Radiated  beyond  the  Bulb  by  the  Filament) 

1000-Watt  1000-Watt 

Biplane  Water-Cooled 

at  27.5  LPW  Mercury 

Ultraviolet   (3000-4000  A)  5  watts  20  watts 

Visible          (4000-7600  A)  145  watts  284  watts 

Infrared        (7600-14,000  A)  690  watts  76  watts 

Total  watts  radiated  840  380 

Lumens  27,500  lumens      65,000  lumens 

Coolness  of  the  Light. — One  of  the  most  valuable  characteristics  of 
the  lamp  is  the  coolness  of  its  light.  This  is  illustrated  in  Table  III, 
where  a  1000- watt  quartz  lamp  is  compared  with  a  high-efficiency 
biplane  lamp.  It  will  be  seen  that  for  equal  lamp  wattage  the 
quartz  lamp  radiates  more  than  21/*  times  the  light  but  only  45  per 
cent  of  the  energy  of  the  tungsten  lamp.  Thus,  to  supply  an  equal 
amount  of  light,  only  42  per  cent  as  much  wattage  is  required  in  a 
water-cooled  quartz  lamp  as  with  the  tungsten-filament  source,  and 
the  radiated  energy  is  reduced  to  one-fifth.  If  the  comparison  were  to 
be  made  on  the  basis  of  photographic  effectiveness,  the  result  would  be 
even  more  favorable  to  the  mercury  lamp. 

*  De  Groot's  formula2  is  based  upon  data  taken  up  to  150  atmospheres  and  550 
volts  per  centimeter.  It  has  been  used  here  with  values  of  gradient  up  to  750 
volts  per  centimeter,  so  that  pressures  above  150  atmospheres  should  be  con- 
sidered as  only  approximately  accurate. 


230 


E.  B.  NOEL  AND  R.  E.  FARNHAM          [j.  s.  M.  p.  E. 


BR1GHT>JESS   DSTRSUTON 

ACROSS   WATER-COOJED 

ARCS 


MILLMETERS  FROM   AXIS  OF    ARC 


FIG.  10.  Variation  in  brightness  across  water-cooled 
mercury  arcs  operating  at  various  pressures  in  tubes  of 
2-mm.  inside  diameter. 


7 


FOOT  CANDLES 


FIG.  11.  Increase  of  temperature  (Centi- 
grade) of  a  portion  of  the  skin  (lower  arm) 
upon  irradiation  with  light  from  tungsten 
lamps  and  water-cooled  mercury  arcs.  For 
equal  increases  in  temperature  41/«  times  as 
much  mercury  light  can  be  employed  as  in- 
candescent lamp  light.  (E.  G.  Dorgelo, 
Technical  Review,  June,  1937.) 


Sept.,  1938]        WATER-COOLED  QUARTZ  MERCURY  ARC  231 

Another  way  of  illustrating  the  coolness  of  this  light  is  by  means  of 
Fig.  11,  which  gives  the  relative  increase  of  temperature  of  the  skin 
with  tungsten  and  with  water-cooled  mercury  illumination.4  For 
equal  increases  in  temperature  4x/2  times  more  mercury  illumination 
can  be  used  than  tungsten.  This  is  important  for  many  applications. 

Operation  of  the  Lamp. — On  60-cycle  a-c.  operation  there  is  a  pro- 
nounced 120-cycle  flicker,  which  is  clearly  evident  in  Fig.  12.  By 
operating  three  lamps  on  three-phase  the  flicker  can  be  sensibly 
eliminated  as  shown  by  the  oscillogram  of  Fig.  13. 


FIG.  12.  Current,  voltage,  and  light  traces  for  1000- 
watt  water-cooled  mercury  arc  operating  on  a  60-cycle 
supply. 


The  lamps  reach  full  brightness  within  a  second  or  two  after  the 
switch  is  closed.  Since  their  heat  storage  is  small  and  cooling  rapid, 
unlike  the  air-cooled  high-intensity  lamps  they  may  be  restarted  at 
once  after  the  current  has  been  turned  off. 

During  life  the  lamp  voltage  gradually  increases  and  the  current 
and  wattage  decrease.  The  useful  life  is  terminated  by  failure  to 
start  or  by  fracture  of  the  quartz  bulb.  Although  the  operating  pres- 
sure is  high,  the  volume  is  so  small  that  failures  are  not  violent.  How- 
ever, because  the  lamp  is  surrounded  by  water  the  outer  jacket  is 
subjected  to  a  shock  when  a  lamp  fails  and  may  crack,  presenting  a 
possible  hazard  of  high  voltage  and  running  water.  Where  necessary 
a  switch  actuated  by  water  line  pressure  can  be  installed  to  turn  off 
the  power  should  a  jacket  break. 


232  E.  B.  NOEL  AND  R.  E.  FARNHAM          [j.  S.  M.  P.  E. 

The  life  of  the  lamp  is  dependent  upon  the  number  of  times  it  is 
started  and  the  type  of  service  in  which  it  is  used.  Although  still 
in  the  developmental  stage  it  is  felt  the  life  is  satisfactory  for  many 
special  applications. 

Equipment. — For  a-c.  operation  of  the  1000- watt  lamp  the  high- 
reactance  transformer  shown  in  Fig.  14  is  used.  The  secondary  sup- 
plies 1200  volts  on  open  circuit  for  striking  the  arc.  At  the  instant 
of  starting,  the  arc  voltage  is  so  low  that  it  is  practically  a  short  cir- 
cuit on  the  winding,  and  the  impedance  of  the  unit  limits  the  current 


'HREE   LAMPS    ON  THREE  PHASE    60    CYCLE 


ZERO  FOR  LIGHT    TRACE 

-•- P      ^^*fc»,. 


FIG.  13.  Oscillograph  of  ripple  in  combined 
light  output  of  three  lamps  operating  on  a  three- 
phase  60-cycle  supply. 


in  this  case  to  2.6  amperes.  As  soon  as  the  inside  tube  walls  become 
warm  the  pressure  builds  up  and  the  voltage  increases  to  840  volts, 
while  current  automatically  drops  to  1.4  amperes. 

The  lamps  operate  on  ballasted  direct  current  with  about  15  per 
cent  less  current  than  on  alternating  current.  D-c.  operation  is  in 
many  ways  more  satisfactory,  but  the  generator  or  rectifier  equip- 
ment is  much  more  bulky  than  the  transformer. 

The  lamp  may  be  run  for  15  to  30  seconds  in  dish  or  bulb  filled  with 
glycerine,  but  for  any  longer  periods  of  operation  it  must  be  run  in 
flowing  water.  The  lamp  surface  must  be  cleaned  occasionally  with 
dilute  HC1  to  remove  deposits,  the  frequency  depending  upon  the 
salts  in  the  water  supply.  Recirculating  cooling  systems  have  been 


Sept.,  1938]        WATER-COOLED  QUARTZ  MERCURY  ARC  233 

built  employing  a  pump  and  radiator,  but  even  then  it  is  necessary 
occasionally  to  clean  the  lamp. 

Several  kinds  of  sockets  have  been  designed  for  this  lamp,  depend- 
ing upon  the  use  intended.  Fig.  15  shows  a  different  type  of  single 
unit  in  which  the  replaceable  part  is  merely  the  lamp  itself  with  brass 
ends.  Figs.  16  and  17  show  two  styles  of  jackets  employing  three  of 
this  same  kind  of  lamp. 

Since  the  lamp  is  still  in  the  developmental  state,  actual  experience 
with  its  possible  applications  is  limited  Any  analysis  of  the  possible 
future  application  of  the  water-cooled  unit  must,  accordingly,  be 


FIG;  14.  Transformer  for  operating  1000- 
watt  water-cooled  mercury  lamp  on  110-  or 
220-volt,  60-cycle  lines. 

based  upon  a  consideration  of  the  characteristics  of  the  lamp  with 
respect  to  the  requirements  of  the  several  potential  services. 

The  forms  of  lamp  illustrated  above  provide  maximum  perform- 
ance, ease  of  replacement  of  the  elements,  and  compactness.  Some 
modification  of  present  forms  may  be  necessary  for  adaptation  to  a 
particular  service;  but  the  capillary  tube  is  an  essential  feature  and 
fixes  the  width  of  the  lighting  element.  In  summary,  the  chief  char- 
acteristics are  these : 

(1)  Source  dimensions. — 1  mm.  by  25  mm.  for  1000  watts.    Complete  assembly 
compact. 

(2)  Light  output. — 65  lumens  per  watt ;  steady  on  d-c. ;  cyclic  variation  almost 
reaching  zero  on  single-phase  a-c.  but  causing  only  slight  ripple  on  three-phase 


234 


E.  B.  NOEL  AND  R.  E.  FARNHAM 


[J.  S.  M.  p.  E. 


(3)  Power  supply. — High  voltage  (840  volts   a-c.,   or   d-c.   for    1000   watts); 
current — 1.4  amperes  a-c.,  1.2  amperes  d-c. 

(4)  Source  brightness. — 30,000  candles  per  square-centimeter. 

(5)  Light  distribution. — Characteristic  of  a  linear  source  of  light. 

(6)  Spectrum. — Continuous,  but  with  most  of  the  light  emanating  from  peaks 


FIG.  15.  Socket  and  jacket  combined,  in  which 
the  replaceable  element  is  the  lamp  itself,  shown 
on  the  right. 

at  5600  A  (yellow-green),  4350  A  (blue-violet),  4100  A  (violet),  and  3650  A  (near 
ultraviolet). 

(7)  Cooling  system. — Circulating  water,  self-contained  system  or  from  mains. 
More  than  90  per  cent  of  infrared  (heat)  radiation  absorbed  by  circulating  water. 

The  following  discussion  will  serve  briefly  to  indicate  the  effect  of 
such  characteristics  upon  several  phases  of  lighting  for  photography 
and  projection. 

MOTION  PICTURE  PRODUCTION 

Black-and-White,  and  in  Color. — The  high  brightness  and  concen- 
tration of  source  provide  the  requisite  beam  control  and  efficiency  of 
light  utilization  with  both  lens  and  reflector  equipments.  To  pro- 


Sept.,  1938]        WATER-COOLED  QUARTZ  MERCURY  ARC 


235 


vide  an  adequate  amount  of  light  several  capillary  elements  may  be 
grouped  together  in  a  single  reflector  or  equipment.  The  color  of  the 
light  is  satisfactory  for  black-and-white  photography,  although  the 
"red"  of  the  properties  may  have  to  be  intensified  for  correct  rendi- 
tion. A  definite  advantage  in  respect  to  the  comfort  of  the  actors 


FIG.  16.     Socket  for  three  lamps  for  single-  or  three-phase 
operation,    with    the    lamps    in  a   triangular  arrangement. 


results  from  the  very  small  proportion  of  infrared  radiation.  The 
spectral  quality  of  the  light  is  not  adapted  to  present  color  processes, 
nor  can  it  be  rendered  suitable  by  filtering  alone. 

The  camera  shutter  or  the  movement  of  the  film  must  be  syn- 
chronized if  the  lamps  are  operated  on  a  single-phase  a-c.  supply. 
Direct  current  or  the  combination  of  several  elements  on  three-phase 
alternating  current  eliminates  this  requirement.  The  cooling  system 
should  be  self-contained,  since  portability  of  equipment  is  important 
in  studio  practice. 


236  E.  B.  NOEL  AND  R.  E.  FARNHAM          [j.  s.  M.  P.  E. 

Ultra  Speed. — The  extremely  high  light-intensities  necessary  for 
photography  at  1000  or  more  pictures  per  second  can  easily  be  ob- 
tained because  the  compact  equipment  can  be  placed  close  to  the  area 
being  photographed.  But  the  greatest  advantage  is  that  there  is  no 
heat  problem.  For  example,  it  has  been  possible  to  take  1000  pic- 


FIG.  17.  Socket  for  three  lamps,  for  single-  or 
three-phase  operation,  with  lamps  arranged  in 
a  plane. 

tures  per  second,  i.  e.,  V^oooth  second  exposure  on  positive  film  at 
f/2.0  with  no  discomfort. 

Three-phase  alternating  or  direct  current  are  necessary  unless 
single-phase  alternating  current  of  the  picture  frequency  or  a  multiple 
thereof  is  obtainable. 

Trick  and  Background  Photography,  Animation,  Tilting. — For 
processes  involving  the  illumination  of  a  copy-board  this  linear  source 
in  a  trough  reflector  of  parabolic  and  cylindrical  cross-section  pro- 
duces high  uniform  illumination  with  minimum  heat.  Where  a  pic- 


Sept.,  1938]        WATER-COOLED  QUARTZ  MERCURY  ARC  237 

ture  is  projected  to  a  screen  and  rephotographed,  the  water-cooled 
lamp  can  be  used  as  the  projector  light-source.  Color  photography 
is  practicable  to  a  limited  extent  by  intensifying  the  reds. 

Film  Printing. — The  relatively  large  proportion  of  ultraviolet 
radiation  suggests  the  use  of  the  water-cooled  lamp  for  motion  pic- 
ture printing  and  production  of  duplicate  negatives.  The  high 
source  brightness  lends  itself  well  to  optical  printers.  Direct  current 
is  necessary  where  the  film  moves  continuously. 

Sound  Recording. — Adaptability  to  optical  control  and  the  favor- 
able color  of  the  light  make  it  especially  applicable  to  sound  recording 
with  both  the  light-valve  and  galvanometer  systems.  Direct  current 
is  necessary  to  eliminate  parasitics. 

TELEVISION    STUDIOS 

The  color  of  the  light  from  the  liquid-cooled  capillary  lamp  matches 
well  the  characteristics  of  the  iconoscope,  which  is  sensitive  particu- 
larly to  the  blue-green.  The  suppression  of  the  infrared  is  important 
in  avoiding  chromatic  aberration.  Since  illumination  levels  must  be 
very  high,  the  cooler  light  is  a  boon  to  the  artists. 

MOTION  PICTURE  PROJECTION 

The  length  of  the  source  is  not  too  great  to  be  efficiently  utilized  in 
a  motion  picture  projector.  The  width  is  insufficient  to  fill  the  lens 
system  unless  a  cylindrical  surface  is  incorporated.  Several  sources 
and  images  may  be  aligned  side  by  side  to  provide  adequate  illumina- 
tion for  large  screens.  The  color  of  the  light  seems  satisfactory  for 
black-and-white  pictures.  For  color  pictures,  reds  must  be  exagger- 
ated in  the  film.  If  the  pictures  are  also  taken  under  capillary  lamps, 
the  intensification  of  the  reds  would  therefore  have  to  be  compounded. 

PHOTOENGRAVING 

Two  steps  are  involved  in  photoengraving:  taking  of  the  negative 
and  printing  on  metal.  For  the  former  the  copy-board  must  be  il- 
luminated from  the  sides,  a  condition  to  which  the  line  source  of  the 
water-cooled  lamp  lends  itself  admirably.  Color  copy  is  photo- 
graphed through  red,  green,  and  blue  filters.  Therefore,  any  dis- 
crepancy in  the  light  output  in  the  respective  colors  can  be  com- 
pensated for  by  the  exposure  ratios.  The  unmodified  color  of  the 
mercury  arc  corresponds  very  closely  with  the  requirements  of  the 
printing  processes. 


238  E.  B.  NOEL  AND  R.  E.  FARNHAM          [J.  S.  M.  p.  E. 

BLUE-PRINTING 

The  same  advantages  that  make  the  lamp  applicable  for  printing 
on  metal  in  photoengraving  make  it  worth  while  for  blue-printing, 
i.  e.,  large  amount  of  light  of  a  color  favorable  to  the  sensitivity  char- 
acteristics of  the  photochemical  materials. 

PHOTO  MURAL  ENLARGING 

There  is  no  entirely  satisfactory  source  now  commercially  available 
for  enlargers  used  in  making  photo  murals.  The  need  for  compact- 
ness, spectral  quality  favorable  to  the  bromide  emulsion,  as  well  as 
freedom  from  heat,  are  amply  met  in  the  new  source. 

Source  shape,  high  brightness,  and  color  will  be  found  favoring 
conditions  in  other  projection  sources,  such  as  searchlights  and  air- 
port lighting.  In  general,  the  water-cooling  system  can  be  either 
self-contained,  with  circulating  pump  or  thermo-syphon,  or  connected 
to  the  city  mains.  Where  portability  of  equipment  is  important 
self-contained  cooling  will  obviously  be  indicated. 

In  order  to  minimize  high-voltage  wiring,  transformers  may  be 
incorporated  in  the  equipment.  For  d-c.  operation,  a  rectifier-filter 
system  or  a  d-c.  generator  appear  equally  feasible.  The  transformer 
supplying  the  high  voltage  to  the  rectifier  and  filter  can  have  high 
leakage  reactance,  thus  practically  eliminating  ballast  losses.  The 
advantage  lies  with  the  generator  when  a  number  of  lamps  are  to  be 
employed. 

In  conclusion,  it  may  be  said  that  the  ultra-high  pressure  quartz 
mercury  lamp  may  find  suitable  application  in  several  places  in  the 
motion  picture  field.  Water-cooling  and  high  voltage  are  necessary, 
and  in  some  cases  it  may  be  desirable  to  employ  a  pressure-actuated 
switch  to  eliminate  the  hazard  of  running  water  and  high  voltage  in 
the  case  of  a  jacket  failure.  The  advantages  are  compactness,  high 
efficiency,  high  actinic  value,  and  remarkably  high  ratio  of  lumen  out- 
put to  radiated  energy. 

The  authors  wish  to  express  their  thanks  to  D.  D.  Hinman,  A.  L. 
Shrider,  M.  A.  Easley,  and  Dr.  B.  T.  Barnes  of  the  Lamp  Develop- 
ment Laboratory  at  Nela  Park  for  many  of  the  measurements  made 
on  these  lamps. 


Sept.,  1938]        WATER-COOLED  QUARTZ  MERCURY  ARC  239 

REFERENCES 

1  "Eine  Neue  Lichtquelle  Hoher  Leistung,"  Das  Licht  (Apr.  15,  1935),  No.  4, 
p.  84. 

BOL,  C.:    "Een  Niewe  Kwiklamp,"  Ingenieur,  50  (June,  1935),  No.  24,  p.  91. 

2  DEGROOT,   W. :     "Het    Emissie   en  Absorptie — Spectrum   van   Kivikdamp 
Bij  Z.  H.  Drukken,"  Ingenieur,  50  (June,  1935),  No.  24,  p.  92. 

3  BARNES,  B.  T.,  AND  FORSYTHE,  W.  E.:    "Characteristics  of  Some  New  Mer- 
cury Arc  Lamps,"  J.  Opt.  Soc.  Amer.,  27  (Feb.,  1937),  No.  2,  p.  83. 

4  DORGELO,  E.  G.:    "Water-Cooled  Mercury  Lamps,"  Philips  Technical  Re- 
view, 2  (June,  1937),  No.  6,  p.  165. 

DISCUSSION 

MR.  KELLOGG:  Relative  to  the  visible  light,  the  ultraviolet  of  a  high-pressure 
arc  is  very  much  less;  but  does  it  decrease  as  the  wattage  and  pressure  increase, 
or  do  they  increase  together,  the  visible  portion  increasing  very  much  faster? 
Also,  is  the  life  with  d-c.  as  long  as  with  a-c?  That  is,  for  the  same  number  of 
startings? 

MR.  NOEL:  The  life  is  good  with  either  a-c.  or  d-c.  The  long-wave  ultraviolet 
increases  as  the  pressure  is  raised,  but  the  short-wave  ultraviolet  in  the  neighbor- 
hood of  2537 A  is  absorbed. 

MR.  RICHARDSON:  I  understand  it  is  proposed  to  use  several  of  these  lamps  to- 
gether, as  a  projector  light-source.  The  light  would  have  to  pass  through  the 
water  jacket  and  several  thicknesses  of  glass.  Would  you  be  able  to  obtain  the 
effect  of  a  solid  light -source? 

MR.  NOEL:  I  believe  so.  The  water  absorbs  infrared  but  not  very  much  visible 
light;  and  since  the  water  and  glass  are  in  contact  there  is  little  loss  at  that  point. 

MR.  KELLOGG  :  With  regard  to  the  light  distribution,  in  spite  of  a  large  increase 
in  the  red  as  well  as  in  the  blue  there  is  always  a  range  of  very  little  radiation,  I 
should  say,  in  the  green.  That  is  not  due  to  absorption,  is  it? 

MR.  NOEL:    No,  it  is  not. 

MR.  DURAT:  In  using  a  bank  of  the  lights,  would  it  not  be  preferable  to  place 
them  all  in  a  single  bath  of  water  so  as  to  have  less  refractive  effect? 

MR.  FARNHAM:  I  do  not  think  we  should  try  to  control  the  light  within  the 
water  unit.  The  water  merely  provides  a  means  of  getting  the  heat  away  from 
the  lamp. 

MR.  DURAT:  I  was  thinking  of  an  auxiliary  water  jacket,  not  to  cool  the  lamps 
but  to  act  as  a  medium  through  which  the  light  could  pass. 

MR.  NOEL:  I  see  no  objection  to  that,  although  we  have  no  trouble  with  the 
lamps  we  have  shown. 


NEGATIVE-POSITIVE   TECHNIC  WITH  THE  DUFAYCOLOR 

PROCESS* 

T.  T.  BAKER** 


Summary. — Progress  in  two  directions  has  greatly  simplified  making  prints  from 
screen-film  negatives.  The  study  of  emulsion  characteristics  and  of  the  mechanics 
of  development  with  silver  bromide  solvents  has  led  to  the  avoidance  of  color  dilution 
in  copying  one  screen  material  from  another.  Sodium  thiosulfate  in  a  metol  de- 
veloper has  been  shown  to  localize  development  in  the  lower  strata  of  the  film,  so  that 
the  silver  image  is  formed  in  close  contact  with  the  reseau,  largely  eliminating  scatter 
at  the  boundaries  of  differently  colored  units;  the  crystalline  structure  of  the  silver  salts 
and  grain-size  frequency  also  assist  in  preventing  scatter.  Residual  color  dilution 
as  the  result  of  the  45 -degree  oriented  reseaux  is  explained,  and  the  way  in  which  this 
has  been  counteracted  by  suitable  choice  of  gammas  in  the  negative  and  positive  ma- 
terial. The  production  of  a  vapor-lamp  emitting  the  line  spectra  of  mercury  and 
cadmium  without  appreciable  spectral  background,  combined  with  a  liquid  didymium 
chloride  filter  has  provided  a  triple  monochromatic  light-source,  the  spectral  lines  of 
which  coincide  with  the  peaks  of  the  reseau  transmissions,  thereby  eliminating  di- 
lution of  color  due  to  overlap,  such  as  has  always  previously  been  present  with  color 
filters  of  the  narrow-cut  type.  The  Dufaycolor  contact  printing  machine  with  auto- 
matic control  of  both  hue  and  printing  light  is  described.  The  technics  of  printing, 
and  development  with  standard  equipment,  are  described. 

A  good  deal  has  been  said  from  time  to  time  about  the  copying  of 
one  color-screen  material  upon  another,  the  fidelity  of  the  copies, 
and  so  on,  and  during  the  past  two  years  a  great  deal  more  has  been 
said  about  making  screen  positives  from  screen  negatives.  In  this 
paper  will  be  described  the  details  of  the  negative-positive  process, 
which  has  furnished  a  solution  to  making  commercial  screen-mosaic 
cine  prints  by  the  Dufay  process. 

In  talking  about  additive  processes,  it  should  be  remembered  that 
all  color  photographs  are  today  taken  by  an  additive  analysis;  that 
is,  by  recording  the  blue-violet,  green  and  red  components.  But 
whereas  in  subtractive  cases  the  separations  are  used  as  a  basis  for 
making  continuous  tone  prints,  in  screen  processes  the  negative 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C. ;    received 
May  9,  1938. 

**  Dufaycolor,  Inc.,  New  York,  N.  Y. 

240 


NEGATIVE-POSITIVE  PROCESS 


241 


separations  are  usually  reversed  to  positive,  the  one  color  matrix 
providing  the  additive  filters  for  viewing  by  the  retinal  process  of 
confusion. 

In  Dufaycolor  negative-positive  technic  the  same  matrix  is  used 
as  base  for  both  negative  and  positive  emulsions.  A  photomicro- 
graph of  it  is  seen  upon  the  screen;  the  individual  blue  and  green 
rectangles  are  approximately  19  to  the  millimeter.  Taking  one  blue 
and  one  green  rectangle,  and  the  piece  of  red  line  contiguous  as  a 
complete  "unit,''  the  areas  of  the  three  elements 
are  balanced  so  as  to  give  white  on  projection. 
The  average  of  a  number  of  readings  made  on  a 
special  form  of  trichromatic  colorimeter  provides 
a  numerical  assay  of  the  balance  of  the  unit,  and 
variations  from  neutrality  are  kept  within  limits 
of  tolerance  that  have  been  agreed  upon  as  the 
result  of  considerable  visual  test.  This  point  is 
mentioned  because,  even  with  the  precision  con- 
trol of  the  relative  areas  in  the  unit,  minute 
deviations  invisible  to  the  eye  can  suffice  to  cause 
off-balance  in  printing.  The  degree  of  off-balance 
in  any  particular  reseau  is  measured,  and  a  code 
number  is  obtained  designating  the  minus-filter 
combination  required  to  give  the  hue  correction. 

The  negative  must  thus  be  graded  for  color 
as  well  as  density,  and  as  printing  is  effected  by 
light  consisting  of  three  monochromatic  bands, 
the  color  correction  is  obtained  by  means  of 
three  sets  of  compensating  filters  each  designed 
to  reduce  the  intensity  of  one  of  the  bands 
without  affecting  the  others.  Minus  colors  of  the  cyan,  ma- 
genta, and  yellow  type,  but  actually  complementaries  of  the  reseau 
colors,  are  used,  and  these  filters  are  dropped  into  the  light- 
beam  by  means  of  light  electromagnets  operated  by  relays  the  ex- 
citation of  which  is  controlled  by  metal  staples  in  the  perforations  of 
a  separate  master  film.  The  film  is  provided  with  two  series  of  these 
metal  staples,  and  passes  through  two  distinct  contact  boxes;  one 
contact  box  actuates  the  magnets  introducing  the  necessary  combi- 
nations of  neutral  gray  filters  to  effect  control  of  light  intensity. 
The  Lawley  printer  has  lent  itself  well  to  these  two  methods  of  con- 
trol, the  stapling  being  done  on  a  full-length  black-and-white  print 


FIG.  1.  CAD- 
mium-mercury- 
vapor  lamp.  (Cour- 
tesy British  Thomp- 
son-Houston Co., 
Ltd.,  Rugby,  Eng- 
land.) 


242  T.  T.  BAKER  [j.  s.  M.  P.  E. 

from  the  negative  so  that  the  latter  can  not  be  mechanically  dam- 
aged. A  separate  feed  and  take-up  are  provided  for  the  control  film. 

The  light-source  is  of  prime  importance  in  making  screen  prints. 
Originally  a  Mazda  lamp  was  employed,  and  narrow-cut  gelatin 
filters,  that  removed  from  the  white  light  those  portions  of  the  spec- 
trum that  were  common  to  any  two  of  the  reseau  primaries.  These 
overlap  quite  considerably,  and  the  overlap  is  greatly  magnified  in 
printing,  causing  marked  dilution  of  color.  Such  filters  are  very 
inefficient,  and  G.  B.  Harrison  in  England  some  time  ago  devised  a 
light-source  composed  of  a  mixture  of  mercury  vapor  and  red  filtered 
Mazda. 

Recently,  however,  cadmium  has  been  introduced  into  high-pres- 
sure mercury- vapor  lamps,  and  such  a  mercury-cadmium  lamp, 
running  at  a  pressure  of  about  1  atmosphere,  has  provided  an  elegant 
solution  of  the  problem  of  producing  a  "tri-monochromatic"  light  - 


I  .  I  .  I  .  I  .  I  .  I  .  I  .  I  .  I  .  I  .  I  .  I  .  I  .  I  .  I 


FIG.  2.     Mercury-cadmium  lines. 

source.  The  cadmium-mercury-vapor  lamp  shown  in  Fig.  1  is  at 
present  made  in  England  but  a  great  deal  of  experimental  work  has 
been  done  on  it  in  this  country;  much  valuable  information  was 
published  on  the  subject  recently  by  Marden,  Beese  and  Meister,1 
who  give  the  figures  in  Table  I  for  the  distribution  of  light  from 
cadmium,  as  measured  with  a  monochromator,  thermopile,  and 
galvanometer : 

TABLE  I 

Cadmium  (%  in  Visible) 

Line  Low  Pressure  High  Pressure* 

6438  A  9.2  17.8 

5086  61.0  58.0 

4800  23.7  14.1 

4678  6.1  5.4 

*  Corrected  for  eye  sensitivity.2 


Sept.,  1938] 


NEGATIVE-POSITIVE  PROCESS 


243 


The  overall  efficiency  of  the  lamp  is  somewhat  lower  than  that  of 
the  plain  mercury  type,  the  visible  radiation  being  about  75  per  cent 
only  of  the  10  or  12  lumens  per  watt  mentioned  by  Dushman  at  the 
Fall  Convention.3 


,  |  .  I  .  I  .i  .  I  .  I  .  I  .  i  .  I.  I.  I  .  I  .  I  .  I  .  I 
40  £°  *° 


FIG.  3.     Absorption  of  saturated  solution  of  didymium 
chloride. 

The  mercury-cadmium  lines  are  shown  in  Fig.  2,  and  it  will  be  seen 
that  there  is  a  very  strong  element  of  red,  actually  about  6  per  cent, 
added  to  the  familiar  mercury  line  spectrum.  Three  lines  are  used 
for  printing,  one  in  the  blue-violet,  one  in  the  green,  and  one  in  the 
red,  at  643  m^u,  546  m/*,  and  436  m/u-  The  remaining  lines  are  ex- 


f* 

\---\-.\  '.I- 

-     _      _    _- 

—  FILM   BAS£ 

^  RESEAU 

.*< 

RICH   BIRIGI   Bl 

RI  a  lei 

s 

—  -  EMULSION   LAYER 

Hi 

g|Gl6|B|-Ql8IRieiBI 


—  F/LM  BASE 


,  —  INSULATING  LAYeff 
EMULSION   LAYFR 


-J       WTI-SCATTEK  PMNT 


FIG.  4.     Showing  relation  of  reseau  to  emulsion 
layer. 

tinguished  by  means  of  a  composite  filter,  the  chief  component  of 
which  is  a  3-inch  deep  liquid  cell  containing  a  saturated  solution  of 
pure  didymium  chloride.  The  marked  absorption  of  this  salt  is 
seen  in  Fig.  3.  As  luck  will  have  it,  the  absorption  bands  come  in  the 
most  fortunate  places,  totally  eliminating,  for  example,  the  yellow 


244 


T.  T.  BAKER 


[J.  S.  M.  P.  E. 


mercury  lines,  which  would  otherwise  pass  through  both  red  and 
green  reseau  elements,  causing  green  to  add  to  red  and  so  give  orange, 
or  red  to  add  to  green  and  so  give  orange-greens.  The  lamp  can,  of 
course,  equally  be  used  in  an  optical  printer. 

When  in  1928  the  first  serious  attempts  at  negative-positive  films 
were  made  in  Paris,  by  Louis  Dufay,  Charles  Bonamico,  and  the 
author  we  experienced  considerable  color  dilution  in  making  prints 
from  the  screen  negatives.  Several  thousand  feet  of  negative  were 
made  in  the  South  of  France,  on  8-line  per  millimeter  reseau,  and 
prints  from  these  on  15-line  reseau  were  shown  at  the  Pavilion 
Theater,  London,  nearly  ten  years  ago!  These  pictures  were  scenes 
of  an  act  by  artists  in  an  orange  grove,  and  it  is  curious  that  the 


l.OO 


0.75 


050 


0.25 


0<4  .08          .12  .16  .20          .M  .28  32 

HYPO.     GRAM    MOLS    PER    .tlTER 

FIG.  5.  Development  in  upper  and 
lower  layers  of  emulsion  film.  (Repro- 
duced from  Phot.  J.) 

oranges  themselves  and  the  blue-greens  of  the  foliage  were  quite 
saturated,  while  all  other  colors  were  badly  diluted.  It  soon  became 
evident  that  two  factors  were  at  work  in  causing  color  dilution.  Ir- 
radiation at  the  reseau  element  boundaries  was  one.  The  light 
scatter  increased  as  the  thickness  of  the  insulating  varnish  layer  be- 
tween emulsion  and  reseau  increased;  for  this  reason  the  thickness 
of  the  insulating  coating  was  reduced  to  between  3  and  4  microns. 
The  importance  of  this  thickness  from  the  point  of  view  of  scatter 
must  be  emphasized.  The  other  cause  was  the  decided  overlap  of 
the  additive  reseau  colors.  The  reason  for  the  purity  of  the  orange 
and  blue-green  colors  in  these  early  prints  was  probably  minimized 
scatter  in  these  regions  owing  to  very  decided  minima  in  the  spectral 


Sept.,  1938] 


NEGATIVE-POSITIVE  PROCESS 


245 


sensitivity  of  our  emulsion  at  that  time.  D.  A.  Spencer4  in  1933 
drew  attention  to  the  results  of  light  scatter  within  the  emulsion — 
actually  the  irradiation  referred  to — and  pointed  out5  that  the  de- 
saturating  effect  is  common  to  negative-positive  and  successive  re- 
versal processes.  He  also  points  out  that  the  effect  of  a  silver  bro- 
mide solvent  (ammonia,  thiocyanate,  thiosulfate,  etc.),  which  is 
ordinarily  used  in  first  development  in  reversal  processing,  causing 
the  degree  of  development  occurring  under  adjacent  color  elements 
to  become  exaggerated,  is  offset  by  the  opposite  effect  of  scatter  in 
subsequent  reversal,  but  that  it  is  not  so  offset  when  developing  as  a 


LOG     EXPOSURE 

FIG.  6.  Characteristic  curve:  upper  curve: 
developed  as  negative  in  DK50;  lower  curve: 
reversed.  (Note:  The  (lower)  reversal  curve 
has  been  plotted  in  reverse  position  for  better 
comparison.) 

negative.  Spencer  has  found  that  by  the  use  of  hypo  as  a  silver 
bromide  solvent  in  the  developer,  the  developed  image  is  confined  to 
the  lower  layers  of  emulsion  grains — that  is,  of  course,  those  nearest 
the  reseau,  and  is  what  we  want  (Fig.  4).  The  solubility  of  silver 
bromide  is  much  greater  in  sodium  thiosulfate  solution  than  potas- 
sium thiocyanate  or  ammonia.  One  hundred  grams  of  solution  con- 
taining 10  grams  of  Na2S2O3  at  20°C  will  dissolve  3.50  grams  of  AgBr; 
a  similar  solution  of  potassium  thiocyanate  at  25  °C  will  only  dissolve 
0.73  gram  of  AgBr;  34  grams  of  NH3  at  0°C  in  100  grams  water  dis- 
solve 1.987  grams  of  silver  bomide.6  A  metol-caustic  soda  bath  con- 
taining hypo  (of  the  type  given  in  a  previous  paper7)  is  being  used. 
Sodium  thiosulfate  added  to  a  metol  developer  produces  an  increase 
in  density,  the  increase  rising  to  a  maximum  with  increasing  concen- 


246 


T.  T.  BAKER 


[J.  S.  M.  P.  E. 


tration  and  thereafter  falling  off  progressively,8  but  when  the  develop- 
ing solution  contains  a  concentration  greater  than  that  that  shows  the 
maximum  effect,  it  produces  relatively  more  active  development  in 
the  depths  of  the  emulsion  than  in  the  surface  layers  (Fig.  5) . 

Scatter  has  to  be  prevented  as  far  as  possible  by  using  emulsions 
of  as  fine  grain  as  is  consistent  with  the  necessary  speed;  here  the 
knowledge  of  the  emulsion  maker  in  preselecting  symmetrically 
shaped  AgBr  crystals,  adequately  peptized,  and  an  emulsion  with  a 
long  grain-size  frequency  curve,  has  proved  of  considerable  value. 
Increase  in  latitude  is  one  of  the  most  important  features  of  the 
negative-positive  process.  Recent  comparisons  made  of  reversals 
against  negatives  developed  in  suitable  baths  show  comparative 

latitudes  (as  measured  on  the 
characteristic  curves  between  a 
7  of  0.25  at  foot  and  shoulder), 
of  0.95  reversal  against  an 
average  of  2.2  negative  (Fig.  6). 
It  is  thus  possible  to  deal  in 
negative  technic  with  a  greatly 
improved  range  of  lighting  in- 
tensity. Control  in  develop- 
ment, however,  is  somewhat 
difficult,  as  with  most  emulsions 
applied  in  the  low  coating 
weight  necessary  for  color- 
screen  work,*  gamma  infinity  is  reached  very  rapidly  (Fig.  7).  We 
work,  therefore,  with  very  dilute  baths.  Dilution  of  color  is  inevit- 
ably caused  in  these  prints  where  the  negative  and  positive  reseau 
elements  cross,  by  microscopic  white  spaces  occurring  at  the  over- 
lapping corners;  for  this  we  endeavor  to  compensate  by  stepping 
up  the  gamma  of  the  print  to  make  the  screen  contrast  as  high  as 
permissible,  this  having  the  physiological  effect  of  increased  satura- 
tion. The  negative  material  has  the  red  lines  running  at  an  angle  of 
27  degrees  to  the  edge  of  the  stock,  with  the  lines  of  alternate  blue- 
green  elements  running  at  right  angles.  In  print  stock  the  lines  are 
inclined  at  an  angle  of  45  degrees.  This  orientation  is  chosen  so 
that  there  is  no  danger  of  moire  when  one  reseau  is  printed  on  the 
other.  But  in  printing  it  necessarily  happens  that  there  are  portions 


(.0 
.8 

f  * 

0 
.4 

.1 

/ 

**^~~ 

/ 

/ 

/ 

1              2 
TIME      IN 

>            4             S           * 
MINUTE  S 

FIG.  7.     Gamma-time  curve. 


*  About  60  mg.  of  silver  halide  per  sq.  decimeter. 


Sept.,  1938]  NEGATIVE-POSITIVE  PROCESS  247 

of  many  reseau  elements  that  are  overlapped  by  portions  of  ele- 
ments of  another  color,  and  in  these  local  spots  of  double  filtration 
not  enough  light  is  transmitted  to  produce  a  developable  effect  upon 
the  emulsion;  hence  the  spots  appear  white  in  the  silver  image, 
thereby  causing  the  effect  of  color  dilution. 

In  split-beam  camera  work  it  is  recognized  that  the  separation 
must  be  substantially  correct,  and  the  balance  of  the  three  images 
correct,  if  satisfactory  subtractive  prints  are  to  be  obtained.  It  is 
equally  important  that  in  a  screen  negative  the  three  intermingled 
images — for  after  all  there  are  three  images — be  correctly  balanced 
and  in  equally  sharp  focus.  The  latter  is,  of  course,  taken  care  of 
by  choice  of  a  reasonably  apochromatic  lens.  But  the  color-balance 
needs  to  be  quite  accurate,  compensation  being  possible  in  printing  for 
lack  of  hue  balance  in  the  reseau  rather  than  for  mistakes  in  lighting. 
We  are  using  Mole-Richardson  arcs,  the  broadsides  and  scoops  being 
used  without  the  straw-filter;  no  filter  is  used  on  the  camera.  Pro- 
vided, as  stated,  the  negative  is  correct,  printing  offers  no  problems 
other  than  the  double  grading  for  density  and  reseau  hue.. 

REFERENCES 

1  MARDEN,  J.  W.,  BEESE,  N.  C.,  AND  MEISTER,  G. :   "Cadmium  and  Zinc  Vapor 
Lamps,"  Thirtieth  Annual  Convention  of  the  Illuminating  Eng.  Soc.,  Buffalo, 
N.  Y.,  Aug.  31  to  Sept.  3,  1936. 

2  HOFFMAN,   R.   M.,    AND    DANIELS,    F.:     "Photochemical    Technique    III, 
Quartz  Capillary  Arc  Lamps  of  Bismuth,  Cadmium,  Lead,  Mercury,  Thallium 
and  Zinc,"  /.  Amer.  Chem.  Soc.,  54  (Nov.,  1932),  p.  4226. 

8  DUSHMAN,  S.:  "Recent  Developments  in  Gaseous  Discharge  Lamps," 
/.  Soc.  Mot.  Pict.  Eng.,  XXX  (Jan.,  1938),  No.  1,  p.  58. 

•  SPENCER,  D.  A.:  Phot.  J.  (Jan.,  1933),  No.  1,  p.  19. 

•  Idem:    (April,  1937),  No.  4,  p.  251. 

•  SEIDELL,  A. :   "Solubilities  of  Inorganic  and  Organic  Compounds,"  p.  602. 

7  BAKER,  T.  T.:    "Some  Lighting  Problems  in  Color  Cinematography,"  /. 
Soc.  Mot.  Pict.  Eng.,  XXIX  (Nov.,  1937),  No.  5,  p.  471. 

8  MURRAY,  H.  D.,  AND  SPENCER,  D.  A.:    "The  Addition  of  Silver  Ion  Reac- 
tants  to  Organic  Developing  Solutions,"  Phot.  J.  (July,  1937),  No.  7,  p.  458. 


APPLICATION  OF  NON-LINEAR  VOLUME 

CHARACTERISTICS  TO  DIALOG 

RECORDING* 


J.  O.  AALBERG  AND  J.  G.  STEWART** 


Summary. — The  advisability  of  using  a  non-linear  volume  characteristic  in  dialog 
recording  is  discussed.  In  this  connection  consideration  is  given  to  the  following 
points:  (a)  the  difference  of  level  existing  between  the  original  and  reproduced 
speech;  (b)  the  advantages  of  a  system  in  which  manual  monitoring  can  be  confined 
to  overall  level  correction  rather  than  to  momentary  peaks;  (c)  the  advantage  of  limit- 
ing the  range  of  all  except  trained  voices  to  assure  the  highest  possible  intelligibility. 
An  analysis  is  then  made  of  the  various  types  of  compression  possible  and  a  terminol- 
ogy is  developed. 

Consideration  is  given  to  the  type  of  device  most  applicable  to  motion  picture  record- 
ing. The  electrical  circuits  and  operating  characteristics  of  a  compressor  that  has 
been  in  commercial  service  for  18  months  are  discussed.  Practical  results  and  ad- 
vantages obtained  by  the  use  of  the  device  during  this  period  are  analyzed  and  the 
possibility  of  addition  applications  is  indicated. 

At  RKO  Studios,  in  1936,  we  began  investigating  a  type  of  annoy- 
ing volume  expansion  present  in  our  variable-area  dialog  recording 
which,  for  brevity,  we  named  the  "jumps,"  the  difficulty  consisting 
of  very  sharp  volume  increases  in  speech,  some  cases  affecting  a  single 
word  and  at  other  times  a  syllable  within  a  word.  Upon  comparing 
our  product  with  variable-density  recording,  we  felt  that  the  effect 
was  absent  from  the  latter.  At  that  time  there  was  insufficient  vari- 
able-area recording  available  from  other  studios  to  permit  arriving 
at  a  general  conclusion ;  however,  we  felt  that  the  effect  was  present 
in  all  variable-area  recording.  Our  first  observations  led  us  to 
believe  that  variable-area  recording  suffered  from  inherent  volume 
expansion  but  extensive  tests  failed  to  reveal  it. 

In  the  course  of  our  investigation,  we  found  that  the  average  level 
used  by  variable-density  licensees  was  such  that  the  high-amplitude 
peaks,  which  apparently  caused  the  trouble,  were  being  recorded 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;  received 
April  11,  1938. 

**  RKO  Radio  Studios,  Inc.,  Los  Angeles,  Calif. 

248 


NON-LINEAR  VOLUME  CHARACTERISTICS  249 

over  the  non-linear  portion  of  the  H&D  curve,  and  were  being  ef- 
fectively compressed.  In  addition,  instantaneous  peaks  of  shorter 
duration  than  the  operating  time  of  the  anti-ground-noise  bias  were 
receiving  further  compression.  Numerous  theater  listening  tests 
proved  that  this  type  of  recording  had  superior  volumetric  smooth- 
ness. 

The  desirability  of  recording  dialog  with  a  non-linear  volume  char- 
acteristic becomes  apparent  on  examination  of  recording  and  repro- 
ducing conditions. 

The  average  level  of  theater  speech  reproduction  is  15  or  20  db. 
greater  than  the  original  speaking  level.  In  arriving  at  a  proper  over- 
all frequency  response,  this  fact  is  taken  into  careful  consideration, 
but  until  now,  has  not  been  regarded  as  important  in  relation  to 
volume  range.  At  normal  speech  loudness,  that  is,  at  the  level  at 
which  speech  is  heard  without  artificial  aid,  considerable  volume 
latitude  is  permissible  without  annoyance.  When  this  average  speech 
is  reproduced  some  20  db.  higher  without  compression  of  momentary 
peaks,  the  loudness  at  these  points  causes  the  listener  extreme  an- 
noyance. This  condition  is  true  when  the  average  reproduced  level 
is  no  greater  than  is  necessary  for  good  intelligibility.  Poor  repro- 
ducer frequency  characteristics  or  high  theater  reverberation  serve 
to  heighten  the  effect.  The  energy  peaks  are  not  necessarily  ex- 
pressive dynamics  used  by  the  actor,  but  may  be  caused  by  lack  of 
breath  control  or  other  vocal  defects,  and  the  less  trained  the  actor 
the  more  noticeable  the  difficulty.  However,  the  dynamics  of  even 
the  well  trained  voice  are  uncomfortably  exaggerated  when  repro- 
duced at  theater  loudness.  These  observations  lead  to  the  con- 
clusion that  compression  of  variable-area  recording  would  be  de- 
sirable. 

In  the  operation  of  recording  equipment,  additional  advantages 
accrue  from  the  use  of  a  non-linear  volume  characteristic.  The  dif- 
ficulty of  producing  a  smoothly  monitored  scene  containing  good 
dramatic  quality  and  at  the  same  time  confining  it  within  the  range 
necessary  to  record  it  on  the  sound-track  is  evident.  The  fact  that 
a  compressor  will  take  care  of  a  wide  input  range  makes  constant 
twisting  of  the  gain  control  unnecessary,  and  results  in  a  superior 
product  free  from  improper  levels  of  short  duration  which  can  never 
be  corrected. 

In  considering  the  characteristics  of  a  device  to  be  used  for  solving 
these  problems,  two  distinct  types  were  available: 


250  J.  O.  AALBERG  AND  J.  G.  STEWART        [j.  s.  M.  P.  E. 

(7)     The  "limiter." 

(2)     The  "compressor"  or  non-linear  amplifier. 

The  two  devices  are  electrically  similar,  differing  only  in  opera- 
tional adjustments.  In  fact,  a  single  amplifier,  by  proper  adjust- 
ment, will  perform  either  function.  There  is,  however,  considerable 
difference  in  the  results  obtained  with  the  two  types. 

To  avoid  confusion  in  terminology,  the  following  terms  are  used  in 
discussing  compression  characteristics.  Two  levels  must  be  desig- 
nated in  order  to  fix  the  operating  limits  of  such  a  device : 

(1)  The  input  level  at  which  compression  starts,  i.  e.,  the  device  being  linear 
below  this  point. 

(2)  The  input  level  at  which  the  compressed  output  reaches  full  track  or  100 
per  cent  modulation. 

Considering  the  compressed  range  as  starting  at  the  first  point  and 
ending  at  the  second,  we  may  speak  of  compressing  so  much  input 
within  these  limits.  For  example,  if  compression  starts  at  —10, 
considering  full  track  to  be  zero  level,  and  the  input  must  be  raised 
25  db.  before  reaching  zero  level  output,  then  the  device  compresses 
25  db.  into  10  db. 

The  limiter  type  is  designed,  as  its  name  indicates,  to  compress  a 
large  input  range  into  a  small  output  range.  In  the  terms  outlined 
above,  such  a  device  compresses  10  or  20  db.  into  2  or  3  db.  When 
recording  with  such  a  device,  if  the  gain  is  set  at  a  point  to  permit  a 
reasonable  amount  of  dynamics,  the  limiter  will  be  actuated  only  by 
extremely  high  input  level  peaks,  and  will  not  assist  in  smoothing 
out  the  average  dialog  levels.  If,  on  the  other  hand,  the  gain  is 
raised  to  a  point  where  the  limiter  is  being  actuated  by  average 
dialog  levels,  the  resulting  product  will  have  very  limited  range  and 
will  be  devoid  of  desirable  dramatics.  With  the  compressor  type, 
non-linearity  starts  below  the  point  of  average  dialog  level,  for  ex- 
ample, 10  db.  below  full  track,  and  compresses  20  or  25  db.  into  10 
db. 

Recordings  were  made  on  both  types,  and  the  compressor  was 
found  superior  for  motion  picture  work,  one  advantage  being  that 
the  degree  of  compression  remains  constant  over  a  large  range  of 
input.  In  other  words,-  the  input  vs.  output  characteristic  of  the 
device  consists  of  a  linear  portion  up  to  the  —10  point,  and  above 
that,  a  straight  line  of  slope  less  than  unity,  the  slope  of  the  second 
portion  being  determined  by  the  amount  of  compression.  This 


Sept.,  1938]  NON-LINEAR  VOLUME  CHARACTERISTICS  251 

allows  great  operating  leeway  and  produces  a  product  of  sufficient 
range  but  free  from  disturbing  volume  peaks.  For  these  reasons, 
it  was  preferred  and  finally  adopted  at  RKO  Studios,  where  it  has 
been  in  use  for  eighteen  months. 

Non-linear  amplifier  design  has  been  well  covered  in  technical 
papers  and  magazine  articles.  The  amplifier  in  use,  however,  has 
the  advantage  of  being  adjustable  over  a  wide  range  of  character- 
istics covering  both  limiter  and  non-linear  types.  Two  adjustment 
controls  are  used.  The  first  adjusts  the  fixed  bias  on  the  rectifier, 
which  is  always  biased  to  or  beyond  cut-off.  This  determines  the 
point  at  which  compression  starts.  With  no  bias,  the  amplifier  is 
non-linear  over  its  entire  range.  As  the  bias  is  increased,  the  start- 
ing point  is  moved  progressively  to  higher  levels.  The  second  con- 
trol adjusts  the  input  signal  voltage  supplied  to  the  rectifier  which 
determines  the  slope  of  the  curve  above  the  starting  point,  i.  e.,  the 
total  amount  of  compression. 

For  present  conditions  of  recording,  a  starting  point  between  6 
and  12  db.  below  full  track,  depending  upon  the  recording  level  in 
use,  has  been  chosen.  This  introduces  sufficient  compression  with- 
out dangerously  reducing  the  ratio  of  normal  dialog  to  set  noise  and 
reverberation.  In  setting  the  second  adjustable  factor,  the  total 
compression,  a  compromise  must  be  reached  between  ease  of  opera- 
tion and  good  dynamics  in  the  product.  A  range  of  12  db.  in  speech 
seems  sufficient  for  good  dynamics,  and  a  setting  based  upon  this 
range  results  in  satisfactory  operating  conditions.  For  our  present 
recording  level,  this  is  accomplished  by  a  starting  point  10  db.  down 
from  full  track  and  the  compression  of  20  db.  into  this  10. 

The  operating  time  constants  of  the  device  are  adjustable.  Under 
ideal  conditions  compression  would  take  place  instantaneously,  and 
a  sufficient  return  delay  would  be  used  to  prevent  the  device  from 
operating  during  a  full  cycle  of  the  lowest  recorded  frequency.  In 
practice,  the  compressor  is  used  with  an  80-cycle  high-pass  filter, 
and  the  return  to  normal  timing  is  adjusted  to  between  25  and  50 
milliseconds.  If  the  return  is  made  too  rapid,  the  device  oscillates, 
and  if  too  slow,  low-level  periods  appear  immediately  after  high-level 
peaks. 

When  recording  with  a  non-linear  volume  characteristic,  several 
problems  are  encountered.  Large  loudness  differences  may  exist  in 
a  compressed  signal  with  small  variations  in  peak  amplitude.  In  the 
extreme  case  of  the  limiter  type,  scenes  having  the  same  peak  indica- 


252  J.  O.  AALBERG  AND  J.  G.  STEWART        fj.  s.  M.  P.  E. 

tion  may  vary  to  the  ear  as  much  as  6  db.  in  loudness.  For  that 
reason,  reliance  must  be  placed  upon  aural  monitoring,  since  com- 
mercial high-speed  visual  indicator  meters  tend  to  read  peak  values. 

It  has  been  our  experience  that  the  compression  characteristic  of 
the  device  tends  to  reduce  the  effect  of  frequency  attenuation  placed 
before  it.  With  increasing  input  level,  the  frequency  output  of  the 
channel  tends  to  become  flat.  It  is  possible  that  some  advantage 
may  be  obtained  by  splitting  the  attenuation,  placing  part  before 
and  part  after  the  compressor,  to  arrive  at  some  balance  that  will 
result  in  a  desirable  change  of  frequency  characteristic  as  the  level 
increases.  The  effect  is  noticed  also  as  a  tendency  to  compensate 
for  momentary  acoustical  or  electrical  peaks  regardless  of  their 
source  and  to  reduce  somewhat  variations  in  quality  due  to  micro- 
phone peaks  and  room  reflections. 

The  device  provides  additional  ground-noise  reduction  by  making 
it  possible  to  record  at  higher  average  modulation  without  danger 
of  overshooting.  Improvement  in  this  direction  is  attained  even 
though  the  product  may  later  be  re-recorded  at  a  lower  level  to  ob- 
tain "Hi-Range"  effects. 

There  are  re-recording  requirements  to  which  the  limiter  is  better 
adapted  than  the  compressor  type.  In  scenes  where  dialog  is  re- 
recorded with  very  high  background  effects,  intelligibility  is  greatly 
improved  by  the  use  of  excessive  compression  of  the  dialog.  This 
is  best  accomplished  by  the  use  of  the  limiter. 

Careful  observation  of  our  compressed  product  under  a  wide  vari- 
ety of  theater  conditions  has  shown  the  absence  of  the  effect  that  was 
erroneously  regarded  as  volume  expansion,  thus  making  it  possible 
to  reproduce  the  product  at  higher  average  levels  with  a  consequent 
improvement  in  intelligibility.  The  occasional  error  of  using  ex- 
cessive dialog  compression  was  evidenced  by  a  lack  of  proper  dy- 
namics in  highly  dramatic  sequences,  with  resulting  loss  of  screen 
presence. 

While  the  RKO  Studio  experience  has  been  confined  to  the  use  of 
this  device  in  variable-area  recording,  all  that  has  been  said  seems 
to  apply  equally  to  linear  variable-density  recording. 

DISCUSSION 

MR.  FRAYNE:  I  question  some  of  Mr.  Aalberg's  theses.  In  regard  to  the 
statement  that  the  blasting  effect  that  is  present  in  variable-area  recording  is 
absent  in  variable-density  due  to  the  flattening  off  of  the  characteristic  curve,  it 


Sept.,  1938]  NON-LlNEAR  VOLUME  CHARACTERISTICS  253 

is  possible  to  process  variable-density  recordings  with  practically  no  flattening  off 
of  the  high  modulation  if  the  proper  print  density  is  chosen.  As  you  know,  it  is 
customary  in  turning  out  release  prints  to  vary  the  density  over  a  very  wide 
range.  In  doing  that  I  have  not  observed  any  evidence  that  as  we  go  from  the 
flattened  out  area  into  the  linear  area  we  get  this  effect.  In  one  Hollywood  studio 
at  the  present  time  the  compression  in  speech  with  the  processing  they  use  is  of 
the  order  of  only  about  1  db.,  yet  there  is  no  evidence  whatever  of  this  blasting. 

I  have  also  heard  recently  some  variable-area  recordings  made  with  a  device 
other  than  a  galvanometer  in  which  the  blasting  was  not  present,  so  I  feel  that 
Mr.  Aalberg  must  be  correcting  for  some  fundamental  deficiency  in  the  recording 
device. 

MR.  KELLOGG:  Mr.  Frayne  states  his  belief  that  compression  in  variable-area 
recording  is  needed  because  of  some  inherent  defect  in  the  equipment  that  results 
in  an  opposite  effect  or  "volume  expansion."  Messrs.  Aalberg  and  Stewart  state 
in  the  paper  that  at  first  they  had  the  same  idea,  but  on  further  study  gave  up  the 
theory.  The  galvanometer  is  usually  the  first  device  suspected.  It  has  been 
subjected  to  the  most  rigorous  tests.  Saturation  if  present  in  appreciable  magni- 
tude, would  give  some  compression,  rather  than  the  volume  expansion  which  would 
have  to  be  compensated  by  a  compressor.  Owing  to  the  large  ratio  of  air-gap  to 
iron  reluctance,  hysteresis  produces  a  negligibly  small  wave  distortion.  Hys- 
teresis loss  is  relatively  greater  at  low  levels,  as  is  well  known.  Measurements  on 
our  older  galvanometers  indicate  that  it  could  account  for  no  more  than  2  db.  loss 
when  the  level  is  40  db.  below  full  modulation,  an  amount  entirely  too  small  to 
account  for  the  criticism,  and  in  our  newer  design  this  loss  has  been  reduced  to  0.5 
db.  Film-transfer  loss  has  been  equally  carefully  studied,  and  again  we  find 
linearity  down  to  the  lowest  signals  that  it  is  practicable  to  measure.  It  was  con- 
siderations such  as  these  that  led  the  authors  of  the  paper  to  abandon  the  theory 
that  there  was  volume  expansion  inherent  in  the  system  or  equipment.  Of 
course  almost  anything  is  possible  with  bad  adjustments  or  processing.  For  ex- 
ample, with  too  narrow  a  zero  line  and  badly  fogged  prints  we  can  produce  volume 
expansion,  but  such  conditions  are  the  result  of  outright  carelessness,  and  are 
clearly  not  what  the  authors  are  talking  about. 

We  come  then  to  the  question  of  whether  the  speech  as  it  reaches  the  micro- 
phone can  often  be  '  'jumpy. ' '  Of  course,  it  can.  We  all  know  hundreds  of  people 
who  talk  that  way,  and  at  a  little  distance,  or  with  some  room  echoes,  they  are  ex- 
tremely difficult  to  understand.  When  the  level  is  raised  above  normal,  as  in 
theater  reproduction,  the  jumpy  effects,  as  the  authors  point  out,  are  more  notice- 
able and  more  annoying. 

Turning  now  to  the  question  of  whether  the  variable-density  track  affords  com- 
pression, it  is,  of  course,  admitted  that  so  long  as  the  conditions  for  straight-line 
or  classical  variable-density  are  adhered  to,  compression  does  not  take  place,  and 
the  observations  that  Mr.  Frayne  mentions  are  for  these  conditions.  It  is  my 
understanding  of  the  paper  that  the  authors  believe  these  conditions  to  be  ex- 
ceeded in  practice  so  much  of  the  time  that  a  very  substantial  amount  of  com- 
pression is  experienced. 

MR.  ALBERSHEIM:  In  experimenting  with  the  variable-area  recording  method 
we  found,  as  pointed  out  by  Mr.  Kellogg,  that  variable-area  sound-tracks  over- 
load more  suddenly  than  variable-density  records.  It  may  be  that  the  blasting 


254  J.  O.  AALBERG  AND  J.  G.  STEWART        [j.  s.  M.  p.  E. 

occurs  only  when  overload  takes  place,  and  is  due  to  the  type  of  harmonics  pro- 
duced by  cutting  over  the  edge  of  a  sharply  limited  sound-track.  I  have  heard 
some  variable-area  recordings  made  at  our  East  Coast  laboratories  that  produced 
this  same  sharpness  of  blasting;  at  the  time  I  believed  it  to  be  due  to  the  genera- 
tion of  disagreeable  high  harmonics  such  as  are  sometimes  produced  in  class  B 
amplifiers.  Therefore,  if  one  avoids  overload  or  sees  to  it  that  the  overload  dis- 
tortion takes  place  gradually,  that  is,  without  sharp  discontinuities,  the  blasting 
will  be  reduced. 

MR.  KELLOGG:  I  would  not  deny  for  a  moment  that  overloading,  which,  of 
course,  frequently  occurs  in  both  kinds  of  records,  may  accentuate  the  impression 
of  blasting  and  jumpy  effects.  But  from  what  Mr.  Stewart  and  Mr.  Aalberg  have 
to  say  about  it,  this  jumpy  quality  is  not  confined  to  cases  where  there  has  been 
overloading. 

MR.  FRAYNE:  I  have  seen  some  oscillograph  records  of  variable-area  dialog 
recently  in  which  a  certain  amount  of  this  blasting  effect  had  been  noticed;  and 
it  was  quite  noticeable  that  even  where  the  modulation  was  within  15  db.  of  the 
top  the  blasting  was  still  present.  So  I  do  not  believe  that  the  overload  is  entirely 
responsible  for  the  quality.  It  is  true,  of  course,  that  variable-density  overload 
is  more  gradual  than  that  found  in  variable-area  recording. 

MR.  KELLOGG:  We  have  made  laboratory  tests  that  entirely  checked  the  ob- 
servations that  Mr.  Albersheim  mentions,  namely,  that  the  gradual  overload- 
ing of  variable-density  is  more  tolerable  to  the  ear  than  overload  in  a  variable- 
width  system.  This,  plus  the  fact  that  it  is  almost  impossible  to  judge  an  over- 
loaded density  track  by  eye,  would  almost  inevitably  lead  to  the  result  that  a  great 
deal  of  overloading  is  permitted  in  density  tracks.  The  fact  that  a  true  straight- 
line  density  track  would  be  as  much  as  5  db.  below  a  variable-area  track  in  out- 
put, but  that  theaters  do  not  have  to  make  nearly  that  much  adjustment  to  main- 
tain about  equal  average  loudness,  is  further  evidence  of  the  wide  prevalence  of 
overloading.  This  is  not  a  criticism  of  the  practice  of  the  sound  departments 
using  variable-density.  Compression  has  been  found  definitely  to  be  useful,  and 
they  would  be  foolish  not  to  take  advantage  of  the  characteristics  of  the  system 
up  to  the  point  where  the  benefits  from  compression  are  more  than  offset  by  the 
harmful  effects  of  distortion.  What  Messrs.  Aalberg  and  Stewart  say  (and  we 
say  it,  too)  is  that  it  is  still  better  to  use  electronic  compression  and  a  track  that 
is  not  overloaded.  To  take  care  of  occasional  overloads,  a  more  gradual  overload- 
ing characteristic  can  be  had  in  the  variable-width  system  by  suitably  shaping 
the  mask  in  the  recording  system. 

The  authors  mention  the  fact,  based  upon  their  tests  and  observations,  that 
when  speech  is  reproduced  at  an  unnaturally  high  level,  some  compression  is  de- 
sirable, which  might  not  be  called  for  if  the  reproduction  were  at  natural  level. 
Although  I  do  not  know  whether  this  relation  has  been  pointed  out  before,  it  seems 
entirely  reasonable. 

The  reasons  are  probably  of  two  kinds:  First,  irregular,  loud  sounds  can  be  ir- 
ritating and  tiresome,  although  the  same  sounds,  with  the  same  total  db.  volume 
range,  could  be  reproduced  at  lower  level  without  any  such  irritating  effect.  In 
the  second  place,  some  compression  would  undoubtedly  be  justified  in  view  of  the 
non-linear  effects  of  masking.  If  loud  syllables  are  quickly  followed  by  weak 
ones,  any  reverberation  results  in  difficulty  in  hearing  the  weak  sounds,  and  obvi- 


Sept.,  1938]  NON-LINEAR  VOLUME  CHARACTERISTICS  255 

ously  if,  by  means  of  compression,  the  difference  in  loudness  can  be  reduced,  articu- 
lation will  be  improved.  This  much  is  true,  regardless  of  the  level  of  reproduction. 
The  non-linear  masking  factor,  however,  results  in  making  matters  worse  as  the 
level  is  raised.  The  loud,  voiced  vowels  which  produce  the  troublesome  rever- 
beration are,  for  the  most  part,  in  the  range  below  1000  cycles,  while  the  mounds 
that  are  likely  to  be  lowest  are,  for  the  most  part,  of  much  higher  frequency. 

In  Speech  and  Hearing  (p.  169)  Fletcher  shows  the  results  of  a  large  number  of 
masking  tests.  In  each  group  of  curves,  the  frequency  of  the  masking  tone  is 
shown  above  and  the  frequency  of  the  tone  that  is  masked  or  drowned  out  is  given 
on  the  scale  at  the  bottom  of  the  figure.  Taking,  for  example,  a  masking  tone  of 
400  cycles,  the  curves  show  that  the  threshold  intensity  for  a  2000-cycle  tone 
is  not  appreciably  affected  until  the  400-cycle  tone  has  reached  40  db.  above  its 
threshold.  If  the  level  of  the  400-cycle  tone  is  raised  from  40  to  60  db.,  the  level 
of  the  2000-cycle  tone  must  be  raised  18  db.  in  order  to  be  audible.  Raising  the 
level  of  the  400-cycle  tone  20  db.  more,  or  from  60  to  80,  makes  it  necessary  to 
raise  that  of  the  2000-cycle  tone  32  db.  to  make  it  again  audible;  and  if  the  400- 
cycle  tone  is  again  raised  from  80  to  100,  the  2000-cycle  tone  must  be  raised  28 
db.  more.  Similar  effects  are  shown  for  masking-tones  of  200  and  800  cycles. 
In  view  of  the  measurements  just  quoted,  we  should  certainly  expect  that  the 
masking  effects  of  the  "hangover"  of  a  loud  low-frequency  sound  would  become 
worse  as  the  levels  are  raised.  This  is  not  saying  that  the  overall  articulation  will, 
in  general,  be  impaired  by  raising  the  level,  for  there  is  an  opposing  factor,  espe- 
cially where  room  noise  is  present  and  some  sounds  may  be  even  below  threshold. 
Under  such  conditions,  raising  the  entire  level,  of  course,  improves  articulation 
and  it  would  not  be  until  quite  high  levels  are  reached  that  the  loss  due  to  abnor- 
mal masking  would  offset  the  gain  resulting  from  raising  the  levels  of  the  fainter 
sounds.  Compression,  of  course,  helps  articulation  by  raising  the  level  of  the 
faint  sounds  and  also  by  reducing  the  masking  if  some  reverberation  is  present. 

MR.  FRAYNE:  Mr.  Kellogg's  remarks  are  extremely  interesting,  but  they  do 
not  explain  to  my  satisfaction  why  the  effect  is  found  only  in  variable-area  rec- 
ords and  not  in  variable-density  records,  where,  up  to  the  overload  point,  no 
considerable  degree  of  compression  is  noticeable. 

MR.  AALBERG:*  Mr.  Frayne's  observations  are  evidently  based  upon  material 
other  than  standard  studio  recordings.  Obviously  there  exists  a  misunderstand- 
ing among  the  users  of  variable-density  recording  systems  as  to  the  true  magni- 
tude of  momentary  peaks  present  in  speech  recording.  Due  to  the  very  definite 
overload  point  on  the  variable-area  systems,  users  of  this  type  of  track  have 
always  been  concerned  about  peak  values.  We  have  compared  the  peak  input 
levels  of  histrionic  speech  with  simultaneously  recorded  variable-area  and  vari- 
able-density track  output  peak  levels  and  found  surprising  compression  in  the 
density  system. 

*  Communicated. 


THE  TRANSMISSION  OF  MOTION  PICTURES  OVER 
A  CO  AXIAL  CABLE* 


HERBERT  E.  IVES** 

Summary. — The  transmission  of  television  signals  over  wire  lines  a  number  of 
years  ago  used  signals  corresponding  to  images  of  coarse  detail,  and  required  frequency 
bands  accommodated  by  existing  types  of  circuits.  The  television  images  now  con- 
sidered necessary  correspond  to  frequency  bands  of  greatly  increased  width,  and  re- 
quire special  wire  networks  and  transmission  means. 

The  coaxial  conductor  recently  in  operation  for  experimental  purposes  between  New 
York  and  Philadelphia  can  transmit  a  band  of  frequencies  of  approximately  1000  kc. 
While  designed  primarily  for  multiple  telephone  channels,  it  offered  the  possibility 
of  transmitting  a  single  wide  band  as  required  for  television. 

The  experiment  consisted  in  providing  television-type  terminal  apparatus  for  pro- 
ducing signals  falling  within  the  available  band,  and  of  developing  and  utilizing 
methods  of  transmission  that  would  make  most  complete  use  of  the  frequency  band 
available.  For  convenience  in  experimental  work,  the  signals  were  generated  from 
motion  picture  film.  The  film  was  scanned  mechanically  by  means  of  a  lens  disk 
containing  240  lenses.  The  film  was  moved  continuously  24  frames  per  second,  and 
iL  motion,  together  with  the  motion  of  the  lenses  in  the  disk,  swept  each  frame  of  the 
film  in  240  juxtaposed  lines.  Light  passing  through  the  film  was  received  on  a  photo- 
sensitive surface;  the  resulting  photoelectric  current  was  amplified  and  by  means  of 
modulating  and  demodulating  apparatus  transmitted  as  a  single  side-band  between 
approximately  150  and  950  kc.  At  the  receiving  end  the  single  side-band  signal  was 
restored  as  a  signal  from  zero  to  800  kc. 

For  reception,  special  cathode-ray  tubes  were  used  in  which  particular  attention 
was  paid  to  the  definition  of  the  spot  and  the  linearity  of  response.  Synchronism  be- 
tween the  two  ends  was  obtained  by  sending  a  single  ft  equency  over  a  separate  channel 
and  using  it  to  operate  sweep  circuits  at  the  receiving  end.  The  use  of  mechanical 
scanning  and  the  high-definition  receiving  tubes  resulted  in  pictures  of  very  satisfactory 
quality  within  the  limitations  set  by  the  frequency  band. 

The  experimental  transmission  of  motion  pictures  over  the  coaxial 
cable  between  New  York  and  Philadelphia,  which  was  demonstrated 
in  November,  1937,  was  not  primarily  an  experiment  with  motion 
pictures.  Motion  picture  film  was  used  in  the  experiment  as  the  most 
convenient  means  for  producing  a  controllable  picture  signal,  capable 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C. ;    received 
April  20,  1938. 

**  Bell  Telephone  Laboratories,  New  York,  N..Y. 
256 


TRANSMISSION  OF  MOTION  PICTURES  257 

of  indefinite  repetition  under  identical  conditions  for  test  purposes. 
The  test  was  not  planned  or  carried  through  with  direct  reference  to 
the  special  problems  that  may  be  presented  by  motion  pictures  as 
television  material,  and  it  is  therefore  to  be  expected  that  many 
questions  that  will  occur  to  motion  picture  engineers  will  not  find 
their  answers  in  this  account  of  the  experiment.  Furthermore,  it 
should  be  made  clear  that  the  experiment  was,  from  the  standpoint 
of  the  communication  engineer,  one  of  several  whose  general  purpose 
was  to  test  the  capabilities  of  the  coaxial  transmission  line  for  carry- 
ing a  wide-band  signal.  In  previous  tests  the  possibilities  were  in- 
vestigated of  providing  a  very  large  number  of  separate  telephone 
channels  (some  240  for  these  tests)  each  requiring  relatively  narrow 
frequency  bands.  In  this  test,  the  problem  for  study  was  the  possi- 
bility of  faithfully  transmitting  signals  requiring  a  single  very  broad 
band  of  frequencies,  that  is,  signals  of  the  television  type. 

The  instrumentalities  of  the  project  fall  naturally  into  two  groups. 
One  group  comprises  the  terminal  apparatus,  whose  function  is  the 
generation  of  electrical  signals  from  the  light  coming  from  the  "scene" 
to  be  transmitted,  and  the  transformation  of  the  electrical  signals, 
after  transmission,  back  into  a  satisfactory  counterpart  of  the  origi- 
nal scene.  The  other  group  comprises  the  transmission  means,  and 
the  associated  apparatus  that  puts  the  signals  from  the  sending  end 
apparatus  into  form  for  most  efficient  transmission,  and  recovers 
the  signals  after  transmission  in  suitable  form  for  use  by  the  receiving 
end  terminal  apparatus. 

While  the  two  groups  of  apparatus  are  different  in  character,  the 
first  being  largely  optical,  the  second  largely  electrical,  there  is  a 
very  close  interrelation  of  requirements  and  limitations  which  de- 
manded at  the  start  certain  decisions  on  the  character  of  the  picture 
that  it  was  planned  to  transmit.  These  decisions  are  listed  below, 
with  some  of  the  reasons  leading  to  them : 

A  dominating  consideration  in  this  work  was  to  make  the  most 
efficient  use  possible  of  the  frequency  band  width  available  in  the 
coaxial  cable  and  associated  apparatus.  This  is  essentially  an  eco- 
nomic consideration,  for  band  width  has  a  definite  money  cost.  The 
starting  point  in  planning  the  system  is  then  the  frequency  band 
available.  Without  going  into  the  considerations  that  determined 
the  characteristics  of  this  particular  coaxial  cable,  it  suffices  here  to 
state  that  the  upper  limit  of  frequency  satisfactorily  handled  by  the 
cable  and  its  associated  repeaters  was  about  1000  kc.  This  does  not 


258 


H.  E.  IVES 


[J.  S.  M.  P.  E, 


mean,  however,  that  television  signals  occupying  a  band  from  0  to 
1000  kc.  can  be  accepted  for  transmission.  The  first  difficulty  en- 
countered is  that  immunity  from  external  disturbance,  which  is 
characteristic  of  the  coaxial  structure,  does  not  extend  to  the  lowest 
frequencies.  These  are,  however,  an  essential  part  of  the  television 
signal.  Recourse  must  therefore  be  made  to  the  use  of  a  "carrier" 
frequency  which  lifts  the  whole  frequency  band  to  be  transmitted  to 
a  higher  value.  When  this  is  done,  by  the  methods  commonly  used 


240  X  -£  ELEMENTS 


j 

III 

TOP  FREQUENCY  =  240  X  240  X       X      X  24  =606.4  KILOCYCLES 


FIG.  1.     Relation  between  picture  elements,  frame  repeti- 
tion frequency,  and  band  width  for  transmission. 

in  radio  the  signal  is  transmitted  as  two  "side-bands,"  one  to  each 
side  of  the  carrier,  each  occupying  the  entire  frequency  band  space 
of  the  original  signal.  If  this  double-side-band  method  were  used 
with  our  coaxial  cable  it  would  mean  that  our  signal  band  would  have 
to  be  less  than  half  of  the  1000  kc.  or  500  kc.  in  width. 

This  factor  of  x/2  would  mean  a  very  serious  loss,  to  be  avoided  if 
possible.  A  method  of  avoiding  this  loss,  at  the  same  time  utilizing 
the  carrier  method  of  placing  signals  at  a  desired  place  in  the  fre- 
quency band  is  offered  by  "single-side-band  transmission."  This 
method,  as  utilized  in  this  experiment,  places  the  single  side-band 


Sept.,  1938]          TRANSMISSION  OF  MOTION  PICTURES  259 

between  approximately  120  and  950  kc.,  thus  furnishing  a  useful 
frequency  band  of  over  800  kc. 

Taking  this  frequency  band  as  a  starting  point  we  can  determine, 
by  calculations  that  are  now  conventional  in  connection  with  image 
transmission,  the  number  of  scanning  lines  to  use  in  our  image 
analysis.  One  variable  in  this  calculation  is  the  number  of  image  repe- 
titions per  second.  With  our  choice  of  motion  picture  film  as  our 
source  of  images,  this  repetition  frequency  is  most  conveniently  taken 
as  the  standard  frame  frequency  of  24  per  second.  Another  variable 
is  the  shape  of  the  picture,  or  frame.  This  was  chosen  close  to  the 
4:3  ratio  of  dimensions  common  in  film;  actually,  because  of  space 
clearances  needed  in  the  apparatus,  with  scanning  in  the  long  direc- 
tion of  the  rectangle,  the  ratio  finally  used  was  7:6.  Using  these 
figures  we  arrive  at  the  number  of  scanning  lines  to  utilize  the  avail- 
able frequency  band  as  follows:  the  number  of  picture  elements, 
assumed  square,  to  fill  the  7 : 6  area  will  be  the  product  of  n  (the 
number  of  scanning  lines)  by  7/&n,  by  /  (the  repetition  frequency). 
Now,  a  single  signal  cycle  consists  of  an  alternation  of  light  and  dark, 
which  may  be  considered  as  two  picture  elements,  as  illustrated  in 
Fig.  1 .  We  therefore  have,  if  we  call  the  top  frequency  F, 

F  =  Va  X  n  X  7/&n  X  24 

Taking  F  as  800  kc.,  this  gives  us  for  n  very  approximately  240.  On 
the  basis  of  these  considerations,  therefore,  a  choice  of  240  scanning 
lines  was  indicated  as  the  upper  limit  capable  of  use  with  the  trans- 
mission line. 

In  the  early  stages  of  the  work,  and  paralleling  the  coaxial  cable 
development,  a  study  of  the  relation  between  picture  quality  and  the 
size  of  picture  elements  was  made  using  motion  picture  films  printed 
out  of  focus.  By  correlating  the  known  size  of  the  circle  of  confusion 
in  these  films  with  the  size  of  the  elements  in  a  television  image,  with 
reasonable  allowances  for  the  effects  of  the  differences  in  image  struc- 
ture, it  appeared  that  a  240-line  image  should  be  capable  of  giving  a 
picture  not  seriously  inferior  in  quality  to  the  average  small  home 
motion  picture  projector,  provided  comparable  freedom  from  visible 
image  structure  were  obtainable,  with  comparable  contrast  and 
fidelity  of  tone  rendering. 

The  use  of  240-line  scanning,  with  24  frames  per  second,  as  de- 
cided upon  for  this  experiment,  deviates  considerably  from  the  figures 
of  441  lines,  and  60  (interlaced)  frames  per  second,  which  are  now 


260 


H.  E.  IVES 


[J.  S.  M.  P.  E. 


being  contemplated  as  "standard"  for  television.  It  was,  however, 
believed  that  the  principal  questions  presented  by  the  problem  of 
transmitting  television  signals  could  be  satisfactorily  answered  by 
this  study,  and  that  the  wider  frequency  bands  demanded  by  the 
newer  television  standards  can  be  handled  by  more  or  less  straight- 
forward extensions  of  the  means  here  used. 


PHOTO-SENSITIVE 
SURFACE  AND 
ELECTRON 
AMPLIFIER 


FIG.  2. 


Diagrammatic  representation  of  opti- 
cal system. 


Signal  Generating  Apparatus. — The  scanning  apparatus  chosen  for 
this  test  was  of  the  simplest  type,  namely,  a  scanning  disk.  The 
disk  was  made  from  a  saw  blank  6  feet,  in  diameter;  near  the  pe- 
riphery of  which  were  mounted,  at  identical  radial  distances,  240 
lenses,  each  consisting  of  a  pair  of  plano-convex  elements.  The 
focal  length  of  the  compound  lenses  was  approximately  1  inch,  and 
the  diameter  ultimately  used  was  about  3/8  of  an  inch. 

A  schematic  diagram  of  the  optical  system  used  is  given  in  Fig.  2, 
while  Fig.  3  shows  a  photograph  of  the  disk  housing  with  the  film- 
driving  mechanism  at  the  top.  The  light-source  was  a  ribbon- 
filament  tungsten  lamp,  operated  on  direct  current,  which  was 


Sept.,  1938] 


TRANSMISSION  OF  MOTION  PICTURES 


261 


imaged  by  means  of  a  condensing  lens  upon  a  square  aperture.  This 
aperture  was  at  the  focus  of  a  collimating  lens  past  which  the  lenses 
in  the  disk  moved.  Each  disk  lens  formed  a  sharp  image  of  the 
aperture  and,  as  the  disk  rotated,  this  image  was  moved  across  the 
film  at  the  focus  of  the  lens.  The  film  was  moving  continuously  so 
that  successive  lens  images  scanned  successive  lines  on  the  film.  In 


FIG.  3. 


Scanning  disk  used  for  generating  signals  from 
motion  picture  film. 


order  to  carry  the  light  after  transmission  through  the  film  to  the 
photosensitive  surface,  a  light- tunnel  was  used  consisting  of  a  rec- 
tangular bar  of  highly  transparent  material  (Pontalite)  in  which, 
through  multiple  total  reflection,  the  light  was  caused  to  emerge  at 
the  far  end  with  uniform  intensity  from  all  positions  of  the  scanning 
lenses. 

On  emerging  from  the  light-tunnel  the  light  falls  upon  a  photo- 
electrically  sensitive  surface,  which  is  the  first  element  of  a  10-stage 
electron  multiplier.  The  signal  delivered  by  this  device  had  a  peak 


262 


H.  E.  IVES 


tf.  S.  M.  P.  E. 


value  of  100  microamperes   and  is   strictly  proportional   to  light- 
intensity. 

For  purposes  of  local  test,  before  connecting  this  terminal  appara- 
tus to  the  coaxial  transmission  system,  a  wide-band  amplifier  was 


FIG.  4.     Cathode-ray  tube  used  for  reception  of 
television  images. 


used,  with  a  range  from  5  cycles  per  second  to  1,000,000  cycles.  In 
conjunction  with  this,  in  order  to  supply  an  equivalent  for  the  direct 
current  not  transmitted,  a  "zero  wander"  current  was  introduced, 
which  automatically  brings  the  black  at  the  end  of  each  scanning 
line  to  a  constant  value. 


Sept.,  1938]          TRANSMISSION  OF  MOTION  PICTURES  263 

Besides  the  picture  signal,  the  sending  end  apparatus  must  supply 
signals  for  synchronizing  the  sending  and  receiving  ends.  These 
were  generated  optically,  using  the  same  lenses  as  for  the  picture 
signals.  Light  flashes  were  produced  from  an  auxiliary  light-source, 
whose  image  was  swept  over  a  small  slit.  The  brief  light  flashes 
(about  3  microseconds  in  duration)  fall  upon  a  second  electron  multi- 
plier, the  output  of  which  is  amplified  to  give  pulses  which  trip  a  gas- 
filled  tube  and  yield  a  saw-tooth  wave.  This  saw-tooth  wave  is 
used  in  the  local  testing  to  control  the  sweep  circuits  of  the  cathode- 
ray  receiving  tube.  For  transmission  purposes  the  saw-tooth  wave 
is  filtered  to  produce  a  5760-cycle  sine  wave.  This  frequency  is 
transmitted  by  the  carrier  equipment  to  the  distant  end,  and  there 
pulses  are  produced  to  control  sweep  circuits  in  the  receiving  ap- 
paratus. The  sine  wave  produced  by  the  light  flashes  was  used  also 


MODULATING      DEFLECTINS  PLATES 


CATHODE      PLATES        'HORIZONTAL  VERTICAL^ 

ftp 

ELECTRON       APERTURE 
LENS  SYSTEM 

FIG.  5.     Construction  of  cathode-ray  tube. 

to  beat  with  the  output  of  a  5760-cycle  precision  tuning  fork,  to  ac- 
tuate a  speed-control  circuit  by  means  of  which  the  speed  of  the  d-c. 
motor  used  to  drive  the  disk  could  be  held  constant  to  one  part  in 
5000. 

Receiving-End  Apparatus. — The  receiving  device  chosen  was  the 
cathode-ray  tube,  and  a  special  precision  type  was  designed  for  this 
test  by  Dr.  C.  J.  Davisson,  attention  being  directed  to  the  construc- 
tion of  a  tube  that  should  give  the  highest  possible  fidelity  of  detail 
and  tone  rendering,  quite  irrespective  of  cost  and  of  considerations 
that  might  enter  were  commercial  production  contemplated. 

The  special  features  of  the  tube  that  contributed  to  its  excellence 
as  a  testing  tool  are  best  brought  out  by  a  description  of  its  essential 
elements.  Fig.  4  is  a  photograph  of  the  tube  and  Fig.  5  is  a  schematic 
diagram  of  its  construction.  It  was  made  of  very  considerable  length 
(5  feet)  in  comparison  to  the  size  of  the  field  (7X8  inch) ,  in  order  to 
minimize  distortion.  The  deflection  of  the  beam  was  controlled  in 


264 


H.  E.  IVES 


[J.  S.  M.  p.  E. 


both  directions  electrostatically.  In  order  to  provide  a  sharply  de- 
nned rectangular  spot  whose  dimensions  across  the  scanning  line 
should  not  change,  an  electron  lens  system  is  provided  that  forms  a 
narrow  beam  of  electrons  from  a  hot  filament  onto  an  aperture 
0.006  inch  square.  Between  the  lenses  and  the  aperture  are  two 
modulating  plates  (actually  two  cross-connected  plates  to  insure 
parallel  displacement  of  the  beam  without  any  angular  component) 


8         10        12        14        16 
MODULATING    VOLTAGE 


FIG.  6.     Characteristic  of  special  cathode-ray  tube. 

connected  to  the  incoming  circuit  in  such  a  way  that  the  potentials 
of  the  plates  vary  according  to  the  strength  of  the  incoming  signals. 
The  electron  beam  is  thus  deflected  so  that  more  or  less  of  it  passes 
through  the  aperture  and  thence  to  the  fluorescent  screen  on  the 
front  of  the  tube.  The  spot  of  light  on  the  screen  is  consequently  a 
rectangle,  of  constant  height  corresponding  to  the  separation  of  the 
scanning  lines,  but  of  variable  width  in  the  direction  that  the  spot  is 
to  be  moved  in  scanning.  When  swept  across  the  screen  these  spots 
of  constant  height  produce  lines  of  light,  which,  with  accurate  sweep 


Sept.,  1938]          TRANSMISSION  OF  MOTION  PICTURES  265 

control  to  juxtapose  the  lines,  result  in  a  very  uniform  structureless 
field.  The  light  from  the  variable-sized  spot  should  vary  linearly 
with  the  strength  of  the  signal  for  faithful  reproduction  of  tone 
values.  In  Fig.  6  is  shown  the  characteristic  actually  obtained  on  a 
representative  tube.  This  shows  the  variation  of  beam  current 
through  the  final  aperture,  to  which  the  light  from  the  fluorescent 
screen  is  closely  proportional,  as  a  function  of  the  modulating  voltage. 
The  mechanical  line-up  of  the  electron  lens  elements  is  in  this  case 
such  that  the  voltage  corresponding  to  the  accurate  centering  of  the 
spot  on  the  aperture  is  not  zero  as  in  the  description  above  but  about 
14,  which  is  taken  care  of  by  a  biasing  potential  on  the  tube.  De- 
pending upon  the  polarity  of  the  signals,  either  slope  of  the  char- 
acteristic can  be  used;  often  one  side  will  be  definitely  better  than 
the  other. 

In  order  to  produce  a  picture  the  'spot  on  the  fluorescent  screen 
must  be  swept  over  the  face  of  the  tube  so  as  to  scan  the  whole  rec- 
tangular area  of  7  X  8  inches  in  l/24  of  a  second.  This  sweeping 
operation  is  performed  by  applying  "saw-tooth"  signals,  derived  from 
the  synchronizing  pulses,  to  two  other  pairs  of  plates,  at  right  angles 
to  each  other  between  the  aperture  above  described,  and  the  fluores- 
cent screen.  The  potential  of  one  of  these  sets  of  plates  is  controlled 
at  a  periodicity  of  5760  times  per  second,  and  sweeps  the  beam  of 
electrons  across  the  screen  from  one  side  to  the  other  in  exactly  the 
same  time  that  the  spot  of  light  from  the  sending-end  lens  disk  tra- 
verses the  film.  At  the  end  of  the  sweep  the  beam  is  quickly  returned 
to  its  initial  position  (by  the  vertical  element  of  the  saw-tooth), 
the  signal  being  reduced  to  zero  during  this  period  by  masking  the 
edge  of  the  film  at  the  sending  end.  The  potential  of  the  other  pair 
of  plates  is  controlled  at  a  periodicity  of  24  times  per  second,  which  is 
the  rate  of  scanning  successive  frames.  These  plates,  being  at  right 
angles  to  the  others,  deflect  the  electron  beam  downward  at  the  same 
relative  speed  as  the  film  is  moving  at  the  sending  end.  This  re- 
sults in  the  passage  of  the  spot  on  the  fluorescent  screen  in  lines  suc- 
cessively displaced  by  the  vertical  height  of  the  spot.  After  the  last 
line  has  been  scanned  the  spot  returns  quickly  to  the  top  of  the  tube, 
and  a  properly  timed  negative  impulse  superimposed  upon  the  signal 
reduces  its  intensity  during  this  travel  so  as  to  render  the  spot  in- 
visible. 

Due  to  the  accurate  definition  of  the  spot  on  the  fluorescent  screen 
and  the  freedom  from  distortion,  the  bright  rectangular  field  produced 


266 


H.  E.  IVES 


tf.  S.  M.  P.  E. 


corresponding  to  clear  film  is  of  a  high  degree  of  uniformity  and  free- 
dom from  visible  structure,  which  permits  close  inspection  of  the  re- 
ceived image.  Because  of  the  close  approximation  to  a  rectilinear 
relation  between  the  signal  (itself  accurately  proportional  to  the 
transmission  of  the  film)  and  the  brightness  of  the  scanning  spot,  a 
high  degree  of  fidelity  of  tone  rendering  is  obtained.  Pictures  pro- 
duced by  directly  coupling  the  sending  and  receiving  apparatus  were 
gratifyingly  close  in  appearance  to  motion  pictures  directly  pro- 
jected to  the  same  size. 

TRANSMISSION  OF  TELEVISION  SIGNALS  OVER  THE  COAXIAL  CABLE* 

Given  the  satisfactory  performance  of  the  signal-generating  and 
signal-recovery  apparatus,  when  directly  connected  to  each  other, 


FIG.  7.     Coaxial  cable. 


the  task  of  a  transmission  system  is  to  reproduce  this  satisfactory 
performance  with  the  sending  and  receiving  apparatus  separated 
from  each  other  by  any  desired  distance.  For  this  to  be  possible  the 
transmission  medium  must  to  a  high  degree  be  immune  to  interference 
from  extraneous  sources  of  electrical  energy;  it  must  be  capable  of 
transmitting  the  wide  frequency  bands  involved,  without  discrimi- 
nation between  frequencies;  and  it  must  be  possible  to  insure  that 
all  frequencies  are  transmitted  at  the  same  speed.  Failure  to  meet 
any  of  these  requirements  will  cause  serious  distortions  in  the  re- 
ceived picture. 

The  coaxial  cable,  shown  dissected  in  Fig.  7,  consists  essentially 
of  a  wire  supported  by  insulators  in  the  middle  of  a  conducting  tube. 

*  A  more  extended  account  of  the  transmission  features  is  given  in  Electrical 
Engineering  (June,  1938),  by  M.  E.  Strieby  who  was  directly  responsible  for  this 
phase  of  the  development. 


Sept.,  1938] 


TRANSMISSION  OF  MOTION  PICTURES 


267 


Due  to  the  "skin-effect"  high-frequency  signal  currents  are  carried 
largely  in  the  outer  skin  of  the  central  conductor  and  along  the  inner 
surface  of  the  outer  conductor.  Currents  caused  by  high-frequency 
external  interference  flow  substantially  on  the  outer  surface  of  the 
outer  conductor,  and  are  therefore  electrically  separated  from  the 
signal  currents  by  the  intermediate  metal  of  the  outer  conductor. 
Because  of  this  protection  from  outside  interference  it  is  possible  to 


1+2.5 
0 
-2.5 
-5.0 

0 
-50 

-ISO 

-250 
-300 
-350 
-400 
-450 
-500 
-550 
-600 

OVERALL.  AFTER 
EQUALIZATION 

^w 

••*•* 

•"••». 

—J  

_i    ** 

^---^  — 

"^X* 

^^ 

\ 

ION  BA 

15 

X 

V 

^ 

• 

T-^ 

x^ 

95.5  MILES 
LINE  ALONE 

X 

N 

' 

\ 

\ 

s 

s 

\ 

V 

200  300         400       500 

FREQUENCY    IN    KILOCYCLES   PER   SECOND 


FIG.  8.     Attenuation  of  signal  strength  in  coaxial  cable. 

subject  the  signals  to  an  enormous  amplification,  and  so  offset  the 
very  considerable  attenuation  of  signal  strength  owing  to  trans- 
mission losses. 

The  attenuation  of  signal  strength  in  the  95  miles  of  cable  between 
New  York  and  Philadelphia  is  shown  in  Fig.  8;  it  increases  with 
frequency  to  a  maximum  of  about  600  db.  at  1000  kc.  To  compensate 
for  this  loss,  repeaters  are  placed  in  the  line  at  intervals  of  10  miles. 
These  repeaters  are  designed  with  proper  attenuation  equalizers  so 
as  to  amplify  the  low  frequencies  less  than  the  high,  giving  a  final 


268 


H.  E.  IVES 


[J.  S.  M.  P.  E. 


very  flat  transmission  characteristic  over  the  entire  frequency  range, 
as  shown  in  the  upper  diagram  of  Fig.  8.  A  photograph  of  an  actual 
two-way  repeater  and  power  supply  is  shown  in  Fig.  9. 

A  characteristic  of  wire  transmission  is  the  distortion  caused  by 
different  times  of  transmission  for  different  frequencies;  the  lower 
frequencies  lagging  behind  the  higher.  In  order  that  the  picture 
details  will  appear  in  the  same  relative  position  in  the  reproduced  as 
in  the  scanned  picture,  all  frequencies  must  be  received  in  closely 
the  same  time  relationship  in  which  they  were  generated.  To  assure 
this,  delay  networks  were  introduced  to  equalize  the  transmission 


FIG.  9. 


Repeater  and  power  supply  used  on  coaxial 
cable. 


speeds  over  the  whole  frequency  range.  The  phase  delay  in  the 
coaxial  circuit  as  a  function  of  frequency  is  shown  in  Fig.  10,  and  in 
the  upper  diagram  a  measured  performance  characteristic  after  the 
delay  equalization. 

As  discussed  earlier  the  coaxial  cable  does  not  offer  sufficient 
shielding  for  very  low  frequencies,  so  that  the  original  television 
signals  must  be  translated  upward  in  the  frequency  spectrum  before 
transmission  in  order  to  raise  them  above  the  region  of  disturbance. 
The  most  efficient  use  of  the  frequency  band  available  is  obtained  by 
using  only  one  of  the  two  side-bands  normally  produced  in  this 
translating  process.  In  order  to  place  the  translated  signal  in  the 
most  advantageous  frequency  position,  a  double-modulation  process 
was  used  which  can  be  followed  with  the  help  of  Fig.  11,  in  which  are 


Sept.,  1938] 


TRANSMISSION  OF  MOTION  PICTURES 


269 


shown  the  two  modulating  steps  at  the  sending  end  and  the  two 
demodulating  steps  at  the  receiving  end  in  four  lines  beginning  at  the 
top.  A  carrier  of  2376  kc.  is  used  for  the  first  modulation,  which 
results  in  a  lower  side-band  from  1570  to  2376  kc.  and  an  upper  side- 
band from  2376  to  3182  kc.  The  carrier  itself  is  eliminated  in  the 
balanced  modulator.  The  output  of  this  modulation  is  passed 
through  a  filter,  but  because  the  two  side-bands  touch  each  other  at 
2376  kc.,  the  filter  can  not  be  designed  to  cut  off  all  the  upper  side- 


*1 
FAST 
0 
SLOW 
-1 
570 

OJ 

§  560 

o 
5   550 

z 

§ 
g  540 

530 

V. 

—  —  —  — 

=> 

^, 

_  * 

^ 

LINE-  REPEATERS   AND 
**VL_              /LOSS  EQUALIZERS 

\ 

—.r-v^^ 

•^ 

••    • 

—  - 

•^  * 

\ 

H  TELEVISION   BAND- 
V 

V 

\ 

95.5  MILES 
^      /  LINE  ALONE 

\ 

V 

> 

\ 

s 

s 

S 

S( 

_!  

60          100  200  500  1000 

FREQUENCY  IN  KILOCYCLES  PER  SECOND 

FIG.  10.     Phase  delay  in  coaxial  circuit. 

band.  At  the  output  of  the  filter  there  is  thus  the  lower  side-band 
plus  a  small  amount  of  the  lower  part  of  the  upper  side-band.  The 
upper  side-bands  from  all  subsequent  modulations  are  readily  elimi- 
nated by  the  filters  which  follow  because  of  the  wide  separation. 

The  carrier  for  the  second  modulation  is  2520  kc.,  and  the  lower 
side-band  extends  from  950  down  to  144  kc.  and  for  a  vestigial  range 
below  144  kc.  equal  to  the  width  of  the  side-band  remaining  from  the 
first  modulation.  The  high-pass  filter  following  this  modulation  is 
accurately  designed  to  pass  with  controlled  attenuation  not  only  a 
group  of  frequencies  just  above  144  kc.  but  also  the  vestigial  side- 
band, which  extends  from  144  to  about  120  kc.  The  resulting  signal 


270 


H.  E. IVES 


[J.  S.  M.  P.  E. 


extending  from  120  to  950  kc.,  is  then  passed  over  the  coaxial  cable 
to  Philadelphia. 

Here  the  transmitted  band,  after  first  passing  another  high-pass 
filter,  is  applied  to  the  first  demodulator,  together  with  a  carrier  of 
2520  kc.;  and  the  lower  side-band,  from  2400  down  to  1570  kc.,  is 
passed  to  the  second  demodulator  where  a  carrier  of  2376  kc.  is  ap- 
plied. The  lowest  frequency  of  the  lower  side-band,  1570  kc.,  is 
converted  to  806  kc.,  becoming  the  highest  frequency  of  the  final 


TRANSMITTING   END 

REJECTED 
U-  —  UPPER  ^ 
SIDE-BAND 

RETAINED      u.         UPPER        ^ 
i                                                                                                         \T"  SIDE-BAND""^ 
TELEVISION                                             PASSED  LOWER  _J^    RcjcrTED    *1 

•v  •'•^'  :--':.':  •:'•:'•:•.'•:•  f('-'-:{                         N^-'^^:::^;;:^^                        ! 

3                                    806                              1570                      2376  (CARRIER)                  3'82 
(FIRST    MODULATION) 

LOWER  SIDE-BAND 
TRANSMITTED  OVER  LINE 

^J£^^J£&^£                                                                                         , 

2520  (CARRIER) 
(SECOND  MODULATION) 


RECEIVING  END 


.        REJECTED          | 
U-_  -UPPER >J 

SIDE-BAND 


2376  (CARRIER) 

(SECOND  DEMODULATION) 
FREQUENCY  IN  KILOCYCLES  PER  SECOND 

FIG.  11.     Modulation  processes  used  in  transmitting  broad  frequency 
band  over  coaxial  cable. 


demodulated  band.  The  frequencies  from  2352  to  2400  kc.  of  the 
side-band  entering  the  second  demodulation  had  been  attenuated 
somewhat  by  the  high-pass  filters  following  the  second  modulator 
at  the  sending  end  and  preceding  the  first  demodulator  at  the  re- 
ceiving end;  and  the  second  demodulating  carrier,  2376  kc.,  falls  in 
the  middle  of  this  attenuated  band  as  shown  in  inset  No.  1.  Fre- 
quencies extending  about  24  kc.  above  the  carrier  are  inverted  by  the 
demodulation,  and  superimposed  upon  the  corresponding  frequencies 
just  below  the  carrier.  The  magnitude  and  phase  of  these  compo- 
nents are  proportioned  by  the  high-pass  filters  and  an  equalizer  so 


Sept.,  1938]          TRANSMISSION  OF  MOTION  PICTURES  271 

that  the  overall  result,  when  they  are  superimposed,  is  an  essentially 
flat  transmission  band  from  0  to  806  kc. 

The  terminal  equipment,  besides  providing  modulators,  ampli- 
fiers, filters,  and  equalizers,  must  provide  also  for  the  generation  of 
the  two  modulating  carriers  accurately  spaced.  This  is  accomplished 
by  deriving  all  carriers  from  a  4000-cycle  reference  frequency  at  the 
transmitting  end.  From  this  source  a  72-kc.  frequency  is  first  ob- 
tained, and  is  then  used  for  deriving  the  modulating  carriers  of  2376 
and  2520  kc.  through  harmonic  generators.  The  same  72-kc.  fre- 
quency is  also  transmitted  over  the  coaxial  line  to  Philadelphia, 
where  exactly  synchronous  carriers  are  derived  from  it  for  demodulat- 
ing. 


PILOT  FREQUENCY 

-SYNCHRONIZING  CARRIER  PILOT 

r CARRIER  FREQUENCY 

->{}*- ORDER- WIRE  CHANNEL 

K- PROGRAM  CHANNEL  T 


'ILL- 

IT 


k TELEVISION  CHANNEL 


I    I 


60(|  ,  84  120  FREQUENCY   IN   KILOCYCLES  PER  SECOND  95° 

66.24 

FIG.  12.     Utilization  of  frequency  band  available. 


Picture  synchronization  at  the  two  ends  is  provided  by  transmit- 
ting a  simple  sine- wave  signal  derived  from  the  sending-end  scanning 
disk  as  previously  described.  This  is  used  to  generate  saw-tooth 
sweep  impulses  for  the  receiving  end  cathode-ray  tube.  The  5760- 
cycle  synchronizing  frequency  produced  by  the  disk  is  modulated 
with  the  72-kc.  carrier  frequency  and  transmitted  as  a  single  fre- 
quency of  66.24  kc.  to  Philadelphia,  where  it  is  demodulated  with  the 
same  72-kc.  carrier  to  recover  the  original  5760-cycle  synchronizing 
frequency. 

A  program  channel  from  72  kc.  to  84  kc.  is  also  provided  in  the  cable 
to  accommodate  the  sound  accompanying  the  motion  picture  signal, 
and  finally  frequency  space  is  provided  for  an  order-wire  talking 
channel  from  60  kc.  to  64  kc.  and  two  pilot  frequencies  at  the  ex- 
treme ends  of  the  transmitted  band,  namely,  60  kc.  and  1024  kc.  for 
automatically  maintaining  a  constant  overall  transmission  level. 

The  total  television  transmission  band  is  indicated  diagrammati- 
cally  in  Fig.  12  which  shows  that  of  the  total  transmitted  band  of 


272  H.  E.  IVES 

1024  —  60  =  964  kc.,  the  actually  useful  part  is  approximately  820 
kc.  or  85  per  cent. 

The  terminal  apparatus  and  the  coaxial  line,  as  above  described, 
were  used  in  a  series  of  demonstrations  to  interested  experts,  the 
motion  picture  film  passing  through  the  apparatus  in  New  York  pro- 
ducing motion  pictures  in  Philadelphia.  It  was  the  generally  ex- 
pressed opinion  that  the  pictures  seen  in  Philadelphia  were  sub- 
stantially the  same  as  those  produced  by  the  directly  connected  termi- 
nal apparatus  in  New  York.  On  critical  examination  some  transients 
and  faint  ghosts  were  detectable  in  the  Philadelphia  picture.  These, 
however,  were  comparable  with  similar  defects  on  the  monitoring 
receiver  at  the  sending  end,  traceable  to  known  characteristics  of  the 
modulating  apparatus  capable  of  improvement;  hence  are  not  charge- 
able to  the  cable  system  and  once  located  are  capable  of  elimination. 
The  experiments  have  proved  that  a  wide  band  signal  of  the  type  re- 
quired for  television  can  be  satisfactorily  transmitted  over  a  coaxial 
system.  Work  is  now  under  way  on  repeaters  and  terminal  appara- 
tus for  transmitting  wider  bands  of  frequency  to  meet  the  standards 
now  being  attempted  in  television. 


MAINTENANCE  OF  A  DEVELOPER  BY  CONTINUOUS 
REPLENISHMENT* 


R.  M.  EVANS** 

Summary. — By  a  series  of  simple  assumptions  that  do  not  appreciably  depart 
from  current  practice,  it  is  shown  that  it  is  possible  to  calculate  readily  the  concentra- 
tion of  any  ingredient  present  in  a  continuously  replenished  developer  solution  during 
use.  The  equations  for  the  equilibria  and  rates  of  growth  of  the  various  substances  are 
derived,  and  applied  to  a  practical  case.  The  benefits  of  chemical  analyses  for  de- 
veloper constituents  both  for  maintenance  of  quality  and  for  economy  are  pointed  out. 
The  analytical  methods  published  by  Lehmann  and  Tausch  are  outlined  briefly. 

In  handling  motion  picture  film  on  continuous  processing  machines, 
or  roll  films  on  intermittent  machines,  it  becomes  essential  that  the 
developer  should  always  have  the  same  properties,  not  only  from  hour 
to  hour  but  from  month  to  month.  This  is  true  largely  because  it  is 
not  economically  practicable  to  vary  the  time  of  development  to  any 
great  extent,  or  to  alter  the  amount  of  exposure  given  the  material 
in  order  to  compensate  for  changes  in  developing  power.  A  single 
reel  of  motion  picture  negative  may  be  printed  from  three  to  five 
hundred  times  over  a  period  of  a  week  or  more  and  then  be  printed 
spasmodically  as  orders  are  received  over  a  period  of  years.  To 
change  the  printing  exposures  from  day  to  day  would  be  much  more 
costly  than  proper  maintenance  of  the  bath.  Variation  in  the  bath 
also  would  not  permit  the  maintenance  of  consistent  quality. 

Accordingly,  the  larger  motion  picture  laboratories  are  confronted 
with  the  problem  of  maintaining  their  developers  at  a  constant  level 
at  all  times.  Since,  from  the  nature  of  the  problem,  replenishing 
must  be  continuous,  it  is  apparent  that  the  situation  is  relatively 
complex.  It  is  possible,  however,  to  reduce  the  problem  to  a  rela- 
tively simple  mathematical  equation  and  deduce  from  this  certain 
important  rules  for  procedure.  Because  of  the  lack  of  previous 
literature  on  the  subject  the  following  discussion  is  relatively  complete. 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;    received 
April  20,  1938.     Communication  No.  673  from  the  Kodak  Research  Laboratories. 
**  Eastman  Kodak  Co.,  Rochester,  N.  Y. 

273 


274  R.  M.  EVANS  [j.  s.  M.  P.  E. 

It  should  be  stated  at  the  outset  that  nothing  short  of  complete 
running  chemical  analyses  of  the  solutions  and  a  frequently  modified 
replenishing  formula  is  possible  for  a  complete  solution  of  the  problem. 
These  extremes  are  seldom  necessary  because  of  the  variations  that 
may  be  permitted  and  the  possibility  of  photographic  tests.  To  the 
writer's  knowledge  such  chemical  analyses  are  not  at  the  present  time 
being  carried  out  in  any  of  the  major  laboratories,  although  the  im- 
portance of  the  problem  and  the  possibilities  for  economy  would 
seem  to  make  them  distinctly  desirable. 

Maintaining  a  solution  constant  involves  correcting  for  variations 
caused  both  by  air  and  by  silver  halide.  Both  these  are  oxidizing 
agents  and  their  effect  varies  to  some  extent  with  the  nature  of  the 
developing  agent.  Lehmann  and  Tausch1'2'3'4  have  shown  that 
when  an  alkaline  mixture  of  elon  and  hydroquinone  is  oxidized  by 
air,  only  the  hydroquinone  reacts.  Only  after  the  hydroquinone  is 
nearly  used  up  does  elon  take  any  appreciable  part  in  the  reaction. 
The  chief  product  of  the  oxidation  is  hydroquinone  monosulfonate, 
which  is  formed  according  to  the  following  equation. 

C6H4(OH)2  +  02  +  2Na2S03  =  C6H3(OH)2.SO3Na  +  Na2SO4  +  NaOH 

The  equation  for  elon  is  the  same  except  that  elon  monosulfonate  is 
formed.  A  small  percentage  of  the  oxidized  developer  does  not  form 
the  monosulfonate  but  passes  on  to  more  complex  structures.  The 
end-product  of  this  small  percentage  is  a  brown  compound  or  mixture 
of  compounds  of  the  humic  acid  type.  It  is  this  portion  of  the  oxida- 
tion products  that  causes  the  familiar  stain  of  severely  exhausted 
developers.  It  appears  that  not  more  than  5  per  cent  of  the  oxidized 
developing  agent  passes  into  this  form. 

When  an  MQ  developer  is  oxidized  by  silver  bromide,  however,  as 
it  is  in  the  normal  process  of  developing  an  image,  it  is  not  the  hydro- 
quinone but  the  elon  that  plays  the  more  important  role.  Under 
most  conditions  there  is  probably  a  considerable  amount  of  hydro- 
quinone also  oxidized  simultaneously.  The  equation  is 


C6H4(OH)2  +  2  AgBr  +  NajsSOa  =  CeHaCOH^.SOgNa  +  2Ag  +  NaBr  +  HBr 

for  hydroquinone  and  a  similar  equation  exists  for  elon. 

Extended  oxidation  by  air  or  silver  bromide  will  produce  consider- 
able quantities  of  the  disulfonates  of  both  hydroquinone  and  elon 
but  since  such  badly  oxidized  solutions  are  not  in  use  they  need  not 
be  discussed  here. 


Sept.,  1938]  MAINTENANCE  OF  A  DEVELOPER  275 

Elon  monosulfonate  may  be  used  as  a  developing  agent,  as  was 
pointed  out  by  Tausch,  and  hydroquinone  sulfonate  as  a  developer 
has  been  known  for  many  years.  Both  these  compounds,  however, 
are  very  weak  in  their  action  and  their  presence  in  an  MQ  developer 
in  small  quantities  produces  no  appreciable  change  in  the  bath.  To 
the  extent  that  these  compounds  form  in  any  given  solution,  they 
may  be  considered  simply  as  so  much  hydroquinone  or  elon  removed. 
Some  of  the  other  products  formed  are  not  at  all  negligible  and  are 
considered  below  in  detail. 

The  present  discussion  will  be  restricted  to  elon-hydroquinone 
developers  that  have  in  their  original  formulas  only  sulfite,  alkaline 
salts,  and  soluble  halides,  in  addition  to  the  developing  agents  them- 
selves. In  order  to  generalize  the  problem  the  specific  nature  of  the 
alkali  will  not  be  assumed. 

Accordingly,  in  a  fresh  batch  of  developer  solution  there  are 
present, 

(1)  Elon 

(2)  Hydroquinone 
(5)     Sodium  sulfite 

(4)  Alkaline  salts 

(5)  Soluble  bromide  (usually  potassium) 

Oxidation  of  this  solution  by  air  will  produce 

(6)  Hydroquinone  monosulfonate 

(7)  Sodium  sulfate 

(8)  Free  hydroxide  (NaOH) 

(9)  Staining  developer  by-products 

Oxidation  by  silver  bromide  emulsions  (which  always  contain  a 
small  percentage  of  silver  iodide)  will  produce  in  addition 

(10)  More  soluble  bromide 

(11)  Soluble  iodide  up  to  equilibrium  with  the  film 

(12)  Elon  monosulfonate 

(13)  Slight  traces  of  elon  and  hydroquinone  disulfonates 

(14)  Free  acid  (HBr) 

(15)  Temporary  (up  to  a  few  hours  after  use)  concentrations  of  unreduced 
dissolved  silver  complexes. 

The  alkaline  water  solution  will  produce 

(77)     Dissolved  gelatin 

(18)     Probable  degradation  products  of  gelatin 


276  R.  M.  EVANS  [j.  s.  M.  p.  E. 

In  addition  there  will  be  a  gradual  accumulation  of  substances 
present  in  the  emulsion  of  the  film  that  dissolve  out  into  the  developer. 
Such  substances  are  sensitizing  dyes  (in  negative  materials),  more 
soluble  bromide,  etc.  Dirt,  calcium  carbonate,  and  extraneous  matter 
will  also  enter  the  tanks  either  on  the  film  or  in  the  water  and  there 
are  probably  small  amounts  of  other  substances  produced  by  chemical 
reactions  of  which  there  is  at  present  no  knowledge. 

The  problem  of  replenishing  such  a  solution  is  two-fold.  Starting 
with  fresh  solution  the  bath  must  be  brought  to  a  state  of  dynamic 
equilibrium  with  film,  air,  and  replenisher,  without  permitting  the 
photographic  properties  to  change  appreciably.  This  equilibrium 
must  then  be  maintained  in  the  face  of  changing  conditions  and,  in 
general,  with  only  the  replenisher  as  an  independent  variable,  since 
film  and  air  quantities  can  not  be  varied  at  will.  In  a  large  industrial 
laboratory  the  amount  of  solution  in  the  machines  may  approximate 
10,000  gallons  and  the  amount  of  film  to  be  processed  may  be  from 
five  to  ten  million  feet  of  motion  picture  positive  per  week.  Corre- 
spondingly lower  figures  hold  for  negative  handling. 

It  is  customary  to  connect  batteries  of  developing  machines  by  a 
system  of  piping  in  such  a  way  that  all  the  developer  may  be  made  to 
circulate  past  a  single  point.  The  volume  of  the  solution  is,  of 
course,  held  constant. 

Dry  film  passes  into  the  developer  at  a  constant  rate  during  the 
operation  of  a  machine  and  carries  with  it  a  small  amount  of  air, 
both  on  its  surfaces  and  in  the  perforations.  The  latent  image  on 
this  film  enables  the  developer  to  reduce  to  metallic  silver  a  quantity 
of  silver  halide  that  varies  widely,  depending  upon  the  nature  of  the 
subject  matter.  Motion  picture  positive  film  contains  per  thousand 
feet,  roughly  fifty  grams  of  metallic  silver  in  the  form  of  halide  salts. 
Of  this,  amounts  varying  from  practically  none  up  to  nearly  the  full 
amount  may  be  developed,  depending  upon  the  subject  of  the  reel. 
Thus,  sound-track  or  black  titles  on  a  clear  ground  may  represent 
only  a  few  grams  of  silver  per  thousand  feet,  while  a  reel  consisting 
largely  of  night  scenes  and  the  like  may  represent  forty  grams  or 
more  of  reduced  silver.  On  the  average,  approximately  one  quarter 
of  the  silver  is  ordinarily  utilized  or  from  10  to  15  grams.  The 
remainder  may  be  recovered  by  an  efficient  hypo  recovery  system. 
With  respect  to  a  given  developing  machine,  however,  the  total 
average  amount  of  silver  reduced  per  day  is  not  constant  unless  care 
is  taken  to  vary  the  type  of  work  being  handled.  With  an  efficient 


Sept.,  1938]  MAINTENANCE  OF  A  DEVELOPER  277 

circulating  system,  good  mixing,  and  several  developing  machines 
operating  simultaneously,  satisfactory  averaging  of  the  work  on  all 
machines  is  possible. 

The  wet  film  after  development  passes  out  of  the  developing  solu- 
tion into  the  rinse  water,  carrying  with  it  a  considerable  quantity 
of  the  solution.  This  quantity  varies  with  the  speed  of  the  film, 
the  design  of  the  machine  and  the  efficiency  of  such  devices  as  may  be 
present  to  prevent  "carry  over."  If  the  surface  of  the  film  carries  no 
surplus  layer  of  liquid  there  is  in  the  gelatin  of  motion  picture  positive 
approximately  one  quart  of  solution  per  thousand  feet.  High  speed 
and  absence  of  devices  to  remove  the  surface  layer  may  triple  this 
figure.  This  solution  loss,  then,  represents  a  definite  minimum 
quantity  of  liquid  that  must  be  added  to  the  system  as  a  whole  to 
maintain  its  volume  constant.  This  quantity  frequently  is  in- 
sufficient and  more  must  be  bled  away  so  that  the  desired  amount  of 
replenisher  may  be  introduced  without  overflowing  the  tanks. 

Since  there  is  seldom  occasion  to  refill  such  a  system  completely 
with  entirely  fresh  solutions,  the  dynamic  equilibrium  that  must  be 
maintained  after  aging  will  be  considered  first.  Since  fresh  re- 
plenisher is  constantly  entering  the  system,  and  developer  that  has 
nearly  the  photographic  properties  of  the  bath  as  a  whole  is  con- 
stantly leaving  the  system,  considerable  economy  can  be  effected  by 
choosing  the  proper  position  for  the  point  on  the  system  at  which 
the  two  occur.  They  should  be  so  situated  that  the  "bleed"  by 
which  solution  is  removed  occurs  in  the  system  just  before  the  point 
at  which  the  replenisher  enters  the  system.  Theoretically,  some 
economy  could  be  effected  also  by  having  the  fresher  developer  at 
the  end  of  the  machine  into  which  dry  film  is  being  fed  and  the 
more  exhausted  developer  removed  from  the  other  end.  This  sets 
up  an  unstable  balance,  however,  which  breaks  down  when  the  ma- 
chine is  stopped  and  so  leads  to  variations  over  which  there  is  little 
control. 

If  the  system  is  so  designed  that  perfect  mixing  may  be  assumed 
at  all  times,  an  equation  may  be  written  for  the  growth  or  decrease 
of  any  constituent  of  the  solution.  For  convenience  in  computation, 
the  figures  will  be  given  in  the  metric  system  for  10,000  gallons  of 
developer  replenished  at  a  rate  of  21/%  gallons  per  minute.  If: 

b     =  replenisher  rate  in  liters  per  minute  =  bleed  rate 

v     =   total  volume  of  the  system  in  liters 

a'    =  initial  total  amount  of  a  given  substance 


278  R.  M.  EVANS  [j.  s.  M.  p.  E. 

x'   =  amount  of  the  given  substance  at  time  t 
k'    =  amount  of  the  substance  added  per  minute 

then  k'dt  -  b  x'dt  =  dx1  or  ft  =  ^L 

*'  -  b-x' 
v 

this  equation  has  as  a  solution 

.     (*'-;'•)    *<    , 

'~5>-H°r'*~ 

A  rather  obvious  axiom  which  greatly  simplifies  the  calculations 
may  be  stated  as  follows.  A  substance  that,  is  being  formed  in  the 
solution  at  a  constant  rate  may  be  considered  as  being  introduced  in  the 
replenisher.  Since  material  is  also  actually  added  in  the  replenisher, 
it  is  convenient  to  convert  the  above  equation  to  concentrations  rather 
than  amounts.  Set 

L/ 

k  =  —  =  concentration  of  material  in  replenisher 

b 

a  =  —  =  initial  concentration  of  the  material  in  the  system 
v 

x  =  —  =  concentration  of  the  material  in  system  at  time  / 

9 

The  equation  may  now  be  converted  to  these  variables,  giving,  as 
a  final  solution, 

x  =  k  -  (k  -  a)  e~* 

This  equation  holds  for  the  growth  of  the  concentration  of  any 
substance  in  the  solution  whether  the  initial  value  is  zero  or  finite. 
An  example  will  make  its  application  clear.  If  the  initial  concentra- 
tion of  potassium  bromide  is  assumed  to  be  one  gram  per  liter  then 
o=l.  Other  figures  may  be  assumed  as  follows: 

b   =   10  liters  per  minute 
v    =  40,000  liters 

If  several  high-speed  developing  machines  are  all  in  operation  on 
the  system  the  amount  of  film  developed  may  be  1000  feet  per  minute. 
From  this  quantity  of  film  we  may  expect  that  bromide  in  amount 
equivalent  to  about  15  grams  of  silver  will  be  released.  This  is 
roughly  the  equivalent  of  15  grams  per  minute  of  potassium  bromide. 
Since  complete  mixing  has  been  assumed,  this  amount  may  be  con- 


Sept.,  1938]  MAINTENANCE  OF  A  DEVELOPER  279 

sidered  for  convenience  as  entering  in  the  replenisher,  which  of  itself 
would  contain  none.  This  gives  k  =  1.5  g./liter  of  replenisher 
solution  per  minute. 

The  equation  for  x,  the  concentration  of  bromide  in  the  bath  as  a 
whole  at  time  t,  becomes  : 

-i°-  * 
x  =  1.5  -  (1.5  -  1)«     4o.ooo 

/ 
or  x  =  .1.5  -  0.5e~  4000 

Since  such  a  system  if  operated  long  enough  will  come  to  equi- 
librium at  a  constant  concentration  of  bromide,  it  is  of  interest  to 
determine  what  this  equilibrium  concentration  is.  Substituting 
/  =  oo  it  is  seen  that  the  last  part  of  the  expression  becomes  zero  and 
x  =  1.5  grams  per  liter  of  potassium  bromide.  That  is,  the  bromide 
has  increased  to  the  concentration  calculated  above  by  dividing  the 
amount  formed  per  minute  by  the  number  of  liters  per  minute  of 
replenisher  added.  This  illustrates  the  fact  that  the  equilibrium 
concentration  of  all  ingredients  except  those  used  up  in  the  process 
(developing  agents  and  sulfite)  tends  to  become  equal  to  that  of  the  re- 
plenisher solution. 

It  is  instructive  to  consider  the  time  taken  to  attain  this  equi- 
librium. Because  in  theory  the  limit  is  approached  exponentially  it 
is  possible  to  determine  only  the  time  required  to  attain  a  given 
percentage.  For  practical  purposes  1.45  grams  per  liter  of  bromide 
is  certainly  indistinguishable  from  1.50.  To  find  the  time  required 
to  reach  this  value  (97  per  cent  of  equilibrium)  it  is  convenient  to 
rewrite  the  equation  so  that  it  gives  /  in  terms  of  x.  That  is  : 


Under  the  above  conditions  then 

t  =  ^2.3X40,000)1  (1.5  -  1) 

[_          10         J  (1.5  -  1.45) 

and  t  =  9200  minutes  or  a  little  more  than  six  days  of  continuous 
operation. 

The  mixing  in  the  above  example  has  been  assumed  perfect.  In 
general,  if  the  inlets  and  outlets  are  properly  placed,  the  time  taken 
would  tend  to  be  less  than  the  above  rather  than  more.  If  there  is  a 
considerable  amount  of  liquid  carried  over  by  the  film  it  may  be  as- 
sumed that  this  liquid  is  somewhat  richer  in  bromide  than  the  solu- 


280  R.  M.  EVANS  [j.  s.  M.  p.  E. 

tion  in  general.  In  this  case  the  amount  of  bromide  removed  per 
minute  is  greater  than  that  assumed  and  the  equilibrium  concentra- 
tion is  somewhat  less.  The  time  taken  to  reach  the  same  percentage 
of  equilibrium  remains  the  same. 

An  exception  was  made  in  the  application  of  these  equations  to 
calculations  of  the  developer  and  the  sulfite  that  are  being  exhausted. 
If  the  replenisher  is  so  increased  in  the  concentration  of  these  ingre- 
dients (above  that  used  in  the  fresh  mix)  that  the  amount  used  up  is 
exactly  equal  to  the  amount  added  there  will  obviously  be  no  change. 
If  under  the  above  conditions  15  grams  of  silver  are  reduced,  then 
from  the  equation  for  the  chemical  reaction  given  earlier,  the  amount 
of  developer  used  up  would  be  approximately  7  grams  if  it  were  all 
hydroquinone  and  12  grams  if  it  were  all  elon  (one  mol  of  developer 
reduces  two  mols  of  silver  bromide) .  In  a  positive  type  of  developer, 
we  may  assume  that  approximately  ten  times  as  much  elon  reacts 
as  does  hydroquinone,  although  this  figure  must  be  determined  for 
every  formula  and  for  every  developing  time.  If  this  figure  is  as- 
sumed, then  0.63  gram  of  hydroquinone  and  10.9  grams  of  elon 
are  used  up  per  minute.  These  amounts  must  be  supplied  by  the 
replenisher.  If  the  rate  of  supply  of  the  replenisher  is  10  liters  per 
minute,  then  0.063  gram  per  liter  of  hydroquinone  and  1.09  grams 
per  liter  of  elon  must  be  present  in  addition  to  the  amount  present  in 
the  regular  formula.  By  the  same  reasoning  0.8  gram  per  liter  of 
anhydrous  sodium  sulfite  is  needed  but  such  a  small  amount  may  be 
neglected . 

The  foregoing  calculations  do  not  include  the  effect  of  air  upon  the 
solution.  It  has  been  shown  that  this  affects  only  the  hydroquinone 
and  the  sulfite  and  it  obviously  depends  to  a  very  large  extent  upon 
the  system  itself.  Variable  sources  of  air  are  the  pumps,  the  speed 
of  the  film,  the  free  air  surfaces,  etc.  If  it  is  assumed,  for  illustration, 
that  the  entire  system  absorbs  and  reacts  with  the  oxygen  in  one 
cubic  foot  of  air  per  minute,  then  the  hydroquinone  equivalent  of 
this  oxygen  equals  27.2  grams  per  minute  (760  mm.  pressure  and 
20 °C).  The  sulfite  equivalent  is  roughly  62  grams.  Replenishing 
at  the  rate  of  ten  liters  per  minute,  therefore,  it  would  be  necessary 
to  add  2.7  grams  of  hydroquinone  and  6.2  grams  per  liter  of  sulfite 
in  addition  to  the  amount  necessary  to  compensate  for  development 
of  the  films.  Note  that  this  is  for  only  one  cubic  foot  of  air  absorbed 
per  minute  in  a  ten  thousand  gallon  system.  Figures  that  would 
show  the  true  extent  of  aerial  oxidation  in  such  a  system  are  not 


Sept.,  1938]  MAINTENANCE  OF  A  DEVELOPER  281 

available.  It  is  apparent,  however,  that  it  is  economical  to  go  to 
some  lengths  to  reduce  aeration  of  the  solution. 

Digressing  for  a  moment  it  should  be  noted  that  the  Lehmann  and 
Tausch  equations  quoted1'2'3'4  above  indicate  a  way  in  which  the 
actual  air  absorption  may  readily  be  measured.  Sodium  sulfate  is 
formed  only  during  aerial  oxidation.  This  product  does  not  appear 
when  silver  halide  is  the  oxidizing  agent.  After  a  bath  has  been  in 
operation  for  some  time  and  has  come  to  equilibrium  with  respect  to 
this  sulfate  a  simple  analysis  will  give  its  concentration  in  grams  per 
liter.  By  the  reasoning  used  above,  this  quantity  multiplied  by  the 
replenisher  rate  in  liters  per  minute  gives  the  average  amount  of 
sulfate  produced  per  minute  by  the  air.  One  mol  of  O2  produces  one 
mol  of  sodium  sulfate  to  a  good  first  approximation.  Since  the 
ratio  of  the  molecular  weights  is  roughly  4.5,  the  grams  per  minute 
of  sulfate  divided  by  this  figure  gives  grams  of  O2  per  minute.  One 
cubic-foot  of  air  at  760  mm.  pressure  and  20°C  contains  7.9  grams 
of  O2.  Hence,  the  grams  of  oxygen  per  minute  divided  by  7.9  gives 
the  number  of  cubic-feet  of  air  absorbed  per  minute.  The  impor- 
tance of  obtaining  this  figure  in  such  a  way  that  is  is  accurately  aver- 
aged over  a  considerable  length  of  time  is  obvious. 

The  equilibrium  concentration  of  any  ingredient  as  well  as  its  con- 
centration at  any  time  after  the  start  of  the  system  may  be  cal- 
culated by  the  methods  already  outlined.  If  the  initial  concentra- 
tion a  of  a  compound  is  zero,  as  in  the  case  of  the  sulfate,  for  example, 
the  equations  are  simplified  to 


x   =  kl  -  e 

' 


where  the  letters  have  the  same  significance  as  before.  The  time 
taken  to  reach  90  per  cent  of  the  equilibrium  concentration  does  not 
change  since  it  depends  only  upon  the  ratio  b/v,  of  replenisher  to  total 
volume. 

It  is  now  possible  to  consider  the  problem  of  starting  with  a  fresh 
bath  and  bringing  it  to  equilibrium  without  serious  change  in  its 
photographic  properties.  The  principle  involved  is  apparent.  For 
all  the  ingredients  that  are  of  importance  it  is  necessary  only  that  the 
original  formula  contain  the  equilibrium  amounts  desired  and  that  the 
replenisher  formula  be  correct.  Under  these  circumstances,  there 
will  be  no  change  in  coming  to  equilibrium.  These  equilibrium 


282  R.  M.  EVANS  [j.  s.  M.  P.  E. 

concentrations  may  be  calculated  easily  since  for  all  cases  they  are 
equal  to  the  amounts  of  the  substances  formed  per  minute  divided 
by  the  liters  per  minute  of  replenisher  to  be  supplied  to  the  solution. 
The  elon,  hydroquinone,  and  sulfite  concentrations  of  the  original 
solution  are  arbitrary,  but  a  correct  replenisher  must  contain  the 
same  amounts  plus  the  amount  per  minute  to  be  used  up  in  the 
machine.  The  total  alkali  concentration  must  be  the  same  in  both 
cases  except  that  since  hydroxide  is  released  by  air  oxidation,  and 
silver  halide  oxidation  releases  acid,  either  acid  or  hydroxide,  re- 
spectively, must  be  added  to  the  replenisher  if  the  rate  of  production 
of  the  one  during  use  of  the  bath  exceeds  that  of  the  other.  The 
addition  should  preferably  be  in  the  form  of  sodium  hydroxide  or 
hydrochloric  acid  so  that  the  alkaline  salt  equilibrium  of  the  solution 
is  not  upset.  Silver  iodide  in  infinitesimal  amounts  may  have  to  be 
added.  Antifoggants  present  in  used  developers  may  call  for  the 
addition  of  small  amounts  of  antifoggants  to  fresh  solutions. 

It  is  important  to  note  in  this  connection  that  the  alkalinity  of  the 
bath  at  equilibrium  can  not  be  calculated  by  the  equations  given  here. 
It  can,  however,  be  held  at  that  of  the  original  mix.  When  free  acid 
or  hydroxide  is  added  to  a  complex  solution  such  as  is  used  for  de- 
velopers, the  change  in  alkalinity  or  £H  of  the  solution  depends  more 
upon  the  nature  and  concentration  of  the  compounds  present  than 
upon  the  amount  of  the  acid  or  alkali  added.  It  is  entirely  possible 
to  calculate  the  amount  of  hydroxide  formed  by  air  (from  sulfate 
determinations)  and  the  acid  released  on  development  (from  bromide 
analyses)  and  to  correct  for  these  by  acid  or  alkali  in  the  replenisher. 
Measurements  of  £H  will  show  whether  or  not  excess  has  been  added 
by  indicating  a  change  in  alkalinity,  although  the  measurements  must 
be  very  precise  if  they  are  to  be  of  value.  In  general,  however,  pH 
measurements  can  not  be  used  to  calculate  the  amount  it  is  necessary 
to  add  unless  careful  calibration  of  the  particular  solution  has  been 
made  in  these  terms. 

While  some  assumptions  have  been  made  in  arriving  at  the  equa- 
tions above,  the  only  serious  discrepancy  to  be  expected  is  that  due  to 
incomplete  mixing  in  the  machine.  This  can  be  estimated  satis- 
factorily only  for  a  given  system.  A  further  assumption  has  been 
made;  namely,  that  air  and  silver  oxidation  are  always  present 
simultaneously.  In  systems  in  which  it  is  customary  to  circulate 
the  solutions  for  a  long  time  before  film  is  started  this  difference  must 
be  taken  into  account.  For  this  problem  there  seems  to  be  no  com- 


Sept.,  1938]  MAINTENANCE  OF  A  DEVELOPER  283 

plete  solution  except  a  different  replenisher  formula  for  each  condition. 

It  is  now  practical  to  consider  the  economic  phase  of  the  problem. 
The  factor  that  determines  the  concentration  of  all  the  products  has 
been  shown  to  be  the  replenisher  rate.  If  a  definite  complete  formula 
for  the  bath  is  prescribed  and  can  not  be  altered,  this  is  where  the 
matter  stops;  there  is  only  one  replenisher  formula  and  one  re- 
plenisher rate  possible.  Assume  for  instance,  that  the  formation  of 
bromide  is  the  most  important  reaction  and  the  original  formula 
which  is  not  to  be  changed  contains  0.5  gram  per  liter  of  this  sub- 
stance. Then  if  15  grams  per  minute  are  formed  by  the  development 
of  the  film,  the  replenisher  rate  for  the  system  must  be  30  liters  a 
minute  regardless  of  its  size.  The  formula  of  the  replenisher  is  then 
fixed  by  the  amounts  of  substances,  such  as  developers,  that  are  used 
up. 

The  determination  of  the  machine  formula  that  will  give  the  most 
economical  operation  is  quite  another  matter.  Certain  things  are 
readily  determined.  Since  as  many  liters  are  thrown  away  as  are 
supplied,  the  formula  should  be  as  dilute  as  possible  in  all  its  original 
constituents  except  bromide.  Since  the  permissible  concentration  of 
reaction  products  formed  determines  the  replenisher  rate,  the  equi- 
librium concentration  of  these  should  be  high.  From  this  point  on, 
the  cost  of  the  individual  chemicals  becomes  important  and  a  great 
many  questions  of  quantity  against  cost  and  photographic  quality 
arise.  The  answers  to  these  questions  will  vary  so  much  with  in- 
dividual conditions  that  no  direct  general  solution  is  possible.  A 
few  of  the  opposing  facts  may  be  noted.  Alkali  is  cheaper  than  de- 
veloping agent  and  so  should  be  high  in  quantity  so  that  developing 
agent  may  be  reduced.  Too  high  a  pH  value  and  too  little  developer 
gives  high  sensitivity  to  bromide  and  interferes  with  picture  quality. 
High  £H  also  usually  increases  the  rate  of  air  oxidation.  Sulfite  is 
cheaper  than  hydroquinone  but  not  enough  so  to  warrant  using  very 
large  quantities.  Larger  quantities  confer  upon  the  bath  only  slightly 
better  keeping  qualities  than  do  reasonable  amounts.  Hydroquinone 
is  cheaper  than  elon  but  the  two  are  not  entirely  equivalent  photo- 
graphically, as  we  have  seen.  The  solution  should  be  as  dilute  as  is 
permissible.  Too  great  a  dilution,  however,  introduces  a  large 
difference  between  the  main  bath  and  the  replenisher.  This  in  turn 
accentuates  circulation  nonuniformities  and  makes  a  bad  situation 
if  any  of  the  main  body  of  the  solution  is  lost  through  leakage.  In 
the  absence  of  other  considerations  the  longer  the  time  of  develop- 


284  R.  M.  EVANS  [j.  s.  M.  p.  E. 

ment  and  the  higher  the  temperature  the  more  efficient  becomes  the 
utilization  of  the  developer.  Limits  are  obviously  set  by  the  size  of 
the  machine,  by  aerial  oxidation,  and  by  the  physical  properties  of 
the  emulsion  gelatin  as  well  as  by  photographic  standards.  A  high 
degree  of  agitation  of  the  developer  at  the  surface  of  the  film  is  de- 
sirable for  uniformity,  and  considerably  increases  the  efficiency  of 
the  bath.  A  saving  by  this  means  is  not  to  be  expected  because 
there  is  a  tendency  toward  excessive  aeration.  Considerable  heating 
of  the  solution  also  puts  an  extra  load  upon  the  cooling  system. 

It  is  true  in  most  cases  that  the  greatest  possibility  of  effecting 
economy  and  at  the  same  time  making  quality  more  uniform  lies  not 
so  much  in  the  use  of  any  of  the  above  devices  as  in  obtaining  knowl- 
edge of  the  exact  status  of  the  bath  at  equilibrium.  With  this 
knowledge  it  is  possible  to  calculate  the  correct  minimum  amount  of 
replenisher  that  may  be  added  and  the  formula  of  the  weakest  re- 
plenisher  that  may  be  used. 

Nothing  has  as  yet  been  said  concerning  methods  by  which  the 
concentrations  of  the  components  of  the  bath  may  be  checked. 
Such  routine  tests  should  be  considered  a  matter  of  necessity.  In- 
crease in  aeration  alone,  due  to  the  sudden  leaking  of  a  pump  or  to  a 
similar  cause  may  throw  the  developer  badly  off  standard.  Photo- 
graphic tests  have,  to  date,  been  nearly  the  only  ones  available. 
These  are  usually  satisfactory  (except  for  the  time  element)  but  leave 
two  important  possibilities  unmeasured.  In  the  first  place,  until 
very  recent  years,  there  has  been  no  method  for  checking  gradual 
changes  since  there  has  been  no  way  of  knowing  whether  the  film  or 
the  developer  has  changed.  The  present  constancy  of  motion  picture 
positive  film  characteristics  has  practically  eliminated  this  problem. 
Second,  it  is  entirely  possible,  and,  in  fact  likely,  that  if  the  formula 
for  the  replenisher  is  varied  to  keep  the  photographic  properties  con- 
stant, there  will  be  a  progressive  change  in  both  the  photographic 
quality  (as  distinct  from  gamma  and  speed)  and  in  the  composition 
of  the  bath.  Sudden  shifts  in  the  quantity  of  oxygen  absorbed  by  the 
system  may  vary  the  hydroquinone  concentration  greatly.  A  sudden 
leak  in  the  system,  if  the  latter  is  of  the  constant-level  automatic 
replenishing  type,  will  introduce  large  quantities  of  replenisher  un- 
intentionally. 

In  order  to  guard  against  these  contingencies  and  to  make  certain 
that  no  large  changes  are  taking  place  unintentionally,  some  sort  of  a 
chemical  analysis  should  be  made  for  all  the  photographically  active 


Sept.,  1938]  MAINTENANCE  OF  A  DEVELOPER  285 

constituents.  The  following  analytical  scheme,  abridged  from  the 
articles  of  Lehmann  and  Tausch  and  the  Tausch  thesis  already  re- 
ferred1'2'3'4 to  represent  a  workable  system.  Much  simpler  and 
faster  methods  must  be  devised  before  analytical  methods  can  be- 
come generally  applicable.  (The  hydroquinone  analysis  given  be- 
low is  a  modification  by  Lehmann  and  Tausch  of  the  method  of 
Pinnow.5) 

To  determine  the  concentrations  of  elon  and  hydroquinone  use  is 
made  of  two  facts :  First,  since  the  oxidation  products  for  the  most 
part  are  the  monosulfonates  of  the  compounds,  they  are  not  ex- 
tractable  from  water  solutions  by  immiscible  organic  solvents  such 
as  ether.  Second,  while  hydroquinone  may  be  extracted  quanti- 
tatively from  water  if  the  solution  is  acidified,  this  is  not  true  for  elon 
since  it  forms  acid  salts.  Elon  may  be  quantitatively  extracted  only 
in  mildly  alkaline  solutions  (pH  approximately  7.6).  At  this  pH 
hydroquinone  is  also  extracted  so  that  it  is  necessary  to  remove  the 
hydroquinone  first. 

The  procedure  used  by  Tausch  was  as  follows:  35.7  cc.  of  de- 
veloper solution  was  acidified  with  sulfuric  acid  to  the  point  where 
a  few  cc.  of  hydroxide  would  again  make  the  solution  alkaline  (per- 
manent blue  coloration  of  Congo  red  paper).  The  released  CC>2  and 
SO2  were  removed  by  evacuation.  A  few  drops  of  methylorange  solu- 
tion were  added  and  the  whole  made  up  to  50  cc. ;  35  cc.  of  this  solu- 
tion was  then  extracted  with  peroxide-free  ether  for  45  minutes  and 
the  ether  solution  separated.  The  acid  water  residue  containing 
the  elon  was  then  made  alkaline  using  methyl  orange  as  indicator.  A 
further  extraction  (20  cc.  of  ether)  for  45  minutes  removed  the  elon 
quantitatively.  After  evaporation  of  the  ether  the  two  compounds 
were  then  titrated  with  iodine  in  water  solution  containing  sodium 
bicarbonate.  From  the  iodine  used  up  the  amounts  of  the  agents 
were  calculated  for  each  case. 

To  determine  the  sulfite  concentration  a  modification  of  well  known 
methods  was  used.  A  weakly  acidified  iodine  solution  (100  cc.)  con- 
taining an  excess  of  iodine  was  placed  in  a  flask  and  2  cc.  of  developer 
was  accurately  introduced.  After  a  short  time  the  solution  was  back- 
titrated  with  thiosulfate  to  the  starch  iodide  end-point. 

Alkali  was  determined  by  titration  with  acid.  Sulfate  was  deter- 
mined by  precipitating  with  barium  salt  and  weighing  the  precipitate. 
Soluble  bromide  was  obtained  in  the  same  manner  after  precipitation 
with  silver. 


286  R.  M.  EVANS 

By  means  of  these  tests  it  is  possible  to  gauge  accurately  the  proper 
rate  of  replenishment  and  the  proper  constitution  for  the  replenisher. 
In  addition,  measurement  of  pH  would  give  a  still  further  check  on 
the  state  of  affairs  in  the  bath.  It  can  not  be  overemphasized,  how- 
ever, that  all  these  tests  taken  together  do  not  specify  the  photographic 
quality  of  the  product.  They  insure  merely  that  the  strength  of  the 
developer  does  not  change.  Sulfide-forming  bacteria  causing  fog, 
by-products  of  development  giving  stain,  and  loss  of  quality  from 
other  sources  must  be  guarded  against  by  an  expert  capable  of 
recognizing  small  changes.  The  present  analysis  is  satisfactory  for 
first-order  control  only.  As  has  been  pointed  out,  however,  the  re- 
plenisher calculations  hold  for  any  product  that  is  continuously 
formed  in  the  bath.  For  this  reason  accurate  determination  of  one 
product  makes  it  possible  to  calculate  the  others  at  once. 

REFERENCES 

1  TAUSCH,  E.:  "Zur  Chemie  der  photographischen  Entwickler,"  Dissertation, 
Berlin,  1934. 

J  LEHMAN,  E.,  AND  TAUSCH,  E. :  "Zum  Chemismus  der  Metol-Hydrochinonent- 
wicklung,"  Phot.  Korr.,  71  (Feb.,  1935),  No.  2,  p.  17;  71  (March,  1935),  No.  3,  p. 
35. 

8  SEYEWETZ,  A.,  AND  SZYMSON,  S.:  "Sur  les  produits  d'oxydation  des  revela- 
teurs  organiques,"  Bull.  soc.  fran$.  Phot.,  21  (April,  1934),  No.  4,  p.  71. 

SEYEWETZ,  A.,  AND  SZYMSON,  S. :  "Influence  de  la  nature  et  de  la  proportion  de 
1'alcali  sur  le  pouvoir  reducteur  des  revelateurs  photographiques,"  Bull.  soc. 
fran$.  Phot.,  21  (Nov.,  1934),  No.  11,  p.  236. 

4  PINNOW,  J.:  "Die  Sulfurierung  des  Hydrochinons,"  Z.  Elektrochem.,  21 
(Aug.,  1915),  No.  15/16,  p.  380. 

6  PINNOW,  J.:  "Zur  Bestimmung  des  Hydrochinons,"  Z.fur  Analytische  Chem., 
50  (1911),  p.  155. 

DISCUSSION 

MR.  TOWNSLEY:  We  have  had  in  our  laboratory  for  the  past  three  years  a 
developing  machine  using  continuous  replenishment.  By  a  process  of  cut  and 
try,  we  have  arrived  at  a  replenishing  solution  that  works  very  well  in  practice. 

We  have  been  able  to  control  both  gamma  and  print  density  within  very  narrow 
limits  without  resorting  to  changes  in  developing  time  or  replenishment  rate  for 
over  18  months.  During  this  time  we  have  processed  approximately  25,000  feet 
of  16-mm.  film  per  week.  The  only  control  necessary  is  to  compensate  for  changes 
in  sensitivity  and  developing'  rate  of  film  of  different  emulsion  batches.  Very 
careful  check  has  been  kept  on  the  installation  as  a  matter  of  engineering  record, 
to  determine  how  well  stability  is  being  maintained  over  a  period  of  time,  and  the 
results  have  been  very  gratifying. 


SOUND-STAGES  AND  THEIR  RELATION  TO 
AIR-CONDITIONING* 


C.  M.  WERT  and  L.  L.  LEWIS** 


Summary. — The  development  and  growth  of  the  modern  motion  picture  sound-stage 
has  almost  paralleled  that  of  sound  pictures.  Weather,  lighting  technic,  and  sound 
recording  brought  about  requirements  not  originally  considered.  Modern  sound-stages 
have  increased  not  only  in  quality  but  in  size,  and  must  have  structural  strength  to 
withstand  the  elements.  Sound  treatment  makes  necessary  other  treatment  for  satis- 
factory occupancy.  Lighting  is  the  greatest  contributor  of  heat  within  the  stage,  is 
variable  as  to  amount  and  duration,  and  must  be  controlled  correctly.  Size  and  num- 
ber of  sets  are  variable  and  create  individual  problems,  and  both  the  number  and  types 
of  persons  on  a  sound  stage  play  their  parts  in  relation  to  the  air-conditioning. 

Construction  that  retards  flow  of  heaj,  through  walls  necessitates  control  of  the  heat. 
High-salaried  personnel,  often  in  costume,  demand  comfort  while  working;  less  time 
is  lost  in  make-up  retouching  and  less  delay  brought  about  by  perspiration  dampened 
costumes. 

An  air-conditioning  system  should  have  the  ability  to  heat,  cool,  ventilate,  and 
clean.  Stages  are  generally  maintained  at  75  °F  and  50  per  cent  relative  humidity, 
with  temperature  settings  above  and  below,  at  the  option  of  the  occupants.  Floor  dis- 
tribution of  air  has  the  advantage  of  more  economical  removal  of  rising  heat  but  the 
disadvantage  of  placing  set  construction  and  personnel  too  near  source  of  cooling. 
Overhead  distribution  has  the  advantage  of  better  temperature  distribution  but  is  less 
economical  in  the  removal  of  rising  heat  from  lights. 

Sound  treatment  of  an  installation  is  necessary  for  continuous  operation.  If  the 
system  does  not  operate  continuously  the  heat  load  builds  up  so  that  the  system  can 
not  adequately  regain  comfortable  conditions  during  non-shooting  periods.  Treatment 
is  by  both  isolation  and  absorption  of  sound,  and  can  be  accurately  determined  and 
specified. 

The  development  and  growth  of  modern  motion  picture  sound- 
stages  has  almost  paralleled  the  development  and  growth  of  sound 
pictures.  The  addition  of  sound  to  action  was  not  the  original  reason 
for  enclosing  the  spaces  where  motion  pictures  are  made.  Weather 
and  the  advancement  of  lighting  technic  undoubtedly  brought  about 
the  original  need  for  enclosed  stages.  The  advent  of  sound  repro- 

*Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;    received 
April  8,  1938. 

**  Carrier  Corp.,  Syracuse,  N.  Y. 

287 


288  C.  M.  WERT  AND  L.  L.  LEWIS  [J.  S.  M.  P.  E. 

duction  not  only  increased  this  necessity,  but  brought  about  certain 
additional  refinements  and  requirements  not  originally  considered. 

Size  of  Stages. — Modern  sound-stages  have  increased  not  only  in 
quality  but  in  size.  A  recent  sound-stage,  completely  sound-treated 
and  completely  air-conditioned,  has  been  built  316  feet  long,  136 
feet  wide,  and  55  feet  high.  The  floor  area  of  this  stage  is  comparable 
to  a  football  gridiron,  and  its  height  to  a  four-story  building.  An- 
other recent  stage,  built  primarily  to  accommodate  the  tremendous 
sets  used  in  the  production  of  the  modern  musical  revues,  has  a  floor 
area  somewhat  smaller;  but  the  ceiling  of  one-half  of  the  stage  is 
66Va  feet  high  and  of  the  other  half  of  the  stage,  96Va  feet.  This 
96 Va  foot  height  is  impressive  and  for  comparison  we  must  visualize 
an  eight-story  building. 

Construction  of  Stages. — The  construction  of  the  sound-stage 
involves  a  great  deal  more  than  the  simple  requirement  of  enclosing  a 
space.  The  entire  structure  must  be  engineered  to  meet  code  re- 
quirements for  earthquake  resistance  and  wind  resistance.  The 
stage  must  have  a  floor  capable  of  carrying  heavy  rolling  equipment, 
large  sets,  and  crowds  of  people.  To  eliminate  columns  the  roof  is 
of  truss  construction,  designed  not  only  according  to  the  requirements 
of  roof  construction,  but  also  to  provide  support  for  scenery,  cat- 
walks and  the  various  braces,  wires,  etc.,  that  seem  literally  to  infest 
the  area  above  a  set.  The  refinements  in  the  design  required  for  the 
proper  reproduction  of  sound  are  themselves  an  engineering  problem 
of  great  magnitude.  This  paper  makes  no  attempt  to  go  into  this 
type  of  engineering.  It  is  sufficient  here  to  say  that  the  entire  stage 
must  be  sound-proofed  against  extraneous  noises  and  sound-treated 
for  the  proper  reproduction  of  sound  within.  These  requirements 
involve  the  selection  of  proper  materials  for  the  control  of  sound, 
both  as  to  transmission  and  absorption.  Also,  it  becomes  necessary 
to  break  the  structural  continuity  of  walls,  floors,  and  ceilings  to 
minimize  the  sound-carrying  vibrations  that  originate  and  progress 
in  the  structure. 

The  floor  of  the  sound-stage,  particularly,  must  not  be  in  rigid 
connection  with  the  wall  structure,  but  must  be  insulated  separately 
to  obviate  ground  noises,  such  as  those  produced  by  passing  trucks. 
The  result  of  all  these  requirements  is  a  structure  that  may  be  com- 
pared to  an  enormously  overgrown  refrigerator  box.  The  stage,  like 
the  box,  is  light-proof,  air-tight,  sound-proofed,  and  its  construction 
retards  the  flow  of  heat  in  either  direction.  In  this  analogy  it  can  be 


Sept.,  1938]         SOUND-STAGES  AND  AIR-CONDITIONING  289 

seen  that  the  obstructions  to  the  passing  of  light,  air,  and  heat  are  all 
intensified  by  the  requirement  of  a  construction  necessary  for  ob- 
structing the  passage  of  sound. 

Stage  Lighting. — The  lighting  of  a  sound-stage  is  the  greatest 
individual  contributor  of  heat  gain  within  the  enclosed  space.  The 
total  light  load  is  greatly  variable,  both  as  to  amount  and  length  of 
time  the  load  is  present.  The  total  light  load  present  depends  pri- 
marily upon  the  size  of  the  set  upon  which  shooting  is  taking  place. 
The  length  of  time  that  the  load  is  present  during  any  one  continuous 
period,  and  the  frequency  of  these  periods,  are  influenced  by  the 
script,  the  director,  the  performers,  and  the  ability  of  the  performers' 
make-up  to  withstand  the  effect  of  the  heat  produced  by  the  lights. 

In  the  case  of  the  two  large  stages  previously  mentioned,  provisions 
were  made  for  11,000  amperes  on  the  larger  stage  and  8000  on  the 
other.  This  is  equivalent  to  an  average  of  28  watts  for  each  square- 
foot  of  stage  area.  The  concentration  of  the  light  is  much  greater, 
since  the  area  covered  by  the  lighted  set  is  never  as  great  as  the  area 
of  the  stage. 

Electricity  for  the  lighting  is  delivered  to  the  stages  in  the  form  of 
direct  current.  On  the  large  lots  this  electricity  is  generated  by 
d-c.  generators  driven  by  a-c.  synchronous  motors.  These  motor- 
generator  sets  are  designed  so  that  the  ripples  in  the  d-c.  voltage  will 
not  exceed  =*=  1  per  cent.  Due  to  the  intensity  of  lighting  required,  a 
greater  variation  in  voltage  would  create  a  change  in  this  intensity 
sufficient  to  register  on  the  photographic  film. 

Due  to  the  heavy  intermittent  load,  which  might  at  times  overload 
the  feeder  to  an  individual  stage,  the  motor-generator  sets  are  over- 
compounded  approximately  6  volts  to  compensate  for  the  drop  in 
voltage  due  to  these  overloads.  Hard  arc  lighting  requires  the  use  of 
choke-coils  to  eliminate  the  sound  or  whistle  created  primarily  by 
commutator  ripple  and  attenuated  by  the  high  frequency  generated 
in  the  arc  crater  of  the  lamp.  Each  arc  light  also  has  its  individual 
resistor. 

Stage  Scenery  or  Sets. — Obviously  there  is  great  variation  in  the 
size  and  number  of  sets  on  a  sound-stage  at  any  one  time.  At  times 
the  entire  stage  may  be  utilized  as  one  large  set;  at  other  times, 
numerous  smaller  sets  may  be  scattered  about  the  stage.  These 
sets  vary  both  as  to  size  and  type,  to  such  an  extent  that  we  might  say 
that  no  two  are  ever  alike. 

Basically,  the  sets  are  three-sided  and  topless.     They  are  stages 


290  C.  M.  WERT  AND  L.  L.  LEWIS  [j.  s.  M.  p.  E. 

within  a  stage,  and,  as  such,  affect  the  acoustic  conditions  of  the  whole. 
Proper  treatment  for  this  situation  provides  a  medium  in  the  con- 
struction of  the  set  that  will  pass  the  sound  bodily  through  the  set  to 
the  treated  walls  and  ceiling  of  the  stage  proper.  Such  procedure 
calls  for  the  elimination  of  all  hard-walled  sets  and  the  construction  of 
sound  sets  to  meet  acoustical  requirements  upon  the  same  basis  as  the 
stage  proper.  One  of  the  steps  toward  overcoming  reverberation 
within  the  confined  area  of  the  set  itself  is  the  use  of  dyed  muslin 
stretched  on  wood  frames  for  all  smooth- walled  sets. 

Sets  within  the  sound  stage  offer  their  problems  also  to  the  lighting 
engineer  and  to  the  air-conditioning  engineer  who  must  deliver  cooled 
air  properly  to  the  area  embraced  by  the  set. 

Occupancy  of  Stages. — The  motion  picture  company,  like  the  elec- 
trical power  company,  sells  to  the  public  something  that  is  intangible. 
Motion  pictures,  through  the  medium  of  reproduced  light  and  sound 
depict  the  emotions  and  personalities  of  one  group  of  persons,  the 
actors,  to  another  group  within  whom  is  created  an  emotional  re- 
action. The  technical  side  of  motion  picture  making  requires  not 
only  a  great  number  of  persons,  but  a  great  variety  of  trades  and 
personalities.  Press  agents  have  given  us  some  idea  as  to  the  per- 
sonalities, but  it  is  not  as  well  known  that  there  are  some  278  different 
trades  and  professions  in  the  motion  picture  industry.  At  one  time 
or  another  a  great  number  of  these  are  represented  on  the  sound- 
stage,  but  we  shall  make  no  attempt  to  enumerate  or  classify  them. 

On  the  large  stages  previously  mentioned,  some  400  persons  have 
been  anticipated  and  provided  for,  but  this  number  may  be  exceeded 
on  occasions.  A  number  of  the  occupants  are,  of  course,  actors  and 
actresses  in  costume  and  make-up.  Human  occupancy  of  the  sound- 
stage  brings  with  it  certain  additional  problems,  some  of  which  we 
must  admit  can  not  be  solved  by  the  slide  rule  of  the  engineer. 

Necessity  of  Air-Conditioning  in  the  Sound-Stage. — All  the  items 
covered  in  the  general  discussion  of  sound-stages  play  a  part  not 
only  in  the  design  of  air-conditioning  systems  for  the  stage  but  also  a 
part  in  the  necessity  of  air-conditioning.  Basically,  sound-stages 
are  being  air-conditioned  in  one  degree  or  another  only  because  air- 
conditioning  has  been  proved  necessary  and  the  results  obtained  are 
of  economical  value. 

Necessity  as  Result  of  Construction. — The  refrigerator  construction 
of  the  modern  sound-stage,  with  its  capacity  for  retaining  the  heat 
generated  within  it,  is  a  contributing  factor  to  the  necessity  of  air- 


Sept.,  1938]         SOUND-STAGES  AND  AIR-CONDITIONING  291 

conditioning.  The  cumulative  effects  of  heat  generation  must  be 
removed  if  the  quality  of  the  stage's  availability  for  continuous  use  is 
to  be  of  the  same  calibre  as  the  quality  of  its  construction.  No  ex- 
pense has  been  spared  to  further  its  ability  to  keep  out  light,  sound, 
and  weather,  and  this  same  expense  furthers  its  ability  to  keep  in 
generated  heat  and  vitiated  air.  The  insulating  value  of  the  sound- 
stage  wall  can  readily  be  perceived  by  considering  the  construction 
from  outside  to  inside:  1-inch  Gunite  plaster,  metal  lath,  water- 
proofed paper  backing,  laminated  wall  panel  containing  air  space, 
2-inch  acoustical  rock  wool,  and  44-40  count  flame-proof  muslin 
protected  with  hardware  cloth  or  chicken  wire. 

The  roof  construction  is  similar  in  character,  although,  of  course, 
the  Gunite  is  replaced  by  roofing.  Floor  construction  consists  of 
1  X  6-inch  T  and  G  finish  flooring  with  2  X  6-inch  sub-flooring,  all 
supported  on  2  X  10-inch  floor  joists  on  12-inch  centers.  The  floor 
level  is  3  to  4  feet  above  ground  level.  The  sound-stage,  with  its 
specially  constructed  doors  closed,  can  be  said  to  be  hermetically 
sealed. 

The  construction  that  we  have  just  described  covers  one  of  the 
most  recent  sound-stages.  All  the  sound-stages  in  use  may  not  be 
typical  in  construction,  but  if  well-designed,  they  are  typical  as 
regards  sound  and  heat  transmission.  From  this  can  be  seen  that  the 
sound-stage  is  a  structure  that  does  not  allow  the  entrance  or  exit  of 
air,  and  so  retards  the  flow  of  heat  that  practically,  if  not  theoretically, 
there  is  no  flow  of  heat  through  the  structure.  This  quality  of  the 
structure  brings  into  being  two  requirements  met  by  the  air-condi- 
tioning system:  (1)  The  use  of  air  delivered  into  the  stage  for  actual 
transportation  of  heat  out  of  the  stage;  (2)  The  furnishing  of  new  air 
to  meet  the  ventilation  requirements  of  the  occupants. 

Necessity  as  Result  of  Lighting. — The  light  load  is  the  most  im- 
portant consideration  of  the  engineer  in  the  design  of  an  air-condi- 
tioning system  for  the  sound-stage  (Fig.  1).  The  production  of 
motion  pictures  is  based  upon  light  and  its  proper  application.  Light 
on  the  sound-stage  is  artificial  light,  and  emits  heat,  most  of  which  is 
in  the  form  of  radiant  energy  that  becomes  sensible  heat  as  soon  as  it 
strikes  an  absorbing  surface.  So-called  cold  light,  such  as  that 
produced  by  the  firefly,  would  be  very  advantageous.  It  is  possible 
to  produce  such  light  by  mixing  a  luminol-caustic  soda  solution  with 
a  hydrogen  peroxide-potassium  ferricyanide  solution,  but  the  cost 
is  more  than  a  million  times  as  great  as  the  light  produced  with  the 


292 


C.  M.  WERT  AND  L.  L.  LEWIS 


[J.  S.  M.  p.  E. 


modern  incandescent  lamp. l     Even  though  there  may  be  reports  to 
the  contrary,  air-conditioning  is  still  more  economical. 

The  air-conditioning  engineer  has  been  familiar  with  the  problem 
of  lighting  and  its  results  for  many  years.  The  tendency  toward 
increased  lighting  in  commercial  establishments  has  not  caught  him 
unprepared.  Published  data  on  the  subject  are  rather  meager,  due, 
we  believe,  to  the  fact  that  possibly  the  "doctor"  has  recognized 
and  treated  the  disease  successfully  without  finding  it  necessary  to 
determine  its  degree.  The  number  of  pills  for  the  patient  has  been 


ROOF  AND  WALLS  THAT  WILL 
'EXCLUDE  EXTRANEOUS  SOUND 
ALSO  EFFECTIVELY  PREVENT 
OUTFLOW  OF  HEAT 


SOUND  STAGE  LIGHTING  50  TO  ISO  WATTS   PER  SQUARE  FOOT 

NORMAL  OFFICE  FROM   t    TO  4       •• 

BRILLIANT  STORE  .LIGHTING  10      ••  « 

FIG.  1.     Diagram  of  heating  element  of  air-conditioning 
problem. 

determined  by  his  size  and  the  effect  of  the  pill  upon  previous  pa- 
tients. 

Sound-stage  lighting  is  a  special  problem  of  great  magnitude  and 
importance.  The  intensity  and  amount  of  sound-stage  lighting  has 
already  been  mentioned.  Light  is  produced  on  the  stage  by  two 
means:  (1)  incandescent  lamps,  and  (2)  carbon  arc  lamps,  each 
having  its  own  characteristics.  The  carbon  arc  lamps  are  required 
for  producing  intensities  beyond  the  scope  of  the  incandescent  lamps. 
On  large  sets,  where  light  must  be  thrown  for  considerable  distance, 
there  will  be  a  preponderant  amount  of  arc  lighting,  possibly  to  the 
extent  of  three  to  one.  On  the  average  set  the  ratio  of  arc  to  in- 
candescent lighting  is  closer  to  unity.  All  the  electrical  energy 
brought  into  the  sound-stage  for  the  production  of  light  eventually  is 
transformed  into  sensible  heat.  Fortunately,  all  the  heat  is  not 


Sept.,  1938]        SOUND-STAGES  AND  AIR-CONDITIONING  293 

released  in  the  area  occupied  by  the  people,  or  what  is  more  commonly 
called  the  "breathing  zone." 

Since  the  size  and  cost  of  an  air-conditioning  system  for  the  sound- 
stage  is  influenced  more  by  the  light  load  than  any  other  single  factor, 
it  is  imperative  that  the  air-conditioning  engineer  correctly  diagnose 
the  effects  of  this  load  in  order  to  produce  the  guaranteed  results 
within  the  breathing  zone.  Providing  refrigeration  for  the  entire 
energy  input  would  be  poor  economy  and,  as  such,  must  be  guarded 
against  by  the  engineer.  Numerous  factors  influence  the  engineer's 
calculations  regarding  the  effect  of  lighting  upon  the  size  of  the  air- 
conditioning  system.  Some  of  these  factors  are: 

(1}  Total  average  maximum  load. 

(2}  Possible  intermittent  maximum  load. 

(5)  Maximum  length  of  time  load  occurs. 

(4)  Frequency  of  load  occurrence. 

(5)  Possible  maximum  concentration  of  load  within  the  stage. 

(6)  Height  of  the  stage. 

(7)  Possible  ratio  of  arc  to  incandescent  lamps. 
(8}  Reflecting  characteristics  of  material  lighted. 
(9)  Location  of  lights. 

The  factors  just  given  are  largely  self-explanatory,  but  two  of  them, 
7  and  8,  warrant  additional  explanation. 

As  mentioned  before,  arc  and  incandescent  lamps  have  certain 
individual  characteristics.  The  gas-filled  incandescent  lamp  oper- 
ated at  normal  voltage  in  still  air  has  an  energy  distribution  about  as 
follows:2 

Per 
Cent 

Radiation  in  the  visible  spectrum  11 

Heat  as  invisible  radiation  in  the  infrared  region  70 
Heat  which  is  conducted  away  from  the  filament  through  the  filament 

supports  and  leads  3 

Heat  dissipated  by  gas  convection  and  conduction  8 

Heat  radiation  by  the  bulb  8 

Hence,  from  a  clear  bulb,  about  90  per  cent  of  the  total  energy  is  in 
radiant  form;  i.  e.,  all  except  that  dissipated  by  the  filament  supports 
and  leads  and  by  air  passing  over  the  bulb.  This  large  amount  of 
radiant  energy  will  not  be  effective  in  raising  the  temperature  in  the 
interior  of  the  stage  until  it  has  been  intercepted  by  an  absorbing 
surface  which,  in  turn,  will  dissipate  the  heat  by  convection.  The 


294  C.  M.  WERT  AND  L.  L.  LEWIS  [J.  S.  M.  p.  E. 

radiant  energy  will,  however,  increase  the  feeling  of  warmth  to  the 
human  body  by  its  radiant  effect. 

On  the  sound-stage  the  aforementioned  percentage  of  energy  in 
radiant  form  is  affected,  to  some  extent,  by  the  housing  or  reflector 
covering  the  bulb.  The  greatest  percentage  of  the  energy,  how- 
ever, is  still  released  in  the  form  of  radiant  energy.  All  this  energy  is 
eventually  absorbed  by  an  absorbing  surface.  The  invisible  radia- 
tion follows  the  same  path  as  the  visible  radiation.  It  is  not  all 
absorbed  by  the  first  intercepting  body  but  only  a  certain  percentage 
of  it,  depending  upon  the  ability  or  inability  of  the  body  to  reflect  it. 

Assuming  that  it  is  possible  to  visualize  a  single  stream  of  radiant 
energy  striking  the  floor  of  a  stage  set  at  an  angle,  a  certain  portion 
of  this  radiant  energy  being  deflected  against  the  wall  of  a  stage  set; 
and  in  turn  visualizing  a  certain  percentage  of  the  energy  being  de- 
flected upward  to  the  top  of  the  stage,  it  can  be  realized  that  a  certain 
amount  of  this  radiant  energy  is  dissipated  on  surfaces  far  above  the 
breathing  zone. 

Arc  lights  have  an  entirely  different  energy  distribution.  The  120 
volts  delivered  to  an  arc  light  set-up  is  reduced  by  resistance  to  72 
volts  across  the  arc  proper.  This  means  that  before  the  arc  is 
produced,  40  per  cent  of  the  incoming  energy  is  released  in  the  form 
of  heat  from  the  resistor  by  convection  and  conduction.  Since  a 
great  number  of  arcs  are  used  to  light  the  set  from  above,  it  can  be 
seen  easily  that  arc  lighting  has  a  different  effect  upon  air-condition- 
ing design  than  does  incandescent  lighting. 

Air-conditioning,  as  regards  the  light-heat  generation,  provides  the 
medium  for  wiping  the  surfaces  exposed  to  the  radiant  heat,  both 
visible  and  invisible ;  thus  increasing  the  heat  removal  by  convection 
and  conduction.  It  also  provides  a  medium  for  removing  the  heat 
not  transformed  into  radiant  energy. 

Necessity  Due  to  Occupancy. — The  fact  that  the  sound-stage  is 
occupied  is,  of  course,  the  basic  reason  for  air-conditioning.  It  has 
long  been  necessary  to  provide  some  means  of  ventilation  for  spaces 
occupied  by  a  group  of  persons  in  order  that  vitiated  air  might  be 
replaced,  and  of  removing  heat  at  a  rate  depending  upon  the  out- 
side temperature.  Certain  combinations  of  various  factors  resulted 
in  comfortable  conditions  within  the  space  while  other  combinations 
did  not. 

Air-conditioning  was  first  used  in  the  industrial  field  for  producing 
and  maintaining  predetermined  temperatures  and  humidities,  regard- 


Sept.,  1938]         SOUND-STAGES  AND  AIR-CONDITIONING  295 

less  of  outside  weather.  Applying  it  to  public  spaces  brought  forth 
the  fact  that  comfort  was  a  marketable  product  and  that  the  public 
would  patronize  more  freely  spaces  that  were  comfortable. 

The  next  step  was  comfort  for  the  purpose  of  obtaining  better  re- 
sults from  salaried  employees.  In  the  sound-stage,'  where  human 
beings  play  such  an  important  part  in  the  scheme  of  things,  comfort 
becomes  a  necessity  rather  than  something  to  be  hoped  for.  Heavy 
costumes  and  make-up  do  not  go  well  with  incandescent  lamps  and 
arcs  when  the  quality  of  the  acting  is  dependent  upon  the  comfort  or 
discomfort  of  the  actors. 

Necessity  from  Economic  Viewpoint. — It  is  doubtful  whether  the 
actual  economic  dollar  value  of  air-conditioning  on  sound-stages  has 
ever  been  calculated.  The  great  number  and  importance  of  intangi- 
ble and  variable  factors  would  complicate  any  such  calculation  to  an 
enormous  extent.  Certain  factors  are  present,  however,  that  are  self- 
evident. 

In  the  moving  picture  business,  as  in  other  businesses,  time  spent 
is  money  spent.  Satisfactory  results  can  be  produced  under  com- 
fortable conditions  more  quickly  than  under  uncomfortable  condi- 
tions. Uncomfortable  and  often  unbearable  conditions  in  un- 
conditioned spaces  are  fought  in  many  ways;  doors  are  opened  be- 
tween shots  for  flushing  the  stage  with  air;  shots  are  delayed;  ice 
cakes  and  dry  ice  are  brought  upon  the  stage;  shots  are  made  at 
night.  All  these  expedients  lead  to  loss  of  time  and  money.  Damage 
by  perspiration  to  costume  and  make-up  is  one  of  the  obvious  factors 
that  can  easily  be  seen  to  have  a  dollar  value.  Probably  the  most 
conclusive  evidence  of  the  economic  value  of  sound-stage  air-con- 
ditioning is  the  fact  that  air-conditioning  systems  are  still  being 
installed  by  companies  that  have  had  previous  experience  with  them. 

Application  of  Air -Conditioning. — Complete  air-conditioning  of  the 
sound-stage  must  meet  many  requirements.  The  system  must  be 
flexible,  able  at  all  times  to  meet  the  requirement  of  heat  and  ventilate 
properly,  clean  the  air,  cool,  remove  smoke  and  fog,  maintain  proper 
temperature  and  humidity  within  the  breathing  zone,  and  properly 
meet  various  other  requirements,  each  of  which  presents  certain 
problems  and  points  of  interest. 

Heating. — Heat  production  on  the  sound-stage  has  been  so  stressed 
that  the  need  for  heating  the  stage  by  the  air-conditioning  system  may 
not  be  evident.  During  the  period  of  set  building,  before  shooting 
can  take  place,  stage  doors  are  thrown  wide  open.  Some  of  these 


296  C.  M.  WERT  AND  L.  L.  LEWIS  [j.  s.  M.  p.  E. 

doors  are  of  tremendous  size,  built  for  the  entrance  and  exit  of  large 
pieces  of  scenery  and  can  accommodate  some  smaller  sets  in  their 
entirety.  Some  of  these  doors  are  24  feet  high  and  18  feet  wide. 
California  nights  are  cool,  and  due  to  the  high  ceilings  and  the  re- 
sultant stack  action  of  heated  air  escaping  from  exhaust  openings, 
the  stage  tends  to  fill  with  cool  air,  particularly  at  the  lower  level. 
If  production  is  due  to  start  in  the  morning,  heat  must  be  supplied  to 
produce  comfortable  conditions  for  the  initial  occupancy,  even  though 
cooling  may  be  required  a  short  time  thereafter.  Heating,  of  course, 
is  seldom  required  during  the  shooting,  except  possibly  on  a  stage  with 
a  small  set  during  cold  weather  and  on  rehearsal  stages  where  no 
shooting  is  taking  place. 

Due  to  this  tendency  of  the  large  stages  to  fill  with  cool  air,  it  is 
considered  necessary  on  one  large  lot  to  have  heat  available  for  nine 
months  of  the  year. 

Ventilation. — Ventilation,  or  the  replacement  of  vitiated  air,  is  the 
oldest  function  of  air-conditioning.  Under  the  artificial  conditions 
of  indoor  life,  air  undergoes  certain  physical  and  chemical  changes 
that  are  brought  about  by  the  occupants.  The  oxygen  content  is 
reduced  somewhat,  and  the  carbon  dioxide  slightly  increased  by  the 
respiratory  process.  Organic  matter,  which  is  usually  perceived  as 
odors,  comes  from  the  nose,  mouth,  skin,  and  clothing. 

The  temperature  of  the  air  is  increased  by  the  metabolic  processes 
and  the  humidity  raised  by  the  moisture  emitted  from  the  skin  and 
lungs.  Contrary  to  old  theory,  the  usual  changes  in  oxygen  and 
carbon  dioxide  are  of  physiological  concern,  because  they  are  too 
small  even  under  the  worst  conditions.  Little  is  known  of  the 
identity  and  physiological  effect  of  the  organic  matter  given  off  in  the 
process  of  respiration.  The  only  certain  fact  is  that  expired  and 
transpired  air  is  odorous  and  offensive,  and  is  capable  of  producing 
loss  of  appetite  and  a  disinclination  for  physical  activity.  These 
reasons,  whether  esthetic  or  physiological,  call  for  the  introduction  of 
a  certain  minimum  amount  of  clean,  outdoor  air  to  dilute  the  odor- 
iferous matter  to  a  concentration  that  is  not  objectionable. 

Ventilation  of  the  sound-stage  always  exceeds,  by  many  times,  the 
actual  requirements  for  comfort  of  the  occupants.  This  excess 
outside  air,  over  and  above  that  required  by  the  occupants,  is  brought 
into  the  sound-stage  for  the  sole  purpose  of  removing  the  concen- 
trated heat  from  the  upper  levels.  After  it  has  performed  this  func- 
tion it  is  exhausted  and  discharged  again  to  the  outside  atmosphere. 


Sept.,  1938]         SOUND-STAGES  AND  AIR-CONDITIONING  297 

Air-conditioning  systems  for  sound-stages  are  often  designed  on  the 
consideration  that  the  minimum  amount  of  outside  air  will  be  50  per 
cent  of  the  total  fan  capacity,  or  the  ability  to  deliver  air  to  the  stage. 
On  the  large  stages  designed  to  hold  400  persons,  this  minimum  quan- 
tity of  outside  air  is  sufficient  for  the  ventilation  requirements  of 
7500  occupants.  For  conservation  of  refrigeration  during  favorable 
outside  weather  conditions  and  also  for  the  quick  purging  of  smoke 
and  artificial  fog,  the  sound-stage  air-conditioning  system  is  always 
designed  for  the  ability  to  handle  100  per  cent  of  its  capacity  from  the 
outside. 

Air  Cleaning. — Air  cleaning,  or  filtering  air,  requires  little  explana- 
tion to  prove  its  importance  in  air-conditioning.  The  atmosphere  in 
all  localities  contains  dirt  and  dust  to  some  degree.  The  accumula- 
tion of  these  particles,  even  though  minute,  will  eventually  interfere 
with  the  economical  operation  of  an  air-conditioning  system.  The 
beneficial  effects  of  clean  air  as  regards  health  and  comfort  are  very 
well  known.  As  regards  the  sound-stage  in  particular,  dust  floating 
in  air  can  not  be  tolerated  since  the  motion  picture  camera  easily 
records  it. 

Cooling. — The  cooling  function  of  an  air-conditioning  system  is  the 
function  most  publicized,  and  as  a  result,  to  the  public,  the  terms 
"air-conditioning"  and  "cooling"  are  synonymous.  To  the  air- 
conditioning  engineer  cooling  also  means  dehumidification,  or  the 
removal  of  moisture  by  condensation;  since  generally  the  two  func- 
tions, removing  heat  and  removing  moisture,  are  necessary  and  are 
performed  by  the  same  equipment  at  the  same  time. 

As  regards  the  sound-stage,  cooling  and  dehumidification  are  the 
functions  of  air-conditioning  systems  that  remove,  from  a  predeter- 
mined volume  of  air,  a  predetermined  amount  of  heat  and  moisture; 
so  that  the  delivery  of  this  predetermined  volume  of  air  to  the  sound- 
stage  and  the  absorption  by  the  air  of  a  certain  amount  of  generated 
heat  and  moisture,  will  result  in  a  temperature  and  humidity  comfort- 
able to  the  occupants. 

The  heat  and  moisture  present  on  the  sound-stage  determine  the 
heat  and  moisture  content  required  of  the  air  delivered  to  the  sound- 
stage.  When  the  temperature  and  humidity  of  the  outside  atmos- 
phere are  higher  than  required  for  the  delivered  air,  refrigeration 
must  be  used  to  produce  the  results  desired.  The  delivered  air  is 
cooled  either  by  contact  with  a  fine  spray  of  cold  water  or  by  con- 
tact with  coiled  metal  surfaces  containing  the  refrigerating  medium, 


298 


C.  M.  WERT  AND  L.  L.  LEWIS 


[J.  S.  M.  P.  E. 


either  gas  or  liquid.  Refrigeration  is  accomplished  by  either  recipro- 
cating or  centrifugal  type  refrigeration  machines. 

The  intermittent  and  variable  heat  load  present  on  sound-stages 
makes  the  storage  type  of  refrigeration  particularly  applicable. 
The  maximum  heat  load  on  the  sound-stage  is  present  during  the 
periods  of  shooting,  which  are  variable  as  to  both  time  and  number. 
Sufficient  instantaneous  capacity  furnished  by  a  refrigeration  machine 
alone  would  require  a  machine  of  great  capacity  (Fig.  2). 

A  storage  type  of  system  combines  a  large  tank  or  reservoir  of 
cold  water,  and  the  refrigeration  machine.  With  this  combination 
it  is  possible  to  use  a  smaller  refrigeration  machine  operating  con- 


STAGE 

STAGE 

A. 

B. 

r 

II 

"1 

STAGE 

STAGE 

i 

1 

E. 

F. 

i 

STAGE 

STAGE 

1 

i. 

C. 

D. 

i  — 

—  1 

L_ 

-L       J.  J 

UNDERGROUND 

j 

COLD    WATER-  ^  ^ 
STORAGE. 

~  "                                   COLD  AND  HO^ 
U*<WATER  PIPE 

1  ;  1         1        LINES. 

CENTRAL   PLANT  FOR          .^ 
COOLING  AND  HEATING--  —  ^ 

I 

WATER. 

FIG.  2.     Water  circulating  system. 

tinuously  at  maximum  efficiency.  During  the  period  when  no  shoot- 
ing is  taking  place  the  excess  capacity  of  the  machine  is  conserved  in 
lowering  the  temperature  of  the  reservoir  of  water.  During  the 
period  of  shooting,  when  the  heat  load  within  the  stage  is  greater  than 
the  capacity  of  the  machine,  additional  cooling  is  furnished  by  the 
tank  in  sufficient  quantity  to  meet  the  requirements  of  the  heating 
load.  A  large  refrigeration  machine  meeting  the  requirements  of 
intermittent  and  variable  loads  does  not  compare  favorably,  eco- 
nomically, with  a  smaller  machine  running  continuously  at  maximum 
efficiency.  The  requirements  and  total  cooling  by  both  set-ups 
are,  of  course,  identical-. 

Exhaust. — The  construction  features  that  render  a  sound-stage 
air-tight  also  lead  to  the  necessity  of  exhausting  air  from  it.  Air 
from  the  outside  is  necessary,  and  unless  air  be  removed  from  the 


Sept.,  1938]         SOUND-STAGES  AND  AIR-CONDITIONING  299 

inside,  the  amount  that  can  be  introduced  will  be  limited  by  the 
pressure-producing  ability  of  the  supply  fan.  When  the  pressure 
within  the  stage  reaches  the  limit  of  the  fan's  capacity,  no  more  air 
from  the  outside  can  enter.  The  expedient  of  providing  openings 
for  relieving  the  inside  pressure  is  not  satisfactory,  since  this  requires 
an  internal  pressure  to  force  out  the  air,  and  the  pressure  required 
would  be  increased  by  the  necessity  of  sound-treating  the  exhaust 
openings.  Pressure  inside  the  sound-stage  is  objectionable  due  to  its 
effect  upon  the  operation  of  the  doors.  An  unbalanced  pressure  on 
the  two  sides  of  the  large  doors  will  prevent  opening  them,  and  inside 
pressure  interferes  with  the  proper  closing  of  the  smaller  pedestrian 
doors. 

Mechanical  exhaust  permits  maintaining  the  pressure  inside  the 
stage  equal  to  the  pressure  outside  the  stage,  by  overcoming  the  re- 
sistance of  the  exhaust  openings.  It  permits  also  the  use  of  smaller 
exhaust  openings,  which  can  be  more  satisfactorily  and  economically 
treated  against  sound  transmission.  Proper  location  of  the  exhaust 
openings  at  the  highest  level  enables  the  exhaust  air  to  pick  up  the 
greatest  amount  of  heat  and  arc  light  smoke  and  carry  it  to  the  out- 
side. 

The  capacity  of  the  exhaust  system  is  variable,  to  agree  with  the 
ability  of  the  supply  system  to  deliver  variable  quantities  of  outside 
air  to  the  stage.  For  very  fast  purging  of  the  stage  after  heavy 
smoke  or  fog  scenes,  full  capacity  of  the  exhaust  system  is  used,  with 
all  doors  opened  and  the  supply  system  not  in  operation. 

Air  Distribution. — Air  distribution  on  the  sound-stage  is  quite 
important  in  that  the  complete  success  of  the  system  depends  largely 
upon  the  results  obtained  by  the  distribution.  It  is  necessary  to 
handle  large  volumes  of  air  to  compensate  for  the  heat  concentration 
without  creating  discomfort  to  the  occupants. 

The  air-distribution  system  must  be  flexible  so  that  extra  air  may 
be  concentrated  at  any  particular  section  of  the  stage  if  desired 
(Fig.  3).  Quite  often  a  distribution  that  is  satisfactory  for  a  certain 
number  of  sets  may  require  alteration  for  another  group  of  sets. 
The  temperature  and  humidity  are  important  only  in  the  breathing 
zone,  and  the  distribution  system  should  not  be  arranged  in  any  man- 
ner that  would  have  a  tendency  to  interfere  more  than  necessary 
with  the  natural  tendency  of  heat  to  rise  and  stratify. 

The  most  economical  air-conditioning  system,  of  course,  would  be 
one  that  conditions  the  floor  area  to  a  height  of  only  seven  or  eight 


300 


C.  M.  WERT  AND  L.  L.  LEWIS 


[J.  S.  M.  P.  E. 


feet.  Practically,  this  is  impossible,  but  the  air-conditioning  engineer 
approaches  this  ideal  as  nearly  as  possible  in  design,  limited  only  by 
other  requirements.  Some  of  the  original  sound-stages  were  con- 
ditioned by  introducing  conditioned  air  along  the  side  walls  and  near 
the  floor  level.  The  air  was  delivered  at  a  low  velocity,  out  across 
the  floor,  where  it  picked  up  the  liberated  heat  in  the  breathing  zone, 
rose  to  the  top  of  the  stage,  and  was  pulled  away  by  an  exhaust  fan. 
This  form  of  distribution  really  delivered  the  air  directly  to  the 


n 


/\      /\ 

\ONomoneo  AIRX 


l\          l\ 


RETURN  AIR  BOX.. 

g^3  G  E3 


PLENUM   SPACE  UNDER   ENTIRE  STAGE 


FIG.  3.     End  section  of  sound-stage. 

breathing  zone,  and  very  little  cooling  effect  was  wasted  at  the  higher, 
unoccupied  level. 

Difficulties  began  to  arise  when  it  was  found  impossible  to  prevent 
the  building  of  sets  and  drops  directly  in  front  of  the  supply  outlets; 
which,  of  course,  prevented  a  part  of  the  air  from  reaching  the  oc- 
cupied spaces  of  the  stage.  Also,  occupants  having  duties  other 
than  acting  often  had  to  be  located  near  the  supply  outlets;  which, 
of  course,  led  to  complaints,  and  rightfully  so,  since  the  temperature 
of  the  air  at  the  delivery  points  was  considerably  below  the  re- 
sulting room  temperature  after  the  air  had  absorbed  its  heat.  These 
objections  were  intensified  by  the  tendency  of  the  companies  to  do 
more  and  more  of  their  shooting  inside  the  stages,  with  a  conse- 
quent increase  in  the  size  of  the  sets  and  bringing  them  closer  and 


Sept.,  1938]         SOUND-STAGES  AND  AIR-CONDITIONING  301 

closer  to  the  walls  of  the  stage.  It  was  then  the  problem  of  the  air- 
conditioning  engineer  to  overcome  these  objections  and  still  retain, 
in  a  measure,  the  original  intention  of  applying  the  conditioning 
primarily  to  the  occupied  space  or  breathing  zone. 

Increased  size  and  variable  location  of  the  sets  made  it  inevitable 
that  the  air  must  be  delivered  from  above  the  set.  This  led  to  a 
design  that  would  enable  delivery  of  conditioned  air  downward 
against  a  blanket  of  heated  air  rising  upward.  The  process  of  adding 
cold  water  to  a  tub  of  water  too  hot  for  comfort  is  well  known — 
the  cold  water  sinks  to  the  bottom  of  the  tub  and  forms  a  cool  layer, 
displacing  the  hot  water,  which  is  forced  upward.  In  order  to  get  an 
even  temperature  it  is  necessary  to  agitate  and  mix  the  cold  and  hot 
water.  Somewhat  the  same  principle  is  applied  to  the  downward 
distribution  of  air.  The  cool,  or  conditioned,  air  is  not  only  heavier 
than  the  warm  air,  but  it  is  started  in  a  downward  direction  by  a  low 
velocity  produced  by  the  supply  fan.  Cool  air  actually  displaces 
the  warmer  air  and  the  mixing  is  accomplished  by  friction  or  con- 
tact along  the  perimeter  of  the  cool  air  stream.  Supply  outlets  are 
designed  to  keep  the  cool  air  stream  as  confined  as  possible  for  as 
great  a  distance  downward  as  possible,  but  also  with  the  purpose  of 
reaching  the  full  area  of  coverage  at  the  top  of  the  breathing  zone. 
This  distribution  can  be  visualized  by  picturing  a  great  number  of 
slender  pyramids  hanging  by  their  apexes  from  the  sound-stage  roof, 
with  their  bases  touching  on  all  four  sides  at  a  level  seven  feet  above 
the  floor.  All  the  space  above  the  bases  and  between  the  pyramids 
would  represent  the  space  through  which  heated  air  could  rise.  This 
final  blanket  of  air  at  the  top  of  the  breathing  zone  must  reach  there 
at  sufficiently  low  velocity  as  not  to  produce  objectionable  drafts. 
Reverting  to  the  bath-tub  analogy,  it  must  be  noted  that  agitation, 
or  mixing,  has  been  guarded  against  as  much  as  possible. 

The  exhaust  openings  of  the  sound-stage  are  located  at  the  roof 
level,  and  the  bottoms  of  the  supply  outlets  are  located  at  the  level 
of  the  bottom  of  the  truss  structure.  The  air-conditioned  sound- 
stage,  when  in  operation,  has  at  the  bottom  a  layer  of  air  in  the  proper 
conditions;  and  at  the  top,  air  that  has  been  heated.  The  air  at  the 
top,  during  operation,  is  generally  warmer  than  outdoor  air,  and  also 
contains  smoke  from  the  arc  lamps.  Being  worthless,  it  is  discharged 
to  the  outside  atmosphere. 

The  conditioned  air  at  the  bottom  of  the  stage  is  often  more  desirable 
than  the  outdoor  air,  and  is  drawn  off  at  the  floor  level  and  returned 


302  C.  M.  WERT  AND  L.  L.  LEWIS  [j.  s.  M.  P.  E. 

to  the  conditioning  system  where  it  is  mixed  with  an  additional  supply 
of  outside  air.  To  maintain  a  balance  of  pressure  inside  and  outside, 
the  exhaust  system  removes  heated  air  from  the  top  of  the  stage  in 
the  exact  quantity  as  outside  air  is  added  to  the  system.  The  quan- 
tities of  air  supplied  to  the  stage,  taken  from  the  outside,  and  ex- 
hausted from  the  stage  are  all  manually  adjustable  from  inside  the 
stage. 

Inside  Atmospheric  Conditions. — Although  other  features  might 
possibly  influence  the  buyer's  satisfaction,  the  resulting  inside  at- 
mospheric condition  is  the  main  yardstick  for  determining  the  success 
of  an  air-conditioning  installation.  Systems  are  designed  for  the 
express  purpose  of  producing  certain  atmospheric  results  within  the 
sound -stage,  and  it  is  normally  a  requirement  of  the  air-conditioning 
contractor  to  guarantee  the  production  of  those  results. 

For  economic  reasons  various  limitations  are  placed  upon  design 
of  air-conditioning  systems.  Extremes  of  short  duration  (in  occu- 
pancy, lighting  load,  and  outside  weather)  are  not  considered; 
especially  since  several  extremes  may  not  simultaneously  occur. 
Guaranteed  summer  cooling  requirements  in  southern  California  are  a 
temperature  not  exceeding  75 °F  and  a  humidity  not  exceeding 
50%;  with  outside  conditions  not  exceeding  90°F  dry-bulb  tem- 
perature and  70° F  wet-bulb  temperature. 

Heating  design  is  generally  based  upon  maintaining  a  temperature 
of  70°F  when  the  outside  temperature  is  not  lower  than  30°F. 
Due  to  the  large  volume  of  the  sound-stages,  a  more  important  re- 
quirement is  sufficient  heating  capacity  to  bring  up  the  temperature 
within  the  stage  to  the  desired  point  within  a  stated  time,  generally 
ninety  minutes. 

With  present-day  knowledge  the  air-conditioning  engineer  can 
predetermine  the  most  economical  design  of  a  system  having  the 
capacity  to  produce  guaranteed  results. 

Present  Air -Conditioned  Stages. — The  history  of  air-conditioning 
of  the  sound-stage  is  almost  covered  by  the  past  ten  years.  The 
present  tendency  toward  doing  more  of  the  work  inside  the  stages, 
aided  considerably  by  the  advances  made  in  using  process  backgrounds 
will  undoubtedly  increase  the  application  of  air-conditioning  to  sound- 
stages.  At  the  present  time  three  major  companies,  namely,  Twen- 
tieth Century-Fox,  Paramount,  and  Metro-Goldwyn-Mayer  have  a 
total  of  thirty-five  air-conditioned  sound-stages. 

Application  of  Sound  Treatment  to  Air- Conditioning. — The  advent 


Sept.,  1938]         SOUND-STAGES  AND  AIR-CONDITIONING 


303 


of  sound  reproduction  into  the  radio  and  motion  picture  industry 
caused  the  air-conditioning  engineer  to  take  up  the  study  of  sound. 
It  not  only  became  necessary  to  provide  air-conditioning  for  broad- 
casting studios  and  sound-stages  without  objectionable  sound,  but 
the  advance  of  sound  pictures  proved  that  many  existing  theater 
installations  required  treatment  and  adjustment.  The  following 
discussion  covers  the  general  application  of  sound  treatment  of  the 


FIG.  4.     Detail  of  supply  apparatus  (plan}. 

air-conditioning  system  for  the  motion  picture  sound-stage  (Figs.  4 
and  5). 

Necessary  for  Sound  Treatment. — At  first  thought  there  seems  to  be 
no  reason  proving  the  necessity  of  sound  treatment  for  sound-stage 
air-conditioning  systems,  since  the  necessity  seems  obvious.  At  the 
present  time  there  are  several  degrees  in  the  quality  of  sound  treat- 
ment, both  on  air-conditioned  stages  and  on  stages  not  conditioned. 
In  some  cases  doubtless  the  requirements  became  more  stringent, 
and  left  the  treatment  inadequate.  Regardless  of  the  reasons  why, 
stages  with  and  without  complete  air-conditioning  can  be  placed  in 
two  classes;  those  on  which  shooting  can  take  place  with  the  system 


304 


C.  M.  WERT  AND  L.  L.  LEWIS 


[J.  S.  M.  P.  E. 


running,  and  those  on  which  the  system  must  be  shut  down.  The 
stage  upon  which  the  equipment  must  be  shut  down  of  course  re- 
ceives no  ventilation  or  cooling  during  the  period  of  greatest  heat 
generation.  This  form  of  operation  leads  to  building  up  the  heat  so 
that  it  may  eventually  get  beyond  the  capacity  of  the  air-conditioning 
equipment  to  handle  it,  and  on  the  unconditioned  stage  leads  much 
faster  to  an  unbearable  condition. 

Proper  sound  treatment,  correctly  engineered,  will  enable  full- 
time  operation  of  the  air-conditioning  system  and  not  interfere  with 
the  reproduction  of  sound.  The  modern  sound-stage  is  a  quality 
structure,  designed  and  built  for  a  specific  purpose,  and  it  is  only  fit 


FIG.  5.     Detail  of  exhaust  apparatus  (plan}. 


and  proper  that  the  air-conditioning  system  for  such  a  structure 
should  be  commensurate  in  quality  and  ability  to  perform  its  duty  at 
all  times. 

Method  of  Sound  Treatment. — The  objectionable  noises  that  might 
enter  the  sound-stage  due  to  the  air-conditioning  installation  may  be 
grouped  into  two  classes: 

(1)  Noise  transmitted  through  the  building  construction,  such  as  from  ma- 
chine mountings  and  vibrations,  and  from  equipment  through  room  walls  and 
floor  surfaces. 

(2)  Noise  transmitted  through  air-carrying  ducts,  such  as  from  fans,  from 
outside  through  duct  walls  into  the  air  stream,  and  noise  generated  by  the  flow 
of  air. 


Sept.,  1938]         SOUND-STAGES  AND  AIR  CONDITIONING  305 

Noise  that  might  be  transmitted  through  the  building  structure  can 
be  taken  care  of  very  rapidly.  All  moving  equipment  is  placed  upon 
properly  designed  isolation  supports  so  that  objectionable  vibrations 
may  be  absorbed.  Flexible  connections  are  used  between  moving  and 
stationary  pieces  of  equipment.  The  equipment  rooms  of  sound- 
stages  are  not  only  designed  to  prevent  passage  of  noise  from  their 
structure,  but  are  located  outside  the  stage. 

Noise  transmitted  through  the  air-carrying  ducts  is  not  so  readily 
overcome.  It  is  impossible  to  select  air-handling  equipment  for 
air-conditioning  that  will  operate  without  producing  some  noise 
that  will  be  carried  by  the  air  stream.  However,  the  noise  is  kept  as 
low  as  possible  by  properly  selecting  the  equipment,  not  only  as 
regards  the  amount  of  noise  produced,  but  as  regards  the  frequency  of 
the  sound.  All  duct  work  outside  the  sound-stage  is  insulated  to  an 
extent  equivalent  to  the  stage  wall's  ability  to  exclude  sound.  Noises 
generated  by  the  flow  of  air  are  prevented  by  properly  designing 
the  duct  system  and  individually  treating  the  parts  of  the  system 
having  a  tendency  to  generate  noises  due  to  contact  with  moving  air. 

After  all  the  prevention  expedients  are  taken  care  of  by  proper 
design,  it  is  possible  to  calculate  the  natural  absorption  of  the  system 
since  all  air-conditioning  systems  using  ducts  for  carrying  the  air 
have  a  certain  capacity  to  lower  the  generated  noise  level.  In  sound- 
stage  applications  the  construction  of  the  stage  and  distance  of  the 
air  openings  from  the  point  of  reproduction  play  a  part  in  reducing 
the  sound  level.  The  allowable  sound  level  is  specified  and  de- 
termined by  the  stage  reproduction  requirements  and  design.  The 
difference  in  sound  level  between  the  allowable  level  and  the  calcu- 
lated level  of  the  system  determines  the  additional  sound  treatment 
that  must  be  applied  to  the  system.  Many  materials  are  now  rated 
by  the  manufacturers  with  sound-absorbing  coefficients,  and  there 
are  several  methods  of  application,  generally  determined  by  the 
arrangement  of  the  parts  making  up  the  installation. 

One  part  of  the  treatment  generally  used  in  sound-stage  condition- 
ing systems  is  the  concentration  of  the  absorbing  material  at  one 
point,  in  cells  or  passes  through  which  the  air  must  flow.  Plenum 
effects,  wherein  fans  are  discharged  into  large  acoustically-lined 
chambers,  the  discharge  velocity  being  impacted  against  the  walls  of 
the  chamber,  have  also  proved  very  effective. 

Space  does  not  permit  going  into  the  details  and  theory  of  sound 
treatment.  Suffice  it  to  state  that  the  required  treatment  can  be 


306  C.  M.  WERT  AND  L.  L.  LEWIS 

determined  as  effectively  as  other  air-conditioning  requirements  of 
the  sound-stage,  to  the  point  of  making  and  delivering  predeter- 
mined sound  level  guarantees. 

Guarantees. — The  following  guarantee,  made  on  a  recent  sound- 
stage  air-conditioning  installation,  points  out  not  only  the  require- 
ments of  the  guarantee,  but  the  ability  of  the  contractor  to  meet  these 
requirements : 

"It  is  agreed  that  the  increase  in  noise  level  in  any  of  the  six  con- 
ditioned stages  resulting  from  the  normal  operation  of  the  completed 
air-conditioning  system  shall  not  exceed  a  value  equivalent  to  an 
energy  level  of  29  decibels  above  an  arbitrary  established  zero  sound 
level  of  10~16  watt  per  square  centimeter  over  a  frequency  range  of 
30  to  300  cycles,  and  shall  not  exceed  a  value  equivalent  to  an  energy 
level  of  19  decibels  over  a  frequency  range  of  300  to  10,000  cycles. 
In  all  cases  the  noise  level  shall  be  measured  at  a  representative 
microphone  location  and  at  a  level  of  five  to  eight  feet  above  the  floor, 
but  in  no  case  shall  the  measurement  be  taken  closer  than  5  feet  to 
any  wall.  The  equivalent  loudness  shall  be  determined  from  30  to 
10,000  cycles  either  by  a  weighted  electrical  network  or  by  a  hand 
frequency  analyzer." 

Acknowledgment. — The  authors  wish  to  acknowledge  their  appre- 
ciation of  information  given  to  them  by  J.  M.  Tobin  and  C.  P. 
Hubert  of  the  Metro-Gold wyn-Mayer  Corp.,  and  E.  L.  Ellingwood, 
Consulting  Engineer,  Los  Angeles,  Calif. 

REFERENCES 

1  STURROCK,  W. :   "Effects  of  Artificial  Lighting  on  Air-Conditioning, "   Heating, 
Piping,  and  Air  Conditioning,  10  (Feb.,  1938),  No.  2,  p.  134. 

2  FORSYTHE,  W.  E.,  AND  WATSON,  E.  M. :    "The  Tungsten  Lamp,"    /.  Franklin 
Inst.,  213  (June,  1932)  No.  6,  p.  623. 


NEW  MOTION  PICTURE  APPARATUS 


During  the  Conventions  of  the  Society,  symposiums  on  new  motion  picture  appara- 
tus are  held  in  which  various  manufacturers  of  equipment  describe  and  demonstrate 
their  new  products  and  developments.  Some  of  this  equipment  is  described  in  the 
following  pages;  the  remainder  will  be  published  in  subsequent  issues  of  the  Journal. 


PROBLEMS  IN  THE  USE  OF  ULTRA-SPEED  NEGATIVE  FILM  * 
P.  H.  ARNOLD** 


New  photographic  problems  have  arisen  from  the  introduction  of  motion  pic- 
ture negative  films  having  a  greater  increase  of  speed  over  the  prevailing  types 
than  the  supersensitive  panchromatic  films  had  at  the  time  of  their  introduction.1 
Some  of  the  problems  confronting  motion  picture  cameramen  and  laboratory 
technicians  can  be  considered  in  the  light  of  solutions  that  have  been  evolved  by 
theory  and  practice. 

In  general,  Ultra-Speed  panchromatic  film,  compared  to  Superpan  negative 
film,  is  much  faster;  slightly  flatter  in  gradation;  similar  in  color-sensitivity, 
with  slightly  greater  response  to  red  light;  and  possessed  of  a  somewhat  coarser 
grain.  Of  these  characteristic  differences,  the  speed  relationship  has  the  greatest 
magnitude. 

The  Problem  of  Correct  Exposure. — A  wide  variety  of  tests  made  under  a  num- 
ber of  conditions  of  practical  photography2  have  shown  that  Ultra-Speed  pan- 
chromatic film  is  correctly  exposed  when  given  two  lens  stops  less  exposure  than 
Superpan  negative  film.  Since  the  principal  application  of  the  film  tends  toward 
those  conditions  of  photography  or  to  cinematographic  subjects  that  have  been 
considered  difficult  to  photograph  or  impossible  to  record  because  of  insufficient 
illumination  (Fig.  1)  the  problem  of  correct  exposure  can  not  always  be  solved  by 
reference  to  correct  exposure  technic  for  supersensitive  panchromatic  negative 
films.  Actinometers,  or  exposure  meters,  are  of  little  assistance  under  these  dim 
light  conditions  since  the  camera  position  is  usually  remote  from  the  subject, 
which,  in  turn,  is  often  inaccessible  for  average  brightness  measurements.  More- 
over, the  photographic  subjects  made  practicable  by  the  Ultra-Speed  panchro- 
matic film  usually  have  too  low  a  brightness  level  to  activate  photoelectric  ex- 
posure meters  in  common  use.  Fortunately  the  sensitivity  characteristics  of  the 
new  film  are  sufficient  to  produce  successful  pictures  under  typical  indoor  illumina- 
tion, with  normal  shutter  angles  and  at  camera  speeds  of  24  frames  a  second,  using 


*  Received  May  4,  1938. 
**  Agfa  Ansco  Corp.,  Binghamton,  N.  Y. 


307 


FIG.  1.  Airplane  view  of  New  York  City:  Taken  about 
7:30  P.M.,  Nov.,  1937,  on  Ultra-Speed  panchromatic  negative 
film  in  Akeley  silent  camera  with  2-inch //1. 4  lens,  by  News  of  the 
Day. 


FIG.  2.  Counting  ballots  in  New  York  City  Armory:  Photographed 
by  Pathe  News  on  Ultra-Speed  panchromatic  film  without  additional 
illumination. 


NEW  MOTION  PICTURE  APPARATUS 


309 


lenses  having  relative  apertures  of  f/2.3  and,  in  some  cases,  //3.5  (Fig.  2).    The 
speed  of  the  film  is  not  appreciably  affected  by  age.    No  allowances  need  be  made 


ULTRA-SPEED   PAN.  356 

Mochine  developed  in  Agfa  17 


LOG  EXPOSURE 


FIG.  3.  Characteristic  curves  obtained  by  exposing 
Ultra-Speed  panchromatic  film  in  a  Type  116  sensitom- 
eter  and  developing  on  a  motion  picture  negative 
developing  machine. 

in  exposing  old  film  since  the  Ultra-Speed  film  has  proved  to  have  exceptional 
stability  with  respect  to  speed  and  gradation,  as  well  as  resistance  to  fog  and  de- 
terioration during  a  period  of  eleven  months. 


ULTRAVIOLET    VIOLET      BLUE     GREEN    YELLOW  ORANGE  RED 


FIG.  4.     Wedge  spectrograms  (tungsten)  on  Superpan  negative  and  Ultra- 
Speed  panchromatic  film. 


In  newsreel  cameras  that  record  sound  on  the  same  film  with  the  picture  image, 
a  reduction  of  lamp  current  of  approximately  15  per  cent  has  been  found  adequate 


310 


NEW  MOTION  PICTURE  APPARATUS        [j.  s.  M.  p.  E. 


to  compensate  for  the  speed  difference  between  Ultra-Speed  panchromatic  film 
and  supersensitive  panchromatic  negative  films.  The  introduction  of  a  Wratten 
No.  47  (C-5  tricolor  blue)  filter  into  the  optical  system  of  the  recorder  accom- 
plishes the  same  purpose  without  requiring  alteration  of  the  lamp  current. 


FIG.  5.     Photographs  of  color  charts  by  light  of  daylight  quality  on  Superpan 
negative  (left)  and  Ultra-Speed  panchromatic  film  (right}. 

When  exposed  on  typical  sensitometers  available  in  commercial  motion  picture 
laboratories,  Ultra-Speed  panchromatic  film  records  density  on  all  the  steps 
(Fig.  3)  because,  when  these  instruments  were  designed,  films  having  the  sensi- 
tivity of  Ultra-Speed  panchromatic  film  possibly  were  not  contemplated ;  whence 

PHYSICAL   .STRUCTURE     OF 

ULTRA-SPEED     NEGATIVE      FILM 


Anti  Abrasion  Surface 
(  OPTIONAL) 

Second  Emulsion  Layer 


,*  Elision  Lo,er 
Non  Halation  Cray  Base  Layer 


Nitrocellulose  Film  Base 


FIG.  b.     Structure  of  Agfa  motion  picture  negative  film, 
showing  location  of  gray  anti-halo  layer. 


the  sensitometers  have  been  calibrated  to  suit  the  speed  characteristics  of  the 
supersensitive  panchromatic  .emulsions.  In  order  to  study  the  threshold  or 
shadow  density  characteristics  of  the  Ultra-Speed  film,  the  addition  of  a  25  per 
cent  neutral  density  filter  has  been  found  advisable,  since  it  produces  sensito- 
metric  strips  having  the  required  range  of  density  without  alt  ering  the  character- 
istics of  the  lamp  or  disturbing  the  calibration  of  the  sensitometer. 


Sept.,  1938J 


NEW  MOTION  PICTURE  APPARATUS 


311 


Other  Problems  of  Exposure. — The  speed  advantage  of  two  diaphragm  stops, 
of  Ultra-Speed  panchromatic  over  Superpan  negative  film,  is  fairly  constant  under 
various  daylight  and  artificial  lighting  conditions,2  indicating  close  similarity  in 
the  color-sensitivity  characteristics  of  the  two  films.  Wedge  spectrograms,  how- 
ever, show  that  the  Ultra-Speed  film  has  a  slightly  greater  range  of  sensitivity  to 
red  light  than  the  previous  film  (Fig.  4)  and  photographs  of  the  color  chart  (Fig. 
5)  show  that  Ultra-Speed  panchromatic  film  has  about  20  per  cent  greater  re- 
sponse to  red-colored  objects  than  the  old  Superpan  negative  film.  The  photo- 
graphic problem  introduced  by  these  color-sensitivity  dissimilarities  is  not  great  and 
in  most  cases  can  be  neglected  with  confidence.  No  special  character  make-up  has 
been  found  necessary  with  the  Ultra-Speed  film  even  under  100  per  cent  tungsten 
illumination. 

Problems  of  Printing  and  Development. — In  timing  negatives  made  on  Ultra- 
Speed  and  Superpan  negative  film,  no  allowances  need  be  made  for  differences 
in  the  gray-base  color,  since  they  both  have  the  same  type  of  neutral  gray  anti- 
halation  layer  (Fig.  6)  on  the  base 
underneath  the  emulsion.  When  com- 
bined for  printing  with  other  negatives 
having  lavender,  pink,  or  orange-tinted 
gray  bases  of  similar  optical  density, 
the  Ultra-Speed  panchromatic  film 
may  appear  to  be  only  three  times 
instead  of  four  times  as  fast,  due  to 
selective  absorption  of  the  printing 
light2  by  the  tinted  gray  bases.  From 
three  to  five  printer  points  may  be 
required  to  compensate  for  the  filter 


Superpan 


TRAY  DEVELOPED  IN  AGFA  17 


16        2O       24       28    MINUTES 


FIG.  7.  Gamma  vs.  developing 
time  relationship  of  Ultra-Speed 
panchromatic  Supreme,  and  Super- 
pan  negative  films. 


effect  of  tinted  gray  bases  that  depart 
markedly  from  a  neutral  gray. 

When  developed  for  a  gamma  of 
0.65  or  lower,  Ultra-Speed  panchro- 
matic film  has  a  flatter  gradation  than 
Superpan  negative  film  given  the  same  treatment  (Fig.  7).  When  developed 
for  a  gamma  of  0.7  or  higher,  the  Ultra-Speed  film  becomes  progressively 
steeper  in  gradation  than  Superpan  negative  film  given  the  same  treatment. 
Considering  the  contrast  relationship  of  the  two  films  in  the  range  of  negative 
gamma  normally  employed  in  professional  motion  picture  work,  together  with 
the  photographic  characteristics  of  the  subjects  that  usually  will  be  photo- 
graphed on  Ultra-Speed  panchromatic  film,  best  screen  results  appear  to  follow 
the  practice  of  developing  Ultra-Speed  panchromatic  film  about  20  per  cent 
longer  than  Superpan  negative  film. 

In  professional  motion  picture  work,  Ultra-Speed  panchromatic  film  will,  of 
necessity,  be  developed  under  normal  negative  processing  conditions  in  prevailing 
types  of  developer,  with  the  correction  in  time  of  development  noted  above. 
Tests  with  a  number  of  developer  solutions  of  interest  to  the  photographer  who 
uses  motion  picture  negative  film  in  miniature  cameras  for  still  photography  have 
shown  that  Ultra-Speed  panchromatic  film  behaves  at  least  as  well  as  Superpan 
negative  in  these  solutions.  For  example,  the  rate  of  exhaustion  of  developer 


312 


NEW  MOTION  PICTURE  APPARATUS        [J.  s.  M.  p.  E. 


DEVELOPER   EXHAUSTION  WITH  S'/t  FOOT  FILM 
STRIPS    PER    LITER 


SUPERS  NEGATIVE 

DEVELOPED  16  MINUTES 
IN    MPG 


First 


DEVELOPER   EXHAUSTION  WITH  S'/t  FOOT  FILM 
STRIPS    PER   LITER 


First 


ULTRA-SPEED  PANCHROMATIC 

DEVELOPED  16  MINUTES 
IN    MPC 


LOG   EXPOSURE 


DEVELOPER  EXHAUSTION  WITH  5*  FOOT  FILM 
STRIPS    PER   LITER 


ULTRA-SPEED  PANCHROMATIC 

DEVELOPED  16  MINUTES  IN  AGFA  17 


FIG.  8.  Rate  of  exhaustion  of  developer  by  successive 
units  of  Ultra-Speed  and  Superpan  negative  films.  The 
exhaustion  rates  of  two  different  developers  are  also 
shown. 


Sept.,  1938] 


NEW  MOTION  PICTURE  APPARATUS 


313 


per  unit  of  film  developed  was  the  same  for  Ultra-Speed  panchromatic  film  as  it 
was  for  Superpan  negative  (Fig.  8).  Experience  gained  in  processing  typical 
motion  picture  negative  films  can  be  freely  applied  to  the  development  of  Ultra- 
Speed  panchromatic  film. 

No  advantage  is  gained  with  the  Ultra-Speed  film  by  the  use  of  fine-grain  de- 
velopers of  the  sort  that  reduce  the  speed  of  the  film.     Greater  efficiency  and 


TRAY  DEVELOPED 

AT  6S'F. 
IN  AGFA  17 


ULTRA- SPEED  PANCHROMATIC 


TRAY  DEVELOPED  AT  6S*F. 
IN  SEASE  NO.3 


ULTDA- SPEED 
PANCHROMATIC 


ULTBA-SPEED  PANCHROMATIC 


FIG.  9.  Characteristic  curves  of  Ultra-Speed  panchromatic  film  developed 
in  various  solutions  used  for  miniature  camera  photography  on  motion  picture 
negative  film. 


better  photographic  quality  is  assured  by  employing  a  film  such  as  Supreme 
negative,3  which  is  already  slower  than  Ultra-Speed  panchromatic  film  (but  twice 
as  fast  as  Superpan  negative)  and  capable  of  exceptionally  fine-grain  results  in 
motion  picture  negative  developers  of  the  types  that  bring  out  the  full  speed  of 
the  film. 

The  sensitometric  characteristics  of  Ultra-Speed  panchromatic  film  developed 
in  a  number  of  developer  solutions  used  with  miniature  camera  exposures  on 
motion  picture  negative  film  are  shown  in  Fig.  9,  and  the  time-gamma  informa- 


314  NEW  MOTION  PICTURE  APPARATUS        [J.  S.  M.  p.  E. 

tion  obtained  in  these  studies  is  compared  in  Table  I.  These  data,  in  some 
cases,  differ  from  recommendations  already  given  for  use  with  some  of  the  solu- 
tions in  developing  Ultra-Speed  panchromatic  film.  The  effect  of  the  several  de- 
velopers upon  the  speed  of  the  film  parallels  the  results  obtained  with  other  nega- 
tive films :  the  highest  effective  film  speeds  were  obtained  with  developers  of  the 
motion  picture  borax  type,  while  the  lowest  speeds  were  obtained  with  the 

TABLE  I 

Gamma  Obtained  in  Various  Solutions  by  Tray  Development  of  Ultra-Speed  Pan- 
chromatic Film  at  65  °F 

Developing  time  in  minutes    8  12  16  20  24 

Agfa  17  0.36  0.56  0.65  0.70 

SeaseNo.  3  0.33  0.50 

Infinol  0.40  0.52  0.62  0.67             0.82 

Finegrainol  F-l^l  0.41  0.51  0.63  0.72 

M.  P.  G.  0.55  0.64  0.76 

Edwam  0.48  0.58  0.64  0.74 

Champlinl5  0.43  0.44  0.55  0.57 

paraphenylenediamine-glycin  developers,  and  intermediate  speeds  resulted  from 
the  latter  type  of  developer  solution  fortified  by  additions  of  metol.  A  com- 
parison of  the  relative  speed  attained  with  the  Ultra-Speed  film  in  the  different 
developers  is  shown  in  Table  II,  the  relationships  being  expressed  in  terms  of 
stops  and  half-stops  on  the  lens  diaphragm  that  would  produce  similar  negatives 
under  the  different  conditions  of  development. 

TABLE  II 

Approximate  Diaphragm  Stop  Required  to  Produce  Negatives  of  Same  Density 
on  Ultra-Speed  Film  Using  Different  Developer  Solutions 

Diaphragm  Stop 

Agfa  17  //16 

Sease  No.  3  11 

Infinol  16 

Finegrainol  F-ll  16 

M.  P.  G.  8 

Edwal  12  11 

Champlin  15  12.5 

Safelight  Requirements. — So  sensitive  is  Ultra-Speed  panchromatic  film  to  light 
of  all  colors  that  it  must  be  handled  and  developed  in  total  darkness.  Green 
safelight  filters  that  have  proved  practicable  for  use  with  supersensitive  panchro- 
matic film  will  fog  the  Ultra-Speed  film.  Very  brief  inspection  of  the  wet  film  is 
permissible  during  development,  using  a  panchromatic  green  safelight  such  as  the 
Agfa  No.  108  with  one-half  the  illumination  that  would  be  safe  for  supersensitive 
panchromatic  film. 


Sept.,  1938]  NEW  MOTION  PICTURE  APPARATUS  315 

REFERENCES 

1HuSE,  E.,  AND  CHAMBERS,  G.  A.:    "Eastman  Supersensitive  Motion  Picture 
Negative  Film,"  /.  Soc.  Mot.  Pic.  Eng.,  XVII  (Oct.,  1931),  No.  4,  p.  560. 

HUSE,  E.,  AND  CHAMBERS,  G.  A.:   "Eastman  Super  X  Panchromatic  Nega- 
tive Motion  Picture  Film,"  Amer.  Cinemat.  XVI  (May,  1935),  No.  5,  p.  186. 

2  ARNOLD,  P.  H.:     "Sensitivity  Tests  with  an  Ultra-Speed  Negative  Film," 
/.  Soc.  Mot.  Pict.  Eng.,  X£X  (May,  1938),  No.  5,  p.  541. 

3  STULL,  W.:    Amer.  Cinemat.,  XIX  (Jan.,  1938),  No.  1,  p.  10. 


PERMANENT-MAGNET  FOUR-RIBBON  LIGHT-VALVE 
FOR  PORTABLE  PUSH-PULL  RECORDING* 


E.  C.  MANDERFELD** 


The  light-valve  described  in  this  paper  has  been  designed  specifically  as  a  part 
of  recently  developed  portable  recording  equipment  when  used  for  push-pull 
recording.  As  space  is  limited  in  portable  equipment,  the  light-valve  was  de- 
signed to  obtain  the  smallest  practical  mechanical  structure  and  yet  allow  the 
adjustment  and  maintenance  advantages  of  the  standard  four-ribbon  valve  used 
with  fixed  channel  recording  machines. 


POLE    PIECES 


CONTACT   FOR 
MAGNET     POLE 


BASE     PLATE 


FIG.    1.    Showing  arrangement  of  pole-pieces  and  base 
plate. 

Referring  to  Fig.  1,  it  will  be  noted  that  four  of  the  pole-pieces  (there  are  four 
on  the  bottom  and  four  on  the  top)  are  mounted  in  a  shallow  slot  in  a  soft  steel 
base-plate.  The  pole-pieces  are  accurately  machined  pieces  of  "Permendur," 

*  Presented  at  the  Spring,   1938,  Meeting  at  Washington,  D.  C.  ;   received 
April  20,  1938. 

**  Electrical  Research  Products,  Inc.,  Hollywood,  Calif. 


316 


NEW  MOTION  PICTURE  APPARATUS        [J.  S.  M.  P.  E. 


a  material  having  the  characteristic  of  high  flux  transmitting  capacity.  The 
pole-pieces  are  located  in  the  proper  position  on  the  base-plate,  as  well  as  the  cap- 
plate,  by  means  of  an  assembly  jig  and  are  locked  in  place  by  small  screws.  Pass- 


FIG.  2.     Top  view  of  pole-piece  assembly. 


ing  through  the  sides  of  the  pole-pieces  on  the  base-plate  are  holes  so  located  in 
each  piece  as  to  form  a  continuous  through  hole  for  each  pair  of  poles  when  prop- 
erly assembled  on  the  base-plate.  This  hole  is  a  clearance  hole  for  a  through 
screw  that  holds  the  ribbon  clamping  and  adjusting  bar  assembly  to  the  sides  of 
the  pole-piece  structure.  The  arrangement  is  shown  in  Fig.  2.  The  clamping 


RIBBON     CLAMPING    CAP 


RIBBON    POSITION 
ADJUSTING    SCREW 


LEAD  CONNECTION 
SCREW 


"CLAMPING    SCREW    HOLES 

FIG.  3.     Clamping  bar. 


bars,  one  of  which  is  shown  in  Fig.  3,  are  made  of  steel  hardened  after  machining. 
The  overall  length  L  of  all  eight  bars  is  identical,  but  the  height  H  and  the  dis- 
tance D  vary.  The  variation  in  height  H  is  to  allow  the  ribbons,  when  clamped, 
to  lie  in  different  planes  so  that  they  can  pass  without  clashing.  In  addition,  the 
two  end  bars  on  each  side  are  provided  with  means  to  move  the  clamping  edge 


Sept.,  1938] 


NEW  MOTION  PICTURE  APPARATUS 


317 


along  the  ribbon  line  for  ribbon-tension  adjustment.     The  ribbon-clamping  caps 
are  made  of  steel  and  are  the  same  for  all  the  clamping  bars. 

The  holes  for  the  screws  holding  the  clamping  bars  against  the  sides  of  the 


LIGHT  VALVE    RIBBONS 


^POLE     PIECES 

FIG.  4.     Cross-sectional  view  showing  positioning  of  ribbons. 

pole-pieces  are  of  sufficient  size  to  allow  electrical  insulation  between  the  clamp 
bars  and  the  clamping  screws.  The  individual  clamping  bars  are  insulated  from 
each  other  by  means  of  thin  bakelite  washers  0.012  inch  thick.  The  electrical 
connections  are  made  at  either  end  of  the  clamping  bars  by  means  of  a  stiff  con- 


FIG.  5.     Arrangement  of  ribbons  over  pole-pieces. 

necting  wire  set  in  a  small  hole  and  locked  in  place  by  a  set  screw.  To  locate  the 
clamping  bars  properly  on  each  side  of  the  pole-piece  structure,  a  jig  is  used  during 
assembly  which  aids  in  obtaining  the  proper  height  H  and  the  proper  distance  D 
of  all  the  bars 


318 


NEW  MOTION  PICTURE  APPARATUS        [J.  S.  M.  P.  E. 


The  cross-section  position  of  the  ribbons  when  placed  between  the  clamping 
points  is  shown  schematically  in  Fig.  4.  It  will  be  noted  that  ribbons  A  and  C 
are  placed  on  a  horizontal  plane  0.002  inch  above  the  top  faces  of  the  pole-pieces, 
whereas  B  and  D  are  placed  slightly  higher  to  give  about  0.0015  inch  of  clearance 
between  the  two  sets  of  ribbons.  Ribbons  A  and  B  act  as  one  pair  and  C  and  D 
as  the  other  pair,  but  being  offset  in  height,  they  will  not  mechanically  clash  if  the 


6.     Refractor  prisms. 

ribbon  amplitude  should  momentarily  exceed  the  prescribed  amount.  The 
spacing  for  either  pair  of  ribbons  can  be  set  for  rather  wide  limits,  but  normally 
it  is  0.001  inch.  The  center-lines  of  the  two  pairs  of  ribbons  are  spaced  0.016 
inch  apart. 

Fig.  5  schematically  shows  how  the  individual  ribbons  are  arranged  over  the 
pole-pieces.  It  shows  how  the  two  end-clamps  are  arranged  to  allow  tuning  ad- 
justment for  any  ribbon,  as  well  as  how  the  electrical  connections  are  made.  It 


FIG  7.    Light-valve  and  double-magnet  assembly. 


will  be  noted  that  although  all  the  ribbons  are  of  the  same  length,  the  dimensions 
are  such  that  the  longitudinal  center  of  each  ribbon  coincides  very  closely  with 
the  center  of  its  associated  pole-piece  opening,  thereby  minimizing  bowing  effect. 
Inasmuch  as  the  center-lines  of  the  two  ribbon  pairs  are  located  0.016  of  an 
inch  apart,  means  must  be  provided  to  align  these  center-lines  at  the  film.  This 
is  done  by  small  refractor  plates  mounted  in  the  cap  pole-pieces,  the  principle  of 
which  is  shown  schematically  in  Fig.  6.  One  refractor  plate  and  one  pair  of  rib- 
bons are  shown  solid  in  this  sketch,  whereas  the  other  set  is  shown  dotted.  The 


Sept.,  1938]  NEW  MOTION  PICTURE  APPARATUS  319 

rays  from  the  condenser  lens  pass  through  the  light-valve  ribbon  opening  and 
strike  the  glass  refractor  plates  at  an  angle.  The  rays  are  then  refracted 
toward  the  normal,  depending  upon  the  angle  of  the  plate  and  its  index  of  refrac- 
tion, and  emerge  from  the  other  side  of  the  refractor  plate  at  the  same  angle  at 
which  they  entered,  but  displaced  in  the  vertical  plane,  provided  the  sides  of  the 
refractor  plates  are  optically  parallel  to  each  other.  Thus  the  objective  lens  sees 
the  two  halves  of  the  light- valve  ribbon  openings  as  if  they  were  in  line. 

The  magnetic  flux  for  the  ribbon  air-gap  is  supplied  by  two  permanent  magnets 
made  of  "Alnico."  This  material  is  an  alloy  of  iron,  aluminum,  cobalt,  and  nickel, 
and  has  the  characteristic  of  very  high  retentivity  along  with  high  magnetomotive 
force,  the  latter  determining  the  value  of  light-valve  sensitivity. 

Stringing  and  adjusting  the  ribbons  of  this  new  type  of  light-valve  is  reasonably 
simple.  As  already  mentioned,  separate  screw  adjustments  are  provided  for 
spacing  and  tuning  each  ribbon  independently,  even  after  the  light-valve  is  com- 
pletely assembled. 

The  entire  light-valve  and  double-magnet  assembly  is  quite  compact,  as  shown 
in  Fig.  7.  The  overall  dimensions  of  the  unit  are  1.4  inch  wide,  1  inch  thick,  and 
4  inches  long  overall.  The  overload  point  is  about  9  db.  above  0.006  watt,  and 
the  closure  current  approximately  170  milliamperes  per  ribbon.  Field  tests  under 
actual  operating  conditions  have  shown  this  type  of  valve  to  be  very  constant  in 
performance  and  easy  to  maintain  in  proper  adjustment. 


A  BASICALLY  NEW  FRAMING  DEVICE  FOR  35-MM  PROJECTORS* 


H.  A.  DsYRY** 


The  motion  picture  projection  machine  has  undergone  fewer  radical  changes 
and  improvements  than  perhaps  any  other  mechanical  electrical  device  in  daily 
use  by  so  many  thousands.  This  is  due  partly  to  the  fact  that  the  old  designers 
did  a  very  good  job  so  that  radical  improvements  seemed  improbable.  However, 
any  mechanical  contrivance  or  machine  that  has  suffered  no  changes  except  re- 
finements in  15  to  20  years  can  hardly  be  expected  to  be  a  really  modern  machine. 

With  this  thought  in  mind  we  have  developed  not  only  an  improvement,  at  least 
so  far  as  simplicity  and  cost  are  concerned,  but  quite  a  novel  and  unique  applica- 
tion of  a  silent  chain  drive,  which  so  far  as  we  or  the  manufacturer  of  the  chain 
know,  has  not  been  made  before. 

The  feature  of  the  device  lies  in  changing  the  course  of  the  chain  without  affect- 
ing the  shutter.  Both  shutter  and  sprocket  are  motivated  by  the  same  chain 
(Fig.  1). 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D,  C.;    received 
February  25,  1938. 
**  H.  A.  DeVry  Corp,,  Chicago,  III 


320  NEW  MOTION  PICTURE  APPARATUS        [J.  S.  M.  p.  E. 

Our  original  idea  of  about  three  years  ago  was  to  frame  the  intermittent  sprocket 
straight  up  and  down  below  the  aperture,  which  worked  out  very  satisfactorily  in 
hundreds  of  machines  in  all  parts  of  the  world.  Another  advantage  of  the  first 
model  was  that  by  removing  three  screws  the  entire  intermittent  assembly  can  be 
exchanged  or  replaced  practically  between  reels. 


FEED  SPROCKET 


INTERMITTENT 


.  FRAMING  LEVER 


•  SHUTTER  SHAFT 


^OVABLE  CONCENTRIC 

'INTERMITTENT  HOUSING 


FIG.  1.     Framer  in  neutral  position;     moving  lever  to  the  right 
moves  film  up,  and  vice  versa. 


The  only  disadvantage  of  this  framing  method,  if  it  can  be  called  a  disadvantage, 
was  that  when  the  intermittent  sprocket  was  positioned  all  the  way  down  (which, 
of  course,  is  not  necessary  when  threaded  by  a  good  projectionist),  it  left  a  space 
of  the  height  of  one  frame  between  the  aperture  plate  and  the  sprocket,  which 
might  cause  some  film  to  buckle  slightly  at  that  point  by  slightly  overthrowing  the 
film. 

When  this  was  called  to  our  attention  this  objection  was  overcome  by  a  slightly 
different  application  of  the  same  basic  principle.  The  revolving  intermittent 
sprocket  framer  was  arranged  as  in  Fig.  2.  Note  that  at  the  point  indicated  by 
the  arrow,  there  is  no  possibility  of  film  buckling,  as  the  sprocket  always  remains 
close  to  the  gate,  regardless  of  the  position  of  the  film. 


Sept.,  1938] 


NEW  MOTION  PICTURE  APPARATUS 


321 


This  particular  type  of  chain  drive  thus  achieves  freedom  from  film  buckling 
while  framing,  and  also  removes  the  possibility  of  the  shutter's  being  put  out  of 
synchronism  with  the  film.  In  addition,  the  cost  of  manufacture  is  cut  to  the 
minimum. 


FIG.  2. 


Showing  arrangement  of  intermittent  sprocket 
framer. 


The  advantage  of  the  silent  chain  drive  is  perhaps  best  attested  by  the  fact 
that  the  Ford  Motor  Company,  like  Cadillac,  Chrysler,  and  other  automobile 
manufacturers,  use  silent  chains  for  driving  cam  shafts,  which  is  perhaps  the 
most  particular  job  on  an  automobile  engine. 


CURRENT  LITERATURE   OF   INTEREST   TO   THE   MOTION   PICTURE 

ENGINEER 


The  editors  present  for  convenient  reference  a  list  of  articles  dealing  with  subjects 
cognate  to  motion  picture  engineering  published  in  a  number  of  selected  journals. 
Photostatic  copies  may  be  obtained  from  the  Library  of  Congress,  Washington,  D.  C., 
or  from  the  New  York  Public  Library,  New  York,  N.  Y.  Micro  copies  of  articles 
in  those  magazines  that  are  available  may  be  obtained  from  the  Bibliofilm  Service, 
Department  of  Agriculture,  Washington,  D.  C. 

Communications 

18  (June,  1938),  No.  6 

Video  Amplifier  Design  (pp.  13,  30).  A.  W.  BARBER 

Features  of  1939  Receivers  (pp.  15-18).  D.    D.    COLE,    G.    G. 

GERLACH,  AND 
W.  P.  SHORT 

Electronics 

11  (June,  1938),  No.  6 
Television  I-F  Amplifiers  (pp.  20-23).  E.  W.  ENGSTROM  AND 

R.  S.  HOLMES 

Rectifier  Filter  Design  (pp.  28-30).  H.  J.  SCOTT 

A  Sound  Effects  Machine  with  High  Impedance  Mixing  M.  J.  WEINER 
(pp.  56,  58). 

International  Photographer 

10  (June,  1938),  No.  5 
Developing  Machines  (p.  8). 

Optical  Printer  Handy  Andy  (pp.  14,  16).  L.  DUNN 

Slyfield's  New  Mixers'  Gallows  (p.  18).  J.  N.  A.  HAWKINS 

Kinotechnik 

20  (June,  1938),  No.  6 
Flimmern    und    Bildwandbeleuchtung    (Flicker    and 

Screen  Illumination)  (pp.  141-143).  H.  NAUMANN 

Der  Farbenausgleich  zwischen  Szenen  und  Szenen- 
teilen  beim  Farbenfilm  (Color  Balancing  between 
Scenes  and  Parts  of  .Scenes  in  Color-Films)  (pp. 
143-144).  L.  KUTZLEB 

Uber  die  Berechnung  photographischer  Belichtungen 
(Computation  of  Photographic  Exposure)  (pp.  145- 
148).  G.  ALBRECHT 

322 


>t.,  1938]  CURRENT  LITERATURE  323 

Quecksilberdampflampen  hoher  Leuchtdichte  (High-  O.  HOPCKE  AND 
Intensity  Mercury  Vapor  Lamps)  (pp.  148-152).  W.  THOURET 

Ein  neuer  Projektor  fur  8-Mm.-Film  (New  8-Mm.  Pro- 
jector (Dralowid))  (p.  153). 

Photographische  Industrie 

36  (June  15,  1938),  No.  24 

Die  Bedeutung  des  elektrischen  Belichtungsmessers  fiir 
die  Kinematographie  I  (Importance  of  Electrical 
Exposure  Meters  for  Motion  Picture  Photography — I) 
(pp.  705-707).  H.  C.  OPFERMANN 

Technique  Cinematographique 

9  (May,  1938),  No.  89 

Nouvel  objectif  pour  le  radiocinematographe  (New 
Lens  for  X-ray  Cinematography)  (pp.  1171-1172). 

Television 

11  (June,  1938),  No.  124 

Baird  Still-Picture  Transmitter  (pp.  324,  341). 

The  London  Television  Service  (pp.  329-331).  T.  C.  MACNAMARA  AND 

D.  C.  BIRKINSHAW 
Mihaly-Traub  Television  (p.  336). 
The   Receiving   Aerial   and    Reception   Fidelity   (pp. 
342-343).  S.  W.  SEELEY 


BOOK  REVIEW 

Motion  Picture  Sound  Engineering:  A  symposium  of  papers  on  Studio  Sound 
Recording  and  Theater  Sound  Reproducing  Equipment  and  Practice,  Academy 
of  Motion  Picture  Arts  &  Sciences  (Taft  Building,  Hollywood,  Calif.),  $4.00. 

This  book  results  from  courses  in  motion  picture  sound  engineering  conducted 
during  1936  and  1937  by  the  Research  Council  of  the  Academy  of  Motion  Picture 
Arts  &  Sciences,  the  lecturers  being  the  qualified  representatives  of  the  major 
sound  departments.  There  are  thirty-nine  chapters,  of  which  the  first  ten  relate 
to  the  practice  of  sound  recording  in  studios  and  sound  reproducing  in  theaters, 
while  the  succeeding  chapters  are  concerned  with  transmission  circuits  and  elec- 
tromagnetic theory. 

After  an  excellent  introductory  chapter  on  the  basis  of  motion  picture  sound, 
the  text  proceeds  to  discuss  the  nature  of  sound,  the  types  of  film  recording  in  use, 
the  acoustic  instruments  used  for  sound  pick-up  and  for  monitoring,  the  mechani- 
cal and  optical  features  of  film  propulsion  and  scanning,  and  the  circumstances 
of  theater  sound  reproduction.  There  are  chapters  explaining  film  processing  and 
the  artifices  of  noise-reduction  as  well  as  the  more  recent  methods  of  recording, 
such  as  push-pull,  squeeze-track,  and  pre-  and  post-equalization.  In  the  discus- 
sion of  these  new  methods  there  is  much  that,  while  not  yet  classical,  dis- 
closes the  processes  of  advance  in  sound  picture  engineering. 

While  the  text  describes  most  of  the  steps  currently  employed  in  film  recording 
and  processing,  there  are  a  few  omissions  as,  for  example,  in  the  chapter  on  film 
processing  there  is  no  reference  to  the  useful  delta-db.  test  in  variable-density 
work  or  of  the  intermodulation  tests  regularly  used  to  determine  the  optimal 
processing  of  variable-width  sound-track. 

Although  the  book  is  devoted  to  photographic  methods,  there  might  well  be 
a  place  for  a  short  discussion  of  disk  recording  and  reproduction,  which  has  a 
definite  place  for  play -back  and  pre-scoring.  The  references  to  loud  speakers 
likewise  might  well  be  amplified  to  include  descriptions  of  the  various  types  of  re- 
ceivers, horns,  and  baffles  in  commercial  use. 

The  earlier  chapters,  /  to  X,  are  descriptive  of  apparatus  and  processes  of  in- 
terest to  the  general  reader,  telling  him  what  the  sound  engineer  has  to  do  and 
how  he  does  it.  The  subsequent  chapters  are  for  the  electrical  engineer,  with 
particular  reference  to  the  mathematical  problems  of  the  sound  engineer.  They 
apply  to  the  design  rather  than  the  operation  of  sound  equipment. 

The  Academy  of  Motion  Picture  Arts  &  Sciences  is  to  be  congratulated  upon 
having  sponsored  the  training  courses  that  resulted  in  the  publication  of  such 
a  useful  compilation  of  information  dealing  with  the  relatively  new  science  of 
sound  recording  and  reproduction. 

H.  G.  KNOX 


324 


FALL,  1938,  CONVENTION 


DETROIT,  MICHIGAN 

HOTEL  STATLER 
OCTOBER  31-NOVEMBER  2,  INCLUSIVE 


G.  AVIL 

A.  J.  BRADFORD 
F.  C.  DICKELY 
E.  H.  FORBES 
W.  M.  HARRIS 


E.  R.  GEIB 


Officers  and  Committees  in  Charge 

W.  C.  KUNZMANN,  Convention  Vice-President 
J.  I.  CRABTREE,  Editorial  Vice-President 
G.  E.  MATTHEWS,  Chairman,  Papers  Committee 
H.  GRIFFIN,  Chairman,  Projection  Committee 
E.  R.  GEIB,  Chairman,  Membership  Committee 
J.  HABER,  Chairman,  Publicity  Committee 


Local  Arrangements 

K.  BRENKERT,  Chairman 
G.  A.  MCARTHUR 

E.  J.  McGLlNNEN 

R.  R.  McMATH 
H.  S.  NORTON 
R.  L.  RUBEN 


G.  J.  SKIMIN 
J.  F.  STRICKLER 
H.  H.  STRONG 
W.  J.  TURNBULL 
E.  F.  ZATORSKY 


Registration  and  Information 

W.  C.  KUNZMANN,  Chairman 


S.  HARRIS 


G.  J.  SKIMIN 


Hotel  and  Transportation  Committee 

A.  J.  BRADFORD,  Chairman 

H.  ANDERS  L.  A.  FIFERLIK  W.  C.  KUNZMANN 

A.  B.  CHERTON  G.  J.  JARRETT  P.  M.  MOLS 

M.  DUDELSON  K.  KALLMAN  E.  J.  SCHAEFER 


A.  J.  BRADFORD 
K.  BRENKERT 
F.  C.  DICKELY 
E.  H.  FORBES 


Projection 

H.  GRIFFIN,  Chairman 
W.  M.  HARRIS 

F.  MOLES 

H.  S.  MORTON 

G.  A.  MCARTHUR 


E.  J.  McGLlNNEN 

R.  L.  RUBEN 
H.  H.  STRONG 
W.  J.  TURNBULL 


Officers  and  Members  of  Detroit  Projectionists  Local  No.  199 


A.  J.  BRADFORD 
K.  BRENKERT 
H.  GRIFFIN 


Banquet 

J.  F.  STRICKLER,  Chairman 
S.  HARRIS 
G.  J.  JARRETT 
W.  C.  KUNZMANN 


R.  R.  McMATH 
H.  H.  STRONG 
E.  F.  ZATORSKY 


325 


326  FALL  CONVENTION  [j.  s.  M.  p.  E. 

Publicity 

J.  HABER,  Chairman 

J.  R.  CAMERON  S.  HARRIS  P.  A.  McGuiRE 

J.  J.  FINN  G.  E.  MATTHEWS  F.  H.  RICHARDSON 

Ladies1  Reception  Committee 

MRS.  J.  F.  STRICKLER,  Hostess 

assisted  by 

MRS.  G.  AVIL  MRS.  F.  C.  DICKELY  MRS.  G.  A.  MCARTHUR 

MRS.  A.  J.  BRADFORD  MRS.  E.  H.  FORBES  MRS.  R.  L.  RUBEN 

MRS.  K.  BRENKERT  MRS.  W.  M.  HARRIS  MRS.  G.  J.  SKIMIN 

Headquarters 

The  Headquarters  of  the  Convention  will  be  at  the  Hotel  Statler,  where  excellent 
accommodations  are  assured.  A  reception  suite  will  be  provided  for  the  Ladies' 
Committee,  who  are  now  engaged  in  preparing  an  excellent  program  of  entertain- 
ment for  the  ladies  attending  the  Convention. 

Special  hotel  rates  guaranteed  to  SMPE  delegates  and  friends,  European  plan, 
will  be  as  follows : 

One  person,  room  and  bath  $3.00  to  $6.00 

Two  persons,  room  and  bath  5.00  to    8.00 

Two  persons  (twin  beds),  room  and  bath  5.50  to    9.00 

Three  persons,  room  and  bath  7.50  to  10.50 

Parlor  suite  and  bath,  for  one  8.50  to  11.00 

Parlor  suite  and  bath,  for  two  12.00  to  14.00 

Room  reservation  cards  will  be  mailed  to  the  membership  of  the  Society  in  the 
near  future,  and  everyone  who  plans  to  attend  the  Convention  should  return  his 
card  to  the  Hotel  promptly  in  order  to  be  assured  of  satisfactory  accommodations. 
Registrations  will  be  made  in  the  order  in  which  the  cards  are  received.  Local 
railroad  ticket  agents  should  be  consulted  as  regards  train  schedules,  and  rates  to 
Detroit  and  return. 

The  following  special  rates  have  been  arranged  for  SMPE  delegates  who  motor 
to  the  Convention,  at  the  National-Detroit  Fireproof  Garage  (the  Hotel  Statler's 
official  garage),  Clifford  and  Elizabeth  Streets,  Detroit:  Self -delivery  and  pick-up, 
12  hours,  $0.60;  24  hours,  $1.00;  Hotel-delivery  and  pick-up,  24  hours,  $1.25. 
Special  weekly  rates  will  be  available. 

Technical  Sessions 

An  attractive  and  interesting  program  of  technical  papers  and  presentations  is 
being  assembled  by  the  Papers  Committee.  All  technical  sessions,  apparatus 
symposiums,  and  film  programs  will  be  held  in  the  Large  Banquet  Room  of  the 
Hotel. 

Registration  and  Information 

Registration  headquarters  will  be  located  at  the  entrance  of  the  Large  Banquet 
Room,  where  members  of  the  Society  and  guests  are  expected  to  register  and  re- 
ceive their  badges  and  identification  cards  for  admittance  to  the  sessions  and  film 


Sept.,  1938]  FALL  CONVENTION  327 

programs.  These  cards  will  be  honored  also  at  the  Fox  Detroit  Theater,  through 
the  courtesy  of  Mr.  David  Idzol,  and  special  passes  will  be  furnished  to  registered 
members  and  guests  for  admittance  to  the  Michigan  United  Artists  and  Palms- 
State  Theaters,  through  the  courtesy  of  the  United  Detroit  Theaters  Corporation. 

Informal  Luncheon  and  Semi- Annual  Banquet 

The  usual  Informal  Luncheon  will  be  held  at  noon  of  the  opening  day  of  the 
Convention,  October  31st,  in  the  Michigan  Room  of  the  Hotel.  On  the  evening  of 
Wednesday,  November  2nd,  the  Semi- Annual  Banquet  of  the  Society  will  be  held 
in  the  Grand  Ballroom  of  the  Hotel  at  8  P.M.  Addresses  will  be  delivered  by 
prominent  members  of  the  industry,  followed  by  dancing  and  other  entertainment. 

Tours  and  Points  of  Interest 

In  view  of  the  fact  that  this  Convention  will  be  limited  to  three  days,  no 
recreational  program  or  tours  have  been  arranged.  However,  arrangements 
may  be  made  for  visits  to  the  Jam  Handy  plant  and  to  other  points  of  technical 
and  general  interest  in  Detroit  on  the  day  following  the  Convention,  namely, 
November  3rd.  Arrangements  for  such  trips  may  be  made  at  the  registration 
headquarters  of  the  Convention. 

In  addition  to  being  a  great  industrial  center,  Detroit  is  also  well  known  for  the 
beauty  of  its  parkways  and  buildings,  and  its  many  artistic  and  cultural  activities. 
Among  the  important  buildings  that  one  may  well  visit  are  the  Detroit  Institute 
of  Arts;  the  Detroit  Historical  Society  Museum;  the  Russell  A.  Alger  House,  a 
branch  of  the  Detroit  Institute  of  Arts;  the  Cranbrook  Institutions;  the  Shrine 
of  the  Little  Flower;  and  the  Penobscot  Building. 

At  Greenfield  Village,  Dearborn,  are  grouped  hundreds  of  interesting  relics  of 
early  American  life,  and  there  also  is  located  the  Edison  Institute,  established  by 
Henry  Ford  in  memory  of  Thomas  A.  Edison. 

On  the  way  to  Greenfield  Village  is  the  Ford  Rotunda,  a  reception  hall  for  visi- 
tors to  the  Ford  Rouge  Plant.  Here' are  complete  reproductions  and  displays  of 
motorcar  design,  and  representations  of  the  famous  highways  of  the  world,  from 
Roman  days  to  modern,  are  on  the  grounds  surrounding  the  building. 

The  General  Motors  Research  Building  and  Laboratory,  located  on  Milwaukee 
Avenue,  will  be  of  particular  interest  to  engineers  visiting  the  City. 

Various  trips  may  be  taken  from  Detroit  as  a  center — to  Canada,  by  either  the 
Ambassador  Bridge  or  the  Fleetway  Tunnel;  to  Bloomfield  Hills,  a  region  of 
lakes;  Canadian  Lake  Erie  trip  from  Windsor,  Ontario;  to  Flint,  Michigan, 
another  center  of  the  automotive  industry;  to  Milford,  General  Motors'  Proving 
Grounds;  and  to  the  Thumb  of  Michigan  Resort  Beaches.  The  City  contains 
also  a  number  of  beautiful  parks  and  golf  courses. 


S.  M.  P.  E. 

STANDARD  TEST-FILMS 


These  films  have  been  prepared  under  the  supervision  of  the  Projection 
Practice  Committee  of  the  Society  of  Motion  Picture  Engineers,  and  are 
designed  to  be  used  in  theaters,  review  rooms,  exchanges,  laboratories, 
factories,  and  the  like  for  testing  the  performance  of  projectors. 

Only  complete  reels,  as  described  below,  are  available  (no  short  sections 
or  single  frequencies).  The  prices  given  include  shipping  charges  to  all 
points  within  the  United  States  ;  shipping  charges  to  other  countries  are 
additional. 


35-Mm.  Sound-Film 

Approximately  500  feet  long,  consisting  of  recordings  of  several  speak- 
ing voices,  piano,  and  orchestra;  buzz-track;  fixed  frequencies  for  focus- 
ing sound  optical  system;  fixed  frequencies  at  constant  level,  for  de- 
termining reproducer  characteristics,  frequency  range,  flutter,  sound- 
track adjustment,  60-  or  96-cycle  modulation,  etc. 

The  recorded  frequency  range  of  the  voice  and  music  extends  to  10,000 
cps.  ;  the  constant-amplitude  frequencies  are  in  15  steps  from  50  cps.  to 
10,000  cps. 

Price  $37.50  each,  including  instructions. 

35-Mm.  Visual  Film 

Approximately  500  feet  long,  consisting  of  special  targets  with  the  aid 
of  which  travel-ghost,  marginal  and  radial  lens  aberrations,  definition, 
picture  jump,  and  film  weave  may  be  detected  and  corrected. 

Price  $37.50  each,  including  instructions. 

16-Mm.  Sound-Film 

Approximately  400  feet  long;  contents  identical  to  those  of  the  35-mm. 
sound-film,  with  the  exception  that  the  recorded  frequency  range  ex- 
tends to  6000  cps.,  and  the  constant-amplitude  frequencies  are  in  11 
steps  from  50  cps.  to  6000  cps. 

Price  $25.00  each,  including  instructions. 

16-Mm.  Visual  Film 

An  optical  reduction  of  the  35-mm.  visual  test-film,  identical  as  to 
contents  and  approximately  400  feet  long. 
Price  $25.00  each,  including  instructions. 


SOCIETY  OF  MOTION  PICTURE  ENGINEERS 

HOTEL  PENNSYLVANIA 

NEW  YORK,  N.  Y. 


JOURNAL 

OF  THE  SOCIETY  OF 

MOTION  PICTURE  ENGINEERS 

Volume  XXXI  OCTOBER,  1938  Number  4 

CONTENTS 

Page 

The  Theory  of  Three-Color  Photography A.  C.  HARDY  331 

The  Fundamentals  of  Color  Measurement. . .  .  D.  L.  MACADAM  343 

Sound  Pictures  in  Auditory  Perspective F.  L.  HUNT  351 

Application  of  Electrical  Networks  to  Sound  Recording  and 

Reproducing H.  R.  KIMBALL  358 

Multiple-Channel  Recording. H.  G.  TASKER  381 

Some  Unusual  Adaptations  of  16-Mm.  Equipment  for  Special 

Purposes J.  L.  BOON  386 

An  Improved  Roller  Type  Developing  Rack  with  Stationary 

Drive C.  E.  IVES  393 

New  Apparatus 

A  Continuous  Optical  Redaction  Sound  Printer 

M.  G.  TOWNSLEY  and  J.  G.  ZUBER  405 

A  New  16-Mm.  Projector H.  C.  WELLMAN  410 

A  Novel  Surgical  Filming  Stand .A.  LENARD  413 

Current  Motion  Picture  Literature 418 

Fall  Convention  at  Detroit 

General 421 

Abstracts  of  Papers 424 

Society  Announcements 435 

Obituary — Norman  McClintock 438 


JOURNAL 

OF  THE  SOCIETY  OF 

MOTION  PICTURE  ENGINEERS 


SYLVAN  HARRIS,  EDITOR 

Board  of  Editors 
J.  I.  CRABTREE,  Chairman 

A.  N.  GOLDSMITH  L.  A.  JONES  H.  G.  KNOX 

A.  C.  HARDY  E.  W.  KELLOGG  G.  E.  MATTHEWS 


Subscription  to  non-members,  $8.00  per  annum;  to  members,  $5.00  per  annum, 
included  in  their  annual  membership  dues;  single  copies,  $1.00.  A  discount 
on  subscriptions  or  single  copies  of  15  per  cent  is  allowed  to  accredited  agencies. 
Order  from  the  Society  of  Motion  Picture  Engineers,  Inc.,  20th  and  Northampton 
Sts.,  Easton,  Pa.,  or  Hotel  Pennsylvania,  New  York,  N.  Y. 
Published  monthly  at  Easton,  Pa.,  by  the  Society  of  Motion  Picture  Engineers. 

Publication  Office,  20th  &  Northampton  Sts.,  Easton,  Pa. 
General  and  Editorial  Office,  Hotel  Pennsylvania,  New  York,  N.  Y. 

West-Coast  Office,  Suite  226,  Equitable  Bldg.,  Hollywood,  Calif. 
Entered  as  second  class  matter  January  15,  1930,  at  the  Post  Office  at  Easton, 
Pa.,  under  the  Act  of  March  3,  1879.     Copyrighted,  1938,  by  the  Society  of 
Motion  Picture  Engineers,  Inc. 

Papers  appearing  in  this  Journal  may  be  reprinted,  abstracted,  or  abridged 
provided  credit  is  given  to  the  Journal  of  the  Society  of  Motion  Picture  Engineers 
and  to  the  author,  or  authors,  of  the  papers  in  question.  Exact  reference  as  to 
the  volume,  number,  and  page  of  the  Journal  must  be  given.  The  Society  is 
not  responsible  for  statements  made  by  authors. 


OFFICERS  OF  THE  SOCIETY 
"President:    S.  K.  WOLF,  1270  Sixth  Ave.,  New  York,  N.  Y. 

*  Past-President:    H.  G.  TASKER,  5451  Marathon  St.,  Hollywood,  Calif. 
*Executive   Vice-President:    K.  F.  MORGAN,  6601  Romaine  St.,  Los  Angeles, 

Calif. 

** Engineering    Vice-President:    L.  A.  JONES,  Kodak  Park,  Rochester,  N.  Y. 
"Editorial  Vice-President:    J.  I.  CRABTREE,  Kodak  Park,  Rochester,  N.  Y. 
**  Financial  Vice-President:    E.  A.  WILLIFORD,  30  E.  42nd  St.,  New  York,  N.  Y. 

*  Convention    Vice-President:    W.   C.   KUNZMANN,   Box  6087,   Cleveland,  Ohio. 
"Secretary:    J.  FRANK,  JR.,  90  Gold  St.,  New  York,  N.  Y. 

"Treasurer:     L.  W.  DAVEE,    76  Varick  St.,  New  York,  N.  Y. 

GOVERNORS 

*J.  O.  AALBERG,  6920  McKinley  St.,  Los  Angeles,  Calif. 
*M.  C.  BATSEL,  Front  and  Market  Sts.,  Camden,  N.  J. 
**R.  E.  FARNHAM,  Nela  Park,  Cleveland,  Ohio. 
*G.  FRIEDL,  JR.,  90  Gold  St.;  New  York,  N.  Y. 
*A.  N.  GOLDSMITH,  444  Madison  Ave.,  New  York,  N.  Y. 
**H.  GRIFFIN,  90  Gold  St.,  New  York,  N.  Y. 

**A.  C.  HARDY,  Massachusetts  Institute  of  Technology,  Cambridge,  Mass. 
*S.  A.  LUKES,  6427  Sheridan  Rd.,  Chicago,  111. 
*Term  expires  December  31,  1938. 
**Term  expires  December  31.  1939. 


THE  THEORY  OF  THREE-COLOR  PHOTOGRAPHY5 
A.  C.  HARDY** 


Summary. — All  methods  of  three-color  photography  are  the  outgrowth  of  a  sugges- 
tion made  in  1855  by  Clerk  Maxwell,  the  illustrious  British  physicist.  The  method 
that  he  suggested  would  now  be  classed  as  an  additive  process,  since  the  final  reproduc- 
tion was  effected  by  projecting  three  lantern-slides  in  register  on  the  same  screen; 
one  lantern  being  supplied  with  a  red  filter,  one  with  a  green  filter*  and  one  with  a  blue 
filter.  Maxwell  suggested  further  that  these  lantern- slides  be  prepared  from  three 
negatives,  each  negative  being  exposed  through  the  same  filter  that  was  to  be  used 
in  projecting  the  corresponding  lantern-slide.  An  extension  of  Maxwell's  reason- 
ing to  subtractive  processes  leads  to  the  conclusion  that  the  dyes  used  in  the  pro- 
duction of  the  positive  images  should  each  be  complementary  in  color  to  the  corre- 
sponding taking  filter. 

Despite  Maxwell's  intimation  that  his  process  was  theoretically  incapable  of 
perfect  reproduction,  the  basic  features  of  Maxwell's  reasoning  have  been  incor- 
porated into  the  commonly  accepted  theory  of  color  reproduction.  The  recent  progress 
in  the  science  of  colorimetry  has  made  it  possible  to  investigate  the  relation  that  should 
obtain  between  the  characteristics  of  the  taking  filters  and  the  colors  of  the  reproduction 
primaries.  Such  an  investigation  shows  that  the  taking  filters  required  for  perfect 
reproduction  have  characteristics  that  are  very  different  from  those  in  common  use. 

The  paper  is  concerned  with  the  establishment  of  the  conditions  that  lead  to  faithful 
reproduction  by  any  three-color  process.  Examples  of  the  application  of  these  funda- 
mental conditions  are  given  for  both  additive  and  subtractive  processes. 

In  another  paper1  presented  at  the  Washington  Convention  of  the 
Society,  D.  L.  MacAdam  showed  that  colorimetry  has  now  acquired 
the  status  of  an  exact  science.  The  motion  picture  film  that  he 
exhibited  demonstrated  how  this  science  can  be  employed  to  test 
the  faithfulness  of  any  process  of  color  photography.  In  this  appli- 
cation, colorimetry  plays  a  role  not  unlike  that  of  the  calipers  in  the 
hands  of  a  machinist  who  undertakes  to  duplicate  a.mechanical  part 
in  a  machine  shop.  By  means  of  the  calipers,  the  machinist  is  able 
to  compare  the  dimensions  of  the  reproduction  with  the  corresponding 
dimensions  of  the  original. 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;  received 
June  22,  1938. 

**  Massachusetts  Institute  of  Technology,  Cambridge,  Mass. 

331 


332  A.  C.  HARDY  [j.  s.  M.  P.  E. 

The  purpose  of  this  paper  is  to  indicate  the  application  of  the  sci- 
ence of  colorimetry  to  the  theory  of  color  photography.  This  may  be 
likened  to  the  design  of  machinery  that  will  produce  automatically 
the  result  that  the  machinist  achieves  by  trial  and  error.  More 
specifically,  this  paper  is  concerned  with  the  determination  of  the 
characteristics  of  three  color  niters  which,  when  used  as  taking  filters 
in  a  three-color  process,  will  enable  negatives  to  be  made  that  will 
control  the  reproduction  primaries  properly  at  every  point  of  the  re- 
production. 

Let  the  subject  contain  an  area  whose  color  can  be  characterized 
by  the  statement  that  the  light  received  from  this  area  by  the  camera 
lens  has  a  spectral  distribution  of  energy  E.  The  tristimulus  values 
of  this  area  are1 


X  =     I     Exd\,  (la) 

Y  =     \     Eyd\,  (ib) 

Jo 

S*a> 

Z    =  Ezd\,  (Ic) 

Jo 

where  x,  y,  and  z  are  the  tristimulus  values  of  unit  amounts  of  the 
spectrum  colors  in  the  colorimetric  system  employed. 

Suppose  the  tristimulus  values  of  unit  amounts  of  the  primaries 
that  are  mixed  to  form  the  positive  reproduction  are  XT  YfZrJ  Xg  YgZg> 
and  Xb  YbZb,  respectively.  Then,  if  an  area  of  the  reproduction  con- 
tains r  units  of  the  red  primary,  g  of  the  green,  and  b  of  the  blue,  the 
tristimulus  values  of  this  area  are 

X'  =  rXr  +  gXg  +  bXb,  (2a) 

Y'  =  rYr  +  gYa  +  bYb,  (2b) 

Z'  =  rZr  +  gZa  +  bZb.  (2c) 

If  this  area  of  the  reproduction  is  to  evoke  the  same  visual  sensa- 
tion as  the  area  of  the  subject  characterized  by  the  energy  distribu- 
tion E,  the  necessary  condition  is 

X'  =  X,  (3a) 

Y'  =   Y,  (3b) 

Z'  =  Z.  (3c) 

Over  a  wide  range  of  brightness  level,  the  reproduction  would  be  en- 
tirely satisfactory  if  the  tristimulus  values  of  the  reproduction  are 


Oct.,  1938]        THEORY  OF  THREE-COLOR  PHOTOGRAPHY  333 

proportional,  but  not  necessarily  equal,  to  those  of  the  corresponding 
area  of  the  original. 

The  first  step  in  virtually  all  methods  of  three-color  reproduction  is 
the  making  of  three  color-separation  negatives  (or  the  equivalent). 
To  simplify  the  mathematical  expressions,  let  the  effective  spectral 
sensitivity  of  the  three  negative  emulsions  be  represented  by  Sr,  Sg, 
and  Sb,  respectively,  it  being  understood  that  the  effective  sensitivity 
at  each  wavelength  is  the  product  of  the  inherent  sensitivity  of  the 
emulsion  and  the  transmittance  of  the  filter  used  in  conjunction 
therewith.  When  these  three  emulsions  are  exposed  to  the  area  of 
the  subject  characterized  by  a  spectral  distribution  of  energy  E,  the 
three  exposures  are  proportional,  respectively,  to 


r  =     f 

Jo 


f 

Jo 


(4a) 


ESbd\.  (4c) 


When  one  follows  the  conventional  procedures,  each  exposure  de- 
termines the  amount  of  one  of  the  reproduction  primaries.  If  the 
conditions  for  tone  reproduction  are  satisfied, 

r  =  k,?r,  (5a) 

g  =  k0?B>  (5b) 

b  =  kb?b.  (5c) 


These  five  sets  of  equations  may  be  combined  algebraically  to  yield 
the  following  equations  : 

krXr    f     ESrd\  +  k0Xg  f  ESgd\  +  kbXb  \  ESbd\  =  ]      Exd\,      (6a) 

Jo                            Jo                            Jo  Jo 

kTYr   ]      ESrd\  +  kg  Yg  f  ESgd\  +  kbYb  f  ESbd\  =  (     Eyd\,     (6b) 

Jo                          Jo                           Jo  Jo 

krZr    f    ESrd\  +  kgZg  f  ESgdX  +  kbZb  \  ESbd\  =  \      Ezd\,      (6c) 

Jo                             Jo                             Jo  Jo 


which  define  the  necessary  and  sufficient  conditions  that  one  color  in 
the  subject  be  reproduced  correctly.  Inspection  of  these  equations 
reveals  that  one  color  in  the  subject  may  be  reproduced  correctly  in 
an  infinite  number  of  ways.  In  other  words,  regardless  of  the  form 
of  the  functions  ST,  Sg,  and  Sb  or  the  tristimulus  values  of  the  repro- 


334  A.  C.  HARDY  [j.  s.  M.  P.  E. 

duction  primaries,  the  constants  may  always  be  chosen  in  such  a 
manner  that  equations  6  will  be  satisfied  for  one  color  of  the  subject. 
The  usual  desideratum  in  color  photography  is  to  reproduce  cor- 
rectly all  colors  of  the  subject  that  lie  within  the  realizable  color 
gamut.  This  means  in  mathematical  language  that  equations  6 
must  be  satisfied  simultaneously,  regardless  of  the  form  of  the  func- 
tion E.  This  will  be  true  if  at  every  wavelength 

krXrSr    +   kaX0Sa    +  kbXbSb    =    X,  (7a) 

krYrSr    +   kgY0Sg    +   kbYbSb    =    J,  (7b) 

krZTSr  +  kgZ6S0  +  kbZbSb  =  I.  (7c) 

Since  only  relative  values  of  Sr,  Sg,  and  Sb  are  required  in  practice, 
equations  7  can  be  written  more  simply  in  terms  of  the  trichromatic 
coefiicients  of  the  reproduction  primaries  rather  than  in  terms  of 
their  tristimulus  values.  When  this  is  done,  the  fundamental  condi- 
tions for  exact  color  reproduction  by  a  three-color  process  become 

xrSr  +  xgSg  +  xbSb  =  x,  (8a) 

yrSr  +  y0Sg  +  ybSb  =  y,  (8b) 

ZrSr  +  ZgSg   +  ZbSb   =    Z.  (8C) 

To  avoid  misunderstanding,  it  may  be  added  that  these  conditions 
are  perfectly  general  in  the  sense  that  the  colors  of  the  subject  may  be 
either  real  or  imaginary.  Likewise,  the  reproduction  primaries  may 
be  either  real  or  imaginary.  In  a  practical  process,  the  reproduction 
primaries  are  real,  and  negative  amounts  of  the  primaries  can  not  be 
employed.  This  limits  the  realizable  color  gamut,  but  it  in  no  way 
alters  the  fundamental  requirements  which  must  be  fulfilled  by  any 
three-color  process,  real  or  imaginary. 

The  application  of  equations  8  to  additive  processes  is  immediately 
evident.  In  such  processes,  the  trichromatic  coefficients  of  the  pri- 
maries are  easily  ascertained  by  the  application  of  procedures  that 
are  well  standardized  in  the  field  of  colorimetry.  Likewise,  the  tri- 
stimulus values  of  unit  amounts  of  the  spectrum  colors  are  well  known 
for  a  normal  observer.2  Equations  8  can  thus  be  solved  for  the  values 
Sr>  Sg,  and  Sb  at  each  wavelength.  Then,  knowing  the  spectral  sen- 
sitivities of  the  emulsions  to  be  employed,  the  characteristics  of  the 
required  color  filters  can  be  computed. 

The  application  of  these  equations  to  subtractive  processes  is  not 
so  obvious,  largely  because  of  the  uncertainty  concerning  the  values 
that  should  be  used  for  the  trichromatic  coefficients  of  the  primaries. 


Oct.,  1938]        THEORY  OF  THREE-COLOR  PHOTOGRAPHY  335 

In  an  ideal  subtractive  process,  each  dye  absorbs  light  uniformly  in  a 
spectral  region  that  is  not  absorbed  by  the  other  two.  Thus,  each 
reproduction  primary  is  determined  by  the  color  of  the  light  absorbed 
by  one  of  the  three  dyes.  In  this  ideal  case,  it  is  a  simple  matter  to 
determine  the  trichromatic  coefficients  of  the  primaries.  By  sub- 
stituting their  values  in  equations  8,  the  required  spectral  sensitivities 
of  the  color-separation  negatives  can  readily  be  determined. 

With  the  dyes  that  are  available  for  use  in  subtractive  processes,  it 
is  impossible  to  assume  that,  at  every  wavelength,  the  absorption  of 
light  is  produced  by  the  action  of  one  dye  alone.  Instead,  the  pri- 
maries of  subtractive  processes  must  be  determined  under  conditions 
that  take  account  of  the  actual  behavior  of  the  dyes.  A  method  by 
which  this  can  be  accomplished  will  be  clear  from  the  spectrophoto- 
metric  curves  shown  in  Fig.  1.  It  will  be  noted  that  curve  F  is  the 
same  in  all  three  illustrations.  This  curve  represents  the  spectral 
transmittance  curve  of  a  piece  of  color-film  whose  color  is  such  that 
it  would  produce  a  light  flesh  tint  when  projected  upon  the  screen. 
A  flesh  tint  was  chosen  as  the  color  of  reference  partly  because  of  its 
importance  in  color  photography  and  partly  because  it  is  not  far 
removed  from  the  center  of  the  realizable  color  solid. 

Now  let  another  piece  of  film  be  prepared  under  identical  conditions 
except  that  the  concentration  of  the  red-absorbing  (blue-green)  dye 
is  slightly  reduced.  The  spectral  transmittance  curve  of  this  film  is 
represented  by  curve  R.  It  will  be  seen  that  reducing  the  concentra- 
tion of  the  red-absorbing  dye  has  brought  about  an  increase  in  the 
amount  of  red  light  transmitted  by  the  film,  as  would  be  expected. 
More  exactly,  curve  R',  which  is  obtained  by  subtracting  the  ordi- 
nates  of  curve  F  from  those  of  curve  R,  indicates  the  spectral  dis- 
tribution of  the  light  controlled  by  the  red-absorbing  dye,  assuming 
the  projection  source  to  emit  equal  amounts  of  energy  throughout 
the  spectrum.  The  trichromatic  coefficients  computed  from  this 
curve,  after  modification  by  the  energy  distribution  of  the  source,  are 
the  required  values  of  xr,  yr,  and  zr.  By  repeating  the  experiment  of 
varying  the  concentration  of  one  dye  at  a  time,  it  is  possible  to  find 
the  trichromatic  coefficients  corresponding  to  curves  G'  and  B' '. 
This  procedure  evidently  determines  the  trichromatic  coefficients  of 
the  primaries,  which  are  needed  for  substitution  in  equations  8. 

When  such  a  test  is  performed  with  the  dyes  that  are  now  available, 
the  trichromatic  coefficients  of  the  primaries  are  found  to  depend  to 
some  extent  upon  the  color  selected  as  the  color  of  reference.  Since 


336 


A.  C.  HARDY 


[J.  S.  M.  P.  E. 


•£.100 


iso 

I- 


soo 

WAVE-LENGTH 


700 


clOO 


50 


SOO 
WAVE-LENGTH 


700 


FIG.  1.  These  spectrophotometric  curves  illus- 
trate a  method  by  which  the  reproduction  pri- 
maries in  a  subtractive  process  can  be  identified. 


Oct.,  1938]        THEORY  OF  THREE-COLOR  PHOTOGRAPHY 


337 


1.0 


1.0 


»-    0 


400 


500  600  700 

WAVE-LENGTH 


\ 


400 


SOO  600 

WAVE-LENGTH 


V 


700 


400  500  600  TOO 

WAVE-LENGTH 


FIG.  2.  These  curves  indicate  the  relative 
spectral  sensitivity  of  the  three  emulsions  to 
be  used  in  making  three-color  separation  nega- 
tives that  will  control  properly  the  reproduction 
primaries  identified  in  Fig.  1. 


338  A.  C.  HARDY  [j.  s.  M.  P.  E. 

a  change  in  the  trichromatic  coefficients  of  the  primaries  should 
theoretically  be  compensated  by  a  modification  in  the  characteristics 
of  the  taking  filters,  the  most  useful  expedient  in  practice  is  to  deter- 
mine the  trichromatic  coefficients  of  the  primaries  for  a  color  of  ref- 
erence near  the  center  of  the  realizable  color  solid.  The  various  con- 
stants of  the  system  may  then  be  chosen  in  such  a  manner  as  ar- 
bitrarily to  make  the  rendition  correct  for  certain  colors  which  should 
preferably  lie  near  the  outside  of  the  realizable  color  solid.  In  this 
way,  the  errors  in  the  color  rendition  are  reduced  everywhere  to  ap- 
proximately their  minimum  values. 

If  one  assumes  a  projection  source  having,  for  example,  an  energy 
distribution  corresponding  to  that  of  the  I.C.I.  Illuminant  C,  the  tri- 
chromatic coefficients  calculated  from  curves  Rf,  G',  and  B'  of  Fig.  1 
are  as  shown  in  Table  I. 

TABLE  I 
Red  Primary  Green  Primary  Blue  Primary 

xr  =  0.4969  xg  =  0.1985  *6=  0.1847 

yr  =  0.3346  ^  =  0.4423  yb  =  0.1265 

zr  =  0.1685  zg  =  0.3592  zb  =  0.6889 

When  these  values  are  substituted  in  equations  8,  the  values  of  Sr, 
Sg,  and  Sb  are  found  to  be  as  shown  in  Fig.  2.  It  will  be  recalled  that 
the  ordinates  of  these  curves  represent  the  effective  spectral  sensi- 
tivity (on  a  relative  scale)  of  the  three  photographic  emulsions  that 
will  result  in  the  color-separation  negatives  that  will  properly  con- 
trol the  reproduction  primaries  identified  by  the  method  illustrated 
in  Fig.  1.  It  will  be  noted  that  the  required  spectral  sensitivity  is  less 
than  zero  at  certain  wavelengths,  an  effect  that  can  not  be  achieved 
directly  by  means  of  color  filters.  In  another  publication,3  numerous 
suggestions  for  the  practical  realization  of  the  required  negative 
values  of  the  spectral  sensitivity  have  been  made.  One  method 
comprises  making  two  negatives,  the  spectral  sensitivity  of  each 
being  such  that,  when  the  exposure  of  one  is  photographically 
subtracted  from  the  exposure  impressed  upon  the  other,  the  result 
will  simulate  one  of  the  curves  in  Fig.  2.  Hence,  by  making  a  total 
of  six  negatives,  the  three  primaries  can  be  controlled  properly. 

Although  the  above  expedient  is  useful  as  an  illustration  of  the 
application  of  the  rigorous  theory,  a  camera  designed  to  expose  six 
negatives  simultaneously  would  be  quite  impracticable.  Three  nega- 
tives may  be  made  to  suffice,  however,  by  abandoning  the  assumption 


Oct.,  1938]        THEORY  OF  THREE-COLOR  PHOTOGRAPHY  339 

incorporated  in  equations  5.  Instead,  let  it  be  assumed  that  the 
amount  of  the  red  primary  is  to  be  made  dependent  to  some  extent 
upon  the  exposure  received  by  all  three  color-separation  negatives. 
If  a  similar  assumption  is  made  with  respect  to  the  green  and  blue 
primaries,  equations  9  are  an  expression  of  the  proposed  technic. 

r  =  k&r  +  k&0  +  k^b,  (9a) 

g    =    k*2r   +   k£g    +  k62bt  (9b) 

b    =    k&r   +  ksZg   +  k^b.  (9C) 

The  practical  realization  of  the  technic  indicated  by  these  equations 
involves  controlling  the  red  primary,  for  example,  by  means  of  a 
photographic  image  of  the  subject  that  is  a  composite  record  of  the 
exposure  of  the  red  negative,  the  exposure  of  the  green  negative,  and 
the  exposure  of  the  blue  negative.  The  extent  to  which  each  exposure 
is  weighted  by  this  record  is  determined  by  tr;e  magnitude  of  the  con- 
stants kit  kz,  and  &3.  When  one  of  the  constants  is  less  than  zero,  a 
positive  image  rather  than  a  negative  image  is  to  be  employed  in 
making  the  composite  record.  Care  must  also  be  taken  that  the 
characteristics  of  the  photographic  materials  are  substantially  linear, 
as  in  the  toe  method  of  sound  recording,  in  order  that  a  true  addition 
or  subtraction  of  exposures  may  be  effected. 

With  this  understanding  of  the  proposed  technic,  let  equations  9 
be  substituted  in  the  previous  development  instead  of  equations  5. 
The  conditions  for  correct  color  rendering  are  then  found  to  take  the 

form 

KiSi  +  -K2S2  +  K3S3  =  x,  (lOa) 

KiSt  +  K5S2  +  KeS3  =  y,  (lOb) 

KjSi  +  K8S2  +  KgS3  =  z,  (lOc) 

where  the  constants  in  the  above  equations  (indicated  by  capital 
letters)  have  the  following  values  : 

Ki  =  ktXr  +  k.Xg  +  k7Xb, 


Z    =    ksXr   -f-  k^Xg   +  kgXb, 

*  =  k,Yr  +  k,Yg  + 
,  =  k2Yr  +  k,Y0  + 

*  =  k,Yr  +  k*Yg  + 

-,  =  kiZr  +  k*Zg  +  k7Zb, 


=  k2Zr  +  k^g  + 

k9Zb. 


340  A.  C.  HARDY  [j.  s.  M.  P.  E 

Equations  10  are  of  the  same  form  as  equations  7,  and  can  be  used  in 
the  same  manner.  In  this  case,  the  spectral  sensitivities,  ST,  Sg,  and 
Sb,  may  be  everywhere  positive  and  are  therefore  readily  realizable  in 
practice.  Those  familiar  with  the  concepts  of  colorimetry  will  rec- 
ognize that  this  technic  involves,  in  effect,  the  preparation  of  a  set  of 
three  negatives  which  would  properly  control  a  set  of  imaginary  re- 
production primaries.  By  making  the  additive  and  subtractive  com- 
binations indicated  by  equations  9,  a  new  set  of  negatives  can  be  pre- 
pared that  will  properly  control  the  reproduction  primaries  employed 
in  any  process,  additive  or  subtractive.  In  the  application  of  this 
technic  to  subtractive  processes,  the  number  of  constants  is  so  great 
that  the  reproduction  may  arbitrarily  be  made  correct  at  several 
points  within  the  boundaries  of  the  realizable  color  solid. 

It  may  be  added  by  way  of  conclusion  that  the  requirements  of  the 
theory  herein  set  forth  are  inescapable.  They  are  the  direct  con- 
sequence of  the  characteristics  of  the  visual  processes  of  the  human 
observer.  No  three-color  process  can  ever  duplicate  the  energy  dis- 
tribution of  each  point  of  the  subject,  but  it  can  be  made  to  duplicate 
the  visual  effect,  provided  the  necessary  conditions  are  satisfied. 
That  the  conventional  color  separation-negatives  do  not  properly 
control  the  reproduction  primaries  has  been  given  tacit  recognition 
by  the  empirical  attempts  at  "correction,"  such  as  masking.  Al- 
though such  methods  of  correction  are  incapable  of  satisfying  the 
conditions  for  perfect  color  reproduction,  the  improvement  resulting 
from  their  use  seems  to  indicate  the  desirability  of  employing  the  type 
of  correction  that  a  rigorous  analysis  of  the  problem  prescribes. 

REFERENCES 

1  MACADAM,   D.  L.:    "The  Fundamentals  of  Color  Measurement,"  /.  Soc. 
Mot.  Pict.  Eng.,  XXXI  (Oct.,  1938),  No.  4,  p.  343. 

2  JUDD,  D.  B.:    "The  1931  (CIE)  Standard  Observer  and  Coordinate  System 
for  Colorimetry,"  J.  Opt.  Soc.  Amer.,  XXHI  (Oct.,    1933),  No.  10,  p.  359. 

"Handbook  of  Colorimetry,"  The  Technology  Press,  Cambridge,  Mass.  (1936). 

3  HARDY,  A.  C.:    "The  Theory  of  Three-Color  Reproduction,"  /.  Opt.  Soc. 
Amer.,  XXVH  (July,  1937),  No.  7,  p.  227. 

DISCUSSION 

MR.  KELLOGG:  Does  your  statement  that  we  should  be  able  to  get  accurate 
reproduction  with  the  existing  primaries  presuppose  that  you  do  not  in  any  case 
have  to  deal  with  colors  above  a  certain  purity? 

MR.  HARDY:  This  mathematical  treatment  takes  no  account  of  whether  the 
color  is  realizable  in  practice  or  not.  If  the  color  is  one  falling  outside  the  gamut 


Oct.,  1938]        THEORY  OF  THREE-COLOR  PHOTOGRAPHY  341 

that  can  be  achieved  with  positive  amounts  of  the  three  primaries,  the  mathe- 
matics would  simply  indicate  the  fact  by  a  change  in  algebraic  signs.  In  practice, 
one  does  not  know  how  to  use  less  than  zero  grams  of  a  certain  dye  in  making  the 
color  reproduction.  Mathematically,  on  the  other  hand,  the  actual  number  of 
grams  required  to  reproduce  a  color  outside  the  existing  gamut  can  be  calculated 
as  easily  as  in  the  case  of  a  realizable  color. 

MR.  KELLOGG  :  You  said  quite  definitely  you  could  make  perfect  reproduction 
with  existing  primaries. 

MR.  HARDY:  One  can  theoretically  achieve  perfect  reproduction  within  the 
permissible  gamut.  Outside  the  permissible  gamut,  negative  amounts  of  the 
primaries  must  be  used. 

MR.  KELLOGG:   We  can  not  do  that. 

MR.  HARDY:  That  is  correct;  but  I  wish  to  emphasize  that  that  assumption  of 
readability  does  not  enter  into  the  derivation  of  the  equations. 

MR.  MAURER:  Mr.  Hardy  has  shown  that  the  characteristics  of  the  filters  to 
be  used  on  the  three-color  camera,  in  order  to  obtain  perfect  color  reproduction 
with  the  assumed  set  of  subtractive  primaries,  are  characteristics  that  are  not 
realizable  in  practice,  for  the  reason  that  negative  transmission  values  are  required 
at  certain  wavelengths.  Have  any  studies  been  made  indicating  whether  or  not 
it  would  be  possible  to  choose  other  sets  of  subtractive  primaries,  perhaps  having 
smaller  regions  of  overlap,  that  would  permit  the  use  of  taking  filters  not  having 
these  regions  of  negative  transmission? 

MR.  HARDY:  These  linear  transformation  equations  show  that  one  element 
in  the  reproduction  cycle  must  be  imaginary.  You  might  make  the  observer 
imaginary,  but  I  do  not  think  that  would  be  good  for  the  box-office.  If  you  want 
to  design  the  system  for  a  human  observer  as  he  exists  today,  then  either  the  repro- 
duction primaries  must  be  imaginary  or  the  filters  must  be  imaginary.  I  think 
the  practical  solution  is  to  use  real  primaries  and  to  employ  procedures  that 
simulate  the  effect  of  imaginary  filters. 

MR.  MAURER:  My  point  was  merely  that  today  rapid  progress  is  being  made 
in  the  production  of  new  synthetic  dyes,  and  possibly  if  a  theoretical  reproduction 
dye  were  indicated,  synthetic  work  would  eventually  produce  that  dye. 

MR.  HARDY:  I  think  not.  The  requirements  would  be  that  the  dyes  used  in 
making  the  reproduction  transmit  less  than  no  light  at  certain  wavelengths. 

MR.  KELLOGG:  The  tricolor  stimulus  values  as  given  in  the  "Handbook  of 
Colorimetry"  and  elsewhere  are  based  upon  three  specified  monochromatic 
primaries.  I  understand  that  you  can  choose  and  define  the  primaries  in  various 
ways,  but  a  certain  three  are  generally  taken  as  the  reference  standard.  As  I 
recall,  there  is  only  one  curve  that  dips  much  below  zero,  and  that  is  the  red. 
You  showed  here  a  set  of  equivalent  curves  for  the  primaries  you  were  last  dis- 
cussing, in  which  each  of  the  curves  show  a  big  dip,  down  almost  to  40  per  cent 
negative.  Do  those  represent  the  theoretically  required  amounts  of  the  various 
colored  lights  in  view  of  the  fact  that  they  were  not  monochromatic  but  each  had  a 
rather  wide  spread? 

MR.  HARDY:  The  primaries  in  the  colorimeter  system  that  Mr.  MacAdam  and 
I  both  have  employed  here  are  not  monochromatic.  I  would  rather  not  go  into 
the  exact  nature  of  the  primaries  in  the  system,  for  the  reason  that  the  primaries 
of  the  system  of  colorimetry  are  not  involved  in  the  results  I  reported.  Color- 


342  A.  C.  HARDY 

imetry  enters  into  this  discussion  merely  as  a  means  for  expressing  the  fact  that  the 
color  of  the  reproduction  is  to  be  like  that  of  the  original.  The  primaries  used 
in  the  colorimetric  system  cancel  out,  provided  the  same  primaries  are  employed 
in  both  cases. 

MR.  KELLOGG:   But  were  not  those  curves  for  a  specific  set  of  primaries? 

MR.  HARDY:  The  filter  transmission  curves  were  for  the  specific  set  that  had 
been  exhibited  in  the  preceding  slides.  I  showed  how,  in  a  typical  subtractive 
process,  to  identify  the  primaries  which  were  energy  distributions  in  the  red, 
green,  and  blue;  and  then,  using  those  primaries,  showed  what  the  filter  curves 
must  be  if  those  primaries  are  to  be  properly  controlled  in  the  reproduction. 

MR.  GOLDEN:  We  all  know  that  the  lighting  in  the  theater  auditorium  has  an 
effect  upon  the  projected  screen  picture.  How  does  the  color  theory  apply  to 
this  effect? 

MR.  HARDY:  When  I  talk  about  color  reproduction  in  the  graphic  arts  and  am 
asked,  "What  happens  when  you  have  three  inks  and  they  happen  to  be  printed 
upon  paper  stock  of  different  colors?"  my  answer  is  that  you  make  the  print 
on  the  stock  you  are  going  to  use  before  you  figure  out  what  filters  should  be  em- 
ployed. 

Now,  of  course,  if  different  theaters  use  lighting  systems  that  are  sufficiently 
different,  then  it  will  be  difficult  to  obtain  release  prints  that  look  right  in  all 
theaters.  It  is  possible  to  select  one  theater,  make  the  tests  under  the  conditions 
obtaining  in  that  theater,  and  design  the  cycle  so  that  it  will  be  exactly  correct. 
For  other  theaters  modifications  should  theoretically  be  made  at  some  point  in  the 
technic. 

MR.  GOLDEN:  Don't  you  think  we  should  go  a  step  farther,  and  standardize 
the  lighting  of  the  theaters  of  the  country? 

MR.  HARDY:  Yes.  As  the  art  advances,  more  and  more  attention  should 
properly  be  paid  to  such  questions. 


THE  FUNDAMENTALS  OF  COLOR  MEASUREMENT' 
D.  L.  MACADAM** 


Summary. — The  modern  science  of  color  measurement  had  its  origin  in  the 
searches  of  Helmholtz,  Maxwell,  and  Grassmann  in  the  years  from  1852  to  1855. 
This  science  found  no  important  practical  application  until  the  opening  of  the 
twentieth  century  when  the  (F.  £.)  Ives  colorimeter  was  applied  to  the  measurement 
and  specification  of  the  colors  of  practical  illuminants.  In  1922  the  Optical  Society 
of  America,  through  its  Committee  on  Colorimetry,  recommended  data  and  technics 
for  color  measurement  which  were  immediately  adopted  throughout  the  world,  re- 
placing numerous  unrelated,  and  often  inconsistent,  technics  that  had  been  developed 
to  meet  the  insistent  demands  of  various  industries  for  color  specifications.  A  set  of 
data  based  upon  the  most  recent  researches  was  recommended  by  the  International 
Commission  on  Illumination  in  1931,  and  these  more  satisfactory  data  have  in  turn 
replaced  the  data  and  extended  the  unification  of  methods  which  orginated  with  the 
O.S.A .  Report  of  1922. 

Standard  I.C.I,  color  specifications  can  be  computed  from  spectrophotometric  data. 
The  fundamental  relations  that  are  used  to  define  the  quantities  in  terms  of  which 
colors  are  specified  are  most  concisely  expressed  in  mathematical  formulas ,  which  will 
be  simply  explained.  As  a  matter  of  fact,  short  cuts  based  upon  the  standard  I.C.I. 
1931  data  have  been  developed  in  the  past  few  years  so  that  no  acquaintance  with  any 
mathematics  other  than  ordinary  arithmetic  is  now  necessary  for  the  performance  of 
any  of  the  essential  operations  encountered  in  standard  color  measurement.  A  typical 
example  will  be  exhibited,  and  the  interpretation  of  the  results  in  terms  of  the  dominant 
wavelength,  purity,  and  brightness  will  be  made  clear  by  use  of  the  chromaticity  dia- 
gram. The  conditions  required  in  order  that  the  colors  of  two  samples  shall  match 
under  some  definite  illuminant  are  that  the  three  quantities  in  terms  of  which  the 
colors  are  specified  must  be  the  same  for  the  two  samples. 

The  purpose  of  this  paper  is  to  describe  a  practical  method  for 
measuring  colors.  Consequently,  the  basic  visual  experiments  that 
justify  the  use  of  the  method  will  be  mentioned  only  briefly.  Such 
experiments  are  based  upon  the  familiar  fact  that  almost  all  the  colors 
encountered  in  nature  and  in  industry  can  be  matched  by  mixtures 
of  any  reasonable  set  of  three  primary  colors  of  suitable  intensities. 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;    received 
April  14,  1938.    Communication  No.  669  from  the  Kodak  Research  Laboratories. 
**  Eastman  Kodak  Co.,  Rochester,  N.  Y. 

343 


344 


D.  L.  MACADAM 


[J.  S.  M.  P.  E. 


In  1930  the  International  Commission  on  Illumination  adopted  the 
results  of  accurate  and  extensive  experiments  of  this  kind  and  recom- 
mended a  method,  based  upon  normal  human  vision,  by  which  the 
intensities  of  three  mathematically  convenient  primary  colors  can 
be  computed  from  the  distribution  of  energy  in  the  spectrum  of  the 
color  to  be  measured.  The  standard  primary  colors  can  not  be  secured 


FIG.  1.     Diagrammatic  representation  of  a  method 
for  computing  the  tristimulus  values  X,  Y,  Z. 

in  any  instrument,  but,  nevertheless,  the  computed  intensities  are  very 
convenient  specifications  of  color.  For  instance,  if  the  intensities 
of  the  standard  primaries  computed  from  the  energy  distribution  of 
two  sample  colors  are  the  same  for  the  two  colors,  then  these  colors 
will  appear  identical. 

Fig.  1  illustrates  the  principle  of  the  method  of  computation  recom- 
mended by  the  International  Commission.  The  curve  in  the  upper 
left  corner  of  the  diagram  represents  the  reflectance  of  a  green  object 
for  every  wavelength  of  the  visible  spectrum,  from  violet  at  the  left 


Oct.,  1938]        FUNDAMENTALS  OF  COLOR  MEASUREMENT  345 

to  red  at  the  right.  Such  a  curve  must  be  determined  for  every  sample 
whose  color  is  to  be  measured.  The  optical  instrument  used  for  the 
determination  of  this  curve  is  called  a  spectrophotometer.  There 
are  many  varieties  of  spectrophotometers,  some  of  which  employ 
human  observers,  while  others  use  photoelectric  cells. 

The  color  of  the  sample  depends  upon  the  reflectance  curve  and 
also  upon  the  distribution  of  energy  throughout  the  spectrum  of  the 
light-source  that  illuminates  the  sample.  The  curve  in  the  upper 
right  corner  of  Fig.  1  represents  the  distribution  of  energy  in  the 
spectrum  of  a  standard  source  of  artificial  daylight.  Such  a  distribu- 
tion curve  must  be  known  for  each  illuminant  with  reference  to  which 
colors  are  to  be  measured.  The  International  Commission  on  Illumi- 
nation has  published  such  data  for  three  light-sources  which  are  de- 
fined as  standards  for  color  measurement.  Data  for  other  light- 
sources  have  been  published  in  many  other  places.  When  satisfac- 
tory data  on  the  distribution  of  energy  in  the  spectrum  of  a  desired 
light-source  are  not  available,  the  data  must  be  obtained  by  use  of  the 
methods  of  spectroradiometry.  These  data  *can  not  be  determined 
with  accuracy  outside  of  a  few  elaborately  equipped  laboratories  where 
a  specialty  is  made  of  such  measurements. 

The  energy  reflected  by  the  sample  at  a  given  wavelength  is  the 
product  of  the  values  at  that  wavelength  indicated  by  the  upper  two 
curves  (Fig.  1),  and  is  shown  in  the  curve  just  below.  The  three  color- 
mixture  functions  adopted  by  the  International  Commission  on  Il- 
lumination are  represented  by  the  curves  labelled  x,  y,  z.  Light  of 
each  wavelength  reflected  from  the  sample  contributes  to  each  pri- 
mary of  the  color  specification  an  intensity  proportional  to  the  product 
of  the  energy  and  the  corresponding  color-mixture  function.  The 
three  curves  resulting  from  these  multiplications  throughout  the 
visible  spectrum  are  shown  in  the  lowest  set  of  diagrams  (Fig.  1). 
The  areas  under  the  curves  are  the  totals  of  the  contributions  at  every 
wavelength  throughout  the  spectrum  to  the  intensities  X,  Y,  Z,  of 
the  standard  primaries  necessary  to  match  the  sample  color.  These 
intensities  are  called  the  tristimulus  values  of  the  color. 

Mathematically  this  procedure  is  represented  by  the  integrals 

X  =  fR-E-~X'd\,         Y  =  fR-E'~yd/\         Z  =  fR-E~z-d\ 

These  integrals  mean  nothing  more  nor  less  than  the  arithmetical  pro- 
cedures represented  in  Fig.  1. 


50 


30 


2.0- 


8,0 


(a) 


\ 


500  600  700 

WAVELENGTH  (MILLIMICRONS) 


50 


(b) 


400 


BOO  feOO 

WAVELENGTH  (MILLIMICRONS) 


100 


50 


4OO 


500  fcOO 

WAVELENGTH  (MILLIMICRONS) 


FIG.  2.  Example  of  the  selected-ordinate  method 
of  computing  tristimulus  values:  (Upper)  X,  (Center)  Y, 
(Lower)  Z. 


FUNDAMENTALS  OF  COLOR  MEASUREMENT 


347 


0.2. 


Another  and  more  rapid  method  of  computing  the  tristimulus 
values  has  been  devised.  This  is  known  as  the  selected-ordinate 
method  and  consists  in  averaging  the  values  that  the  reflectance 
curve  of  each  sample  attains  at  certain  wavelengths,  which  have  been 
published.  The  thirty  vertical  lines  in  Fig.  2 (a)  are  drawn  at  the 
wavelengths  at  which  the  reflectances  should  be  read  from  the  curve 
of  the  sample,  and  averaged  in  order  to  compute  the  tristimulus 
value  X.  The  values  of  the  reflectance  at  the  wavelengths  indicated 
by  the  vertical  lines  in  Fig.  2(6)  should  be  averaged  in  order  to  com- 
pute the  tristimulus  value  Y.  Finally,  the  values  read  from  the 
curve  of  the  sample  of  the  wave* 
lengths  shown  in  Fig  2(c)  should 
be  averaged  to  compute  the  tri- 
stimulus value  Z.  Transparent 
templates,  on  which  lines  are 
ruled  corresponding  to  the  verti- 
cal lines  in  Figs.  2 (a),  (b),  and  (c) 
can  be  prepared,  to  be  placed 
temporarily  over  any  spectro- 
photometric  curve  drawn  to  a 
standard  wavelength  scale,  as 
aids  in  computation.  The  three 
sets  of  wavelengths  have  been 
derived  from  the  color-mixture 
functions,  adopted  by  the  Inter- 
national Commission  and  shown 
in  Fig.  1,  and  from  the  energy 
distribution  of  the  light-source.  These  wavelengths  are  tabulated 
in  the  Handbook  of  Colorimetry,1  which  describes  in  detail  the 
entire  procedure  of  color  measurement. 

If  the  tristimulus  values  of  one  color  are  some  fraction  of  the 
tristimulus  values  of  a  second  color,  then  these  colors  will  look  alike, 
except  that  the  first  will  be  less  bright.  The  brightnesses  of  all  colors 
are  measured  by  the  second  tristimulus  value,  Y,  alone.  The  ratios, 

x  -  X/(X  +  Y+Z),       y  =  Y/(X+Y+Z),       %  -  Z/(X+F+Z) 

are  called  trichromatic  coefficients,  and  are  the  same  for  all  colors  that 
differ  only  in  brightness.  Such  colors  are  said  to  have  the  same 
ckromaticity,  and  the  chromaticity  can  be  represented  by  a  point  in 
the  chromaticity  diagram  shown  in  Fig.  3.  The  value  of  z  can  always 


o.o 


o.o 


0.6          0.0 


D.e         OA 

k 

FIG.  3.  Chromaticity  diagram. 
Illuminant  C  (artificial  daylight)  has 
been  used  for  the  specifications  of  the 
white  and  green  samples. 


348  D.  L.  MACADAM  [j.  s.  M.  P.  E. 

be  computed  from  the  indicated  values  of  x  and  y,  since  x  +  y  +  z  = 
1  for  all  colors.  The  chromaticities  at  the  various  wavelengths  of 
the  spectrum  are  represented  by  the  points  on  the  curve.  The  chro- 
maticity  of  daylight  is  represented  by  the  point  near  the  center.  The 
green  sample  used  for  illustration  in  Figs.  1  and  2  is  represented  by 
the  point  above  the  white  point.  The  brightness,  19  per  cent,  of 
this  sample  relative  to  the  brightness  of  a  perfect  white  in  the  same 
illumination  is  written  beside  the  point  representing  the  chromaticity. 
The  dominant  wavelength,  526  imz,  analogous  to  the  artist's  hue,  is 
the  wavelength  at  which  the  straight  line  drawn  through  the  white 
point  and  the  sample  point  cuts  the  spectrum  curve.  The  purity, 
22  per  cent,  analogous  to  the  artist's  saturation,  measures  the  dis- 
tance from  the  white  point  to  the  sample  point  as  a  fraction  of  the 
distance  from  the  white  point  to  the  dominant  spectrum  color. 

Samples  that  should  match  in  color  should  have  the  same  tristim- 
ulus  values.  This  condition  can  be  satisfied  without  requiring  that 
the  energy  distributions  of  the  light  reflected  from  the  samples  are 
identical.  Samples  that  match  in  color  will  be  represented  at  the 
same  point  in  the  chromaticity  diagram  and  will  have  the  same 
dominant  wavelength  and  purity.  Errors  in  color  matching  can  be 
represented  as  distances  in  the  chromaticity  diagram,  and  can  be 
analyzed  into  errors  of  dominant  wavelength  and  of  purity. 


After  the  presentation  of  the  paper,  a  450-ft.  16-mm.  Kodachrome  motion  picture 
was  shown  entitled  "Color  Measurement  and  Its  Application  to  Color  Photography." 
This  film  demonstrated  the  details  and  use  of  the  method  of  color  measurement  de- 
scribed in  the  paper.  A  glimpse  of  the  final  steps  in  the  preparation  of  a  three-color 
subtr active  print  served  as  an  introduction.  A  modified  General  Electric  recording 
spectrophotometer  was  shown  in  operation,  recording  the  spectrophotometric  character- 
istics of  the  colors  of  a  chart  and  of  a  subtractive  reproduction  of  the  chart.  Close-up 
scenes  emphasized  important  details  of  the  double-prism  monochromator,  of  the  photom- 
eter mechanism,  and  of  the  modified  integrating  sphere  and  sample  holders.  The 
computation  of  tristimulus  values,  using  the  selected-ordinate  method,  was  demon- 
strated  in  detail.  In  this  demonstration,  the  speed  and  simplicity  of  the  computations 
and  of  the  recommended  computing  equipment  were  made  evident.  The  interpretation 
of  the  colorimetric  specifications  was  demonstrated,  making  use  of  the  chromaticity 
diagrams  published  in  the  "Handbook  of  Colorimetry."1  All  the  colors  of  the  original 
color-chart  and  of  the  photographic  reproduction  were  represented  as  points  on  a 
chromaticity  diagram.  The  separations  between  points  representing  corresponding 
colors  of  the  original  and  the  reproduction  were  pointed  out  and  compared  with  the 
visually  apparent  errors  of  the  reproduction.  This  comparison  led  to  the  conclusion 
that  the  representation  of  the  colors  on  the  chromaticity  diagram  furnishes  an  adequate 
and  unambiguous  representation  of  all  the  visually  important  color  errors. 


Oct.,  1938]        FUNDAMENTALS  OF  COLOR  MEASUREMENT  349 

REFERENCE 

1  Handbook  of  Colorimetry,"  The  Technology  Press,  Cambridge,  Mass.  (1936). 

DISCUSSION 

MR.  RICHARDSON:  Do  those  errors  represent  the  differences  between  the 
colors? 

MR.  MACADAM:  The  errors  represented  were  the  differences  between  the 
colors  of  the  original  color-chart  and  the  corresponding  colors  of  the  reproduction. 
The  colors  used  in  the  chart  were  picked  as  representative  colors,  likely  to  occur 
in  any  scene.  The  other  ends  of  the  error  lines  were  simply  the  colors  we  found 
to  have  been  produced  by  the  color  reproduction  process.  Perfect  color  reproduc- 
tion would  result  in  zero  errors.  Every  color  in  the  final  color  picture  should  fall 
on  the  same  point  in  the  diagram  as  the  corresponding  color  of  the  original  color 
chart. 

MR.  BAKER:  In  determining  a  color  by  dominant  wavelength,  purity,  and 
brightness,  has  that  method  definitely  ruled  out  the  use  of  the  trichromatic 
colorimeter? 

MR.  MACADAM:  I  think  not.  We  use  dominant  wavelength,  purity,  and 
brightness  because  they  give  us  quantities  that  are  more  meaningful.  It  does 
not  avail  one  much  to  know  that  a  color  is  35  per  cent  f  reen  plus  10  per  cent  red 
plus  5  per  cent  blue ;  but  if  you  tell  him  that  a  color  has  a  dominant  wavelength 
of  526  millimicrons,  and  if  he  is  familiar  with  the  appearance  of  the  spectrum,  he 
knows  that  the  hue  is  a  very  definite  type  of  green.  If  you  tell  him  further  that 
the  color  has  a  purity  of  22  per  cent,  he  knows  that  it  is  a  relatively  unsaturated 
green,  as  compared  with  the  spectrum;  and  a  brightness  of  19  per  cent  indicates 
that  it  is  a  moderately  dark  green.  Consequently,  it  is  easy  to  interpret  dominant 
wavelength,  purity,  and  brightness.  That  does  not  mean  we  are  going  to  carry 
out  monochromatic  colorimetry.  We  are  going  to  use  a  spectrophotometer  of 
some  sort  and  compute  the  dominant  wavelength,  purity,  and  brightness  as 
outlined  in  the  paper.  If  we  use  any  type  of  colorimeter  we  must  use  an  observer 
who  is  in  our  employ,  and  we  must  not  use  very  many  observers;  consequently, 
the  values  we  get  in  visual  colorimetry  are  subject  to  some  uncertainty  as  to 
whether  the  observers  are  normal. 

MR.  KELLOGG:  How  do  you  specify  dominant  wavelength  when  the  hue  is 
purple? 

MR.  MACADAM:  The  dominant  wavelength  of  a  purple  is  nonexistent,  and 
we  specify  the  wavelength  of  the  complementary  color ;  for  instance,  the  magenta 
has  a  complementary  wavelength  of  about  520  millimicrons.  That  is  the  wave- 
length of  the  spectral  color  necessary  to  produce  a  neutral  color  in  a  color  mixture 
with  the  magenta.  If  we  extend  a  straight  line  from  the  point  representing  the 
magenta  color  through  the  white  point,  it  will  intersect  the  spectral  curve  at 
some  wavelength,  for  instance,  520  millimicrons.  That  is  the  complementary 
wavelength. 

MR.  RICHARDSON:  Suppose  a  colored  film  is  to  be  shown  to  an  audience; 
what  would  be  the  differences  in  reproduction  with  different  light-sources;  for 
example,  low-  and  high-intensity  arcs,  Suprex,  Mazda,  and  so  on? 

MR.  MACADAM:    Fortunately  there  would  not  be  any  large  difference.    The 


350  D.  L.  MACADAM 

color  of  the  screen  where  we  expect  a  white  image  seems  to  establish  a  standard 
by  which  we  judge  all  the  other  colors.  The  film  we  have  just  shown  was  pro- 
jected several  weeks  ago  with  a  high-intensity  carbon  arc  projector,  and  today 
with  a  high-efficiency  tungsten  lamp,  and  I  can  not  notice  any  difference  in  thei 
colors.  It  is  interesting  and  fortunate  that  the  relative  quality  of  the  colors  does! 
not  seem  to  depend  seriously  upon  the  quality  of  the  illuminant. 

MR.  HARDY:  Does  not  the  difference  in  the  reproduction  correspond  to  observ- 
ing a  magazine  illustration  under  daylight  and  under  tungsten  light?  The  differ- 1 
ence  in  the  quality  of  the  light-source  in  that  case  is  probably  greater  than  whatj 
Mr.  Richardson  had  in  mind. 

MR.  KELLOGG:  Since  the  sensitivity  of  the  eye  to  brightness  goes  up  so  radi- 
cally in  the  green  as  compared  with  the  red  and  blue,  why  does  not  white  light 
look  green  to  us? 

MR.  MACADAM  :  That  is  a  question  that  must  be  answered  by  a  rather  philo- 
sophic argument:  White  is  the  appearance  of  the  stimulus  to  which  we  are  most 
accustomed,  such  as  daylight.  All  other  colors  have  hues  with  respect  to  this 
most  familiar  (i.  e.,  "colorless")  stimulus. 

MR.  RICHARDSON:  Theaters  are  now  projecting  much  colored  film,  and  I 
certainly  feel  that  projectionists  and  exhibitors  should  be  informed  of  the  differ- 
ences in  color  reproduction  with  the  various  kinds  of  light-sources  in  use. 

MR.  MACADAM:  I  think  it  is  rather  generally  expected  that  there  will  be 
differences.  Whether  they  are  important  depends  upon  the  observer,  and  I 
think  we  had  better  let  the  color-film  people  decide  what  light-source  is  best  for 
the  films  resulting  from  each  particular  process. 

MR.  KELLOGG  :  Can  we  at  least  say  that  the  complete  spectrum  must  be  pretty 
well  represented  to  get  satisfaction;  in  other  words,  that  there  must  not  be  any 
bad  "holes"  in  the  spectrum? 

MR.  MACADAM:  I  am  afraid  the  questions  are  getting  beyond  the  scope  of 
my  investigations. 

MR.  JONES  :  I  think  under  certain  conditions,  at  least,  one  can  see  the  difference 
between,  let  us  say,  high-intensity  arc  and  tungsten  projection  of  some  colors. 
The  adaptation  of  the  eye,  while  it  is  great,  is  not  under  all  conditions  sufficient 
to  compensate  for  this  difference  in  light-source  quality.  Commercial  organiza- 
tions working  on  the  development  of  color-films  are  studying  the  problem. 


SOUND  PICTURES  IN  AUDITORY  PERSPECTIVE* 
FRANKLIN  L.  HUNT** 

Summary. — Soon  after  sound  reproduction  in  auditory  perspective  was  demon- 
strated over  telephone  circuits  between  Philadelphia  and  Washington  in  1933,  ex- 
perimental sound  pictures  in  auditory  perspective  were  made  at  the  Bell  Telephone 
Laboratories'  sound  picture  laboratory.  Listening  tests  showed  that  they  distinctly 
enhanced  the  illusion  that  the  sound  originated  at  its  apparent  source  on  the  screen 
and  they  strikingly  improved  the  feeling  of  spaciousness  and  reality.  The  auditory 
perspective  effect  is  not  primarily  dependent  upon  perfect  synchronism  of  the  two 
sound-tracks  required,  nor  on  frequencies  above  the  present  commercial  range.  Exist- 
ing equipment  can  be  converted  to  project  sound  pictures  in  auditory  perspective  with" 
out  great  difficulty. 

An  auditor  at  the  theater  knows  by  his  sense  of  hearing  as  well  as 
by  sight  when  an  actor  moves  about  the  stage,  and  he  can  tell  in  what 
parts  of  an  orchestra  the  various  instruments  are  playing.  Each  of 
his  ears  hears  sound  from  a  slightly  different  direction,  and  he  has 
learned  by  experience  to  associate  the  intensity  and  quality  with  the 
direction  of  origin  of  the  sound.  In  a  sound  picture  theater,  on  the 
contrary,  the  sound  always  comes  from  one  fixed  source,  namely, 
the  loud  speakers  behind  the  screen.  This  makes  the  reproduction 
resemble  sound  heard  when  an  auditor  listens  directly  to  speech  or 
music  with  only  one  ear.  Under  these  conditions  the  perception  of 
direction  is  seriously  impaired. 

It  has  been  shown1  that  reproduced  sound  can  be  made  to  appear 
to  move  from  one  side  of  a  stage  to  the  other  by  connecting  two  or 
more  independent  sets  of  loud  speakers  by  separate  circuits  to  sepa- 
rate microphones.  That  this  method  gives  startling  effects  was  dem- 
onstrated in  1933  when  symphonic  music  was  transmitted  by  such 
means  over  telephone  lines  from  Philadelphia  and  reproduced  in 
Washington.  In  these  experiments  the  sound  was  picked  up  by 
three  microphones  placed  near  the  front  of  the  stage  at  Philadelphia. 
Each  microphone  was  connected  by  a  separate  telephone  circuit  to  a 


*  Received  June  4,  1938. 
**  Bell  Telephone  Laboratories,  New  York,  N.  Y. 


351 


352  F.  L.  HUNT  [j.  s.  M.  P.  EJ 

separate  set  of  loud  speakers  at  Washington.  With  this  arrangement! 
the  audience  was  able  to  locate  sounds  from  different  parts  of  the 
orchestra  and  there  was  a  feeling  of  spaciousness  which  gave  the 
reproduced  music  a  remarkable  sense  of  reality. 

This  perspective  effect  still  persists  if  two  microphones  are  used 
instead  of  three.  In  such  case  the  middle  microphone  is  omitted, 
and  the  remaining  two  are  placed  several  feet  apart  in  front  of  the 
orchestra.  The  output  of  each  microphone  is  then  amplified  sepa-| 
rately  and  applied  to  a  separate  set  of  loud  speakers  located  behind  a 
screen  at  positions  corresponding  to  those  occupied  by  the  micro- 
phones on  the  stage  where  the  sound  originated. 

The  application  of  this  multichannel  method  of  reproduction  to 
sound  pictures  requires  in  principle  only  the  introduction,  between 
the  microphones  and  loud  speakers,  of  recording  machines  to  store 
the  sound  and  reproducers  to  project  it.  Means  for  keeping  the 
cameras  and  sound  recorders  in  synchronism  obviously  have  to  be 
included.  These  facilities  were  available  in  the  Bell  Telephone  Labora- 
tories' sound  picture  laboratory  and  an  investigation  was  presently 
begun  into  the  possibilities  of  this  multichannel  method. 

To  study  some  of  the  effects  that  can  be  achieved,  a  series  of  ex- 
perimental sound  pictures  was  recorded  in  auditory  perspective. 
Several  scenes  were  made  in  a  sound  picture  set  built  of  reinforced 
plywood  flats  like  those  commonly  used  in  commercial  sound  studios. 
In  accord  with  the  usual  practice  the  set  had  three  walls.  It  was  open 
in  front  and  above  to  provide  easy  access  for  the  cameras  and  to  per- 
mit lighting  the  scene.  Two  electrodynamic  microphones  were  used 
to  record  the  sound.  They  were  located  about  ten  feet  apart  at  the 
front  of  the  set  in  positions  that  were  found  by  listening  tests  to  cover 
the  set  most  uniformly  These  listening  tests  were  carried  out,  and 
the  sound  was  monitored  during  recording,  by  diverting  part  of  the 
output  of  each  microphone  to  a  separate  loud  speaker  located  in  the 
monitoring  room  associated  with  the  stage.  The  output  of  each  mic- 
rophone was  connected  by  a  separate  channel  to  a  standard  film-re- 
cording machine.  The  two  recording  machines  and  the  camera  that 
photographed  the  action  were  synchronized  by  a  standard  Western 
Electric  interlock  system.2  The  sound  records  and  the  picture  were 
originally  recorded  on  separate  films  but  afterward  the  picture  and 
one  sound-track  were  printed  on  one  film  in  accordance  with  standard 
practice.  The  second  sound-track  was  printed  on  another  film. 

The  sound  picture  scenes  recorded  were  selected  primarily  to  de- 


Oct.,  1938]  SOUND  PICTURES  IN  PERSPECTIVE  353 

termine  how  faithfully  the  sound  appeared  to  localize  itself  at  its 
apparent  source  on  the  screen,  and  included  the  following  scenes : 

(1)  A  person  walking  about  the  set  from  side  to  side,  front  to  back,  and  for- 
ward again,  speaking  as  he  walked. 

(2)  A  banjo  player  walking  about  the  stage  while  playing. 

(3)  A  banjo  and  saxophone,  played  alternately  on  opposite  sides  of  the  stage. 
(4}     A  piano  played  on  one  side  of  the  stage. 

To  reproduce  the  records  two  standard  sound  picture  projectors 
were  used,  coupled  by  a  flexible  shaft  to  keep  them  in  synchronism. 
The  combined  picture  and  sound-track  were  projected  by  one  ma- 
chine and  the  second  sound-track  by  the  other.  The  output  from 
each  sound-track  was  amplified  by  a  separate  amplifier  and  supplied 
to  a  separate  loud  speaker.  Western  Electric  cone  speakers  were 
used  for  most  of  the  tests  but  in  some  cases  high-frequency  units  were 
added.  It  was  found,  however,  that  the  latter  were  not  necessary  to 
produce  the  auditory  perspective  effect.  The  loud  speakers  were  lo- 
cated behind  the  screen  near  the  right-  and  left-hand  edges,  and  about 
half-way  up  from  the  bottom  of  the  screen.  Tests  were  also  made 
with  the  loud  speakers  just  outside  of  the  screen  and  again  about  five 
feet  away  at  each  side.  Neither  of  these  positions  gave  as  satis- 
factory an  illusion  as  when  the  speakers  were  behind  the  screen,  al- 
though the  difference  was  not  great  when  they  were  just  outside. 
In  some  of  the  experiments  low-pass  filters,  cutting  off  frequencies 
above  7000  cps.,  were  connected  in  the  loud  speaker  circuits  to 
determine  whether  the  auditory  perspective  effect  depended  upon 
the  presence  of  frequencies  above  the  7000-cps.  limit.  It  persists 
without  them. 

The  recordings  were  reproduced  before  several  groups  of  observers, 
who,  in  a  blind  test,  were  asked  to  distinguish  between  the  auditory 
perspective  records  and  one  or  more  of  the  following  conditions : 

(1)  The  output  of  one  of  the  two  auditory  perspective  sound-tracks  applied 
to  a  single  loud  speaker  in  the  usual  location. 

(2)  The  output  of  the  two  sound-tracks  combined  electrically  and  projected 
through  a  single  loud  speaker  located  behind  the  screen  at  the  center. 

(3}  The  output  of  one  sound-track  applied  simultaneously  to  the  two  loud 
speakers — one  at  each  side  of  the  screen. 

(4)  The  output  of  the  two  sound-tracks  combined  electrically  and  projected 
from  the  two  loud  speakers. 

The  tests  were  made  by  switching  back  and  forth  quickly  between 
the  conditions  mentioned  above  and  requiring  the  observers  to  de- 


354  F.  L.  HUNT  [j.  s.  M.  P.  E  i 

cide  which  condition  prevailed  at  the  moment.  In  most  of  the! 
tests  two  conditions  were  compared  at  a  time,  but  in  some  instances! 
there  were  three.  An  audible  signal  was  used  to  indicate  that  ap 
change  was  about  to  be  made  because  the  action  on  the  screen  con-| 
tinued  without  interruption.  To  assure  an  unbiased  decision,  how-i 
ever,  the  change  signal  was  sometimes  given  without  changing  thel 
sound  circuit. 

Comparisons  were  made  also  between  the  auditory  perspective! 
recording  of  the  first  scene  and  one  recorded  by  present  commercial} 
methods  with  a  single  microphone  located  at  the  center  of  the  stage. 
Quick  shifts  from  one  condition  to  the  other  could  not  be  arranged  for} 

TABLE   I 

Per 

Cent 
Observa- 

Circuit  Number  of        tions 

Test      Observers  Combinations  Observations    Correct  Kind  of  Record 

1  A  2T-2S  vs.  IT-IS  15  100     Piano 

2  A  2T-2S  vs.  1T-2S  16  8 1\  Speech- walking 

13  100  (  Banjo-walking 

4  100 1  Saxophone  and  banjo 

23  96/  Piano 

3  B  2T-2S  vs.  IT-IS  16  100     Piano 

4  B  2T-2S  vs.  1 T-2S  20  100}  Speech-walking 

8  50  (  Banjo-walking 

17  82  j  Saxophone  and  banjo 

14  93  /  Piano 

this  part  of  the  test  because  equipment  was  not  available  to  project 
two  pictures  and  three  sound- tracks  simultaneously;  nevertheless, 
the  auditory  perspective  recordings  were  preferred  by  all  who  heard 
the  comparison. 

Experimental  Results. — The  results  are  summarized  in  Tables  I  and 
II,  where  a  letter  is  used  to  designate  each  of  the  seven  observers. 
The  circuit  combinations  are  indicated  by  the  number  of  sound-tracks 
(T)  and  loud  speakers  (S)  used.  For  example,  2T-2S  is  the  auditory 
perspective  condition.  2T  comb. -2 S  means  two  sound-tracks  com- 
bined electrically  and  applied  to  two  loud  speakers.  The  first  table 
gives  the  per  cent  of  correct  observations  and  the  second  the  per  cent 
of  correct  choices  for  each  circuit  combination  as  they  were  played  in 
succession.  In  tests  1  to  4,  7  and  8,  the  observers  were  told  which 
combination  was  to  be  tested  and  were  asked  to  indicate  which  one 


Oct.,  1938] 


SOUND  PICTURES  IN  PERSPECTIVE 


355 


prevailed  each  time  after  the  signal  for  the  change  was  given.  In 
tests  5  and  6,  the  three  combinations  used  in  each  test  were  assigned 
numbers  and  then  played  successively  at  random.  At  each  change 
the  operator  announced  the  number  of  the  combination  being  switched 
in  at  that  time,  and  after  the  test:  each  observer  indicated  the  com- 
bination that  he  thought  corresponded  to  the  given  number. 

TABLE  II 


Per  Cent 
of 
Correct 
Observa- 
tions 
for 
Each 

Circuit 

Numbers 

Com- 

Circuit 

of 

bina- 

tnbinations 

Observations 

tion 

Ki 

2T-2S 

12 

100 

Paino 

1T-2S 

12 

75 

Piano 

IT-IS 

12 

75 

Piano 

2T-2S 

12 

75 

Speed 

1T-2S 

12 

50 

Banjo- 

IT-IS 

12 

75 

Saxopl 

2T-2S 

44 

73 

Piano 

2T  comb.-2S 

44 

62 

Piano 

2T  comb.-lS 

36 

69 

Piano 

2T-2S 

/78 

64 

Speech 

2T  comb.-2S 

92 

53 

Banjo- 

2T  comb.-lS 

77 

75 

Saxopl 

Kind  of  Record 


Test         Observers 

5  CDEF 


CDEF 


DEFG 


DEFG 


The  tables  show  that  the  ability  to  distinguish  between  the  audi- 
tory perspective  condition  (2T-2S)  and  either  single  loud-speaker 
reproduction  from  one  sound-track  (IT-IS)  or  single  sound-track  re- 
production from  two  loud  speakers  (1 T-2S)  is  of  high  order.  When 
three  conditions  are  imposed,  as  in  the  last  four  series,  the  number 
of  errors  is  larger  but  still  small  enough  to  indicate  that  the  effects 
are  real  and  can  not  be  explained  as  selection  by  chance. 

To  show  the  effect  of  imperfect  synchronization  of  the  films  the 
experiment  of  displacing  one  sound-track  relative  to  the  other  was 
tried.  As  the  displacement  increased,  an  increase  in  the  apparent 
reverberation  of  the  sound  occurred.  This  became  obvious  with  a 
displacement  of  between  one  and  two  frames.  When  increased  to 
four  frames  the  effect  was  very  obvious,  and  when  the  difference  be- 
came eight  frames  the  time  lag  was  sufficient  to  give  a  distinct  echo. 


356  F.  L.  HUNT  [j.  s.  M.  P.  E.| 

Synchronism  was  maintained  within  a  quarter  of  a  frame,  that  is,  I 
within  one  sprocket  hole,  when  the  sound-tracks  were  printed. 

It  was  agreed  by  those  who  heard  these  auditory-perspective  sound  I 
pictures  that  they  distinctly  enhanced  the  illusion  that  the  sound 
originated  from  the  source  shown  on  the  screen  and  that  the  sound  t 
appeared  to  follow  the  image  of  the  source  as  it  moved.     There  was 
striking  improvement  in  the  feeling  of  spaciousness  and  reality,  that 
is,  the  feeling  that  the  sound  originated  in  an  actual  room  of  three  j 
dimensions.     In  previous  auditory-perspective  demonstrations  fre-l 
quencies  up  to  15,000  cps.  have  been  reproduced,  but  these  experi- 
ments show  that  the  effects  still  persist  strongly  when  combined  with 
motion  pictures  if  frequencies  up  to  only  7000  cps.  are  used. 

Since  these  experiments  were  carried  out  the  art  has  been  advanced 
by  others.  A  public  demonstration  of  sound  pictures  incorporating 
these  ideas  in  practical  form  was  given  by  Electrical  Research  Prod- 
ucts, Inc.,  at  Bell  Telephone  Laboratories  in  1937. 3  In  these  tests 
two  sound-tracks  were  recorded  simultaneously  on  a  single  film  in  the 
space  ordinarily  occupied  by  one  sound-track.  For  this  purpose  a 
light-valve  with  two  pairs  of  ribbons  was  used.  One  pair  was  ac- 
tuated by  current  from  the  channel  at  the  right  side  of  the  stage  and 
the  other  by  the  channel  at  the  left.  To  reproduce  the  records  the 
outputs  of  the  two  sound-tracks  were  picked  up  by  a  double  photo- 
electric cell,  each  unit  of  which  was  connected  to  a  separate  ampli- 
fying system  and  to  separate  loud  speakers.  Each  loud  speaker 
comprised  two  units :  a  cone  with  a  box  baffle  to  radiate  the  low  fre- 
quencies, and  a  multicellular  horn  for  frequencies  above  300  cps. 
The  range  radiated  was  from  50  to  8000  cps. 

The  pictures  shown  included  that  of  a  large  orchestra,  which  gave 
the  audience  an  opportunity  to  observe  that  the  sounds  from  the 
various  instruments  emanated  from  the  positions  where  the  instru- 
ments appeared  in  the  picture.  In  another  scene  the  sound  of  a 
ping-pong  ball  striking  the  bat  or  table  passed  from  side  to  side  as 
the  ball  was  struck  back  and  forth.  A  third  scene  started  with  an 
unlighted  screen  from  which  noise  and  voices  came  as  the  actors 
apparently  stumbled  about  in  the  dark.  Later  a  third  actor  ar- 
rived. As  he  turned  on  the  lights,  the  picture  of  a  somewhat  dis- 
ordered living  room  appeared  upon  the  screen.  This  gave  the  audi- 
ence an  opportunity  to  compare  the  apparent  origins  of  the  sounds 
occurring  at  the  moment  with  the  actors'  actual  positions  in  the 
picture. 


Oct.,  1938]  SOUND  PICTURES  IN  PERSPECTIVE  357 

These  demonstrations  and  those  previously  described  show  that 
sound  pictures  in  auditory  perspective  can  be  added  to  present-day 
sound  picture  equipment  without  great  difficulty  and  that  they  dis- 
tinctly enhance  the  realism  of  the  presentation.  The  practical  ap- 
plication of  the  method  gives  promise  of  being  another  significant 
step  in  perfecting  the  new  art  that  has  played  so  large  a  part  in  revo- 
lutionizing popular  entertaiment  during  recent  years. 

REFERENCES 

1  JEWETT,  F.  B.:     "Perfect  Quality  and  Auditory  Perspective  in  the  Trans- 
mission and  Reproduction  of  Music,"  Science,  77  (May  12,  1933),  No.  2002,  p.  435. 

STEINBERG,  J.  C.,  AND  SNOW,  W.  B.:  Electrical  Engineering,  53  (Jan., 
1934),  No.  1,  p.  12. 

MAXFIELD,  J.  P.,  COLLEDGE,  A.  W.,  AND  FRIEBUS,  R.  T.:  "Pick-Up  for 
Sound  Motion  Pictures  (Including  Stereophonic),"  /.  Soc.  Mot.  Pict.  Eng.,  XXX 
(June,  1938),  No.  6,  p.  666. 

2  STOLLER,  H.  M.:     "Synchronization  and  Speed  Control  of  Synchronized 
Motion  Pictures,"  Trans.  Soc.  Mot.  Pict.  Eng.,  XII  (Sept.,  1928),  No.  35,  p.  696. 

3  MAXFIELD,  J.  P.:     "Demonstration  of  Stereophonic  Recording  with  Motion 
Pictures,"  /.  Soc.  Mot.  Pict.  Eng.,  XXX  (Feb.,  1938),  No.  2,  p.  131. 


APPLICATION  OF  ELECTRICAL  NETWORKS  TO  SOUND 
RECORDING  AND  REPRODUCING* 


H.   R.  KIMBALL** 

Summary. — The  use  of  electrical  networks  with  recording  and  reproducing  systems 
to  accomplish  beneficial  results  has  been  steadily  increasing.  Two  types  of  networks 
are  in  general  use,  namely,  wave-filters  and  attenuation  equalizers.  This  paper  dis- 
cusses in  some  detail  the  use  of  these  networks  with  sound  systems  as  reflected  by 
present  practices  and  later  presents  practical  data  for  engineering  the  networks  with 
a  minimum  of  time  and  effort.  The  uses  to  which  attenuation  equalizers  are  put 
divide  these  networks  into  two  general  classes:  first,  fixed  equalizers  to  provide  fixed 
equalization  for  sound  channels;  and,  second,  variable  equalizers  to  provide  means 
for  varying  at  will  the  relative  amplitudes  of  the  frequency  components  of  sound 
signals.  Although  the  means  for  engineering  variable  networks  is  far  from  being  ideal, 
the  review  given  in  the  paper  of  present  practices  should  be  valuable. 

Electrical  networks  such  as  wave-filters,  attenuation  equalizers, 
transformers,  etc.,  are  devices  used  as  links  in  transmission  systems 
for  altering  in  some  specified  manner  the  transmitted  electrical  signals. 
Networks  of  this  sort  have  been  important  parts  of  signal-transmis- 
sion systems  for  some  time.  In  the  communication  field,  for  in- 
stance, many  of  the  facilities  in  daily  use  would  be  impossible  without 
such  networks.  In  fact,  realization  of  the  commerical  applications 
of  networks  by  the  communication  industry  is  mainly  responsible 
for  the  great  amount  of  effort  put  forth  to  perfect  the  devices. 

At  the  time  sound  with  motion  pictures  became  commercially 
practicable,  the  development  of  networks  had  reached  an  advanced 
stage,  making  them  directly  available  for  use  in  the  new  industry. 
But  new  fields  of  endeavor  require  new  methods  of  design  and  applica- 
tion. Such  has  been  the  experience  in  sound  pictures.  The  technic 
of  using  networks  with  sound  recording  systems  differs  from  that  of 
using  them  with  communication  systems.  Progress  has  been  made 
toward  applying  networks  to  sound  picture  purposes  but  much  yet 
remains  to  be  done.  This  paper  outlines  some  of  the  applications  of 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;    received 
April  19,  1938. 

**  Metro-Goldwyn-Mayer  Pictures,  Culver  City,  Calif. 
358 


APPLICATION  OF  ELECTRICAL  NETWORKS  359 

networks  to  sound  picture  work  and  gives  some  useful  data  especially 
arranged  to  meet  the  needs  of  studio  sound  departments. 

Sound  originates  from  its  source  in  the  form  of  pressure  variations 
in  the  air.  The  microphone,  when  properly  placed,  converts  these 
acoustic  variations  into  corresponding  electrical  variations  which, 
when  amplified,  may  be  recorded  on  film.  The  simplest  form  of  sound 
is  a  pressure  wave  varying  sinusoidally  with  time.  Complex  waves, 
such  as  speech,  music,  etc.,  consist  of  large  numbers  of  these  simple 
components  variously  arranged  with  respect  to  amplitude,  phase, 
time  spacing,  and  time  duration.  The  frequencies  involved  may 
range  anywhere  between  twenty  cycles  per  second  and  twenty 
thousand  cycles  per  second.  For  speech  and  music  these  components 
consist  of  constantly  shifting  fundamental  frequencies  and  their 
harmonics.  Sound,  then,  is  identified  by  the  frequency  components 
contained  in  the  pressure  wave.  Any  change  made  in  the  components 
changes  the  character  of  the  sound  as  identified  by  the  ear  in  the  same 
manner  as  if  the  signal  were  emitted  in  the  changed  form  initially. 

Electrical  networks  when  arranged  for  use  with  sound  systems  are 
provided  with  a  pair  of  input  terminals  for  connecting  to  a  system  to 
receive  energy,  and  a  pair  of  output  terminals  to  permit  delivery  of 
the  modified  signal  back  to  the  system.  A  signal  in  traversing  the 
system  from  the  input  terminals  to  the  output  terminals  can  be  modi- 
fied by  the  network  in  only  a  few  ways.  For  instance,  (1)  the  signal 
can  be  delayed  in  time  by  means  of  delay  networks,  (2)  the  relative 
phase  relation  of  its  frequency  components  can  be  altered  by  net- 
works known  as  phase  correctors,  (3)  the  signal  can  be  decreased  in 
volume  with  the  use  of  attenuators,  (4)  the  band  of  frequencies  freely 
transmitted  can  be  restricted  to  some  definite  limits  by  means  of 
wave-filters,  and  (5)  the  relative  amplitudes  of  its  frequency  com- 
ponents can  be  altered  to  effect  a  change  in  quality  by  means  of  net- 
works known  as  attenuation  equalizers.  Ordinarily  the  first  two  of 
these  items  are  not  of  value  in  sound-picture  work — the  first  for  the 
reason  that  time-delay  by  means  of  networks  is  too  costly  for  the 
benefits  received,  and  the  second  because  phase  correction  of  the  type 
easily  obtained  with  networks  is  not  usually  needed  in  sound  work. 
The  other  networks,  attenuators,  attenuation  equalizers,  and  wave- 
filters  are  used  quite  freely. 

As  already  mentioned,  an  attenuation  equalizer  is  a  network 
whose  attenuation  loss,  over  a  given  frequency  range,  varies  with 
frequency  in  some  desirable  manner.  This  means  that  if  a  number  of 


360  H.  R.  KIMBALL  [J.  s.  M.  P.  E. 

frequencies  of  given  amplitudes  are  simultaneously  impressed  upon 
the  input  terminals  of  an  equalizer,  the  relative  amplitudes  of  these 
frequencies  will  be  changed  when  delivered  to  a  load  connected  to  the 
output  terminals.  The  manner  in  which  this  change  takes  place  is 
determined  and  can  be  controlled  by  the  design  of  the  equalizer.  In 
sound  picture  work,  the  frequency  range  required  extends  from  about 
40  or  50  to  7500  or  8000  cycles  per  second.  This  is  called  the 
transmission  band.  Equalizers  for  sound  work  then,  are  usually 
arranged  to  render  a  specified  transmission  characteristic  in  this 
range  and  little  attention  is  given  to  what  they  do  outside  the  range. 

Wave-filters  provide  the  means  for  defining  the  recorded  band; 
that  is,  they  freely  pass  the  above-mentioned  frequency  range  and 
considerably  attenuate  other  frequencies.  The  filters  used  in  sound 
recording  and  reproducing  channels  are  either  of  the  low-pass  or  the 
high-pass  type,  there  being  little  need  for  band-pass  designs. 

Two  general  types  of  such  networks  are  used  in  sound  systems; 
that  is,  fixed  networks  and  variable  networks.  By  a  fixed  network 
is  meant  one  whose  transmission  characteristic  can  not  readily  be 
changed;  while  a  variable  network  is  one  provided  with  controls 
for  varying  its  characteristic  over  a  prescribed  range.  Fixed  net- 
works are  usually  used  with  recording  and  reproducing  equipment  to 
compensate  for  any  unavoidable  distortions  occurring,  for  various 
reasons,  in  the  equipments,  and  to  provide  the  fixed  transmission 
characteristics  that  have  been  found  to  produce  the  best  average 
product  with  the  recording  and  reproducing  equipments  available. 
These  characteristics  for  the  different  parts  of  a  system  may  or  may 
not  be  linear,  depending  upon  the  equipment  limitations.  Variable 
type  networks  or  "patch-in"  networks  are  usually  concentrated  al- 
most exclusively  at  the  re-recording  mixer  positions,  where  the  sound 
quality  for  the  complete  picture  can  be  made  uniform  and  sound 
effects  rehearsed  and  altered  as  desired  to  obtain  the  best  overall 
results. 

Recording  Networks  and  Complementary  Recording. — The  networks 
used  in  the  original  recording  of  sound  are  few  in  number  and  simple 
in  construction.  They  often  consist  of  a  high-pass  filter  of  one  or 
two  sections  having  a  cut-off  at  about  60  cps.,  and  a  low-pass  filter 
with  a  cut-off  at  about  7500  cps.  These  define  the  recording  band 
from  the  frequency  standpoint.  The  high-pass  filter  is  to  remove 
excessive  stage  boominess  in  a  low-frequency  range  that  is  otherwise 
not  important.  The  low-pass  filter  removes  unimportant  frequencies 


Oct.,  1938] 


APPLICATION  OF  ELECTRICAL  NETWORKS 


361 


in  the  upper  part  of  the  frequency  range.  In  the  case  of  variable- 
density  recording,  this  is  an  important  function  as  it  prevents  over- 
loading and  perhaps  breakage  of  the  light-valve  in  the  vicinity  of 
valve  resonance.  • 

Recently  a  method  of  recording  known  as  complementary* 
recording  was  put  into  effect  at  one  major  studio,  requiring  the 
use  of  one  equalizer  in  the  recording  circuit  to  pre-equalize  the 
recorded  material,  and  another  in  the  reproducing  circuit  to  post- 
equalize  this  circuit  in  a  complementary  manner.  Fig.  1  shows 
the  recording  characteristic  obtained  with  the  pre-equalizer  and 


RECOR  DING      C 


CHARACTER 


T 


PRE-EQUALIZER 

FIG.  1. 


POST -EQUALIZER  ( 

Complementary  recording. 


I  the  reproducing  characteristic  derived  from  the  post-evualizer. 
When  these  two  equalizers  are  used  in  this  manner,  the  overall 
amplitude-frequency  characteristic  is  unchanged  because  of  the  com- 

:  plementary  nature  of  the  equalizers,  the  amplitude  distortion  in- 
troduced by  the  pre-equalizer  being  compensated  for  by  the  post- 
equalizer.  Referring  to  Fig.  1,  it  will  be  noted  that  the  pre-equalizer 
has  an  insertion  loss  of  about  12  db.  at  100  cps.,  6  db.  at  1000  cps.,  and 


*  Because  of  the  necessity  of  employing  a  post-equalizer  in  the  reproducing 
system,  complementary  recording  can  not  as  yet  be  used  for  release  prints.  It  is 
the  hope  that  joint  action  to  provide  post-equalizers  for  all  theater  equipment 
will  soon  be  possible. 


362  H.  R.  KlMBALL  [J.  S.  M.  P.  E. 

very  little  loss  at  the  high  frequencies.  In  general,  most  of  the  transi- 
tion from  12  db.  loss  to  0  db.  loss  occurs  in  the  frequency  range  from 
300  to  3000  cps.  The  half-loss  frequency  of  1000  cps.  is  one  of  the 
design  parameters  of  the  equalizers. 

It  is  well  known  that  a  large  part  of  the  energy  content  of  sound 
signals  lies  in  the  low-frequency  range,  say  from  200  to  500  cps. 
Insertion  of  the  above-described  pre-equalizer  into  a  normal  recording 
channel  without  any  change  in  the  channel  gain  removes  a  large  part 
of  the  signal  load  from  the  recording  mechanism  and  the  film,  leaving 
the  high-frequency  content  at  approximately  the  same  level.  Be- 
cause of  the  removal  of  the  low-frequency  load,  it  is  possible  to  in- 
crease the  recording  channel  gain,  thus  increasing  the  recorded  level 
of  the  high-frequency  content  and  achieving  a  greater  ratio  of  high- 
frequency  signal  to  static  surface  noise ;  that  is,  an  increase  in  noise- 
reduction.  Subsequent  post-equalization  does  not  destroy  this  in- 
creased noise-reduction  because  of  the  concentration  of  surface  noise 
in  the  upper  part  of  the  frequency  spectrum. 

Complementary  recording  also  effectively  eliminates  "breathing," 
by  which  is  meant  the  audible  change  in  surface  noise  caused  by  the 
recording  mechanism's  being  placed,  by  the  noise  reduction  equip- 
ment, in  the  proper  position  to  handle  the  signal.  For  normal  re- 
cording the  greater  the  signal  volume  the  greater  is  the  breathing, 
and  since  most  of  the  signal  energy  lies  in  the  low-frequency  range, 
much  of  the  breathing  is  produced  by  the  lower-frequency  components 
of  the  signals.  It  may  be  mentioned  also  that  masking  is  a  factor  in 
breathing  because  when  breathing  is  produced  by  a  high-frequency 
signal,  the  surface  noise  is  masked  somewhat  by  the  signal.  Use  of 
this  type  of  pre-equalizer  in  the  recording  circuit  therefore  con- 
siderably reduces  breathing  because  the  recording  mechanism  is  not 
modulated  nearly  as  much  by  the  low-frequency  signal  content. 

Complementary  recording  has  also  a  few  other  associated  benefits. 
For  instance,  intermodulation,  causing  spurious  signal  products,  is 
reduced  because  of  the  lower  level  of  the  low-frequency  components. 
Bias  current  components  also  are  reduced  for  the  same  reason.  In 
addition,  wave-top  clipping  on  steep  wave-fronts,  caused  by  the 
sluggishness  of  the  noise-reduction  equipments,  is  reduced.  Still 
again,  complementary  recording  provides  greater  margin  of  operation 
for  the  low-frequency  components  thus  permitting  occasional  high- 
peaked  signals  to  be  handled  with  less  overload.  This  is  equivalent 
to  an  increase  in  volume  range. 


3ct.,  1938]        APPLICATION  OF  ELECTRICAL  NETWORKS 


363 


In  conclusion,  it  may  be  mentioned  that  complementary  recording 
iccomplishes  beneficial  results  for  two  basic  reasons;  first,  the  energy 
iistribution  of  acoustic  signals  lies  in  the  lower  part  of  the  audible 
'requency  spectrum,  and,  second,  film  surface  noise  is  concentrated 
n  the  upper  part  of  the  frequency  range.  Reducing  the  level  of  the 
•ecorded  signals  in  the  low-frequency  range  does  not  materially  in- 
crease the  signal-to-static  surface-noise  ratio  in  this  same  range,  but, 


TO 
RECORDING 

CHANNEL 


FIG.  2. 


Mixer  circuit;    12-db.  insertion  loss  (x  =  constant- 
resistance  patching  points. 


:>n  the  contrary,  permits  the  over-riding  of  surface  noise  in  the  upper 
i  frequency  range.  This,  in  connection  with  the  reduction  in  breath- 
ling,  decreased  intermodulation  effects,  and  the  other  items  outlined 
!  above  constitute  the  benefits  of  this  method  of  recording. 

Re-recording  Arrangements.  —  Re-recording  rooms  are  usually  ar- 
i  ranged  to  have  acoustic  characteristics  approximating  those  of  aver- 
ige  large  motion  picture  theaters.  This  is  necessary  in  order  that 
;  the  re-recording  mixers  may  adjust  the  sound  quality  and  effects  to 
produce  the  results  desired  when  the  record  is  reproduced  in  an 
average  theater.  Facilities  are  made  available  to  permit  joining 


364  H.  R.  KIMBALL  [j.  s.  M.  p. : 

the  sounds  from  a  number  of  sound-tracks,  by  means  of  a  mixir 
table,  to  form  one  composite  signal  for  monitoring  and  for  re-recor< 
ing.  Combining  as  many  as  eight  tracks  into  one  is  not  unusual,  ar 
sometimes  as  many  as  twelve  sound-tracks  are  joined.  The  mixir 
table  is  arranged  so  that  each  track  may  be  dealt  with  separately  < 
a  number  of  tracks  as  a  unit. 

Fig.  2  shows  a  mixing  table  arrangement  permitting  joining 
maximum  of  sixteen  sound-tracks  into  one.  Patching  points  a: 
available  for  the  insertion  of  networks  into  the  circuit  of  each  soum 
track  or  at  points  where  the  sound-tracks  are  combined  in  groups  < 
four.  At  each  point  where  networks  may  be  inserted,  the  circu 
impedances  are  equal  resistances  in  the  two  directions,  so  that  ar 
inserted  network  will  operate  between  its  designed  resistance 
Where  constant-resistance  networks  are  inserted,  this  permits  tl 
operation  of  any  number  in  tandem  without  altering  the  characteri 
tics  of  the  individual  networks.  This  constant-resistance  featu: 
at  the  patching  points  is  made  possible  by  the  design  of  the  mix 
coil,  which  may  be  designed  to  combine  any  number  of  circuits 
multiples  of  two  into  one  channel.  For  instance,  the  sixteen-positic 
mixer  of  Fig.  2  could  be  handled  by  means  of  only  one  mixer  co 
For  flexibility  of  patching,  however,  the  four-position  coil  seen 
more  practicable.  The  insertion  loss  through  the  mixing  circuit  • 
Fig.  2  is  12  db.,  or  10  log  16.  This  is  the  minimum  loss  that  can  1 
obtained  for  the  sixteen  positions. 

The  above-described  mixing  circuit  is  only  one  of  a  number  of  a 
rangements  that  can  be  used.  Usually  it  is  not  necessary  to  pro  vie 
as  many  as  sixteen  mixer  positions.  Some  saving  in  equipment  cs 
be  achieved  where  a  smaller  number  of  mixer  positions  is  satisfactory 
The  general  requirements  are  to  provide  minimum  insertion  los 
flexibility  of  patching,  and  constant  resistance  at  the  patching  point 

A  large  variety  of  fixed  and  variable-type  equalizers  and  filte 
are  available  for  re-recording.  There  are  at  the  present  time  no  stan< 
ard  networks  in  use  by  all  the  studios  although  many  of  the  studic 
have  quite  similar  equipments. 

Reproducing  Networks. — As  in  recording  systems,  the  networl 
required  in  reproducing  sound  are  few  in  number  and  simple  in  desigi 
Most  reproducing  systems  employ  only  two  networks:  one  a  lo\ 
pass  filter  to  suppress  system  and  surface  noise  lying  above  the  us< 
ful  signal  frequencies,  and  the  other  a  dividing  network  for  use  wit 
the  loud  speaker  system.  The  low-pass  filter  is  often  of  the  variab 


>ct.,  1938]         APPLICATION  OF  ELECTRICAL  NETWORKS  365 

ype,  permitting  adjustment  of  its  cut-off  to  suit  the  theater  in  which 
;  is  installed.  Information  is  given  later  in  this  paper  regarding  the 
arious  types  of  dividing  networks.  In  addition  to  these  types  of 
etworks  some  reproducing  systems  eniploy  equalizers  for  compen- 
ating  for  loud  speaker  characteristics,  but  these  are  of  special  design 
nd  will  not  be  discussed  here. 

Miscellaneous  Networks. — In  addition  to  the  above-mentioned  net- 
works, which  are  more  or  less  standard,  a  number  of  different  types 
f  networks  are  used  in  various  test  equipments,  and  for  special 
urposes  such  as  for  equalizing  microphones  of  different  types,  for 
ompensating  for  room  effects,  etc.     These  are  usually  of  conven- 
onal  design  and  present  no  great  difficulties.* 
Attenuation  Equalizers. — As   already  mentioned,   an   attenuation 
qualizer  is  a  four-terminal  network  whose  attenuation  loss,  over  a 
iven  frequency  range,   varies   with  frequency   in   some   desirable 
lanner.     This  means  that  if  a  number  of  frequencies  of  given  am- 
litudes  are  simultaneously  impressed  upon  the  input  terminals  of 
n  equalizer,  the  relative  amplitudes  of  these  frequencies  will  be 
langed  when  delivered  to  a  load  connected  to  the  output  terminals, 
he  manner  in  which  the  change  takes  place  is  determined  and  can 
e  controlled  by  the  design  of  the  equalizer.     In  practice  the  shapes 
equired  of  the  insertion-loss  curves  of  equalizers  appear  to  vary  over 
|  wide  range.     Actually,  many  equalizer  problems  are  but  duplica- 
tions of  others  with  different  values  assigned  to  the  network  con- 
;tants. 

'  From  the  great  amount  of  work  that  has  been  done  on  the  design 
f  attenuation  equalizers  a  number  of  general  circuit  arrangements 
nave  emerged  that  have  proved  to  be  the  most  satisfactory  for  general 
ise.  The  network  engineer  does  not  necessarily  restrict  himself  to 
he  use  of  these  few  types  but  they  do  represent  a  large  part  of  his 
:it  of  tools.  These  equalizer  circuits  are  designated  in  the  following 
nanner : 

>1)     Series  impedance  type. 
#)    Shunt  impedance  type. 

3)  Full  series  type. 

4)  Full  shunt  type. 

5)  rtype. 

6)  Bridged-  T  type. 

7)  Lattice  type. 

*  Some  of  the  information  from  this  point  on  is  summarized  from  data  in 
'Motion  Picture  Sound  Engineering."     (Cf.  ref.  1,  p.  380.) 


366 


H.  R.  KlMBALL 


Network  Type 

Series 
Imp. 


[J.  S.  M.  P. 
Insertion 


Not  Not  2f)  ,      ^o  + 

Constant         Constant.  R0 


, 


~*      Shunt 
4      Imp. 


Not  Not  ?n ,      RQ  + 

Constant         Constant  8       Z2 


Ro 


Not 


o  9n  ,  „  -o 

Constant         20  log 


+ 


Ful1 

Shunt 


R* 


Not  2f)  . 

Constant        20  log 


20  log 


R. 


Bridged 


2o  log  ^ 


Lattice 


NOTES: 

(1)  Z!Z2  =  -Ro2  for  all  networks 


(3)  Working  Circuit  = 


FIG.  3.     Fundamental  equalizer  types. 


Oct.,  1938]         APPLICATION  OF  ELECTRICAL  NETWORKS  367 

Fig.  3  shows  these  seven  equalizer  types  in  schematic  form.  For 
these  circuits,  it  is  assumed  that  the  system  impedances  to  which 
connection  is  made  for  operation  are  equal  resistances  of  RQ  ohms. 
In  sound  picture  work  RQ  has  values  of  the  order  of  500  ohms,  200 
ohms,  16  ohms,  and  various  other  resistances.  The  variable  char- 
acteristics of  the  equalizers  are  made  to  depend  upon  two  general 
impedances  denoted  in  the  circuits  as  Z\  and  Z2  and  defined  as  being 
inverse  to  each  other  with  respect  to  the  line  resistance  RQ]  that  is, 


It  is  noted  that  the  insertion-loss  formula,  as  expressed  by  the 
equation 

T  T  RQ  +  Zl  RQ  +  Z2 

I.L.  =  20  log  --  =  20  log  - 
AO  Z2 

is  applicable  to  each  of  the  equalizer  types.  This  means  that  an 
insertion-loss  characteristic  obtained  with  one  of  the  equalizer  types 
can  be  duplicated  by  any  of  the  other  types.  The  formula  shows 
also  that  the  shapes  of  the  insertion  loss  curves  of  the  equalizers 
of  Fig.  3  are  determined  solely  by  the  inverse  arms  of  the  networks 
as  represented  by  impedances  Zi  and  Z2.  This  feature  makes  it 
practicable,  in  a  design  problem,  to  determine  the  circuits  of  the 
inverse  arms  independently  of  the  equalizer  types  with  which  they 
are  to  be  used. 

Since  the  same  insertion  loss  characteristic  may  be  obtained  with 
any  of  the  equalizers  of  Fig.  3,  the  question  naturally  arises  as  to  the 
advantages  of  one  type  over  another.  In  this  connection  it  will  be 
noted  from  the  figure  that  the  input  and  output  impedances  for  the 
types  are  not  the  same.  For  the  first  two  types,  both  these  impe- 
dances vary  with  frequency  ;  for  the  next  two  types  one  impedance  is 
constant  and  the  other  one  varies;  and  for  the  last  three  types,  both 
Zi2  and  Z34  are  constant.  Then,  for  instance,  where  a  constant- 
impedance  network  is  needed,  one  of  the  last  three  types  must  be 
used.  Commercial  features  also  help  in  making  this  decision,  as 
one  would  select  the  type  easiest  to  build  which  meets  the  circuit 
requirements. 

The  impedances  Zi  and  Z2  may  take  any  form  of  circuit  arrange- 
ment so  long  as  they  are  inverse  to  each  other.  In  practical  work 
a  few  common  circuit  arrangements  are  sufficient  for  most  purposes. 
Fig.  4  shows  eight  pairs  of  simple  inverse  circuits  for  which  data 


368 


H.  R.  KlMBALL 


[J.  S.  M.  P.  E 


II 


\ 


T 


i 


5* 

>>  * = .§ 

' 


S 


3ct.,  1938]         APPLICATION  OF  ELECTRICAL  NETWORKS 


369 


LOSS  =10  LOG 


FIG.  5.     Insertion  loss — No.  1  inverse  arms. 


5.0  TO  10O 


FIG.  6.     Insertion  loss — No.  4  inverse  arms. 


370  H.  R.  KlMBALL 

are  given  in  this  paper.  Each  of  these  pairs  may  be  used  with  an> 
of  the  equalizers  of  Fig.  3,  provided  the  modifications  shown  foi 
the  various  types  in  Fig.  3  are  made;  that  is,  2Zb  Zi/2,  Z2/2,  2Z2 
etc. 

The  insertion-loss  formula  for  each  pair  of  inverse  arms  and  the 
general  form  of  the  insertion  loss  characteristic  are  also  given  (Fig.  4) 
It  will  be  noted  that  the  insertion-loss  curves  for  the  first  foui 
pairs  of  arms  range  from  zero  to  infinity.  This  is  because  these  in 
verse  arms  are  purely  reactive,  and  their  impedances  vary  betweer 
zero  and  infinity.  For  these  four  pairs  of  inverse  arms  the  fre 
quency  fa  is  defined  as  the  frequency  where  a  3-db.  insertion  losj 
is  obtained.  This  frequency  fa  is  a  design  parameter.  The  symbo 
fr  is  used  to  designate  the  resonance  or  anti-resonance  frequencies  ol 
the  arms,  where  of  course,  such  points  exist.  Because  of  the  inverse 
relation  between  Z\  and  Z2,  the  resonance  frequency  of  one  is  the 
anti-resonance  frequency  of  the  other.  The  symbol  a  is  used  to  de 
note  the  ratio  of  fr  to  fa,  that  is,  a  =  fr/fa.  In  cases  where  fa  mighl 
be  either  greater  or  less  than  / ,  the  lower  frequency  is  selected  foi 
fa  so  as  to  make  the  value  of  a  always  greater  than  unity. 

The  networks  obtained  by  the  use  of  the  last  four  pairs  of  inverse 
arms  have  no  infinite  insertion-loss  points,  but  vary  between  zerc 
and  some  finite  value  determined  by  the  symbol  k.  That  is,  the 
maximum  insertion  loss  is  20  log  k,  and  therefore  k  is  a  design  pa 
rameter  that  becomes  known  when  the  maximum  loss  desired  for  £ 
network  is  known.  The  symbol  fb  is  used  to  indicate  the  frequency 
where  one-half  the  maximum  loss  is  secured  or  10  log  k.  The  symbol 
b  denotes  the  ratio  fr/fb,  and  again  fb  is  always  selected  to  be  less 
than  fr  so  that  b  is  always  greater  than  unity. 

The  values  assigned  to  k,  fr,  fa,  and  /„  determine  the  electrical 
elements  for  the  inverse  arms.  Having  decided  upon  a  particulai 
pair  of  these  arms,  they  may  be  used  with  any  of  the  equalizer  types 
of  Fig.  3.  The  formulas  for  computing  the  elements  from  a  knowl- 
edge of  RQ,  k,  fr,  fa)  and/»  are  given  in  Fig.  4. 

For  design  work  it  is  useful  to  have  curves  available  to  aid  ir 
selecting  the  fundamental  design  parameters.  These  have  beer 
prepared  to  cover  a  wide  range  of  applications.  Figs.  5,  6,  7,  8,  and 
9  are  examples  of  such  curves.  The  recent  book1  on  sound  engineer- 
ing contains  a  complete  set  of  design  charts  and  tables  as  well  as 
material  showing  the  preparation  and  use  of  the  formulas.  These 
data  are  too  voluminous  to  be  given  here. 


FIG.  7.     Insertion  loss — No.  7  inverse  arms. 


0.2  0.3        0.4     0.5          0.7  1.0  2.0  3.0        40     SO  7.0          10.O 

FIG.  8.     Insertion  loss — No.  7  inverse  arms. 


12  0.3        04    OS          07  10  20  30        4.0     5.0  70          K» 

FIG.  9.     Insertion  loss — -No.  8  inverse  arms. 


372  H.  R.  KlMBALL  [J.  S.  M.  P.  E. 

Wave-Filters. — Electric  wave-filters,  like  attenuation  equalizers, 
are  four-terminal  networks  having  a  pair  of  input  terminals  and  a 
pair  of  output  terminals.  Between  the  input  and  output  terminals 
is  an  orderly  array  of  electrical  elements  arranged  so  as  to  produce  a 
specified  insertion-loss  characteristic  when  connected  between  the 
proper  terminal  impedances.  Unlike  equalizers,  resistive  elements 
are  excluded  from  wave-filters;  only  inductive  and  capacitive  ele- 
ments being  used  to  interconnect  the  input  and  output  terminals. 
The  reason  for  the  exclusion  of  resistive  conductors  is  contained 
in  the  purpose  of  a  filter;  i.  e.,  to  transmit,  without  appreciable  loss, 
all  frequencies  of  the  transmission  band,  and  to  attenuate  by  a  pre- 
scribed amount  frequencies  lying  outside  this  band.  If  resistive 
elements  were  used  attenuation  would  result  within  the  transmission 
band. 

Electric  wave-filters  consist  usually  of  a  number  of  filter  sections 
of  unit  four-terminal  networks  connected  in  tandem  on  a  matched- 
impedance  basis  to  form  the  complete  filter.  It  is  not  necessary  that 
a  filter  consist  of  more  than  one  section,  but  usually  the  transmission 
characteristic  desired  is  such  as  to  require  the  use  of  multiple  sections. 
In  this  respect  filters  are  different  from  equalizers,  where  in  a  great 
many  cases,  the  desired  equalization  curves  may  be  secured  without 
tandem  operation  of  sections. 

Conventionally  designed  wave-filters  seldom  provide  constant  im- 
pedances at  their  terminals  over  the  operating  frequency  range,  and 
for  that  reason  it  is  usually  not  possible  to  achieve  a  match  of  im- 
pedance between  the  wave-filter  and  the  system  to  which  it  is  con- 
nected, even  though  the  impedances  of  the  latter  are  constant  resis- 
tances. In  general,  the  terminal  impedances  of  filters  are  largely 
resistive  in  their  transmission  bands  and  reactive  in  the  attenuation 
ranges.  In  addition,  in  the  transmission  range  the  resistive  char- 
acteristics vary  with  frequency,  especially  in  the  cut-off  region. 
While  various  methods  are  available  of  stabilizing  these  impedances 
to  almost  any  desired  precision,  most  filters,  as  arranged  for  com- 
mercial purposes,  provide  some  mis-match  at  their  terminals.  The 
insertion  loss  of  a  filter  takes  into  account  these  terminal  effects  and 
for  that  reason  it  is  important  in  operating  filters  to  make  sure  that 
the  proper  connecting  impedance  conditions  are  obtained. 

Although  wave-filters  transmit  the  frequencies  of  their  transmis- 
sion band  without  appreciable  attenuation  loss,  they  do  shift  the 
relative  phases  of  all  the  frequencies.  This  is  an  inherent  feature 


Oct.,  1938]         APPLICATION  OF  ELECTRICAL  NETWORKS 


373 


of  filters  that  can  not  be  avoided,  although  in  some  cases  means  are 
available  for  controlling  the  phase-shift  characteristic  so  as  to  mini- 
mize its  effect  upon  transmission.  In  many  transmission  systems, 
the  effect  of  phase-shift  is  not  of  sufficient  magnitude  to  require  cor- 
rection, while  in  certain  types  of  systems  corrective  means  must  be 
employed.  In  sound  pictures  it  has  not  been  found  necessary  to 
correct  for  the  phase-shift  in  the  filters  generally  used. 


FREQUENCY 


FREQUENCY 


FREQUENCY 


FREQUENCY 


FIG.  10.     Filter  transmission  bands. 


For  design  and  nomenclature  purposes,  wave-filters  are  classified 
into  four  types,  in  accordance  with  their  attenuation  characteristics: 

(1)  Low-pass  filters. 

(2)  High-pass  filters. 
(5)     Band-pass  niters. 

(4)     Band-elimination  filters. 

For  low-pass  filters,  the  passing  band  includes  the  frequency  range 
from  zero  frequency  to  some  finite  frequency.  For  high-pass  filters 
the  passing  band  covers  the  range  from  infinite  frequency  down  to 
some  finite  frequency.  A  band-pass  filter  transmits  a  definite  band 
of  frequencies,  and  attenuates  frequencies  lying  outside  the  band. 
A  band-elimination  filter  transmits  all  frequencies  except  a  band  of 
frequencies  to  be  attenuated.  Band-elimination  filters,  although 
forming  an  integral  part  of  classified  filter  theory,  are  seldom  used, 
for  the  reason  that  there  is  very  little  commercial  need  for  filters 
having  that  type  of  attenuation  characteristic.  Fig.  10  shows  the 
transmission  and  suppression  ranges  for  the  different  types  of  filters. 

Figs.  11  and  12  show  the  low-pass  and  high-pass  filter  sections  most 
commonly  used  in  practice.  Filters  consisting  of  tandem  sections 
are  obtained  by  joining  together  the  various  sections  shown  on  a 
matched  image-impedance  basis.  The  terminals  of  the  sections 
having  like  image  impedances  are  indicated  in  Figs.  11  and  12.2 


374  H.  R.  KlMBALL 

Dividing  Networks.— In  the  design  of  linear  sound  reproducing 
equipments  where  it  is  desired  to  reproduce  faithfully  tones  from  about 
50  cycles  per  second  to  about  8000  cycles  per  second,  it  is  common 
practice  to  divide  the  frequency  range  into  two  or  more  parts  and 
provide  one  or  more  loud  speakers  for  each  of  these  frequency  ranges. 
The  speakers  employed  for  the  different  bands  are,  of  course,  dif- 
ferently designed,  each  speaker  being  particularly  suitable  for  its 
own  band.  Since  it  is  not  possible  to  design  loud  speakers  that  will 
faithfully  and  efficiently  reproduce  frequencies  in  one  preassigned 
band,  and  sharply  attenuate  frequencies  outside  the  band,  it  is  neces- 
sary to  supply  an  electrical  network  between  the  final  power  am- 
plifiers and  the  loud  speakers  to  deliver  the  correct  frequency  band 
to  each  set  of  loud  speakers.  These  networks  have  acquired  the 
name  of  "dividing  networks." 

In  practice,  loud  speaker  systems  may  be  of  the  two-way  or  three- 
way  types.  Because  of  the  preeminance  of  the  two-way  system,  only 
networks  for  use  with  such  systems  are  discussed  here.  For  the  two- 
way  system  the  speakers  handling  the  lower  frequencies  are  termed 
the  low-frequency,  or  low-range,  speakers.  In  like  manner,  the 
speakers  that  reproduce  higher  frequencies  are  called  the  upper- 
frequency  speakers  or  upper-range  speakers.  For  each  of  the  two 
frequency  bands  one  speaker  unit  or  a  number  of  speakers  are  ar- 
ranged in  series-parallel  combinations  to  secure  the  proper  combined 
load. 

Dividing  networks  are  not  usually  of  the  sharp  cut-off  type;  that 
is,  they  are  not  arranged  to  transmit  uniformly  frequencies  of  a  given 
band  and  then  attenuate  sharply  all  other  frequencies.  Rather,  they 
transmit  the  band  frequencies  almost  uniformly  and  gradually  slope 
off,  thereby  providing  a  certain  amount  of  overlap  between  the  as- 
signed frequency  ranges.  While  theoretically  it  may  seem  desirable 
to  arrange  dividing  networks  to  cut  off  sharply,  from  a  commercial 
standpoint  the  sharpness  of  cut-off  is  necessarily  a  compromise  be- 
tween expense  and  effectiveness.  For  well  designed  loud  speaker 
systems,  the  rate  of  change  of  attenuation  should  be  sufficient  at 
least  to  suppress  objectionable  irregularities  in  the  response  of  one 
horn  in  its  transmitting  range  because  of  sound  coming  from  the  other 
horn  in  its  suppression  range.  From  an  analysis  of  a  large  number 
of  speaker  systems  it  appears  that  dividing  networks  should  provide 
at  least  10  to  12  db.  of  attenuation  one  octave  away  from  their  cut- 
offs. In  considering  networks  having  greater  rates  of  change  of 


BASIC 

TTPCS 


o — ££-^£ 


SERIES 

TO-DERIVED 

TYPES 


SHUNT 

TTVCXRtVED 
TYPES 


— *;—     i 


T       o 

LQ  —  —T 


1-M* 


Co 


7 
I 


TTX/Z/oCo 
2 


FIG.  11.     Low-pass  filters. 


BASIC 
TYPES 


-flSSa- 


scft.-cs 

Tn-OEBlVEO 

TYPES 


SHUNT 

TO-  DERIVED 

TYPES 


47T/C 

1 


VI - 


m  =  Vl-(/K//c)2 


Zl  =  RoVl-(fc/f)* 


VI  ~ 


,     = ^ 

27TVLJC1 


TTENOATIO* 

CURVES 


PHASE 

CURVES 


-ID-SERIES 
IMPEDANCE 


A 


MID-SHUNT 

IMAGE 
IMPEDANCE 


FIG.  12.     High-pass  filters. 


APPLICATION  OF  ELECTRICAL  NETWORKS 


377 


Parallel    Type 
Dividing  Network 

Series    Type 
Dividing   Network 

1—  vlAJULr—  T— 

1 

* 

L,                                                               L2 

OJJLtU  ^)                      O                       .  fl  ft  *  " 

1 

Low 
Frequency 
Speakers                                     C,  Z 

L   4 

Low 
Frequency 
Speakers 

gC 

I 

•:         4 

'   fr  T 

High 
Frequency 
Speakers 

Frequency 
Speakers 

W 

°                                                           II 

(b) 

Low 
1.       Frequency 
Speakers 

LCL' 

Low 

Frequency 
Speakers 

£ 

Input 

High 
Frequency 
Speakers 

L'l 

High 
Frequency 

H 

FIG.  13.     Filter-type  dividing  networks. 


0 

4 

"- 

N 

,/^ 

a_ 

!*_ 
!*_ 
ZO 

NETWORK  LOSS  DB 

TERMINATIONS  «  K0 

/ 

\ 

PHASE 
AT  CKOS 

AN&  (b)  OF  FIG.  4 
DIFFERENCE 
SOVER  -  321° 

/ 

\ 

/ 

\ 

/ 

\ 

24              o 

s 

o 

S 

0 

g 

3 

^ 

f/£ 

*•                  "5 

pi 

o 

5 

Q 

z 

0 

3 

c 

Q 

9 

c 

0 

4 

^ 

^ 

s 

N 

^ 

a_S 

11,1 

V 
16    ? 

TERMINATIONS  «l?0 

/ 

\ 

NETWORKS   (c)  AND  (d)  OF  FI6.  4 
PHASE    DIFFERENCE 
AT   CKOSSOVEK  -221  • 

/ 

/ 

\ 

/ 

\ 

(- 
u 

«)2 

/ 

\ 

f.4              3 

i 

2 

8 

^ 

§ 

§ 

§ 

9 

*   a 

\ 

0 

^ 

0 
V 

q 
« 

0 

K. 

Q 

<*. 

0 

°i 

Q 

2 

0 

^ 

FIG.    14.     Transmission    loss    of    filter-type    dividing    networks. 

378  H.  R.  KlMBALL  [J.  S.  M.  P.  E. 

attenuation  it  should  be  remembered  that  increased  attenuation  is 
accompanied  by  increased  loss  in  the  transmitting  ranges,  which, 
for  high-powered  systems  at  least,  is  to  be  avoided.  Costs  also  may 
mount  unreasonably  if  a  large  amount  of  filtering  is  employed.  For 
these  reasons,  and  considering  the  magnitude  of  the  irregularities 
that  one  speaker  produces  in  the  transmitting  range  of  the  other,  it 
appears  that  few  dividing  networks  should  employ  more  attenua- 
tion than  about  18  db.  per  octave. 

In  a  two-way  system,  the  frequency  at  which  both  sets  of  loud 
speakers  receive  equal  amounts  of  energy  is  called  the  cross-over 
point.  In  other  words,  the  cross-over  point  is  the  point  of  separation 
between  the  two  bands  of  frequencies.  In  developing  loud  speaker 
systems  a  trial  cross-over  point  is  usually  arbitrarily  selected,  keeping 
in  mind  the  characteristics  of  the  upper-  and  lower -range  speakers 
that  are  to  be  used,  and  the  costs  and  other  items.  This  point  is 
then  later  moved  one  way  or  the  other  if  found  unsatisfactory  when 
the  system  is  operated  as  a  whole. 

A  two-way  dividing  network  consists  of  a  low-pass  filter  and  a 
high-pass  filter  designed  to  operate  from  a  common  source  at  their 
input  terminals.  Two  methods  are  in  general  use  for  connecting  the 
filters  in  series  or  in  parallel  at  their  input  terminals;  namely,  (1) 
the  filter  method;  and  (2)  the  constant-resistance  method.  Each 
of  these  methods  is  capable  of  good  results.  The  filter  method  is 
the  more  commonly  used — probably  because  it  is  better  known,  and 
is  somewhat  more  flexible  in  design. 

Fig.  13  shows  circuits  for  four  filter  type  dividing  networks.  Cir- 
cuits (c)  and  (d)  are  the  more  commonly  used  in  practice.  The 
symbol  RQ  denotes  the  resistance  of  the  speakers  connected  to  the 
low-frequency  and  high  frequency  terminals.  The  symbol  fa  denotes 
the  cross-over  frequency.  The  transmission  characteristics  for  these 
networks  are  shown  in  Fig.  14. 

Fig.  15  shows  four  types  of  constant-resistance  dividing  networks. 
For  these  networks,  circuits  B  and  D  are  the  more  commonly  used. 
Here  again  the  symbol  RQ  is  used  to  denote  the  speaker  resistances 
and  fa  indicates  the  cross-over  frequency.  These  networks  measure 
a  constant  resistance  at  the  input  terminals  when  the  proper  loads 
are  connected  to.  the  speaker  terminals.  Fig.  16  shows  the  transmis- 
sion characteristics  for  the  different  circuits. 

Variable  Networks. — Networks  whose  transmission  characteristics 
may  be  smoothly  varied  over  a  wide  range  by  means  of  a  single 


Oct.,  1938] 


APPLICATION  OF  ELECTRICAL  NETWORKS 


379 


R0 

m 

-co                r$R 

«0 

JPUT 

RO 
L°                 SP 

RO=LOW- 
FREQUENCY 

SPEAKERS 


RO»HIGH- 
FREQUENCY 

SPEAKERS 


Circuit  A 


RO»  LOW- 
FREQUENCY 
SPEAKERS 


£NCY 
SPEAKERS 


-%r~^ 

Circuit  B 


Rg=LOW- 
'                                               FREQUENCY                                                                  r 
"                                             SPEAKERS                                                                  *< 

ROSLOW- 

=  FREQUENCY 
SPEAKERS 

\F°           o 

f               f.     . 

RQ=HICH- 
FREQUENCY 

SPEAKERS 

Lj 

FREQUENCY 
SPEAKERS 

Circuit  C                                          Circuit  D 

L,  -  -^                  L,  =  ^                  L,  =  V2L, 

Ci  =  V2C0 


fa  =  cross-over  frequency  of  network 
FIG.  15.     Constant-resistance  dividing  networks. 


FIG.  16.  Constant-resistance  network — insertion  loss;  (-4)  net- 
work of  circuits  A  and  C,  Fig.  15;  (B)  networks  of  circuits  B  and  D, 
Fig.  15. 


380  H.  R.  KlMBALL 

control  are  especially  useful  in  the  re-recording  work  of  motion  pic- 
ture studios.  At  the  time,  however,  the  methods  available  for  engi- 
neering such  networks  are  not  all  that  can  be  desired,  with  the  result 
that  occasionally  the  re-recording  mixers  are  somewhat  handicapped 
in  their  technic.  The  requirements  for  variable  networks  are  three 
in  number:  namely,  (1)  minimum  loss  for  the  result  accomplished, 
(2)  constant-resistance  impedances  at  the  input  and  output  terminals, 
and  (3)  a  smoothly  variable  transmission  characteristic. 

The  networks  now  in  use  usually  attempt  partially  to  meet  these 
requirements  by  a  variety  of  methods.  One  common  method  is  to 
provide  constant  resistance  and  minimum  loss  by  varying  the  trans- 
mission characteristic  in  a  step-by-step  manner.  This  is  done  by 
multiple  switching  arrangements  to  connect  to  tapped  electrical 
elements.  This  method  results  in  a  complicated  mechanical  and 
electrical  structure  and  often  introduces  noise  in  the  circuit  while 
the  step  changes  are  being  made.  In  addition,  it  is  often  necessary 
to  compromise  on  the  network  design  because  of  the  added  mechani- 
cal difficulties. 

Another  method  in  common  use  is  to  sacrifice  the  constant-resis- 
tance and  minimum-loss  features  in  order  to  provide  a  smoothly  vary- 
ing transmission  characteristic  by  means  of  potentiometer-type  vari- 
able resistors  inserted  somewhere  in  the  circuit.  Aside  from  the 
above-mentioned  sacrifices  the  chief  difficulty  with  this  method  is  that 
flexibility  of  design  is  not  realized,  with  the  result  that  even  the 
transmission  characteristic  is  a  compromise.  The  greatest  advantage 
of  this  method  is  simplicity  of  mechanical  and  electrical  structure. 

It  is  hoped  that  in  the  not  too  distant  future  a  more  suitable  design 
technic  will  be  made  available  for  this  purpose.  Whether  this  will 
require  the  development  of  entirely  new  network  structures  or  altera- 
tion of  existing  structures  the  writer  is  not  able  to  say. 

REFERENCES 

1  "Motion  Picture  Sound  Engineering,"  D.    Van  Nostrand  Co.,  New  York, 
N.  Y.  (1938);    ed.  by  Academy  of  Motion  Picture  Arts  &  Sciences,  Hollywood, 
Calif. 

2  Ibid.,  pp.  260-272. 


MULTIPLE-CHANNEi:  RECORDING* 
H.  G.  TASKER** 


Summary. — Multiple-channel  recording  is  a  device  for  achieving  flexibility  at  the 
time  of  dubbing  or  re-recording  orchestral  music  presented  as  such  in  the  picture.  If 
one  could  predict  for  the  music  and  sound  departments  which  portions  of  the  orchestra 
would  be  seen  from  which  angles  in  the  final  picture,  or  if  the  editing  could  be  com- 
pleted before  the  music  was  recorded,  there  would  be  less  merit  in  multiple-channel 
recording. 

The  reverse  is  true:  The  music  is  recorded  first,  the  musicians  photographed  later, 
synchronizing  their  movements  to  a  play-back  of  record.  Meanwhile,  the  pictorial 
treatment  has  taken  partial  shape  in  the  minds  of  producer  and  director.  Still  later 
it  takes  final  shape  in  the  hands  of  the  film  editor.  Sound  and  action  are  then  placed 
in  the  hands  of  the  sound  department  for  dubbing,  but  it  is  then  too  late  for  more  than 
an  ineffectual  raising  and  lowering  of  volume.  The  violins  or  the  woodwinds  can  not 
be  lifted  above  the  surrounding  sections  to  match  a  close-up  of  the  picture. 

The  multiplicity  of  sound-tracks  (recorded,  of  course,  in  advance  of  the  photography) 
provides  the  dubbing  mixer  with  the  means  of  easily  blending  a  final  sound-track  that 
will  be  wholly  in  keeping  with  the  final  edition  of  the  picture.  The  application 
of  this  method  to  the  recent  production  "100  Men  and  a  Girl"  is  described.  The  use 
of  "close-mix"  tracks,  separate  vocal  tracks,  etc.,  in  conjunction  with  multiple  record- 
ing is  also  described. 

In  the  case  of  expensive  sound  sources,  such  as  symphony  or- 
chestras, it  has  long  been  the  practice  to  make  two  or  more  identical 
records  from  a  given  source  of  sound  by  employing  two  or  more  re- 
cording machines  each  of  which  is  ordinarily  energized  from  some 
common  point  in  the  amplifying  channel  but  which  might  equally 
well  be  assigned  a  complete  channel  of  its  own.  In  contrast  to  this 
procedure  the  term  "multiple-channel  recording"  as  used  in  this 
paper,  refers  to  the  use  of  a  number  of  recording  machines  each  as- 
sociated with  a  separate  and  complete  sound  channel  to  make  simul- 
taneous records  of  different  aspects  of  a  complex  sound  source. 

A  simple  form  of  multiple-channel  recording  has  been  practiced  in 
Hollywood  for  a  number  of  years  wherein  the  vocal  effort  of  a  soloist 
is  recorded  through  one  channel  while  simultaneously  the  accompany- 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C. 
**  Universal  Pictures  Corp.,  Universal  City,  Calif. 

381 


382  H.  G.  TASKER  [j.  s.  M.  P.  E. 

ing  orchestration  is  recorded  through  another  channel.  This  pro- 
cedure affords  several  advantages  which  will  be  mentioned  later,  but 
among  them  is  one  that  inspired  the  much  more  extensive  multiple- 
channel  recordings  that  form  the  principal  subject  of  this  paper. 
This  advantage  lies  in  the  ability  to  postpone  the  "balancing"  (that 
is,  the  adjustment  of  relative  loudness)  of  the  two  principal  sound 
elements  (vocal  and  instrumental)  until  the  picture  has  reached  its 
finishing  or  dubbing  stage. 

The  magnitude  of  this  advantage  can  be  best  appreciated  when  it 
is  remembered  that  musical  numbers,  especially  vocal  ones,  are  al- 
most always  pre-recorded.  In  this  method  the  sound-track  is  re- 
corded before  the  picture  is  photographed,  the  latter  taking  place  by 
the  process  known  as  "playback"  wherein  the  vocalist  sings  a  duet 
with  herself  and  each  of  the  instrumentalists  plays  a  duet  with  him- 
self as  the  original  record  is  played  back  on  the  set  during  the  photo- 
graphing. This  is  repeated  for  as  many  different  angles,  close-ups, 
long  shots,  etc.,  as  are  desired,  and  as  many  takes  of  each  as  may  be 
required  to  obtain  the  desired  degree  of  perfection.  Following  the 
photographic  step  the  scene  is  edited  by  intercutting  the  various 
takes  and  angles  until  the  best  possible  entertainment  or  story  values 
have  been  incorporated  in  the  scene. 

Now,  if  all  our  producers,  directors,  musical  directors,  and  music 
mixers  were  supergeniuses,  then  the  music  mixer  might,  by  con- 
ferring with  the  others,  successfully  visualize  the  exact  form  that  the 
final  edited  scene  should  take,  and  hence  could  balance  the  sound  at 
the  time  of  recording  for  a  perfect  interpretation  of  the  scene.  Not- 
withstanding the  claims  of  studio  press  agents  to  the  contrary,  no 
such  degree  of  genius  exists  in  Hollywood,  and  every  attempt  to 
balance  the  vocal  and  instrumental  portions  of  recording  for  the  final 
editing  has  proved  in  some  measure  disappointing;  hence  the  de- 
sirability of  postponing  the  balancing  until  all  the  creative  work 
of  producer,  director,  and  editor  has  crystallized  in  the  edited  film. 
This  obvious  benefit  to  the  rendition  of  vocal  numbers  is  realized  with 
very  little  complexity  of  the  recording  system  since  only  two  separate 
channels  are  required,  one  for  the  voice  and  one  for  the  orchestra. 

Extension  of  this  idea  to  the  rendition  of  strictly  orchestral  music, 
as  for  example,  a  number  by  a  famous  band  or  symphonic  orchestra, 
involves  much  more  complexity  because  it  is  desired  to  feature  on  the 
screen  from  moment  to  moment  various  sections  of  the  orchestra, 
pr  even  individual  performers,  and  to  provide  acoustic  balance  ap- 


Oct.,  1938]  MULTIPLE-CHANNEL  RECORDING  383 

propriate  to  the  scene  in  all  cases.  To  Leopold  Stokowski,  famed 
conductor  of  the  Philadelphia  Symphony  Orchestra,  goes  credit  for 
the  first  application  of  this  method  to  tjie  rendition  of  large  orchestral 
numbers  in  the  motion  picture  production  One  Hundred  Men  and  a 
Girl.  He  was  not  without  opposition  from  skeptics  in  both  technical 
and  non-technical  ranks,  including  those  who  questioned  whether 
the  re-recording  machinery  could  ever  synchronize  the  resulting  six 
or  eight  sound-tracks  to  the  required  degree. 

Preliminary  study  convinced  us,  however,  that  this  objection  was 
not  serious.  We  had  had  extensive  experience  with  a  technic  known 
as  "close  mixing,"  in  which  a  microphone  is  supplied  for  each  principal 
section  of  the  orchestra — for  example,  violins,  cellos,  woodwinds, 
brasses,  etc. — the  several  microphone  outputs  being  fed  to  a  mixer 
panel  where  they  are  suitably  balanced  before  the  recording.  In  this 
method  the  directional  properties  of  ribbon  microphones  are  employed 
to  give  best  possible  separation  between  the  several  sections,  yet  it 
is  obvious  that  the  violin  microphone  will  pick  up  some  of  the  energy 
from  each  of  the  other  sections  and  each  other  microphone  will  do 
likewise.  Since  the  microphones  are  placed  at  an  average  of  eight 
feet  apart  there  is  considerable  delay  between  the  arrival  of  the  violin 
sounds  at  the  violin  microphone  and  its  arrival  at  the  other  micro- 
phones. This  is  identical  in  effect  to  the  slight  errors  of  synchroniza- 
tion that  might  occur  in  multiple-channel  recording  and  results  in  a 
reverberant  quality  but  which  is  never  as  severe  as  is  the  reverberant 
effect  when  recording  with  a  single  microphone  placed  far  enough 
away  to  be  equidistant  from  most  of  the  sections  of  the  orchestra. 

It  is  obvious  that  the  degree  of  synchronism  need  only  be  compar- 
able to  that  of  the  several  microphones  placed  throughout  the  orches- 
tra. The  available  degree  of  synchronism  being  approximately  Y2 
frame,  corresponding  to  about  25  feet  of  air  distance,  we  concluded, 
and  experience  later  proved,  that  no  difficulty  would  be  encountered 
from  this  source. 

In  connection  with  these  recordings  for  One  Hundred  Men  and  a 
Girl  there  was  more  than  ordinary  need  for  such  an  arrangement  to 
permit  postponing  the  balancing  of  the  orchestra:  the  recordings 
were  to  be  made  in  April  for  a  picture  that  was  to  begin  production 
in  May ;  they  were  to  be  recorded  in  Philadelphia  for  a  picture  to  be 
photographed  in  Hollywood ;  and  the  scenes  in  which  they  would  be 
employed  had  not  yet  fully  crystallized  in  the  minds  of  the  writers  and 
producer.  With  these  facts  in  mind,  we  requested  the  RCA  Manu- 


384  H.  G.  TASKER  [j.  s.  M.  P.  E. 

facturing  Company  to  provide  at  the  Academy  of  Music  in  Phila- 
delphia eight  separate  channels.  Six  were  to  be  used  for  the  simul- 
taneous recording  of  the  several  sections  of  the  orchestra,  one  to 
record  the  orchestra  as  a  whole  from  a  pair  of  overall,  or  "long-shot" 
microphones,  and  one  to  record  the  voice  of  Deanna  Durbin  with 
orchestral  accompaniment.  In  view  of  the  considerable  expense  of 
assembling  the  talent  and  equipment  for  these  recordings  it  seemed 
the  better  part  of  wisdom  to  provide  one  more  channel  equipped 
with  six  microphones  and  a  conventional  mixer  panel  so  that  our 
usual  close-mixed  track  could  be  made  simultaneously,  as  a  protec- 
tion in  case  anything  went  wrong  with  any  other  part  of  the  system. 
Each  of  the  separate  channels  consisted  of  a  microphone,  the  custom- 
ary amplifier,  and  gain  controls,  and  the  recording  machine ;  and  was 
manned  by  a  mixer  and  a  recordist.  The  close-mix  channel  had  six 
microphones  and  a  six-position  mixing  panel  controlled  by  Mr.  Bern- 
ard Brown,  head  of  the  music  and  dubbing  section  of  Universal's 
Sound  Department,  who  was  sent  to  Camden  as  our  representative 
for  the  whole  recording  operation.  The  six  microphones  of  the  "close- 
mix"  channel  were  placed  as  close  as  possible  to  the  six  "separate 
channel"  microphones,  respectively.  With  these  arrangements  all  the 
symphonic  and  two  vocal  numbers  for  the  picture  were  recorded. 

The  great  merit  of  multiple-channel  recording  is  especially  well 
demonstrated  in  this  motion  picture  by  the  rendition  of  Liszt's  Second 
Hungarian  Rhapsody  on  the  staircase  of  Stokowski's  home.  The 
director,  Henry  Koster,  chose  to  portray  a  great  deal  of  this  scene  in 
a  series  of  "approach"  shots  to  the  several  sections  of  the  orchestra 
and  to  various  principals  of  the  story.  When  the  resulting  edited 
picture  was  experimentally  projected  with  the  conventional  close- 
mixed  track  it  was  found  to  be  quite  "flat"  and  unconvincing.  It  al- 
most completely  lacked  the  inspiring  vigor  that  it  later  acquired  as  a 
result  of  appropriate  mixing  from  the  individual  tracks  of  the  multi- 
ple-channel recording. 

While  multiple-channel  recording,  as  just  described,  can  yield  re- 
markable results  in  connection  with  the  rendition  of  orchestral  num- 
bers, the  number  of  such  scenes  that  occur  in  the  course  of  a  year's 
production  in  any  one  studio  is  relatively  small  and  it  could  not  be 
expected  to  find  a  very  extensive  field  of  application  unless  it  were  to 
prove  materially  helpful  in  the  more  common  type  of  musical 
numbers,  namely,  vocal.  However,  the  instrumental  accompaniment 
/or  vocal  numbers  has  little  need  of  the  discriminative  balancing  of 


Oct.,  1938]  MULTIPLE-CHANNEL  RECORDING  385 

sections  from  moment  to  moment  because  its  level  must  be  low 
enough  to  accompany  the  voice  of  a  singer  suitably  and  because  in- 
dividual sections  of  the  orchestra  are  rarely  featured  on  the  screen 
during  such  a  number. 

For  these  reasons  the  simple  form  of  multiple-channel  recording 
mentioned  earlier  has  been  adopted  as  the  standard  method  of  re- 
cording vocal  numbers  at  this  studio  except  for  the  inclusion  of  a  third 
channel.  On  this  third  channel  is  produced  a  combined  vocal  and 
orchestral  track  which  serves  a  double  purpose.  It  affords  protec- 
tion in  the  event  of  failure  of  either  of  the  other  two  tracks,  and 
provides  an  immediately  available  work-track  in  which  the  two  ele- 
ments are  reasonably  well  blended. 

To  simplify  the  operations  of  this  three-channel  system  the  mixer 
dial  of  the  vocal  channel  appears  on  the  same  panel  with  the  six 
mixer  dials  of  the  orchestral  channel.  Their  outputs  are  led  sepa- 
rately through  their  respective  channels  to  their  respective  recording 
machines,  but  by  means  of  bridging  amplifiers  the  third  channel  plus 
the  mixer's  monitor  circuit  are  energized  from  the  combined  outputs 
of  the  vocal  and  orchestral  microphones. 

In  addition  to  the  advantage  already  described  for  such  a  system 
a  second  important  advantage  is  often  gained  in  that  it  is  not  neces- 
sary to  obtain  simultaneously  a  perfect  orchestral  recording  and  a 
perfect  vocal  recording  plus  a  perfect  balance  of  each  with  respect  to 
the  other.  If,  for  example,  a  vocalist  is  not  adequately  rehearsed  or 
becomes  "out  of  voice"  it  is  possible  to  make  the  instrumental  track 
first  and  then  dismiss  the  expensive  orchestra  (often  $500  to  $700  per 
hour)  and  arrange  for  the  vocal  recording  on  the  following  day  or  at 
any  convenient  time  after  a  choice  take  of  the  instrumental  track  has 
been  developed  and  printed.  In  this  subsequent  recording  the  vocalist 
hears  the  reproduced  instrumental  track  through  the  headphones  and, 
singing  to  this  accompaniment,  repeats  the  performance  so  often  as 
necessary  until  a  perfect  vocal  recording  has  been  made.  Especially 
in  the  case  of  young  or  nervous  performers,  the  total  absence  of  the 
orchestra  and  any  accompanying  high  pressure  often  proves  very 
helpful.  Since  the  orchestral  track  is  not  being  re-recorded  at  this 
time,  but  will  be  combined  with  the  vocal  track  at  a  later  date,  ar- 
rangements are  made  to  aid  the  mixer  in  his  judgment  of  the  vocal 
quality  by  introducing  the  desired  level  of  the  orchestra  into  his 
monitor  through  bridging  amplifiers,  so  that  his  basis  of  judgment  is 
almost  identically  the  same  as  if  the  orchestra  were  present. 


SOME  UNUSUAL  ADAPTATIONS  OF   16-MM.  EQUIPMENT 
FOR  SPECIAL  PURPOSES* 


J.  L.  BOON** 


Summary. — A  casual  observer,  looking  over  the  existing  standard  amateur  photo- 
graphic equipment,  would  probably  be  of  the  opinion  that  there  is  little  need  of  altering 
a  camera  to  do  a  special  job.  However,  closer  observation  of  the  various  problems  that 
photography  serves  reveals  that  the  standards  of  practice  have  been  chosen  merely  to 
suit  the  needs  of  a  common  majority  of  users,  and  the  minority  are  almost  forgotten. 
Further  observations  show  that  an  alteration  to  a  standard  camera  to  make  it  fit  a 
specific  purpose  usually  precludes  its  usefulness  for  many  of  the  purposes  for  which 
it  was  originally  designed,  and  also  its  utility  for  other  special  purposes. 

In  this  paper  are  made  known  some  of  the  unusual  adaptations  of  16-mm.  motion 
picture  equipment,  each  to  fulfill  a  definite  purpose,  and  it  is  shown  that  industry  is 
becoming  more  conscious  of  the  utility  of  such  photographic  equipment  as  tools  in 
solving  some  of  its  problems. 

A  casual  observer  looking  over  the  existing  standard  amateur 
photographic  equipment  would  probably  be  of  the  opinion  that  there 
is  little  need  for  altering  a  camera  to  do  a  special  job.  However,  closer 
observation  of  the  various  problems  that  photography  serves  reveals 
that  the  standards  of  practice  have  necessarily  been  chosen  primarily 
to  suit  the  needs  of  a  majority  of  users.  Usually  an  alteration  to  a 
standard  camera  to  make  it  fit  a  specific  purpose  precludes  its  use- 
fulness for  many  of  the  purposes  for  which  it  was  originally  designed 
and  also  its  utility  for  other  special  purposes. 

At  one  time  some  of  the  features  now  included  on  standard  motion 
picture  equipment,  such  as  speeds  other  than  normal,  lenses  of  various 
focal  lengths,  variable  shutter  openings,  etc.,  would  have  come 
within  the  scope  of  this  paper.  The  incorporation  of  these  features 
in  standard  cameras,  however,  has  not  decreased  the  inflow  of  requests 
for  equipment  for  special  uses. 

Extension  of  Camera  Speed  Range. — Fortunately,  the  simplest 
form  of  alteration  is  the  one  most  often  requested,  that  is,  the  ex- 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;    received 
April  19,  1938. 

**  Eastman  Kodak  Co.,  Rochester,  N,  Y. 

386 


ADAPTATIONS  OF  16-MM.  EQUIPMENT 


387 


tension  of  the  speed  range.  At  one  end  of  the  range,  exposure  in- 
intervals  of  as  long  as  one  per  day  would  be  useful.  If  the  long  in- 
terval is  also  a  fixed  interval,  a  simple  method  of  achieving  the  result 
is  to  let  a  continuously  running  synchronous  clock  motor  wind  a 
small  coiled  spring  one  turn  per  fixed  time  interval,  at  the  completion 
of  the  turn  releasing  the  spring,  which  then  drives  the  camera  shutter 


FIG.  1. 


Electric  release  and  control  for  making  exposure 
at  variable  intervals. 


and  pull-down  through  one  revolution,  exposing  and  advancing  the 
film.  The  motor  may  also  close  a  light  circuit  for  illuminating  the 
subject  during  the  exposure  interval.  If  greater  accuracy  of  timing  is 
required  than  such  an  arrangement  permits,  the  motor  is  stopped  after 
one  turn  of  spring  winding,  and  an  external  impulse  releases  the 
spring  for  driving  the  camera  and  also  starts  the  spring-winding  mo- 
tor. Another  method  proposed  for  limited  use  is  to  enclose  the  camera 
and  subject  in  a  light-tight  box,  moving  the  film  continuously  or 


388 


J.  L.  BOON 


[J.  S.  M.  P.  E. 


intermittently.  The  exposure  is  made  by  flashing  a  light  by  means 
of  an  accurate  external  source.  The  resulting  film  would  probably 
be  unsatisfactory  for  motion  picture  projection,  but  individual  frames 
could  be  viewed  or  enlarged. 

A  variable-interval  device  operating  automatically  has  been  manu- 
factured for  the  Cine  Kodak  Special  (Fig.  1).  Timing  is  accomplished 
by  means  of  a  condenser  discharge  operating  a  relay,  which  in  turn 
sends  an  electrical  impulse  to  a  solenoid  on  the  camera  single-frame 
shaft.  The  camera  spring  furnishes  the  driving  power  for  the  mecha- 
nism; the  solenoid  merely  allows  the  single-frame  shaft  to  make 
one  or  one-half  a  turn.  Batteries  are  included  with  the  control  box, 


Film 
Plane  1 


Reference 
Point  1 


FIG.  2.  Plan  for  taking  pictures  of  take-off  and  land- 
ing of  airplanes,  showing  image  displacement  for  two  dis- 
tances (not  drawn  to  scale). 


eliminating  a  further  source  of  power.    A  secondary  interval  multi- 
plier increases  the  interval  range  at  the  longer  end. 

Although  there  are  many  uses  for  cameras  with  long  intervals  be- 
tween exposures,  the  majority  of  requests  are  for  cameras  that  operate 
at  speeds  greater  than  normal.  Many  motion  picture  cameras,  other 
than  those  for  sound,  will  operate  at  64  pictures  per  second.  For 
most  motion  analysis  this  speed  merely  indicates  what  might  be 
learned  if  higher  camera  speeds  were  used.  It  is  not  very  difficult  to 
drive  a  camera  at  120  frames  per  second,  but  driving  it  on  batteries 
with  a  speed  variation  of  less  than  0.5  per  cent  is  somewhat  more 
difficult.  It  was  done,  however,  by  using  a  synchronous  motor  for 
driving  the  camera;  and  by  changing  the  gear  ratio  between  the 
motor  and  the  camera,  various  camera  speeds  were  attained,  each 
within  close  tolerance. 


Oct.,  1938]  ADAPTATIONS  OF  16-MM.  EQUIPMENT  389 

Photographing  Airplane  Take-Off  and  Landing. — A  method  was  de- 
vised for  the  Department  of  Air  Commerce  for  measuring  the  distance 
and  altitude  of  an  airplane  as  it  makes  a  take-off  or  landing.1  Two 
Cine  Kodak  Specials  sixty  feet  apart,  or  multiples  thereof,  were  used 
to  photograph  the  runway  (Fig.  2).  It  was  found  that  pictures  taken 
at  the  rate  of  four  per  second  gave  satisfactory  readings.  This  speed 
could  be  attained  readily  and  synchronously  by  using  a  solenoid 
release  on  each  camera  and  operating  both  on  a  single  impulse  from 
the  control  box.  Matched  lenses  of  21/2-hich  focal  length  were  used. 
The  cameras  were  slightly  "toed  in"  to  converge  in  field  at  a  distance 


FIG.  3.  Side  view  of  twin  projectors  used  in  taking 
data  from  pictures  of  the  take-off  and  landing  of  air- 
planes. 

of  1600  feet  for  the  60-foot  base  line,  3200  feet  for  the  120-foot  base 
line,  etc. 

It  was  necessary  to  build  a  special  twin  projector  for  taking  read- 
ings from  the  film,  since  slight  displacements  of  the  airplane  images 
on  the  two  films  had  to  be  measured  at  the  same  time  (Figs.  3  and  4). 
A  separate  projector  is  used  for  each  roll  of  film  of  the  pair,  but 
both  films  are  advanced  frame  by  frame  by  a  common  drive,  so  that 
right  and  left  pictures  move  in  synchronism  after  they  have  once  been 
set  in  matched  pairs.  Geneva  drives  are  used  and  the  film  is  held  in 
the  gate  between  glass  plates  which  separate  as  the  film  is  moved. 
The  lens  on  one  projector  is  movable  horizontally  and  that  on  the 
other  vertically  so  that  corrections  may  be  made  for  slight  film  dis- 
placements. All  the  controls  are  operated  from  the  viewing  side 


390  J.  L.  BOON  [j.  s.  M.  P.  E. 

of  the  two  adjacent  translucent  projection  screens.  The  two  images 
of  the  airplane  taken  at  the  same  time  gradually  separate  as  the  air- 
plane moves  farther  away.  This  separation  is  measurable  directly 
in  feet  by  means  of  a  special  transparent  scale  at  the  projection 
screen,  to  a  distance  of  about  2500  feet  with  a  60-foot  camera  base 
line.  From  the  distance  reading,  the  altitude  is  also  read  directly  on  the 
scale.  The  camera  base  line  may  be  increased  so  that  distances  of 
more  than  2500  feet  are  readable  on  the  scale. 

A  " Shutterless"  Camera. — In  making  a  motion  picture  camera  for 
recording  a  subject  of  low  intensity,  such  as  the  x-ray  image  on  a 


FIG.  4.     Screen  and  direct-reading  scale  for  measuring 
altitude  and  distance  of  airplane. 

fluorescent  screen,  it  is  not  only  necessary  to  use  the  fastest  lens  and 
film  available,  but  also  a  shutter  of  almost  100  per  cent  efficiency; 
that  is,  no  shutter  at  all.  This  means  that  the  pull-down  time  must 
be  less  than  5  per  cent  of  the  exposure  time  to  eliminate  travel-ghost. 
A  spring  was  attached  to  the  pull-down  claw  in  such  a  way  as  to  ac- 
celerate its  film  pull-down  motion.  An  overrunning  clutch  was  at- 
tached to  the  pull-down  shaft  to  prevent  any  chance  of  reverse  mo- 
tion of  the  pull-down.  The  shaft  is  independent  of  the  drive  in  its 
forward  motion,  but  the  motion  ceases  at  completion  of  the  pull- 
down stroke;  until  a  driver,  which  runs  concentrically  with  the  pull- 
down shaft  and  which  turns  at  a  definite  speed,  catches  up  with  it  and 
rotates  it  through  the  remaining  half  of  the  stroke.  This  driving  also 
stretches  the  spring  to  full  tension  so  that  it  is  again  in  position  to 


Oct.,  1938]  ADAPTATIONS  OF  16-MM.  EQUIPMENT  391 

accelerate  the  pull-down  of  the  film  when  the  driver  rotates  the  pull- 
down shaft  a  little  beyond  dead  center.  The  tension  in  the  spring 
determines  the  pull-down  speed,  and  the  exposure  time  is  approxi- 
mately the  reciprocal  of  the  number  of  pictures  taken  per  second.  It 
was  thought  that  8  pictures  a  second  would  be  the  most  satisfactory 
compromise,  and  in  order  to  project  these  pictures  at  the  taking  speed 
without  flicker,  a  projector  was  altered  to  give  48  shutter  interrup- 
tions at  a  film  speed  of  8  frames  a  second.  This  could  be  done  without 
destroying  the  balance  between  blurring  and  stuttering  of  the  screen 
image,  since  the  motion  photographed  is  somewhat  slower  than 
normal.  Alterations  in  the  projector  involved  doubling  the  shutter 
shaft  speed  with  respect  to  the  pull-down  up-and-down  motion  and 
a  change  in  the  in-and-out  pull-down  motion  to  decrease  the  time  that 
the  pull-down  claw  is  engaged  with  the  film. 

Abnormal  Picture  Proportions. — Requests   for   abnormal   picture 
proportions  have  been  few  but  are  usually  well  founded.     A  recent 


FIG.  5.     Stereoscopic  pictures  on  16- mm.  film  mounted  in  a  cassette. 

one  was  for  motion  pictures  on  16-mm.  film  with  the  height-to-width 
ratio  changed  from  3  X  4  to  4  X  3.  This  could  be  accomplished  quite 
easily  by  photographing  with  the  camera  on  its  side.  The  problem  of 
altering  a  standard  projector  to  give  an  erect  image  was  a  bit  more 
difficult.  Prisms  or  mirrors  in  the  optical  path  were  tried  and  found 
satisfactory  under  laboratory  conditions  but  were  subject  to  strain, 
collected  dust,  and  caused  considerable  loss  of  light.  This  led  to 
trying  the  same  trick  on  the  projector  as  on  the  camera,  that  is,  turn- 
ing it  on  its  side.  The  lamp  house  was  rebuilt  so  that  the  lamp 
burned  in  a  vertical  position,  and  the  supporting  base  was  remade 
to  suit  the  conditions.  In  general,  this  has  proved  quite  satisfactory, 
and  it  is  thought  that  slight  unsteadiness,  which,  of  course,  shows 
up  horizontally  instead  of  vertically,  is  less  noticeable. 

The  same  customer  requested  also  a  means  of  photographing  a 
subject,  making  several  thousand  small,  still  pictures  in  color  in  a 
short  period  of  time,  and  projecting  ten  or  twelve  pictures  of  different 
subjects  on  a  translucent  screen  with  an  automatic  means  of  changing 


392  J.  L.  BOON 

the  picture  after  a  fixed  time  interval.  Although  these  pictures  were 
to  be  used  as  stills,  it  seemed  necessary  to  take  them  in  a  motion 
picture  camera,  since  they  had  to  be  made  in  a  short  period  of  time 
and  were  to  be  in  color.  The  most  satisfactory  height-to-width 
ratio  was  found  to  be  3  to  2.  On  16-mm.  sound-film,  the  maximum 
width  that  can  be  used  for  pictures  is  about  l/2  inch,  which  would 
make  the  height  about  2x/2  frames.  Allowing  tolerance  for  mounting, 
a  little  more  than  three  frames  was  desirable  for  each  picture.  With 
this  much  known,  alterations  on  a  Cine  Kodak  Special  were  begun. 
The  aperture  in  the  gate  was  increased  in  width  and  height,  the  pull- 
down stroke  doubled,  the  sprocket  speed  doubled,  and  the  shutter 
speed  cut  in  half.  With  the  increased  angle  subtended  by  the  aper- 
ture from  the  shutter  center,  it  was  necessary  to  decrease  the  shutter 
opening.  Exposure  with  the  camera  running  at  four  pictures  a  second 
is  about  the  same  as  with  a  normal  16-mm.  camera  at  normal  speed. 

Two  cameras  of  this  type  were  built  to  operate  side  by  side  from 
the  same  power  source,  doubling  the  output  or  making  stereoscopic 
pairs.  The  film  could  be  processed  normally  and  the  individual  pic- 
tures cut  to  fit  die-cast  cassettes  (Fig.  5).  These  cassettes  hold  ten 
pictures  or  five  pairs  of  stereoscopic  pictures,  each  stereoscopic  pair 
being  mounted  with  interocular  separation.  The  cassettes  then  serve 
two  purposes.  They  may  be  used  in  a  simple  stereoscope  for  single- 
station  viewing,  or  projected  singly  upon  a  screen.  The  projector 
built  for  the  latter  purpose  consisted  of  lamp  house,  condenser,  and 
projection  optics,  translucent  screen,  and  the  cassette  carrier  and  as- 
sociated mechanism.  The  mechanism  allows  each  picture  to  be 
projected  for  about  eight  seconds  and  then  advances  the  cassette 
holders  for  the  next  picture  to  be  projected. 

The  Eastman  high-speed  camera,2  the  race-timing  camera,3  and 
the  associated  rapid  developing  and  enlarging  unit3  have  already 
been  described  in  the  JOURNAL. 

REFERENCES 

1  "To  End  Guessing  on  Runway  Lengths,"  American  Aviation,  1  (July  15,  1937), 
No.  4. 

2  TUTTLE,   F.   E.:     "A  Non-Intermittent  High-Speed  16-Mm.  Camera,"   /. 
Soc.  Mot.  Pict.  Eng.,  XXI  (Dec.,  1933),  No.  6,  p.  474. 

3  TUTTLE,  F.  E.:    "Photographic  Race-Timing  Equipment,"  /.  Soc.  Mot.  Pic. 
Eng.,  XXVII  (Nov.,  1936),  No.  5,  p.  529. 


AN  IMPROVED  ROLLER  TYPE  DEVELOPING  RACK  WITH 
STATIONARY  DRIVE* 


C.  E.  IVES** 


Summary. — In  a  previous  paper  a  rack  was  described  that  provided  for 
continuous  motion  of  a  200-ft.  length  of  motion  picture  film  during  processing  but 
could  be  used  with  the  rack-and-tank  equipment.  The  purpose  of  this  roller  rack 
was  to  give  a  type  of  treatment  in  processing  essentially  similar  to  that  given  by 
a  continuous  machine  while  retaining  the  features  of  batch  equipment  that  are 
helpful  in  experimental  processing. 

The  rack  previously  described  included  a  built-in  driving  motor  and  reduction 
gear,  an  arrangement  that  was  most  feasible  for  a  single  unit.  With  more  extensive 
use  it  became  desirable  to  have  multiple  units  operated  from  stationary  drives  at  the 
tanks  and  at  the  loading  and  unloading  stations. 

A  new  design  has  been  worked  out  in  which  the  weight  of  the  rack  was  reduced 
greatly  by  the  use  of  stationary  drives.  Further  reduction  in  weight  was  attained 
by  the  substitution  of  tensioning  springs  for  the  weighted  supporting  beam  associated 
with  the  movable  lower  shaft  in  the  earlier  model.  This  shaft  was  mounted  upon  the 
frame  by  lever  arms  in  such  a  way  as  to  use  the  torsional  rigidity  of  the  shaft  itself 
to  maintain  it  parallel  to  the  upper  shaft  while  allowing  it  the  necessary  vertical 
movement. 

In  an  earlier  paper1  a  rack  was  described  which  provided  for  con- 
tinuous motion  of  a  200-ft.  length  of  motion  picture  film  during  proc- 
essing and  which  could  be  used  with  rack-and-tank  processing  equip- 
ment. The  purpose  of  this  rack  was  to  facilitate  the  conduct  of 
experimental  work  by  the  provision  of  a  type  of  treatment  similar  to 
that  given  by  a  continuous  processing  machine  with  equipment 
which  could  be  used  under  conditions  of  batch  operation  favorable  to 
frequent  change  of  developer  and  time  of  treatment. 

The  film  was  carried  in  a  helical  path  over  a  succession  of  rollers 
at  the  top  and  bottom  of  the  rack,  the  upper  and  lower  rollers  each 
having  a  common  shaft.  In  order  to  permit  continuous  motion  in 
one  direction,  the  film  strands  from  the  ends  of  the  helix  were  joined 
to  form  a  closed  loop.  The  return  strand  so  formed  was  located 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C. ;  Communica- 
tion No.  671  from  the  Kodak  Research  Laboratories. 
**  Eastman  Kodak  Co.,  Rochester,  N.  Y. 

393 


394 


C.  E.  IVES 


[J.  S.  M.  P.  E. 


along  the  bottom  of  the  rack.  Thus,  starting  at  one  end,  the  film 
reached  the  other  end  of  the  rack  by  following  a  helical  path,  turning 
around  rollers  along  the  top  and  bottom,  left  the  last  upper  roller  to 
go  to  the  lower  corner  of  the  rack  while  making  a  quarter  turn,  tra- 
versed the  length  of  the  rack  on  the  supporting  rollers  along  the 
bottom,  and  then  after  making  another  quarter  turn  arrived  at  the 
starting  point.  The  drive  motor  and  reduction  gear  were  built  in. 


FIG.  1.     Elevation  of  new  roller  type  of  developing  rack. 

This  rack  was  found  to  fill  a  definite  need  and  consequently  was 
used  extensively.  With  an  increasing  volume  of  work  it  became 
necessary  to  have  additional  units  in  service.  An  opportunity  was, 
therefore,  presented  for  making  certain  improvements  in  design  and 
reducing  the  weight  of  the  rack. 

Desirable  Features. — After  reexamination  of  the  features  of  the 
existing  rack,  it  was  concluded  to  provide  for  a  210-ft.  film  length 
with  the  same  film  path,  the  completely  submerged  film  path  being 
retained. 

A  running  speed  of  approximately  150  feet  a  minute  was  thought 
desirable  in  order  to  simulate  continuous  machine  conditions  and  to 


Oct.,  1938 J  ROLLER  TYPE  DEVELOPING  RACK  395 

obtain  some  improvement  in  development  uniformity.  The  higher 
speed  would  also  have  the  particular  advantage  with  the  roller  rack 
of  assuring  greater  uniformity  of  treatment  throughout  the  200-ft. 
length  by  increasing  the  number  of  times  the  whole  path  was  tra- 
versed during  development. 

With  multiple-rack  operation  it  would  be  practicable  to  install 
driving  means  at  the  processing  tanks  and  at  loading  and  unloading 
stations,  thus  making  possible  the  removal  of  the  drive  from  the  rack 
with  a  considerable  reduction  of  weight  of  the  latter.  Drives  located 
at  the  processing  tanks  would  be  partly  submerged  in  the  bath  so 
that  the  design  would  have  to  dispose  of  the  problems  of  corrosion, 
contamination,  and  leakage. 

Accommodation  for  expansion  of  the  film  when  wetted  and  pro- 
vision for  redistribution  of  slack  would  have  to  be  furnished  by  move- 
ment of  one  of  the  shafts  in  the  vertical  direction  under  tension,  while 
it  was  maintained  parallel  to  the  other.  The  use  of  a  slide  or  track 
for  this  movement  should  be  avoided  because  of  the  friction  intro- 
duced. 

The  rack  frame  should  be  rigid  and  light  in  weight  and  should 
have  clean  lines  and  an  open  construction  favorable  to  quick  drain- 
age of  the  solutions.  The  presence  of  mechanical  parts  other  than 
the  rollers  within  the  film  loops  was  considered  sufficiently  objection- 
able to  warrant  a  redesign  of  the  evener  mechanism. 

In  order  to  be  used  with  existing  tank  equipment  the  rack  should 
not  exceed  2  inches  in  width  and  54  inches  in  length.  The  height 
should  be  about  48  inches.  The  improved  rack  is  illustrated  in 
Fig.  1  and  its  features  are  explained  by  means  of  the  figures  and  de- 
scription which  follow. 

The  Driving  Shaft. — In  order  to  obtain  a  compact  and  simple  drive 
unit  it  was  decided  to  drive  through  the  upper  shaft  and  maintain 
the  film  loops  taut  by  means  of  a  spring-tensioned  movable  lower 
shaft.  With  the  driving  unit  located  at  one  end  of  the  tanks  near  the 
top,  it  was  necessary  only  that  the  upper  shaft  be  extended  slightly 
beyond  the  end  of  the  rack  and  fitted  with  suitable  means  for  engage- 
ment with  the  drive  gearing.  In  order  to  obtain  immediate  starting 
and  a  simplicity  of  manipulation  fitted  to  working  in  total  darkness, 
direct  engagement  with  the  running  drive  was  decided  upon.  A 
means  of  accomplishing  this,  described  by  White  in  an  article  on 
equipment  for  testing  motion  picture  film,2  was  considered  for  the 
present  purpose  but  did  not  lend  itself  well  to  use  in  the  2V4-inch 


396  C.  E.  IVES  [J.  S.  M.  P.  E. 

space  available.  The  design  chosen  consisted  of  direct  engagement 
(radially)  of  two  spur  gears  at  a  peripheral  speed  of  about  200  feet  a 
minute.  Good  service  has  been  obtained  with  a  12-pitch,  22-tooth, 
V2-inch  face  gear  of  reinforced  bakelite  on  the  rack  and  a  similar, 
slightly  wider  stainless  steel  gear  on  the  drive.  The  bakelite  gear  has 
undergone  some  wear  under  this  shock  loading  during  !1/2  years  of 
use  but  is  still  in  service.  Wear  on  the  steel  gear  has  been  negligible. 
The  upper  shaft  consists  of  a  1-inch  outside  diameter  ground 
stainless-steel  tube  closed  at  both  ends.  It  is  supported  by  three 
plain  bearings  of  reinforced  bakelite  which  receive  the  required  lubri- 
cation from  the  processing  liquids.  The  bearings  at  center  and  right 
in  Fig.  1  are  for  axial  loads  only,  all  thrust  being  taken  by  the  bearing 
at  the  left.  At  this  point  the  shaft  diameter  is  stepped  down  to  7/ie 
inch  by  means  of  an  extension  piece  which  is  sweated  into  the  tube. 
Beyond  the  bearing  to  the  left  is  the  bakelite  gear  which  is  held  in 
position  from  one  side  by  a  pin  through  the  shaft  and  on  the  other 
by  a  jam  nut  and  lock  washer. 

This  end  bearing  is  fastened  by  screws  to  a  bracket  on  the  frame. 
When  the  screws  are  loosened  the  shaft  can  be  passed,  with  the 
gear  in  place,  through  an  opening  in  the  end  frame  member  of  the 
rack  to  permit  removal  of  rollers  at  the  opposite  end  of  the  rack. 
The  bearing  block  is  extended  5/ie  inch  outside  the  frame,  where  it 
is  turned  to  a  cylindrical  shape  to  act  as  a  trunnion,  by  whose  engage- 
ment with  a  guide  plate  on  the  drive  unit  the  gear  center  distance  is 
maintained. 

Film  Supporting  Rollers. — In  the  model  described  previously,  in 
which  hard-rubber  rollers  were  used,  only  one  flange  to  the  roller  was 
used  to  save  space.  At  the  present  time  rollers  are  made  of  reinforced 
bakelite  which  is  sufficiently  strong  to  permit  the  use  of  much  nar- 
rower flanges.  This,  in  combination  with  other  changes  in  the 
frame  providing  additional  space,  has  made  possible  the  use  of 
double-flange  rollers,  with  a  resulting  improvement  in  film  guiding. 

All  rollers  are  equipped  with  soft-rubber  treads  which  eliminate  the 
scratching  usually  seen  along  the  perforation  track  of  machine-proc- 
essed film.  These  treads  grip  the  surface  of  the  film  support  very 
strongly  so  that,  when  slack  is  being  redistributed  along  the  rack, 
any  slippage  must  be  between  the  rollers  and  the  shaft.  At  the  same 
time  it  is  necessary  to  apply  some  driving  force  over  and  above  that 
furnished  by  the  friction  between  the  rollers  and  the  shaft.  This 
additional  friction  is  furnished  by  the  use  of  six  rollers  with  friction- 


Oct.,  1938]  ROLLER  TYPE  DEVELOPING  RACK  397 

drive  pads  of  the  type  shown  in  Fig.  2.  The  pads  are  pressed  against 
the  shaft  by  the  arcuate  flat  stainless-steel  spring  with  sufficient  force 
to  require  a  tension  of  eleven  ounces  at  the  film  line  to  cause  slippage. 

The  lower  shaft  rollers  are  similar  to  the  remaining  upper  rollers 
except  for  the  bore. 

The  Lower  Shaft. — Differences  in  the  expansion  of  various  materials 
when  wetted,  as  for  example,  coated  film  and  uncoated  leader,  cause 
looseness  of  the  film  at  one  point  or  another  along  the  rack.  Re- 
distribution of  this  slack  is  brought  about  by  compelling  the  lower 
shaft  to  remain  parallel  to  the  upper  shaft  while  it  moves  up  and 
down.  If  parallelism  is  maintained,  then  any  slack  which  appears 
while  the  film  is  running  is  immediately  redistributed,  because  the 
shorter  strands  receive  the  full  tensioning  force  applied  to  the  shaft. 


FIG  .  2 .     Drive  roller  with  auxiliary  friction  pads. 

In  the  previous  model  the  required  downward  force  was  provided 
by  the  weight  of  a  heavy  stainless  steel  beam  which  supported  the 
shaft  at  three  bearing  points.  Two  extension  coil  springs  of  stainless 
steel  supply  the  tension  in  the  new  model.  The  most  suitable  loca- 
tion for  the  springs  is  in  the  channel  members  forming  the  upright 
rack  ends  (Figs.  1  and  3).  Here  they  are  suspended  from  an  ad- 
justable screw  while  the  spring  tension  is  transmitted  to  the  movable 
shaft  by  means  of  a  7  X  7,  Vie-inch  diameter  stainless-steel  stranded 
cable.  The  cable  is  anchored  to  the  frame  just  below  the  spring, 
passes  over  a  pulley  block  suspended  from  the  latter,  from  which 
point  it  goes  to  the  bottom  corner  of  the  rack,  and,  after  passing  under 
a  sheave,  reaches  a  quadrant  affixed  to  the  movable  lower  shaft. 
This  cable  is  strong,  economical  of  space,  and  tolerant  of  slight  mis- 
alignment. 

Mechanism  for  Obtaining  Parallel  Shaft  Movement. — With  the  elimi- 
nation of  the  lower  shaft  beam  and  the  old  type  of  parallel  motion 
gear,  both  of  which  were  formerly  located  above  the  lower  shaft  within 
the  film  loops,  a  new  means  of  supporting  the  shaft  and  of  effecting 


398 


C.  E.  IVES 


[J.  S.  M.  P.  E. 


parallel  movement  was  required.  It  was  found  that  the  shaft  itself, 
although  so  slender  as  to  have  little  beam  strength,  was  of  suitable 
proportions  to  act  as  a  quite  rigid  torsional  evener. 

The  operation  of  the  evener  is  described  conveniently  by  reference 
to  Fig.  3,  which  shows  schematically  the  lower  shaft  mechanism  and 
spring- tensioning  system.  The  shaft  is  clamped  at  three  points  in 
crank  arms  (see  also  Fig.  4)  which  pivot  on  three  pins  supported  by 
the  frame  on  a  common  horizontal  axis.  Downward  pull  to  hold  the 
film  loops  taut  is  applied  by  the  cables  which  are  fastened  to  the  quad- 
rants associated  with  the  cranks  at  the  ends  of  the  shaft. 

Vertical  movement  of  the  shaft 
caused  by  a  change  in  the  length 
of  the  film  loops  results  in  move- 
ment of  the  cranks  about  the 
pivots  and  a  corresponding  rota- 
tion of  the  shaft.  Thus,  if  one 
end  of  the  shaft  is  lowered  slightly 
with  consequent  rotation  about 
its  axis  and  the  other  is  held  up 
by  a  shorter  film  loop,  the  tor- 
sional rigidity  of  the  shaft  tends 
to  cause  a  corresponding  rota- 
tion at  the  latter  point  as  well. 
Rotational  force  at  the  attached 
crank  causes,  in  turn,  an  in- 
creased downward  tension  upon 
the  short  loop  and  thus  brings 
about  the  desired  redistribution 
of  the  film  on  the  rack.  For  a  small  displacement,  the  movement 
employed  may  be  compared  to  that  of  a  shaft  carrying  three  pinions 
moving  along  racks.  The  rigidity  of  the  stainless-steel  shaft  of 
3/8-hich  diameter  is  sufficient  to  transmit  the  16-pound  force  through 
the  length  of  48  inches  with  less  than  0.1 -inch  vertical  displace- 
ment. With  this  tension  applied  at  each  end,  any  slack  is  im- 
mediately redistributed. 

Bowing  of  the  shaft  is  prevented  by  locating  another  crank  and 
pivot  at  the  midpoint  which  employs  the  torsional  strength  of  the 
shaft  in  the  manner  described  above  to  maintain  the  shaft  at  the 
point  of  attachment  approximately  in  line  with  the  shaft  ends.  With 
a  0.812-inch  distance  between  crank  centers  and  a  vertical  movement 


FIG.  3.  Schematic  representation 
of  parallel  movement  mechanism  and 
tensioning  system. 


Oct.,  1938] 


ROLLER  TYPE  DEVELOPING  RACK 


399 


of  about  0.923  inch,  the  lateral  movement  is  only  0.144  inch.  The 
spring  design  is  such  that  the  tension  changes  only  20  per  cent  with 
the  full  vertical  movement  of  the  shaft. 

The  Return  Path. — As  formerly,  the  path  by  which  the  film  returns 
from  one  end  of  the  helix  to  the  other  is  located  along  the  bottom  of 
the  rack.  The  seven  supporting  rollers  are  carried  within  the  bottom 
frame  member  on  shafts  fastened  to  the  sides  of  the  channel  by  means 
of  countersunk  screws.  For  removal 
of  the  screws  the  shaft  can  be  held 
by  a  pin  inserted  in  a  hole  in  the 
roller  and  shaft. 

The  Frame. — The  frame  is  made 
entirely  of  16-gauge  stainless-steel 
sheet  stock  and  comprises  four  prin- 
cipal members.  These  are  of  chan- 
nel form  for  the  bottom  and  the 
two  upright  ends,  and  triangular  for 
the  top  piece,  providing  for  rigidity 
and  convenience  in  lifting  the  rack 
from  the  tanks.  These  parts  and 
the  lower  corner  gusset  plates  are  as- 
sembled by  butt  welding.  Brackets 
are  attached  by  spot  welding.  The 
weight  of  the  frame  was  reduced 
slightly  by  punching  out  holes  in  the 
larger  surfaces.  The  frame  is  suffi- 
ciently rigid  for  the  mechanical 
movements  employed. 

Drives  on  the  Tanks. — The  tanks 
in  which  the  rack  is  used  have  di- 
mensions of  60  inches  in  length,  54 
inches  in  depth,  and  either  6  or  10  inches  in  width.  To  avoid  diffi- 
culties in  alignment  and  to  obtain  a  simple  drive  presenting  a  mini- 
mum contamination  and  corrosion  hazard,  individual  splashproof 
motors  were  mounted  on  each  tank  (Fig.  5).  The  only  points  re- 
ceiving oil  lubrication  are  the  well  guarded  motor  bearings.  Direct 
speed  reduction  from  the  1150-rpm.  motor  shaft  to  the  385-rpm. 
rack  drive  gear  in  the  bath  is  obtained  through  a  chain  drive. 
A  9-tooth  sprocket  is  mounted  on  an  extension  of  the  motor  shaft. 
The  Vs-inch,  V2-inch  pitch  roller  chain  engages  this  and  the  27- 


FIG.  4.     Close-up  of  lower  cor- 
ner of  rack. 


400 


C.  E.  IVES 


[J.  S.  M.  P.  E. 


tooth  sprocket  on  the  drive  gear.  These  parts  are  of  stainless  steel. 
The  drive  gear  has  a  combination  bushing  and  thrust  washer  of 
reinforced  bakelite  which  runs  on  a  stainless-steel  stud  with  the  proc- 
essing solution  for  lubrication.  This  gear  is  held  in  position  by  the 
stainless-steel  apron  which  covers  all  of  the  moving  parts  and  acts 
as  a  splash  and  safety  guard.  The  apron  is  entirely  open  at  the 
bottom  to  facilitate  cleaning. 

Racks  are  guided  into  the  tank  (Fig.  6)  by  the  strips  welded  to  the 


-TEMPERATURE 
CONTROL.  COIL 


FIG.  5.     Drawing  of  drive  unit  on  tank. 


face  of  the  apron.  Correct  positioning  of  the  rack  gear  relative  to  the 
drive  gear  is  maintained  by  causing  the  rack  trunnion  to  rest  in  the 
recess  in  a  guide  plate  fastened  to  the  apron.  The  rack  is  also  sup- 
ported at  the  diagonally  opposite  bottom  corner  where  a  shelf  is  lo- 
cated a  few  inches  above  the  tank  bottom.  Angular  misalignment 
of  the  gears  in  the  horizontal  direction  is  limited  by  the  rack  guides 
at  the  opposite  end  of  the  tank  to  approximately  1  degree  in  either 
direction,  which  is  acceptable  for  the  purpose.  Space  is  provided  for 
temperature  control  pipes  which  enter  back  of  the  apron. 


Oct.,  1938]  ROLLER  TYPE  DEVELOPING  RACK  401 

The  Loading  Station. — At  another  point  in  the  developing  room  a 
drive  is  installed  for  running  the  rack  while  it  is  being  loaded  (Fig.  7) . 
In  this  case  a  reduction  gear  of  conventional  desfgn  is  used,  since  the 
corrosion  and  contamination  problems  are  not  severe.  To  facilitate 
locating  the  rack  on  the  loading  stand,  guides  are  mounted  behind  the 
rack  position  near  the  drive  and  at  the  supporting  shelf  at  the  bottom. 

Loading  is  carried  out  by  opening  a  splice  in  the  leader  with  which 
the  rack  is  always  threaded  when  not  in  use,  and  then  attaching  the 
film  to  one  of  the  ends.  The  drive  is  started,  causing  the  film  to  be 
led  onto  the  rack  while  the  leader  is  taken  up  on  a  rewind  at  the  point 


FIG.  6.     Tank  with  rack  in  position. 


where  it  is  leaving  the  rack.  In  this  operation  and  later  when  the 
rack  is  being  unloaded,  a  guide  roller  with  soft  rubber  treads  (visible 
at  the  top  of  the  rack  in  Fig.  7)  is  brought  into  bearing  against  the 
edge  portion  of  the  film  at  the  point  where  the  leader  or  film  is  leaving 
the  rack.  This  assures  sufficient  contact  of  the  film  with  the  roller 
on  the  rack  to  provide  the  necessary  drive.  The  guide  roller  is  carried 
by  a  resilient  mounting  which  is  slipped  onto  the  upper  frame  member 
when  needed.  A  friction  hold-back  on  the  feeding  roll  is  adjusted  to 
maintain  enough  tension  in  the  entering  film  strand  to  prevent  the 
lower  rack  shaft  from  rising  or  falling.  Operation  of  the  drive  motor 
is  controlled  by  a  foot  switch.  The  maximum  loading  speed  is  200 
feet  a  minute. 


402  C.  E.  IVES  [J.  S.  M.  P.  E. 

Splices  are  made  by  means  of  metallic  clips  put  in  by  a  hand-held 
device.  Reasonably  accurate  alignment  is  required  for  proper  run- 
ning of  the  film  but  perforations  are  not  registered. 

The  Unloading  Truck.—- The  processed  film  is  passed  through  a  port- 
able pneumatic  squeegee3  and  transferred  to  reels  for  drying.  During 
this  operation  the  rack  is  carried  on  a  movable  truck  (Fig.  8)  equipped 


FIG.  7.     Rack  threaded  with  film  standing  in  the  load- 
ing station. 


with  a  drive  similar  to  that  used  on  the  loading  station.  As  the  film  is 
removed  leader  stock  is  fed  in  from  a  stock  roll  carried  on  the  truck. 
The  motor  is  controlled  by  means  of  a  portable  switch  cord  which  the 
operator  can  attach  to  his  clothing.  Running  speed  is  limited  to  100 
feet  a  minute  or  less  by -the  capacity  of  the  squeegee. 

Operating  Procedure. — The  loading  operation  is  managed  in  such  a 
way  as  to  maintain  the  movable  shaft  in  the  upper  half  of  its  range  of 
movement. 


Oct.,  1938]  ROLLER  TYPE  DEVELOPING  RACK  403 

Positive,  negative,  and  sound  developers  are  used.  Development  is 
timed  by  the  use  of  an  electric  darkroom  clock  with  an  error  of  less 
than  5  seconds.  The  rack  is  handled  by  two  meri.  The  rack  is  con- 
tinuously driven  in  the  stop-bath  and  fixing  bath,  but  the  film  is  ad- 
vanced on  the  rack  only  occasionally  in  the  course  of  washing. 

When  picture  negative  film  is  developed,  there  is  a  tendency  to  form 
airbells  on  the  emulsion4  at  the  point  at  which  the  bottom  roller  enters 
the  developer.  They  can  be  dislodged  during  the  first  minute  of  de- 
velopment by  holding  a  soft  pad  of  absorbent  cotton  lightly  against 


FIG.  8.     Rack  on  unloading  truck  in  drying 
room. 


the  emulsion  surface  at  one  or  two  points  near  the  upper  shaft  rollers ; 
or  better,  a  soft  rubber  sponge  of  good  quality  cut  to  form  a  strip 
l3/s  X  3  X  */2  inch  may  be  used.  It  is  undesirable  to  have  porous  ma- 
terial such  as  this  attached  to  the  rack  because  of  the  danger  of  con- 
taminating the  film  or  developer  with  hypo. 

Performance. — Good  uniformity  of  processing  has  been  attained 
because  of:  (a)  the  high  running  speed  of  150  feet  a  minute,  (b)  the 
strong  agitation  of  the  developer  by  compressed  air,  and  (c)  the  use  of 
an  acid  stop-bath. 

Acknowledgment. — The  assistance  rendered  by  Mr.  J.  R.  Turner 
and  Mr.  E.  W.  Jensen  in  working  out  several  features  in  this  new  de- 
sign is  gratefully  acknowledged. 


404  C.  E.  IVES 

REFERENCES 

1  IVES,  C.  E. :     "A  Roller  Developing  Rack  for  Continuously  Moving  the 
Film  During  Processing  by  the  Rack-and-Tank  System,"  /.  Soc.  Mot.  Pict.  Eng., 
XXIV  (March,  1935),  No.  3,  p.  261. 

2  WHITE,  D.  R. :     "Equipment  for  Developing  and  Reading  Sensitometric 
Tests,"  /.  Soc.  Mot.  Pict.  Eng.t  XXVI  (April,  1936),  No.  4,  p.  427. 

3  CRABTREE,  J.  I.,  AND  IVES,  C.  E.:    "A  Pneumatic  Film  Squeegee,"  Trans. 
Soc.  Mot.  Pict.  Eng.,  XI  (Aug.,  1927),  No.  30,  p.  270. 

4  CRABTREE,  J.  I.,  AND  IVES,  C.  E.:    "Rack  Marks  and  Airbell  Markings  on 
Motion  Picture  Film,"  Trans.  Soc.  Mot.  Pict.  Eng.,  IX  (Oct.,  1925),  No.  24,  p.  95. 


NEW  MOTION  PICTURE  APPARATUS 


During  the  Conventions  of  the  Society,  symposiums  on  new  motion  picture  appara- 
tus are  held  in  which  various  manufacturers  of  equipment  describe  and  demonstrate 
their  new  products  and  developments.  Some  of  this  equipment  is  described  in  the 
following  pages;  the  remainder  will  be  published  in  subsequent  issues  of  the  Journal. 


A  CONTINUOUS  OPTICAL  REDUCTION  SOUND  PRINTER 

M.  G.  TOWNSLEY  AND  J.  G.  ZUBER  ** 


Sound  has  been  commercially  recorded  on  16-mm.  film  by  a  variety  of  methods, 
including  direct  recording  on  16-mm.  negative,  re-recording  from  35-mm.  nega- 
tive to  16-mm.  positive,  and  optical  reduction  from  35-mm.  to  16-mm.  Any  of 
these  methods  that  involve  recording  on  16-mm.  film  are  subject  to  severe  losses 
in  frequency  response  due  to  the  slit  effect  in  recording.  Batsel  and  Sachtleben1 
show  this  loss  to  be  approximately  12  db.  at  5000  cps.  for  an  0.5-mil  slit. 

Optical  reduction  prints  may  be  made  either  by  making  an  optically  reduced 
negative  from  a  35-mm.  positive  and  printing  by  contact,  or  directly  from  a 
35-mm.  negative  to  a  16-mm.  positive.  The  overall  frequency  response  is  nearly 
the  same  for  either  method,  since  the  slight  gain  in  contact-printing  the  35-mm. 
positive  offsets  the  16-mm.  contact-printing  frequency  losses.  Contact  printing 
tends  to  introduce  the  further  difficulties  of  uneven  slippage  and  poor  contact, 
which  adversely  affect  the  sound  quality.  This  consideration,  together  with  the 
obvious  advantage  of  economy  of  materials  and  time,  indicates  the  desirability  of 
making  16-mm.  sound-track  prints  by  direct  optical  reduction  from  the  35-mm. 
negative. 

The  present  paper  describes  an  optical  reduction  printer  having  several  new 
features  designed  to  facilitate  operation  and  improve  the  quality  of  the  finished 
sound-track.  The  printer  departs  from  conventional  design  in  that  the  film 
rolls,  instead  of  being  arranged  in  a  vertical  plane,  are  horizontal.  This  con- 
struction has  resulted  in  considerable  simplification  in  des:gn,  and  presents  im- 
portant advantages  in  the  operation  of  the  printer.  Oil-damped  filters  and  flood- 
lubricated  working  parts  are  made  possible  without  the  use  of  friction-producing 
oil  seals.  There  is  no  possibility  of  lubricating  oil  reaching  any  part  of  the  film 
path.  Several  other  advantages  of  the  construction  will  be  apparent  from  the 
following  description. 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;  received 
April  18,  1938. 

**  Bell  &  Howell  Company,  Chicago,  111. 

405 


406 


NEW  MOTION  PICTURE  APPARATUS        [j.  s.  M.  p.  E. 


Fig.  1  shows  the  external  appearance  of  the  complete  printer.  The  16-mm. 
positive  is  at  the  top  of  the  machine  where  it  is  readily  accessible  for  threading. 
Each  film  roll  rests  upon  a  driving  flange.  The  negative  feed  and  take-up  flanges 
are  on  the  same  spindles  as  the  positive  flanges.  The  covers  A  are  placed  over  the 
negative  film  during  printing  to  protect  it  from  dust  and  other  possible  damage. 
Since  the  printer  is  designed  to  print  alternately  from  beginning  and  end  of  the 


FIG.  1      View  of  complete  printer. 

negative,  and  is  arranged  to  stop  at  the  end  of  the  negative  with  the  leader  still 
threaded,  it  is  necessary  to  have  access  to  the  negative  only  when  changing 
negatives.  A  negative,  once  threaded,  remains  in  the  printer  without  further 
attention  until  the  complete  run  of  positives  has  been  made.  A  pre-set  stop 
mechanism  stops  the  motor  at  the  end  of  the  negative  and  sets  the  reversing 


FIG.  2.     Main  drive  assembly  without  motor. 


switches  so  that  at  the  next  starting  the  machine  will  operate  in  the  reverse 
direction. 

Fig.  2  shows  the  main  drive  assembly  without  the  motor.  The  entire  mecha- 
nism is  driven  from  the  main  worm  shaft,  which  is  coupled  to  the  motor  by  a 
safety  clutch  to  protect  the  motor  and  working  parts  in  case  of  jamming  in  the 
mechanism.  The  printer  is  reversed  by  reversing  the  3-phase  220-volt  syn- 
chronous motor.  The  printing  speed  is  60  feet  of  35-mm.  film  per  minute.  All 


Oct.,  1938J 


NEW  MOTION  PICTURE  APPARATUS 


407 


the  driving  gears  are  flood-lubricated  by  oil  carrier  gears  which  dip  into  the  oil 
and  carry  it  to  the  gear  teeth. 

The  flywheel  is  driven  by  the  central  worm,  and  the  take-up  spindles  are  driven 
by  the  two  worm  gears  B.     Unidirectional  clutches  are  arranged  so  that  the  take- 


FIG.  3.     35-mm.  sprocket. 

up  spindle  is  driven  and  the  feed  spindle  remains  stationary.  Hold-back  and  take- 
up  tension  is  maintained  by  "arguto"  washers  upon  which  the  film  flanges  rest, 
the  weight  of  the  film  supplying  the  major  part  of  the  friction.  This  construction 
maintains  very  uniform  film  tension  throughout  the  length  of  the  film  roll. 

Uniform  film  motion  is  the  most  important  condition  imposed  upon  an  optical 
reduction  printer.     The  excellence  of  the  finished  print  depends  entirely  upon 


FIG.  4.     Flywheel  worm  drive. 


driving  the  positive  and  negative  films  past  the  printing  point  at  the  proper  rela- 
tive speeds,  synchronized  frame  for  frame,  and  without  flutter  or  other  improper 
motion.  Synchronization  requires  that  the  two  films  be  driven  by  positively  con- 
nected sprockets.  Uniformity  of  motion  is  attained  most  readily  by  means  of  a 
flywheel,  carrying  the  films  at  the  printing  point  on  toothless  drums.  Shrinkage 


408 


NEW  MOTION  PICTURE  APPARATUS        [J.  S.  M.  P.  E. 


I6mm    Film 


35mm  Rim 


differences  between  positive  and  negative  and  variations  in  negative  shrinkage 
make  it  impossible  to  connect  the  positive  and  negative  film  drums  rigidly.  Print- 
ers embodying  various  devices  to  reconcile  these  requirements  have  been  described 
in  the  literature  from  time  to  time.2'3-4 

In  the  present  printer,  synchronism  is  achieved  by  mounting  the  sprockets  in 
pairs,  a  16-mm.  and  a  35-mm.  sprocket  to  a  pair,  each  pair  on  a  common  shaft. 
Each  sprocket  shaft  is  driven  from  the  flywheel  through  helical  gears.  Slippage 
of  the  film  over  the  root  of  the  sprocket  teeth  is  prevented  by  the  two-piece  con- 
struction of  the  sprockets  (Fig.  3) .  The  film  is  supported  by  a  cylinder  slightly 
larger  than  the  root-circle  of  the  sprocket  and  free  to  rotate  upon  needle  bearings 
on  the  sprocket  itself,  so  that  the  film  clears  the  root  circle  by  approximately  1 

mil.  This  construction  enables  the 
film  to  move  over  the  sprocket,  as  it 

G    A       /\| [Tj must  to  accommodate  for  shrinkage, 

yj  without  sliding  contact,  thus  prevent- 

ing scratches.  In  addition,  support- 
ing the  film  over  its  entire  width 
reduces  the  strain  on  the  edges  of  the 
film  and  prevents  negative  breakage. 

A  massive  flywheel  and  an  oil  drag 
drive  are  employed  to  insure  exact  uni- 
formity of  motion  of  the  film  by  a 
combination  of  "brute  force"  and  vis- 
cous filtering.  The  large  mass  of  the 
flywheel  makes  it  impracticable  to 
drive  the  flywheel  by  the  film.  In- 
stead, the  driving  motor  drives  the 
flywheel  through  the  worm  and  gear 
shown  in  Fig.  4.  Worm  gear  A  is 
free  to  rotate  upon  the  flywheel  shaft 
which  it  drives  through  filter  springs  B. 
The  natural  period  of  oscillation  of  this 
assembly  is  sufficiently  low  effectively 
to  prevent  transmission  of  any  possible 
motor  or  gear-tooth  disturbances  to  the 
flywheel.  Each  printing  drum  is  independently  coupled  to  the  flywheel  by  oil 
friction.  This  coupling  consists  of  an  interleaved  set  of  thin  plates,  alternately 
connected  to  flywheel  and  film  drum,  and  immersed  in  heavy  oil.  This  cou- 
pling permits  slow  relative  motion  between  the  positive  and  negative  films  to 
accommodate  for  negative  shrinkage.  There  will  be  a  constant  uniform  relative 
motion  between  the  two  drums  in  direct  proportion  to  the  deviation  of  the  actual 
negative  shrinkage  from  the  shrinkage  for  which  the  drums  are  designed.  While 
permitting  this  necessary  slow  relative  movement,  the  viscous  coupling  com- 
pletely eliminates  any  flutter  or  wow  from  sprocket  teeth,  splices,  or  film  imper- 
fections by  offering  very  high  resistance  to  sudden  movements.  The  area  of 
contact  and  the  film  tension  are  sufficient  effectively  to  prevent  slipping  of  either 
film  over  its  drum. 

Tension  is  maintained  by  spring-loaded  idler  rollers  between  the  sprockets  and 


FIG.  5. 


Oct.,  1938]  NEW  MOTION  PICTURE  APPARATUS  409 

drums.  Instantaneous  response  to  film  disturbance  results  from  keeping  the 
mass  of  the  rollers  as  small  as  possible.  Any  disturbance  is  taken  up  by  move- 
ments of  these  idlers  and  bending  of  the  film  without  affecting  the  film  drum  ex- 
cept by  a  slow  drift. 

Positive  and  negative  films  are  guided  by  these  rollers,  the  positive  film  on  the 
edge  and  the  negative  by  the  perforations  adjacent  to  the  sound-track. 

The  optical  train  is  self-contained,  and  is  removable  as  a  complete  unit  by  un- 
locking two  clamping  screws.  All  adjustments  are  made  and  the  unit  is  sealed  at 
the  factory,  making  the  optical  units  interchangeable  and  replaceable.  The  ways 
that  locate  the  unit  and  the  design  of  the  clamping  screws  enable  positive  posi- 
tioning and  focusing. 

Optical  printing  from  35-mm.  to  16-mnt.  requires  the  production  on  the  16-mm. 
film  of  an  image  of  the  35-mm.  track,  moving  in  the  same  direction  as  the  16-mm. 
image  and  at  the  same  speed,  with  a  longitudinal  magnification  of  0.400  and  a 
transverse  magnification  of  0.857.  These  requirements  can  be  fulfilled  only  by 
a  system  containing  cylindrical  elements.  In  the  present  design,  the  proper 
direction  of  motion  of  the  image  is  achieved  without  resorting  to  complicated  erect- 
ing systems.  Fig.  5  shows  the  optical  layout.  The  negative  is  illuminated  from 
inside  the  drum  by  lamp  A,  condenser  B  and  prism  C.  An  anastigmat  lens  D 
and  a  right-angled  prism  E  form  a  full-size  image  of  the  moving  35-mm.  track  in 
the  field  lens  F.  Right-angled  prism  G  and  the  two  achromatic  cylindrical  com- 
ponents H,  J  form  an  image  of  this  intermediate  image  in  the  16-mm.  film  plane, 
with  the  proper  magnification,  moving  in  the  proper  direction.  An  area  0.063  X 
0.100  is  scanned  on  the  negative.  Provision  is  made  for  printing  two  opaque 
lines  along  the  edges  of  the  track  to  cut  down  background  noise  and  mask  the 
edge  of  the  printed  area. 

The  lamp  is  a  photocell  exciter  lamp,  10-volt,  7.5  amperes,  burned  in  a  hori- 
zontal position  in  a  water-cooled  lamp  house.  The  lamp  is  mounted  in  a  special 
ring  to  assure  accurate  positioning  of  the  filament. 

Lamp  current  is  supplied  by  a  pair  of  6-volt  storage  batteries  and  a  full-wave 
charger.  The  charger  is  set  to  charge  at  approximately  115  per  cent  of  the 
normal  lamp  current,  so  that  the  lamp  power  is  supplied  by  the  charger  with  the 
batteries  acting  as  ballast  to  remove  the  120-cycle  modulation  in  the  charger 
current.  This  arrangement  and  the  high  thermal  inertia  of  the  lamp  filament 
provide  very  constant  illumination.  Careful  tests  with  an  0.5-mil  slit  showed 
complete  absence  of  120-cycle  modulation. 

Lamp  current  is  controlled  by  a  pair  of  rheostats  and  an  ammeter  mounted  in 
the  control  unit  above  the  printing  drums. 

A  signal  device  is  provided  to  make  it  possible  to  make  any  necessary  changes 
in  exposure  during  printing.  Notches  in  the  edge  of  the  negative  actuate  a  roller 
contactor  which  signals  the  change  point.  A  standard  card-rack  is  provided  for 
timing  cards.  Safety  switches  automatically  stop  the  motor  should  the  negative 
break.  The  printer  is  intended  to  be  operated  in  a  darkroom,  and  is  equipped 
with  the  necessary  safelights  for  convenient  operation. 

REFERENCES 

1  BATSEL,  C.  N.,  AND  SACHTLEBEN,  L.  T.:  "Some  Characteristics  of  16-Mm. 
Sound  by  Optical  Reduction  and  Re-Recording,"  /.  Soc.  Mot.  Pict.  Eng.,  XXIV 
(Feb.,  1935),  No.  2,  p.  95. 


410  NEW  MOTION  PICTURE  APPARATUS        [J.  S.  M.  P.  E 

2  SANDVIK,  O.,  AND  STREIFFERT,  J.  G.:     "A  Continuous  Optical  Reduction 
Sound  Printer,"  /.  Soc.  Mot.  Pict.  Eng,,  XXV  (Aug.,  1935),  No.  2,  p.  117. 

3  VICTOR,  A.   F.:     "Continuous  Optical  Reduction  Printing,"  /.   Soc.   Mot. 
Pict.  Eng.,  XXIII  (Aug.,  1934),  No.  2,  p.  96. 

4  COLLINS,  M.  E.:     "Optical  Reduction  Sound  Printer,"  J.  Soc.  Mot.  Pict 
En*.,  XXVH  (July,  1936),  No.  1,  p.  105. 


A  NEW  16-MM.  PROJECTOR' 


H.  C.  WELLMAN** 


The  mechanism  of  the  Model  G  Kodascope  is  completely  housed  in  aluminum 
die  castings,  and  is  held  to  close  tolerances  both  in  parts  and  in  assemblies  (Figs.  1 
and  2).  All  shafts  are  ground  to  insure  straightness,  finish,  and  size.  Diametei 
size  is  held  within  tolerances  of  =*=  0.0002  inch.  All  bearings  are  of  the  oilles? 
type,  vacuum  impregnated  with  oil  shortly  before  assembly  to  give  minimum  weai 
over  long  periods  of  time.  The  teeth  of  the  pull-down  gears  are  cut  after  as- 
sembly to  the  shaft.  Every  assembly  is  checked  for  eccentricity,  tooth  spacing 
and  finish;  the  allowable  accumulative  error  in  these  assemblies  is  0.0005  inch 
and  further  refinement  is  gained  by  the  use  of  an  adjustable  sleeve  for  the  bear 
ings  of  the  pull-down  shaft.  The  out  side  of  the  sleeve  is  eccentric  with  the 
bearing,  so  that  each  shaft  may  be  adjusted  for  minimum  backlash  and  correcl 
tooth  mesh  of  the  mating  gears  and  then  locked  in  position.  The  intermittenl 
movement  consists  of  a  tandem  claw  selectively  hardened  at  points  of  wear,  actu- 
ated by  a  Lumiere-type  cam  for  the  pull-down  stroke,  with  a  second  cam  govern- 
ing the  in-and-out  movement.  The  Lumiere  cam  and  the  pull-down  claw  are 
fitted  together  and  kept  in  pairs  during  assembly.  The  periphery  of  the  Lumiere 
cam  is  ground  on  a  special  grinder  used  only  for  this  purpose,  the  overall  distance 
across  its  face  being  held  within  a  tolerance  of  0.0003  inch  measured  at  any  point 
With  this  refinement  and  care  in  assembly,  the  operation  of  the  mechanism  i< 
exceptionally  smooth  and  quiet. 

Threading  is  conventional  and  extremely  easy.  Sprocket  frames  open  foi 
easy  access  to  the  sprockets,  and  the  film  slides  into  the  gate.  To  facilitate  this 
operation,  the  out  position  of  the  pull-down  claw  is  designated  by  a  milled  side 
on  the  threading  knob  so  that  its  position  can  be  noted  by  touch  as  well  as  by 
sight  (Fig.  3). 

Stills  are  shown  by  merely  declutching  the  mechanism  from  the  motor,  al 
which  time  an  automatic  safety  shutter  swings  into  position  to  protect  the  film 
while  the  motor  and  fan  continue  to  run  for  adequate  lamp  protection.  By  throw- 
ing a  switch,  the  motor  is  reversed  and  pictures  may  be  projected  backwards 
Framing  is  accomplished  by  shifting  the  pull-down  claw  in  relation  to  the  aperture 
so  that  there  is  no  movement  of  the  picture  on  the  screen.  Sprockets,  sprocket 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;    received 
April  18,  1938. 

**  Eastman  Kodak  Co.,  Rochester,  N.  Y. 


Oct.,  1938] 


NEW  MOTION  PICTURE  APPARATUS 


411 


guards,  film-gate,  aperture  plate,  and  pull-down  claw  are  all  designed  to  operate 
sound-film  without  injury. 

Two  features  of  the  Model  G  deserve  special  mention.  JThe  first  is  the  rewind. 
For  rewinding,  the  movement  of  a  single  lever  engages  the  rewind  drive  and  re- 
leases the  take-up  reel.  This  lever  is  not  only  conveniently  located  for  operation, 
but  is  so  designed  that  it  effectively  obstructs  the  passage  of  film  through  the 
gate  if  left  in  the  "rewind"  position. 


FIG.  1.     The  Kodascope  model  G. 


Second,  a  single  switch  controls  motor,  threadlight,  and  projection  lamp  (Fig. 
i).  This  switch  has  four  positions:  in  the  first  position,  motor,  threadlight,  and 
amp  are  turned  off;  in  the  second  position,  the  threadlight  is  turned  on;  in  the 
:hird  position,  the  motor  is  started  and  the  threadlight  remains  on  so  that  the 
operator  can  momentarily  check  his  threading;  and  in  the  fourth  position,  the 
notor  continues  to  run  while  the  projection  lamp  is  turned  on  and  the  thread- 


412 


NEW  MOTION  PICTURE  APPARATUS        [J.  S.  M.  P.  E 


FIG.  2. 


The  mechanism  of  the  Koda- 
scope  Model  G. 


FIG.  3. 


Front  view,  showing  threading  knob  and 
still  picture  control. 


Oct.,  1938] 


NEW  MOTION  PICTURE  APPARATUS 


413 


light  is  turned  off.  A  single  knob  adjacent  to  this  switch  controls  the  motor 
|  speed.  The  threadlight  is  located  at  the  side  of  the  objective  lens,  and  illuminates 
I  the  upper  and  lower  sprocket  and  the  gate  so  that  no  other  light  is  needed  for 
changing  reels  in  a  darkened  room. 

The  lamp  house  and  the  fan  are 
designed  to  give  adequate  cooling  for 
high-wattage  lamps,  insuring  ample 
lamp  life.  The  optical  system  was 
specially  designed,  and  is  remarkably 
efficient  both  as  to  picture  quality  and 
screen  brilliance. 

Elevating  or  tilting  either  upward  or 
I  downward  to  center  the  picture  upon 
he  screen  is  accomplished  by  pivoting 
he  mechanism  on  the  pedestal  base. 
This  is  controlled  by  an  elevating 
mob  which  actuates  a  new  elevating 
nechanism;  it  operates  easily  and 
iffords  a  fine  adjustment.  Similar  to 
:he  Model  EE  Kodascope,  the  base  of 
.he  Model  G  fits  over  the  handle  of 
:he  carrying  case,  which  may  be  used 
is  a  projection  stand. 

A  new  2-inch,  //1. 6  lens,  especially 
lesigned  for  flatness  of  field,  is 
standard  equipment.  Other  lenses 
nclude  a  1-inch  f/2.5  for  short  throws, 
md  either  a  3-inch //2.0  or  a  4-inch  f/2.5  for  longer  throws.  These  lenses,  with 
he  400-,  500-,  and  750-watt  lamp's  permit  selection  from  twelve  possible  com- 
)inations.  The  standard  model  is  fitted  with  arms  for  400-ft.  reels;  however,  a 
nodel  for  1600-ft.  reels  will  be  available.  The  machine  is  finished  in  hand- 
ubbed  glossy  black  lacquer,  with  all  fittings  in  buffed  chrome  plate. 


FIG.    4.     Unit    control    for    thread- 
light,  motor,  and  lamp. 


A  NOVEL  SURGICAL  FILMING  STAND* 


A.  LENARD** 


Up  to  now  surgical  filming  has  always  been  accompanied  by  sundry  difficulties, 
vhich  have  often  resulted  in  the  decision  not  to  film  certain  types  of  operations 
hat  may  not  have  been  of  paramount  interest  or  the  outcome  of  which  could  not 
>e  predicted.  This  is  easy  to  understand  when  one  stops  to  consider  all  the  com- 
)lications  and  preparations  necessary  before  undertaking  to  film  an  operation,  the 


*  Received  June  15,  1938. 
**  Budapest,  Hungary. 


414 


NEW  MOTION  PICTURE  APPARATUS        [J.  s.  M.  P.  I 


many  accessories  and  paraphernalia  required  in  the  operating  room,  and  the  tim 
taken  to  get  everything  ready  for  filming  such  feats.  In  the  case  of  emergenc 
operations  it  has  been  nearly  impossible  to  rig  up  the  equipment  in  the  short  tim 
available,  and  it  is  fairly  safe  to  say  that  the  preparations  for  filming  an  operatic 
required  at  least  half  an  hour  before  bringing  in  the  patient. 

Some  of  the  difficulties  generally  er 
countered  are  cited  below;  but,  in  ac 
dition,  special  problems  arise  in  almos 
every  case  that  have  to  be  solved  in  th 
shortest  possible  time. 

It  is  obvious  that  the  cameraman  muj 
stand  outside  the  sterile  zone  and  wor 
in  such  a  way  as  not  to  hinder  th 
surgeon;  in  spite  of  which  he  nearl 
always  wants  extreme  close-up  shot; 
The  lighting  is  perhaps  the  "trickiest 
problem.  Everybody  who  has  tried  t 
take  pictures  of  operations  knows  ver 
well  how  difficult  it  is  to  place  the  light 
in  such  positions  as  to  provide  reall 
uniform  illumination  over  the  area  c 
interest;  not  interfere  with  the  surgeor 
assistants,  and  nurses;  and  yet  be  suffi 
ciently  removed  from  the  sterile  zone 
Nothing  must  be  in  the  way  of  th 
light-beams  that  will  cast  shadows  upo: 
the  operation  field  and  the  rubber 
covered  cables  must  be  led  along  th 
walls  so  that  no  one  may  tread  upo: 
them.  To  accomplish  all  this  the  light 
have  usually  been  placed  very  higt 
necessitating  the  use  of  very  high  stands 
High  stands  of  sufficient  rigidity  for  us 
in  operating  rooms  are  not  of  the  low 
priced  variety.  When  the  operation 
were  performed  within  cavities,  as  withii 
the  throat,  ear,  nose,  teeth,  and  i] 
gynecological  and  other  operations,  th 
lighting  offered  generally  such  insur 
mountable  difficulties  that  as  a  rule  sue! 
regions  were  rarely  if  ever  filmed.  Ii 

these  instances  the  light-source  can  be  only  a  single  unit,  must  be  constructed  s< 
as  to  provide  a  very  narrow  beam,  and  should  be  positioned  as  near  the  optica 
axis  of  the  taking  lens  as  possible.  The  ideal  condition  would  be  realized  if  thi 
beam  could  be  made  coincident  with  the  optical  axis.  At  the  same  time  the  bean 
must  be  able  to  follow,  within  certain  limits,  such  pan  or  tilt  movements  of  th< 
camera  as  may  be  necessary  during  the  shooting.  Since  there  is  only  a  singL 
beam  in  such  cases,  it  must  be  highly  concentrated;  but  it  must  not  be  allowed  t< 


FIG.    1. 


General   view   of  surgical 
camera  stand. 


Oct.,  1938] 


NEW  MOTION  PICTURE  APPARATUS 


415 


cause  excessive  heating  of  the  tissues  and  consequent  discomfort  of  the  patient  in 
cases  when  no  anesthetic  is  used.  A  very  important  matter  is  the  possibility  of 
making  quick  adjustments  of  the  camera  during  the  operation,  so  that  the  camera- 
man may  avoid  positions  from  which  the  surgeon  would  obstruct  the  view.  The 
ability  to  change  cameras  is  very  useful  when  the  reel  runs  empty  during  an  in- 
teresting phase  or  when  the  camera  is  spring-driven  rather  than  electrical. 

The  difficulties  outlined  above  have  been  eliminated  effectively  and  by  the 
surgical  filming  stand  of  original  construction  shown  in  Fig.  1.     The  stand  is 
completely  self-contained  and  once  it  is  rolled  into  place  the  cameraman  needs 
only  to  make  the  single  connection  to  the 
current  output  and  connect   two  rubber 
hoses  to  the  water  drain,  which  requires 
about  ten  minutes. 

The  base  is  of  heavy  cast  iron,  to 
provide  the  necessary  strength  and  elimi- 
nate all  vibration  even  when  working  at 
high  speeds  for  slow-motion  effects.  With 
minute  adjustments  at  full  lens  opening 
it  is  important  that  the  camera  should 
not  move  because  the  depth  of  field  is 
then  very  critical.  Also,  when  shooting 
small  areas  (teeth,  etc.)  with  the  telephoto 
lens  by  using  extension  rings  under  the 
lens  and  thus  working  from  great  dis- 
tances, the  slightest  wabbling  of  the  stand 
can  easily  spoil  the  macro-shot  or  even 
displace  the  camera  sufficiently  so  as  not 
to  take  in  the  required  field.  The  total 
weight  of  the  stand  is  about  50  kilograms. 
It  moves  on  three  rubber-covered  rollers, 
and  when  in  position  is  fixed  by  screwing 
three  steel  points  down  to  the  floor,  thus 
obviating  the  slightest  chance  of  wabble 
or  vibration.  The  upright  of  the  stand 
telescopes  in  two  sections.  One  section 
provides  the  rough  setting  in  height  and 

the  second  (with  a  hand-wheel)  is  an  accurate  vernier  adjustment.  All  adjust- 
ments can  be  fixed  rigidly  when  in  place.  When  raising  or  lowering  the  camera 
the  lenses  always  point  in  the  same  direction.  The  lowest  position  of  the  tripod 
head  is  85  cms.,  the  highest  152  cms.  above  the  ground.  Thus  every  possible 
taking  angle  can  be  covered  in  minimum  time. 

A  special  lamp  house  clamped  to  the  lower  part  of  the  stand  has  been  developed 
into  a  medical  spotlight  (Fig.  2).  The  lamp  house  is  positioned  vertically  because 
[most  projection  lamps  require  a  vertical  filament  position.  The  beam  is  directed 
through  a  condenser  and  concave  mirror  system  to  an  internal  plane  mirror, 
j  which  throws  the  beam  upward  and  through  a  second  lens  system  which  produces 
'  the  required  directional  spotlight  effect.  The  lamp  house  is  cooled  by  a  revolving 
fan  and  the  funnel-like  middle  piece  has  ample  holes  for  ventilation.  Under  the 


FIG.  2.  Lamp  house  attached 
to  base  of  stand,  showing  cooling 
fan  and  hose  connection  for  water 
circulation. 


416  NEW  MOTION  PICTURE  APPARATUS        [J.  S.  M.  P.  E. 

top  lens  is  a  waterholder  to  cool  down  the  beam  although  in  practice  this  is  not 
really  necessary,  except  when  photographing  inflamed  tissues.  The  water  can 
circulate  through  the  reservoir,  entering  by  one  rubber  hose  and  leaving  by  the 
other.  The  lamp  is  a  standard  250-watt  projection  bulb  with  two  plane  filaments, 
and  provides  ample  light  for  all  purposes,  even  for  slow-motion  shots  at  64  frames 
per  second  on  supersensitive  reversal  material  at  a  distance  of  about  2  meters 
from  the  stand  with  a  stop  of  f/2.8. 

The  stand  has  a  conventional  pan  and  tilt  tripod  head  for  supporting  the 
camera.  A  special  device  allows  instantaneous  attachment  of  the  camera  to  the 
head  by  clamping,  without  screws,  so  that  cameras  may  be  changed  in  one  second 
of  time.  Thus  a  loaded  camera  may  be  always  held  ready  and  put  into  place  at 


FIG.  3.     Detail  of  camera,  showing  plane  mirror  for  di- 
recting light  on  operation  field. 

the  moment  the  one  on  the  stand  runs  empty.  There  is  always  time,  however, 
to  rewind  the  taking  camera  upon  the  stand  between  phases  of  the  operation. 
An  electrical  drive  may,  of  course,  be  provided  to  permit  shooting  the  full  length 
of  the  100-ft.  reel,  when  required,  without  rewinding;  but  in  practice  this  has 
never  been  found  to  be  necessary,  the  18-ft.  run  of  the  spring-drive  having  always 
been  adequate.  A  wire  release  operated  by  means  of  a  pedal  allows  the  surgeon 
to  make  shots  himself  during  an  examination  or  an  easy  operation.  Of  course, 
he  must  have  an  assistant  in  any  event. 

The  beam  of  the  spot  is  directed  to  the  operating  field  by  a  plane  mirror  fixed 
to  the  pan  and  tilt  head  (Fig.  3).  This  mirror  can  be  moved  and  clamped  in  any 
desired  direction  by  the  universal  ball-joint  on  its  back.  The  area  illuminated  is 
checked  in  the  view-finder,  and  the  beam  can  be  made  fairly  close  to  the  optical 
axis  of  the  lens,  giving  the  best  illumination  for  every  purpose  and  the  most  ex- 


Oct.,  1938]  NEW  MOTION  PICTURE  APPARATUS  417 

cellent  results  when  photographing  cavities.  Furthermore,  as  the  mirror  moves 
together  with  the  camera  when  tilting  or  panning  within  reasonable  limits  (such 
as  occur  in  work  of  this  sort)  the  beam  always  follows  th&  direction  of  the  lens  and 
illuminates  the  photographed  area  in  all  cases.  The  divergence  of  the  beam  has 
been  calculated  to  have  an  angle  of  divergence  of  approximately  30  degrees  so  as 
to  cover  the  field  to  its  borders  even  with  relatively  generous  angles  of  tilt  and 
pan. 

A  Paillard  Bolex  16-mm.  camera  was  used,  equipped  with  a  special  eyepiece  for 
controlling  the  focus  from  the  back.  Also  extension  rings  were  used  under  the 
telephoto  lens  to  make  macro-shots  from  relatively  great  distances.  The  inside 
of  the  throat  of  a  dog,  for  instance,  filled  the  whole  screen.  The  shot  was  made 
using  an  extension  ring  with  a  telephoto  lens  of  75-mm.  focus  from  a  distance  of 
1.5  meters. 

As  an  example  of  the  splendid  results  attained  with  this  stand  may  be  men- 
tioned a  slow-motion  shot  of  vibrating  vocal  chords  taken  in  the  living  throat 
Of  course,  the  spotlight  may  be  put  out  of  use  if  not  needed;  for  simple  surgical 
shots  two  horizontal  rod-holds  are  provided  for  two  regular  photoflood  bulbs  in 
standard  reflectors  on  both  sides  of  the  camera.  It  is  believed  that  cameramen 
using  this  stand  for  surgical  shots  will  greatly  enjoy  the  extraordinary  facilities 
that  its  use  makes  possible. 


CURRENT  LITERATURE  OF  INTEREST  TO  THE  MOTION  PICTURE 

ENGINEER 


The  editors  present  for  convenient  reference  a  list  of  articles  dealing  with  subjects 
cognate  to  motion  picture  engineering  published  in  a  number  of  selected  journals. 
Photostatic  copies  may  be  obtained  from  the  Library  of  Congress,  Washington,  D.  C., 
or  from  the  New  York  Public  Library,  New  York,  N.  Y.  Micro  copies  of  articles 
in  magazines  that  are  available  may  be  obtained  from  the  Bibliofilm  Service,  Depart- 
ment of  Agriculture,  Washington,  D,  C. 


Journal  of  the  Acoustical  Society  of  America 

10  (July,  1938),  No.  1 
On  Distortion  in  Sound  Reproduction  from  Phonograph 

Records  (pp.  14-28). 
Finite  Solid  Acoustic  Filters  (pp.  41-44). 

Acoustical  Output  of  Air  Sound  Senders  (pp.  50-62). 


J.    A.    PIERCE    AND 

F.  V.  HUNT 

R.  B.  LINDSAY  AND 

A.  B.  FOCKE 

O.  DEVIK  AND 

H.  DAHL 


American  Cinematographer 

19  (July,  1938),  No.  7 
Just  One  Camera  Problem  after  Another  Created  by 

Speedy  Sonja  (pp.  268-9,  271).  J.  J.  MESCALL 

Dr.  Carter  Outlines  History  of  Search  for  Permanent 

Photograph  (pp.  270-1).  R.  W.  CARTER 


Journal  of  the  British  Kinematograph  Society 

1  (May,  1938),  No.  2 
Screen  Brightness  and  its  Measurement  (pp.  68-89). 

The  Structure  of  the  Industry  (pp.  90-98). 

A  Precision  Instrument  for  the  Determination  of  Expo- 
sure (pp.  99-119). 

Photographic  Technique  for  Variable-Area  Recording 
(pp.  120-36). 

A  Brief  Description  of  the  British  Realita  Process  (pp. 
137-40). 

Communications 

18  (July,  1938),  No.  7 

Notes  on  New  Television  Standards  (pp.  5-8,  34). 
Standard  Speech-Input  Assemblies  (pp.  15-18,  24,  29- 

31). 
An  Impedance  Meter  (pp.  23-4). 

418 


C.  G.  KEYS  HALLETT 
AND  A.P.CASTEELAIN 
S.  ROWSON 

L.  MOEN 
S.  R.  BADE 


R.  F.  WILD 

O.  RICHARDSON 
A.  W.  BARBER 


CURRENT  LITERATURE 


419 


Electronics 

11  (July,  1938),  No.  7 

A  Laboratory  Television  Receiver  (pp.  16-20). 
Volume  Indicator- Attenuator  (pp.  22-4). 
A  New  Television  Film  Projector  (p.  25). 


D.  G.  FINK 
S.  G.  CARTER 
H.  S.  BAMFORD 


RMA  Completes  Television  Standards  (pp.  28-9,  55).        A.  F.  MURRAY 

International  Photographer 

10  (July,  1938),  No.  6 
News  of  New  Products  (pp.  1-7). 

Protize  Process  (pp.  9-10).  S.  P.  SOLOW 

Grip  Equipment  (pp.  14,  16).  G.  M.  HAINES 

Analysis  of  Developing  Solutions  (p.  22).  D.  K.  ALLISON 

SMPE  Theater  Survey  Report  (pp.  24-7). 

International  Projectionist 

13  (June,  1938),  No.  6 
Take-Up  Troubles:    How  to  Locate  and  Correct  Them 

(pp.  7-8,  34).  A.  C.  SCHROEDER 

Sound  Equipment  Troubles:  Hum  (pp.  11-12,  14).  A.  NADELL 

MGM  Film  Lubrication  Policy  (p.  14).  J.  M.  NICKOLAUS 

Academy  Research  Council  Nomenclature  for  Release- 
Print  Sound-Tracks  (pp.  22-24).  J.  K.  HILLIARD 

13  (July,  1938),  No.  7 

Some  Common  Sources  of  Noise  in  Theater  Sound  Sys- 
tems (pp.  7-8,  11,  13).  A.  NADELL 

Academy  Recommendations  on  Theater  Sound  Repro- 
ducing Equipment  (pp.  14-15,  29,  30). 

Take-Up  Troubles :  How  to  locate  and  Correct  Them 

(pp.  17-19).  A.  C.  SCHROEDER 

Kinematograph  Weekly 

257  (July,  1938),  No.  1629 

New  Apparatus  from  Vinten  Workshops:  Gamma 
Gauge,  Negative  Grader,  and  a  High-Speed  Camera 


(P.  33). 

Kinotechnik 

20  (July,  1938),  No.  7 

Wiedergabe  tiefer  Tone  hoher  Leistung.  (High-Fre- 
quency  Reproduction)  (pp.  172-3). 

Die  Kinotechnik  in  der  Lehrschau  der  Ufa  (Ufa  Educa- 
tional Exhibit)  (pp.  174-6). 

Eine  neue  Kleinapparatur  fur  Tonfilmaufnahme  (New 
Small  Sound  Recording  Camera)  (pp.  176-9). 

Konstruktion  von  Schmalfilmprojektoren  nach  licht- 
technischen  Grundsatzen  (Contruction  of  Substand- 
ard Projectors  on  the  Principles  of  Light  Optics)  (pp. 
179-83). 


R.  HOWARD  CRICKS 


H.  BENECKE 


M.  DIETRICH 


ING.  M.  NAGEL 


420 


CURRENT  LITERATURE 


Allgemeine  raumakustische  Betrachtungen  zur  elektro- 
akustischen  Schallaufnahme  (General  Observations 
on  Room  Acoustics  for  Electrical  Recording)  (pp. 
183-6). 

Die  Messung  des  photographischen  Gleichrichteref- 
fektes  (Measurement  of  Photographic  Rectifying  Ef- 
fect) (p.  187). 


Neue  Umkehr-Emulsionen  fur  Schmalfilm  (New 
versal  Emulsions  for  Substandard  Film)  (p.  193). 


Re- 


Journal  of  the  Optical  Society  of  America 

28  (July,  1938),  No.  7 

An  Experimental  Study  of  Latent-Image  Formation  by 
Means  of  Interrupted  and  Herschel  Exposures  at  Low 
Temperatures  (pp.  249-63). 

Philips  Technical  Review 

3  (Apr.,  1938),  No.  4 

The  Behavior  of  Amplifier  Valves  at  Very  High  Fre- 
quencies (pp.  1©3-11). 

Photographische  Industrie 

36  (July  6,  1938),  No.  27 

Filmpflege,  ihre  physikalischen  und  chemischen  Beding- 
ungen.  I.  (Physical  and  Chemical  Limitations  in 
the  Care  of  Film.  I)  (pp.  783-6). 

36  (July  13,  1938),  No.  28 

Filmpflege,  ihre  physikalischen  und  chemischen  Beding- 
ungen.  II.  (Physical  and  Chemical  Limitations  in 
the  Care  of  Film.  II)  (pp.  807-10). 


E.  MEYER 


A.  NARATH  AND 
W.  Vox 


J.    H.    WEBB 
C.  H.  EVANS 


AND 


M.  J.  O.  STRUTT  AND 
A.  VAN  DER  ZIEL 


O.  TREICHEL 


O.  TREICHEL 


FALL,  1938,  CONVENTION 


DETROIT,  MICHIGAN 

HOTEL  STATLER 
OCTOBER  31-NOVEMBER  2,  INCLUSIVE 


Officers  and  Committees  in  Charge 

W.  C.  KUNZMANN,  Convention  Vice-President 
J.  I.  CRABTRBB,  Editorial  Vice-President 
G.  E.  MATTHEWS,  Chairman,  Papers  Committee 
H.  GRIFFIN,  Chairman,  Projection  Committee 
E.  R.  GEIB,  Chairman,  Membership  Committee 
J.  HABER,  Chairman,  Publicity  Committee 


G.  AVIL 

A.  J.  BRADFORD 
F.  C.  DICKELY 
E.  H.  FORBES 
W.  M.  HARRIS 


E.  R.  GEIB 


Local  Arrangements 

K.  BRBNKERT,  Chairman 

G.  A.  McARTHUR 
E.  J.  MCGLINNEN 

R.  R.  McMATH 
H.  S.  NORTON 
R.  L.  RUBEN 


G.  J.  SKIMIN 
J.  F.  STRICKLER 
H.  H.  STRONG 
W.  J.  TURNBULL 
E.  F.  ZATORSKY 


Registration  and  Information 

W.  C.  KUNZMANN,  Chairman 


S.  HARRIS 


G.  J.  SKIMIN 


Hotel  and  Transportation  Committee 

A.  J.  BRADFORD,  Chairman 

H.  ANDERS  L.  A.  FIFERLIK  W.  C.  KUNZMANN 

A.  B.  CHERTON  G.  J.  JARRETT  P.  M.  MOLS 

M.  DUDELSON  K.  KALLMAN  E.  J.  SCHAEFBR 


M.  C.  BATSEL 
A.  J.  BRADFORD 
K.  BRENKERT 
F.  C.  DICKELY 
E.  H.  FORBES 


Projection 

H.  GRIFFIN,  Chairman 
W.  M.  HARRIS 

F.  MOLES 

H.  S.  MORTON 

G.  A.  MCARTHUR 


E.  J.  MCGLINNEN 
R.  L.  RUBEN 
H.  H.  STRONG 
W.  J.  TURNBULL 
M.  J.  YAHR 


Officers  and  Members  of  Detroit  Projectionists  Local  No.  199 


A.  J.  BRADFORD 
K.  BRENKERT 
H.  GRIFFIN 


Banquet 

J.  F.  STRICKLER,  Chairman 
S.  HARRIS 
G.  J.  JARRETT 
W.  C.  KUNZMANN 


R.  R.  McMATH 
H.  H.  STRONG 
E.  F.  ZATORSKY 


421 


422  FALL  CONVENTION  [j.  s.  M.  P.  E. 

Publicity 

J.  HABER,  Chairman 

J.  R.  CAMERON  S.  HARRIS  P.  A.  McGuiRE 

J.  J.  FINN  G.  E.  MATTHEWS  F.  H.  RICHARDSON 

Ladies'  Reception  Committee 

MRS.  J.  F.  STRICKLER,  Hostess 

assisted  by 

MRS.  G.  AVIL  MRS.  F.  C.  DICKELY  MRS.  G.  A.  MCARTHUR 

MRS.  A.  J.  BRADFORD  MRS.  E.  H.  FORBES  MRS.  R.  L.  RUBEN 

MRS.  K.  BRENKERT  MRS.  W.  M.  HARRIS  MRS.  G.  J.  SKIMIN 

Headquarters 

The  Headquarters  of  the  Convention  will  be  at  the  Hotel  Statler,  where  excellent 
accommodations  are  assured.  A  reception  suite  will  be  provided  for  the  Ladies' 
Committee,  who  are  now  engaged  in  preparing  an  excellent  program  of  entertain- 
ment for  the  ladies  attending  the  Convention. 

Special  hotel  rates  guaranteed  to  SMPE  delegates  and  friends,  European  plan, 
will  be  as  follows : 

One  person,  room  and  bath  $3.00  to  $6.00 

Two  persons,  room  and  bath  5.00  to    8.00 

Two  persons  (twin  beds),  room  and  bath  5.50  to    9.00 

Three  persons,  room  and  bath  7.50  to  10.50 

Parlor  suite  and  bath,  for  one  8.50  to  11.00 

Parlor  suite  and  bath,  for  two  12.00  to  14.00 

Room  reservation  cards  will  be  mailed  to  the  membership  of  the  Society  in  the 
near  future,  and  everyone  who  plans  to  attend  the  Convention  should  return  his 
card  to  the  Hotel  promptly  in  order  to  be  assured  of  satisfactory  accommodations. 
Registrations  will  be  made  in  the  order  in  which  the  cards  are  received.  Local 
railroad  ticket  agents  should  be  consulted  as  regards  train  schedules,  and  rates  to 
Detroit  and  return. 

The  following  special  rates  have  been  arranged  for  SMPE  delegates  who  motor 
to  the  Convention,  at  the  National-Detroit  Fireproof  Garage  (the  Hotel  Statler's 
official  garage),  Clifford  and  Elizabeth  Streets,  Detroit:  Self -delivery  and  pick-up, 
12  hours,  $0.60;  24  hours,  $1.00;  Hotel-delivery  and  pick-up,  24  hours,  $1.25. 
Special  weekly  rates  will  be  available. 

Technical  Sessions 

An  attractive  and  interesting  program  of  technical  papers  and  presentations  is 
being  assembled  by  the  Papers  Committee.  All  technical  sessions,  apparatus 
symposiums,  and  film  programs  will  be  held  in  the  Large  Banquet  Room  of  the 
Hotel. 

Registration  and  Information 

Registration  headquarters  will  be  located  at  the  entrance  of  the  Large  Banquet 
Room,  where  members  of  the  Society  and  guests  are  expected  to  register  and  re- 
ceive their  badges  and  identification  cards  for  admittance  to  the  sessions  and  film 


Oct.,  1938]  FALL  CONVENTION  423 

programs.  These  cards  will  be  honored  also  at  the  Fox  Detroit  Theater,  through 
the  courtesy  of  Mr.  David  Idzol,  and  special  passes  will  be  furnished  to  registered 
members  and  guests  for  admittance  to  the  Michigan  United  Artists  and  Palms- 
State  Theaters,  through  the  courtesy  of  the  United  Detroit  Theaters  Corporation. 

Informal  Luncheon  and  Semi-Annual  Banquet 

The  usual  Informal  Luncheon  will  be  held  at  noon  of  the  opening  day  of  the 
Convention,  October  31st,  in  the  Michigan  Room  of  the  Hotel.  On  the  evening  of 
Tuesday,  November  1st,  the  Semi-Annual  Banquet  of  the  Society  will  be  held 
in  the  Grand  Ballroom  of  the  Hotel  at  8  P.M.  Addresses  will  be  delivered  by 
prominent  members  of  the  industry,  followed  by  dancing  and  other  entertainment. 

Tours  and  Points  of  Interest 

In  view  of  the  fact  that  this  Convention  will  be  limited  to  three  days,  no 
recreational  program  or  tours  have  been  arranged.  However,  arrangements 
may  be  made  for  visits  to  the  Jam  Handy  plant  and  to  other  points  of  technical 
and  general  interest  in  Detroit  on  the  day  following  the  Convention,  namely, 
November  3rd.  Arrangeir ents  for  such  trips  may  be  made  at  the  registration 
headquarters  of  the  Convention. 

In  addition  to  being  a  great  industrial  center,  Detroit  is  also  well  known  for  the 
beauty  of  its  parkways  and  buildings,  and  its  many  artistic  and  cultural  activities. 
Among  the  important  buildings  that  one  may  well  visit  are  the  Detroit  Institute 
of  Arts;  the  Detroit  Historical  Society  Museum;  the  Russell  A.  Alger  House,  a 
branch  of  the  Detroit  Institute  of  Arts;  the  Cranbrook  Institutions;  the  Shrine 
of  the  Little  Flower;  and  the  Penobscot  Building. 

At  Greenfield  Village,  Dearborn,  are  grouped  hundreds  of  interesting  relics  of 
early  American  life,  and  there  also  is  located  the  Edison  Institute,  established  by 
Henry  Ford  in  memory  of  Thomas  A.  Edison. 

On  the  way  to  Greenfield  Village  is  the  Ford  Rotunda,  a  reception  hall  for  visi- 
tors to  the  Ford  Rouge  Plant.  Here  are  complete  reproductions  and  displays  of 
motorcar  design,  and  representations  of  the  famous  highways  of  the  world,  from 
Roman  days  to  modern,  are  on  the  grounds  surrounding  the  building. 

The  General  Motors  Research  Building  and  Laboratory,  located  on  Milwaukee 
Avenue,  will  be  of  particular  interest  to  engineers  visiting  the  City. 

Various  trips  may  be  taken  from  Detroit  as  a  center — to  Canada,  by  either  the 
Ambassador  Bridge  or  the  Fleetway  Tunnel;  to  Bloomfield  Hills,  a  region  of 
lakes;  Canadian  Lake  Erie  trip  from  Windsor,  Ontario;  to  Flint,  Michigan, 
another  center  of  the  automotive  industry;  to  Milford,  General  Motors'  Proving 
Grounds;  and  to  the  Thumb  of  Michigan  Resort  Beaches.  The  City  contains 
also  a  number  of  beautiful  parks  and  golf  courses. 


ABSTRACTS  OF  PAPERS  OF  THE 
FALL  CONVENTION 


AT 


DETROIT,  MICH.,  OCT.  3i-NOV.  2, 1938 


The  Papers  Committee  submits  for  the  consideration  of  the  membership  the  follow- 
ing abstracts  of  papers  to  be  presented  at  the  Fall  Convention.  It  is  hoped  that  the 
publication  of  these  abstracts  will  encourage  attendance  at  the  meeting  and  facilitate 
discussion.  The  papers  presented  at  Conventions  constitute  the  bulk  of  the  material 
published  in  the  Journal.  The  abstracts  may  therefore  be  used  as  convenient  refer- 
ence until  the  papers  are  published. 

G.  E.  MATTHEWS,  Chairman 
L.  A.  AICHOLTZ,  Chairman,  West  Coast 

P.  ARNOLD  C.  FLANNAGAN  F.  H.  RICHARDSON 

C.  N.  BATSEL  L.  D.  GRIGNON  C.  R.  SAWYER 

L.  N.  BUSCH  E.  W.  KELLOGG  P.  R.  VON  SCHROTT 

O.  O.  CECCARINI  R.  F.  MITCHELL  H.  G.  TASKER 

A.  A.  COOK  W.  A.  MUELLER  C.  K.  WILSON 

L.  J.  J.  DIDIEE  I.  D.  WRATTEN 

"  Some  of  the  Problems  Ahead  in  Television";  I.  J.  Kaar,  General  Electric  Co. 
Bridgeport,  Conn. 

Now  that  television  standards  have  been  agreed  upon  in  the  United  States, 
commercial  receiving  sets  will  undoubtedly  be  available  very  soon,  and  regularly 
scheduled  television  programs  may  be  expected  at  the  same  time.  How  good 
will  the  television  be  and  what  are  the  problems  yet  to  be  solved  before  television 
reaches  the  technical  maturity  that  radio  has  today?  These  are  questions  of  con- 
siderable interest  to  engineers  in  related  fields,  and  are  the  subject  matter  of  the 
present  paper.  The  quality  of  present-day  television  pictures  is  compared  with 
that  of  motion  pictures  both  in  the  theater  and  in  the  home.  A  discussion  is  given 
of  the  problems  that  have  been  solved  to  make  television  what  it  is  today,  and  con- 
sideration is  given  to  the  problems  that  must  be  solved  to  make  television  what  we 
hope  it  will  be  tomorrow.  The  problems  of  signal  propagation  and  interference 
are  discussed,  and  the  matter  of  network  program  distribution  is  considered. 
Finally,  a  short  introduction  is  given  to  the  commercial  problems  in  television. 

"Some  Production  Aspects  of  Binaural  Recording  for  Sound  Motion  Pictures"; 
W.  H.  Offenhauser,  Jr.,  New  York,  N.  Y.,  and  J.  J.  Israel,  Brooklyn,  N.  Y. 

Binaural  sound  recording  for  motion  pictures  has  a  long  development  history  of 
worthy  achievement,  yet  to  date  it  has  not  found  application  in  our  everyday  en- 
tertainment sound  motion  picture.  Inspection  of  the  situation  reveals  that,  like 

424 


FALL  CONVENTION  425 

stereoscopic  pictures,  there  is  not  complete  acceptance  of  any  of  the  various  theo- 
ries and  that  the  shades  of  interpretation  are  so  many  that  it  is  difficult  to  secure 
a  consensus  on  what  constitutes  binaural  sound  recording  for  motion  pictures. 
Instances  are  cited  to  show  that  "theoretically  perfect "*sound  is  not  necessarily 
the  objective ;  in  fact,  since  it  is  the  illusion  produced,  both  by  sound  and  picture 
that  is  in  the  final  analysis  important,  "theoretically  perfect"  sound  may  even  de- 
stroy the  illusion  we  are  trying  to  create. 

The  history  of  binaural  sound  recording  for  motion  pictures  is  reviewed  and 
especial  reference  is  made  to  the  early  developments  of  Rosenberg  and  Kuechen- 
meister.  A  short  review  of  the  developments  since  the  work  of  these  pioneers 
covers  in  a  general  way  the  advance  of  the  binaural  sound  motion  picture  recording 
art  to  date.  The  production  requirements  of  binaural  sound  recording  for 
motion  pictures  are  analyzed  briefly  and  the  importance  of  the  editing  process  in 
the  production  of  the  finished  picture  is  outlined. 

A  new  binaural  sound  motion  picture  production  technic  is  suggested,  based  upon 
the  developments  of  the  authors,  that  may  be  quite  readily  adapted  to  present- 
day  monaural  production  technic.  It  is  pointed  out  that  the  perspective  sound 
control,  which  is  an  important  added  feature,  does  not  affect  shooting  stage  op- 
erations; this  control  is  suggested  as  a  logical  part  of  dubbing-room  operations. 
Some  of  the  effects  produced  include  variation  of  apparent  recording-room  size 
from  very  small,  say,  1000  cu.  ft.  to  very  large,  say,  500,000  cu.  ft.  Another 
important  effect  is  the  simultaneous  yet  essentially  independent  movement  of  one 
sound-source  with  respect  to  another  and  the  essentially  independent  left-right 
movement.  All  these  effects  are  possible  wi+h  no  movement  whatever  of  the 
sound-source  or  sources  with  respect  to  the  microphones.  Essentially  the  same 
effects  can  be  obtained  with  the  pseudo-binaural  system,  a  system  in  which  it  is 
possible  to  take  a  completed  picture  of  the  conventional  monaural  type  and  by  a 
simple  dubbing  operation,  provide  practically  all  the  important  binaural  charac- 
teristics without  any  additional  original  sound  recording  whatever.  The  effects 
described  will  be  demonstrated. 

"The  Spectraheliokinematograph";  R.  R.  McMath,  McMath-Hulbert  Ob- 
servatory, University  of  Michigan,  Ann  Arbor,  Mich. 

Taking  motion  pictures  of  celestial  phenomena  that  show  change  is  not  as 
simple  as  it  would  appear  at  first  thought.  This  work  was  started  in  1928,  and 
in  1931  the  instrumentation  was  donated  by  the  founders  of  the  McMath-Hulbert 
Observatory  to  The  University  of  Michigan. 

The  combined  tower  telescope  and  spectroheliokinematograph  of  the  McMath- 
Hulbert  Observatory  at  Lake  Angelus,  Mich.,  is  now  one  of  the  most  powerful 
pieces  of  solar  apparatus  in  the  world.  The  optical  train  will  be  explained  by 
means  of  slides,  and  then  the  apparatus  itself  will  be  illustrated  by  motion  pic- 
tures. A  second  reel  will  show  solar  prominences  in  motion. 

"Underwater  Cinematography";  E.  R.  F.  Johnson,  Mechanical  Improvements 
Corp.,  Moorestown,  N.  J. 

The  dates  of  the  first  recorded  use  of  underwater  photography  and  the  tenden- 
cies toward  its  increasing  use  by  producers  are  noted.  The  author's  early  ex- 
periences in  this  field  are  described.  The  opinion  is  expressed  that  for  work  in 
natural  settings  the  most  useful  equipment  consists  of  submergeable  cameras 


426  FALL  CONVENTION  [j.  s.  M.  P.  E. 

placed  on  the  bottom  and  operated  by  divers.  The  rest  of  the  paper  deals  with 
the  problems  of  and  equipment  for  such  work.  It  is  pointed  out  that  studio 
tank  work  shares  most  of  these  problems. 

The  optical  properties  of  water  are  described.  Since  water  is  less  transparent 
than  air,  photography  by  natural  light  is  limited  to  small  depths  and  more  power 
is  required  for  artificial  illumination  under  water.  Since  colors  are  not  absorbed 
equally,  accurate  monochrome  rendering  and  photography  in  natural  color 
are  complicated.  Water  haze  limits  the  distance  at  which  pictures  can  be  taken 
under  water.  This  haze  is  largely  confined  to  a  part  of  the  spectrum  and  can  be 
eliminated  partially  by  color-filters.  It  is  polarized  and  can  therefore  be  elimi- 
nated also  by  polarizing  plates.  The  advantages  of  this  method  are  briefly 
stated:  they  do  not  distort  the  monochrome  rendering,  and  may  be  used  in  natu- 
ral-color photography.  The  ideal  attributes  of  equipment  for  use  in  under- 
water cinematography  are  outlined  and  available  equipment  is  briefly  described. 

"Improving  the  Fidelity  of  Disk  Records  for  Direct  Playback";  H.  J.  Has- 
brouck,  RCA  Manufacturing  Co.,  Inc.,  Camden,  N.  J. 

Recent  advances  in  equipment  design  and  in  materials  of  which  recording  disks 
are  composed,  have  resulted  in  improved  fidelity.  Both  the  volume  range  and 
the  frequency  range  have  been  extended,  satisfying  present-day  requirements  of 
motion  picture  and  broadcast  applications. 

For  reproduction,  there  is  provided  a  new  lighter  weight  lateral  pick-up  having 
high  sensitivity  and  equipped  with  a  permanent  diamond  point.  This  reproducer, 
in  combination  with  its  associated  circuit,  is  suitable  for  use  on  all  laterial-cut 
disk  records. 

Pre-  and  post-equalization  are  employed  in  the  method  described  for  making 
high-fidelity  records,  insuring  an  extremely  low  noise-level.  This  absence  of 
background  noise  together  with  the  wide  frequency  range  and  low  overall  dis- 
tortion create  an  illusion  of  reality  or  "presence"  during  reproduction. 

Usually  a  great  many  playings  are  not  required  of  direct  playback  disks. 
However,  because  of  the  low  mechanical  impedance  of  the  new  RCA  pick-up  and 
the  improved  composition  of  the  disks  it  is  possible  to  reproduce  75  to  100  times 
without  appreciable  increase  in  noise  or  distortion.  Great  differences  in  record 
life  under  various  conditions  of  handling  have  been  noted  and  are  attributed 
chiefly  to  accumulation  of  fingerprints  and  dust  on  the  record  surface.  Gradual 
oxidation  of  the  lacquer  coating  must  also  be  considered  and  guarded  against  by 
special  care  when  records  of  this  type  are  intended  for  long  preservation. 

"Characteristics  of  Film-Reproducing  Systems";  F.  Durst,  International  Pro- 
jector Corp.,  New  York,  N.  Y. 

An  analysis  of  sound-picture  reproducing-system  characteristics,  including 
electrical  and  acoustical  response  data  collected  in  the  interest  of  determining  the 
possibilities  involved  in  obtaining  an  average  characteristic  for  reproducing  vari- 
ous film  products  with  uniform  response  over  several  combinations  of  loud  speaker 
equipment.  With  the  aid  of  a  curve  tracer  having  a  long-persistent  cathode-ray 
screen,  a  photographic  record  was  made  of  the  characteristics,  starting  with 
various  forms  and  amounts  of  equalization  and  exploring  their  relationship  to  the 
power-handling  capacity  of  amplifiers.  Following  through  the  system,  this 
record  shows  the  characteristics  of  dividing  networks  under  various  conditions  of 


Oct.,  1938]  FALL  CONVENTION  427 

load,  and  finally  the  acoustical  response  curves  taken  for  comparison  of  the  loud 
speaker  equipments  under  study. 

The  measurements  of  loud  speaker  combinations  included  various  types  of 
units,  both  permanent-magnet  and  energized,  low-frequency  horns  ranging  from 
open  back  baffles  to  folded  horns  with  specially  designed  rear-loading  compart- 
ment, and  high-frequency  multicellular  horns  of  various  configurations  and  con- 
structional details. 

After  establishing  the  natural  characteristics  of  the  various  equipments  in- 
volved, careful  listening  tests  were  made  over  an  extended  period  with  samples  of 
commercial  prints  and  other  recordings.  A  description  follows  of  the  difficulties 
and  problems  involved  in  an  effort  to  obtain  one  overall  characteristic,  which 
would  give  satisfactory  reproduction  for  all  types  of  material.  The  final  results 
are  shown,  with  a  short  discussion  of  the  methods  for  duplication  in  other  equip- 
ment combinations,  and  conclude  with  recommendations  for  future  designs  and 
ratings. 

"Some  Practical  Accessories  for  Motion  Picture  Recording";  R.  O.  Strock, 
Eastern  Service  Studios,  Long  Island  City,  N.  Y. 

The  addition  of  practical  operational  accessories  to  standard  recording  chan- 
nels as  purchased  expedites  operation  and  saves  time.  At  the  Eastern  Service 
Studios  a  number  of  such  accessories  have  been  designed  and  will  be  described 
briefly.  It  is  the  purpose  of  this  paper  to  show  what  has  been  done  at  one  studio 
in  the  hope  that  it  may  be  of  some  interest  and  help  to  others  who  are  engaged  in 
recording  work. 

Included  in  the  equipment  are  the  following  items :  A  small  collapsible,  portable 
microphone  boom  for  location  work;  a  special  microphone  suspension  to  pre- 
vent mechanical  noises  from  getting  into  the  recording  system;  a  small  mixer 
console  for  stage  work,  to  permit  the  mixerman  to  operate  close  to  the  scene  of 
action;  an  accurate  illumination  meter,  using  a  microammeter,  for  setting  and 
checking  the  recording  machine  exposure;  a  compact  re-recording  mixer  console 
equipped  with  equalizers,  effect  filters,  amplifiers,  and  attenuators;  a  projected 
volume  indicator  and  footage  counter  for  use  in  re-recording  rooms;  a  film  play- 
back adapter  for  use  on  a  Western  Electric  film  machine  for  location  use;  play- 
back horns  for  stage  and  location  use;  and  an  air-brush  adaptation  for  blooping 
re-recording  tracks. 

"The  Lighting  of  Theater  Interiors";  F.  M.  Falge,  General  Electric  Company, 
Cleveland,  Ohio. 

Here  and  there  a  theater  is  planned  with  lighting  features  utilizing  the  funda- 
mental principles  that  have  been  expounded  on  many  occasions.  In  too  many 
cases,  however,  interior  lighting  has  lagged  far  behind  exterior  lighting  for  ad- 
vertising, and  owner  and  public  alike  have  suffered.  In  too  many  cases,  also, 
the  theater  falls  far  short  of  complementing  the  attractive  scenes  so  well  pro- 
jected upon  the  screen. 

This  paper  reiterates  the  aims  and  advantages  of  proper  lighting,  and  outlines 
the  problem  of  locating,  coloring,  and  controlling  the  lighting  properly  so  that  it 
will  be  comfortable  and  pleasing  and  an  aid,  psychologically.  It  discusses  the 
possibilities  of  systems  of  lighting  such  as  downlighting  and  fluorescent  lighting. 
New  materials  and  new  light-sources  will  be  demonstrated  and  discussed. 


428  FALL  CONVENTION  [j.  s.  M.  p.  E 

New  equipment  for  brightness  measurement  will  also  be  shown  as  an  aid  11 
building  up  a  quantitative  background  of  what  conditions  conduce  to  comfor 
and  satisfaction. 

"The  Evolution  of  Arc  Broadside  Lighting  Equipment";  P.  Mole,  Mole-Rich 
ardson  Co.,  Hollywood,  Calif. 

From  the  earliest  days  of  artificial  lighting  of  motion  picture  sets  the  broad 
side  type  of  unit  has  been  a  fundamental  lighting  tool.  Regardless  of  the  typ 
of  light-source  used  in  such  lamps — whether  mercury-vapor  tubes,  carbon  arcs,  o 
incandescent  filament  globes — the  broadside  is  a  lamp  of  the  floodlight  type,  de 
signed  to  emit  a  relatively  wide  flood  of  soft,  moderately  powerful  illumination 
It  has  withstood  innumerable  sweeping  changes  in  lighting  and  photograph! 
technic,  including  the  introduction  and  acceptance  of  spotlighting,  the  chang 
from  orthochromatic  to  panchromatic  film  materials,  the  changes  from  silent  fc 
talking  pictures  and  from  arc  to  incandescent  light-sources,  and  the  present  grow 
ing  popularity  of  natural-color  photography. 

The  present  paper  will  trace  the  evolution  of  arc  broadsides  only.  It  will  com 
ment  upon  the  design  and  performance  of  the  early-day  units,  which  were  adapte< 
almost  intact  from  previous  similar  lamps  used  in  photoengraving.  It  will  follow 
the  evolution  of  the  broadside  through  successive  improvements  in  silent-pictur 
usages;  through  its  decline  at  the  introduction  of  sound  and  Mazda  lighting 
through  the  relatively  recent  rebirth  of  arc  lighting  due  to  the  requirements  o 
modern  natural-color  photography;  and  the  most  recently  introduced  units  o 
this  type  which  are  replacing  equipment  designed  less  than  five  years  ago  at  th 
introduction  of  the  three-color  Technicolor  process.  Comparison  will  be  mad* 
between  the  early,  intermediate,  and  modern  units  as  regards  color  distribution 
light  distribution,  steadiness  and  length  of  burning  period,  indicating  that  thougl 
less  public  attention  has  been  given  to  these  types  than  to  the  more  familiar  spot 
lighting  units,  the  broadside  has  kept  pace  with  advances  in  lighting  and  equip 
ment  design. 

Report  of  the  Projection  Practice  Committee;  H.  Rubin,  Chairman. 

This  report  deals  with  two  major  projects  completed  by  the  Committee  withh 
the  past  six  months,  namely,  the  third  revision  of  the  Projection  Room  Plans  anc 
the  proposed  revision  of  the  NFPA  "Regulations  for  Handling  Nitrocellulose 
Motion  Picture  Film."  These  two  projects  are  given  in  detail.  Other  project: 
now  under  consideration  by  the  Committee  are  briefly  mentioned. 

"A  Machine  for  Artificial  Reverberation";  S.  K.  Wolf,  Acoustic  Consultants 
Inc.,  New  York,  N.  Y. 

Sometimes  there  arises  the  necessity  of  introducing  into  recorded  sound  a  live 
ness  that  is  not  present  in  the  original  sound-waves  impinging  upon  the  micro 
phones  in  the  recording  studio.  Reverberation  chambers  have  been  used  to  pro 
vide  the  additional  liveness,  but  such  chambers  are  not  very  flexible  in  use  and  an 
costly  to  install. 

A  new  machine  has  been  developed  by  means  of  which  reverberation  may  b< 
introduced  into  the  recorded  sound  artificially.  The  sound  is  recorded  upon  ai 
endless  magnetic  sound-carrier  or  tape,  which  passes  beneath  a  number  of  pick 
ups  or  reproducers  at  intervals  along  the  carrier.  These  pick-ups  are  connectec 
to  a  mixer  panel,  and  the  sound  level  of  each  is  adjusted  to  produce  the  reverber 


Oct.,  1938]  FALL  CONVENTION  429 

ant  effect  required.     After  passing  the  last  pick-up  head  in  the  series,  the  sound 
is  "wiped  off"  the  magnetic  carrier. 

Such  a  machine  finds  many  applications,  and  is  useful  not  only  in  studios  for 
direct  recording,  but  also  for  adding  liveness  to  records  during  the  process  of 
dubbing. 

"A  Silent  Wind  Machine  for  the  Production  Stage";  F.  G.  Albin,  United  Art- 
ists Studio  Corp.,  Hollywood,  Calif. 

The  machines  generally  used  on  the  motion  picture  production  set  to  create 
wind  for  pictorial  effects  are  large  motor-driven  propeller  fans  mounted  on  floor 
stands.  The  noise  level  produced  at  high  velocities  is  so  high  that  satisfactory 
sound  recording  of  the  scene  is  practically  impossible.  Furthermore,  the  size  and 
shape  of  these  machines  are  such  that  they  must  be  placed  at  such  a  distance  that 
the  directivity  is  not  readily  controllable.  The  additional  hazard  to  sound  re- 
cording of  causing  wind  around  the  microphone  always  exists  and,  commonly,  the 
desirable  microphone  placement  is  sacrificed  in  order  to  avoid  the  wind. 

A  new  type  of  wind  machine  has  been  adopted  and  used  for  several  years  with  a 
great  improvement  realized.  The  new  type  is  a  centrifugal  blower,  such  as  is 
commonly  used  in  ventilating  systems.  The  air  is  conducted  by  means  of  light 
canvas  ducts  from  the  exhaust  of  the  blower  to  the  set  where  the  scene  is  being 
enacted.  The  ducts  are  equipped  with  variously  shaped  fittings  and  nozzles  so 
that  the  air  stream  may  be  directed  as  desired. 

It  has  been  found  expedient  to  locate  the  blower  outside  the  stage  building  and 
enter  the  duct  through  a  special  portal.  Thereby,  the  greatest  noise  source,  the 
blower,  is  remotely  located  and  insulated  from  the  scene  by  the  walls  of  the  stage 
building.  Furthermore,  it  incidentally  serves  as  a  ventilator,  supplying  fresh  air 
to  the  scene.  Measurements  of  noise  level  for  various  wind  velocities  indicate 
improvements  up  to  70  decibels  in  noise  reduction.  Thus  sound  recordings  of 
scenes  requiring  wind  are  made  possible  where  heretofore  it  was  necessary  to 
photograph  the  scene  without  sound  and  provide  synchronized  sound  subse- 
quently. 

"Silent  Variable-Speed  Treadmill";  J.  E.  Robbins,  Paramount  Pictures,  Inc., 
Hollywood,  Calif. 

Treadmills  of  various  designs  have  been  used  by  the  motion  picture  industry 
for  many  years  for  obtaining  animated  shots  in  front  of  moving  backgrounds. 
The  adoption  of  sound  practically  eliminated  them  except  for  synchronized  and 
other  types  of  silent  scenes. 

This  loss  was  keenly  felt,  and  as  a  result  immediate  steps  were  taken  to  develop 
a  unit  that  could  operate  throughout  a  wide  range  of  speed,  with  fine  control, 
instantaneous  start  and  stop,  and  ability  to  reverse  in  the  same  shot,  still  main- 
taining a  noise  level  that  would  allow  the  recording  of  intimate,  quiet  dialog. 
This  was  not  as  simple  as  it  appeared,  due  to  the  fact  that  in  addition  to  the 
above-mentioned  requirements  it  also  had  to  support  the  weight  of  two  horses 
running,  fifteen  or  twenty  men  on  a  inarch,  automobiles  and  motorcycles  in  mo- 
tion, etc.  This  all  had  to  be  accomplished  with  a  unit  restricted  in  size  and 
weight  in  order  to  maintain  mobility. 

The  paper  discusses  the  problems  confronting  the  engineering  and  mechanical 
departments  throughout  the  design  and  construction  of  a  machine  that  comes 
fairly  close  to  doing  all  that  was  hoped  for  originally. 


430  FALL  CONVENTION  [j.  s.  M.  P.  E. 

"Independent  Drive  for  Camera  in  the  A-c.  Interlock  Motor  System";  F.  G. 
Albin,  United  Artists  Studio  Corp.,  Hollywood,  Calif. 

The  "Selsyn"  or  alternating-current  interlock  motor  system  used  to  drive 
cameras,  recording,  re-recording,  and  projection  machines  in  synchronism,  is  a 
popular  type  of  motor  system  in  large  studios.  It  has  special  advantages  in  such 
applications  as  driving  projector  and  camera  for  projection  background  process. 
The  one  inexpedient  feature  is  that  the  system  is  generally  started  from  a  central 
point  such  as  the  recording  room,  and  the  cameraman  does  not  have  means  for 
running  his  camera  independently  as  is  so  often  required  for  photographing  slates, 
exposure  tests,  and  silent  scenes. 

An  addition  has  been  made  to  the  a-c.  interlock  system  to  give  it  the  advantages 
possessed  by  the  synchronous  motor  system:  namely,  the  facilities  enabling  the 
cameraman  to  operate  his  camera  at  will  at  regular  speed . 

The  addition  consists  of  a  set  of  relays  with  control  circuits,  and  a  frequency 
changer  and  field  exciter  set.  Normally,  the  camera  motors  are  connected  to  the 
common  interlock  system  through  the  relays.  If,  however,  the  button  provided 
at  the  camera  is  depressed,  the  pilot  relay  operates  and  energizes  the  main  relays 
which  transfer  the  camera  motor  circuit  to  the  bus  of  the  frequency  changer  and 
field  exciter  set.  The  camera  motor  is  operated  as  a  true  synchronous  motor. 
One  phase  of  the  rotor  is  short-circuited,  and  the  remainder  is  excited  with  direct 
current  and  serves  as  the  field.  The  three-phase  stator  is  supplied  with  three- 
phase  power  of  a  frequency  that  will  cause  the  motor  to  run  at  the  required  speed, 
the  same  speed  as  when  driven  with  the  interlock  system. 

The  power  developed  by  the  a-c.  interlock  camera  motor  when  operated  as  a 
synchronous  motor  is  approximately  the  same  as  under  normal  operating  condi- 
tions. The  acceleration  is  typical  of  small  synchronous  motors  when  the  power 
supply  is  suddenly  connected.  The  pull-in  torque  is  superior  to  the  slotted-rotor 
type  of  as-synchronous  motor.  The  operation  of  the  system  is  smooth,  simple, 
and  efficient,  and  has,  after  several  years  of  use.  proved  its  value. 

"A  16-Mm.  Studio  Recorder";  R.  W.  Benfer,  Electrical  Research  Products, 
Inc.,  New  York,  N.  Y. 

Recent  advances  in  the  commercial  use  of  16-mm.  sound-film  have  stressed  the 
importance  of  improving  the  product.  Certain  limitations  imposed  by  the  optical 
reduction  process  for  obtaining  16-mm.  sound  prints  are  eliminated  by  recording 
16-mm.  negatives  expressly  for  contact  printing.  A  studio  recorder  for  this  pur- 
pose is  described.  The  paper  deals  briefly  with  the  results  of  considerable  investi- 
gation to  determine  the  desirable  recording  characteristics  and  concludes  with  a 
demonstration  of  experimental  recordings. 

"New  Sound  Recording  Equipment";  D.  R.  Canady  and  V.  A.  Welman,  Can- 
ady  Sound  Appliance  Co.,  Cleveland,  Ohio. 

Recorder  for  16-Mm.  Film. — This  recorder  is  characterized  by  its  constancy  of 
speed  and  its  convenience  and  simplicity  of  operation.  The  constant-speed  drum 
is  not  affected  by  temperature  changes.  The  recorder  has  an  aluminum  magazine 
of  400-ft.  capacity,  with  friction  take-up  and  fitted  for  either  galvanometer  or 
glow-lamp  recording,  the  glow  lamp  being  preferred  because  of  its  simplicity. 

Noise- Reduction  Unit  for  Glow-Lamp  Recording. — A  self-contained  unit,  either 
portable  or  for  panel  mounting,  which  provides  polarizing  voltage  and  noise 


Oct.,  1938]  FALL  CONVENTION  431 

reduction  for  glow-lamp  recording.  It  has  simple  adjustments  for  setting  the 
minimum  and  maximum  current  desired,  and  when  these  adjustments  are  set  the 
unit  is  fully  automatic.  It  is  variable  over  a  wide  range  and  will  give  recordings 
from  5  to  25  ma.  of  current  or  from  nearly  clear  negative  to  fully  exposed  negative. 
It  has  no  time  lag,  can  not  react  in  any  way  with  the  amplifier,  and  may  be  con- 
nected to  any  amplifier. 

Galvanometer  for  35-  or  16-Mm.  Recording. — An  oil-damped  galvanometer,  so 
designed  that  each  of  its  component  parts  is  readily  adjustable,  making  it  possible 
to  be  fitted  to  almost  any  recorder.  The  galvanometer  has  a  straight-line  output 
to  10,000  cycles. 

Projector  for  Background  Projection. — A  claw  projector,  noiseless  in  operation 
and  rock-steady,  designed  for  the  extreme  requirements  of  background  projection. 
The  claws  have  three  teeth  on  each  side,  the  tension  shoes  are  long,  with  adjustable 
tension,  and  the  wear  on  the  film  is  a  minimum.  The  mechanical  parts  are  en- 
closed and  lubricated  by  an  oil  pump  from  an  oil  sump. 

"A  Color-Temperature  Meter";  E.  M.  Lowry,  Kodak  Research  Laboratories, 
Rochester,  N.  Y. 

The  recent  advances  in  color  photography  have  made  more  apparent  than  ever 
before  the  need  for  some  simple  and  accurate  method  for  the  estimation  of  the 
color-temperature  of  light-sources.  Photographers,  whether  professional  or 
amateur,  are  only  too  well  aware  of  the  influence  that  the  quality  of  the  illu- 
mination has  upon  the  color  rendering  of  photographic  subjects.  For  example, 
the  difference  in  color-temperature  between  general-purpose  tungsten  filament 
lamps,  and  studio  modeling  lamps,  or  between  modeling  lamps  and  photoflood 
lamps,  is  often  the  deciding  factor  between  correct  and  incorrect  photographic 
color  reproduction.  In  order  that  the  photographer  may  easily  determine  the 
quality  of  the  lighting  he  is  using  and  make  the  proper  adjustments  to  secure 
standard  lighting  conditions,  an  instrument  that  is  at  once  compact,  simple  in 
operation,  and  accurate,  has  been  developed  in  these  laboratories.  No  auxiliary 
light-source  is  required  for  making  measurements  since  each  source  is  tested  by 
means  of  the  radiant  energy  that  it  itself  emits.  In  this  paper  a  discussion  of 
the  principles  applied  in  construction  of  the  instrument,  a  description  of  the 
instrument,  and  data  showing  the  probable  error  of  results  are  given. 

"Some  General  Characteristics  of  Chromium-Nickel-Iron  Alloys  as  Corrosion- 
Resisting  Materials";  R.  Franks,  Union  Carbide  and  Carbon  Co.,  Inc.,  Niagara 
Falls,  N.  Y.,  and  F.  L.  LaQue,  International  Nickel  Co.,  Inc.,  New  York,  N.  Y. 

Those  features  of  the  chromium-nickel  stainless  steels  are  described  that  make 
these  alloys  useful  as  corrosion-resisting  materials,  and  data  are  presented  on  the 
influence  of  the  several  alloying  elements  commonly  present.  It  is  shown  how 
the  high  chemical  activity  of  chromium  benefits  corrosion-resistance  by  reaction 
with  oxygen  or  other  oxidizing  agents  to  form  inert  films  which  prevent  progres- 
sive attack.  The  effect  of  chromium  content  upon  corrosion  resistance  in 
typical  reducing  and  oxidizing  solutions  is  illustrated  by  test  data. 

Data  are  presented  to  illustrate  the  effect  of  nickel  in  achieving  the  desirable 
austenitic  state,  in  increasing  the  stability  of  the  alloys,  and  in  supplementing 
the  protective  film-forming  properties  of  chromium.  Included  in  the  discussion 
are  iron-base  alloys  with  chromium  predominating,  iron-base  alloys  with  nickel 


432  FALL  CONVENTION  [j.  s.  M.  P.  E. 

predoirinating,  and  nickel-base  alloys  containing  high  percentages  of  chromium. 
The  peculiar  usefulness  of  each  type  of  alloy  is  indicated  and  illustrated  with 
appropriate  data. 

The  effect  of  molybdenum  is  treated  in  much  the  same  way  as  the  effect  of 
nickel.  The  usefulness  of  molybdenum  in  improving  corrosion  resistance  under 
both  oxidizing  and  reducing  conditions  is  pointed  out,  as  well  as  its  specific 
beneficial  effects  in  connection  with  organic  acids  and  vapors,  and  in  reducing 
the  susceptibility  to  local  attack  or  pitting  by  chlorides  or  other  halogen  com- 
pounds. 

There  is  included,  also,  a  discussion  of  the  effects  of  carbon  upon  corrosion- 
resistance  with  especial  reference  to  intergranular  corrosion  of  the  austenitic 
alloys.  Supplementing  this  discussion  of  carbon  there  is  a  description  of  several 
methods  of  avoiding  intergranular  corrosion,  including  the  use  of  such  stabilizing 
elements  as  columbium  and  titanium. 

"  Coordinating  the  Acoustical  and  Architectural  Design  of  the  Motion  Picture 
Theater";  C.  C.  Potwin,  Electrical  Research  Products,  Inc.,  New  York,  N.  Y., 
and  B.  Schlanger,  New  York,  N.  Y. 

Successful  design  of  the  motion  picture  auditorium  involves  the  effective  co- 
ordination of  both  auditory  and  visual  requirements.  Past  practice  has  favored 
vision  and  decorative  treatment,  usually  leaving  the  acoustical  problem  as  a 
final  consideration. 

In  this  paper  a  study  is  made  of  the  basic  outline,  the  volume,  and  the  detailed 
form  of  a  motion  picture  auditorium,  to  show  that  auditory  and  visual  require- 
ments can  both  be  met  successfully  if  they  are  treated  with  equal  importance  in 
fundamental  planning.  This  does  not  preclude  the  ability  to  obtain  economical 
design  and  pleasing  architectural  form.  Actually,  the  study  proves  that  eco- 
nomical construction  and  creative  architectural  forms  are  more  readily  inspired. 

"Chemical  Analysis  of  an  MQ  Developer";  R.  M.  Evans  and  W.  T.  Hanson, 
Jr.,  Kodak  Research  Laboratories,  Rochester,  N.  Y. 

The  maintenance  of  developer  activity  over  a  long  period  of  time  is  among  the 
most  important  problems  of  a  motion  picture  laboratory.  The  developer  is 
oxidized  by  the  silver  halide  in  the  emulsion  and  by  air.  When  known  amounts 
of  these  two  oxidizing  materials  react  with  the  developer,  simple  calculations, 
which  were  presented  in  a  previous  paper,  are  sufficient  to  determine  the  equi- 
librium condition  of  the  developer  as  well  as  the  replenisher  formula  to  give  a 
chosen  equilibrium.  Under  ordinary  conditions  there  are  large  variations  in  the 
amount  of  developer  oxidation.  A  chemical  analysis  immediately  detects  any 
deviation  from  the  correct  equilibrium  and  permits  readjustment  of  the  replen- 
isher formula.  Chemical  analyses  are  presented  which  require  a  minimum  of 
equipment  and  time.  In  most  cases,  ease  of  manipulation  and  speed  have  been 
considered  as  more  important  factors  than  a  high  degree  of  accuracy  but  in  all 
cases  the  methods  are  capable  of  giving  results  to  an  accuracy  of  five  per  cent 
or  better.  Whenever  possible  the  analyses  are  colorimetric  in  nature,  the  mea- 
surements being  made  on  an  instrument  called  an  Opacimeter.  One  operator  can 
make  a  complete  analysis  in  about  half  an  hour.  Analysis  for  any  one  con- 
stituent may  be  made  in  a  much  shorter  time.  It  is  emphasized  that  no  one 
control  variable  is  significant  for  specifying  the  activity  of  a  developer.  Sensito- 


Oct.,  1938]  FALL  CONVENTION  433 

metric  curves  are  included  demonstrating  the  time  lag  in  pH  equilibrium  but  not 
in  photographic  equilibrium  when  hydroxide  is  added  to  or  released  in  the  de- 
veloper. The  aim  of  chemical  control  is  to  insure  a  constant  condition  of  the 
developer  and  thus  constant  photographic  quality,  rather  than  to  determine  the 
degree  of  development. 

"Opacimeter  Used  in  Chemical  Analysis";  R.  M.  Evans  and  G.  P.  Silberstein, 
Kodak  Research  Laboratories,  Rochester,  N.  Y. 

The  opacimeter  is  an  optical  instrument  designed  to  measure  the  light  trans- 
mission of  a  colored  or  turbid  solution.  A  Loewenthal  photronic  type  light- 
sensitive  cell  connected  to  a  microammeter  is  used  to  measure  the  intensity  of 
the  light  transmitted  by  the  solution  under  test.  The  light  intensity  falling  upon 
the  sensitive  cell  is  kept  within  a  fixed  range  by  varying  the  distance  of  the  cell 
from  the  source.  The  instrument  is  arranged  so  that  a  30-cc.  test  tube  or  a 
300-cc.  Kohle  flask  may  contain  the  reaction  mixture.  The  results  of  analyses 
are  determined  from  calibration  curves  prepared  from  known  solutions. 

"Some  Television  Problems  from  the  Motion  Picture  Standpoint";  G.  L. 
Beers,  E.W.  Engstrom,  and  I.  G.  Maloff,  RCA  Manufacturing,  Co.,  Inc.,  Camden, 
N.J. 

There  are  certain  characteristics  of  television  that  have  counterparts  in  motion 
pictures.  Also,  motion  picture  film  and  motion  picture  practice  are  applicable 
to  television;  some  of  the  problems  and  limitations  are  outlined. 

The  following  television  image  characteristics  are  briefly  discussed:  (1) 
number  of  scanning  lines  and  the  relationship  to  image  size  and  viewing  distance ; 
(2}  number  of  frames;  (3)  interlacing.  The  effect  of  film  and  optical  system 
limitations  upon  reproduced  television  images  is  illustrated  by  photographs. 
Curves  are  given  showing  the  spectral  characteristics  of  Iconoscopes.  The 
screen  color  characteristics  of  Kinescopes  are  discussed.  The  overall  range  and 
gamma  characteristics  of  a  television  system  are  reviewed. 

"Unidirectional  Microphone  Technic";  J.  P.  Livadary,  Columbia  Pictures 
Corp.,  Hollywood,  Calif.,  and  M.  Rettinger,  RCA  Manufacturing  Co.,  Inc.,  Los 
Angeles,  Calif. 

The  paper  contains  a  description  of  the  construction  of  the  unidirectional 
microphone,  and  an  equation  is  obtained  showing  the  cardioid  directional  re- 
sponse for  this  microphone. 

Four  definite  advantages  are  listed  for  the  use  of  this  microphone  in  the  re- 
cording of  sound  in  motion  picture  studios.  These  advantages  are  (1)  attenuation 
of  undesirable  sounds  striking  the  microphone  from  the  tear;  (2)  lack  of  frequency 
discrimination  for  sounds  striking  the  microphone  within  its  solid  cone  of  recep- 
tion because  of  the  directional  response  of  the  microphone,  which  is  practically 
independent  of  frequency;  (3)  the  greater  permissible  microphone  distance  to 
obtain  the  same  ratio  of  direct  to  reflected  sound  that  exists  at  the  position  of  a 
pressure-operated  transmitter;  and  (4)  the  large  solid  angle  of  reception,  which 
allows  the  use  of  fewer  microphones  to  cover  an  action. 

Six  illustrations  are  given  to  show  how  this  transmitter  may  be  used  to  ad- 
vantage under  specific  set  conditions,  and  four  diagrams  illustrate  its  use  for  the 
recording  of  various  types  of  music. 


434  FALL  CONVENTION 

"A  Super  Sound  and  Picture  Printer";  O.  B.  Depue,  Burton  Holmes  Films, 
Inc.,  Chicago,  111. 

An  improved  contact  printer  for  the  continuous  printing  of  16-mm.  sound  und 
picture  has  some  new  film-handling  features.  The  film  may  be  threaded  over 
either  picture  sprocket  or  sound  printing  drum  or  both,  according  as  the  negative 
is  of  the  double-  or  single-film  system.  The  picture  is  printed  while  the  film  is 
supported  by  a  sprocket  engaging  the  perforated  edge  of  the  film.  At  the  same 
time,  the  other  edge  is  supported  on  a  roller  tread  and  flange  which,  instead  of 
being  carried  on  the  extended  sprocket  shaft,  has  its  own  ball-bearing  mounting 
and  is  driven  by  the  film.  In  this  way  the  section  of  shaft  is  eliminated  from  the 
center  of  the  sprocket,  making  possible  a  better  location  of  the  printing  illumina- 
tion beam.  Thus  it  is  possible  without  the  addition  of  complicated  optical  ele- 
ments to  have  the  illumination  fall  perpendicularly  upon  the  film  at  the  center  of 
the  area  of  contact  between  negative  and  positive.  The  sound  printing  takes  place 
similarly  on  a  nearby  drum.  Provision  is  made  at  this  point  for  the  insertion  of 
an  optical  filter.  Lamp  current  is  supplied  by  a  built-in  motor-generator  set  at 
any  required  voltage  between  90  and  130. 

The  printer  is  driven  through  a  rubber  disk  vibration  filter.  All  bearings  are 
either  enclosed  grease-packed  ball  bearings  or  "oilite"  oilless  bronze.  Sprockets 
are  made  of  stainless  steel.  The  electrical  system  is  protected  by  the  use  of  an 
overload  cut-out  instead  of  fuses 


SOCIETY  ANNOUNCEMENTS 


DETROIT  CONVENTION 

Details  of  the  Convention  are  given  on  page  421  of  this  issue  of  the  JOURNAL. 
The  Tentative  Papers  Program  will  be  mailed  to  the  membership  of  the  Society 
about  the  middle  of  October.  Members  who  plan  to  attend  the  Convention  are 
urged  to  return  their  hotel  reservation  cards  as  promptly  as  possible  in  order  to  be 
assured  of  satisfactory  accommodations. 

PROJECTION  PRACTICE  COMMITTEE 

Several  meetings  of  the  Sub-Committee  on  Projection  Room  Plans  were  held 
during  the  summer,  the  last  one  being  on  September  9th,  at  the  office  of  the 
Society.  The  result  of  this  work  was  the  completion  of  the  third  revision  of  the 
Projection  Room  Plans,  which,  together  with  the  proposed  revision  of  the  NFPA 
"Regulations  for  Handling  Nitrocellulose  Film,"  completed  by  the  Committee 
several  months  ago,  will  form  the  report  of  the  Projection  Practice  Committee 
to  be  presented  at  the  Detroit  Convention. 

A  meeting  of  the  entire  Committee  was  held  on  September  15th  to  edit  a  pre- 
liminary draft  of  the  report,  and  another  meeting  will  be  held  on  October  13th 
to  approve  the  final  draft. 

MID-WEST  SECTION 

On  Thursday,  Septembei  20lh,  at  the  meeting  rooms  of  The  Western  Society 
of  Engineers,  the  Mid-West  Section  of  the  Society  held  its  first  meeting  of  the 
season.  Mr.  Richard  Leitner  of  the  Gumbiner  Syncro-Sound,  Inc.,  of  Los  Angeles 
presented  a  paper  describing  "  A  Professional  16-Mm.  Sound-on-Film  Camera." 

The  meeting  was  well  attended  and  an  interesting  discussion  followed  the  pres- 
entation. 

ADMISSIONS  COMMITTEE 

At  a  recent  meeting  of  the  Admissions  Committee,  at  the  General  Office  of  the 
Society,  the  following  applicants  for  membership  were  admitted  to  the  Associate 
grade : 


BAMFORD,  H.  S. 
485  California  St., 

San  Francisco,  Calif. 
BAUMBACH,  H.  L. 
669  Los  Lomas  Ave., 

Pacific  Palisades,  Calif. 
CROWLEY,  W.  G. 

11204  Brookhaven  St., 
West  Los  Angeles,  Calif. 


DEFARIA,  A. 

Rua  Plombagina  328, 
Bello  Horizonte, 

Estado  de  Minas,  Brazil. 
DUDGEON,  R.  F. 

No.  6  Flat  Hackney  Manor, 
360  Carlisle  St., 
St.  Kilda  S2, 

Victoria,  Australia. 


435 


436 


SOCIETY  ANNOUNCEMENTS 


[J.  S.  M.  P.  E 


FEINSTEIN,  A.  L. 

1108  So.  Shenandoah  St., 

Los  Angeles,  Calif. 
GALLIANO,  F. 
Via  Sabotino, 

2  Rome,  Italy. 
GIBBS,  C.  R. 

Kodak  Aktiengesellschaft, 
Lindenstrasse  27, 

Berlin,  Germany. 
HENDERSON,  F.  J. 
63  Marionville  Rd., 

Edinburgh,  Scotland. 
KAUSER,  J. 

VIII  Gyulaipal  U.  5, 

Budapest,  Hungary. 
KELMAN,  S.  C. 

2850  Leeward  Ave., 

Los  Angeles,  Calif. 
KLEIN,  A. 

Dufay-Chromex  Ltd., 
14  Cockspur  St., 

London,  England. 
KOKAT,  A.  G. 
2016  E.  Firth  St., 
Philadelphia,  Penna. 

KORFMANN,  F.  W. 

88-35  Elmhurst  Ave., 

Elmhurst,  Long  Island,  N.  Y. 
KOTWAL,  S.  N. 

c/o  Evergreen  Pictures, 
Saklat  House, 

15  New  Queen's  Road, 

Combay,  India. 
KRITZBERG,  S. 
723  Seventh  Ave., 

New  York,  N.  Y. 
MALSTROM,  V.  J. 
1976  So.  7  East, 
Salt  Lake  City,  Utah. 


MARTINEZ,  M.  J. 
P.  O.  Box  101, 

Arecibo,  Puerto  Rico. 

MARZARI,  A. 
San  Marco  557, 
Venezia,  Italy. 

MIATT,  R.  W. 
Kinelab, 

Adams'  Building, 
484  George  St., 
Sydney,  Australia. 

NAVARRO,  R.  F. 

Parlatone  Hispano  Filipino, 
Motion  Picture  Co., 
Manila,  P.  I. 

NEUHARDT,  C.  W. 
138— 28th  St., 
Wheeling,  W.  Va. 

PETERSON,  S. 
Kodak  Limited, 
Stockholm,  Sweden. 

SARBER,  H. 
6331  Florio  St., 
Oakland,  Calif. 

SAVELLI,  O.  G. 

Viale  Vittorio  V.  24, 
Milan,  Italy. 

SEILER,  J.  T. 

5718  Hillcrest  Drive, 
Los  Angeles,  Calif. 

THOMAS,  J.  L. 

90  E.  Palmer  Ave., 
Detroit,  Mich. 

WILLOCK,  W.  W.,  JR. 
P.  O.  Box  263, 
Syosset,  N.  Y. 


In  addition,  the  following  applicants  have  been  admitted  by  vote  of  the  Board 
of  Governors  to  the  Active  grade. 


DUDIAK,  F. 
Fairmont  Theater, 
Fairmont,  W.  Va. 


KANTUREK,  O. 
6  Stanmore  Hall, 
Stanmore, 

Middlesex,  England. 


Oct.,  1938]  SOCIETY  ANNOUNCEMENTS  437 

LAMB,  R.  T.  SEWELL,  B.  C. 

Estudios  San  Miguel,  Pinewood  Studios, 

Bella  Vista  F.C.P.,  Iver  Heath, 

Buenos  Aires,  Argentina.  Bucks',  England. 

WEITZEL,  A. 

923  Hardesty  Blvd., 
Akron,  Ohio. 


SOCIETY  SUPPLIES 

The  following  are  available  from  the  General  Office  of  the  Society,  at  the  prices 
noted.  Orders  should  be  accompanied  by  remittances. 

Aims  and  Accomplishments. — An  index  of  the  Transactions  from  October, 
1916,  to  December,  1929,  containing  summaries  of  all  articles,  and  author  and 
classified  indexes.  One  dollar  each. 

Journal  Index. — An  index  of  the  JOURNAL  from  January,  1930,  to  December, 
1935,  containing  author  and  classified  indexes.  One  dollar  each. 

SMPE  Standards. — The  revised  edition  of  the  SMPE  Standards  and  Recom- 
mended Practice  was  published  in  the  March,  1938,  issue  of  the  JOURNAL,  copies 
of  which  may  be  obtained  for  one  dollar  each. 

Membership  Certificates. — Engrossed,  for  framing,  containing  member's  name, 
grade  of  membership,  and  date  of  admission.  One  dollar  each. 

Lapel  Buttons. — The  insignia  of  the  Society,  gold  filled,  with  safety  screw  back. 
One  dollar  each. 

Journal  Binders. — Black  fabrikoid  binders,  lettered  in  gold,  holding  a  year's 
issue  of  the  JOURNAL.  Two  dollars  each.  Member's  name  and  the  volume 
number  lettered  in  gold  upon  the  backbone  at  an  additional  charge  of  fifty  cents 
each. 

Test- Films. — See  advertisement  in  this  issue  of  the  JOURNAL. 


NORMAN  McCLINTOCK 

1868-1938 

Professor  Norman  McClintock,  distinguished  photo-naturalist  and  member  of 
the  Society,  died  of  a  heart  attack  at  Orlando,  Florida,  on  February  26,  1938. 
Professor  McClintock  joined  the  staff  of  Rutgers  University  at  New  Brunswick, 
N.  J.,  in  1931  as  a  special  lecturer,  and  retained  the  position  to  the  time  of  his 
death. 

Norman  McClintock  received  his  B.A.  degree  from  Yale  University  in  1891. 
He  became  interested  actively  in  motion  picture  photography  of  insect  life,  plant 
life,  wild  birds,  and  big  game  about  1914.  For  nearly  a  quarter  of  a  century  he 
devoted  his  full  time  to  these  studies,  and  was  one  of  the  first  to  make  fine  quality 
motion  picture  studies  of  bird  and  plant  life.  His  services  as  a  lecturer  were  much 
in  demand  because  of  the  remarkable  films  which  he  showed  and  the  unusual  per- 
sonality of  the  speaker. 


NORMAN  MCCLINTOCK 

No  one  could  talk  to  Professor  McClintock  for  more  than  a  few  minutes  with- 
out feeling  some  of  the  joy  and  thrill  which  he  got  from  the  work  in  which  he  was 
engaged.  Professor  McClintock  spoke  on  several  occasions  at  the  semi-annual 
conventions  of  the  Society  and  always  delighted  his  audiences  with  his  rare  wit 
and  anecdotes  of  his  personal  experiences. 

Some  of  the  time-lapse  motion  pictures  of  the  growth  of  plants  are  considered 
classics  in  this  field.  He  devised  several  ingenious  devices  for  controlling  auto- 
matically the  duration  of  exposure  and  illumination  for  these  investigations. 

The  world  has  lost  a  unique  research  worker  in  the  field  of  natural  history. 
438 


JOURNAL 

OF  THE  SOCIETY  OF 

MOTION  PICTURE  ENGINEERS 

Volume  XXXI  NOVEMBER,  1938  Number  5 

CONTENTS 

Page 
Electrical  Networks  for  Sound  Recording F.  L.  HOPPER     443 

A  Non-Intermittent  Projector  for  Television  Film  Transmission 

H.  S.  BAMFORD    453 

Silent  Gasoline  Engine  Propelled  Apparatus.  .J.  E.  ROBBINS     462 
A  Technic  for  Testing  Photograpihic  Lenses .  .  .  .  W.  C.  MILLER     472 

Report  of  the  Projection  Practice  Committee 

Projection  Room  Plans 480 

Proposed  Revision  of  Regulations  of  the  National  Board  of 
Fire  Underwriters  for  Nitrocellulose  Motion  Picture  Film 
as  Pertaining  to  Projection  Rooms 498 

New  Motion  Picture  Apparatus 

A  New  Sound  System G.  FRIEDL,  JR.     511 

Variable  Matte  Control  (Squeeze  Track)  for  Variable-Den- 
sity Recording .G.  R.  CRANE  531 

An  Improved  Editing  Machine J.   L.   SPENCE     539 

Current  Literature 542 

Abstracts  of  Papers  for  the  Detroit  Convention 544 

Society  Announcements 547 


JOURNAL 

OF  THE  SOCIETY  OF 

MOTION  PICTURE  ENGINEERS 


SYLVAN  HARRIS,  EDITOR 

Board  of  Editors 
J.  I.  CRABTREE,  Chairman 

A.  N.  GOLDSMITH  L.  A.  JONES  H.  G.  KNOX 

A.  C.  HARDY  E.  W.  KELLOGG  G.  E.  MATTHEWS 


Subscription  to  non-members,  $8.00  per  annum ;  to  members,  $5.00  per  annum, 
included  in  their  annual  membership  dues;  single  copies,  $1.00.  A  discount 
on  subscriptions  or  single  copies  of  15  per  cent  is  allowed  to  accredited  agencies. 
Order  from  the  Society  of  Motion  Picture  Engineers,  Inc.,  20th  and  Northampton 
Sts.,  Easton,  Pa.,  or  Hotel  Pennsylvania,  New  York,  N.  Y. 
Published  monthly  at  Easton,  Pa.,  by  the  Society  of  Motion  Picture  Engineers. 

Publication  Office,  20th  &  Northampton  Sts.,  Easton,  Pa. 
General  and  Editorial  Office,  Hotel  Pennsylvania,  New  York,  N.  Y. 

West-Coast  Office,  Suite  226,  Equitable  Bldg.,  Hollywood,  Calif. 
Entered  as  second  class  matter  January  15,  1930,  at  the  Post  Office  at  Easton, 
Pa.,  under  the  Act  of  March  3,  1879.     Copyrighted,  1938,  by  the  Society  of 
Motion  Picture  Engineers,  Inc. 

Papers  appearing  in  this  Journal  may  be  reprinted,  abstracted,  or  abridged 
provided  credit  is  given  to  the  Journal  of  the  Society  of  Motion  Picture  Engineers 
and  to  the  author,  or  authors,  of  the  papers  in  question.  Exact  reference  as  to 
the  volume,  number,  and  page  of  the  Journal  must  be  given.  The  Society  is 
not  responsible  for  statements  made  by  authors. 


OFFICERS  OF  THE  SOCIETY 

•President:    S.  K.  WOLF,  1270  Sixth  Ave.,  New  York,  N.  Y. 
•Past-President:    H.  G.  TASKER,  5451  Marathon  St.,  Hollywood,  Calif. 
•Executive   Vice-President:    K.  F.  MORGAN,  6601  Romaine  St.,  Los  Angeles, 

Calif. 

** Engineering    Vice-President:     L.   A.  JONES,  Kodak  Park,  Rochester,  N.  Y. 
•Editorial  Vice-President:    J.  I.  CRABTREE,  Kodak  Park,  Rochester,  N.  Y. 
••Financial  Vice-President:    E.  A.  WILLIFORD,  30  E.  42nd  St.,  New  York,  N.  Y. 
•Convention    Vice-President:    W.   C.   KUNZMANN,   Box  6087,   Cleveland,  Ohio. 
•Secretary:    J.  FRANK,  JR.,  90  Gold  St.,  New  York,  N.  Y. 
•Treasurer:    L.  W.  DAVEE,    76  Varick  St.,  New  York,  N.  Y. 

GOVERNORS 

*J.  O.  AALBERG,  6920  McKinley  St.,  Los  Angeles,  Calif. 
*M.  C.  BATSEL,  Front  and  Market  Sts.,  Camden,  N.  J. 
**R.  E.  FARNHAM,  Nela  Park,  Cleveland,  Ohio. 
*G.  FRIEDL,  JR.,  90  Gold  St.,  New  York,  N.  Y. 
*A.  N.  GOLDSMITH,  444  Madison  Ave.,  New  York,  N.  Y. 
**H.  GRIFFIN,  90  Gold  St.,  New  York,  N.  Y. 

**A.  C.  HARDY,  Massachusetts  Institute  of  Technology,  Cambridge,  Mass. 
*S.  A.  LUKES,  6427  Sheridan  Rd.,  Chicago,  111. 
*Term  expires  December  31,  1938. 
**Term  expires  December  31,  1939. 


ELECTRICAL  NETWORKS  FOR  SOUND  RECORDING* 
F.  L.  HOPPER** 

Summary. — Electrical  networks  are  employed  in  sound  recording  for  modifying 
and  limiting  the  frequency-response  characteristic.  The  necessity  for  their  use,  ap- 
plication, and  design  is  described.  Particular  emphasis  is  placed  upon  the  constant- 
resistance  type  of  structure. 

The  design  philosophy  for  a  transmission  system  to  translate  the 
spoken  word  or  music  into  some  form  of  record  has  been  one  pre- 
dicated upon  the  use  of  elements  having  uniform  response-frequency 
characteristics.  In  sound  recording  a  number  of  factors  exist  that 
necessitate  certain  modification  and  limitation  of  these  character- 
istics in  order  to  achieve  pleasing  results.  Some  of  these  factors  are : 

(a)  The  effects  due  to  the  acoustical  conditions  surrounding  the  point  of 
pick-up. 

(&)     The  response  characteristic  of  the  microphone. 

(c)  The  properties  of  the  modulating  device  and  noise-reduction  system. 

(d)  In  re-recording,  the  ability  to  compensate  for  defects  occurring  in  record- 
ing, and  the  introduction  of  characteristics  providing  certain  dramatic  effects. 

All  these  alterations  of  characteristic  are  accomplished  by  the  use 
of  various  passive  electrical  networks.  Those  employed  for  modifica- 
tion make  use  of  the  properties  of  resonant  circuits,  combinations  of 
capacity  or  inductance  with  resistance,  or  the  grouping  of  such  ele- 
ments into  the  lattice  or  bridged-  T  type  of  constant-resistance  net- 
work. 

Limitation  of  the  frequency-response  characteristic  is  accomplished 
by  grouping  inductance  and  capacity  elements  into  high-  and  low- 
pass  filter  structures.  Occasionally,  constant-resistance  networks, 
alone  or  in  combination  with  filter  sections,  are  used. 

The  choice  of  a  particular  type  of  network  depends  upon  the  re- 
quired insertion  loss,  the  impedance  of  the  circuit  in  which  it  is  to 
operate,  and  the  reaction  of  the  network's  impedance  characteristic 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;  received 
April  18,  1938. 

**  Electrical  Research  Products,  Inc.,  Hollywood,  Calif. 

443 


444  F.  L.  HOPPER  [j.  s.  M.  P.  E. 

upon  the  frequency-response  of  the  equipment  associated  with  it. 
The  last  factor  is  of  considerable  importance  when  a  network  is  con- 
nected to  the  input  circuit  of  an  amplifier,  since  frequently  the 
amplifier  response  is  altered  when  working  into  an  incorrect  or  vary- 
ing impedance.  A  comparable  condition  may  exist  when  a  network 
is  operated  on  the  output  of  an  amplifier,  particularly  if  the  amplifier 
output  stage  contains  pentodes.  In  addition,  if  a  number  of  net- 
works are  to  be  connected  in  tandem,  the  constant-resistance  type  is 
advisable.  Generally,  one  end  of  a  constant-resistance  structure 
must  be  terminated  ideally  if  terminal  effects  are  to  be  made  negli- 
gible. Several  constant-resistance  networks  in  tandem  will  add 
their  respective  loss  characteristics  without  interaction  provided 
they  are  designed  for  the  same  nominal  terminating  resistance,  and 
are  actually  terminated  in  this  resistance  at  one  end.  If  neither  end 
is  well  terminated,  or  if  some  non-constant  resistance  network  is 
included  in  the  chain,  the  overall  loss  characteristic  will  show  inter- 
action effects.  The  generally  desirable  features  of  networks  of  this 
type  have  resulted  in  their  nearly  universal  use  for  modifying  the 
characteristic  in  sound  recording. 

These  same  criteria  apply  to  the  choice  of  filter  structures  for 
limiting  the  frequency-response  characteristic.  Usually  the  filter  is 
composed  of  combinations  of  constant-^  and  Af-derived  sections, 
since  the  constant-resistance  network  does  not  usually  introduce  in- 
sertion loss  with  sufficient  rapidity.  A  number  of  the  commonly 
used  types  of  networks,  their  functions,  types  of  service,  and  char- 
acteristics are  given  in  Table  I. 

The  networks  shown  by  no  means  constitute  a  complete  list,  but 
may  be  regarded  as  representative  of  those  in  use  in  many  of  the 
studios.  Among  other  types  having  more  limited  use  are  those  for 
equalizing  monitoring  systems  and  a  number  of  special  types  em- 
ployed in  re-recording,  which  permit  attenuating  certain  restricted 
bands  of  frequencies  to  achieve  special  effects. 

The  designs  of  filters  used  for  limiting  the  frequency-response  char- 
acteristic are  well  covered  in  the  literature.1  Design  data  pertaining 
to  the  constant-resistance  type  of  network  are  probably  not  so  well 
known. 

Since  this  structure  has  so  many  applications  in  the  recording  field, 
it  is  of  interest  to  consider  its  design.  We  may  choose  the  bridged- T 
form,  since  nearly  all  transmission  circuits  wherein  such  equalizers 
are  employed  are  grounded  on  one  side.  In  addition,  this  type  re- 


Nov.,  1938]        ELECTRICAL  NETWORKS  FOR  RECORDING 


445 


TABLE  I 


Network 


Function 


Service 


Response 


Dialog  Equalizer          Compensates  for  stage  con-       Recording 
ditions. 


Microphone  Equal-      Compensates     for     micro-      Recording 
izer  phone  irregularities  or  cer- 

tain acoustical  response  ef- 
fects. 


Depends  upon 
microphones  » 


Presence  Equalizer      Corrects  for  certain  Acous-       Recording 
tic  Pick-up  Effects. 


Pre-Equalizer  Increases       highs       subse-       Recording  and 

Post- Equalizer  quently  attenuated  in  re-       Reproducing 

producing.     Used     to    re- 
duce noise. 


Film  Equalizer  Compensates       for       film       Re-recording 

losses. 


Low-Frequency  Permits  adjustment  of  re-       Re-recording 

Corrective  sponse    for    corrective    or 

dramatic  effects. 


High-Frequency  Permits  adjustment  of  re-       Re-recording 

Corrective  sponse    for    corrective    or 

dramatic  effects. 


I're-.-q 


I'ost-Eq 


Max. 


Max. 


High-Pass  Filter          Limits    low-frequency    re-      Recording  and 
sponse.  Re-recording 


Low-Pass  Filter  Limits   high-frequency   re-       Recording  and 

sponse,  depending  partially       Re-recording 
upon    modulating    devices 
characteristic. 


446 


F.  L.  HOPPER 


[J.  S.  M.  P.  E. 


quires  fewer  elements  than  the  lattice  structure.     The  general  form 


of  the  network  is  shown  in  Fig.  1 


FIG.    1.     Simple   bridged-  T  network: 
A  =  A  =  R/c;  B  =  (C*-1)R/2C. 


The  resistances  A,  A,  and  B  form 
a  conventional  T  type  of  "pad." 
This  may  be  of  either  the  finite  or 
infinite  loss  type,  depending  upon 
the  design  problem.  The  ele- 
ment Zu  is  arbitrarily  chosen  as 
the  independent  variable  deter- 
mining the  transmission  charac- 
teristic of  the  network.  The 
elements  comprising  Zn  may  be 
reactive,  resistive,  or  a  combina- 
tion of  both.  Networks  used 
in  sound  recording  usually  em- 
ploy elements  consisting  essen- 
Consequently,  this  case  will  be  con- 


tially  of  pure  reactance, 
sidered  first. 

The  factors  determining  the  insertion  loss,  in  decibels,  of  a  given 
network  are: 

(a)     The  loss  of  the  T  pad. 
(6)     The  impedance  of  the  reactive  element  Zu. 

(c)  The  iterative  impedance,  R,  of  the  circuit  in  which  the  network  is  to 
operate. 

An  equation  relating  these  quantities  is  derived  in  the  appendix  of 
this  paper.  In  Fig.  2,  a  family  of  curves  representing  various  pad 
losses  has  been  plotted  as  a  function  of  the  impedance  Zu  as  abscissa, 
and  the  corresponding  network  insertion  losses  as  ordinates.  R  is 
assumed  to  be  500  ohms.  The  relations  between  Z\\  and  Z%\t  their 
use  as  elements  in  various  networks,  and  the  characteristics  of  such 
networks  are  shown  in  Fig.  3. 

In  the  design  of  a  particular  network  Fig.  3  enables  a  choice  of 
element  Zu  to  effect  a  certain  shape  of  characteristic.  If  the  re- 
quired characteristic  is  somewhat  complex,  it  may  be  necessary  to 
achieve  the  final  desired  characteristic  by  employing  one  or  more 
networks,  the  sum  of  their  individual  characteristics  resulting  in  the 
required  one.  In  addition,  the  following  data  are  necessary  : 

(a)     The  maximum  required  insertion  loss,  determining  the  pad  value. 

(&)  The  insertion  loss  at  some  particular  frequency  which  effectively  deter- 
mines the  shape  of  the  insertion  loss  characteristic.  This  in  turn  determines  the 
value  of  Zu  (from  Fig.  2)  and  from  Fig.  3  the  values  of  the  reactive  elements  L  and 


Nov.,  1938]       ELECTRICAL  NETWORKS  FOR  RECORDING 


447 


C  may  be  computed.     From  these,  the  impedance  Zu  may  be  computed  for  other 
frequencies  and  the  insertion  loss  read  from  the  charts  of  Fig.  2. 

An  example  of  such  a  computation  is  given  in  the  appendix. 

It  is  apparent  from  an  inspection  of  Fig.  2  that  the  insertion  loss 
approaches  the  pad  loss  for  large  values  of  the  impedance  Zn,  and 
hence  does  not  become  infinite.  If  the  T  pad  is  of  the  infinite-loss 


x-x  -  R 


FINITE   LOSS    TYPE 


INHNITE   LOSS    TYPE 


20 


100 


2  3        456789  IpOO  2 

IMPEDANCE    Zu      OHMS 


9  10,000 


FIG.  2.     Constant-resistance  network  design  chart  (curves  give  insertion  loss 
in  a  500-ohm  circuit). 


type,  i.e.,ifA=A=R  and B is  zero,  the  insertion  loss  of  the  network 
becomes  increasingly  large  as  Zn  increases,  approaching  infinity  as 
Zn  approaches  infinity  and  Z>n  approaches  zero.  A  design  curve  for 
this  type  of  structure  is  included  in  Fig.  2. 

Another  special  condition  having  practical  use  in  the  design  of 
variable  attenuators  is  the  case  when  Zn  is  resistance  only.  This 
affords  the  opportunity  of  designing  a  bridged-  T  type  of  attenuator 


448 


F.  L.  HOPPER 


[J.  S.  M.  P.  E. 


having  constant-resistance  properties.     Design  information  for  this 
case  is  also  presented  in  Fig.  2. 

Phase-shift  introduced  into  a  circuit  by  the  resistance-arm  bridged- 
T  structure  shown  in  Fig.  1  will  usually  be  less  than  40  degrees  for 


TYPE 
NETWORK 


IV 


ELEMENTS 
Zu  Zzi 


IMPEDANCE 


Zu 


U)L 


1 
OJC 


OJCi 


00  Li 


1 

(DC 


OJL 


OJLa 
U^LzCa-l 


RESPONSE 
CHARACTERISTIC 


FORMULAE 


ALL  TYPES 
H  xZ2,-R2 


TYPES  1  &  It 


L,C,-L2C2 

J=2  =  R2 
Ci 


FIG.  3.     Equalizer  chart. 


TYPES  Ull  IV 


2H~y  L2C2 


networks  employing  finite  pads,  and  will  approach  90  degrees  as  a 
maximum  for  networks  employing  an  infinite-loss  type  of  pad. 

The  wide  adaptability  of  constant-resistance  networks  to  the 
equalization  requirements  of  sound  recording  is  best  demonstrated 
by  their  wide-spread  use.  The  methods  outlined  here  simplify  the! 
design  of  such  networks  to  meet  specific  characteristics. 


Nov.,  1938]        ELECTRICAL  NETWORKS  FOR  RECORDING  449 

APPENDIX 

Referring  to  Fig.  1,  the  general  form  of  the  bridged-  T  network,  the  resistances 
R/c,  R/c,  and  (c*  —  l)R/2c  form  a  conventional  T  type  of  pad.  The  value  of 
c  for  a  given  pad  loss  is  given  by 

Pad  loss  in  db.  =  20  log  -  =  20  log™  n  (1) 

iz 

where  *']   =  current  in  the  load  resistance  when  the  pad  is  not  in  the  circuit. 

iz  =  current  in  the  load  resistance  when  the  pad  is  inserted  in  the  circuit. 

c  is  then  defined  as 

°  =  ^\  (2} 

For  the  network,  Zn  is  arbitrarily  taken  as  the  independent  variable  determin- 
ing the  propagation  constant.  Z2i  is  dependent  upon  Zn  through  the  relation 

Zu  X  Z21  =  R2  (3) 

The  propagation  constant  of  the  network  is  given  by  Zobel2  as: 

,    (c  +  1)   Zn 
2        ~R 


, 


2          R 

From  eq.  4  both  the  attenuation  and  phase  constants  may  be  obtained  since 

m+jn  (5) 


and  ea  =  Aw2  +  w2  (0) 

where  a  is  the  attenuation  constant  in  napiers. 
The  phase  constant  0  in  degrees  is  given  by 

tan/3   =   -  (7) 

m 

A  general  solution  of  eq.  4,  assuming  that  Zn  is  composed  of  both  reactance  and 
resistance  gives 


Zu  =  ^Tcos0  R  =»=  R  r-cose      +e—  (8) 


6  =  angle  between  the  resistance  and  reactance  components  of  Zu.     For  the 


450  F.  L.  HOPPER  [j.  s.  M.  P.  E 

case  when  Z\\  is  reactance  only  eq.  8  may  be  simplified,  since  6  is  90  degrees  an 
cos  0  =  0.     Eq.  8  then  becomes 


Eq.  9  may  be  simplified  for  direct  substitution  by  converting  the  attenuatio: 
in  napiers  to  attenuation  in  decibels,  resulting  in 


where  db.  =  the  insertion  loss  of  the  network. 

Zu  =  impedance  in  ohms  of  the  reactive  element  of  the  network. 
Eq.  10  has  been  plotted  for  design  purposes  assuming  R  is  500  ohms  in  Fig.  2 
For  the  infinite-loss  type  of  pad  c  =  1,  and  the  pad  resistances  become  A  = 

A  =  R,  and  5  =  0.     Substituting  c  =  1  in  eq.  10  gives 

Zn  =  R  Ve*«  -  1  (11) 

This  is  plotted  in  Fig.  2,  assuming  R  to  be  500  ohms. 

Referring  to  eq.  8,  if  no  reactance  is  involved  but  only  resistance,  6  is  zero  de 
grees,  and  cos  0  =  1;   hence 


For  an  infinite-loss  type  of  pad  c  =  1,  r  =  s  =  1  and  eq.  12  becomes 

Zn  =  £(e«  -  1)  (15) 


This  equation  permits  the  design  of  a  bridged-  T  type  of  attenuator  having  con 
stant-resistance  properties.     It  has  been  plotted  in  Fig.  2. 

The  phase  change  introduced  by  a  network  employing  a  finite  pad  may  be  com 
puted  from  eq.  7,  and,  for  the  case  where  Z\\  is  reactance  only,  becomes 


Examples  of  the  use  of  this  design  data  follow. 

Low-Frequency  Attenuating  Network.  —  Assume  that  the  requirements  for  thiij 
network  are  an  insertion  loss  of  4  db.  at  100  cycles,  and  about  8  db.  at  20  cycles) 
when  connected  in  a  500-ohm  circuit.  Reference  to  Fig.  3  indicates  that  Zi, 
should  be  a  capacity  C,  and  Z2i  an  inductance  L.  Since  the  maximum  require^ 
loss  is  8  db.,  a  pad  of  that  value  is  chosen.  The  insertion  loss  at  100  cycles  deter 


Nov.,  1938]        ELECTRICAL  NETWORKS  FOR  RECORDING  451 

mines  the  value  of  Zn  or  C  as  follows:  From  Fig.  2  for  an  8-db.  pad  and  4-db. 
insertion  loss  Zn  is  490  ohms.  Since  Zn  =-  1/taC  and  w  at  100  cycles  is  2v  X  100 
nre  have 


=  3.24  mfd. 


coZn      628  X  490 
md  L  =  R2C  =  5002  X  3.24  X  10~«  =  0.81  h 

having  determined  these  constants  the  insertion  loss  at  other  frequencies  may  be 
:ound  as  follows : 


Freq.  «                                   o>C  wC    ~  ^t? 

20  125  407X10-'  2460              7.6db. 

40  252  817  1220  6.8 

100  628  2030  490  4.0 

200  1256  4060  246  1.7 


Equalizer  for  Re-Recording  System  to  Simulate  Poor  Radio  Quality.  —  Assume  that 
he  requirements  for  this  network  are  no  insertion  loss  at  800  cycles,  7  db.  at  300 
ycles,  and  with  increasing  insertion  losses  at  both  extreme  low  and  high  frequen- 
ces. The  network  is  to  operate  in  a  500-ohm  circuit.  Fig.  3  indicates  the  choice 
if  a  series-resonant  circuit  comprised  of  LI  and  Ci  for  Zn,  and  an  anti-resonant 
:ircuit  composed  of  L2  and  C2  for  Z2i.  Since  the  network  losses  are  to  increase 
>utside  the  specified  limits,  an  infinite-loss  type  of  pad  is  used.  The  values  of 
*i,  Ci  are  determined  from  the  insertion  loss  requirement  of  7  db.  at  300  cycles 
^  follows: 

Since  fr  occurs  at  800  cycles,  the  frequency  for  no  insertion  loss, 

4X1°" 


.nd  Zn  for  a  7-db.  insertion  loss  with  an  infinite-loss  pad  (from  Fig.  2)  is  990  ohms. 


or 


L,  —   CiR*  •=  0.464  X  10-«  X  500'  =  0.116  h. 


nd  ft  =  .  0.345  mfd. 

0.116 


452 


F.  L.  HOPPER 


Insertion  losses  at  other  frequencies  are: 


Freq. 

CO 

O)' 

CO 

'Lid 

«»Li 

Ci-l 

cod 

Zn 

Ins.  Loss 
(Fig.  2) 

100 

628 

0 

.39  X  106 

0 

.0155 

0. 

985 

0.000291 

3380 

16. 

8db. 

300 

1,880 

3 

.51 

0 

.14 

0 

.86 

0.00087 

990 

7 

.0 

500 

3,140 

9 

.8 

0 

.39 

0 

.61 

0.00145 

420 

2 

.3 

800 

5,020 

26 

1 

.0 

0 

0.00233 

0 

0 

1000 

6,280 

39 

1 

.56 

0 

.56 

0.0029 

193 

>1 

.0 

2000 

12,560 

157 

6 

.28 

5 

.28 

0.00581 

910 

6 

.5 

3000 

18,800 

352 

14 

.1 

13 

.1 

0.0087 

1510 

10 

.0 

REFERENCES 

T.  E.:     "Transmission  Networks  and  Wave-Filters,"  D.  Van  N 
strand  Co.  (New  York). 

8  ZOBEL,  O.  J.:     "Distortion  Correction  in  Electrical  Circuits,"  Bell.  Sy 
Tech.  J.,  VII  (July,  1928),  No.  7,  p.  438. 


A  NON-INTERMITTENT  PROJECTOR  FOR  TELEVISION 
FILM  TRANSMISSION* 


H.  S.  BAMFORD** 


Summary. — A  continuous  machine  is  described  for  the  projection  of  images  from 
Im  into  the  pick-up  camera  for  television  transmission  of  motion  pictures.  The 
imera  tube  can  be  either  of  the  instantaneous  or  the  storage  type.  The  images  are 
wident  upon  the  cathode  during  scansion  and  the  optical  image  transition  interval 
>  less  than  the  scanning  flyback  interval  with  which  it  is  synchronized.  Certain  ad~ 
intages  are  taken  in  the  construction  of  a  double-lens  disk  type  of  optical  compensator 
»  obtain  an  image  steadiness  determined  only  by  the  number  of  lenses  per  disk,  such 
'rors  as  are  introduced  by  lens  setting  and  gearing  being  negligible. 

The  telecine  projector  to  be  described  operates  upon  the  principle 
f  optical  compensation  as  the  film  moves  continuously  through  the 
1m  gate  and  can,  therefore,  be  called  a  continuous  or  non-inter- 
littent  type  of  machine.  As  a  telecine  projector,  it  is  applicable 
trictly  to  the  projection  of  images  from  film  for  television  pick-up, 
nd  the  images  so  projected  are  substantially  stationary. 

Fig.  1  is  a  photograph  of  such  a  machine,  constructed  to  project 
:om  3 5 -mm.  sound  recorded  film,  and  similarly  the  principle  of 
peration  can  be  applied  to  16-mm.  sound-film  projection  when  the 
umber  of  images  per  second  is  24. 

The  machine  is  operable  with  a  pick-up  tube  of  either  the  in- 
;antaneous  or  the  storage  type.  By  instantaneous  type  of  pick-up 
Ube  is  meant  a  tube  wherein  the  elemental  signal  leaving  the  tube  is 
^presentative  of  the  optical  image  element  at  the  instant  it  is  scanned, 
nd  is  of  an  intensity  determined  by  the  light-intensity,  sensitivity 
E  the  cathode  surface,  the  element  area,  and  the  time  required  to 
:an  the  element  area.  Obviously,  the  absence  of  an  optical  image 
pon  the  cathode  during  the  whole  or  part  of  the  scansion  interval 
isults  in  either  a  total  blank  or  an  image  with  a  horizontal  blank  bar 
le  width  of  the  image,  and  of  a  height  determined  by  the  interval  of 
ptical  image  cut-off. 

*  Received  July  1,  1938. 
**  Farnsworth  Television,  Inc.,  Philadelphia,  Pa. 

453 


454 


H.  S.  BAMFORD 


[J.  S.  M.  P.  E. 


A  pick-up  tube  of  the  storage  type  is  one  in  which  the  optical 
image  incident  upon  the  cathode  gives  rise  to  a  charge  image  which 
remains  until  it  is  removed  by  scansion,  and  the  resulting  elemental 
signal  leaving  the  tube  is  representative  of  the  elemental  charge 
stored  upon  the  cathode  during  optical  image  incidence  of  an  intensity 
determined  by  the  intensity  of  the  light,  sensitivity  of  the  cathode 
surface,  the  element  area,  the  tune  required  to  completely  scan  one 
frame,  and  a  factor,  K. 

The  Farnsworth  "dissector"  is  an  example  of  the  instantaneous 
type  of  pick-up  tube;  the  iconoscope,  emitron,  and  image  amplifier, 
examples  of  the  storage  type. 


FIG  .  1 .    Telecine  pro j  ector . 

Such  a  universal  application  can  be  better  understood  and  certain  I 
advantages  recognized  when  we  consider  that  the  projected  image  is  | 
stationary  upon  the  cathode  of  the  pick-up  device  and  has  a  duration  j 
equal  to  the  scanning  time,  changes  from  image  to  image  occurring  i 
only  during  the  scanning  flyback  interval.  According  to  present  j 
standards,  the  time  allowed  for  flyback  between  scansions  is  10  per 
cent  of  the  field  scansion  tune,  or  Veoo  second.  Such  a  requirement 
should  make  obvious  the  need  for  a  machine  of  the  continuous  type ! 
in  which  optical  image  transition  can  be  accomplished  at  very  high  j 
speed  as  compared  with  the  intermittent  type  projector,  wherein  the  I 
optical  image  transition  tune  is  limited  to  a  speed  determined  by  the , 
ability  of  the  film  to  withstand  the  effect  of  the  acceleration  with  in-  j 
creasing  tension  necessary  at  the  film  gate  to  maintain  steadiness. ; 


Nov.,  1938] 


A  NON-INTERMITTENT  PROJECTOR 


455 


A  72-degree  intermittent  jerking  the  film  into  its  successive  positions 
in  Vwo  second  is  by  no  means  a  slow  intermittent  movement.  In 
addition,  various  methods  of  selection  of  optical  image  sequence  can 
be  simply  accommodated,  including  the  method  wherein  successive 
images  are  superimposed  for  a  brief  transition  interval,  during  which 
interval  the  total  light  is  kept  constant  by  the  selector  disk. 

Many  systems  of  optical  compensation  have  been  designed  and 
tried  in  the  past  for  theater  projection,  using  lenses,  prisms,  or  mir- 
rors, and  many  more  systems  can  be  conceived,  using  them  in  combi- 
nation, giving  almost  perfect  first-order  results.  However,  the 
first-order  derivation  is  not  sufficient  to  predict  the  overall  per- 
formance of  the  system.  The  presence  of  third-order  aberrations  in 
sufficient  magnitude  will  destroy  what  might  look  to  be  a  perfect 


FIG.  2.     Illustrating  method  of  optical  compensation. 

design.  In  addition,  the  physical  setting  of  the  component  elements 
and  the  mechanical  drive  of  the  system  are  obviously  of  extreme  im- 
portance. The  effects  upon  the  projected  optical  image  by  a  machine 
in  which  these  faults  are  present  are  unsteadiness  during  image  in- 
cidence and  lack  of  coincidence  of  successive  image  frames.  Both  in 
effect  constitute  image  jump,  and  their  effects  are  more  destructive 
in  telecine  projection  due  to  the  present  system  of  interlacing  than 
they  would  be  for  direct  viewing  or  non-interlaced  scanning. 

Some  systems  lend  themselves  admirably  to  the  fulfillment  of  the 
above-described  requirements,  while  others  do  not.  It  is  not  possible 
in  a  limited  space,  nor  would  it  be  of  general  interest,  to  discuss  in 
detail  various  systems  of  optical  compensation  and  their  qualities 
and  failings,  though  it  might  be  well  to  inject  some  general  con- 
siderations. A  system  in  which  the  optical  compensator  is  a  single 
unit  is  going  to  require  that  the  driving  gear  be  extremely  accurate; 


456  H.  S.  BAMFORD  [j.  s.  M.  P.  E. 

many  times  more  accurate  than  the  pair  of  gears  required  to  drive 
the  optical  compensator  of  the  symmetrical  double-unit  type.  That 
the  optical  elements  can  be  corrected  with  no  great  difficulty,  if  at  all, 
is  another  consideration.  The  following  is  intended  to  indicate  an 
approach  to  the  ideal  optical  compensator  for  the  particular  purpose 
outlined. 

Fig.  2  illustrates  a  method  of  optical  compensation  wherein  the 
motion  of  a  lens  is  made  to  compensate  for  film  motion,  so  that  the 
projected  image  is  stationary,  and  equation  1  gives  these  required 
motion  relationships  : 

*  =  -y  (l/m  -  1)  (i) 

di  =  film  displacement. 
y  =  lens  displacement. 
m  =  magnification. 

Equal  numbers  of  lenses  mounted  upon  two  oppositely  rotating 
disks  in  optical  mesh  can  be  made  to  constitute  a  succession  of  well 
corrected  projection  objectives  of  very  closely  matched  focal  length 
and  magnification.  By  optical  mesh  is  meant  that  each  lens  on  the 
one  disk  overlaps  a  lens  on  the  other,  so  that  they  form  substantially 
a  symmetrical  objective.  As  the  disks  rotate  through  the  necessary 
angle,  the  component  lenses  move  apart  in  equal  amounts  in  opposite 
directions,  and  by  selecting  a  slightly  different  focal  length  for  the 
one  disk  the  effects  of  these  horizontal  displacements  upon  the  pro- 
jected image  are  mutually  annulled. 

Two  components  of  a  composite  lens  contribute  to  the  total  mag- 
nification of  the  system  in  amounts  : 


mfi  +/2 

(3) 


fi  +/2  -  a 

fi    =  focal  length  of  the  first  lens. 
/2    =  focal  length  of  the  second  lens. 
Wi  =  magnification  by  the  first  lens. 
W2  =  magnification  by  the  second  lens. 
a     =  separation  of  the  component  lenses. 

The  displacement  of  an  image  point  by  the  displacement  of  a  lens  is  : 

x  =  y  (1  -  w)  (4) 

m  =  mim2  =  magnification  of  the  system. 
Therefore,  for  complete  annullment  of  the  horizontal  displacements 


Nov.,  1938]  A  NON-INTERMITTENT  PROJECTOR  457 

of  the  two  component  lenses,  the  focal  lengths  must  be  related  as 
follows  : 

/,./,-  iOSL+i)  (5) 

m  —  1        . 

Should  the  focal  lengths  of  the  two  component  lenses  be  the  same, 
fa  =  /2)  the  horizontal  displacement  error  can  be  computed  from 
equation  6,  wherein  yi  =  —y2: 


EH 


2/1  —  a 


EH   —  horizontal  displacement  error. 

yt      =  horizontal  displacement  of  lens  No.  1. 

y2      =  horizontal  displacement  of  lens  No.  2. 

Substitution  in  equation  6,  for  the  particular  system  used,  will  indi- 
cate a  negligible  value  of  EH  when  the  focal  length  of  the  lens  on  the 
front  disk  is  similar  to  that  of  the  lens  on  the  rear,  with  consequent 
advantages  in  construction. 

The  vertical  component  of  the  lens  motion  is  parallel  to  the  motion 
of  the  film  and  constitutes  to  an  acceptable  degree  the  compensating 
motion,  y,  as  set  forth  in  equation  1.  This  vertical  motion  of  the 
lens  varies  as  the  sine  of  the  angle  of  rotation  of  the  disks  and  is, 
therefore,  nonuniform,  while  the  film  is  moved  through  a  plane  gate 
at  a  uniform  rate.  Obviously,  the  projected  image  will  not  be  per- 
fectly stationary,  but  will  be  periodically  displaced  vertically  a  small 
amount,  such  amount  being  termed  the  vertical  displacement  error. 
This  vertical  displacement  error  contributes  to  the  overall  image 
jump.  By  the  proper  selection  of  the  lens  disk  radius,  a  minimum 
vertical  displacement  error  can  be  derived  for  a  given  magnification 
and  angular  projection  interval  of  the  disks.  The  number  of  lenses 
per  disk  determines  the  angular  projection  interval,  while  the  number 
selected  is  determined  by  the  allowable  vertical  displacement  error, 
and  the  allowable  horizontal  separation  of  the  overlapped  component 
lenses. 

The  use  of  a  curved  film  gate  in  allowing  an  average  correction  of 
the  lens  disk  sine  error  introduces  a  displacement  error  by  virtue  of 
its  distorting  effect.  Defocusing  also  results  when  the  image  is  pro- 
jected from  film  running  through  a  curved  gate  onto  a  plane.  Ob- 
viously, lens  curvature  can  only  make  an  average  correction  for  gate 
curvature,  while  curvature  of  the  cathode  must  include  consideration 
of  the  electron  optical  system. 


458  H.  S.  BAMFORD  [j.  s.  M.  P.  E. 

In  consideration  of  the  following,  the  diameters  of  the  lenses  are 
such  that  only  the  required  amount  of  light  is  projected,  and  not  a 
needless  excess;  and  the  system  magnification,  determined  by  the 
lens  disk  radius,  is  such  that  the  projected  image  needs  little  modifica- 
tion by  a  fixed-axis  auxiliary  lens.  The  third-order  aberrations  all 
vary  as  some  function  of  the  lens  aperture.  The  magnification  of 
the  lens  disk  gear  errors  is*  proportional  to  the  ratio  of  the  lens  disk 
diameter  to  the  pitch  diameter  of  the  gear.  Still  more  reasons  can  be 
cited  to  indicate  the  importance  of  the  correct  determination  of  the 
lens  aperture;  the  reasons  given  above  are  obviously  most  important. 

The  mounting  of  the  lenses  upon  the  disks  in  their  correct  positions 
is  made  possible  to  a  reasonably  high  degree  of  precision  by  virtue  of 
the  fineness  of  lens  correction  and  uniformity.  The  grinding,  cen- 
tering, and  edging  of  the  component  elements  must  be  well  done  and 
a  reasonable  uniformity  maintained  in  element  thicknesses.  A  high 
degree  of  uniformity  of  focal  length  is  facilitated  by  the  ability  to 
modify  slightly  when  cementing  the  component  elements.  The 
cemented  achromat  is  mounted  in  a  holder,  preferably  of  the  same 
metal  as  the  disks,  and  gripped  so  that  there  will  be  no  strain.  Slip- 
ping after  the  settings  are  made,  either  of  the  holder  on  the  disk  or 
the  lens  in  the  holder,  must  not  occur.  It  is  not  abnormally  difficult 
to  mount  these  lenses  in  their  holders  upon  the  disks  spaced  from  each 
other  and  similar  in  radii  to  within  0.0002  inch.  As  the  effect  upon 
the  projected  image  is  divided  between  the  two  overlapped  lenses — 
equations  2,  3,  and  4 — and  each  lens  has  its  own  setting  error  not  ex- 
ceeding 0.0002  inch,  the  image  displacement  will  be  some  average  not 
exceeding  0.0002(1  —  m)  inch,  or  possibly  zero  when  the  setting  errors 
of  the  two  lenses  are  equal  and  opposite.  A  detailed  description  of 
the  alignment  procedure  is  impossible  in  a  limited  space;  it  is  suf- 
ficient to  say  that  the  order  of  accuracy  involves  in  the  aligning  in- 
strument a  good  degree  of  thermal  and  mechanical  stability. 

The  lens  disks  are  geared  directly  to  the  film  drive  sprocket  shaft 
so  that  the  errors  due  to  nonuniformity  of  drive  are  not  present  in 
the  projected  image.  The  gear  train  from  the  film  drive  sprocket  to 
the  lens  disks  is  so  designed  that  annullment  of  eccentric  error  is 
accomplished  to  a  high  degree  and  the  transmission  of  residual  errors 
is  reduced  in  proportion  to  the  ratio  of  the  pitch  diameters  of  the 
common  shaft  gears.  The  four  gears  driving  the  two  lens  disks  can 
be  so  arranged  that  their  eccentric  errors  are  subtractive  by  virtue  of 
the  optical  mesh.  Such  advantages  of  gear  arrangement  can  not  be 


Nov.,  1938] 


A  NON-INTERMITTENT  PROJECTOR 


459 


taken  in  most  other  systems  with  consequent  requirements  of  almost 
impossible  precision  in  gear  cutting  and  attendant  high  cost.  The 
gears  are  bronze  mating  with  steel  cut  on  a  gear  shaper  and  enveloped 
to  give  what  might  be  called  a  commercial  high-precision  gear.  En- 
veloping, or  shaving,  as  it  is  sometimes  called,  is  very  effective  in 
finishing  a  well  cut  gear  so  as  to  correct  eccentricity,  nonuniformity 
of  tooth  spacing,  and  involute  profile,  beside  smoothly  finishing  the 


\ 


' 


FIG.  3.     Selection  disk  in  relation  to  lens  disks. 

tooth  faces.     This  smooth  finish  has  much  to  do  with  maintaining 
accuracy  over  a  period  of  time. 

The  driving  of  the  film  through  the  film  gate  constitutes  another 
problem  to  which  attention  must  be  given.  Due  to  the  fact  that  the 
image  is  projected  while  the  film  is  moving,  variations  in  that  motion 
naturally  result  in  an  unsteady  image.  If  the  film  is  pulled  through 
the  gate  by  a  sprocket,  and  the  sprocket  teeth  do  not  accurately 
match  the  film  perforations,  periodic  slipping  of  the  film  will  result  at 
a  frequency  of  96  per  second,  for  35-mm.  film.  Obviously,  the 
images  projected  from  a  film  so  driven  will  have  a  periodic  vertical 
jump.  Variation  in  shrinkage  of  films  according  to  their  age  and 


460 


H.  S.  BAMFORD 


[J.  S.  M.  p.  E. 


treatment  makes  it  impossible  to  determine  a  fixed  sprocket  size  that 
will  give  acceptable  results.  A  sprocket  with  a  variable  diameter, 
graduated,  will  accommodate  different  films  and  was  tried  experi- 
mentally with  considerable  success.  That  the  shrinkage  is  suf- 
ficiently uniform  throughout  the  reel  to  satisfy  present  requirements 
for  a  given  setting  has  been  indicated  in  the  results  so  far  obtained. 
Framing  the  film  in  the  gate  is  very  simply  done  with  the  sprocket 
drive  method  by  increasing  or  decreasing  a  loop  between  the  gate 
and  the  film  drive  sprocket  with  a  displaceable  idling  roller. 

The  images  are  projected  upon  the  cathode  of  the  pick-up  tube  in 
correct  sequence  for  scanning  by  a  predetermined  selection  of  the 


FIG.  4.     Operating  side  of  telecine  projector. 

projection  lenses  on  the  lens  disks.  Fig.  3  illustrates  a  method  of 
selection  in  which  a  disk  with  spiraled  slots  rotates  directly  in  front 
of  the  lens  disks  occulting  all  but  the  desired  lens.  The  spiraled  slot 
follows  the  lens  in  its  downward  travel  and  allows  the  projection  of  a 
single  frame  for  a  predetermined  time,  after  which  time  the  first  lens 
is  occulted  and  the  next  lens  uncovered  to  project  the  following  frame. 
The  selector  disk,  as  shown,  is  slotted  to  allow  the  projection  of  suc- 
cessive images  of  such  time  duration  that  they  can  be  scanned  alter- 
nately two  and  three  times  with  a  transition  interval  of  less  than 
Veoo  second.  By  adjusting  the  phase  relationship  between  the  syn- 
chronous projector  motor  and  the  projector,  the  image  transition 


Nov.,  1938]  A  NON-INTERMITTENT  PROJECTOR  461 

intervals  are  made  to  coincide  with  the  scanning  flyback  intervals. 
The  above  allows  scansion  of  single  images  with  a  minimum  angular 
projection  interval  of  the  lens  disks. 

Fig.  4  pictures  clearly  the  operating  side*  of  the  telecine  projector 
wherein  the  film  is  uniformly  illuminated  in  the  gate  by  a  Mazda  in- 
candescent lamp,  an  image  of  the  source  being  projected  in  the  plane 
of  the  selector  disk.  A  uniformly  bright  image  is  maintained  during 
the  projection  interval  by  constriction  of  the  slots  in  the  selector 
disk  according  to  the  lens  position  in  the  light-spot.  For  the  machine 
described,  the  amount  of  light  so  projected  is  in  excess  of  40  lumens. 
The  image  size  can  be  modified  by  adjustments  of  the  low-power 
auxiliary  lens  shown  directly  in  front  of  the  pick-up  tube  and  the 
telecine  camera  racking  table.  Measurements  of  the  image  projected 
by  the  experimental  machine  indicate  that  the  combined  errors  con- 
tributed by  the  gears,  lens  setting,  etc.,  are  negligible  and  that  within 
reading  error,  image  unsteadiness  does  not  exceed  1/8  per  cent. 


SILENT  GASOLINE  ENGINE  PROPELLED  APPARATUS* 
J.  E.  ROBBINS** 


Summary. — Problems  are  discussed  connected  with  the  design,  construction,  and 
operation  of  electrical  generators  and  water  pumps  running  under  full  load  sufficiently 
silently  to  permit  satisfactory  sound  recording.  The  units  described  were  the  result 
of  demands  for  silent  power  equipment  for  making  shots  on  boats,  trains,  bus  in- 
teriors, inaccessible  canyons,  etc.  As  an  example  of  what  is  sometimes  required,  one 
of  the  largest  units  was  installed  in  the  hold  of  a  windjammer  used  throughout  the 
Paramount  Production  "Souls  at  Sea"  and  although  the  microphone  was  at  times 
directly  above  (approximately  30  feet)  the  spot  occupied  by  the  generator,  no  noises  were 
picked  up  by  the  sound  recording  equipment. 

Four  units  are  described,  namely,  one  144-kw.  Hispano  Suiza,  one  57-kw.  Lincoln 
Zephyr,  and  one  41-kw.  Ford  V-8  generator,  and  one  high-pressure  Ford  V-8  water 
pump.  In  each  case  the  entire  mechanical  unit  is  rubber-mounted  on  a  sub-frame 
within  a  semi-airtight  compartment  constructed  of  an  outer  shell  of  22-gauge  auto- 
body  steel,  four  inches  of  sound-absorbing  material  with  an  inner  lining  of  asbestos 
cloth.  The  entire  exhaust  system  is  water-cooled,  employing  special  mufflers  also 
housed  within  the  case.  One  radiator,  mounted  outside,  cools  the  water  for  the  engine 
as  well  as  the  exhaust.  All  are  practically  automatic  in  operation,  with  electrical 
governors,  temperature  regulators,  etc.  The  machines  have  been  in  operation  ap- 
proximately fifteen  months  and  have  required  very  little  service  other  than  normal 
maintenance. 


Prior  to  the  advent  of  sound  in  motion  pictures  any  reliable  source 
of  power,  regardless  of  noise,  was  acceptable  for  operating  generators, 
water  pumps,  and  water  churns  on  the  lots  as  well  as  on  location. 
Sound  radically  changed  the  entire  condition.  It  was  immediately 
necessary  to  move  the  equipment  800  to  1200  feet  from  the  camera, 
depending  upon  conditions  which  were  aggravated  by  changes  in 
wind  direction,  difficult  set-ups,  enclosed  canyons,  etc.  Effects  of 
water  in  motion,  ripples,  and  rain  were  generally  shot  sync  (sound 
dubbed  in  later),  due  to  the  impracticability  of  obtaining  working 
pressures  from  these  distances. 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;  received  April 
4, 1938. 

**  Paramount  Pictures,  Inc.,  Hollywood,  Calif. 

462 


GASOLINE  ENGINE  PROPELLED  APPARATUS  463 

Many  futile  attempts  were  made,  in  the  years  that  followed,  to 
silence  the  existing  equipment.  Failures  were  caused  by  the  fact 
that  openings  had  to  be  left  on  both  sides  of  the  machines  to  insure 
adequate  cooling  of  the  engines  and  generators*.  They  would  function 
properly  with  everything  in  their  favor  but  would  fail  miserably  when 
placed  in  boat  holds,  railroad  cars,  small  barges,  etc. 

After  seven  years  of  such  difficulties  it  was  quite  evident  that  the 
standards  utilized  in  normal  automotive  practice  would  have  to  be 


FIG.  1.  Radiator  end,  Ford  V-8  generator.  Note 
rubber  mountings  along  bottom  of  frame.  Fans  op- 
erated by  independent  four-speed  Yi-hp.  motors.  Hole 
between  side  doors  serves  as  exhaust  for  main  genera- 
tor blower  fan  exhausting  approximately  150  cubic-feet 
per  minute. 

abandoned  and  an  entirely  new  design  created.  With  this  in  mind 
our  Engineering  Department  set  out  to  build,  on  paper,  the  perfect 
power  plant  that  would  meet  the  following  requirements : 

(1)  Be  silent  in  operation. 

(2)  Be  foolproof. 

(3)  Operate  semi-automatically. 

(4)  Be  light  in  weight. 

(5)  Be  compact. 

(6)  Maintain  constant  voltage. 

Very  little  calculation  was  necessary  to  prove  that  the  only  way 
to  make  it  run  silently  would  be  to  operate  it  in  a  vacuum,  an  im- 


464 


J.  E.  ROBBINS 


[J.  S.  M.  P.  E. 


"!;fi!lt 

^•.s  o>.s£  && 


Si*  fife  if  S 

8  ft  9?  v  F  v  p 

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ollllll^ 
.il|alsd 

M»P8' 

•   G    G    O    r"    S          w 
Q.S  W  .5    >_    .j 

Sl^vil^g 

JS  4>.fa'S  ^  d,-S 
wcfi  oS  F«  S'w 


^ 


Nov.,  1938]      GASOLINE  ENGINE  PROPELLED  APPARATUS  465 

practicable  solution,  of  course.  A  sound-proof  case  housing  the 
engine,  coupling,  mufflers,  and  generator  seemed  to  present  the  next 
best  medium.  When  entirely  enclosed,  the  heat-dissipation  problem 
had  to  be  contended  with.  There  could  be  no-  blast  of  air  across  the 
working  parts,  no  huge  body  of  water  to  circulate  through  the  engine, 
as  in  the  case  of  motorboat  applications.  All  exhaust  lines  would 
have  to  be  water-cooled.  The  magnitude  of  the  problem  will  be 
readily  understood  when  it  is  explained  that  approximately  1,200,000 
Btu.  per  hour  had  to  be  carried  off  the  motor  alone. 

The  generators,  in  order  to  comply  with  requirements  4  and  5, 
would  have  to  be  about  one-half  the  normal  output  size,  which  is 
satisfactory  as  concerns  portables  but  not  for  constant  power-house 
service.  Due  to  the  fact  that  the  average  scene  seldom  exceeds  fifteen 
minutes'  duration,  a  100  per  cent  overload  is  not  unreasonable.  How- 
ever, these  excessive  loads  do  create  heat  and  unless  the  heat  is 
carried  away  immediately  it  will  transfer  from  surface  to  internal 
with  an  attendant  efficiency  loss. 

After  carefully  considering  each  problem,  the  final  design  was  ap- 
proved and  the  work  started.  For  obvious  reasons,  various  sizes  were 
built,  and  will  be  referred  to  here  as  350  (Fig.  1),  475  (Figs.  2  and  3), 
and  1200  (Fig.  4)  ampere  machines.  These  terms  are  strictly  "motion 
picture"  and  are  used  in  lieu  of  kilowatts  when  determining  loads. 
Ford  V-8  engines  were  used  in  the  350;  Lincoln  Zephyr  in  the  475 
and  Hispano  Suiza  in  the  1200,  with  standard  commercial  generators 
of  35-,  50-,  and  85-kilowatt  capacities. 

The  engines  selected  for  the  large  machines  were  300-hp.  Hispano 
Suiza,  wartime  aviation  type,  picked  because  of  their  high  output 
per  pound  of  weight  and  their  ability  to  withstand  the  punishment 
of  long  idling  periods  at  1800  rpm.  as  well  as  loads  of  one-half  total 
capacity  thrown  on  and  off  in  rapid  succession.  Many  changes  were 
made  in  the  motors  before  installation,  in  order  partially  to  modernize 
them.  New  valves,  different  valve-springs,  battery  ignition  system, 
modern  fuel  pumps,  new  carburetors,  higher  capacity  oil  pump,  etc., 
were  used. 

The  engines  and  the  generators,  directly  connected  through 
especially  designed  pin  and  rubber  flexible  couplings,  are  mounted 
rigidly  to  a  sub-frame  which  is  in  turn  mounted  on  the  main  frame 
through  commercial  vibration  dampeners  (rubber  in  shear). 

(Fig.  5)  To  the  main  frame,  also  mounted  on  the  same  type  damp- 
ener,  are  bolted  the  two  vertical  ends  of  the  sound-proof  case.  Four 


466 


J.  E.  ROBBINS 


[J.  S.  M.  P.  E. 


FIG.  4.     Radiator  end,  Hispano  Suiza. 


FIG.  5.  Operating  end,  Hispano  Suiza,  showing 
gasoline  tanks,  instrument  panel,  bus  bars.  Entire 
unit  lifts  off  trailer. 


Nov.,  1938]      GASOLINE  ENGINE  PROPELLED  APPARATUS  467 

water  and  two  exhaust  lines  come  through  one  end,  and  on  the  op- 
posite end  are  located  the  bus  bars  and  the  instrument  panel,  con- 
sisting of  throttle,  spark  control,  circuit-breaker,  choke,  ammeter, 
voltmeter,  rheostat  control,  governor  control?  oil  gauge,  vacuum 
gauge  and  the  switches  for  gas  pump,  oil  pump,  fans,  and  ignition. 

The  top  cover,  tunnel  shaped,  fits  over  these  end  pieces,  resting  on 
full-length  strips  of  y2-mch  felt  and  bolts  through  the  same  dampeners 
to  the  main  frame.  The  ends  and  top  cover  are  fabricated  of  angle- 
iron  framework.  The  outer  cover  is  22-gauge  auto  body  steel.  Next 
to  this  is  placed  a  P/Vinch  thickness  of  corkoustic,  a  sheet  composi- 
tion of  cork  and  felt,  a  1-inch  layer  of  hair  felt,  another  iVa-inch  of 
corkoustic  and  an  inner  lining  of  asbestos  cloth.  All  this  is  held  in 
place  by  strips  of  spring  steel. 

The  measured  insulation  of  the  1200-ampere  unit,  using  the  gen- 
erator as  a  source  of  sound  is  22  db.  The  effective  noise  reduction  is 
actually  more  than  that  due  to  the  fact  that  valve  noises  are  almost 
completely  eliminated,  but  the  high  frequencies  produced  by  the 
valve  mechanism,  while  very  objectionable  during  recording,  con- 

;  tribute  a  relatively  small  amount  of  sound  power  as  measured  by  a 
noise  meter.  The  actual  noise  level  of  the  machine  at  approximately 
three-quarter  load,  measured  thirty  feet  away,  was  +60  measured 
with  a  General  Radio  noise-level  meter  using  a  70-db.  weighting 
characteristic. 

The  350-ampere  unit,  again  using  the  generator  as  the  source  of 
sound,  is  24  db.  The  noise  level  measured  at  a  distance  of  five  feet 

I  is  +65  measured  with  a  General  Radio  noise-level  meter,  using  a 

|  70-db.  weighting  characteristic. 

The  exhaust  system  is  comprised  of  five  units  (Fig.  6) :  the  engine 
manifolds,  elbows,  water-cooled  mufflers,  outside  leads,  and  the  outer 
air-cooled  mufflers.  The  manifolds,  mufflers,  elbows,  and  leads  are 
all  especially  designed  and  are  water-cooled.  They  are  made  of  16- 
gauge  galvanized  iron  with  1  inch  of  water  around  all  units.  The 
inner  mufflers  are  merely  long  tanks  with  perforated  baffles  spaced  2 

i  inches  apart.  The  outer  air-cooled  mufflers  are  used  only  when  operat- 
ing in  very  close  quarters.  The  efficiency  of  this  set-up  can  best 

!  be  explained  by  the  fact  that  normal  full-load  temperatures,  at  the 
port,  1300°F,  are  reduced  to  approximately  120°F  at  the  tail  pipes. 
This  reduction,  with  the  attendant  contraction  of  gas  pressures,  mini- 
mizes the  possibility  of  drumming  and  whistling  noises. 
The  radiator  sizes,  number  and  capacities  of  fans  and  fan  motors, 


468 


J.  E.  ROBBINS 


[J.  S.  M.  P.  E 


inlet  and  outlet  flows,  and  other  cooling  factors  (Figs.  1,  4,  and  7] 
were  determined  by  using  the  standard  formulas  and  ratios  of  trans 
ference  of  metal  to  water  to  metal  to  air  plus  15  per  cent.  The  addec 
15  per  cent  was  figured  to  compensate  for  the  normal  loss  of  radiatior 
by  air  across  the  engine  and  to  allow  for  a  longer  period  of  high  loac 
time  with  the  fans  on  low  speed.  To  date,  no  absolutely  silent  aii 
delivery  fans  are  available,  to  our  knowledge.  The  fans  used  are  2^ 
inches  in  diameter  with  eight  blades,  and  are  independently  driven  b> 
Y2-hp.  four-speed,  250-,  500-,  800-,  and  1100-rpm.,  d-c.,  motors  con 
trolled  by  switches  on  the  instrument  panel.  At  top  speed  each  far 


FIG.  6.  Hispano  Suiza  generator  plant  with  engine 
and  generator  door  openings.  Note  water-cooled  ex- 
haust manifold  (through  left  opening)  with  flexible 
water-cooled  connection  between  manifold  and  elbow 
running  to  water-cooled  mufflers  above. 

actually  delivers  4000  cubic-feet  per  minute.  To  reduce  static  pres 
sures,  the  air  is  pulled  from  behind  through  the  radiator  and  thei 
through  the  blades.  The  fan  motors  are  kept  cool  in  this  manner  anc 
the  possibility  of  chopping  noises  is  also  diminished.  With  this  set 
up  it  is  possible  to  run  the  unit  under  full  load  for  18  minutes  allowing 
the  water  temperature  to  change  from  140°  to  190°F  on  the  low  silen 
fan  speed.  At  the  end  of  the  shot,  the  switches  are  turned  to  higl 
speed  and  with  no  load  the  water  temperature  can  be  dropped  bacl 
to  140°  in  4  minutes. 

Under  full  load,  the  temperature  inside  the  motor  housing  seldon 
exceeds  110°F.  To  maintain  this  temperature,  air  is  drawn  througl 
a  sound-trap  in  the  floor  of  the  set,  up  across  the  generator  armature 


Nov.,  1938]      GASOLINE  ENGINE  PROPELLED  APPARATUS 


469 


FIG.  7.  Radiator  end  Ford  V-8  water 
pump;  water-cooled  mufflers  inside  box, 
air-cooled  mufflers  along  both  sides  of  radi- 
ator. Fans  driven  by  F-belts  off  extended 
motor  shaft. 


FIG.  8.  Pump  end,  Ford  V-8  water  pump.  Door  re- 
moved to  show  rubber  engine  mountings,  crankcase  en- 
largement for  greater  oil  capacity,  and  space  for  circulat- 
ing coils  for  water  from  outside  pump.  Brackets  on  cylin- 
der heads  support  water-cooled  mufflers.  Asbestos  inner 
lining  and  spring  steel  strips  for  holding  insulation  in 
place.  Automatic  engine  vacuum-operated  pump-primer 
shown  just  behind  coupling. 


470  J.  E.  ROBBINS  [J.  S.  M.  P.  E 

and  into  the  carburetor.  On  the  first  machines  an  additional  scaven- 
ger system  was  needed  to  offset  the  difference  in  engine  air  consump- 
tion at  idling  speeds.  The  latest  unit,  the  475-ampere  Lincoln  Zephyr 
is  built  with  the  motor  in  a  separate  compartment  over  the  generatoi 
(Figs.  2  and  3).  The  air,  in  this  instance,  is  drawn  up  through  the 
lower  compartment  into  the  carburetor.  In  this  manner,  no  engine 
heat  ever  reaches  the  generator  and  the  entire  unit  runs  cooler  withoul 
the  aid  of  extra  blowers. 

In  many  recent  boat  hold  installations,  this  particular  design  has 
proved  especially  advantageous.  In  Souls  at  Sea,  a  recent  Paramounl 
production,  two  sets  were  placed  on  the  second  deck,  approximately 
12  feet  below  the  main  deck.  Flumes  connected  to  the  front  of  the 
radiator  carried  all  heat  and  gases  to  the  rear  portholes  and  outside 
No  masks  were  required  by  the  operators  and  no  sound  was  detected 
by  the  microphones. 

The  large  machines  are  12  feet  long,  60  inches  high,  56  inches  wide, 
and  weigh  10,000  pounds.  They  are  all  electrically  governed.  The 
governors  used  can  not  be  obtained  commercially.  They  are  espe- 
cially designed  such  that  it  is  impossible  to  exceed  a  predetermined  volt- 
age setting.  Also,  they  are  so  constructed  that  their  throttle  opening 
action  is  instantaneous,  which  obviously  prevents  the  possibility  ol 
decreased  voltage  which  would  materially  affect  the  value  of  the 
light.  A  10-volt  variation  in  either  direction  would  be  immediate!}; 
detected  by  the  camera.  This  regulation  may  not  appear  difficult, 
However,  50  rpm.  on  the  motor  will  account  for  a  differential  of  ap- 
proximately 8  volts.  The  reaction  of  the  motor  when  instantly  re- 
lieved of  two-thirds  of  its  load  is  similar  to  what  would  happen  if  the 
drive  shaft  of  an  automobile  should  snap  while  being  driven  up  a 
slight  grade  with  a  full  throttle  at  60  miles  per  hour.  The  opposite 
action  takes  place  when  loads  are  put  back  in  like  proportions. 

As  previously  explained,  six  generators  of  the  same  design  have 
been  constructed  in  various  sizes.  To  date,  the  only  unit  other  then 
the  previously  described  generators,  is  a  high-pressure  water-pump 
(Fig.  8).  This  unit  employs  a  Ford  V-8  engine  and  a  two-stage  4  X 
4-inch  pump.  The  motor  is  entirely  enclosed,  as  in  the  case  of  the 
generators,  but  the  pump  is  outside. 

For  creating  eddies,  waves,  and  water  in  motion,  we  have  designed 
a  portable  propeller  machine  that  will  be  gas-engine  driven  as  described 
above.  It  will  be  very  silent.  No  radiator  will  be  used,  the  water 
being  circulated  from  a  pool  so  that  no  fans  will  be  required. 


Nov.,  1938]      GASOLINE  ENGINE  PROPELLED  APPARATUS  471 

No  absolutely  silent  air  mover  is  available  at  present.  All  types 
were  investigated  at  the  time  of  construction  and  many  peculiar 
designs  to  accommodate  squirrel-cage  and  other  types  considered  be- 
fore going  to  the  accepted  multi-blade  fan. 

The  1200-ampere  machines  outside  have  been  used  successfully 
200  feet  from  the  cameras;  the  Lincoln  Zephyr,  150  feet;  and  the 
Fords,  100  feet.  Twelve  feet  was  mentioned  previously;  however, 
that  was  in  connection  with  a  boat  where  the  deck  afforded  additional 
insulation.  Such  distances  may  seem  excessive,  but  for  the  reader's 
satisfaction,  he  may  set  the  hand  throttle  of  his  automobile  at  ap- 
proximately 60  miles  per  hour  speed,  in  neutral  gear,  start  walking 
out  in  front  of  the  car,  and  measure  the  distance  when  he  can  no 
longer  hear  the  engine. 


A  TECHNIC  FOR  TESTING  PHOTOGRAPHIC  LENSES 
W.  C.  MILLER** 


Summary. — Different  makes  of  lenses  have  different  properties  and  characteristics 
that  may  render  a  lens  good  for  one  purpose  and  totally  undesirable  for  another.  Lenses 
of  a  given  make  and  series  often  vary  in  quality  among  themselves.  To  obtain  the 
best  lens  for  a  specific  purpose  it  is  necessary  to  subject  the  various  makes  to  tests  that 
will  reveal  their  characteristics.  Once  the  type  of  lens  for  a  specific  purpose  has 
been  chosen,  it  is  of  great  importance  to  be  able  to  select  the  best  of  that  type  from  a 
group  submitted  by  the  manufacturer. 

Equipment  and  technic  used  in  tests  that  make  such  discrimination  possible  are 
described.  A  few  general  hints  and  precautions  are  given  that  will  aid  in  determining 
the  characteristics  most  desirable  for  various  purposes. 

Due  to  the  vast  number  of  lenses  available  at  the  present  time,  the 
prospective  buyer  is  faced  not  so  much  with  the  question  of  where  to 
get  lenses  as  which  lenses  to  choose  from  the  multitude  presented  to 
him.  With  so  many,  each  with  its  various  features,  it  becomes  a  seri- 
ous task  to  select  a  certain  make  and  be  sure  that  it,  more  than  any 
other,  possesses  the  qualities  required.  It  is  impossible  to  detect  any 
but  the  grossest  errors  by  merely  holding  the  lens  in  the  hand  and 
looking  through  it.  And  since  lens  makers,  in  common  with  most 
other  manufacturers,  describe  their  products  to  the  best  advantage, 
one  is  at  a  loss  to  know  how  to  decide  which  lenses  possess  the  char- 
acteristics most  desired. 

Lens  manufacturers  have  always  been  loath  to  publish  critical  data 
concerning  their  products.  Until  they  consent  to  do  so  the  purchaser 
must  find  means  for  himself  of  determining  which  of  the  many  lenses 
available  possess  the  qualities  that  best  fill  his  needs.  It  is  not  an  easy 
task,  especially  since  the  science  of  optics  is  avoided  by  most  persons 
as  being  in  the  realm  of  the  supernatural  and  comprehensible  to  only 
a  few  chosen  master-minds.  This  is  totally  unfounded,  as  the  funda- 
mentals required  for  a  working  knowledge  of  lenses  and  lens  testing 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C. ;  received 
Aug.  12,  1938. 

**  Paramount  Pictures,  Inc.,  Hollywood,  Calif. 

472 


TESTING  PHOTOGRAPHIC  LENSES  473 

are  no  more  difficult  to  acquire  than  those  required  for  work  in  sound, 
electricity,  or  radio.  They  have  merely  been  shrouded  in  a  cloak  of 
mystery  that  has  frightened  away  many  an  interested  student.  It  is 
time  that  anyone  having  anything  to  do  with  lenses  in  any  capacity 
learns  how  to  tell  the  good  from  the  bad.  This  paper  gives  a  few  ele- 
mentary tests  that  anyone  can  comprehend  and  carry  out,  and  a  few 
simple  principles  that  will  be  of  service  to  anyone  faced  with  the  neces- 
sity of  selecting  new  lenses. 

It  is  possible  to  go  to  great  extremes  to  detect  errors  in  lenses.  It 
is  therefore  necessary  first  to  determine  just  what  extremes  are  justi- 
fied. 'This  depends  primarily  upon  how  the  lens  is  to  be  used  and 
what  is  to  be  expected  of  it.  Once  that  has  been  determined  it  is  pos- 
sible to  set  up  equipment  and  a  technic  that  will  reveal  the  characteris- 
tics of  interest. 

The  tests  and  specifications  outlined  here  are  intended  primarily  for 
use  with  standard  35-mm.  camera  lenses.  The  principles  are,  how- 
ever, applicable  to  lenses  of  other  types  with  slight  modifications. 
The  tests  will  be  found  to  be  sufficiently  searching  for  ordinary  pro- 
duction lenses.  Added  refinements  and  still  other  tests  can  be  made 
when  occasion  demands. 

Since  no  lens  designer  is  as  yet  able  to  design  a  lens  free  from  all 
aberrations,  every  lens  is  necessarily  a  compromise  between  numerous 
errors.  Various  designers  feel  differently  about  which  aberrations 
should  be  sacrificed  for  others,  so  that  almost  every  make  of  lens  per- 
forms in  its  own  way.  It  therefore  becomes  our  task,  once  we  have 
decided  what  characteristics  are  most  desirable,  to  choose  the  lenses 
whose  corrections  lend  themselves  most  advantageously  to  our  pur- 
poses. 

More  than  that,  once  the  type  or  make  has  been  selected,  it  is 
necessary  to  test  the  individual  lenses  before  they  are  purchased,  to 
eliminate  any  that  fall  below  certain  standards.  Lenses  of  a  given 
make  vary  among  themselves  as  do  other  commercially  manufactured 
products.  True,  certain  tolerances  are  placed  upon  them  by  the 
makers,  but  it  is  wise  to  check  each  lens  to  make  sure  that  the  manu- 
facturers' tolerances  are  acceptable. 

It  would  be  unwise  to  stipulate  here  certain  definite  qualities  which 
should  be  required  of  any  lens ;  these  can  be  determined  best  by  the 
individual  user  from  experience,  personal  preference,  and  the  demands 
of  the  job  at  hand.  A  few  of  the  more  general  characteristics  common 
to  lenses  will  be  mentipned  and  methods  given  for  detecting  them. 


474  W.  C.  MILLER  [j.  s.  M.  P.  E. 

Some  of  the  most  insidious  evils  that  need  not,  and  should  not,  be 
tolerated  will  be  so  specified.  But  the  degree  to  which  the  other  cor- 
rections must  be  carried  is,  of  necessity,  left  to  the  user's  own  good 
judgment. 

The  fundamental  principle  to  be  kept  in  mind  when  using  modern 
lenses  and  panchromatic  film  stock  is  that  all  colors  to  which  the  film 
is  sensitive  must  come,  within  small  limits,  to  a  common  focus.  Mod- 
ern lenses  can  be  held  within  such  small  tolerances  in  this  respect 
that  there  should  be  no  detectable  discrepancy  between  the  foci  of 
the  red,  the  green,  and  the  blue  light  when  the  lens  is  tested  photo- 
graphically on  a  suitable  target. 

A  satisfactory  target  for  this  test  can  be  made  by  ruling  on  a  white 
card  of  adequate  size  a  series  of  parallel,  horizontal  lines  separated  by 
about  an  inch  and  numbered  each  way  from  the  center-line.  This 
target  is  set  up  a  short  distance  in  front  of  the  camera  at  an  inclina- 
tion of  about  45  degrees  and  evenly  illuminated.  With  the  lens  fo- 
cused on  the  central  line,  a  series  of  exposures  is  made  of  this  target, 
using  a  standard  set  of  tricolor  filters.  No  change  should  be  made  in 
the  focal  setting  of  the  lens  between  exposures.  Any  change  of  the 
relative  sharpness  of  the  lines  of  the  target  seen  on  the  resulting  nega- 
tives is  an  indication  of  the  extent  by  which  the  various  colors  fail  to 
come  to  a  common  focus.  There  should  be  no  detectable  difference 
in  any  of  the  three  images  taken  with  a  good  lens.  If  some  color  fails 
in  actual  practice  to  come  to  a  common  focus  when  the  lens  is  used 
with  panchromatic  stock,  the  resulting  image  will  not  be  sharp  and 
clear. 

For  lenses  that  are  to  be  used  only  with  stock  sensitive  to  the  blue 
or  blue-green  this  restriction  is  not  so  great,  for  in  that  case  should  the 
red  light  fail  to  come  to  the  same  focus  as  the  blue  and  green,  the  pho- 
tographic image  would  not  suffer  as  the  film  is  insensitive  to  the  red. 
It  is  therefore  unnecessary  to  pay  the  extra  price  for  panchromatic 
lenses  unless  they  are  to  be  used  with  panchromatic  stock. 

When  a  lens  is  focused  wide  open  the  image  may  be  as  sharp  and 
clear  as  desired;  but  when  the  iris  is  stopped  down  preparatory  to 
making  the  exposure,  the  images  formed  by  some  lenses  will  be  found 
to  go  out  of  focus  without  any  movement  of  the  lens  itself.  This  is 
due  to  zonal  spherical  aberration  in  the  lens,  and  is  often  called  "dia- 
phragm focus."  To  recapture  the  sharpest  possible  image  it  is  neces- 
sary to  refocus  the  lens,  using  the  aperture  at  which  the  exposure  is  to 
be  made. 


Nov.,  1938]  TESTING  PHOTOGRAPHIC  LENSES  475 

In  selecting  new  lenses  a  series  of  exposures  should  be  made  of  the 
test-chart  used  in  the  color  test,  first  with  the  lens  wide  open  at  its 
best  visual  focus,  and  then  at  selected  smaller  apertures  with  no 
change  in  the  focal  setting  of  the  lens.  Upon  examination  of  the 
negatives,  the  change  in  the  apparent  focus  of  any  of  the  exposures 
should  be  negligibly  small.  Most  of  the  modern  fast  lenses  show  this 
"diaphragm  focus"  to  a  greater  or  lesser  degree.  The  user  must  de- 
termine just  how  much  he  can  tolerate. 

Any  lens  already  in  use  that  displays  diaphragm  focus  should  al- 
ways be  focused  at  the  aperture  at  which  the  exposure  is  to  be  made. 
This  is  often  difficult  to  do  when  a  small  stop  is  required,  but  it  is  the 
only  way  to  be  sure  that  diaphragm  focus  will  not  influence  the  sharp- 
ness of  the  picture. 

Some  types  of  lenses  show  a  tendency  toward  internal  reflections 
that  give  rise  to  "flares"  or  "ghosts."  Such  a  tendency  can  be  de- 
tected easily  by  placing  a  ground  glass  in  the  focal  plane  of  the  lens 
and  moving  a  bright  light  some  distance  in  front  of  the  lens  all  about 
the  field  of  view  while  watching  the  ground  glass. 

Any  tendency  of  a  lens  to  produce  flares  in  actual  use  will  be  greatly 
enhanced  and  the  relative  merits  of  various  makes  can  be  judged. 
Generally  the  fewer  air-glass  surfaces  there  are,  the  less  is  the  tendency 
to  cause  flares.  Consequently  slow  lenses  of  the  three-element  type 
should  be  favored  when  a  scene  requiring  great  contrasts  is  to  be 
photographed . 

All  lenses  possess  a  characteristic  that  finds  such  frequent  use  that, 
although  it  is  in  nowise  a  test,  it  deserves  mention  here.  When  a  lens 
is  focused  upon  a  point  A  a  given  distance  away,  other  points  lying 
short  distances  in  front  of  and  behind  A  will  also  be  in  fair  focus.  It 
is  found  that  the  focus  carries  with  reasonable  sharpness  a  greater  dis- 
tance behind  A  than  in  front  of  it.  If  two  other  points,  B  and  C,  are 
chosen,  one  before  and  one  behind  A,  which  are  equally  sharp,  they 
will  occupy  definitely  specified  positions  with  respect  to  the  lens  and 
the  point  A .  It  is  therefore  possible  to  determine  just  where  to  focus 
between  two  objects  to  make  them  both  appear  equally  sharp  in  the 
picture,  provided  one  knows  the  distances  of  the  two  objects  from  the 
lens.  Substituting  the  distances  B  and  C  in  the  formula 

2B  C 

~FTc 
the  result  is  the  distance  from  the  lens  to  the  intermediate  point  A . 


476  W.  C.  MILLER  [j.  s.  M.  P.  E. 

As  an  example  assume  that  one  person  is  standing  10  feet  from  the 
camera  and  another  30  feet.  A  is  then  15  feet,  and  if  we  focus  upon  a 
point  at  that  distance,  both  objects  will  register  with  equal  sharpness. 
This  method  gives  results  that  are  amply  accurate  for  ordinary  use. 
Whether  or  not  the  two  objects  will  be  perfectly  sharp  depends,  of 
course,  upon  such  factors  as  the  focal  length  of  the  lens  and  the  aper- 
ture used. 

The  optical  definition  of  a  lens,  or  its  ability  to  render  clearly  small 
detail  within  its  usable  field,  is  a  quality  that  can  vary  greatly  de- 
pending upon  the  purpose  for  which  the  lens  is  intended.  For  por- 
traiture sharp  definition  is  rarely  desired,  particularly  around  the 
field.  For  ordinary  work,  where  that  illusive  property  known  as 
"quality"  is  desired,  more  definition  is  needed,  but  more  uniformly 
distributed  over  the  field.  For  miniatures,  process  work,  or  for  pic- 
tures that  are  to  be  greatly  enlarged,  every  bit  of  definition  that  can 
be  had  is  usually  required  over  the  entire  field.  Likewise  for  optical 
printing  and  copying.  Therefore,  depending  in  what  field  of  work  the 
lens  is  destined  to  be  used,  various  amounts  and  distributions  of  defi- 
nition must  be  selected. 

To  test  a  lens  for  definition  all  that  is  required  is  a  chart  upon  which 
are  placed  cards  bearing  lines  of  letters  or  numbers  of  gradually  de- 
creasing size,  much  like  the  Snellen  charts  used  in  testing  the  eyes. 
With  these  cards  distributed  advantageously  over  the  chart,  exposures 
can  be  made  with  the  vaiious  lenses  at  their  positions  of  sharpest 
central  focus.  Care  must  be  taken  to  see  that  the  test-chart  covers 
the  entire  usable  field  of  the  lens  in  order  that  the  character  of  the 
image  in  all  parts  of  the  field  can  be  studied.  Also  the  lens  must 
shoot  squarely  at  the  center  of  the  target,  for  if  it  is  cocked  one  way  or 
another  misleading  results  will  be  obtained. 

Examination  of  the  resulting  negatives  under  sufficient  magnifica- 
tion will  reveal  that  different  types  of  lenses  have  different  degrees  of 
definition  in  different  parts  of  the  field.  But  it  will  be  found  that  for 
equal  definition  at  the  center  some  lenses  will  have  much  better  defi- 
nition at  the  edges  than  others.  These  are  said  to  have  better 
"covering  power." 

To  determine  how  much  definition  is  required  and  how  it  should  be 
distributed  over  the  field  requires  experience  and  skill.  For  the  un- 
initiated the  best  way  to.  determine  this  quickly  is  to  test  lenses  that 
are  giving  satisfactory  results  in  production  and  to  select  any  new 
lenses  that  have  about  the  same  correction.  Experiments  with  new 


Nov.,  1938]  TESTING  PHOTOGRAPHIC  LENSES  477 

types  of  lenses  may  reveal  that  even  better  results  can  be  attained  with 
some  of  them. 

A  defect  often  found  in  lenses  is  known  as  "chemical  focus."  Ex- 
pressed simply,  this  means  that  the  focal  setting  determined  visually 
does  not  agree  with  the  one  found  photographically.  In  reality  it  is 
due  to  peculiarities  of  the  color  correction,  but  it  often  shows  up  as  if 
it  were  a  separate  characteristic.  It  can  be  checked  by  focusing  a  lens 
visually  for  best  central  definition  and  then  making  a  series  of  expo- 
sures at  the  same  setting  and  at  others  departing  by  small  amounts 
on  either  side  of  the  visual  one.  It  will  be  found  that  steps  of  0.001 
inch  will  be  satisfactory.  If  it  is  found  that  the  negative  having  the 
sharpest  central  definition  has  a  setting  other  than  the  visual  one  the 
lens  has  the  chemical  focus  of  the  amount  of  the  discrepancy.  In  bad 
cases  with  short-focus  lenses  this  may  amount  to  many  thousandths 
of  an  inch.  A  lens  showing  more  than  two  or  three  thousandths 
should  be  rejected. 

A  lens  will  be  encountered  occasionally  that  vignettes  due  to  im- 
proper construction.  Some  lenses  do  so  when  wide  open,  the  edges  of 
the  lens  mounts  cutting  in  at  the  corners  of  the  picture.  These  can 
generally  be  improved  by  stopping  down  the  iris.  Sometimes  vignet- 
ting increases  when  a  lens  is  stopped  down,  and  is  due  to  the  improper 
location  of  the  iris  with  respect  to  oblique  rays  of  light  passing  through 
the  lens. 

These  two  conditions  can  be  checked  by  making  exposures  with  the 
iris  wide  open  and  again  stopped  down  to  about //9.O.  If  the  corners 
of  either  negative  are  cut  in,  the  lens  should  be  rejected.  Obviously, 
care  must  be  taken  to  insure  that  no  lens  shade  or  matt  box  in  front  of 
the  lens  is  the  offending  member. 

A  peculiar  effect  is  obtained  with  some  lenses  in  motion  picture  work 
when  a  scene  is  "panned."  An  object  entering  at  one  side  of  the  field 
grows  or  shrinks  in  size  as  it  moves  across  the  picture,  again  returning 
to  its  former  size  at  the  other  edge.  The  fault  shows  itself  also  when 
the  lens  is  used  to  photograph  architectural  subjects :  lines  near  the 
edge  of  the  field  are  bent  either  in  or  out.  It  is  very  disconcerting  if 
this  tendency  is  pronounced.  To  obtain  good  pictures,  lenses  should 
be  used  that  do  not  display  such  a  characteristic.  A  quick  way  to  de- 
termine whether  they  will  or  not  is  to  project,  by  means  of  the  lens 
under  test,  an  accurate  aperture  plate  whose  opening  is  equal  to  the 
film  aperture  for  which  the  lens  was  designed.  If  the  projected  image 
of  the  aperture  as  seen  upon  a  screen  is  defined  by  straight  boun- 


478  W.  C.  MILLER  [j.  s.  M.  P.  E. 

daries,  the  lens  is  free  from  this  trouble.  However,  if  the  edges  of  the 
image  are  curved,  bending  either  in  or  out  at  the  middle,  this  disturb- 
ing effect  will  be  obtained  with  the  lens  in  use. 

To  determine  how  much  distortion  is  present,  measure  the  height 
of  the  projected  aperture  image  at  one  side  and  again  at  the  center. 
The  difference  of  the  measurements  divided  by  the  smaller  should  not 
exceed  0.005.  Lenses  in  which  this  quantity  is  as  small  as  0.001  are 
obtainable. 

The  effect  obtained  by  panning  with  lenses  having  distortion  should 
never  be  confused  with  the  effect  of  panning  about  an  axis  not  coinci- 
dent with  the  optical  center  of  the  lens.  The  latter  condition  gives 
rise  to  changes  of  perspective  due  to  swinging  the  lens  in  an  arc.  This 
also  causes  certain  undesirable  effects  on  the  screen.  To  obtain  per- 
fect optical  results  when  panning,  the  lens  must  be  free  from  distortion 
and  must  be  swung  about  a  vertical  axis  running  through  the  optical 
center  of  the  lens.  This  insures  that  there  will  be  no  disturbing 
changes  in  the  sizes  of  objects  passing  across  the  field  and  changes  in 
perspective  and  point  of  view. 

Another  test  that  should  be  made  can  best  be  done  in  a  machinist's 
lathe.  The  lens  should  be  mounted  and  accurately  centered  on  the 
threads  and  shoulder  of  the  lens  mount.  If  a  small  light  is  then  placed 
in  such  a  position  that  its  reflection  can  be  seen  in  the  various  lens 
surfaces,  it  will  often  be  found  that  these  reflected  images  will  move 
when  the  lens  is  rotated  slowly  in  the  lathe.  When  such  is  the  case, 
it  indicates  that  the  individual  glass  elements  are  not  truly  centered  in 
the  cells.  Often  the  effect  will  be  visible  in  a  number  of  the  elements 
at  once. 

Although  a  small  eccentricity  of  the  elements  is  rarely  detectable  in 
the  image,  it  does  have  an  effect.  If  several  of  the  elements  are  eccentric 
the  total  effect  will  be  very  noticeable  and  undesirable.  It  takes  ex- 
perience to  determine  how  much  is  tolerable. 

The  user  or  prospective  purchaser  of  the  lens  should  never  attempt 
to  center  the  elements  in  their  cells ;  it  is  a  job  for  the  manufacturer. 
In  fact,  lenses  should  never  be  taken  apart  to  the  extent  of  removing 
the  glass  elements  from  their  cells,  for  they  can  rarely  be  put  back  into 
exactly  their  original  positions.  An  excellent  lens  can  be  spoiled  by 
not  centering  all  the  elements  correctly  on  the  optical  axis. 

After  years  of  work  with  lenses  one  becomes  aware  of  a  quality  of 
optical  images  that  can  be  described  only  as  "contrast"  or  "bril- 
liance." It  is  completely  separate  from  the  contrast  obtained  due  to 


Nov.,  1938]  TESTING  PHOTOGRAPHIC  LENSES  479 

to  the  processing  of  the  film  or  print,  and  is  inherent  in  the  image  of 
the  lens  whether  photographed  or  viewed  visually.  It  makes  a  great 
difference  in  the  results  attainable  with  a  lens  whether  or  not  the  lens 
possesses  this  desirable  quality.  In  general,  it  is  due  to  the  type  of 
lens :  the  fewer  the  number  of  air-glass  surfaces  the  more  brilliant  the 
image.  But  it  is  due  also  to  other  things  such  as  the  polish  of  the  lens 
surfaces  and  their  cleanliness,  both  of  which  affect  the  amount  of 
diffused  and  scattered  light  in  the  image  plane  and  thereby  the  bril- 
liance of  the  image.  There  is  often  detectable  among  lenses  of  a  given 
make  and  focal  length  a  difference  in  the  contrast  of  the  image. 
In  selecting  lenses  this  should  be  watched  for  and  any  lens,  however 
perfect  otherwise,  that  gives  a  flat,  dull  picture,  should  be  discarded. 

Frequent  tests  of  lenses  in  constant  use  will  be  found  very  advan- 
tageous. Accidental  damage  of  a  minor  nature,  or  looseness  of  the 
lenses  in  the  mounts  due  to  vibration  or  shock,  can  be  detected  and 
remedied  before  they  become  so  serious  as  to  impair  production.  De- 
terioration in  optical  performance  can  be  detected  and  traced  to  its 
source,  and  can  often  be  remedied  if  caught  in  time.  The  most  com- 
mon occurrence  of  this  sort  is  the  "feathering"  of  the  balsam  used  to 
cement  some  of  the  glass  elements  together.  The  lenses  can  be 
cleaned  thoroughly  when  they  are  tested  by  someone  skilled  in  this 
type  of  work.  More  lenses  are  damaged  by  careless  or  ignorant  clean- 
ing than  by  any  other  cause. 

Absorbent  cotton  is  cheap,  soft,  and  in  every  way  one  of  the  best 
cleaning  materials  available.  Breathing  gently  on  the  surface  will 
moisten  it  and  greatly  facilitate  the  removal  of  dust  and  spots. 
Cleaning  solutions  and  soaps  should  be  avoided  whenever  possible. 
Anything  that  will  not  yield  to  the  moisture  of  the  breath  can  be  re- 
moved by  barely  moistening  the  cotton  with  carbon  tetrachloride. 
Nothing  more  severe  than  this  should  ever  be  used.  Always  clean 
lenses  with  a  circular  motion,  blowing  strongly  against  the  surface 
with  the  last  few  strokes  to  remove  any  lint. 

Careful  application  of  the  principles  outlined  in  this  paper  for  the 
selection  of  lenses  will  be  found  to  improve  greatly  the  quality  of  the 
resulting  pictures.  The  results  attained  on  the  screen  can  be  no 
better  than  the  lens  that  made  them.  It  is  therefore  useless  to  lavish 
money  on  sets  and  costumes  that  will  never  show  clearly  on  the  screen 
due  to  poor  lenses  on  the  cameras.  Greater  improvement  will  be 
obtained  in  proportion  to  the  required  expenditure  by  using  the  best 
lenses  available  and  keeping  them  in  good  condition  by  constant  care. 


REPORT  OF  THE  PROJECTION  PRACTICE  COMMITTEE* 


Summary.— This  report  contains  the  reports  of  four  of  the  Sub- Committees  of  the 
Projection  Practice  Committee,  viz.,  on  the  Motion  Picture  Theater  Survey,  on  Screen 
Illumination,  on  Projection  Room  Plans,  and  on  the  Proposed  Revision  of  the  NFPA 
Regulations  for  Nitrocellulose  Motion  Picture  Film.  A  preliminary  report  is  ren- 
dered by  the  Sub-Committees  on  Theater  Survey  and  Screen  Brightness.  The  Pro- 
jection Room  Plans  and  Revision  of  the  Fire  Regulations  are  presented  in  full. 

During  the  past  year,  the  Committee  has  been  engaged  in  a  number 
of  important  projects,  the  principal  ones  being  the  following: 

(1)  Motion  picture  theater  survey. 

(2)  Study  of  screen  brightness  and  methods  of  measuring  it. 
(5)     Revision  of  the  Projection  Room  Plans. 

(4)  Revision   of   NFPA    Regulations   for   Handling   Nitrocellulose   Motion 
Picture  Film. 

(5)  Study  of  the  tolerances  and  clearances  permissible  in  motion  picture 
projection  equipment  and  means  of  measuring  and  checking  these  values. 

As  these  projects  involve  a  great  deal  of  work  and  require  con- 
siderable time  for  complete  study,  it  will  not  be  possible  to  report  on 
them  all  at  this  time.  The  present  report  deals  only  briefly  with 
item  1,  since,  following  the  publication  of  the  comprehensive  theater 
survey  last  spring,  more  time  is  required  for  analysis  of  the  data  and 
formulation  of  recommendations.  With  regard  to  item  2,  the  Com- 
mittee has  long  been  searching  for  suitable  means  of  measuring  screen 
brightness  in  theaters,  and  the  present  report  of  the  Sub-Committee 
indicates  considerable  progress  in  solving  the  problem. 

Items  3  and  4  are  dealt  with  in  great  detail  in  the  present  report. 
With  regard  to  projection  room  plans,  it  is  the  hope  of  the  Com- 
mittee that  all  those  who  contemplate  building  new  projection 
rooms  or  revamping  existing  projection  rooms,  will  give  serious 
thought  to  the  recommendations  contained  in  these  Plans.  The 
Fire  Regulations  are  subject  to  revision  pending  action  by  the  Com- 
mittee on  Hazardous  Chemicals  and  Explosives  of  the  NFPA,  to 
whom  the  proposed  revision  has  been  submitted.  This  matter  is 
more  fully  described  in  the  preamble  of  the  report,  on  p.  498. 

*  Presented  at  the  Fall,  1938,  Meeting  at  Detroit,  Mich. ;  received  September 
20,  1938. 
480 


PROJECTION  PRACTICE  COMMITTEE  481 

Work  on  project  5  has  just  about  begun,  so  that  no  more  can  be 
done  at  the  present  time  than  to  state  that  this  subject  is  receiving 
the  earnest  attention  of  one  of  the  Sub-Qommittees. 

The  Chairman  wishes  to  commend  the  various  members  of  the 
Committee  who  have  worked  so  hard  and  spent  so  much  time  on 
these  projects.  It  is  felt  that  the  reports  of  the  Committee  presented 
at  both  this  and  the  last  Convention  represent  contributions  of 
major  importance  to  the  motion  picture  industry. 

PROJECTION  PRACTICE  COMMITTEE 

H.  RUBIN,  Chairman 

THEATER  SURVEY 

Report  of  the  Sub-Committee  on  Theater  Structures,  comprising 
an  analysis  of  a  survey  of  theaters  of  the  industry  as  regards  their 
physical  dimensions  and  structural  proportions,  was  presented  at 
the  last  Convention  as  was  published  in  the  June,  1938,  issue  of  the 
JOURNAL.  This  report  has  aroused  considerable  interest  among 
motion  picture  theater  architects  both  here  and  abroad.  Although 
the  work  has  not  yet  progressed  to  the  point  where  the  data  of  the 
survey  can  be  used  for  determining  ideal  structural  conditions  for 
projecting  and  viewing  motion  pictures,  the  work  is  proceeding  and 
it  is  hoped  that  the  Sub-Committee  may  be  able  to  report  on  the 
subject  at  the  next  Convention.  The  subject  is  a  complex  one  and 
requires  very  careful  analysis. 

In  connection  with  the  rising  interest  throughout  the  industry 
in  good  projection  and  good  viewing  in  motion  picture  theaters,  the 
Projection  Practice  Committee  has  thought  it  advisable  to  state 
specifically  its  policy  with  regard  to  the  view  of  the  screen  provided 
for  each  patron  of  the  theater : 

The  Committee  regards  clear  and  unobstructed  viewing  of  the 
screen  as  an  essential  and  major  factor  in  audience  satisfaction.  It 
disapproves  any  form  of  auditorium  design  or  seating  arrangement 
that  will  prevent  any  patron  from  seeing  all  parts  of  the  screen  at 
all  times,  regardless  of  the  positions  of  other  patrons. 

There  are  several  degrees  of  obstruction  of  view  of  the  screen. 
Arranged  in  order  of  diminishing  desirability,  these  are : 

(1}  Clear  vision  regardless  of  positions  of  patrons  one  or  more  rows  ahead. 
(2)  Clear  vision  regardless  of  positions  of  patrons  two  or  more  rows  ahead. 
(5)  Partially  obstructed  vision  under  almost  any  conditions. 


482  PROJECTION  PRACTICE  COMMITTEE         [j.  s.  M.  P.  E. 

To  reduce  obstruction  of  view,  there  are  several  methods  available, 
including  the  following : 

(a)  Staggering  the  seats  of  successive  rows  (which  may  reduce  the  number 
of  seats  or  cause  "ragged"  aisles). 

(&)  Raising  the  level  of  each  row  of  seats  relative  to  the  row  before  it  (which 
may  lead  to  an  impracticable  amount  of  rise  in  some  theaters  from  front  to  back). 

(c)  Adopting  a  suitable  combination  of  fall  and  rise  of  successive  rows  of  seats 
from  front  to  back  (which  method  requires  further  study  in  practice  on  a  wider 
scale  under  various  conditions). 

One  or  more  of  these  methods  should  be  seriously  considered  by 
theater  architects.  In  no  case  does  the  Projection  Practice  Com- 
mittee approve  any  seating  arrangement  falling  appreciably  below 
Grade  1  above;  that  is,  the  Committee  disapproves  any  noticeable 
obstruction  of  the  screen  view  of  one  patron  by  any  other  normally 
seated  patrons  no  matter  where  located. 

SUB-COMMITTEE  ON  THEATER  SURVEY 

B.  SCHLANGER,  Chairman 

SCREEN  ILLUMINATION 

The  product  that  the  motion  picture  theater  offers  to  the  public 
is  the  picture  on  the  screen.  The  two  essential  factors  in  the  produc- 
tion of  a  good  screen  picture  are  the  film,  over  which  the  exhibitor 
has  no  control,  and  the  projection  light.  It  is  only  through  the  pro- 
vision and  maintenance  of  an  adequate  light-source  that  the  manage- 
ment can  exercise  control  over  its  product. 

During  the  past  few  years  theater  owners  and  managers  have  be- 
come light-conscious.  This  has  brought  about  the  necessity  for  a 
small,  compact,  portable,  and  inexpensive  light-meter  that  can  be 
as  easily  read  as  the  ordinary  voltmeter  or  ammeter.  With  these 
considerations  in  mind  the  Projection  Practice  Committee  set  out  to 
determine  the  best  type  of  meter  obtainable. 

There  are  three  places  at  which  the  light  might  be  measured : 

(1)  Directly  hi  front  of  the  projector. 

(2)  Incident  upon  the  picture  screen. 

(3)  Reflected  from  the  picture  screen. 

The  provision  of  a  single  instrument  capable  of  making  all  three 
kinds  of  measurements  was  considered,  and  was  rejected  for  the 
reason  that  such  a  meter,  like  all  previous  instruments,  would  be  too 
cumbersome,  complicated,  and  expensive  for  general  use.  On  the 
other  hand,  a  meter  capable  of  measuring  the  light  incident  upon  the 
picture  screen  fulfills  the  needs  of  95  per  cent  of  the  light-measuring 


Nov.,  1938] 


PROJECTION  PRACTICE  COMMITTEE 


483 


requirements.     At  the  same  time  such  a  meter  is  both  simple  and 
low  in  price  (Fig.  1). 

A  meter  of  this  type  has  been  developed,  with  which  is  provided  a 
visual  correction  filter  which  the  Committee  feels  is  essential  to  the 
accurate  evaluation  of  light-sources  in  terms  of  human  eye  response. 
Tests  with  this  meter  calibrated  in  tungsten  light  at  3000  °K  showed 
that  the  errors,  when  measuring  low-  and  high-intensity  arc  sources 
were  less  than  3  per  cent.* 

The  meter  reads  from  0  to  30  foot-candles.  It  was  felt  that  this 
range  was  ample  for  present  commercial  levels  of  screen  illumination 
inasmuch  as  many  theaters  do  not  average 
more  than  4  to  8  foot-candles  although  the 
SMPE  recommended  average  is  about  10  to 
20  foot-candles  with  the  shutter  running.** 

In  using  the  meter  for  measuring  screen 
illumination,  it  is  recommended  that  nine 
readings  be  taken  as  follows :  At  the  center 
of  the  screen,  at  the  four  corners,  and  at  the 
centers  of  top,  bottom,  and  both  sides. 
When  making  a  measurement  the  meter  is 
held  flat  against  the  screen,  the  cell  opening 
facing  the  projector,  with  the  projector 
shutter  running  and  no  film  in  the  gate. 

These  readings  not  only  measure  the 
incident  light  but  also  indicate  the  uni- 
formity of  distribution  of  the  light,  which 
is  ordinarily  expressed  as  the  ratio  between 
the  readings  at  a  side  and  at  the  center. 
A  ratio  of  80  per  cent  is  considered  very  good  and  is  obtainable 
by  manipulating  the  optical  system  of  the  projector  lamp  in  a 
manner  familiar  to  all  projectionists. 


FIG. 


1.     Screen  illumina- 
tion meter. 


SUB-COMMITTEE  ON  SCREEN  ILLUMINATION 

E.  R.  GEIB,  Chairman 


*  Of  the  meters  available  for  such  measurements,  the  one  tested  by  the  Sub- 
Committee  was  the  new  Weston  model  703. 
**  Actually  7  to  14  foot-lamberts. 


484  PROJECTION  PRACTICE  COMMITTEE         [j.  s.  M.  P.  E 

PROJECTION  ROOM  PLANS 

The  projection  room  plans  that  follow  represent  the  third  revisioi 
of  the  plans  originally  published  by  the  Committee  in  August,  1932 
The  second  revision  appeared  in  October,  1935. l  Such  revisions  ar< 
necessary  from  time  to  time  in  order  to  keep  pace  with  the  change; 
and  developments  in  the  art  and  practice  of  projecting  sound  motior 
pictures.  The  Committee  urgently  recommends  the  adoption  o: 
these  recommendations  by  all  architects  and  builders  in  designing 
and  remodeling  projection  rooms  so  that  greater  uniformity  of  con 
struction  and  greater  efficiency  in  projection  will  exist  in  the  future 

In  following  these  recommendations,  proper  authorities  should 
in  all  cases,  be  consulted  for  possible  deviation  therefrom.  An) 
fire-protection  requirements  specified  herein  are  in  accordance  witl 
the  Regulations  of  the  National  Board  of  Fire  Underwriters  and  th< 
National  Electric  Code,  which  should  be  consulted  for  details. 

Projection  facilities  shall  consist  of  (1)  the  projection  room  proper 
(2)  a  film  rewind  and  storage  room,  (3)  a  power  equipment  room 
and  (4)  a  lavatory  (Fig.  1). 

PROJECTION  ROOM  PROPER 

(1.1)  Construction. — The  projection  room  shall  be  fire-proof,  anc 
shall  be  supported  upon  or  hung  from  fire-proof  structural  steel  01 
masonry.     It  shall  have  a  minimum  height  of  8  feet  and  a  minimun 
depth  of  12  feet.     The  length  of  the  room  shall  be  governed  by  th< 
quantity  and  the  kind  of  equipment  to  be  installed,  but  shall  in  n< 
case  be  less  than  16  feet.     Consideration  should  be  given  to  probabli 
future  needs. 

The  Committee  recommends  that  the  projection  room  prope: 
be  so  located  with  respect  to  the  screen  that  the  vertical  projectioi 
angle  shall  not  exceed  18  degrees.  Optical  axes  of  the  projector 
shall  be  5  feet  apart.  When  two  projectors  are  used,  the  optica 
axes  shall  be  equidistant  from  the  center-line  of  the  auditorium 
when  three  projectors  are  used,  the  optical  axis  of  the  center  projecto: 
shall  be  on  the  center-line  of  the  auditorium. 

(1.2)  Floor. — The  floor  of  the  projection  room  shall  be  sufficient!] 
strong  and  solid  for  the  load  it  is  to  bear,  and  shall  be  constructed  ir 
accordance  with  local  building  regulations.     A  generous  factor  o 
safety  should  be  allowed.     A  type  of  construction  recommended  b} 
the  Committee  consists  of  (1)  a  reinforced  concrete  floor-slab  not  lesi 
than  4  inches  thick ;  (2)  a  tamped  cinder  fill  above  the  floor-slab,  not  lesi 


Nov.,  1938] 


PROJECTION  PRACTICE  COMMITTEE 


485 


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486  PROJECTION  PRACTICE  COMMITTEE         [j.  s.  M.  P.  E 

than  2  inches  thick;  and  (3)  a  troweled  cement  finish  above  the 
cinder  fill  not  less  than  2  inches  thick.  Items  (2)  and  (3)  have  been 
provided  in  order  to  accommodate  concealed  electrical  conduits,  which 
should  be  installed  prior  to  placing  the  fill  and  finish.  (See  Sec.  6.1.) 

(1.3)  Walls. — The  projection  room  walls  shall  be  built  of  brick, 
tile,  or  plaster  blocks  plastered  on  the  inside  with  3/4-inch  cement 
plaster,  or  all  concrete.     The  core  of  the  wall  shall  be  not  less  than 
4  inches  thick.     When  plaster  block  is  used,  it  shall  be  supported 
upon  steel  framework.     All  electrical,  conduits  shall  be  placed  into 
masonry  chases  in  the  wall  construction  so  that  no  pipes  shall  project 
beyond  the  main  finish  line.     (See  Sec.  6.1.)     In  all  cases,  the  inside 
surface  of  the  front  wall  shall  be  smooth  and  without  structural 
projections.     (See  Sec.  1.11.) 

(1.4)  Doors. — A  door  shall  be  provided  at  each  end  of  the  pro- 
jection room,  at  least  2  feet  6  inches  wide  by  6  feet  8  inches  high. 
Doors  shall  be  of  the  approved  1-hour  fire-test  type  and  shall  be  ar- 
ranged so  as  to  close  automatically,  swinging  outwardly,  and  shall 
be  kept  closed  at  all  times  when  not  used  for  egress  or  ingress.     It 
shall  be  possible  at  all  times  to  open  either  door  from  the  inside 
merely  by  pushing  it.     Door  jams  shall  be  made  of  steel. 

(1.5)  Windows. — Where  a  projection  room  is  built  against  the 
exterior  wall  of  a  structure,  one  or  more  windows  may  be  provided 
in  the  wall.     Window  construction  shall  be  entirely  of  steel,  and  the 
glass  shall  be  of  the  shatter-proof  type.     Metal  adjustable  louvres  or 
other  similar  means  may  be  used  to  exclude  light. 

(1.6)  Ports. — (General.)     Two  ports  shall  be  provided  for  each 
projector  or  single-lens  stereopticon,  one  through  which  the  picture 
is  projected,  known  as  the  "projection  port"  (see  Sec.  1.7),  and  the 
other  for  observation  of  the  screen  by  the  projectionist,  known  as  the 
"observation  port"  (see  Sec.  1.8). 

The  observation  port  shall  be  located  above  and  to  the  right  of  the 
projection  port.  The  distance  between  the  horizontal  center-lines 
of  the  projection  port  and  observation  port  shall  be  14  inches;  the 
distance  between  the  vertical  center-line  shall  be  21  inches. 

Where  separate  spotlight  or  floodlight  machines  are  installed  in 
the  same  projection  room  with  motion  picture  projectors,  not  more 
than  one  port  opening  (see  Sec.  1.9)  for  each  machine  shall  be  pro- 
vided for  both  the  projectionist's  view  and  for  the  projection  of  the 
light,  but  two  or  more  spotlights  or  floodlights  may  be  operated 
through  the  same  port. 


Nov.,  1938] 


PROJECTION  PRACTICE  COMMITTEE 


487 


(1.7)  Projection  Ports.— The  finished  ports  shall  be   10    X    10 
inches,  measured  on  the  inside  wall  (Fig.  1). 

The  required  height  of  the  center-line  of  the  projection  port  from 
the  floor  varies  with  the  make  and  design  of  th'e  projection  and  sound 
equipment  and  also  with  the  projection  angle.  Manufacturers  of 
equipment  being  considered  for  the  projection  room  should  be  con- 
sulted for  these  dimensions.  In  no  case  shall  any  part  of  the  pro- 
jector be  less  than  4  inches  from  the  front  wall  of  the  projection  room. 
Table  I  lists  two  constants  for  various  angles  of  projection  which 
when  substituted  in  the  formula,  will  permit  calculating  the  height 
of  the  center-line  of  the  port  from  the  floor,  when  certain  dimensions 
of  the  projector  are  known. 

(1.8)  Observation  Ports. — The  finished  observation  port  shall  be 
not  greater  than  12  inches  wide  X  14  inches  high,  measured  on  the 
inside  wall  of  the  projection  room. 

(1.9)  Other  Ports. — All  other  ports,  such  as  for  effect  projectors 

TABLE  I 

Method  of  Locating  Projector  Port 
h  =  H  +  rA  -  DB 


Projection 

Angle 
(Degrees) 

0 

2 

4 

6 

8 
10 
12 
14 
16 
18 
20 
22 
24 
26 
28 
30 


1.00 
1.00 
.00 
.01 
.01 
.02 
.02 
.03 
.04 
.05 
.06 


.09 

.11 

.13 

1.16 


B 

0.00 
0.04 
0.07 
0.11 
0.14 
0.18 
0.21 
0.25 
0.29 
0.33 
0.36 
0.40 
0.45 
0.49 
0.53 
0.58 


H  is  the  height  of  the  center  of  the  projector  pivot  from  the  floor;  r  is  the 
radial  distance  of  the  optical  center-line  above  the  center  of  the  pivot;  D  is  the 
distance  of  the  center  of  the  pivot  from  the  front  wall  of  the  projection  room; 
4>  is  the  angle  of  projection;  and  h  is  the  required  height  of  the  center  of  the  port 
from  the  floor  of  the  projection  room.  Select  the  values  of  A  and  B  corresponding 
to  the  angle  of  projection,  and  substitute  in  the  formula. 


488  PROJECTION  PRACTICE  COMMITTEE         [j.  S.  M.  P.  E. 

or  spotlamps,  shall  be  as  small  as  practicable,  and  in  no  case  shall 
exceed  71/*  square-feet  in  area  per  machine.  The  location  of  these 
ports  will,  of  course,  be  determined  by  the  dimensions  of  the  equip- 
ment and  the  size  and  shape  of  the  auditorium  and  stage,  which 
determine  the  angles  through  which  the  light-beams  must  be  pro- 
jected. The  dimensions  should  be  obtained  from  the  manufacturers 
of  the  equipment. 

(1.10)  Ceiling. — The  ceiling  shall  be  constructed  of  4-inch  con- 
crete slabs  or  precast  concrete,  or  of  3-inch  plaster  blocks  supported 
by  a  steel  structure  and  plastered  on  the  inside  with  3/4-inch  cement 
plaster.     All  wiring  conduit  in  the  ceiling  shall  be  concealed  (see 
Sec.  1.11). 

(1.11)  Acoustic  Treatment. — It  is  recommended  that  an  approved 
fire-proof  acoustic  material  be  used  on  the  walls  above  a  height  of  4 
feet  from  the  floor  and  on  the  ceiling  to  reduce  the  transmission  of 
noise  into  the  auditorium. 

REWIND    ROOM 

(2.1)  Construction. — The  rewind  room  shall  be  of  fire-proof  con- 
struction.     It  shall  have  a  minimum  area  of  80  square-feet  (Fig.  1). 

(2.2)  Floor.— See  Sec.  1.2. 

(2.3)  Walls.— See  Sec.  1.3. 

(2.4)  Doors. — The  door  shall  be  of  the  approved  1-hour  fire-test 
type,  shall  be  arranged  so  as  to  close  automatically,  swinging  out- 
wardly, and  shall  be  kept  closed  at  all  times  when  not  used  for  egress 
or  ingress.     Door  jams  shall  be  made  of  steel. 

(2.6)  Ports. — An  observation  port  shall  be  provided  through 
which  the  motion  picture  screen  may  be  seen  from  within  the  rewind 
room.  The  port  shall  be  at  the  same  height  from  the  floor  as  the 
observation  ports  in  the  projection  room  proper,  as  described  in 
Sec.  1.6. 

(2.8)  Observation  Port.— See  Sec.  1.8: 

(2.9)  Other  Ports. — An  observation  window  shall  be  provided 
between  the  projection  room  and  rewind  room,  consisting  of  a  fixed, 
fire-proof  frame  and  polished  plate  wire  glass.     The  window  shall 
be  not  greater  than  14  inches  square. 

(2.10)  Ceiling.— See  Sec.  1 .10. 

(2.11)  Acoustic  Treatment— See  Sec.  1.11. 


Nov.,  19381  PROJECTION  PRACTICE  COMMITTEE  489 

POWER  EQUIPMENT  ROOM 

(3.1)  Construction. — The  room  shall  be  fire-proof  and  shall  be 
similar  in  construction  to  the  rewind  room  (with  the  exception  of  the 
openings  (see  Fig.  1)).  The  size  shall  be  governed  by  the  quantity 
and  kind  of  equipment  to  be  installed.  Consideration  should  be 
given  to  probable  future  needs. 

LAVATORY 

(4.1)  Construction. — The  lavatory  shall  be  provided  with  running 
water  and  modern  sanitary  facilities,  with  tiled  floor  and  built-in 
flush-type  medicine  closet. 

EXITS 

(5.1)  General. — Two  exits  shall  be  provided,  one  at  each  end  of 
the  projection  room  suite  (Fig.  1),  permitting  direct  and  unobstructed 
egress,  and  shall  conform  to  the  regulations  of  local  authorities  having 
jurisdiction.  Any  stairs  communicating  with  these  exits  should 
have  risers  not  in  excess  of  8  inches  and  minimum  tread  of  not  less 
than  9l/z  inches.  The  distance  between  walls  should  be  not  less 
than  36  inches.  Winding  or  helical  treads  should  be  avoided.  A 
platform  equal  in  length  to  the  width  of  the  door  shall  be  provided 
between  the  door  and  the  first  riser.  Neither  ladders  nor  scuttles 
or  trap-doors  should  be  used  as  means  of  entrance  or  exit. 

CONDUITS  AND  CIRCUITS 

(6.1)  Locations  and  Sizes. — Locations  and  sizes  of  conduits  for 
projection,  control,  and  sound  equipment  are  determined  by  the  type 
and  design  of  the  equipment.  Manufacturers  of  the  equipment 
should  be  consulted  with  regard  to  the  proper  layout  and  sizes  of  the 
conduit  systems  before  floors,  walls,  and  ceilings  are  finished  (see 
Sees.  1.2  and  1.3).  Conduits  shall  in  all  cases  be  concealed,  and  all 
boxes  shall  be  of  the  flush-mounting  type  in  walls  and  ceiling.  Con- 
duits terminating  in  the  floors  should  extend  6  inches  above  the 
finished  floor  level. 

Conduits  and  wiring  should  generally  be  provided  for  the  following 
circuits : 

( 1 )  Pro j  ector  mechanism 

(a)     motor 

(6)     changeover 

(c)     pilots 

(2)  Projector  arcs  and  spotlights 

(a)     rheostats,  generators,  or  rectifier 


490  PROJECTION  PRACTICE  COMMITTEE         [j.  s.  M.  P.  E. 

(5)     Sound  equipment 

(a)     a-c.  power  supply 
(&)     loud  speaker  circuits 

(c)  amplifier  and  controls 

(d)  ground  wire 

(4)  Projection  room  lighting 

(a)     general  (ceiling  and  Reelites) 
(6)     emergency 

(5)  Theater  auditorium  lighting 

(a)     dimmer 
(&)     emergency 

(6)  Projector  ventilation  equipment 

(a)     normal 

(7)  General  ventilation  system 

(a)    normal 
(6)     emergency 

(8)  Miscellaneous 

(a)  stage  curtain 

(6)  telephone 

(c}  buzzer 

(d)  receptacles 

Fig.  2  shows  the  general  arrangement  of  the  equipment  requiring 
these  conduits. 

(6.2)  Projection  Arc  Supply  and  Location. — In  cases  where  the 
projection   arc  supply   consists  of  rotating  machinery  generating 
acoustical  hum  or  mechanical  vibration,  acoustical  or  mechanical 
insulation  will  be  required.     Arc  supply  equipment  should  be  located 
in  the  power  equipment  room  adjacent  to  the  projection  room,  and 
at  least  four  feet  from  any  sound  amplifier  equipment. 

(6.3)  Power  Supply  to  Equipment. — Where  line-voltage  variations 
are  greater  than  ±3  per  cent,  the  local  power  company  should  be 
requested  to  rectify  the  condition.     In  cases  where  it  is  impossible 
to  maintain  a  steady  line-voltage  into  the  theater,  either  manually 
controlled  or  automatic  regulators  should  be  installed. 

LIGHTING 

(7.1)  Projection  Room  Lighting. — Approved  vapor-proof  ceiling 
fixtures  should  be  installed  for  general  illumination,  as  indicated  in 
Fig.  2,  and  arranged  to  be  lighted  on  either  the  normal  or  the  emer- 
gency lighting  circuit. 

An  individual  vapor-proof  relight  with  wire  guard  shall  be  located 
near  each  projector  or  spotlamp,  as  indicated  in  Fig.  2. 


Nov.,  1938] 


PROJECTION  PRACTICE  COMMITTEE 


491 


All  lights  in  the  projection  room  and  associated  rooms,  shall  be 
shaded  so  as  to  prevent  light  from  entering  the  auditorium  through 
the  ports. 

(7.2)  Rewind  Room. — An  approved  vapor-proof  ceiling  fixture 
shall  be  installed  for  general  illumination.  A  drop-light  or  wall 
bracket  fixture  with  approved  vapor-proof  globe  shall  be  provided 


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FIG.  2.     Projection  room  equipment,  showing  conduits,  ventilation  systems, 
lights,  and  switches. 

(1)  Three  conduits  in  floor  to  a-c.  control  panel:     for  pilot  light,  change- 
over and  motor  feed,  for  both  projectors. 

(2)  Conduit  in  floor  to  d-c.  control  panel  and  motor  generator:     for  both 
projectors  and  spot  (or  stereo)  via  polarized  plug-box  on  front  wall  of  room. 

(3)  Conduit  to  pipe  ground  for  each  projector,  and  conduit  to  loud  speak- 
ers on  stage. 

(4)  Vapor-proof   ceiling   fixtures,    and    vapor-proof    Reelites    with    wire 
guards  for  each  projector  and  spot  (or  stereo). 

(5)  Dimmer  and  emergency  lighting  control. 

(6)  Projector  and  spot  (or  stereo)  ventilation  system  and  control  switch. 

(7)  General  ventilation  system  (normal  and  emergency),  with  switches 
inside  and  outside  of  doors  of  projection  room. 

(8)  Wall  receptacles. 

(9)  Wall  switches,  two-way  type,  individually  controlling  each  ceiling  light 
fixture  from  either  entrance  door. 


492 


PROJECTION  PRACTICE  COMMITTEE         [j.  s.  M.  P.  E. 


near  or  over  the  rewind  table.     These  lights  should  be  on  a  separate 
circuit  from  the  projection  room  proper. 

VENTILATION 

(8.1)  Arcs  or  Spotlight. — In  permanent  projection  rooms,  venti- 
lation shall  be  provided  for  the  arc  lamps  independently  of  the  general 
and  emergency  ventilating  system  of  the  room.  Each  arc  lamp 
housing  shall  be  connected  by  a  flue  to  a  common  duct,  which  duct 
shall  lead  directly  out  of  doors  and  shall  contain  an  exhaust  fan  or 
blower  having  a  capacity  of  at  least  50  cubic-feet  per  minute  of  air 
for  each  arc  lamp  connected  thereto.  This  exhaust  fan  or  blower 
shall  be  electrically  connected  to  the  projection  room  wiring  system 


FIG.  3.  Equipment  ventilation  system:  blower  capacity  400  cu.-ft.  per 
min. ;  minimum  air  movement  through  lamp  houses  with  blower  idle,  15  cu.- 
ft.  per  min. 


and  controlled  by  a  separate  switch  with  pilot  lamp  within  the  room. 
There  shall  at  no  time  be  less  than  15  cubic-feet  of  air  per  minute 
flowing  through  each  lamp  house  into  an  exhaust  system  connected 
to  the  air  outside  the  building.  Fig.  3  shows  the  general  arrange- 
ment of  the  system. 

(8.2)  Projection  Room  and  Rewind  Room. — General  ventilation 
of  the  projection  room  and  rewind  room  shall  be  provided  by  a  duct 
having  outlets  at  one  or  more  points  in  the  ceiling  and  leading  directly 
to  the  outer  air.  Said  duct  shall  be  capable  of  maintaining  a  natural 
circulation  of  air,  without  blower  or  fan,  at  the  rate  of  not  less  than 
20  cubic-feet  per  minute.  Auxiliary  circulation  in  said  duct  shall  be 
provided  by  an  exhaust  fan  or  blower  having  a  capacity  of  not  less 
than  200  cubic-feet  per  minute  for  normal  circulation  and  having  a 
rated  capacity  of  not  less  than  2000  cubic-feet  per  minute  for  operation 
in  emergency,  i.  e.,  fire.  In  no  case  shall  the  exhaust  duct  system  of 


Nov.,  1938]  PROJECTION  PRACTICE  COMMITTEE  493 

the  room  be  connected  with  the  ventilating  system  of  the  building 
proper.  The  emergency  operation  of  said  fan  shall  be  controlled  by 
a  switch  (Fig.  6)  operated  automatically  by  the  shutter  control 
mechanism  when  the  latter  is  actuated  either  manually  or  by  melting 
of  the  fusible  links.  This  exhaust  fan,  providing  general  and  emer- 
gency ventilation  of  the  projection  room  and  rewind  room  shall  be 
connected  to  the  emergency  lighting  circuit  of  the  room,  and  shall  be 
controlled  for  normal  circulation  by  a  switch  and  pilot  lamp  within 
the  room. 

The  ducts  shall  be  of  incombustible  material,  and  shall  be  kept  at 
least  2  inches  from  combustible  material  or  separated  therefrom  by 
approved  non-combustible  heat-insulating  material,  not  less  than  1 
inch  thick. 


FIG.  4.     General  and  emergency  ventilation  system :     normal  blower  ca- 
pacity 200  cu.-ft.  per  min.;   emergency  capacity  2000  cu.-ft.  per  min. 

(A)     Switch  and  pilot  lamp  for  normal  operation,  inside  projection  room ; 
(B)  switch  and  pilot  lamp  for  emetgency  operation,  outside  door  of  projec- 
tion room;   also  connected  to  port  fire-shutter  control  mechanism. 
(Two  or  more  fresh-air  intakes  required  at  or  near  the  floor  at  opposite  ends 

of  the  room) 


Projection  rooms  and  rewind  rooms  shall  have  two  or  more  separate 
fresh  air  intake  ducts  at  or  near  the  floor  and  at  opposite  ends  of  the 
room,  entirely  independent  of  and  in  no  way  connected  to  the  exhaust 
ducts  of  the  room.  Such  air  intake  ducts  may  be  connected  into  the 
main  ventilating  system  of  the  building.  (See  Fig.  4  for  general 
arrangement.) 

PORT  SHUTTERS 

(9.1)  Construction. — Each  port  opening  shall  be  provided  with 
a  gravity  shutter  of  approved  construction.  Said  shutter  and 
guides  shall  be  made  of  not  less  than  10-gauge  iron,  and  the  shutter 
should  set  into  the  guides  not  less  than  1  inch  at  sides  and  bottom 
and  overlap  the  top  of  the  port  opening  by  not  less  than  1  inch,  when 


494 


PROJECTION  PRACTICE  COMMITTEE         [J.  S.  M.  P.  E. 


FIG.  5.     Example  of  port  shutter  construction.     Although  this  construc- 
tion shows  rivets,  spot  welding  is  preferable. 


Nov.,  1938] 


PROJECTION  PRACTICE  COMMITTEE 


495 


closed.  Guide  parts  should  preferably  be  welded  (see  Fig.  5). 
Shutters  shall  be  suspended,  arranged,  and  inter-connected,  so  that 
all  port  shutters  will  close  upon  the  operating  of  some  suitable 
fusible  or  mechanical  releasing  device,  designed  to  operate  auto- 
matically in  case  of  fire  or  other  contingency  requiring  immediate 
and  complete  isolation  of  the  contents  of  the  projection  room  from 
other  portions  of  the  building.  Each  shutter  shall  have  its  own 
individual  fusible  link  directly  above  it.  A  fusible  link  shall  be 
located  also  above  each  upper  projector  magazine,  which  upon  operat- 
ing shall  close  all  the  shutters.  There  shall  also  be  provided  suitable 
means  for  manually  closing  all  shutters  simultaneously  from  any 


FIG.  6.     One  of  many  possible  arrangements  of  the  port  fire-shutter  con- 
trol.    The  automatic  switch  operates  the  exhaust  fan  and  emergency  lights 


projector  head  and  from  a  point  near  each  door  within  the  projection 
room.  Shutters  shall  be  free-acting.  Shutters  on  openings  not  in 
use  shall  always  be  kept  closed.  Fig.  6  indicates  one  of  many  ways 
of  arranging  the  shutter  control  system.  All  large  shutters  such 
as  for  spotlamps  and  special-effect  machines  (when  used)  shall  be 
provided  with  weights  to  facilitate  operating  them  manually. 

(9.2)  Noise  Transmission. — The  Committee  recommends  the  use 
of  means  other  than  glass  in  projection  ports  to  prevent  transmission 
of  noise  from  the  projector  room  to  the  auditorium,  such  as  reducing 
the  free  aperture  of  the  port  to  the  minimum  size  necessary  for  pro- 
jection by  use  of  fire-proof  sound  baffles. 

Observation  ports  shall  be  fitted  with  a  good  grade  of  plate  glass 
set  in  a  metal  frame  at  an  angle  to  the  vertical  to  avoid  direct  re- 


496 


PROJECTION  PRACTICE  COMMITTEE         [J.  S.  M.  P.  E. 


flection,  and  easily  removable  from  the  inside  of  the  projection  room 
for  cleaning.  The  purpose  of  this  glass  is  to  prevent  transmission  of 
noise  into  the  auditorium. 

HEATING 

(10.1)  General. — Proper  provision  shall  be  made  for  heating  the 
projection  room.  The  same  facilities  used  for  heating  the  theater 
should  be  extended  to  the  projection  room. 


FIG.  7.     Rewind  room  layout,  showing  required  equip- 
ment. 

PAINTING  AND  FLOOR  COVERING 

(11 .1}  Painting. — The  color  of  the  walls  shall  be  olive  green  to 
the  height  of  the  acoustic  plaster.  The  latter  should  be  painted  in 
accordance  with  the  instructions  of  the  manufacturer  of  the  material, 
preferably  a  dull  buff  color.  The  ceiling  should  likewise  be  painted 
white.  All  iron  work  of  the  projection  ports  shall  be  covered  with 
at  least  two  coats  of  flat  black  paint. 


Nov.,  1938]  PROJECTION  PRACTICE  COMMITTEE  497 

(11.2)  Floor  Covering. — Where  local  regulations  permit,  the 
floors  of  the  projection  room  and  rewind  room  should  be  covered 
with  a  good  grade  of  battleship  linoleum  cemented  to  the  floor.  The 
floor  covering  should  be  laid  before  the  equipment  is  installed. 


EQUIPMENT 

(12.1)  Projection  Room. — All  equipment  to  be  used  in  the  pro- 
jection room  should  be  of  approved  type,  including  the  projectors, 
arc  lamps,  sound  equipment,  etc. 

All  shelves,  furniture,  and  fixtures  within  the  projection  suite  shall 
be  constructed  of  metal  or  other  incombustible  material.  A  metal 
container  for  hot  carbon  stubs  shall  be  provided. 

Adequate  locker  space  shall  also  be  provided. 

(12.2)  Rewind  Room. — In  the  rewind  room  shall  be  provided  an 
approved  fire-proof  film  safe  or  cabinet,  a  table,  approved  rewind 
equipment,  a  splicer,  and  approved  scrap  film  can  (Fig.  7). 

The  film  safe  or  cabinet  shall  be  capable  of  holding  25,000  feet  of 
35-mm.  film. 

All  tables  and  racks  and  all  furniture  shall  be  of  metal  or  other  non- 
combustible  material  and  should  be  kept  at  least  4  inches  away  from 
any  radiator  or  heating  apparatus.  Tables  shall  not  be  provided 
with  racks  or  shelves  beneath  them  whereon  may  be  kept  film  or  other 
materials. 

The  scrap  film  can  shall  have  an  automatic-closing  hinged  cover 
and  so  arranged  that  the  scrap  film  is  kept  under  water  at  all  times. 

Quantities  of  collodion,  amyl  acetate,  or  other  similar  inflammable 
cements  or  liquids  kept  in  the  rewind  room  for  the  purpose  of  splicing 
film,  shall  not  exceed  x/2  pint. 

No  stock  of  inflammable  materials  of  any  sort  whatsoever  shall 
be  permitted  within  the  rewind  suite  except  as  specifically  mentioned 
herein. 

All  splices  of  film  shall  be  made  with  approved  mechanical  cutting 
and  splicing  machines.  No  hand  cutting  or  splicing  shall  be  per- 
mitted. 

Film  shall  be  kept  in  the  film  cabinets  at  all  times  except  when 
being  projected  or  rewound.  Any  films  in  addition  to  those  used  for 
the  current  showing  or  in  excess  of  that  permitted  by  local  authorities 
shall  be  kept  in  their  original  shipping  containers. 

(12.3)  Fire  Extinguishing  Equipment. — Local  authorities  having 


498  PROJECTION  PRACTICE  COMMITTEE         [J.  S.  M.  P.  E. 

jurisdiction  with  regard  to  fire  extinguishing  equipment  should  be 
consulted  regarding  the  proper  types,  numbers,  and  locations. 

MISCELLANEOUS 

(13.1)  "No  smoking"  signs  should  be  posted  in  prominent  places 
and  matches  should  not  be  carried  by  any  employee. 

(13.2)  Operation. — Motion  picture  projectors  shall  be  operated 
by  and  shall  be  in  charge  of  qualified  projectionists  who  shall  not 
be  minors.     The  projectionist  should  be  stationed  constantly  at  the 
operating  side  of  the  projector  while  it  is  in  operation.     A  proper 
factor  of  safety  in  operation,  as  well  as  avoidance  of  imperfect  opera- 
tion of  projection  equipment,  or  unjustified  interruptions  of  service 
can  be  attained  only  by  having  an  adequate  personnel  in  the  pro- 
jection room. 

(13.3)  Action  in  Case  of  Fire. — In  the  event  of  film  fire  in  the 
projector  or  elsewhere  in  a  projection  or  rewind  room,  the  projection- 
ist shall  immediately  shut  down  the  projector  and  arc  lamps,  operate 
the  port  shutter  release  at  the  point  nearest  him,  turn  on  the  audi- 
torium lights,  leave  the  projection  room  immediately,  and  notify 
the  manager  of  the  theater  or  building.     An  automatic  switch  is 
recommended  for  the  electrical  operations  mentioned. 

SUB-COMMITTEE  ON  PROJECTION  ROOM  PLANS 

S.  HARRIS,  Chairman 

A.  GOODMAN  C.  C.  DASH 

B.  SCHI.ANGER  P.  J.  LARSEN 
J.  J.  SEFING                 J.  S.  PESCE 

E.  R.  MORIN 


PROPOSED  REVISION  OF  REGULATIONS  OF  THE  NATIONAL  BOARD 

OF  FIRE  UNDERWRITERS  FOR  NITROCELLULOSE 

MOTION  PICTURE  FILM  AS  PERTAINING  TO 

PROJECTION  ROOMS* 

For  a  long  time  it  has  been  recognized  that  numerous  conflicts 
existed  between  the  provisions  of  the  Regulations  of  the  National  Board 
of  Fire  Underwriters  for  Nitrocellulose  Motion  Picture  Film  and  the 
National  Electric  Code.  In  addition,  when  the  revision  of  the  Pro- 
jection Room  Plans  issued  by  the  Projection  Practice  Committee  in 
19351  was  brought  to  the  attention  of  the  National  Fire  Protection 
Association,  a  number  of  conflicts  between  the  Plans  and  the  Regula- 

*  Readers  of  the  JOURNAL  are  requested  to  transmit  their  comments  concern- 
ing these  revisions  to  the  General  Office  of  the  Society. 


Nov.,  1938]  PROJECTION  PRACTICE  COMMITTEE  499 

tions  were  discovered.  In  view  of  this  confusion,  steps  were  taken 
by  the  NFPA  to  make  their  Committee  on  Hazardous  Chemicals  and 
Explosives,  authors  of  the  Regulations,  responsible  for  the  prepara- 
tion of  all  material  relating  to  motion  picture  ^fire  prevention.  All 
such  material  to  appear  in  future  issues  of  the  National  Electric 
Code  will  be  taken  from  the  revised  Regulations. 

To  assist  in  this  work,  the  Projection  Practice  Committee  of  the 
SMPE  agreed  to  submit  its  recommendations  for  revising  the  portions 
of  the  Regulations  pertaining  to  projection  rooms,  with  respect  to 
which  most  of  the  conflicts  have  occurred. 

Such  recommendations  have  been  prepared  and  have  been  sub- 
mitted to  the  NFPA  Committee  on  Hazardous  Chemicals  and  Explo- 
sives, of  which  Mr.  A.  H.  Nuckolls  is  Chairman.  A  special  sub- 
committee has  been  appointed  by  the  Committee  on  Hazardous 
Chemicals  and  Explosives  for  considering  these  recommendations. 
The  Chairman  of  this  sub-committee  is  Mr.  George  W.  Booth,  Chief 
Engineer  of  the  National  Board  of  Fire  Underwriters,  and  the  per- 
sonnel of  the  sub -committee  includes  engineers  long  experienced  in 
the  field  of  fire  prevention.  The  Chairman  of  the  Sub-Committee  on 
Projection  Room  Fire  Regulations  represents  the  Projection  Practice 
Committee  on  the  NFPA  sub-committee. 

The  proposed  revisions  are  published  herewith  for  the  purpose  of 
soliciting  expressions  of  opinion  concerning  them  from  the  motion 
picture  industry. 

In  the  following  proposals,  sections  of  the  Regulations  pertaining  to 
exchanges,  studios,  storage  vaults,  etc.,  not  dealing  with  projection  or 
projection  rooms,  were  not  considered.  Where  no  change  is  proposed, 
the  section  is  marked  "Unchanged";  added  words  or  clauses  are  un- 
derlined; sections  completely  rewritten  are  marked  "Rewritten" ;  pro- 
posed new  sections  are  marked  "New";  sections  recommended  for 
deletion  are  marked  "Deleted." 

Attention  should  be  called  to  one  very  important  departure  in  these 
proposals :  In  the  original  Regulations,  structural  details  of  permanent 
projection  rooms  and  temporary  projection  booths  were  grouped  to- 
gether in  the  same  sections  and  sub-sections  (Sec.  191).  The  Pro- 
jection Practice  Committee  deemed  it  advisable  to  remove  from 
Section  191  all  references  to  temporary  projection  booths;  and  since 
it  is  recommended  that  the  existing  Section  192  be  deleted  from  the 
Regulations,  the  material  pertaining  to  temporary  projection  booths 
may  be  assigned  to  this  Section  192. 


500  PROJECTION  PRACTICE  COMMITTEE         [J.  S.  M.  p.  E. 

PART  I 

GENERAL  PROVISIONS   REGARDING  THE  STORAGE  AND  HANDLING  OF 
MOTION  PICTURE  FILM 


Section  11 — Construction  and  Arrangement  of  Buildings 

(111)  (Unchanged)  Motion  picture  film  should  preferably  be  stored 
or  handled  only  in  buildings  of  fire-proof  construction. 

(114)  Exits. — It  is  essential  that  all  rooms  in  which  film  is  handled 
be  provided  with  adequate  aisle  space,  not  less  than  30  inches  clear, 
wherever  walking  is  necessary  between  any  two  pieces  of  equipment,  so  as 
to  provide  safe  means  of  egress.     Rooms  in  which  film  is  handled  and 
in  which  more  than  two  persons  work  shall  have  two  or  more  exits, 
remote  from  each  other.    Every  exit  shall  be  marked  Exit  in  letters 
not  less  than  6  inches  high,  or  by  an  illuminated  sign  with  letters  of 
the  same  height 

(115)  Vents. — All  new  buildings  erected  to  be  used  as,  and  all  exist- 
ing buildings  remodeled  for,  film  occupancies,  except  as  related  to  pro- 
jection rooms,  rewind  rooms,  and  rooms  associated  therewith,  shall  be 
provided  in  every  room,  where  film  is  to  be  stored  or  handled,  with 
vents  that  will  open  automatically  in  case  of  fire.    These  should  be 
of  ample  size;   they  may  be  in  the  form  of  automatic  skylights  or 
automatic-opening  window  sash.     All  rooms,  except  as  aforemen- 
tioned, in  which  film  is  stored  or  handled  in  existing  buildings,  shall  be 
provided  with  such  vents  wherever  practicable. 

(117)  (Unchanged)  Tables  and  Racks. — Tables  and  racks  used  in 
connection  with  the  handling  of  film  (joining,  inspection,  and  assem- 
bling tables,  for  example)  shall  be  of  metal  or  other  non-combustible  j 
material.  They  should  be  kept  at  least  4  inches  away  from  any  radia- 
tors or  heating  apparatus.  Tables  shall  not  be  provided  with  racks 
or  shelves  underneath  them  that  might  be  used  for  keeping  film  or 
other  materials. 

Section  12 — Electrical  Equipment 

(121)  (Unchanged)  Artificial  illumination  in  any  room  where  film 
is  handled  or  stored  shall  be  restricted  to  incandescent  electric  lights, 
except  that  arc  lights  or  other  forms  of  electric  lights  may  be  used  in 
studios. 

(122)  (Unchanged)  All  electrical  wiring  and  equipment  shall  con- 
form to  the  National  Electrical  Code.    Wiring  shall  be  in  metal  conduit, 
and  fuses  shall  be  enclosed. 


Nov.,  1938]  PROJECTION  PRACTICE  COMMITTEE  501 

(123)  ( Unchanged)  Lighting  fixtures  shall  be  firmly  fixed  in  place, 
and  lights  shall  be  protected  by  vapor-proof  globes.  All  lights  shall 
be  equipped  with  keyless  sockets  and  operated  by  wall  switches. 

(125)  (Rewritten)  Portable  electric  lamps  on  extension  cords  are 
prohibited  in  any  room  in  wjiich  film  is  handled  or  stored,  except  that 
portable  electric  lamps  provided  with  approved  keyless  sockets  and 
metal  protective  lamp  guards  and  having  service  cords  of  types  S 
or  SJ  with  twist-lock  plugs  are  permissible  in  projection  rooms. 

(126)  (Unchanged)  Motors  shall  be  of  the  non-sparking  type,  or 
shall  be  of  an  enclosed  type,  so  arranged  as  to  minimize  the  danger  of 
sparks. 

(127)  Motion  picture  projectors  and  associated  electrical  equip- 
ment shall  be  of  approved  type  and  safeguarded  in  accordance  with 
the  requirements  of  the  National  Electric  Code,  Article  540. 

(128)  (New  Section)    Motor-generator   sets,    transformers,    recti- 
fiers, rheostats,  and  similar  equipment,  for  the  supply  or  control  of 
current  to  arc  lamps  on  motion  picture  projectors,  shall  if  practicable 
be  located  in  a  room  separate  from  the  projection  room  or  booth. 
Such  separate  room  shall  be  suitably  ventilated.     No  rheostats  ex- 
ceeding 30-ampere  capacity  shall  be  installed  in  a  projection  room  or 
booth. 

Motor-generator  sets  shall  have  the  commutator  end  or  ends  pro- 
tected as  provided  in  the  National  Electric  Code,  Section  5310.  Rheo- 
stats shall  be  constructed  and  installed  as  provided  by  the  National 
Electric  Code,  Article  470. 

When  motor-generators,  transformers,  rectifiers,  and  similar  equip- 
ment are  installed  in  the  projection  room  or  booth  they  shall  be  so 
located  and  guarded  that  arcs  or  sparks  caused  thereby  can  not  come 
into  contact  with  film,  and  shall  be  so  located  as  to  provide  at  least 
30  inches  of  clear  aisle  space  between  any  two  pieces  of  equipment 
where  walking  is  necessary.  Rheostats  for  arc  lamps  (not  exceeding 
30-ampere  capacity)  when  installed  in  the  projection  room  or  booth 
shall  be  installed  near  the  ceiling  upon  suitably  supported  heavy 
metal  shelves  provided  with  metal  pans  having  upturned  sides.  The 
rheostats  shall  be  electrically  and  heat  insulated  therefrom. 

Section  13 — Heating  Equipment 

(131)  (Unchanged)  Artificial  heating  in  any  building  or  room, 
rther  than  a  vault,  in  which  motion  picture  film  is  used,  handled,  or 


502  PROJECTION  PRACTICE  COMMITTEE          [J.  S.  M.  P.  E. 

stored,  shall  be  restricted  to  steam  not  exceeding  15  pounds'  pressure 
or  hot  water,  provided,  however,  that  this  shall  not  be  construed  as 
prohibiting  the  installation  of  an  indirect  system  employing  high- 
pressure  steam  when  the  radiators  or  heating  coils  of  such  system  are 
not  located  in  the  room  or  rooms  to  be  heated.  Heat  generating  ap- 
paratus shall  be  in  a  separate  room. 

Note. — Ordinary  hot-air  furnaces  are  prohibited.  Gas,  oil,  and  electric  heaters 
are  prohibited  in  rooms  where  film  is  handled  or  stored. 

(132)  (Unchanged)  All  steam  pipes  within  6  feet  of  the  floor,  and 
where  passing  through  partitions  or  racks  or  near  woodwork,  shall 
be  covered  with  approved  pipe  covering.  All  radiators,  heating  coils, 
and  pipes  and  returns  that  are  near  the  floor  or  are  so  located  as  to 
permit  any  combustible  material,  waste,  or  dirt  to  come  in  contact 
therewith  shall  be  guarded  and  protected  by  means  of  V-rinch  mesh 
galvanized  steel  wire  cloth  No.  20  B.  &  S.  gauge,  or  by  its  equivalent. 
The  bottoms  of  such  guards  shall  be  arranged  so  as  to  lift  up  for 
cleaning  purposes  and  the  tops  to  slope  so  that  guards  can  not  be 
used  as  shelves.  Guards  shall  be  so  constructed  that  no  film  can  come 
within  4  inches  of  the  heating  surface,  and  shall  be  made  with  a  sub- 
stantial metal  framework  that  will  prevent  the  wire  mesh  from  being 
forced  against  the  radiator  or  pipes. 

Section  14 — Sprinklers  and  Other  Fire  Protection  Appliances 

Note. — See  Sub-Section  174  regarding  sprinklers  in  film  vaults. 

(141)  (Unchanged)  Every  room  in  which  film  is  stored  or  handled 
in  quantities  greater  than  50  pounds  (10  standard  rolls),  except  in 
motion  picture  projection  booths  or  rooms  and  rewinding  rooms  con- 
nected therewith,  shall  be  equipped  with  an  approved  system  of  auto- 
matic sprinklers.  Buildings  or  sections  of  buildings  used  as  exchanges, 
laboratories,  or  studios  shall  be  equipped  with  automatic  sprinklers, 
as  provided  under  Sub-Sections  221,  231,  and  241.  All  buildings  used 
for  the  storage  or  handling  of  film  should  be  completely  equipped 
with  automatic  sprinklers. 

(144)  Every  room  in  which  film  is  stored  or  handled,  except  film 
vaults  and  projection  rooms,  shall  be  provided  with  first-aid  fire  ap- 
pliances of  types  using  water  or  water  solutions. 

Note. — Small  hose  equipment  is  recommended,  and  the  following  types  of  ex- 
tinguishers are  considered  suitable:  soda  acid,  calcium  chloride,  pump  tank, 
water  pails,  and  loaded  stream. 

See  Regulations  on  First-Aid  Fire  Appliances,  and  Standpipe  and  Hose  Systems, 


Nov.,  1938]  PROJECTION  PRACTICE  COMMITTEE  503 

Section  15 — Storage  of  Film 

(151)  (Unchanged)  The  storage  of  motion  picture  film,  not  in 
process  or  being  worked  upon,  and  except  as  hereinafter  specifically 
provided  shall  be  in  accordance- with  the  following  rules: 

(a)  Except  as  provided  in  paragraph  (6): 

(1)  Amounts  in  excess  of  25  pounds  (5  standard  rolls  but  not  in  excess 
of  1000  pounds  (200  standard  rolls)  shall  be  kept  in  approved  cabinets 
if  not  in  vaults; 

(2)  Amounts  in  excess  of  1000  pounds  shall  be  kept  in  vaults; 

(3)  Storage  for  any  considerable  length  of  time  should  be  in  vaults  only. 

(b)  Unexposed  film   enclosed  in  the  original  shipping  cases,  conforming  to 
I.  C.  C.  regulation  with  each  roll  in  a  separate  container,  shall  be  kept  in  a 
sprinkler  room,  and  if  over  5  cases  aggregating  in  excess  of  750  pounds  (150 
standard  rolls)  shall  be  kept  in  a  sprinklered  room  used  for  no  other  purpose. 

Section  18— Handling  of  Film 

(181)  (Unchanged)  Film  shall  be  in  containers.    All  film  shall  be 
kept  in  closed  containers  except  during  the  actual  time  it  is  being 
worked  upon  or  examined.     This  is  very  essential  from  the  standpoint 
of  fire  hazard  and  safety  to  life.    I.  C.  C.  shipping  containers  and  in- 
dividual containers  for  each  roll  of  film  with  proper  corrugations  on 
each  side  are  recommended. 

(182)  (Unchanged)  Film  shall  not  be  placed  or  kept  under  benches, 
tables,  or  other  surfaces  that  would  shield  it  from  the  discharge  of 
sprinklers. 

(183)  (Unchanged)  Scrap  Film. — Scrap  film  shall  be  kept  separate 
from  waste  paper  and  other  rubbish,  and  shall  be  kept  under  water  at 
all  times.    It  shall  be  collected  from  work  rooms  at  least  once  daily, 
and  removed  to  a  room  used  for  no  other  purpose,  where  it  shall  be 
kept  under  water  in  steel  drums  with  tight  covers.    These  drums  shall 
be  disposed  of  at  frequent  intervals.    Discarded  film  in  full  or  part  rolls 
shall  be  kept  in  vaults.    Scrap  film  shall  not  be  baled  or  burned. 

Note. — Motion  picture  film  in  the  form  of  clippings  and  short  lengths  is  in  a 
very  hazardous  form.  Safe  precautions  in  the  handling  of  such  scraps  are  most 
essential.  Baling  and  burning  of  film  are  processes  offering  a  distinct  fire  hazard. 
Sending  film  to  a  central  reclaiming  plant  is  recommended  in  lieu  of  burning. 

Section  19 — Motion  Picture  Projection  and  Special  Processes 

(191)  (Rewritten)  Permanent  Enclosures  for  Motion  Picture  Pro- 
jectors.— Enclosures  are  classified  into  two  types,  permanent  and  tem- 
porary. The  permanent  type  of  enclosure  in  permanent  installations 


504  PROJECTION  PRACTICE  COMMITTEE         [J.  S.  M.  P.  E. 

are  known  as  Projection  Rooms;  the  temporary  type  of  enclosure  as 
Temporary  Projection  Booths.  (See  Sec.  192.) 

(a)  Projection  Rooms. — Motion  picture  projectors  using  nitrocel- 
lulose film  in  structures  or  buildings  definitely  intended  for  motion 
picture  exhibition  purposes  shall  be  operated  or  set  up  for  operation 
only  within  an  approved  projection  room.  For  one  machine  the 
projection  room  shall  be  not  less  than  8  feet  wide  by  10  feet  deep  by 
8  feet  high;  and  for  two  machines,  not  less  than  14  feet  wide  by  10 
feet  deep  by  8  feet  high.  Not  less  than  30  inches  of  clear  aisle  space, 
where  walking  is  necessary,  shall  be  allowed  between  any  two  pieces 
of  equipment  or  between  projectors. 

Note. — Motion  picture  projectors  capable  of  operating  only  with  35-mm.  cellu- 
lose acetate  film  (i.  e.,  slow-burning  or  non-inflammable  film)  may  be  operated 
without  an  enclosure  but  only  by  permission  of  local  authorities  having  jurisdic- 
tion. 

(6)  The  projection  room  walls  shall  be  built  of  brick,  tile,  or  plaster 
blocks  plastered  on  the  inside  with  3/4  inch  of  cement  plaster,  or  all 
concrete.  The  core  of  the  wall  shall  be  not  less  than  4  inches 
thick.  When  plaster  block  is  used  it  shall  be  supported  upon  a  steel 
framework. 

The  ceiling  shall  be  constructed  of  4-inch  concrete  slabs  or  precast 
concrete;  it  may  be  constructed  of  3 -inch  plaster  blocks  supported 
by  a  steel  structure  and  plastered  on  the  inside  with  3/4  inch  of  cement 
plaster. 

Note. — Approved  fire-proof  acoustic  material  may  be  used  on  ceiling  and  walls 
above  a  height  of  4  feet  from  the  floor. 

The  floor  shall  be  a  reenforced  concrete  slab  not  less  than  4  inches 
thick. 

All  projection  room  construction  shall  be  supported  upon  or  hung 
from  fire-proof  structural  steel  or  masonry. 

All  exposed  steel  shall  be  covered  with  a  minimum  of  I1/*  inches  of 
cement  plaster. 

(c)  Two  doors  shall  be  provided,  one  at  each  end  of  the  projection 
room,  each  at  least  30  inches  wide  by  6  feet  high.  They  shall 
be  of  the  approved  one-hour  fire-test  type  and  shall  be  arranged  so 
as  to  close  automatically,  swinging  outwardly,  and  shall  be  kept  closed 
at  all  times  when  not  used  for  egress  or  ingress.  It  shall  be  possible 
at  all  times  to  open  either  door  from  the  inside  merely  by  pushing  it. 
Door  jams  shall  be  of  steel. 

These  exits  shall  be  provided  strictly  in  accordance  with  regula- 


Nov.,  1938]  PROJECTION  PRACTICE  COMMITTEE  505 

tions  of  local  authorities  having  jurisdiction,  particularly  with  refer- 
ence to  other  sizes  and  locations.  At  least  one  of  these  exits  should 
be  of  the  conventional  stairway  tyrje,  with  risers  not  in  excess  of  9 
inches  and  a  minimum  tread  to  each  step  of  not  less  than  7  inches. 
Stairs  shall  be  sufficiently  wide  to  permit  easy  egress. 

(d)  Two  orifices  or  openings  for  each  motion  picture  projector  or 
stereopticon  shall  be  provided:     one   for   the   projectionist's  view 
(observation  port)  shall  be  not  larger  than  200  square-inches,  and  the 
other,  through  which  the  picture  is  projected  (projection  port)  shall 
be  not  larger  than  120  square-inches.    Where  separate  spotlight  or 
floodlight  machines  are  installed  in  the  same  projection  room  with 
motion  picture  projectors,  not  more  than  one  port  opening  for  each 
such  machine  shall  be  provided  for  both  the  operator's  view  and  for 
the  projection  of  the  light,  but  two  or  more  machines  may  be  operated 
through  the  same  port  opening.    Such  port  openings  shall  be  as  small 
as  practicable,  and  in  any  case  shall  not  exceed  7J/2  square-feet  in 
area. 

(e)  Each  port  opening  shall  be  provided  with  a  gravity  shutter  of 
approved  construction.    Said  shutter  and  guides  shall  be  made  of  not 
less  than  10-gauge  iron,  and  the  shutter  shall  set  into  the  guides  not 
less  than  1  inch  at  sides  and  bottom  and  overlap  the  top  of  the  port 
opening  by  not  less  than  1  inch,  when  closed.    (See  Fig.  5.)    Shutters 
shall  be  suspended,  arranged,  and  interconnected  so  that  all  port 
shutters  will  close  upon  the  operating  of  some  suitable  fusible  or 
mechanical  releasing  device,  designed  to  operate  automatically  in 
case  of  fire  or  other  contingency  requiring  immediate  and  complete 
isolation  of  the  contents  of  the  projection  room  from  other  portions 
of  the  building.     Each  shutter  shall  have  its  own  individual  fusible 
link  directly  above  it.    A  fusible  link  shall  be  located  also  above  each 
upper  projector  magazine,  which  upon  operating  shall  close  all  the 
shutters.    There  shall  also  be  provided  suitable  means  for  manually 
closing  all  shutters  simultaneously  from  any  projector  head  and  from 
a  point  near  either  door  within  the  projection  room.    Shutters  shall 
be  free-acting  and  regularly  tested.    Shutters  on  openings  not  in  use 
shall  always  be  kept  closed. 

(/)  All  shelves,  furniture,  and  fixtures  within  the  projection  room 
shall  be  constructed  of  metal  or  other  incombustible  material.  Tables 
shall  be  in  accordance  with  Section  117.  No  stock  of  inflammable 
material  of  any  sort  whatever  shall  be  permitted  or  allowed  to  be 
within  the  projection  room,  except  what  is  required  for  the  regular 


506  PROJECTION  PRACTICE  COMMITTEE        [j.  s.  M.  P.  E. 

and  immediate  operation  of  the  equipment,  the  films  used  in  the 
operation  of  the  machines,  and  film  cement.  (See  Sec.  214.) 

(g)  In  permanent  projection  rooms,  ventilation  shall  be  provided 
for  the  arc  lamps  independently  of  the  general  and  emergency  venti- 
lating system  of  the  room.  Each  projector  arc  lamp  housing  shall  be 
connected  by  a  flue  to  a  common  duct,  which  duct  shall  lead  directly 
out  of  doors  and  shall  contain  an  exhaust  fan  or  blower  having  a 
capacity  of  at  least  50  cubic-feet  per  minute  of  air  for  each  projector 
arc  lamp  connected  thereto.  This  exhaust  fan  or  blower  shall  be 
electrically  connected  to  the  projection  room  wiring  system  and  con- 
trolled by  a  switch  with  pilot  lamp  within  the  room.  There  shall  at 
no  time  be  less  than  15  cubic-feet  of  air  per  minute  flowing  through 
each  lamp  house  into  the  exhaust  system  connected  to  the  air  outside 
the  building. 

General  ventilation  of  the  projection  room  shall  be  provided  by  a 
duct  having  outlets  at  one  or  more  points  in  the  ceiling  and  leading 
directly  to  the  outer  air.  Said  duct  shall  be  capable  of  maintaining 
a  natural  circulation  of  air,  without  blower  or  fan,  at  a  rate  of  not 
less  than  20  cubic-feet  per  minute.  Auxiliary  circulation  in  said 
duct  shall  be  provided  by  an  exhaust  fan  or  blower  having  a  capacity 
of  not  less  than  200  cubic-feet  per  minute  for  normal  circulation  and 
having  a  rated  capacity  of  not  less  than  2000  cubic-feet  per  minute 
for  operation  in  emergency,  i.  e.,  fire.  In  no  case  shall  the  exhaust 
duct  system  of  the  room  be  connected  with  the  ventilating  system  of 
the  building  proper.  The  emergency  operation  of  said  fan  shall  be 
controlled  by  a  switch  operated  automatically  by  the  shutter  control 
mechanism  when  the  latter  is  operated  either  manually  or  by  melt- 
ing of  the  fusible  links.  This  exhaust  fan,  providing  general  and 
emergency  ventilation  of  the  projection  room,  shall  be  connected  to 
the  emergency  lighting  circuit  of  the  room,  and  shall  be  controlled 
for  normal  circulation  by  a  switch  and  pilot  lamp  within  the  room. 

The  ducts  shall  be  of  incombustible  material,  and  shall  be  kept  at 
least  2  inches  from  combustible  material  or  separated  therefrom  by 
approved  non -combustible  heat-insulating  material  not  less  than  1 
inch  thick. 

Projection  rooms  shall  have  two  or  more  separate  fresh-air  intake 
ducts  at  or  near  the  floor  and  at  opposite  ends  of  the  room,  entirely 
independent  of  and  in  no  way  connected  to  the  exhaust  ducts  of  the 
room.  Such  air  intake  ducts  may  be  connected  into  the  main  venti- 
lating system  of  the  building. 


Nov.,  1938]  PROJECTION  PRACTICE  COMMITTEE  507 

(192)  (Delete)  Not  more  than  five  motion  picture  projectors  shall 
be  located  in  one  room,  unless  the  projectors  are  of  a  type  using 
incandescent  electric  lights  of  not  over*  25-watt  size,  when  not  more 
than  ten  projectors  shall  be  located  in  one  room. 

(192)  (New  Section)  Temporary  Projection  Booth. — Motion  picture 
projectors  using  nitrocellulose  film,  when  used  in  other  places  than  in 
permanent  enclosures,  (i.  e.,  in  projection  rooms),  shall  be  set  up  and 
operated  in  a  temporary  enclosure  known  as  a  Temporary  Projection 
Booth.  However,  such  temporary  projection  booths  shall  be  installed 
only  by  permission  of  local  authorities  having  jurisdiction,  and  then 
only  for  a  limited  number  of  exhibitions  of  motion  pictures  in  a  struc- 
ture or  building  suitable  therefor  and  not  regularly  licensed  for  such 
purpose.  In  no  case  shall  temporary  projection  booths  be  allowed  as 
part  of  the  structures  or  buildings  definitely  intended  for  motion  pic- 
ture exhibition  purposes. 

(a)  Temporary  projection  booths  shall  conform  to  Section  191  (a) 
with  regard  to  dimensions. 

(b)  The  sides,  walls,  and  ceiling  shall  be  constructed  of  Y^inch 
hard  sheet  asbestos  board,  and  the  floor  of  3/8-inch  hard  sheet  asbestos 
board,  the  whole  securely  riveted  or  bolted  to  a  rigid  metal  frame  of 
not  less  than  1 V4  by  1  */4  by  l/±-moh.  angle-irons  properly  braced.    The 
sheet  asbestos  boards  shall  sheath  the  entire  interior  of  the  frame 
work,  and  no  metal  frame  supports  shall  be  allowed  to  remain  ex- 
posed within  the  enclosure.    All  joints  shall  be  made  as  air-tight  as 
possible  to  prevent  the  discharge  of  smoke. 

(c)  One  entrance  door  shall  be  provided  which  shall  conform  to  the 
requirements  for  the  main  entrance  door  of  Section  191  (c)  with  the 
following  exceptions : 

(1)  the  fire  resistance  of  the  door  shall  be  equivalent  to  the  fire  resistance  of 
the  rest  of  the  construction,  and 

(2)  clear  aisle  space  or  passageway  shall  be  provided  around  the  projection 
booth  and  from  the  entrance  door  thereof  to  the  nearest  exit  of  the  structure  or 
building  in  which  the  projection  booth  is  installed. 

(d)  Observation  and  projection  ports  shall  conform  to  the  specifica- 
tions of  Section  191  (d). 

(e)  Port  shutters  shall  conform  to  the  requirements  of  Section  191. 
(/)  All  shelves,  furniture,  and  fixtures  within  the  projection  room 

shall  conform  to  the  requirements  of  Section  191  (/).      There  shall 
additionally  be  provided  an  approved  can  for  scrap  film,  having  an 


508  PROJECTION  PRACTICE  COMMITTEE        [j.  s.  M.  P.  E. 

automatically  closing  hinged  cover;  also  a  similar  container  for  re- 
ceiving hot  carbon  stubs,  said  container  to  be  partly  filled  with  sand. 

(g)  The  ventilation  system  of  the  temporary  projection  booth  shall 
conform  to  all  the  requirements  of  Section  191(g). 

(h)  Rewinding  film  in  temporary  projection  booths,  as  in  perma- 
nent, shall  be  done  in  accordance  with  Section  212(c). 

(i)  Quantity  of  film  contained  within  a  temporary  projection  booth 
shall  be  in  accordance  with  Sub-Section  213(a)(3). 

(j)  Projection  equipment  in  temporary  projection  rooms  shall  be 
operated  in  accordance  with  Section  213. 

(193)  Processing  Film. — The  processing  of  film,  as  cleaning,  polish- 
ing, buffing,  and  other  special  treatment,  shall  not  be  done  in  rooms 
where  other  operations  are  performed,  except  that  in  the  case  of  motion 
picture  theaters,  such  processing  or  cleaning  of  film  shall  be  done  in  the 
rewind  room.  See  Section  212  (a). 

Special  processes  for  treating  film  shall  be  provided  with  such 
proper  safeguards  as  are  necessary  for  protection  against  the  haz- 
ards involved.  The  inspection  department  having  jurisdiction  shall 
be  consulted  in  regard  to  the  protection  needed. 

(196)  (Unchanged)   Film   Cement. — Compounds   of   all   collodion, 
amyl  acetate,  or  similarly  inflammable  cements  shall  not  be  kept  in 
the  rooms  where  they  are  used,  in  quantities  greater  than  1  quart; 
and  such  material  in  excess  of  this  quantity  shall  be  kept  in  a  vault. 
The  use  of  these  materials  in  motion  picture  theaters  and  other 
special  occupancies  is  covered  in  Sub-Section  214. 

(197)  (Unchanged)  Smoking. — Smoking,  except  in  rooms  especially 
provided  for  the  purpose,  should  be  prohibited  in  any  establishment 
handling  or  storing  film,  and  conspicuous  No  Smoking  signs  should  be 
posted  in  prominent  places.    Matches  should  not  be  carried  by  any 
employee. 


PART  II 
SPECIAL  PROVISIONS  FOR  SPECIAL  OCCUPANCIES 

Section  21 — Motion  Picture  Theaters  and  Other  Occupancies  in  Which  the 
Principal  Use  of  Film  Is  in  Motion  Picture  Projection 

(211)  Enclosure  for  Projectors. — Motion  picture  projectors  shall  be 
installed  in  a  projection  room  in  accordance  with  Sub-Section  191. 

(212)  (Rewritten)  Rewinding. — (a)  Rewinding  film  is  permitted  in 
permanent   projection   rooms    (but  not   recommended)    when   pro- 


Nov.,  1938]  PROJECTION  PRACTICE  COMMITTEE  509 

jectors  and  lamps  are  not  in  use.  There  shall  be  provided  an  approved 
can  for  scrap  film,  having  an  automatically  closing  hinged  cover. 
When  rewind  table  and  approved  film  cabinets  are  in  the  projection 
room,  such  table  and  cabinets  must  be  at  least  30  inches  from  the 
rear  of  any  projector. 

(b)  Where  rewinding  of  film  in  permanent  installations  is  done 
in  a  separate  room,  at  approved  location  adjacent  to  or  near  the 
projection  room,  such  rewinding  rooms  shall  be  of  construction  similar 
to  that  of  the  permanent  projection  room,  as  specified  in  Sub-Section 
191 .    Such  room  shall  be  not  less  than  80  square-feet  in  area  and  shall 
have  clear  walking  spaces  not  less  than  30  inches  wide.    The  venti- 
lating system  shall  be  connected  directly  to  the  outside  air  and  shall 
conform,  as  to  capacity,  to  the  specifications  of  Sub-Section  191  (g), 
and  may  be  combined  with  the  general  ventilation  system  of  the 
projection  room. 

(c)  Rewinding  film  shall  not  be  done  in  temporary  projection 
booths  except  when  projectors  and  lamps  are  not  in  use  and  are  cool. 

(213)  (Unchanged)  Care  and  Use  of  Film. — Motion  picture  film 
used  in  connection  with  the  projection  of  motion  pictures  (as  in 
theaters,  motion  picture  theaters,  screening  or  projection  rooms, 
sound  recording  studios,  and  motion  picture  titling  studios)  shall  be 
limited  and  kept  as  follows : 


(a)  (Rewritten)  The  quantity  of  film  in  any  projection  room  or  booth  or  re- 
winding room  shall  be  limited  to  that  given  below: 

(1)  (Rewritten)    In  a  projection  room,  constructed  to  conform  to  Section 
191:  not  exceeding  125  pounds  (25,000  feet  of  35-mm.  film); 

(2)  (  Unchanged)  In  a  rewinding  room  constructed  and  vented  to  conform  to 
Section  191  and  Sub-Section  212  (b)  and  separated  from  the  projection  room 
with  openings  thereto  protected  with  approved  fire  doors:  not  exceeding  125 
pounds  (25,000  feet  of  35-mm.  film); 

(3)  (Rewritten)  In  a  temporary  projection  booth,  constructed  to  conform 
to  Section  192:  not  exceeding  75  pounds  (15  feet  of  35-mm.  film); 

(4)  (Rewritten)  In  a  special  room  constructed  and  vented  as  required  for 
rewinding  rooms  (see  Sub-Sec.  212),  when  approved  by  the  inspection  de- 
partment having  jurisdiction:  not  exceeding  125  pounds  (25,000  feet  of  35-mm. 
film)  may  be  kept  in  lieu  of  the  amount  permitted  in  either  the  projection  room 
or  the  rewinding  room.     The    total  quantity  in  the  three  rooms  shall  not 
exceed  250  pounds  (50,000  feet  of  35-mm.  film). 

(b)  The  above  quantities  of  film  shall  be  kept  as  follows: 

(1)  Up  to  40  pounds  (8000  feet  of  35-mm.  film)  of  film  may  be  kept  in 
Interstate  Commerce  Commission  shipping  containers,  or  approved  cabinet 
in  each  room; 


510  PROJECTION  PRACTICE  COMMITTEE 

(2)  If  the  amount  of  film  on  hand  exceeds  40  pounds,  an  approved  cabinet 
shall  be  provided,  in  which  the  amount  of  film  in  excess  of  40  pounds  shall  be 
kept. 

(214)  (Unchanged)  No  collodion,  amyl  acetate,  or  other  similar 
inflammable  cement  or  liquid  in  quantities  greater  than  1/2  pint  shall 
be  kept  in  the  projection  room  or  rewinding  room. 

(215)  (New  Section)  All  splices  of  film  shall  be  made  on  approved 
mechanical  cutting  and  splicing  machines  in  approved  manner.    No 
hand  cutting  or  splicing  shall  be  permitted. 

(216)  (Unchanged)  Location. — The  number  and  location  of  mo- 
tion picture  projection  rooms  or  booths  in  any  non-sprinkler ed  build- 
ing shall  be  subject  to  the  approval  of  the  inspection  department  hav- 
ing jurisdiction. 

(217)  (New  Section)  Operation. — Motion  picture  projectors  in  per- 
manent or  temporary  projection  rooms  shall  be  operated  by  and  shall 
be  in  charge  of  qualified  projectionists,  who  shall  not  be  minors. 

(218)  (New  Section)  Action  in  Case  of  Fire. — In  the  event  of  film 
fire  in  the  projector  or  elsewhere  in  a  projection  or  rewind  room,  the 
projectionist  shall  immediately  shut  down  the  projection  machine  and 
arc  lamp,  operate  the  port  shutter  release  at  the  nearest  point  to  him, 
turn  on  the  auditorium  lights,  leave  the  projection  room  promptly, 
and  notify  the  manager  of  the  theater  or  building. 

REFERENCE 

1  Report  of  Projection  Practice  Committee,  J.  Soc.   Mot.  Pict.  Eng.,  XXV 
(Oct.,  1935),  No.  4,  p.  341. 

SUB-COMMITTEE  ON  FIRE  REGULATIONS 

S.  HARRIS,  Chairman 

A.  S.  DICKINSON  M.  GESSIN  P.  J.  LARSEN 

J.  FRANK,  JR.  A.  GOODMAN  P.  A.  McGuiRE 

R.  R.  FRENCH  J.  J.  HOPKINS  E.  MORIN 


NEW  MOTION  PICTURE-  APPARATUS 

During  the  Conventions  of  the  Society,  symposiums  on  new  motion  picture  appara- 
tus and  materials  are  held  in  which  various  manufacturers  of  equipment  describe  and 
demonstrate  their  new  products  and  developments.  Some  of  this  equipment  is  de- 
scribed in  the  following  pages;  the  remainder  will  be  published  in  subsequent  issues 
of  the  Journal. 

ANEW  SOUND  SYSTEM* 
G.  FRIEDL,  JR.** 

Recent  improvements  in  film  recording  technic  have  made  practically  obsolete 
the  older  types  of  theater  reproducing  equipments  that  do  not  employ  high- 
power  amplifiers,  rotary  stabilizer  sound  mechanisms,  and  multicellular  loud 
speakers.  Since  the  commercial  introduction  of  sound  motion  pictures,  various 
equipment  changes  have  been  introduced,  mostly  as  modification  to  existing 
equipment,  making  the  original  apparatus  more  suitable  for  the  particular  ap- 
plication of  reproducing  sound  in  motion  picture  theaters.  With  such  moderni- 
zation, however,  it  is  often  difficult  to  effect  an  overall  improvement  without 
making  radical  and  expensive  changes  in  all  the  components  of  the  system. 
For  example,  when  the  frequency  range  of  the  amplifier  is  extended  it  is  neces- 
sary to  modify  the  loud  speaker  system  so  that  it  will  adequately  transform  and 
distribute  the  increased  range,  and  it  is  also  necessary  to  modify  the  sound  mecha- 
nism or  reproducer  set  to  insure  uniform  film  movement  at  the  scanning  beam 
so  that  high  frequencies  will  be  reproduced  without  harshness  or  flutter.  Such 
changes,  when  carried  through  consistently  and  effectively,  become  very  expen- 
sive, and  a  point  is  reached  where  it  is  economically  impracticable  to  attempt  fur- 
ther "patching-up"  of  the  system.  Complete  replacement  is  therefore  more 
desirable.  This  is  of  significance  to  the  small  theater  owner  whose  equipment  is 
not  adequate  to  reproduce  properly  the  pictures  now  being  produced  by  Holly- 
wood. Recognizing  the  importance  of  making  available  reasonably  priced 
reproducing  equipment  that  will  provide  sufficient  volume  and  life-like  reproduc- 
tion equivalent  to  that  generally  found  only  in  the  largest  theaters,  this  new 
sound  system  has  been  produced. 

DESIGN  REQUIREMENTS 

General. — The  Simplex  Sound  System  is  built  to  present-day  requirements  de- 
termined after  a  survey  made  in  cooperation  with  persons  who  are  conversant 
with  the  actual  operating  conditions  of  the  theater — it  is  built  for  theater  usage , 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;   received 
September  20,  1938. 

'*  International  Projector  Corp.,  New  York,  N.  Y. 

511 


512 


NEW  MOTION  PICTURE  APPARATUS        [J.  S.  M.  P.  E. 


and  is  not  an  adaptation  of  apparatus  built  for  other  fields.  High  quality 
dependability,  easy  operation,  economical  maintenance,  and  installation  are  para- 
mount features.  The  practice  of  making  equipment  of  sub-standard  quality  in 
order  to  place  it  in  a  suitable  competitive  price  class  for  the  small  theater  is 
avoided.  All  the  features  that  contribute  to  sound  reproduction  of  the  highest 
quality  are  included  in  every  system.  The  variables  that  distinguish  one  size  of 
system  from  another  are  the  number  of  power  amplifiers  operating  in  parallel  to 
provide  the  proper  output,  and  the  number  and  types  of  loud  speakers  to  provide 
adequate  capacity  and  distribution. 

In  analyzing  the  requirements  of  film  reproducing  systems  for  the  theater,  the 
equipment  has  been  divided  into  four  groups,  viz.,  the  sound  mechanism  equip- 


Constants 


Variables 


Small 

(1000  Seats) 
(84%) 


Medium 
(2000  Seats) 
(13%) 

Large 

(4000  Seats) 
(3%) 


Sound  Mechanism 

Control 

Power  Amplifier 

Loud  Speaker 

Equipment 

Equipment 

Equipment 

Equipment 

35-Mm.  film 

Change-over 

1%  Total  harmonic 

Two-way  system 

30  Feet/minute 

2000-Ft.  reels 

at  50  cycles 

400-Cycle    cross- 

Standard, push-pull 

Volume  control  at 

-35  Db.  noise  level 

over 

Dual  channel 

each  machine 

Multicellular  horn 

2-3  Sec.  pick-up 

±0.15%  total  flutter 

None 

None 

Power 

Power,  Coverage 

Identical 

Identical 

throu 

fhout 

throu 

jhout 

a 

A 

(15  watt) 

B 

2a 

2A 

(30  watt) 

2B 

4fl 

2C 

(60  watt) 

4D 

FIG.  1.     Analysis  of  design  requirements. 


ment,  control  equipment,  power  amplifier  equipment,  and  loud  speaker  equipment, 
as  shown  in  Fig.  1. 

The  tabulation  is  divided  into  three  horizontal  sections  representing  the  small, 
the  medium,  and  the  large  theaters,  and  at  the  head  of  each  equipment  group  are 
shown  the  salient  requirements  or  "constants"  of  design.  Under  "Sound  Mecha- 
nism," regardless  of  the  size  of  theater,  the  equipment  is  to  operate  with  35-mm. 
film  running  90  feet  a  minute;  it  is  to  reproduce  standard  track  and  be  adaptable 
to  push-pull  and  "dual  track"  reproduction  with  simple  modification;  it  must 
come  up  to  speed  in  2  to  3  seconds,  and  the  flutter  and  weave  should  be  held  to 
the  same  low  limits.  There  are  no  "variables" ;  that  is,  there  is  no  reason  to  relax 
on  any  of  the  requirements  for  smaller  theaters.  Thus  one  policy  of  the  design 
is  established — the  sound  mechanism  shall  be  identical  for  the  small,  the  medium, 
and  the  large  systems. 


Nov.,  1938] 


NEW  MOTION  PICTURE  APPARATUS 


513 


The  requirements  of  the  "Control  Equipment"  include  the  apparatus  for  volume 
control  and  change-over.  With  the  standardization  of  2000-ft.  release  print  reels 
the  same  number  of  change-overs  is  required  in  the  small  theater  as  in  the  large 
theater,  and  the  change-over  should  be  made  with  the  same  accuracy  and  facility. 
Convenient  volume  control  should  be  provided  at  each  machine.  These  are  the 
"constants"  of  the  equipment  design;  there  are  no  "variables."  Thus  the  second 
policy  of  the  design  is  established — the  control  equipment  shall  be  identical  for 
the  small,  medium,  and  large  systems. 

At  this  point  the  question  may  be  raised,  "What  are  the  justifiable  differences 
between  small,  medium,  and  large  systems?"  Technically  speaking  there  are  none. 
It  would  be  best  to  have  all  systems  alike  because  the  more  undistorted  power 
available,  the  greater  is  the  factor  of  safety  against  overload  and  the  more  adapt- 


SOUND  CONTPOL 

MCCHAN1SM  fQUIPMENT 


LOUDSPCAKtBS 


r 

L — -i        i—i        !_-! 


FIG.  2.     Schematic  diagram  of  system. 


able  will  be  the  system  to  future  developments.  But  due  to  commercial  considera- 
tions we  must  provide  a  group  of  systems  offering  economical  combinations  for 
each  size  of  theater  with  high-power  systems  for  the  small  theaters  as  well  as  the 
larger  ones.  Thus  we  generally  establish  the  main  "variable"  of  design — power. 
This  is  a  quantitative  variable  only;  qualitatively  the  power  for  all  systems  must 
be  the  same.  The  quality  in  the  small  theater,  so  far  as  the  amplifier  is  concerned, 
should  be  just  as  good  as  in  the  larger  theaters.  Referring  again  to  Fig.  1  it  will  be 
noted  under  "Power  Amplifier  Equipment"  that  the  requirements  of  permissible 
harmonic  distortion,  noise  level,  and  hum  content  are  the  "constants"  of  design. 
The  "variable,"  power,  is  indicated  as  a  for  the  small  system,  2a  for  the  medium 
system,  and  4a  for  the  large  system.  To  concentrate  on  the  development  of  an 
amplifier  that  would  meet  these  requirements,  a  single  amplifier  was  designed  for 
use  on  a  unit  basis — that  is,  one  unit  for  the  small  system,  two  units  in  parallel  for 
the  medium  system,  and  four  units  in  parallel  for  the  large  system,  all  of  the  same 


514 


NEW  MOTION  PICTURE  APPARATUS        [J.  S.  M.  P.  E. 


quality.    The  total  harmonic  distortion  is  less  than  1  per  cent  with  the  amplifier 
delivering  rated  power  at  50  cycles. 

Under  "Loud  Speaker  Equipment,"  power  is  again  the  variable  factor.  The 
main  interest  is  to  provide  loud  speakers  that  will  handle  the  power  delivered  to 
them  by  the  amplifiers  and  convert  it  into  acoustical  energy  efficiently,  thus  pro- 


40 


38 


34 


24 


•MO 

*5 

3 
*     0 

«- 


SMALL 


MEDIUM 


LARGE 


60 


30 


<00  200  500  (000  2000  AOOO 

SEATING  CAPACITY  OF  THEATRE    (NUMBER  OF  SEATS) 


40    5   6  7  8  9  100 


2          3      456789  »000  2 

FREQUENCY  IN  CYCLES  PEP  SECOND 


3      456  7094000 


FIG.  3  {Upper)  Recommended  amplifier  output  in  electri- 
cal watts  in  terms  of  seating  capacity  of  theater  (Research 
Council,  Academy  of  Motion  Picture  Arts  &  Sciences.) 

FIG.  4  (Lower}  Academy  standard  electrical  characteris- 
tic for  two-way  reproducing  systems  in  theaters. 


ducing  sufficient  loudness  in  the  auditorium.  Coverage  is  also  a  variable  factor, 
depending  upon  the  proportions  of  the  theater.  The  important  "constants"  of 
design  are  met  by  the  use  of  two-way  speaker  systems  with  multicellular  high- 
frequency  horns  and  folded  low-frequency  horns  in  all  systems,  adhering  to  the 
general  principles  of  the  most  acceptable  systems  used  today.1  The  cross-over 
frequency  of  400  cycles  is  standard  for  all  systems.  This  and  other  "constants" 
are  shown  in  Fig.  1  under  the  "Loud  Speaker  Equipment"  column.  The 


Nov.,  1938] 


NEW  MOTION  PICTURE  APPARATUS 


515 


various  loud  speaker  combinations  are  also  shown.  The  small  system  employs 
one  A  type  high-frequency  unit  and  one  B  type  low-frequency  unit;  the  medium 
system,  two  A  and  two  B  units;  and  the  larger  system,  two  Cand  four  D  units. 
The  C  and  D  units  differ  from  the  A  and  B  mainly  in  power-carrying  capacity. 


•H5 


4-10 


2    -5 


-10 


-20 


-25 


L-l 


3       43676  3K>,000 


40     5    6  7  8  9  K>0  2          3       456789 1000 

FREQUENCY  IN  CYCLES  PER  SECOND 

FIG.  5.     Electrical  characteristic  of  Simplex  sound  systems. 


H-2 


H-3 


H-4 


Fig.  2  is  a  schematic  diagram  of  the  system.  The  systems  are  engineered  for 
two-projector  installations  which  represent  the  majority  of  the  cases,  but  a  third 
projector  can  be  added  as  shown  by  the  broken  lines.  The  power  unit  supplies 
exciter  lamp  power  for  two  or  three  projectors.  The  control  equipment  consists 
of  one  volume  control  and  change-over  unit,  supplied  with  each  machine;  a 


PROJECTION  ROOM 


FIG.  6.     Typical  conduit  layout. 


third  unit  can  be  added  for  the  third  projector  position.  The  outputs  of  the 
volume  control  amplifiers  are  connected  to  the  main  power  amplifier — the  single- 
unit  amplifier  is  used  in  the  small  system.  In  the  medium-size  system  another 
amplifier  is  added,  as  indicated  by  the  broken  lines ;  and  in  a  still  larger  system  the 
third  and  fourth  amplifiers  are  added  as  shown.  The  two-way  network  and  the 


516 


NEW  MOTION  PICTURE  APPARATUS        [J.  S.  M.  P.  E. 


monitor  speaker  in  the  projection  room  are  shown  in  solid  lines,  as  they  are  used 
in  all  systems.  The  loud  speakers  for  the  small  system  consist  of  one  low-fre- 
quency and  one  high-frequency  unit ;  for  the  larger  systems,  to  accommodate  the 
increased  power  of  additional  amplifiers,  greater  power-handling  capacity  is  pro- 
vided by  adding  high-  and  low-frequency  units,  as  shown  in  broken  lines. 

Academy  Electrical  Characteristic. — In  addition  to  studying  the  field  conditions 
and  requirements  with  experts  in  the  theater  field,  conferences  were  held  with 
studio  technicians  and  the  Research  Council  of  the  Academy  of  Motion  Picture 
Arts  &  Sciences.  The  work  of  the  Council  Committee  on  Theater  Standardiza- 


FIG.  7.  (Upper)     Sound  mechanism,  operating  side. 
FIG.  8.  (Lower)     Same,  non-operating  side. 


tion  is  well  known.  Under  the  Chairmanship  of  J.  K.  Hilliard,  the  Committee 
has  set  up  and  adjusted  various  types  of  reproducing  systems  to  sound  reasonably 
alike,  and  from  these  experiments  an  average  electrical  characteristic  for  film  re- 
producing systems  has  been  established.2  The  primary  objective  of  this  work  was 
to  determine  what  considerations  were  required  to  insure  uniformly  good  repro- 
duction of  the  products  of  various  Hollywood  studios  in  the  small  as  well  as  the 
large  theaters.  Unfortunately,  the  past,  where  reproduction  by  small  theater 
equipment  has  been  inferior  to  that  of  large  theater  equipment,  the  dramatic 
appeal  of  many  productions  has  been  impaired.  This  has  quite  seriously  af- 
fected the  general  acceptance  of  some  features  as  the  small  theaters  (under  1000 
seats)  represent  at  least  84  per  cent  of  the  houses  in  the  country.  The  medium- 


Nov.,  1938] 


NEW  MOTION  PICTURE  APPARATUS 


517 


size  theaters  (1000  to  2000  seats)  represent  about  13  per  cent,  and  the  larger 
theaters  (over  2000  seats)  about  3  per  cent.3  Our  interest  has  been  to  develop 
good  equipment  for  the  small  and  medium-sizextheaters  as  well  as  for  the  large 
theaters.  To  assist  further  in  a  coordinated  program,  the  Academy  Committee 
has  summarized  general  requirements  for  theater  reproducing  equipment.  These 
have  been  carefully  regarded  throughout  the  design. 

With  respect  to  power  output  level,  there  have  been  established  certain  re- 
quirements regarding  amplifier  power  for  theaters  of  different  size.4  Fig.  3  shows 
a  curve  that  has  been  agreed  upon  by  various  groups  working  with  the  Research 
Council.  The  abscissa  shows  seating  capacity  of  the  theater  and  the  ordinate 
power  output  in  decibles  and  in  watts  (0.006-watt  reference  level).  The  solid  line 
is  the  preferred  power  rating;  the  lower  line  represents  the  minimum,  and  the 
upper  line  the  desirable.  In  the  new 
Simplex  systems  these  requirements 
have  been  met  in  the  small  as  well 
as  in  the  medium  and  large  systems, 
with  at  least  15  watts  (34  db.)  for 
the  small,  30  watts  (37  db.)  for  the 
medium,  and  60  watts  (40  db.)  for 
the  large  systems.  Larger  systems 
are  planned  with  the  same  con- 
sideration. 

Although  the  characteristic  of  the 
power  amplifier  may  be  made  flat 
within  ±1  db.  up  to  15,000  cycles, 
experience  indicates  that  theater  sys- 
tems must  be  attenuated  at  high 
frequencies.  Fig.  4  shows  the 
standard  electrical  characteristic 
recommended  by  the  Academy  Com- 
mittee.2 The  lower  curve  represents 
the  average  for  metallic  type  dia- 
phragms, and  the  dotted  curve  the 
average  for  nonmetallic  diaphragms.  Recognizing  that  these  curves  can  not  be 
used  in  all  houses  because  of  the  variation  of  acoustic  conditions,  facilities  have 
been  provided  in  the  design  for  obtaining  other  curves  as  shown  in  Fig.  5.  (The 
two  curves  of  Fig.  4  are  shown  on  Fig.  5  as  H\  and  H3.)  These  characteristics  are 
easily  obtained  by  interconnection  of  elements  provided  as  standard  on  a  con- 
veniently located  terminal  strip.  Many  other  characteristics  can  be  obtained 
by  strapping  the  resistance  and  capacitance  elements  in  other  combinations. 

One  of  the  most  important  developments  in  recording  has  been  the  increase  of 
volume  range,  which  allows  exhibitors  to  realize  the  full  dynamic  sound  response 
and  affords  theater  patrons  complete  realism  in  voice  and  music.  A  reduction  in 
noise  level  as  well  as  the  increase  of  power  is  required  to  accomplish  this.  Each 
amplifier  unit  is  tested,  to  be  assured  that  the  noise  level  is  at  least  as  low  as 
—35  db.  and  that  the  power  output  is  at  least  +34  db.  (15  watts/0.006-watt 
reference  level). 

One  of  the  critical  limitations  to  volume  range  is  the  development  of  extraneous 


FIG.  9.      Volume  control  amplifier. 


518 


NEW  MOTION  PICTURE  APPARATUS        [J.  S.  M.  p.  E. 


noise  in  the  sensitive  amplifier  circuits,  often  caused  by  dirty  and  imperfect  con- 
tacts in  the  sound  circuit  and  by  the  vibration  of  transformer  laminations  in 
circuits  where  iron-core  transformers  and  chokes  are  employed.  In  the  Simplex 
sound  system  the  number  of  mechanical  contacts  in  the  sound  circuit  from  the 
photoelectric  cells  to  the  loud  speaker  voice-coil  has  been  reduced  to  a  minimum. 
The  main  amplifier  gain  adjustment  and  the  sound  change-over  have  been  placed 

in  isolated  circuits.  The  main  amplifier 
gain  adjustment  is  in  the  feedback  circuit 
and  the  change-over  is  accomplished  by 
bias  control  in  the  volume  control  ampli- 
fier. The  individual  volume  controls  at 
the  machines  are  of  special  design,  to 
reduce  the  introduction  of  noise  from  dirty 
sliding  contacts.  The  reduction  of  the 
number  of  transformers  and  chokes  ma- 
terially lowers  the  noise  level  and  greatly 
improves  stability.  The  use  of  a  coaxial 
cable  to  couple  the  photoelectric  cell  and 
the  volume  control  amplifier  further  re- 
duces noise.  The  reduction  of  noise  and 
increase  of  power  are  the  means  through 
which  wide  volume  range  is  obtained. 


DESIGN  FEATURES  AND  DETAILS 

Having  reviewed  the  important  require- 
ments of  present-day  reproducing  equip- 
ments with  brief  reference  to  the  way 
these  requirements  have  been  met  in  this 
new  sound  system,  the  following  is  a  more 
detailed  description  of  the  design  features. 
Fig.  6  is  a  schematic  layout  of  a  typical 
installation,  showing  the  two  projector 
positions  with  the  volume  control  ampli- 
fiers and  change-overs  and  the  main 
amplifier  cabinet  and  the  monitor  located 
in  the  projection  room,  with  the  loud 
speakers  on  the  stage.  Note  the  simplicity 
of  installation,  with  conduits  running  from 
one  position  to  the  other,  terminating  directly  in  the  apparatus  cabinets.  All 
circuits  are  easily  pulled,  the  wires  terminating  in  the  cabinets  without  pulling 
through,  thus  simplifying  installation. 

Another  consideration  was  the  conservation  of  space  in  the  projection  room ; 
with  the  development  of  larger  pedestals  and  larger  lamps  there  is  not  much 
space  available  in  many  projection  rooms.  Space  taken  by  the  amplifier  equip- 
ment was  reduced  by  making  the  cabinet  serviceable  from  the  front,  so  that  the 
equipment  does  not  have  to  stand  out  from  the  wall  in  order  to  provide  space 
in  the  rear  for  access.  All  the  conduits  can  be  concealed  because  the  construction 


FIG.  10.     Volume  control  amplifier 
(open). 


Nov.,  1938] 


NEW  MOTION  PICTURE  APPARATUS 


519 


of  the  cabinets  is  such  that  they  can  be  sunk  partially  into  the  wall  without  inter- 
ferring  with  operation  or  ventilation.  The  wiring  in  the  main  cabinet  is  facilitated 
by  the  elimination  of  cable  forms ;  the  wires  pass  down  behind  the  terminal  strips 
which  are  mounted  on  studs  forming  a  raceway.  Jumpers  between  units  are  very 
easily  installed.  Specially  designed  terminal  punchings  insure  good  connections. 

Fig.  7  shows  the  sound  mechanism,  operating  side.  Film  motion  past  the 
scanning  light -beam  is  controlled  by  the  well  known  rotary  stabilizer  principle, 
insuring  constant  speed.  The  4-ampere,  9- volt  prefocused  exciter  lamp,  of  new 
design,  has  a  short,  sturdily  supported  filament  minimizing  vibration.  The  exciter 
lamp  bracket  is  easily  removable  and  is  designed  to  permit  vertical  and  lateral 
adjustments  for  exact  positioning  of  the  filament.  The  exciter  lamp  compartment 
is  well  ventilated,  and  careful  shielding  prevents  any  stray  light  from  entering  the 
photoelectric  cell  compartment. 

A  highly  efficient  oil-proof  optical  system  projects  a  uniformly  illuminated 
0.084  X  0.0012-inch  image  upon  the  sound-track.  A  micrometer  adjustment  is 


CHANG£OV£R  #t 


3  CHANGEOVER  t^ 


COM. 
A(V.C.A1H)     o- 


C(V.C.A.  ft) 


FIG.  11.     Arrangement  of  change-over  system. 


provided  for  focusing.  The  reflector  directs  the  light-rays  to  the  photocell.  It 
is  a  highly  efficient  ground  and  polished  mirror.  The  guard  ring  around  the  mirror 
minimizes  the  possibility  of  putting  finger  marks  on  the  lens  while  threading.  The 
reflector  is  readily  removable  for  cleaning  and  is  easy  to  adjust. 

The  photoelectric  cell  is  vertically  mounted,  eliminating  vibration  and  micro- 
phonic  noise.  It  is  located  away  from  the  sprockets  and  out  of  the  way  of  thread- 
ing the  machine.  It  is  easily  accessible  for  replacement;  the  front  of  the  housing 
is  hinged  so  that  it  can  be  opened  easily,  exposing  the  cell  completely.  Because 
of  the  cell  position  it  is  impossible  for  oil  to  reach  and  saturate  the  connecting 
wires  and  the  socket,  which  are  well  protected  in  the  cast  photoelectric  cell  arm 
housing,  and  shielded  from  stray  fields  and  static.  The  wires  are  cambric  covered 
to  eliminate  trouble  ordinarily  caused  by  oil  on  wires. 

Lateral  film  guide  and  pressure  rollers  are  equipped  with  a  trigger  control. 
By  merely  pushing  down  on  a  lever  the  roller  locks  in  position,  and  by  a  light 
touch  on  the  lower  lever  it  is  tripped  open.  There  are  no  knobs  or  handles  to  pull 
out  or  turn.  In  open  position  the  roller  is  well  out  of  the  way.  As  a  safety  feature, 
it  has  been  arranged  that  the  film  compartment  door  can  not  be  closed  with  the 
roller  in  open  position. 


520 


NEW  MOTION  PICTURE  APPARATUS        [J.  S.  M.  P.  E. 


The  "sound  bracket"  is  a  unit  assembly  consisting  of  the  exciter  lamp,  optical 
system,  rotary  stabilizer,  scanning  drum,  reflector,  and  photoelectric  cell,  and  is 
rigidly  mounted  on  a  heavy  bracket  attached  to  the  main  frame  with  a  three- 
screw,  shock-absorbing  mounting.  The  bushings  are  impervious  to  oil. 

The  drive  motor  is  a  cradle-suspended,  oversize,  V-i-hp.,  split-phase  induction 
motor  with  ball-bearing  mounted  rotor,  and  thrust  bearings  on  both  ends,  insuring 


FIG.  12.  (Left}     Main  cabinet. 
FIG.  13.  (Right)     Showing  method  of  mounting  two-cabinet  assembly. 


constant  speed  with  a  variation  of  less  than  0.5  per  cent  with  voltages  from  102 
to  125  volts.  A  flywheel  insures  correct  starting  speed  meeting  the  SMPE. 
Projection  Practice  Committee's  recommendations  of  two  to  three  seconds.  The 
manually  operated  motor  brake  quickly  stops  the  machine  in  case  of  film  breakage. 
The  knob  on  the  end  of  the  motor  facilitates  threading,  and  a  flexible  coupling 
between  the  motor  and  the  gear  box  filters  out  mechanical  vibrations. 

The  film-drive  sprockets  consist  of  a  sound  sprocket  and  a  hold-back  sprocket, 
to  prevent  the  reflection  of  take-up  jerks  from  disturbing  the  film  at  the  scanning 
point.  All  shafts  of  the  drive  mechanism  rotate  on  dust-proof  ball  bearings. 


Nov.,  1938] 


NEW  MOTION  PICTURE  APPARATUS 


521 


MOfiMJi  POSIT/ON 
W/7MA/  r/ff  CABINET 


Special  shaft  construction  insures  alignment  of  the  sprockets,  avoiding  variation 
caused  by  the  accumulation  of  allowances  on  the  individual  parts. 

The  drive  mechanism  is  one  assembly.  It  qpnsists  of  the  gear-box,  sprockets, 
shafts,  pad  rollers,  and  stripper  plates,  all  of  which  are  easily  removable  as  a 
single  unit  by  removing  four  screws.  This  construction  affords  the  facility  of 
building  a  gear-box  as  a  precision  unit  and  then  mounting  it  into  the  main  frame 
casting  in  a  manner  similar  to  that  normally  employed  for  intermittent  move- 
ments in  projectors. 

Fig.  8  shows  the  oil  gauge  which  gives  visual  indication  of  the  oil  level  in  the 
reservoir.  Proper  lubrication  of  the  sound  mechanism  is  insured  when  the  oil 
level  is  maintained. 

The  sound-head  design  insures  accurate  alignment  of  the  projector  drive  gears 
and  easy  installation  or  removal  of  the  projector  mechanism.  Micrometer  ad- 
justment is  provided  to  obtain  proper  and  accurate  gear  mesh.  A  bar  is  fastened 
to  the  bottom  of  the  projector  mechanism. 
This  bar  fits  into  a  slot  in  the  top  of  the 
sound  mechanism.  It  is  under-flush  with 
respect  to  the  sound  mechanism  slot,  so 
that  the  finished  pads  of  the  projector 
mechanism  are  in  contact  over  their  entire 
area  with  the  finished  pads  on  the  sound 
mechanism.  The  projector  mechanism  is 
locked  to  the  sound  mechanism  by  two 
machine  screws  which  pass  through 
elongated  holes  in  the  bar.  No  serious 
strain  can  be  caused  by  pulling  down  on 
these  screws  because  the  bar  is  very 
narrow  and  the  base  of  the  projector 
mechanism  casting  is  in  contact  with  the 
sound  mechanism  over  a  large  area.  The 
micrometer  adjustment  is  provided  by  a 
screw  in  the  front.  When  the  projector 
mechanism  with  the  bar  is  set  on  the 
sound  mechanism,  the  screw  is  run  up  so 
as  to  prevent  clashing  of  the  gears  and 
breaking  of  the  teeth.  After  the  mecha- 
nism is  in  position  the  screw  can  be  backed 
out  and  the  mechanism  moved  so  that  the 
gears  come  into  proper  alignment.  The  40-thread  pitch  of  the  screw  permits  easy 
adjustment  for  accurate  gear  mesh,  insuring  long  life  and  reduced  operating  noise. 

The  sound  head  is  designed  for  the  future,  as  it  may  be  easily  and  economically 
converted  for  the  reproduction  of  push-pull  or  stereophonic  recordings  whenever 
these  forms  of  recording  become  popular. 

Fig.  9  is  in  view  of  the  volume  control  amplifier  unit.  The  cabinet  is  neat  and 
compact;  permits  mounting  on  the  front  wall  of  the  projector  room.  Fig.  10 
shows  the  inside  of  the  cabinet.  The  amplifier  consists  of  a  two-stage  resistance- 
coupled  voltage  amplifier  employing  RCA  6J7  tubes;  it  has  46-db.  gain.  Its 
normal  operating  position  is  26  db.,  which  puts  the  volume  control  mid-range. 


FIG.  14. 


Main  cabinet  chassis 
positions. 


522  NEW  MOTION  PICTURE  APPARATUS        [J.  S.  M.  P.  E. 

Metal  type  6J7  tubes  were  selected  for  their  shielding,  uniformity,  and  freedom 
from  microphonic  tendencies.  The  coaxial  cable  coupling  the  photoelectric  cell  to 
the  volume  control  amplifier  enters  the  cabinet  in  such  a  manner  that  the  con- 
necting lead  to  the  amplifier  is  very  short.  The  cable  is  shielded  and  covered 
with  a  cambric  tubing  to  prevent  entrance  of  oil;  over  the  tubing  is  an  armored 
sheath  to  protect  it  mechanically.  The  volume  control  for  the  system  is  a  specially 
designed  detented  step-by-step  potentiometer  having  nineteen  2-db.  steps. 

Fig.  11  shows  schematically  the  circuit  of  the  electronic  sound  change-over, 
which  comprises  a  three-way  switching  arrangement,  one  at  each  projector  sta- 
tion, to  control  the  bias  of  the  second  stage  of  the  volume  control  amplifier.  This 
method  of  change-over  control  eliminates  relays  and  mechanically  interlocked 
switches;  it  is  instantaneous  and  noiseless,  since  it  avoids  the  necessity  of  break- 
ing the  signal  circuit.  Switching  may  be  done  at  either  projector.  The  exciter- 
lamp  circuit  is  transferred  simultaneously.  The  photo-electric  cell  balancers 


FIG.  15.     Power  amplifier. 

equalize  the  signal  input  to  the  power  amplifier  at  predetermined  levels  to  obtain 
uniform  output  from  each  machine.  A  handy  control  with  a  slider  and  a  clamp 
is  provided.  The  pilot  light  in  the  volume  control  amplifier  cabinet  indicates 
which  machine  is  in  use. 

The  cabinet  is  designed  to  accommodate  two  amplifier  units,  which  can  be 
connected  to  provide  an  emergency  volume  control  stage  or  dual  channel  opera- 
tion. A  switch  on  the  terminal  strip  of  each  unit  makes  connections  simple  and 
practicable.  Extra  units  can  be  added  at  any  time.  The  two  amplifiers  are  iden- 
tical and  mount  so  that  their  volume  controls  are  operated  simultaneously  by  the 
one  control  knob. 

Fig.  12  shows  the  main  cabinet,  which  is  a  three-section  unit  designed  for  floor 
or  wall  mounting.  In  a  single-cabinet  installation  it  is  usually  mounted  on  the 
wall.  Where  two  cabinets  are  used,  one  is  placed  above  the  other  mounted  on  a 
set  of  feet  as  shown  in  Fig.  13.  Louvers  on  the  front  and  sides  provide  adequate 
ventilation.  The  front  panel  clips  into  place  and  is  quickly  and  easily  removed 
without  tools.  Each  unit  in  the  cabinet  may  be  partly  withdrawn  and  rotated 


Nov.,  1938] 


NEW  MOTION  PICTURE  APPARATUS 


523 


180  degrees  for  examination  or  servicing  while  in  operation,  as  shown  in  Fig.  14 
which  schematically  shows  the  arrangement  of  the  cabinet.  Three  chassis  posi- 
tions are  shown :  the  normal  position  within  the  cabinet ;  the  position  when  with- 
drawn before  rotating,  and  the  inverted  position,  after  being  rotated  180  degrees. 
The  chassis  can  not  be  inverted  until  it  is  drawn  out ;  this  provides  a  fool-proof 
feature  and  prevents  interference  between  chassis.  This  arrangement  permits 
compact  construction. 


I 


FIG.  16.      Power  unit  in  single-section  cabinet. 

Fig.  15  shows  the  power  amplifier.  It  employs  resistance  coupling  interstage. 
The  elimination  of  iron-core  transformers  and  reactors  reduces  noise.  The  only 
iron-core  component  in  the  signal  circuit  is  a  matching  transformer  to  couple 
power  tubes  to  the  speaker  network.  The  power  output  is  15  watts  at  frequencies 
as  low  as  50  cycles,  with  less  than  one  per  cent  total  harmonic  distortion.  The 
a-c.  circuit  is  separately  fused  with  the  fusetron  conveniently  located. 

The  entire  system  is  designed  to  employ  a  minimum  number  of  standard  tubes 
of  metal  or  glass  types  universally  obtainable.  Although  metal  6J7  tubes  are 
used  for  the  reason  given,  glass  6L6  type  tubes  are  preferred  for  uniformity  and 
dependability.  The  tubes  in  the  power  amplifier  are  6J7  in  the  driver  stage,  6J7 


524  NEW  MOTION  PICTURE  APPARATUS        [J.  S.  M.  p.  E. 

in  the  phase  inversion  stage,  two  6L6G  tubes  in  the  push-pull  power  output  stage, 
and  a  5Z3  full-wave  rectifier.  A  meter  is  mounted  on  the  power  amplifier  panel 
for  testing  the  condition  of  the  tubes.  The  scale  on  the  meter  is  blocked  off  in 
red  and  green  sectors.  Green  means  the  tube  is  all  right,  and  red  indicates  that 
replacement  of  the  tube  whose  number  appears  in  the  red  block  is  desirable. 

An  auxiliary  volume  control  in  the  feed-back  circuit  of  the  amplifier  affords 
variable  control  over  a  12-db.  range  and  permits  extension  of  this  potentiometer 
circuit  for  remote  volume  control.  The  arrangement  known  as  the  "warping 
circuit,"  for  adjustment  (by  soldered  connections)  of  the  electrical  characteristics, 
are  connected  into  the  feed-back  circuit.  Adjustments  are  provided  that  permit 
four  curves  hi  the  low-frequency  range  and  four  in  the  high-frequency  range. 

Parallel  operation  of  the  amplifiers,  as  previous  described,  affords  a  very  eco- 
nomical means  of  providing  emergency  facilities  in  any  system  where  more  than 
one  power  amplifier  unit  is  used,  as  a  simple  switching  arrangement  is  incorporated 
that  permits  selection  of  various  units  individually  or  as  parallel  groups.  The 
circuits  are  arranged  so  as  to  isolate  the  defective  units  and  permit  repairs  or  re- 
placements to  be  made  while  the  system  is  in  operation.  In  the  small  system  em- 
ploying one  amplifier,  a  second  unit,  together  with  a  selective  switching  arrange- 
ment, can  be  easily  added.  Means  for  mounting  the  switches  are  provided  in  the 
lower  stationary  panel  of  the  cabinet. 

The  exciter  lamp  power  unit  (Fig.  16)  employs  two  2-ampere  Tungar  bulbs  to 
furnish  direct  current  held  within  close  limits,  variations  in  line  voltage  being 
compensated  for  by  a  ballast  lamp  regulating  circuit.  The  lamp  of  the  operating 
machine  is  connected  to  the  rectified  output  of  the  power  unit  while  the  lamp  of 
the  "OFF"  machine  is  connected  to  a  transformer  at  one-fourth  the  normal  a-c. 
operating  voltage.  On  change-over  the  circuits  are  automaticaly  switched. 
Keeping  the  lamp  hot  insures  uniform  volume  on  change-over  without  burning 
the  lamp  at  full  rating  at  all  times.  Using  alternating  current  on  the  "OFF" 
machine  provides  a  more  economical  arrangement  for  several  reasons:  first,  the 
lamp  life  is  preserved;  second,  the  rectifier  construction  and  power  consumption 
are  less  expensive.  Furthermore,  by  the  same  facilities  and  by  simple  operation 
of  one  switch,  the  lamps  may  be  operated  on  alternating  current  at  normal  rating, 
thus  providing  an  emergency  operating  condition  in  the  event  of  failure  of  the 
rectifier  circuit.  The  a-c.  circuit  employs  a  separately  fused  transformer  and  cir- 
cuit that  permit  testing  and  inspecting  the  rectifier  while  the  system  is  in  opera- 
tion. A-c.  operation  of  the  exciter  lamp  also  provides  a  very  convenient  test 
circuit  for  balancing  the  photoelectric  cell  output  when  adjusting  the  sound 
mechanism  for  reproduction  of  push-pull  tracks;  that  is,  to  determine  the  can- 
cellation effect. 

The  loud  speaker  network  shown  in  Fig.  17  couples  the  amplifier  output  to  the 
two-way  loud  speaker  system  with  a  400-cycle  cross-over.  Special  design  features, 
careful  selection  of  capacitors,  resistors,  and  other  parts  afford  stability  of  opera- 
tion under  all  conditions.  The  control  panel  incorporates  two  switches,  marked 
HF  and  LF,  which  permit  high-  or  low-frequency  speakers  to  be  operated  as 
separate  groups.  This  feature  is  of  special  value  in  testing  and  for  continuing 
operation  in  the  event  of  failure  of  any  speaker  unit.  Where  more  than  one  high- 
or  low-frequency  speaker  is  used,  additional  selective  switching  arrangements 
may  be  added  for  further  flexibility.  Holes  are  already  provided  in  the  panel  for 


Nov.,  1938]  NEW  MOTION  PICTURE  APPARATUS  525 

easy  installation  and  a  terminal  strip  is  provided  to  facilitate  connections.  The 
panel  also  includes  the  monitor  loud  speaker  volume  control  and  a  jack  for  head- 
set monitoring.  The  volume  control  of  the  mgnitor  loud  speaker  can  be  adjusted 
from  the  amplifier  location,  which  is  usually  mounted  convenient  to  the  machines. 
With  the  HF  and  LF  switches  set  to  disconnect  all  loud  speakers,  a  terminating 
resistance  is  automatically  connected  across  the  amplifier  output,  permitting  a 
volume  indicator  or  output  meter  to  be  conveniently  plugged  into  the  monitoring 
jack  for  checking  the  amplifier  frequency  characteristics.  When  the  HF  switch 
only  is  operated,  so  that  the  high-frequency  loud  speaker  leg  is  disconnected,  the 
network  is  automatically  by-passed,  and  the  low-frequency  loud  speaker  operates 
directly  from  the  amplifier  output  as  a  full-range  speaker,  thus  permitting  emer- 
gency operation.  When  only  the  LF  switch  is  operated,  so  that  the  low-frequency 
loud  speaker  leg  is  disconnected,  a  resistance  is  automatically  substituted  for  this 
speaker  unit  thus  permitting  the  high-frequency  speaker  to  continue  operation 
in  the  normal  manner. 


FIG.  17.     Loud  speaker  network. 

Fig.  18  shows  the  loud  speaker  system  for  the  small  theater.  The  high-fre- 
quency loud  speaker  assembly  consists  of  a  multicellular  exponential  horn  of  new 
design  employing  a  spherical  mouth  opening  and  eight-cell  construction  for  high 
quality  and  wide-angle  distribution,  insuring  uniform  balance  of  the  frequency 
spectrum.  The  high-frequency  unit  is  of  the  permanent-magnet  dynamic  type.  It 
incorporates  a  high  safety  factor  in  relation  to  power  limits  required  in  normal 
operation. 

The  low-frequency  speaker  is  a  folded  exponential  horn  of  solid  and  sturdy 
wood  construction.  New  and  unique  in  design,  it  avoids  undesirable  reflection 
conditions.  The  enclosed  back  minimizes  back-stage  reflections  and  draping. 
The  low-frequency  unit  is  of  the  permanent-magnet  dynamic  type.  It  possesses 
high  power-handling  capacity  and  efficiency  over  the  frequency  range  for  which  it 
is  designed.  This  type  of  equipment  is  used  in  the  small  and  medium  systems. 

The  use  of  permanent-magnet  loud  speaker  units  brings  to  the  theater  reproduc- 
ing field  one  of  the  lastest  most  important  improvements  in  loud  speaker  equip- 
ment. Improved  alloys  make  it  possible  to  produce  practicable,  dependable,  and 


NEW  MOTION  PICTURE  APPARATUS        LJ.  S.  M.  P.  E. 


Is 

00 


Nov.,  1938]  NEW  MOTION  PICTURE  APPARATUS  527 

economical  permanent  magnets  where  the  field  structures  required  are  not  too 
large.  Permanent  magnets  have  been  used  in  light-valves,  microphones,  and  preci- 
sion instruments,  where  uniformity  is  paramount.  Permanent-magnet  field 
structures  on  loud  speaker  units  eliminate  the  loud  speaker  rectifier  and  the  elec- 
tromagnet. Both  these  elements  are  susceptible  to  operating  variations  that 
affect  the  magnetic  field  strength  and  the  speaker  performance :  for  example,  the 
output  of  the  rectifier  may  vary  as  a  function  of  the  input  voltage  and  the  con- 


FIG.  20.  ( Upper)     Monitor  loud  speaker. 
FIG.  21.  (Lower)     Monitor  amplifier. 

dition  of  the  tubes;  the  voltage  at  the  loud  speaker  fields  is  dependent  upon  the 
voltage  drop  in  the  stage  line;  the  magnetic  field  strength  may  be  further  varied 
by  the  operating  tempera tue  of  the  field  coil.  Variation  of  these  factors  can  not 
be  detected  easily,  and  the  cumulative  effect  in  degrading  the  system  performance 
may  be  appreciable.  Permanent-magnet  fields  are  not  subject  to  such  variations. 
The  field  strength  is  constant  and  the  performance  uniform  for  indefinite  periods. 
"Ageing"  is  negligible.  Installation  expenses  of  rectifiers  and  stage  lines  for 
field  supply  are  eliminated  as  well  as  maintenance  expense. 


528  NEW  MOTION  PICTURE  APPARATUS        [J.  s.  M.  P.  E. 

Fig.  19  shows  the  loud  speaker  equipment  proposed  for  use  with  the  large 
system. 

The  monitor  loud  speaker  shown  in  Fig.  20  consists  of  a  permanent-magnet 
8-inch  cone  unit  with  a  two-way  baffle  arrangement.  The  high  frequencies  are 
projected  through  the  center  grille  directly  from  the  front  of  the  loud  speaker 
cone  and  the  low  frequencies  are  radiated  through  the  louvers  on  both  sides  of 
the  grille,  being  reinforced  by  the  folded  baffle  path  between  the  rear  of  the  cone 
and  the  louvers.  The  design  extends  the  frequency  response  over  that  generally 
found  in  monitor  speakers.  It  offers  a  truer  and  more  pleasant  degree  of  repro- 
duction. It  permits  easy  cueing  of  dialog  and  also  gives  low-frequency  response, 
enabling  the  projectionist  to  detect  extraneous  noises  such  as  sprocket-hole  and 
frame  line  modulation. 

The  monitor  amplifier  shown  in  Fig.  21  can  be  used  with  any  system  to  provide 
more  power  in  the  projection  room  for  the  monitor  level.  It  employs  a  type  6N7 
metal  tube  as  a  push-pull  stage.  Installation  is  simple,  since  it  plugs  into  a 
socket  provided  on  the  loud  speaker  network  chassis.  A  switch  mounted  on  the 
speaker  network  chassis  permits  by-passing  the  monitor  amplifier,  in  which  case 
the  monitor  speaker  functions  directly  from  the  power  amplifier  with  the  same 
volume  control  potentiometer. 

OPERATING  ADVANTAGES 

There  is  nothing  more  serious  than  a  black  screen  in  the  theater.  A  unique 
degree  of  dependability  is  incorporated  in  this  new  Simplex  sound  system,  which 
permits  uninterrupted  operation  under  a  wide  variety  of  conditions,  precluding 
the  possibility  of  any  protracted  failure  of  sound.  To  summarize: 

(a)  Simplex  main  amplifiers  are  all  designed  to  permit,  by  the  simple  operation 
of  a  switch,  parallel  operation  with  provisions  for  emergency  operation  and  isola- 
tion of  the  faulty  unit  or  units. 

(&)  Volume  control  amplifier  cabinets  are  designed  to  accommodate  two  am- 
plifiers and  suitable  switches.  In  the  event  that  one  fails,  operation  may  be  in- 
stantly continued  on  the  other. 

(c}  The  power  unit  furnishes  direct  current  to  the  exciter  lamps  for  highest- 
quality  reproduction  and  includes  a  switch  permitting  instantaneous  operation 
of  the  exciter  lamps  from  alternating  current  through  a  separate  transformer. 

(d)  The  use  of  modern  permanent-magnet  dynamic  speakers  eliminates  the 
loud  speaker  field  supply  rectifier  and  insures  uniform  uninterrupted  performance. 

(e)  Provision  is  made  to  operate  either  the  high-frequency  or  low-frequency 
loud  speaker  units  alone  in  case  of  emergency,  by  the  simple  operation  of  a  switch. 

Designed  for  the  Future. — While  it  is  difficult  to  foresee  all  the  possible  develop- 
ments that  may  be  made  in  the  future  in  the  sound  motion  picture  field,  provisions 
have  been  made  in  the  design  of  the  Simplex  sound  system  for  those  developments 
that  to  date  have  shown  outstanding  merit  and  the  application  of  which  is  being 
encouraged  by  certain  Hollywood  producers  to  add  greater  realism  to  the  sound: 
namely,  post-equalization,  push-pull  and  stereophonic  reproduction,  and  increased 
power,  for  which  Simplex  sound  systems  incorporate  the  necessary  design  flexi- 
bility and  space  for  easy  and  economical  adaptation. 

The  sound  mechanism  can  reproduce  push-pull  and  stereophonic  recordings 
by  the  simple  addition  of  a  few  items:  for  push-pull  the  reflector  and  the  photo- 


Nov.,  1938]  NEW  MOTION  PICTURE  APPARATUS  529 

electric  cell  can  be  replaced  and  a  coupling  mesh  added;  for  stereophonic  the  re- 
flector and  photoelectric  cell  can  be  replaced  and  a  second  coaxial  cable  added. 
The  volume  control  equipment  can  be  modified  for  stereophonic  reproduction  by 
the  addition  of  a  second  amplifier  unit  in  the  present  cabinet.  Dual  channel 
operation  of  the  amplifier  system  can  be  accomplished  easily  by  splitting  up  the 
units  of  any  system  or  by  adding  units  of  uniform  physical  size.  Extra  amplifier 
units  for  increased  power  can  also  be  installed  easily  because  of  the  unit  construc- 
tion and  cabinet  design.  The  post-equalizer  can  be  added  to  the  volume  control 
cabinet  assembly  as  it  is  designed  to  replace  the  name  plate  in  the  lower  part  of 
the  cabinet. 

REFERENCES 

1  MILLIARD,  J.  K.:    "A  Study  of  Theater  Loud  Speakers  and  the  Resultant 
Development  of  the  Shearer  Two- Way  Horn  System,"  /.  Soc.  Mot.  Pict.  Eng., 
XXVII  (July,  1936),  No.  1,  p.  45;  reprinted  from  Bull.  Academy  of  Motion  Pic- 
ture Arts  &  Sciences,  March  3,  1938. 

2  MILLIARD,  J.  K.:    Projects  of  the  Committee  on  Standardization  of  Theater 
Sound  Projection  Equipment  Characteristics  of  the  Academy  of  Motion  Picture 
Arts  &  Sciences,  /.  Soc.  Mot.  Pict.  Eng.,  XXX  (Jan.,  1938),  No.  1,  p.  81;  Bull. 
Academy  of  Motion  Pictures  Arts  &  Sciences,  June  8,  1937. 

3  "Summation  of  Location  and  Capacities  of  U.  S.  Theaters,"  Motion  Picture 
Herald,  131  (May  28,  1938),  No.  9,  p.  61. 

4  HILLIARD,  J.  K. :  "Notes  on  the  Procedure  for  Handling  High- Volume  Release- 
Prints,"  /.  Soc.  Mot.  Pict.  Eng.,  XXX  (Feb.,  1938),  No.  2,  p.  209. 

"Procedure  for  Projecting  Hi-Range  Prints  in  the  Theater,"  Bull.  Academy  of 
Motion  Picture  Arts  &  Sciences,  Nov.  24,  1937. 

5  SCOVILLE,  R.  R.:  "A  Portable  Flutter-Measuring  Instrument,"  /.  Soc.  Mot. 
Pict.  Eng.,  XXV  (Nov.,  1935),  No.  5,  p.  416. 

"A  Laboratory  Flutter-Measuring  Instrument,"  J.  Soc.  Mot.  Pict.  Eng.,  XXIX 
(Aug.,  1937),  No.  2,  p.  209. 

DISCUSSION 

MR.  DEVRY:  What  instrument  is  used  to  determine  the  0.15-per  cent  nutter? 

MR.  FRIEDL:  The  flutter  was  measured  on  an  ERPI  flutter  bridge,  an  instru- 
ment designed  and  used  for  studio  work  as  well  as  theater  testing.  Several 
papers  describing  the  equipment  were  published  in  the  Journal  by  R.  R.  Scoville.5 

MR.  CRABTREE  :  I  understand  that  the  energy  emanating  from  an  orchestra 
may  be  as  high  as  150  watts.  Your  power  maximum  is  15  watts.  Is  that  enough 
output  to  similate  a  full  orchestra? 

MR.  MAXFIELD:  There  are  some  occasional  instantaneous  peak  values  whose 
duration  is  less  than  one-eighth  of  a  second  each.  These  contribute  little  to  the 
loud  ness.  The  average  maximum  is  about  8  db.  below  these  short  duration 
peaks.  Instantaneous  peaks  are  all  knocked  out  in  the  recording  mechanism 
anyway,  and  therefore  do  not  enter  into  the  problem. 

MR.  CRABTREE:  Can  you  connect  together  two  or  three  more  amplifiers  and 
increase  the  output? 


530  NEW  MOTION  PICTURE  APPARATUS        [j.  s.  M.  p.  E. 

Mr.  FRIEDL:  Yes,  although  we  do  not  know  how  far  we  can  go  in  that  di- 
rection. Our  present  systems  are  meeting  the  recommended  power  requirements ; 
and  as  a  matter  of  fact  the  capacities  are  much  higher  than  those  of  similar  systems 
used  hi  many  theaters  today,  the  small  one  being  15  watts. 

MR.  FISHER:  The  data  given  in  Fletcher's  paper  are  hi  acoustic  watts,  and 
the  data  here  are  in  electric  watts;  15  watts  here  probably  represents  3  or  4 
acoustic  watts. 

MR.  FRAYNE  :  Is  there  a  transformer  in  the  output  circuit  of  the  photoelectric 
cell? 

MR.  FRIEDL:    It  is  coupled  directly  by  the  coaxial  cable. 

MR.  FRAYNE:    What  is  the  length  of  the  cable? 

MR.  FRIEDL:  Between  five  and  six  feet,  because  of  the  distance  of  the 
mechanism  from  the  wall. 

MR.  FRAYNE:    You  have  no  trouble  on  that  basis? 

MR.  FRIEDL:    No. 

MR.  FRAYNE:    Do  you  have  to  equalize  for  it? 

MR.  FRIEDL:  No.  The  loss  is  very  low  and  corresponds  to  the  attenuation 
rate  of  the  recommended  electrical  characteristic. 

MR.  CRABTREE:  What  is  the  advantage  of  the  permanent  magnets  in  the 
speakers,  and  is  there  any  loss  of  magnetism  with  time? 

MR.  FRIEDL:  They  avoid  rectifier  equipment,  which  is  subject  to  failure,  and 
also  the  field  coil,  which  is  likely  to  break  down  and  which  varies  with  temperature. 
The  life  of  the  magnets  is  indefinite  so  far  as  measurements  indicate. 

MR.  ROBERTS:  Since  the  reproducing  drum  and  the  sound  sprocket  are  not 
mounted  on  the  same  casting,  how  critical  is  the  axial  alignment  between 
them?  I  am  thinking  of  possible  film  weave  due  to  misalignment  of  drum  and 
sprocket. 

MR.  FRIEDL:  We  control  that  by  a  construction  that  does  not  depend  upon 
a  resilient  mounting  for  alignment.  There  is  definite  alignment  even  though 
the  sound  bracket,  which  is  a  separate  assembly,  is  insulated  from  the  main 
frame.  It  is  not  set  out  on  a  spring  or  on  a  unit  that  might  sag. 

MR.  FRAYNE:  Are  the  horns  in  this  installation  capable  of  transmitting  the 
frequency  range  beyond  that  shown  in  the  characteristic  curves  for  the  high  end? 
The  curves  show  a  drop,  say,  of  about  20  db.  at  8000  cycles. 

MR.  FRIEDL:  On  this  system  here  we  are  using  the  H%  characteristic  which 
falls  between  the  Academy  "metallic"  curve  and  the  Academy  "non-metallic" 
curve. 

MR.  FRAYNE  :  The  curves  that  the  Academy  published  were  formulated  on 
the  basis  of  tests  using  the  horn  system  then  available.  It  is  probable  that 
some  new  tests  will  be  necessary  to  establish  new  curves  with  these  particular 
horns? 

MR.  FRIEDL:  Possibly;  recognizing  that  possibility,  we  do  not  insist  upon 
using  the  metallic  characteristic,  Hs,  but  provide  for  the  additional  characteristic 
H2.  Incidentally,  the  tests  made  hi  Hollywood  were  made  on  only  very  large, 
expensive  loud  speaker  equipment  far  too  expensive  to  be  offered  commercially 
to  a  small  theater. 

MR.  DEVRY:  Is  it  not  expensive  to  use  two  15-watt  amplifiers  to  get  a  30- 
watt  output,  rather  than  to  use  one  made  for  30-watt  in  the  first  place?  I  imagine 


Nov.,  1938]  NEW  MOTION  PICTURE  APPARATUS  531 

that  the  expense  would  be  probably  75  per  cent  over  what  it  would  be  in  a  30-watt 
amplifier. 

MR.  FRIEDL:  That  would  probably  be  so  if  we  were  building  only  30-watt 
amplifiers;  but  since  we  must  build  a  15-watt  a/nplifier  we  can  standardize  on  it, 
thereby  transferring  the  economy  to  the  customer  and,  in  addition,  giving  him  an 
emergency  operating  provision,  which  is  very  important.  When  one  30-watt 
amplifier  fails,  the  house  is  dead;  two  15-watt  channels  operating  in  parallel 
permit  carrying  the  show  on  either  channel,  switching  facilities  having  been 
provided  for  such  contingency. 

MR.  DAY:  How  long  does  it  take  the  flywheel  to  attain  full  speed  after  the 
machine  starts? 

MR.  FRIEDL:    Approximately  six  seconds. 

MR.  DAY:    Does  it  slip  over  the  drum,  or  does  the  oil  clutch  provide  the  slip? 

MR.  FRIEDL:  I  believe  both  things  happen.  The  oil  clutch  is  the  well-known 
rotary  stabilizer.  Incidentally,  one  potential  danger  is  oil  leakage,  which  would 
affect  the  damping  of  the  unit.  We  have  dead-ended  the  drum  so  that  there 
is  no  possibility  of  leakage.  We  have  eliminated  screws  and  gaskets  on  the 
cover  by  spinning  the  shell  enclosed  over  the  cover,  so  that  it  will  stand  at  least 
85  pounds  pressure  with  no  sign  of  leakage. 


VARIABLE  MATTE  CONTROL  (SQUEEZE  TRACK)  FOR  VARIABLE- 
DENSITY  RECORDING* 


G.  R.  CRANE** 


Since  the  advent  of  sound  motion  pictures,  the  need  has  been  felt  for  an  in- 
creased sound  volume  range  in  the  theater  to  provide  for  the  greatest  possible 
dramatic  and  musical  expression.  For  special  occasions  the  gain  of  the  reproduc- 
ing system  may  be  altered  continually  or  intermittently  by  cues,  but  for  the  aver- 
age theater  this  practice  is  expensive  and  inconvenient,  and  it  is  generally  conceded 
that  the  recording  medium  by  itself  should  provide  the  total  possible  volume 
range.  With  film  as  the  recording  medium  the  upper  limit  is  generally  repre- 
sented by  the  overload  point  of  the  photographic  record.  The  lower  limit  is 
usually  that  of  the  film  background  noise,  which  at  the  present  time  is  still  some- 
what above  the  audience  noise  during  moments  of  dramatic  interest. 

A  number  of  methods  of  increasing  the  total  volume  range  on  the  film  have 
been  suggested  and  some  have  been  used  with  a  fair  measure  of  success;  but  this 
paper  describes  one  method  in  which  the  width  of  variable-density  sound-track  is 
reduced  during  quiet,  or  relatively  low-level,  portions.  This  system,  commonly 
known  as  "squeeze"  or  matted  track,  appears  to  have  been  first  used  on  a  com- 
mercial scale  by  MGM  Studio.  It  was  originally  used  as  a  means  of  adjusting 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C,;  received 
April  18,  1938. 

**  Electrical  Research  Products,  Inc.,  Hollywood,  Calif, 


532  NEW  MOTION  PICTURE  APPARATUS        [J.  S.  M.  P.  E. 

the  volume  of  the  release  print,  either  in  the  printing  or  hi  the  re-recording  process, 
as  described  in  a  paper  by  W.  C.  Miller,  1930. J 

The  upper  limit  of  signal  volume  is  essentially  fixed  by  the  present  film  emul- 
sions, but  an  extension  of  the  total  range  may  be  obtained  by  a  reduction  of  the 
background  noises.  Therefore,  in  any  system  of  noise  reduction,  the  fundamental 
purpose  is  that  of  keeping  the  ratio  of  significant  signal  to  the  background  noise 
as  high  as  possible.  During  the  louder  passages  of  the  reproduced  sound-track, 
the  background  noise  is  masked  by  the  signal  and  becomes  objectionable  only 
during  the  low-level  or  silent  passages.  Therefore,  the  noise-reduction  system 
acts  upon  the  sound-track  in  such  a  manner  as  to  reduce  the  background  noise 
and  permit  recording  lower- volume  signals  without  loss  of  intelligibility. 

The  principal  causes  of  background  noise  are  generally  film-grain  noise  and  the 
hiss  of  the  photoelectric  cell,  excluding,  of  course,  the  miscellaneous  noises  caused 
by  scratches  and  dirt  on  the  film.  It  has  been  found  that  the  background  noise 
varies  with  the  amount  of  light  falling  upon  the  photoelectric  cell.  To  reduce 
the  noise,  the  transmission  of  the  sound-track  may  be  automatically  reduced 
during  quiet  passages  as  is  done  in  the  variable-density  noise-reduction  system; 
or  the  track  modulation  may  be  followed  by  a  masking  envelope,  as  is  employed 
by  the  variable-area  noise-reduction  systems.  With  the  variable-density  sys- 
tem, the  width  of  the  sound-track  may  also  be  reduced,  which,  of  course,  fur- 
ther reduces  the  amount  of  light  falling  upon  the  photoelectric  cell. 

The  relationship  between  the  width  of  the  sound-track  and  the  resulting  signal 
and  background  noise  is  the  basis  for  the  application  of  squeeze  track  to  variable- 
density  recording,  and  it  might  be  in  order  to  review  the  fundamentals  of  this 
relationship.  One  manner  of  approach  is  to  consider  the  sound-track  as  composed 
of  a  summation  of  a  large  number  of  small  tracks,  side  by  side.  These  tracks  are 
modulated  and  scanned  by  a  single  slit ;  and  if  we  consider  the  voltage  generated 
by  the  photoelectric  cell,  each  small  track  will  contribute  a  voltage  that  is  in  phase 
with  every  other  voltage  component,  and  the  total  voltage  is  the  sum  of  the  in- 
dividual voltages.  Expressed  as  an  equation,  the  total  voltage,  SE  —  e\  +  e2  +  es 
-f-  . . . .  en,  and  it  follows  that  for  a  uniformly  modulated  track,  uniformly  scanned, 
the  signal  output  will  vary  directly  with  the  width  of  the  track. 

In  like  manner  we  may  consider  the  film  background  noise  due  primarily  to 
film  emulsion  graininess.  The  individual  noise  voltages  generated  by  each  track 
are  altogether  random  and  differ  in  magnitude,  phase,  and  frequency.  As  in  the 
case  of  other  physical  phenomena  involving  the  summation  of  random  distribu- 
tion, the  total  voltage,  £„<,;„„  =  'S/ei2  +  e22  +  e32  +  . . .  enz.  Applying  these 
relationships  to  the  simple  case  of  two  identical  tracks,  for  example,  the  signal 
voltage  becomes  2e,  whereas  the  noise  voltage  becomes  V  e^  +  e22,  which  is 
•\/2e.  From  this  it  may  be  seen  that  signal  output  varies  directly  with  track 
width,  whereas  noise  varies  as  the  square-root  of  the  width.  Consequently, 
doubling  the  sound-track  increases  the  signal  6  db.,  but  the  noise  is  increased  by 
only  3  db.,  and  the  signal-to-noise  ratio  is  thereby  increased  by  3  db.  for  the  ideal 
case.  These  relationships  have  been  discussed  in  greater  detail  in  a  recent  paper 
by  W.  J.  Albersheim,2  and  -have  been  demonstrated  experimentally  as  described 
in  an  unpublished  paper  by  W.  R.  Goehner  and  N.  R.  Stryker  of  the  Bell  Tele- 
phone Laboratories. 


Nov.,  1938] 


NEW  MOTION  PICTURE  APPARATUS 


533 


As  previously  mentioned,  squeeze  track  is  applied  only  during  relatively  low- 
level  passages,  during  which,  for  a  given  reproduced  volume,  the  modulation 
is  relatively  higher  and  the  sound-track  narrower  than  for  a  standard  sound- 
track, resulting  in  less  background  noise.  In  re-recording  practice,  squeeze  track 
may  be  employed  in  either  of  two  ways.  In  the  first  method  it  may  be  used  by 
the  mixer  as  a  volume-reduction  device  instead  of  the  reduction  of  modulation  by 
the  volume  control.  If,  for  example,  it  is  required  to  re-record  a  given  passage 
at,  say,  10  db.  down  from  normal,  he  may  either  introduce  10  db.  of  attenuation 
in  the  recording  circuit,  or  he  may  squeeze  the  track  by  10  db.  Either  operation 
will  give  the  same  signal  output  from  the  film,  but  in  the  latter  case  he  will  have 
reduced  the  background  noise  by  5  db.  and  increased  the  signal-to-noise  ratio  by 
the  same  amount.  The  second  method  of  use  is  that  of  obtaining  additional  noise 
reduction.  On  low-level  passages  the  mixer  may  squeeze  the  track,  say,  10  db., 


FIG.  1.     Schematic  diagram  of  equipment. 


and  simultaneously  increase  the  modulation  by  10  db.,  thereby  reducing  the  noise 
5  db.  but  not  changing  the  signal  output  from  the  sound-track.  When  using  the 
equipment  in  this  manner,  suitable  precautions  must  be  taken,  of  course,  to  pre- 
vent overload  of  the  light-valve.  Obviously,  the  two  methods  are  functionally 
identical,  and  differ  only  from  the  standpoint  of  operation  and  circuit  arrange- 
ment. It  should  be  pointed  out  also  that  to  attain  the  maximum  benefit  from 
squeezed  track,  it  is  essential  that  the  material  being  recorded  be  fully  modulated 
with  the  greatest  possible  signal-to-noise  ratio. 

The  limit  to  which  the  track  width  may  be  reduced  is  not  fixed  definitely  but 
experience  has  indicated  that  it  is  somewhere  between  10  and  15  db.  At  12  db., 
for  example,  the  track  has  been  reduced  from  76  to  19  mils,  or  if  a  W  type  mask  is 
used  the  two  tracks  are  8.5  mils  each.  For  widths  less  than  8.5  mils,  noise  intro- 
duced by  miscellaneous  dirt  particles  or  scratches  on  the  track  tends  to  become 
serious,  since  for  a  given  size  of  particle  the  percentage  modulation  increases  as 


534  NEW  MOTION  PICTURE  APPARATUS        [J.  S.  M.  P.  E. 

the  track  width  decreases.  At  the  present  time,  10  to  12  db.  appears  to  be  the 
practical  limit  for  commercial  use. 

Sound-track  matting  equipment  has  therefore  been  developed  to  provide  the 
facilities  for  10  db.  of  sound-track  matting  to  be  used  with  the  existing  studio 
channel  equipment  and  the  standard  types  of  variable-density  recording  ma- 
chines. It  is  a  system  composed  of  four  principal  units  which  are  coupled  and 
driven  by  Selsyn  type  interlock  motors  to  provide  a  means  of  altering  the  width 
of  the  sound-track  by  remote  control  and  simultaneously  changing  the  amount 
of  attenuation  in  the  recording  or  monitoring  circuit.  Fig.  1  is  a  schematic  dia- 
gram of  the  system. 

The  four  principal  units  are  the  recorder  masking  unit,  the  foot  pedal  control 
unit,  the  indicating  meter  unit,  and  the  attenuator  unit.  In  addition  to  these, 
a  junction  box  is  provided  for  termination  for  the  cables  to  the  control  unit  and 
the  meter  unit ;  and  a  power-supply  unit  is  required  because  of  the  differences  in 
electrical  characteristics  of  the  several  motors  involved. 


FIG.  2.     Foot-pedal  control  unit. 

Foot-Pedal  Control  Unit. — This  unit  consists  of  a  foot-pedal  mounted  upon  a 
small  gear-box  which  drives  a  type  I  Autosyn  motor  as  shown  in  Fig.  2.  The 
angle  of  rotation  of  the  foot-pedal  is  about  34  degrees  with  a  gear-box  adjusted  to 
give  the  driving  motor  a  total  rotation  of  exactly  720  degrees.  These  values  were 
chosen  somewhat  arbitrarily  with  a  view  in  mind  to  provide  a  large,  but  convenient 
angle  for  operation  of  the  pedal  by  the  foot.  One  fixed  and  one  adjustable  stop 
are  provided  as  well  as  an  adjustable  friction  clutch,  so  that  the  operator  may  rest 
or  remove  his  foot  from  the  pedal  without  altering  the  setting.  The  unit  is 
mounted  upon  a  steel  base-plate  covered  with  sheet  rubber,  and  the  weight  is 
sufficient  to  prevent  it  from  sliding  on  the  floor  when  operated  by  the  foot.  The 
motor  leads  are  covered  with  a  rubber  sheath  and  terminated  by  a  Cannon  plug, 
to  allow  it  to  be  disconnected  quickly. 

Indicating  Meter  Unit. — The  indicating  meter  unit  is  an  assembly  built  within 
a  standard  type  of  meter  case  and  driven  by  a  type  769  Autosyn  motor  as 
shown  by  Fig.  3.  The  meter  assembly  includes  a  gear  reduction  between  the 
motor  and  the  pointer  of  6:1  so  that  the  pointer  travels  through  120  degrees,  cor- 
responding to  the  motor  rotation  of  720  degrees.  The  dial  is  calibrated  in  1-db. 


Nov.,  1938]  NEW  MOTION  PICTURE  APPARATUS  535 

steps  from  0  to  10  db.  It  is  mounted  in  a  sheet  metal  case,  as  shown  in  Fig.  3, 
with  the  meter  dial  indirectly  illuminated.  A  shielded  cable  carries  the  motor 
circuits  and  also  terminates  in  a  Cannon  jack.  The  meter  unit  can  be  supplied 
without  the  case,  although  the  case  permits  placing  the  meter  at  any  point  con- 
venient for  the  operator. 

Attenuator  Unit. — This  unit  consists  of  a  type  I  Autosyn  motor  driving  a  special 
potentiometer  through  the  proper  gear  reduction,  and  is  mounted  upon  a  standard 
relay  rack  panel  as  shown  by  Fig.  4.  The  potentiometer  travels  through  its  com- 
plete range  corresponding  to  the  720-degree  rotation  of  the  motor.  It  has  two 
electrically  separate  potentiometers,  each  having  10  db.  of  attenuation  in  steps  of 
l/z  db.  They  are  mechanically  one  unit  driven  by  a  common  shaft,  one  of  which 
increases  attenuation  as  the  other  decreases.  Two  relays  switch  these  potentiom- 
eters by  the  operation  of  a  key  located  at  the  mixer  position  or  elsewhere.  In 
the  construction  of  this  potentiometer,  care  has  been  taken  to  insure  good  contact 
between  the  wiper  and  the  studs  with  a  minimum  of  friction,  the  detent  assembly 
being  omitted.  A  steel  cover  acting 
as  a  dust  and  magnetic  shield  is 
readily  removed.  One  terminal  strip 
is  used  for  motor  circuits  and  another 
for  the  speech  circuits. 

Recorder  Masking  Unit. — Fig.  5 
shows  the  recorder  masking  unit 
mounted  upon  the  optical  bench  of 
the  100- A  A  recorder.  It  is  essen- 
tially a  conventional  light-valve 
magnet  and  a  new  optical  system, 
both  of  which  are  mounted  in  FlG  3  indicating  meter  unit, 

special  support  casting. 

The  optical  system  consists  of  two  units.  The  larger  unit  is  a  tube  having  a 
combination  cylindrical  and  aspheric  condenser  lens  in  one  end  and  a  so-called 
"collector"  lens  at  the  other.  The  small  unit  containing  an  achromatic  doublet, 
called  the  "relay"  lens,  is  mounted  inside  the  magnet  bore  near  the  front  of  the 
magnet.  With  this  optical  system,  a  diffuse  image  of  the  lamp  filament  may 
be  brought  to  a  focus  by  the  condenser  lens  at  a  plane  just  beyond  the  collec- 
tor lens  and  just  behind  the  light-valve  magnet.  A  movable  mask  is  placed  at 
this  plane,  and  the  mask  and  filament  image  are  then  focused  upon  the  plane  of 
the  light-valve  ribbons  by  the  relay  lens.  It  is  apparent,  therefore,  that  by 
changing  the  dimensions  of  the  mask,  the  length  of  the  illuminated  area  of  light- 
valve  slit  may  be  altered,  thereby  altering  the  width  of  the  sound-track  propor- 
tionately. The  function  of  the  collector  lens  is  to  avoid  loss  of  light  by  focusing 
the  aperture  of  the  condenser  lens  upon  the  aperture  of  the  relay  lens. 

The  mask  opening  has  been  designed  in  the  shape  of  a  circular  wedge  sector 
rotating  through  an  angle  of  36  degrees,  being  driven  by  an  Autosyn  type  781 
motor  through  a  gear  reduction  of  20:1.  The  mask  has  been  designed  for  a  track 
reduction  of  10  db.  starting  from  a  basic  width  of  76  mils.  This  track  width  was 
selected  so  that  the  sound-track  will  always  be  its  own  masking  agent,  and  have 
adequate  clearance  within  the  normal  80-  to  84-mil  mask  provided  by  the  repro- 
ducing optical  system.  This  condition  is  necessary  if  the  proper  ratio  of  track 


536  NEW  MOTION  PICTURE  APPARATUS        [J.  s.  M.  P.  E. 

reduction  is  to  be  realized  on  all  the  types  of  reproducing  equipment.  In  addition 
to  this  requirement,  the  studio  receiving  the  first  set  of  equipment  requested  a  W 
type  mask  which  inserts  a  septum  in  the  center  of  the  track  as  part  of  the  re- 
duction in  width.  Fig.  6  shows  the  masking  unit  with  the  guard  removed,  allow- 
ing the  mask  to  be  rotated  out  into  full  view.  The  mask  as  shown  was  cut  for  a 
reduction  of  10  db.  in  steps  of  1  db.,  as  described  later. 

This  unit  may  be  mounted  on  the  standard  recorder  without  extensive  modifica- 
tions of  the  recorder.  The  lamp  in  each  case  is  mounted  by  means  of  the  lamp 
bracket  supplied  with  the  recorder.  Equipment  has  not  at  this  time  been  de- 
signed for  use  with  the  smaller  portable  type  recorders. 

Power-Supply  Unit. — This  unit  contains  the  step-down  transformer  supplying 
power  to  the  small  motors,  and  three  small  transformers  are  connected  3-<£  Y  to 
couple  the  rotor  circuits  of  the  small  and  large  motors.  Terminal  strips  are  pro- 
vided to  serve  as  a  termination  for  the  motor  circuits  to  the  various  units.  This 
equipment,  together  with  a  switch  and  signal  light,  is  mounted  in  a  relay  rack 
panel  and  could  be  combined  with  either  the  attenuator  unit  or  the  junction  box, 


FIG.  4.     Attenuator  unit. 


if  desired,  but  has  been  kept  as  a  separate  unit  to  provide  flexibility  hi  equipment 
arrangement. 

Junction  Box. — A  junction  box  terminates  the  permanent  wiring  to  the  mixer's 
position  and  provides  plug  connections  for  the  foot-pedal  and  the  indicating  meter 
units.  It  also  mounts  a  key  to  operate  the  attenuator  unit  relays  controlling  the 
potentiometer  circuits.  This  unit  could  readily  be  eliminated,  but  is  required  in 
case  several  stages  are  wired  for  this  equipment,  since  foot-pedal  and  meter  units 
may  then  be  moved  quickly  from  one  stage  to  another. 

Motor  Drive  System. — The  motors  used  in  this  equipment  are  of  the  single-phase, 
Selsyn  type,  which  are  marketed  under  the  trade  name  "Autosyn."  The  foot- 
pedal  control  unit  and  the  attenuator  unit  employ  two  of  the  larger  size  motors 
known  as  the  type  /,  which  require  110  volts  a-c.  on  the  stators.  The  recorder 
masking  unit  uses  a  small  type  known  as  the  851,  and  the  meter  unit  uses  the  type 
769.  These  two  small  motors  are  identical  except  for  the  length  of  the  stator  and 
rotor,  the  851  being  approximately  Va  inch  longer  and  having  nearly  twice  the 
torque  of  the  769.  These  motors  require  32  volts  a-c.  which  is  supplied  by  a 
step-down  transformer.  Each  of  these  motors  has  a  3-phase  winding  with  in- 
duced voltages  of  54  volts  in  the  large  motors  and  24  volts  in  the  small  motors. 


Nov.,  1938]  NEW  MOTION  PICTURE  APPARATUS  537 

In  order  that  these  circuits  may  be  properly  coupled,  it  is  necessary  to  supply  a 
3-phase  F-connected  autotransformer  of  appropriate  voltage  ratio. 

These  motors  have  a  lag  not  exceeding  ll/2  degrees  at  zero  torque  and  an  addi- 
tional displacement  from  the  true  interlock  position  which  is  small,  but  proportional 
to  the  torque  imposed.  In  order  to  minimize  this  error,  the  system  has  been  de- 
signed so  that  the  motors  turn  through  a  considerably  greater  angle  than  the 
operating  elements,  which  was  chosen  to  be  two  complete  revolutions,  or  exactly 
720  degrees.  In  each  of  the  units  described,  appropriate  gear  ratios  have  been 
supplied  to  operate  the  moving  elements  as  required.  Each  motor  has  one  inter- 
lock position  per  revolution  and  it  is  therefore  possible  to  energize  the  system  and 
have  one  or  more  motors  out  of  proper  relationship  by  either  360  or  720  degrees. 
By  the  use  of  definite  and  rugged  end-stops  on  each  unit,  one  complete  cycle  or 
operation  of  the  foot-pedal  automatically  aligns  all  motors  in  the  system.  During 


FIG.  5.     Recorder  masking  unit. 

this  operation  any  motor  that  is  out  of  alignment  will  come  against  its  limiting 
stop  and  will  pull  through  one  interlock  position  to  the  next,  and  thus  all  motors 
are  brought  into  proper  relationship.  The  normal  operation  of  the  system  is 
limited  only  by  the  adjustable  stop  on  the  foot-pedal,  the  end-stops  on  all  the  other 
units  having  slight  clearance  from  the  normal  end-positions  of  their  mechanisms. 
This  is  necessary  to  prevent  possible  chattering  of  the  stop  mechanisms  when  the 
system  is  set  for  either  end -position. 

Each  motor-driven  unit  is  provided  with  an  adjustment  for  accurately  aligning 
its  movement  with  that  of  the  foot-pedal.  The  foot-pedal  unit  is  set  up  with 
reference  to  a  standard,  so  that  any  unit  of  a  system  may  be  interchanged 
without  disturbing  its  adjustment.  Additional  motors  could  be  connected  to 
the  system  for  other  purposes,  the  number  depending  upon  the  capacity  of  the 
foot-pedal  driving  motor,  and  the  method  of  operation. 

Mask  Design. — The  mask  is  designed  empirically,  taking  into  account  the  non- 
uniformities  in  commercial  recording  and  reproducing  systems.  As  previously 
mentioned,  the  mask  openings  are  designed  to  give  the  required  reduction  starting 
from  a  full  track  width  of  76  mils  with  ten  1-db.  steps  including  one  step  in  the 


538  NEW  MOTION  PICTURE  APPARATUS        [J.  s.  M.  p.  E. 

septum.  To  conform  to  studio  practice  we  have  provided  a  mask  of  the  W  type 
which  inserts  a  septum  as  part  of  the  reduction  in  width.  This  tends  to  make 
the  film  reduction  in  output  more  nearly  conform  to  the  expected  values  based  on 
sound-track  dimensions,  since  the  remaining  portions  of  the  matted  track  are 
neither  center  nor  edge  portions,  but  intermediate  areas  which  tend  to  be  about 
average  with  respect  to  modulation,  track  density,  etc.  A  second  advantage  in 
the  W  mask  lies  in  the  fact  that  it  is  also  well  suited  for  use  with  push-pull  sound- 
track. Because  of  the  septum  line  of  the  push-pull  track,  the  first  step  will  be 
less  than  1  db.  and  the  successive  steps  will  be  in  1-db.  increments;  and  this  may 
be  compensated  for  by  an  adjustment  in  the  attenuator.  If  the  system  is  to  be 
used  interchangeably  for  standard  and  push-pull  recording,  the  indicating  meter 


FIG.  6.     Recorder  masking  unit;     partial  assembly 
showing  mask. 

could  be  supplied  with  two  scales  on  the  dial  to  give  accurate  indication  for  either 
condition. 

The  mask  is  cut  in  a  milling  machine  in  definite  steps  of  1  db.,  with  the  division 
between  steps  beveled  and  rounded.  Test  recordings  have  been  made  with  and 
without  modulation  to  determine  whether  the  step  mask  moving  rapidly  will 
introduce  any  low-frequency  noise,  but  none  has  been  detected. 

Test  recordings  give  the  expected  film  output  levels  within  =*=  x/2  db.  of  the  ideal 
values,  when  reproduced  over  the  several  types  of  commercial  reproducing 
machines.  At  the  present  time,  this  degree  of  accuracy  is  generally  conceded  to 
be  satisfactory. 

Transmission  Circuits. — The  application  of  this  equipment  to  a  recording  chan- 
nel will  vary  with  the  arrangement  of  the  transmission  circuits  at  the  particular 
installation,  the  desired  operating  routine,  and  the  physical  arrangement  of  equip- 
ment. Fig.  1  shows  the  general  arrangement. 


Nov.,  1938]  NEW  MOTION  PICTURE  APPARATUS  539 

The  recording  attenuator  is  placed  in  a  500-ohm  circuit  just  ahead  of  a  bridging 
amplifier  or  equivalent,  which  feeds  the  film  recorder  equipped  with  the  masking 
unit.  An  additional  10  db.  of  gain  is  necessary  to  ^overcome  the  10-db.  loss  in  the 
attenuator  corresponding  to  normal  recording  with  full- width  track.  The  monitor- 
ing attenuator  is  also  placed  in  a  500-ohm  circuit,  usually  just  ahead  of  the  monitor- 
ing amplifier.  Both  potentiometers  have  no  insertion  loss  on  the  zero  step. 

When  the  system  is  used  for  volume  reduction,  as  previously  discussed,  the 
recording  attenuator  is  switched  out  of  the  circuit  and  replaced  by  a  10-db.  fixed 
pad  as  indicated  by  the  diagram.  An  additional  10  db.  of  gain  in  the  circuit 
balances  the  10-db.  pad  loss  to  make  the  equivalent  of  a  standard  recording  cir- 
cuit. The  monitoring  attenuator  is  placed  in  the  direct  monitoring  circuit  so 
that  it  will  reflect  the  relative  output  from  the  film  and  balance  with  the  photo- 
electric cell  monitor  at  all  times. 

When  the  system  is  used  in  the  second  manner  to  obtain  additional  noise  re- 
duction, the  10-db.  fixed  pad  is  replaced  by  the  recording  attenuator  which  de- 
creases attenuation  from  10  to  0,  as  the  track  width  is  reduced  from  0  to  10  db. 
The  monitoring  attenuator  is  out  of  the  circuit. 

The  use  of  the  matting  device  permits  a  degree  of  control  of  output  volume  as 
well  as  a  means  of  extending  the  signal-to-noise  ratio  on  a  release  sound-track  of 
the  variable-density  type,  which  can  not  be  obtained  to  the  same  degree  with  any 
other  type  of  sound  recording.  It  can  safely  be  said  that  this  method  adds  an 
effective  5  db.  to  the  signal-to-noise  ratio  of  release  prints  without  introducing 
any  deterioration  whatever  in  the  sound  quality.  Its  fairly  wide  application  in 
the  industry  at  the  present  time  is  sufficient  proof  that  it  is  proving  its  worth  in 
enabling  the  industry  to  give  improved  sound  reproduction  to  the  patrons  of  the 

theaters. 

REFERENCES 

1  MILLER,  W.  C.:     "Volume  Control  by  the  Squeeze-Track,"  /.  Soc.  Mot.  Pict. 
Eng.,  XV  (July,  1930),  No.  1,  p.  53. 

2  ALBERSHEIM,  W.  J.:      "Mathematical  Relations  between  Grain,  Background 
Noise,  and  Characteristic  Curve  of  Sound-Film  Emulsions,"  J.  Soc.  Mot.  Pict. 
Eng.,  XXIX  (Oct.,  1937),  No.  4,  p.  417. 


AN  IMPROVED  EDITING  MACHINE* 
J.  L.  SPENCE** 

Realizing  the  need  for  better  facilities  for  the  film  editor,  a  new  type  of  editing 
machine  radically  different  in  many  respects  from  devices  hitherto  used  has 
been  designed  by  J.  F.  Leventhal  and  the  author.  This  machine  performs  all 
the  operations  desired  by  the  film  editor,  such  as  matching,  spotting,  dubbing, 
synchronizing,  etc.,  as  well  as  the  ordinary  functions  of  editing. 

A  new  optical  compensator  makes  it  possible  to  construct  a  machine  without  in- 
termittent movements  or  oscillating  parts,  and  one  in  which  the  film  glides  silently 

*Presented  at  the  Fall,  1936,  Meeting  at  Rochester,  N,  Y. 
**  Akeley-Leventhal  Corp.,  New  York,  N.  Y. 


540  NEW  MOTION  PICTURE  APPARATUS        [J.  S.  M.  P.  E. 

past  the  aperture  without  coming  to  a  stop  at  each  frame,  as  in  the  older  machines. 
The  machine  has  many  other  unusual  features  in  addition  to  its  great  flexibility, 
and  its  simplicity  of  operation  results  in  greater  speed. 

Threading  is  accomplished  easily  in  a  minimum  of  time ;  the  film  is  merely  laid 
in  a  track,  a  simple  operation  locks  the  retaining  rollers  into  place,  and  the  ma- 
chine is  ready  to  run.  The  film  moves  forward  or  backward  with  equal  facility, 
and  can  be  brought  to  a  stop  by  a  simple  hand-control  wheel.  Footage  and  frame 
counters  for  both  picture  and  sound  afford  an  accurate  check  for  length  and  for 
spotting  sound  and  picture  effects. 

Since  the  machine  operates  very  quietly,  without  distracting  noises,  it  becomes, 
upon  demand,  a  miniature  projection  room.  The  sound  quality  is  exceptionally 
fine,  and  the  power  output  of  10  watts  is  more  than  enough  for  normal  require- 
ments. Jacks  are  provided  for  several  head-sets  so  that  the  machine  may  be  used 


FIG.  1.     Editing  machine. 

without  disturbing  others  in  the  room.  The  sound  is  cut  off  automatically  when 
the  film  is  run  backward. 

Since  there  is  no  pressure  on  the  film  at  any  point  along  the  picture  area,  and 
since  no  pressure  pads  or  shoes  are  required  as  in  standard  projection  apparatus, 
there  is  no  tendency  to  develop  scratches;  and  thus  negative  as  well  as  positive 
films  may  be  projected  with  perfect  safety. 

In  an  editing  machine  it  is  desirable  to  have  a  clear  sharp  picture  of  a  size  large 
enough  to  permit  close  inspection.  The  picture  in  this  machine  is  projected  upon 
a  screen  large  enough  to  be  viewed  by  several  persons.  Single-picture  inspection 
is  possible  over  any  length  of  time  without  danger  of  overheating  the  film. 

One  of  the  novel  features  of  the  "editor"  is  a  splicing  attachment  that  permits 
making  temporary  splices  rapidly  and  without  losing  frames,  thus  allowing  the 
operator  to  make  as  many  preliminary  cuts  as  he  desires. 

A  selector  unit  permits  operating  either  the  picture  or  the  sound  alone  or  to- 
gether. A  synchronizing  arrangement  is  provided  for  the  sound  print  channel 
so  that  the  sound  may  be  brought  into  synchronism  with  the  picture  while  running. 


Nov.,  1938]  NEW  MOTION  PICTURE  APPARATUS  541 

This  eliminates  the  necessity  for  rethreading  and  makes  it  possible  for  the  opera- 
tor easily  to  achieve  synchronism  in  cases  where  "sync"  marks  are  lost. 

Unusual  facilities  are  afforded  for  sound-track  manipulation.  Combined  track 
and  picture  prints  may  be  projected  simultaneously  with  separate  track  prints. 
It  is  possible  also  to  project  a  separate  track  print  with  the  picture  print  in  the 
same  channel,  thus  affording  an  opportunity  to  hear  several  tracks  at  the  same 
time  that  the  picture  is  being  edited. 

The  machine  is  provided  with  a  variable-speed  drive  which  can  be  controlled 
from  6  to  60  frames  per  second.  This  is  in  addition  to  a  separate  standard  con- 
stant-speed drive  of  24  frames  per  second. 

Other  features  included  new  trouble-free  "lift-off"  take-ups,  which  prevent  the 
film  from  breaking  when  taking  up  slack;  reel  spindle  brake  drums,  which  keep 
the  film  from  overriding,  regardless  of  reel  speed;  2000-ft.  capacity  take-ups; 
special  film  "slip-off"  flanges;  and  unit,  construction. 


CURRENT  LITERATURE  OF  INTEREST  TO  THE  MOTION  PICTURE 

ENGINEER 

The  editors  present  for  convenient  reference  a  list  of  articles  dealing  with  subjects 
cognate  to  motion  picture  engineering  published  in  a  number  of  selected  journals. 
Photo  static  copies  may  be  obtained  from  the  Library  of  Congress,  Washington,  D.  C., 
or  from  the  New  York  Public  Library,  New  York,  N.  Y.  Micro  copies  of  articles 
in  magazines  that  are  available  may  be  obtained  from  the  Bibliofilm  Service,  Depart- 
ment of  Agriculture,  Washington,  D.  C. 

Communications 

18  (Aug.,  1938),  No.  8 
On  Synthetic  Reverberation  (pp.  8-9)  S.  J.  BEGUN  AND 

S.  K.  WOLF 
High-Frequency  Correction  in  Resistance- Coupled 

Amplifiers  (pp.  11-14,  22)  E.  W.  HEROLD 

Automatic  Equalization  in  Disc  Recording  (pp.  15- 

19,  24)  G.  J.  SALIBA 

Electronics 

11  (Aug.,  1938),  No.  8 
Television   V-F  Circuits  (pp.  18-21)  E.  W.  ENGSTROM  AND 

R.  S.  HOLMES 

Practical  Remote  Amplifiers  (pp.  25,  55)  R.  W.  CARLSON 

A  Laboratory  Television  Receiver — II  (pp.  26-29)      D.  G.  FINK 

Institute  of  Radio  Engineers 

26  (Aug.,  1938),  No.  8 

A  High-Efficiency  Grid-Modulated  Amplifier  (pp.      F.  E.  TERMAN  AND 
929-945)  J.  R.  WOODYARD 

A  Unique  Method  of  Modulation  for  High-Fidelity 

Television  Transmitters  (pp.  946-962)  W.  N.  PARKER 

High-Efficiency  Modulation  System  (pp.  963-982)    R.  B.  DOME 

A  Phase-Opposition  System  of  Amplitude  Modula- 
tion (pp.  983-1008)  L.  F.  GAUDERNACK 

Notes  on  the  Impedance  of  a  Carbon  Microphone 

(pp.  1009-1010)  F.  OFFNER 

The  Causes  for  the  Increase  of  the  Admittances  of 
Modern  High-Frequency  Amplifier  Tubes  on 
Short  Waves  (pp.  1001-1132)  M.  J.  O.  STRUTT  AND 

A.  VAN  DER  ZlEL 

International  Photographer 

10  (Aug.,  1938),  No.  7 

The  Story  of  Kalart  (pp.  9-11)  H.  C.  McKAY 

Studio  Contacts  Aid  Lamp  Design  (pp.  15-18) 

542 


CURRENT  LITERATURE  543 

International  Projectionist 

13  (Aug.,  1938),  No.  8 
Some  Common  Sources  of  Noise  in  Theatre  Sound  A.  NADELL 

Systems  (pp.  7-8,  10,  13) 
The  Theory  of  Commutation  (pp.  14-16) 
Accident  Prevention — Not  Insurance — Is  Key  to 

Projection  Room  Safety  (pp.  17-19)  T.  P.  HOVER 

Kinotechnik 

20  (Aug.,  1938),  No.  8 

20  Jahre  Zeitlupe  (20  Years  of  High  Speed  Cam- 
eras) (pp.  197-199)  H.  JOACHIM 

Praktische  Losungsmoglichkeiten  fur  die  raumakus- 
tische  Behandlung  von  Filmateliers  (Practical 
Treatment  of  Stereo-Acoustic  Problem  in  Film 
Studios)  (pp.  200-203)  H.  JOACHIM 

Pruffilme  fur  Tonabtastspalte  (Test  Film  for  Sound 

Scanning  Slit)  (pp.  204-205)  H.  ORLICH 

Die  Anwendung  des  Filmes  als  Forschungsmittel  in 
Chemie,  Physik  and  Technik  (Motion  Pictures  for 
Experimental  Work  in  Chemistry,  Physics  and 
Technology)  (p.  207)  I.  W.  FORSTMANN 

Lichtquellen  der  Kinoprojektion  (Light  Sources  in 
Motion  Picture  Projection)  (pp.  208-209) 

Tonfilm  "80,000  Bilder  in  einer  Sekunde"  ("80,000 
Pictures  Per  Second"  on  Sound  Film)  (pp.  211-212) 

Die  Kinotechnik  in  der  neuesten  Patentstatistik 
(Patent  Statistics  for  Motion  Pictures)  (p.  221)  E.  EARTH 

Philips  Technical  Review 

3  (July,  1938),  No.  7 
Compression  and  Expansion  in  Transmission  Sound 

(pp.  204-210)  V.  C.  HENRIQUEZ 

Phenomena  in  Amplifier  Valves  Caused  by  Secondary 

Emission  (pp.  211-216)  J.  L.  H.  JONKER 

An  Apparatus  for  the  Measurement  of  Scanning 

Speeds  of  Cathode  Ray  Tubes  (pp.  216-219)          L.  BLOK 

Television  and  Short-Wave  World 

11  (Aug.,  1938),  No.  126 

Continuous  Film  Television,  a  New  Method  (p.  452) 
A  Simplified  Television  Receiver  Using  a  1  In.  Cath- 
ode-ray Tube  (pp.  453^57)  D.  E.  OSMAN 
The  Baird  Big-Screen  Theatre  Receiver,  Complete 
Technical  Details  (pp.  459-460) 


ABSTRACTS  OF  PAPERS  FOR  THE  DETROIT  CONVENTION 

The  following  abstracts  were  received  too  late  for  inclusions  in  the  October  Journal 
and  are  published  here  for  reference  purposes: 

"Technicolor  Adventures  in  Cinemaland";  H.  T.  Kalmus,  Technicolor  Motion 
Picture  Corp.,  New  York,  N.  Y. 

An  historical  review,  on  a  somewhat  technical  basis,  of  the  problems  of  the 
application  of  color  processes,  and  particularly  the  Technicolor  process,  to  the 
motion  picture  industry. 

Standards  Committee  Report;  E.  K.  Carver,  Chairman 

The  items  under  consideration  at  the  present  time  are  as  follows: 

(1}  Cores  for  35-mm.  and  16-mm.  motion  picture  film  have  been  given 
initial  and  final  approval  and  will  be  published  in  an  early  issue  of  the  JOURNAL. 
These  cores  are  practically  the  same  as  the  cine  positive  cores.  The  type  of 
core,  such  as  is  ordinarily  used  for  negative,  with  the  key  instead  of  the  keyway, 
is  considered  non-standard. 

(2}  The  question  of  sound-track  dimensions  is  being  held  in  abeyance  await- 
ing a  report  of  the  Academy  Committee  investigating  this  subject. 

(5)  A  preliminary  drawing  for  16-mm.  sound-film  sprockets  has  been  given 
initial  approval  and  has  been  sent  out  for  criticisms. 

(4)  A  definition  of  safety  film,  which  limits  the  per  cent  of  nitrogen  in  such 
film  to  0.36  per  cent  and  which  adopts  the  so-called  Lehman  burning  test  and 
Lehman  ignition  temperature  test,  has  been  given  initial  approval. 

(5)  The  question  of  the  reduction  ratio  for  35  mm.  to  16  mm.  is  in  the  hands 
of  a  sub-committee,  but  no  action  has  yet  been  taken. 

(6)  The  question  of  a  universal  perforation  with  the  basic  dimensions  of  the 
Bell  &  Howell  and  with  the  shape  of  the  positive  perforation  is  still  under  study. 
A  report  by  Mr.  Arnold  is  expected  at  this  meeting. 

(7)  In  regard  to  the  term  "variable-area"  or  "variable-width,"  an  investiga- 
tion by  the  Committee  has  shown  that  the  term  "variable-area"  is  preferred  to 
the  term  "variable-width,"  but  that  both  may  be  considered  good  usage. 

"The  Stability  of  the  Viscose  Type  of  Ozaphane  Photographic  Film";  A.  M. 
Sookne  and  C.  G.  Weber,  National  Bureau  of  Standards,  Washington,  D.  C. 

Viscose  Ozaphane,  a  new  type  of  film  with  a  base  of  regenerated  cellulose  sheet- 
ing, and  having  certain  advantages  for  record  use,  was  tested  to  determine  its 
comparative  stability.  Its  stability  was  compared  with  that  of  cellulose  nitrate, 
and  also  with  that  of  cellulose  acetate,  which  is  widely  used  for  slide-films  and 
which  has  been  found  to  be  a  very  stable  material  for  preserving  records  in 
libraries.  The  viscose  type  of  film  apparently  is  not  suitable  for  permanent  rec- 
ords, but  does  appear  to  have  properties  to  recommend  its  use  for  reading-room 
copies  that  can  be  replaced  when  they  become  unserviceable.  The  stability  was 
determined  by  measuring  changes  in  the  chemical  and  physical  properties  under 
accelerated  aging.  The  changes  observed  were  increase  in  acidity  and  copper 
number,  and  decrease  in  viscosity,  weight,  and  flexibility. 
544 


ABSTRACTS  OF  PAPERS  545 

"The  Evaluation  of  Motion  Picture  Films  by  Semimicro  Testing";  J.  E.  Gib- 
son, The  National  Archives,  Washington,  D.  C.,  and  C.  G.  Weber,  National 
Bureau  of  Standards,  Washington,  D.  C. 

Test  methods  for  the  evaluation  of  motion  picture  film  for  permanent  records 
require  test  specimens  too  large  to  be  removed  from  certain  archival  films. 
To  assist  those  charged  with  the  preservation  of  such  films  in  determining  the 
quality  and  checking  the  condition  of  them,  suitable  semimicro  methods  were 
developed  for  acidity,  viscosity,  and  residual  hypo  content.  Specimens  as  small 
as  7  milligrams  in  weight,  removed  from  the  film  with  a  small  hand  punch,  gave 
satisfactory  results  for  the  purpose. 

Report  of  the  Studio  Lighting  Committee;    C.  W.  Handley,  Chairman 

In  a  previous  report  the  need  of  a  catalog  of  studio  lighting  equipment  was  em- 
phasized. A  number  of  papers  have  been  published  describing  in  detail  the 
various  lamps  and  light-sources,  but  there  has  not  been  assembled  in  one  paper  a 
symposium  of  all  types  of  equipment  and  light-sources.  It  is  the  intention  of  the 
Committee  to  correlate  the  published  and  unpublished  data  on  motion  picture 
studio  light-sources  in  such  form  as  to  make  this  report  a  reference  for  complete 
information  on  the  subject. 

The  various  lighting  units  are  numbered  and  briefly  described.  Photographs 
of  popular  lamps  are  shown.  Tables  give  minimum  and  maximum  beam  di- 
vergences, carbon  and  bulb  sizes.  JOURNAL  references  are  given  as  a  key  to 
further  specific  information  on  any  lamp  or  illuminant.  Data  on  light  control 
devices  and  lamp  filters  is  included. 

"Latest  Developments  in  Variable-Area  Processing";  A.  C.  Blaney,  RCA 
Manufacturing  Co.,  Inc.,  Hollywood,  Calif.,  and  G.  M.  Best,  Warner  Bros. 
Pictures,  Inc.,  Hollywood,  Calif. 

A  series  of  curves  is  presented  showing  the  photographic  control  of  variable- 
area  sound-tracks  as  obtained  in  commercial  production  at  Warner  Bros.  Studio, 
and  to  show  the  wide  tolerances  in  film  processing  that  are  permissible  with 
class  A  push-pull  recording,  a  factor  of  especial  interest  in  connection  with  the 
daily  production. 

The  results  of  a  study  of  the  technic  involved  in  fine-grain  photographic  dupli- 
cating of  variable-area  sound-track  for  foreign  release  is  also  discussed. 

"The  Metro-Goldwyn-Mayer  Semi- Automatic  Follow-Focus  Device";  J. 
Arnold,  Metro-Goldwyn-Mayer  Studios,  Culver  City,  Calif. 

During  recent  years  an  important  problem  in  major-studio  cinematography 
has  been  that  of  following  focus.  Due  to  the  shallow  depth  of  field  in  modern 
lenses  when  used  at  maximum  apertures,  it  is  necessary  to  alter  the  focus  fre- 
quently during  the  filming  of  a  scene.  In  moving-camera  shots,  which  are  being 
used  with  increasing  frequency,  this  problem  is  naturally  aggravated,  since 
both  camera  and  players  may  move.  The  use  of  "blimped"  cameras  for  sound 
pictures  also  aggravates  the  cameraman's  problems,  as  finder  parallax  is  greatly 
increased  by  placing  the  finder  outside  the  camera  "bungalow." 

At  the  Metro-Goldwyn-Mayer  Studio  these  problems  have  been  simplified 
by  the  use  of  the  semi-automatic  follow-focus  device.  This  consists  of  a  finder 
which  is  both  focused  and  pivoted  to  correct  for  parallax  as  the  lens  is  focused. 
Individual  cams  coordinate  the  finder  movement  with  the  characteristics  of  any 
given  lens. 


546  ABSTRACTS  OF  PAPERS  [j.  s.  M.  P.  E. 

So  successful  is  this  coordination  that  it  is  possible  to  determine  whether  or 
not  an  object  is  correctly  focused  in  the  camera  by  observing  the  object's  focus 
and  position  in  the  finder.  The  device  has  been  applied  to  all  cameras  used  in 
production  at  the  Metro-Goldwyn-Mayer  Studio,  and  has  over  a  period  of  several 
years  proved  to  be  accurate,  dependable,  and  has  facilitated  production  to  a  note- 
worthy degree. 

"A  Motion  Picture  Dubbing  and  Scoring  Stage";  C.  L.  Lootens  and  D.  J. 
Bloomberg,  Republic  Productions,  Inc.,  North  Hollywood,  Calif.,  and  M.  Ret- 
tinger,  RCA  Manufacturing  Corp.,  Hollywood,  Calif. 

A  new  dubbing  (re-recording)  and  scoring  (music  recording)  building  recently 
completed  on  the  Republic  lot  consists  of  the  recording  stage,  a  scoring  monitor- 
ing room,  projection  booth,  machine  room,  maintenance  room,  power  room,  and 
recording  truck  testing  platform. 

The  recording  equipment  consists  essentially  of  2  complete  RCA  high-fidelity 
recording  channels,  with  associated  equipment  of  film-phonographs,  test  racks, 
power  rectifiers,  dubbing  and  scoring  consoles,  acetate  recorder,  and  projection 
equipment. 

The  stage  is  of  the  live-end,  dead-end  type  and  has  dimensions  conforming  to 
the  recommended  1:2:3  ratio.  The  live  end  is  provided  with  permanent  side- 
wall  and  ceiling  reflecting  panels  which  increase  the  reverberation  and  diffusion. 
The  remainder  of  the  stage  is  treated  with  4-inch  rockwool  battens,  placed  be- 
tween the  studs  and  retained  in  place  by  a  dual  muslin  covering.  The  measured 
reverberation  characteristic  of  the  stage  fulfills  recommended  requirements  and 
is  between  0.95  and  1.00  second  for  the  frequency  band  of  540  to  7000  cps.  The 
stage  is  also  equipped  with  an  8-position  console  so  that  dubbing  may  be  done  in  a 
room  having  theater  sound  characteristics. 


JOURNAL 

OF  THE  SOCIETY  OF 

MOTION  PICTURE  ENGINEERS 

Volume  XXXI  DECEMBER,  1938  Number  6 

CONTENTS 

Page 

Proceedings  of  the  Semi- Annual  Banquet  at  the  Fall  Conven- 
tion at  Detroit,  Mich 551 

Technicolor  Adventures  in  Cinemaland H.  T.  KALMUS     564 

A  Method  for  Determining  the  Scanning  Losses  in  Sound  Op- 
tical Systems E.  D.  COOK  AND  V.  C.  HALL    586 

The  Use  of  Photoelectric  Exposure-Meters  in  the  Hollywood 
Studios W.  STULL     604 

The  Stability  of  the  Viscose  Type  of  Ozaphane  Photographic 
Film A.  M.  SOOKNE  AND  C.  G.  WEBER     611 

Report  of  the  Standards  Committee 619 

Report  of  the  Membership  and  Subscription  Committee 623 

Current  Literature 624 

Fall,  1938,  Convention  Program 626 

Society  Announcements % 630 

Index,  July-December,  1938 

Author  Index 638 

Classified  Index..  641 


JOURNAL 

.      OF  THE  SOCIETY  OF 

MOTION  PICTURE  ENGINEERS 


SYLVAN  HARRIS,  EDITOR 

Board  of  Editors 
J.  I.  CRABTREE,  Chairman 

A.  N.  GOLDSMITH  L.  A.  JONES  H.  G.  KNOX 

A.  C.  HARDY  E.  W.  KELLOGG  G.  E.  MATTHEWS 


Subscription  to  non-members,  $8.00  per  annum;  to  members,  $5.00  per  annum, 
included  in  their  annual  membership  dues;  single  copies,  $1.00.  A  discount 
on  subscriptions  or  single  copies  of  15  per  cent  is  allowed  to  accredited  agencies. 
Order  from  the  Society  of  Motion  Picture  Engineers,  Inc.,  20th  and  Northampton 
Sts.,  Easton,  Pa.,  or  Hotel  Pennsylvania,  New  York,  N.  Y. 
Published  monthly  at  Easton,  Pa.,  by  the  Society  of  Motion  Picture  Engineers. 

Publication  Office,  20th  &  Northampton  Sts.,  Easton,  Pa. 
General  and  Editorial  Office,  Hotel  Pennsylvania,  New  York,  N.  Y. 

West-Coast  Office,  Suite  226,  Equitable  Bldg.,  Hollywood,  Calif. 
Entered  as  second  class  matter  January  15,  1930,  at  the  Post  Office  at  Easton, 
Pa.,  under  the  Act  of  March  3,  1879.     Copyrighted,  1938,  by  the  Society  of 
Motion  Picture  Engineers,  Inc. 

Papers  appearing  in  this  Journal  may  be  reprinted,  abstracted,  or  abridged 
provided  credit  is  given  to  the  Journal  of  the  Society  of  Motion  Picture  Engineers 
and  to  the  author,  or  authors,  of  the  papers  in  question.  Exact  reference  as  to 
the  volume,  number,  and  page  of  the  Journal  must  be  given.  The  Society  is 
not  responsible  for  statements  made  by  authors. 


OFFICERS  OF  THE  SOCIETY 

•President:    S.  K.  WOLF,  1270  Sixth  Ave.,  New  York,  N.  Y. 
*  Past-President:     H.  G.  TASKER,  5451  Marathon  St.,  Hollywood,  Calif. 
•Executive   V ice-President:     K.   F.  MORGAN,  6601   Romaine  St.,  Los  Angeles, 

Calif. 

"Engineering    Vice-President:     L.   A.  JONES,  Kodak  Park,   Rochester,   N.   Y. 
•Editorial  Vice-President:    J.  I.  CRABTREE,  Kodak  Park,  Rochester,  N.  Y. 
"Financial  Vice-President:    E.  A.  WILLIFORD,  30  E.  42nd  St.,  New  York,  N.  Y. 
•Convention    Vice-President:    W.   C.   KUNZMANN,   Box  6087,   Cleveland,  Ohio. 
•Secretary:    J.  FRANK,  JR.,  90  Gold  St.,  New  York,  N.  Y. 
•Treasurer:    L.  W.  DAVEE,    76  Varick  St.,  New  York,  N.  Y. 

GOVERNORS 

*J.  O.  AALBERG,  6920  McKinley  St.,  Los  Angeles,  Calif. 

*M.  C.  BATSEL,  Front  and  Market  Sts.,  Camden,  N.  J. 

**R.  E.  FARNHAM,  Nela  Park,  Cleveland,  Ohio. 

*G.  FRIEDL,  JR.,  90  Gold  St.,  New  York,  N.  Y. 

*A.  N.  GOLDSMITH,  444  Madison  Ave.,  New  York,  N.  Y. 

**H.  GRIFFIN,  90  Gold  St.,  New  York,  N.  Y. 

**A.  C.  HARDY,  Massachusetts- Institute  of  Technology,  Cambridge,  Mass. 

*S.  A.  LUKES,  6427  Sheridan  Rd.,  Chicago,  111. 

*Term  expires  December  31,  1938. 

**Term  expires  December  31,  1939. 


PROCEEDINGS  OF  THE  SEMI-ANNUAL  BANQUET 

OF  THE 

SOCIETY  OF  MOTION  PICTURE  ENGINEERS 

STATLER  HOTEL 
DETROIT,  MICH. 

NOVEMBER  1,  1938 

Nearly  200  members  and  guests  of  the  Society  assembled  at  the 
Fall,  1938,  Semi-Annual  Banquet  held  at  the  Hotel  Statler,  Detroit, 
Mich.,  on  November  1st.  Guests  at  the  speakers'  table  were  Mr. 
G.  R.  Giroux,  of  the  Technicolor  Motion  Picture  Corporation;  Mr. 
J.  Frank,  Jr.,  Secretary  of  the  Society;  Mr.  A.  S.  Dickinson,  Motion 
Picture  Producers  and  Distributors  of  America,  Inc.;  Mr.  H.  Griffin, 
International  Projector  Corporation;  Mr.  E.  P.  Curtis,  Eastman 
Kodak  Company;  Mr.  G.  F.  Rackett  and  Dr.  H.  T.  Kalmus,  Techni- 
color Motion  Picture  Corporation;  Mr.  S.  K.  Wolf,  President  of  the 
Society;  Dr.  K.  S.  Gibson,  National  Bureau  of  Standards;  Mr.  E.  A. 
Williford,  National  Carbon  Company;  Dr.  J.  B.  Engl,  of  Berlin, 
Germany;  Mr.  J.  I.  Crabtree,  Eastman  Kodak  Company;  Dr.  A.  N. 
Goldsmith,  consulting  engineer;  and  Mr.  M.  Hobart,  Technicolor 
Motion  Picture  Corporation. 

After  introducing  those  seated  at  the  speakers'  table,  President 
Wolf  announced  the  results  of  the  annual  election  of  officers  for  1938, 
and  introduced  Mr.  E.  A.  Williford,  President-elect,  whose  remarks 
follow : 

MR.  WILLIFORD  :  Mr.  Chairman,  Honored  Guests,  Members  of  the 
Society,  and  Friends :  I  am  not  going  to  make  a  speech,  but  I  think 
it  would  be  really  ungrateful  of  me  if  I  did  not  express  to  you  my  deep 
appreciation  of  the  kind  ovation  you  have  given  upon  the  announce- 
ment of  my  election  to  the  presidency. 

Shortly  after  I  was  informed  of  my  election,  my  education  began. 
One  of  my  very  closest  friends  in  the  profession,  one  that  I  have 

551 


552  PROCEEDINGS  OF  SEMI-ANNUAL  BANQUET  [j.  s.  M.  p.  E. 

counted  an  intimate  over  the  years,  began  to  tell  me  what  was  wrong 
with  the  Society  and  with  me,  and  there  was  much  truth  in  what  he 
said.  From  other  sources  since  then  I  have  learned  that  the  job  of 
being  President  of  this  independent  thinking  group  of  individualistic 
persons  is  a  real  job. 

All  I  would  like  to  say  to  you  is  this :  those  who  are  not  as  close  to 
the  scenes  of  what  is  going  on  in  motion  picture  research  and  de- 
velopment probably  think  there  isn't  much  progress  being  made. 
It  looks  very  much  like  the  same  picture,  sounds  very  much  like  the 
same  sound;  but  those  of  us  who  are  more  active  in  it  know  that 
steady  progress  is  going  on  and  will  go  on  for  many  years  to  come. 

I  only  hope  that  in  my  administration  of  this  Society's  job,  as 
President  during  the  next  two  years,  I  can  see  the  Society  as  an  or- 
ganization grow  in  usefulness  and  in  service  to  the  industry  in  the 
same  manner  in  which  our  two  particularly  honored  guests  tonight 
have  been  instrumental  in  making  progress  in  the  industry  itself. 

Thank  you  all. 

President  Wolf  next  introduced  the  remaining  officers-  and  gover- 
nors-elect as  follows: 

Executive  V ice-President  N.  LEVINSON 

Editorial  V ice-President  J.  I.  CRABTREE 

Financial  Vice-President  A.  S.  DICKINSON 

Convention  Vice- President  W.  C.  KUNZMANN 

Secretary  J.  FRANK,  JR. 

Treasurer  L.  W.  DAVEE 

Governors  M.  C.  BATSEL 

H.  G.  TASKER 


The  other  officer  and  governors  of  the  Society  whose  terms  do  not 
expire  for  another  year  were  also  introduced  by  President  Wolf,  as 
follows  : 

Engineering  Vice-President  L.  A.  JONES 

Governors  A.  C.  HARDY 

H.  GRIFFIN 
R.  E.  FARNHAM 

During  the  introductions,  Mr.  J.  Frank,  Jr.,  the  Secretary,  called 
for  a  rising  vote  of  appreciation  for  the  work  done  by  Mr.  Wolf  during 
his  incumbency. 


Dec.,  1938]  PROCEEDINGS  OF  SEMI- ANNUAL  BANQUET  553 

Next,  referring  briefly  to  the  two  awards  made  each  year  by  the 
Society,  namely,  the  Journal  Award  and  the  Progress  Award,  Presi- 
dent Wolf  asked  Mr.  E.  A.  Williford  to  read  the  citation  on  the  work 
of  Dr.  Kasson  Stanford  Gibson,  prepared  by  Mr.  N.  D.  Golden: 


CITATION  ON  THE  WORK  OF  KASSON  STANFORD  GIBSON 

For  the  second  year  in  succession  a  member  of  the  staff  of  the 
National  Bureau  of  Standards  of  the  Department  of  Commerce  is  to 
be  honored  with  the  Journal  Award  of  this  Society.  In  1937,  Dr. 
Dean  Brewster  Judd  was  given  this  honor.  It  is  my  privilege  on 


KASSON  STANFORD  GIBSON 

behalf  of  the  Journal  Award  Committee  to  announce  that  the  paper 
by  Dr.  Kasson  Stanford  Gibson,  "The  Analysis  and  Specification  of 
Color,"  appearing  in  the  April,  1937,  issue  of  the  Society's  JOURNAL, 
has  won  this  award  for  1938. 

It  is  appropriate  to  review  briefly  Dr.  Gibson's  career  and  scientific 
background.     Dr.  Gibson  was  born  at  Afton,  N.  Y.,  on  January  7, 


554  PROCEEDINGS  OF  SEMI- ANNUAL  BANQUET  [J.  S.  M.  P.  E. 

He  received  his  early  education  in  the  public  schools  of 
Norwich,  N.  Y.,  graduating  from  the  High  School  in  1908.  In  1912 
he  received  his  Bachelor  of  Arts  degree  from  Cornell  University  and 
in  1916  his  degree  of  Doctor  of  Philosophy  from  the  same  University. 
Dr.  Gibson  was  also  elected  to  the  honorary  societies  of  Phi  Beta 
Kappa  and  Sigma  Xi  while  at  Cornell,  and  was  an  instructor  in  the 
Department  of  Physics  from  1912  to  1916. 

After  Dr.  Gibson  received  his  Doctor  of  Philosophy  at  Cornell 
University,  he  joined  the  staff  of  the  National  Bureau  of  Standards 
in  1916  in  the  Colorimetry  and  Spectrophotometry  Section  as  an 
Assistant  Physicist.  In  1919  he  rose  to  the  position  of  Associate 
Physicist,  in  1922  he  became  a  Physicist,  and  in  1928  a  Senior  Physi- 
cist; in  1933  he  was  made  Chief  of  the  Section  and  in  1936  Principal 
Physicist,  the  position  which  he  is  now  holding. 

Dr.  Gibson  has  published  more  than  forty  scientific  papers  and 
reports,  in  the  Journals  of  the  Optical  Society  of  America,  American 
Physical  Society,  Society  of  Motion  Picture  Engineers,  Illuminating 
Engineering  Society,  and  American  Oil  Chemists  Society,  in  the 
Journal  of  Research  of  the  National  Bureau  of  Standards,  and  in  the 
Proceedings  of  the  Signal  Section  of  the  Association  of  American 
Railroads,  the  International  Commission  on  Illumination,  and  the 
International  Congress  of  Photography. 

Dr.  Gibson  is  a  Fellow,  in  the  American  Association  for  Advance- 
ment of  Science,  and  the  American  Physical  Society,  and  holds 
membership  in  the  Optical  Society  of  America,  having  been  an  associ- 
ate editor  of  their  Journal  since  1927,  a  member  of  their  Board  of 
Directors  since  1935  and  a  Vice- President  of  the  Optical  Society 
since  1937. 

Dr.  Gibson  is  also  associated  with  other  scientific  organizations, 
among  which  are  the  Illuminating  Engineering  Society,  American 
Oil  Chemists  Society,  Washington  Academy  of  Sciences,  and  the 
Philosophical  Society  of  Washington. 

Dr.  Gibson  is  a  recognized  authority  in  the  field  of  colorimetry, 
Spectrophotometry,  heterochromatic  photometry,  artificial  daylight, 
and  spectral  filters.  It  is  with  pleasure  that  I  present  to  the  Society 
of  Motion  Picture  Engineers  Dr.  Kasson  S.  Gibson  as  the  recipient  of 
the  1938  Journal  Award. 

After  receiving  the  Journal  Award  certificate  from  President  Wolf, 
Dr.  Gibson  responded  as  follows : 


Dec.,  1938]  PROCEEDINGS  OF  SEMI- ANNUAL  BANQUET  555 

DR.  GIBSON:  Mr.  Chairman,  Ladies,  and  Gentlemen:  I  appre- 
ciate this  honor  very  much  indeed.  When  the  Chairman  of  your 
Journal  Award  Committee  notified  me  that  my  paper  had  been  se- 
lected for  this  honor,  he  spoke  about  the  complexity  of  the  subject 
of  color.  One  of  the  reasons  why  the  subject  seems  so  complicated 
is  because  of  the  different  ways  in  which  the  word  "color"  is  used  by 
various  groups.  You  may  be  interested  in  some  of  these  ways. 

This  afternoon,  for  example,  I  gathered  that  to  the  motion  picture 
engineers  color  means  a  departure  from  black  and  white,  and  this 
usage  of  the  word  is  consistent  with  that  of  the  artist,  who  divides 
his  palette  into  colors  and  grays.  But  I  imagine  if  some  of  the  ladies 
in  the  audience  were  asked  the  colors  of  their  dresses  they  would  not 
hesitate  to  say  "white"  or  "gray"  or  "black,"  if  the  dresses  didn't  hap- 
pen to  be  "cactus  green"  or  "glamor  gold"  or  "rhythm  red." 

The  psychologist  defines  color  as  a  sensation  or  perception,  but 
the  physicist  talks  about  the  reflection  and  absorption  of  colors ;  the 
chemist  discusses  whether  or  not  colors  obey  Beer's  law,  and  we  have 
the  paint  manufacturer  buying  and  selling  colors  by  the  pound,  dry 
colors  at  that. 

Then  we  have  the  expression  "pure  color."  To  the  physicist  that 
means  that  the  light  is  of  a  single  wavelength;  to  the  dye  chemist  it 
means  an  unadulterated  dye;  to  the  psychologist  it  means  one  of 
the  unitary  hues;  whereas  to  the  designer  it  means  maximum  de- 
parture from  gray. 

The  word  "white"  is  used  to  refer  to  the  color  of  daylight  or  sun- 
light or  to  any  source  that  has  a  continuous  spectrum ;  or  it  may  re- 
fer to  the  color  of  the  tablecloth,  or  to  the  color  of  water,  as  when 
certain  liquids  are  designated  as  "water- white." 

When  my  son  comes  home  from  school  he  tells  me  that  his  teacher 
says  that  black  is  the  absence  of  color.  That  usage  is  certainly  con- 
trary to  the  one  that  designates  the  black  race  as  the  "colored  race." 
Finally,  as  many  of  you  know,  we  have  the  theoretical  black  body, 
which  may  be  any  color — red,  orange,  yellow,  white,  or  blue,  depend- 
ing upon  the  temperature. 

I  therefore  felt  highly  complimented  when  the  Chairman  of  the 
Committee  referred  to  the  clarity  with  which  I  presented  the  subject 
of  color.  However,  I  assume  the  award  was  given  for  writing  and 
not  for  talking,  and  I  am  therefore  going  to  conclude  these  remarks 
immediately. 

I  wish  to  thank  the  Journal  Award  Committee  and  the  members  of 


556  PROCEEDINGS  OF  SEMI-ANNUAL  BANQUET  [j.  s.  M.  P.  E. 

the  Society  for  this  honor.  I  deeply  appreciate  it,  as  I  have  said, 
and  it  will  be  a  source  of  great  encouragement  to  go  forward  with 
our  work  in  color  at  the  National  Bureau  of  Standards. 

PRESIDENT  WOLF:  The  highest  award  that  the  Society  can  offer 
to  its  members  is  known  as  the  Progress  Medal.  This  award  goes  to 
the  person  selected  by  the  Committee  who  has  contributed  most  to 
the  science  and  art  of  our  industry.  We  have  the  pleasure  tonight 
to  present  to  you  Mr.  G.  F.  Rackett,  who  will  read  the  citation  for 
the  recipient  of  the  Progress  Award  Medal : 


HERBERT  THOMAS  KALMUS 

CITATION  ON  THE  WORK  OF  HERBERT  THOMAS  KALMUS 

Motion  pictures  are  unique  in  being  a  commercialized  art  form 
whose  combination  of  applied  science  and  engineering,  together  with 
the  modern  creative  arts,  has  engaged  the  widespread  interest  of  the 
public  over  the  world.  It  is  not  unexpected  that  such  a  field  of 
endeavor  would  invite  the  energies  of  outstanding  experts  in  the 
sciences,  engineering,  and  the  arts,  with  the  consequence  that  per- 


Dec.,  1938]          PROCEEDINGS  OF  SEMI-ANNUAL  BANQUET  557 

formance  meriting  distinction  becomes  distinction  indeed.  In  the 
three  Progress  Awards  that  have  been  made  by  the  Society  of  Motion 
Picture  Engineers,  its  Progress  Award  Committee  has  exhibited 
judgment  that  merits  the  commendation  of  the  motion  picture 
industry  and  it  is  therefore  with  a  feeling  of  pride  and  humility  that 
I  proceed  with  the  great  privilege  of  presenting  the  citation  of  the 
fourth  recipient  of  the  Progress  Award  medal,  Dr.  Herbert  T.  Kalmus. 
In  addition  to  having  a  knowledge  born  of  direct  contact  with  the 
outstanding  achievements  of  Dr.  Kalmus  during  recent  years,  to- 
gether with  a  review  of  his  broad  achievements  of  record  previous  to 
that  period,  it  has  been  my  further  privilege  to  know  him  in  work  and 
in  play,  to  become  acquainted  with  his  leadership,  and  to  enjoy  his 
friendship. 

Dr.  Kalmus  is  a  rugged  product  of  New  England,  with  a  back- 
ground characterizing  the  stability,  conservatism,  and  modesty  of 
that  older  section  of  our  country.  This  background  took  him  to  the 
Massachusetts  Institute  of  Technology  from  which  he  received  his 
Bachelor  of  Science  Degree  in  1904.  It  is  noteworthy  that,  during 
his  tour  of  education  at  M.  I.  T.,  among  other  things  Dr.  Kalmus  was 
called  upon  to  perform  some  consulting  work  in  connection  with  the 
construction  of  the  aqueduct  which  was  later  to  supply  the  City  of 
New  York  with  water.  The  problem  was  solved  with  a  directness 
and  practicality  characteristic  of  his  subsequent  achievements. 

As  a  graduate  fellow  of  the  Massachusetts  Institute  of  Technology 
Dr.  Kalmus  studied  in  Europe,  first  at  the  University  of  Berlin  under 
Professors  Paul  Drude,  Walter  Nernst,  and  J.  H.  Vant  Hoff,  and 
subsequently  at  the  University  of  Zurich  where  he  completed  his 
work  for  a  degree  of  Doctor  of  Philosophy.  His  thesis  was  an  ex- 
tensive experimental  and  theoretical  study  of  "Electrical  Conductiv- 
ity and  Viscosity  of  Fused  Electrolytes."  Returning  to  M.  I.  T., 
Dr.  Kalmus  spent  the  next  six  years  as  Research  Associate  in  the 
laboratory  of  Professors  A.  A.  Noyes  and  H.  M.  Goodwin,  conducting 
experimental  investigations  in  the  field  of  physical  chemistry.  In- 
dependently he  published  papers  on  various  subjects  in  a  wide  field, 
including  destruction  of  bacteria  by  radiation  from  electrical  dis- 
charges, electromotive  forces  set  up  in  the  human  body  by  emotions, 
etc. 

In  1913  Dr.  Kalmus  left  the  Massachusetts  Institute  of  Technology 
in  response  to  an  invitation  to  join  the  faculty  of  Queen's  University, 
Kingston,  Ontario,  where  he  became  Professor  of  Physics.  Out- 


558  PROCEEDINGS  OF  SEMI- ANNUAL  BANQUET  [j.  s.  M.  p.  E. 

standing  performance  was  reflected  in  his  appointment  as  Director  of 
Research,  laboratory  of  electrochemistry  and  metallurgy  for  the 
Canadian  Government  which  led  into  important  activities  in  the 
industrial  field.  His  study  of  the  then  relatively  little  known  metal, 
cobalt,  was  covered  by  six  articles  published  by  the  Canadian  Bureau 
of  Mines,  laying  the  groundwork  for  practical  industrial  uses  of  the 
metal.  Other  industrial  applications  included  the  recovery  of 
metallic  values  of  waste  materials  by  centrifuging  and  the  production 
of  alumina  from  nephalene  cyanates. 

Interests  seeking  an  equivalent  of  alundum  and  carborundum 
for  the  rapidly  narrowing  abrasives  supply  called  on  Dr.  Kalmus  to 
solve  the  problem.  His  work  in  this  field,  together  with  some  patents 
resulting  therefrom,  were  the  basis  of  The  Exolon  Company  which 
Dr.  Kalmus  developed  to  an  important  and  profitable  business,  be- 
coming successively  vice-president,  treasurer,  and  president.  Dr. 
Kalmus  retired  from  this  business  when  its  technical  problems  were 
well  in  hand  and  it  had  become  an  important  factor  in  the  abrasive 
industry.  With  Dr.  D.  F.  Comstock,  Dr.  Kalmus  organized  a  firm  of 
consulting  engineers,  Kalmus,  Comstock  &  Wescott,  Inc.,  which 
investigated  a  considerable  number  of  live  industrial  problems. 
Some  of  them  were  undertaken  and  solved  with  extraordinary  facility. 

One  of  these  problems  had  long  engaged  the  attention  of  many 
scientists,  experimenters,  and  engineers  in  their  quest  to  relieve  the 
drabness  of  the  black  and  white  motion  picture  from  its  monochrome 
limitation  and  to  bring  to  the  screen  the  naturalness  of  color.  Out 
of  this  endeavor  Technicolor  was  born  and  has  engaged  the  principal 
attention  of  Dr.  Kalmus  for  the  past  fifteen  years. 

We  were  both  entertained  and  instructed  today  when  some  phases 
of  the  romance  of  this  development  were  described  by  Dr.  Kalmus 
in  his  paper,  ' 'Technicolor  Adventures  in  Cinemaland." 

In  charting  the  course  of  Technicolor  so  as  to  develop  a  practical 
engineering  solution  to  the  problems  of  putting  natural  color  on  the 
screen,  Dr.  Kalmus  soon  found  much  necessary  work  to  be  done  not 
apparently  connected  with  color.  For  it  must  be  borne  in  mind  that 
in  the  neighborhood  of  1920  the  state  of  black  and  white  motion 
pictures  was  still  relatively  undeveloped,  for  cameras,  photographic 
materials,  processing  and  projection  equipment  were  in  an  elemental 
state.  Furthermore,  at  that  time  available  facilities  were  extremely 
limited  and  had  to  be  created  as  work  proceeded. 

But  Dr.  Kalmus  had  an  ideal,  and,  more  importantly,  the  ability 


Dec.,  1938]  PROCEEDINGS  OF  SEMI-ANNUAL  BANQUET  559 

to  analyze  the  technical  aspects  of  the  problem,  to  develop  and 
supervise  a  staff  of  scientists,  experimenters,  and  engineers  exploring 
and  solving  these  problems  in  a  well  conceived  and  directed  plan, 
travelling  always  toward  the  ultimate  goal  of  natural  color  in  a  form 
practical  for  use  in  the  motion  picture  theater.  The  story  of  Techni- 
color's achievement,  first  in  exploring  and  ultimately  abandoning 
additive  methods  of  color  photography,  is  generally  known.  This 
was  followed  by  the  exploration  and  development  of  a  two-color 
subtractive  process  which  remains  today  as  the  most  practical 
solution  to  this  intermediate  stage  of  bringing  natural  color  to  the 
screen.  This  problem,  however,  was  only  completed  to  be  aban- 
doned, for  it  was  but  a  step  along  the  road  to  the  problem  visualized 
by  Dr.  Kalmus,  which  was  not  to  bring  part  of  the  spectrum  to  the 
screen  but  to  bring  all  of  the  spectrum  to  the  screen.  His  compre- 
hensive leadership  is  perhaps  no  better  typified  than  in  the  wisdom 
and  foresight  which  enabled  him  to  authorize  and  direct  the  develop- 
ment of  the  first  practical  three-color  subtractive  process  for  motion 
pictures  during  the  post-depression  period  when  limited  budgets  and 
an  industry  busy  with  the  developments  of  new  technics  in  an  ex- 
panding art  form  had  little  time,  interest,  or  money  to  experiment  in 
the  color  medium.  In  his  accomplishment  Dr.  Kalmus  is  responsible 
not  only  for  the  leadership  of  the  men  who  were  directly  responsible 
for  the  technical  development  and  solution  of  this  complex  problem, 
but  at  the  same  time  with  a  comprehensive  view  of  the  economics  of 
the  problem  whose  business  aspects  are  fully  as  complex  and  de- 
manding as  the  technical  requirements.  It  is  seldom  in  the  annals 
of  technical  development  that  the  ability  to  direct  the  business, 
economic,  and  technical  aspects  of  a  highly  specialized  enterprise 
have  been  successfully  carried  out  by  a  scientist  whose  ability  reached 
equally  into  the  fields  of  technology,  economics,  and  business. 

This  comprehensive  ability  invited  and  merited  the  support  of 
business  and  financial  leaders  whose  confidence  in  the  record  of  Dr. 
Kalmus  made  available  to  him  the  necessary  large  units  of  finance  to 
undertake  this  extensive  work  which  embraced  the  development  of  a 
process  and  the  construction  of  cameras,  photographic  equipment, 
manufacturing  plants,  and  corollary  facilities.  These  have  developed 
into  a  Technicolor  of  international  proportions  whose  principles  and 
policies  have  reflected  his  leadership  and  have  merited  the  outspoken 
commendation,  not  only  of  the  motion  picture  industry,  but  of  allied 
business  interests. 


560  PROCEEDINGS  OF  SEMI-ANNUAL  BANQUET  [j.  s.  M.  p.  E. 

The  confidence  reposed  in  Technicolor  by  the  important  producers 
of  the  motion  picture  industry  is  perhaps  best  exemplified  by  Techni- 
color's stewardship  of  the  negative  of  major  productions  in  which  re- 
side large  investments  whose  return  is  dependent  upon  the  rapid  and 
reliable  production  of  high  quality  prints.  The  organization  of 
Technicolor,  capable  of  assembling  and  delivering  answer  prints  of 
twelve-reel  feature  pictures  in  approximately  one  week,  the  Techni- 
color plant  in  Hollywood  with  capacity  of  130,000,000  feet  per  year 
and  its  plant  in  England  with  capacity  of  more  than  25,000,000  feet 
per  year,  represent  but  a  part  of  the  enterprise  which  rests  on  the 
shoulders  of  Dr.  Kalmus. 

This  citation  would  not  be  complete,  however,  if  it  were  limited 
to  an  exposition  of  the  past  achievements  of  Dr.  Kalmus.  In  engi- 
neering we  plot  progress  curves,  not  entirely  because  we  are  interested 
in  what  has  happened  but  also  because  we  are  interested  in  the  indi- 
cation of  these  curves  as  to  what  will  happen.  The  progress  curve  of 
Dr.  Kalmus  leaves  little  doubt  not  only  that  it  will  continue  to  main- 
tain its  upward  gradient  but  that  its  form  will  be  exponential.  This 
citation,  then,  is  of  a  man  whose  achievements  have  been  great  and 
whose  unspoken  promise  of  achievement  is  looked  forward  to  by  all  of 
his  associates  whose  highest  praise  is  probably  couched  in  their  fre- 
quent reference  to  the  fact  that  he  has  never  let  them  down.  In  his 
growing  stature  of  technical  and  business  leadership,  Dr.  Kalmus 
casts  a  lengthening  shadow  which,  singularly  enough,  appears  as  a 
rainbow  whose  arc  plots  its  points  of  natural  color  on  the  screens  of 
the  motion  picture  theaters  of  the  world. 

At  the  conclusion  of  Mr.  Rackett's  citation,  the  Progress  Medal  of 
the  Society  for  1938  was  presented  to  Dr.  Kalmus  by  President  Wolf. 
Dr.  Kalmus  responded  as  follows: 

DR.  KALMUS:  Mr.  President,  Mr.  Rackett,  Members  of  the  So- 
ciety, Friends :  Frankly  I  was  surprised  when  Dr.  Goldsmith  notified 
me  some  weeks  ago  that  the  award  of  the  Progress  Medal  of  the 
Society  for  1938  had  been  made  to  me.  I  am  greatly  honored  and  I 
wish  first  to  express  my  deep  appreciation  to  the  members  of  the 
Committee  who  made  the  recommendation,  to  the  members  of  the 
Board  of  Governors  of  the  Society  who  approved  the  recommenda- 
tion, and  to  the  Society  itself. 

This  award  has  been  made  but  three  times  before — to  Dr.  Edward 
C.  Wente  for  the  volume  and  importance  of  his  contributions  to 


Dec.,  1938]          PROCEEDINGS  OF  SEMI-ANNUAL  BANQUET  561 

motion  picture  art;  to  Dr.  C.  E.  Kenneth  Mees  for  outstanding  and 
distinctive  achievement  in  the  field  of  motion  picture  photography; 
and  to  Mr.  Edward  W.  Kellogg  for  outstanding  achievement  in 
motion  picture  technology. 

Tonight,  in  so  graciously  conferring  this  medal  upon  me,  our 
President  has  stated  that  it  is  for  pioneer  activities,  broad  planning, 
and  important  contributions  to  the  development  of  color  motion 
picture  photography.  Mr.  Rackett,  too,  has  been  most  liberal  in  his 
praise  of  my  efforts. 

To  me  all  this  signifies  remarkable  breadth  of  view  among  those 
gentlemen  who  are  shaping  the  destinies  of  this  great  Society.  As 
further  evidence  I  quote  from  Mr.  Kellogg's  remarks  upon  receiving 
the  award  a  year  ago:  ".  .  .It  is  only  proper  that  we  technical  men 
should  express  our  recognition  of  the  fact  that  contributions  to 
progress  take  many  forms  and  that  while  the  working  out  of  purely 
technical  problems  is  an  essential  part,  there  are  other  equally  im- 
portant roles.  Directors  and  managers  who  express  their  faith  in  the 
future  make  progress  possible  by  appropriating  liberal  sums  to  re- 
search, and  by  backing  their  men  through  periods  of  little  apparent 
accomplishment.  .  .  .  Executives  who  see  that  emphasis  is  placed 
upon  the  most  valuable  projects  and  who  can  keep  enthusiasm  alive 
in  their  organization,  engineers  who  put  developments  into  com- 
mercial shape,  salesmen  who  push  the  best  things,  workers  in  the 
field  who  find  the  best  ways  of  using  things  and  give  us  the  benefit  of 
their  experience — all  these  play  an  indispensable  part  in  furnishing 
the  public  with  something  better  than  it  had  before.  ..." 

It  was  such  a  point  of  view  as  this  which  gave  me  the  courage  some 
years  ago  to  abandon  the  relatively  snug  situation  of  conducting 
physical,  chemical,  and  metallurgical  research  within  the  more  or  less 
cloistered  wall  of  the  University  and  to  a  considerable  extent  for  the 
Government,  in  order  to  tackle  the  job  of  planning,  managing,  and 
financing  a  number  of  technical  ventures. 

I  organized  and  had  general  direction  of  a  group  of  scientists  and 
engineers  whose  researches  and  experiments  yielded  the  first  two- 
color,  additive  Technicolor  process.  This  was  about  1916.  Some 
twenty  years  later  our  very  distinguished  member,  Dr.  Mees,  en- 
couraged me  not  a  little  by  remarking:  "I  don't  know  which  is  the 
greater  achievement,  the  work  you  have  done  in  planning,  managing, 
and  financing  Technicolor  through  all  these  difficult  years,  or  the 
actual  scientific  and  technical  progress  that  has  been  made." 


562  PROCEEDINGS  OF  SEMI-ANNUAL  BANQUET  [j.  s.  M.  P.  E. 

It  is  especially  gratifying  to  me  that  the  story  of  my  work  should 
be  presented  here  tonight  by  Mr.  Rackett,  who  has  been  in  the  thick 
of  the  Technicolor  fray  with  me  during  the  last  ten  years,  and  to 
whom  I  give  the  greatest  credit  for  having  solved  many  perplexing 
engineering,  operating,  and  plant  personnel  problems.  The  solution 
of  these  practical  problems  has  made  possible  higher  quality  coupled 
with  lower  costs  and  has  enabled  us  in  Technicolor  to  employ  as  a 
part  of  our  day-to-day  print  manufacturing  procedure  certain  inven- 
tions of  our  research  department  which  otherwise  might  have  re- 
mained merely  paper  patents. 

Some  weeks  ago  my  good  friend,  Mr.  Albert  W.  Hawkes,  President 
of  Congoleum  Nairn,  Inc.,  and  a  director  of  the  Technicolor  com- 
panies, sent  me  a  copy  of  an  article  from  the  August,  1938  issue  of 
Advertising  Age.  It  is  too  long  to  quote  completely,  but  with 
apologies  to  Mr.  F.  C.  Bierne,  its  author,  I  am  taking  the  liberty  of 
paraphrasing  a  portion  of  it  as  follows : 

"An  executive  has  to  decide  what  is  to  be  done;  to  tell  somebody 
to  do  it;  to  listen  to  reasons  why  it  should  not  be  done,  why  it  should 
be  done  by  somebody  else,  or  why  it  should  be  done  in  a  different  way ; 
to  follow  up  to  see  if  the  thing  has  been  done ;  to  discover  that  it  has 
not  been  done ;  to  listen  to  excuses  from  the  person  who  should  have 
done  it ;  to  follow  up  a  second  time ;  to  discover  that  it  has  been  done 
but  incorrectly ;  to  point  out  how  it  should  have  been  done ;  to  con- 
clude that  as  long  as  it  has  been  done  it  might  as  well  be  left  as  it  is  ...  ; 
to  consider  how  much  simpler  or  better  the  thing  would  have  been 
done  had  he  done  it  himself  in  the  first  place;  and  finally  to  reflect 
sadly  that  if  he  had  done  it  himself  he  would  have  been  able  to  do  it 
right  in  twenty  minutes  but  that  as  things  turned  out  he  himself 
spent  two  days  trying  to  find  out  why  it  took  somebody  else  three 
weeks  to  do  it  wrong." 

I  admit  that  some  days  did  seem  like  that  and  still  do  but  they 
are  the  exceptions  not  the  rule  for  as  I  look  back  over  the  years  of 
struggle  with  Technicolor  I  am  convinced  that  the  choice  of  well- 
trained,  able,  resourceful,  loyal  associates  and  assistants,  with  whom 
no  such  procedure  as  that  was  necessary,  was  largely  responsible  for 
the  progress  that  has  been  made. 

In  the  earliest  years  and  during  the  development  of  the  two-color 
process,  up  to  approximately  the  time  of  The  Black  Pirate,  Daniel  F. 
Comstock,  W.  Burton  Wescott,  and  the  late  Professor  E.  J.  Wall 
played  leading  parts,  with  J.  A.  Ball,  E.  A.  Weaver,  and  the  late 


Dec.,  1938J          PROCEEDINGS  OF  SEMI- ANNUAL  BANQUET  563 

Leonard  T.  Troland  assisting  them.  Later  Ball  and  Troland  carried 
on  from  where  Comstock  and  others  left  off.  In  the  transition  to  the 
present  three-color  process,  Ball  took  the  lead,  whereas  Troland  was 
responsible  for  our  earliest  excursions  into  the  field  of  monopack. 

Through  the  years  Natalie  Kalmus  and  George  Cave  and  more 
recently  Robert  Riley  and  Henri  Jaffa  have  had  much  to  do  in  the 
field  of  preparation,  color  direction,  and  photography,  to  bring  to- 
gether, smoothly  and  practically,  the  essential  conditions  for  Techni- 
color and  the  existing  practical  procedure  in  the  studio  and  on  loca- 
tion. Mr.  Frank  R.  Gates  and  Mr.  Kay  Harrison  are  carrying  on  in 
England,  and  I  have  already  referred  to  the  exceptional  work  of  Mr. 
Rackett  and  his  staff. 

And  last  but  by  no  means  least,  I  would  acknowledge  the  tremen- 
dous support  which  our  endeavors  have  at  all  times  received  from 
Eastman  Kodak  Co.  No  account  of  Technicolor  would  be  accurate 
without  acknowledgment  to  Dr.  Mees,  to  Mr.  E.  P.  Curtis,  and  to 
Mr.  John  Capstaff  of  constant  inspiration  and  much  practical  help. 

And  so,  Mr.  President,  with  full  credit  to  all  my  associates  and 
assistants,  both  within  and  without  the  Technicolor  organization, 
except  for  whose  able  performance  and  splendid  loyalty  all  leader- 
ship, whether  planning,  managing,  selling,  or  financing  would  have 
gone  for  naught,  and  in  the  splendid  broad  spirit  of  this  Society  as 
exemplified  by  the  language  of  the  award  itself  and  by  the  remarks  I 
have  quoted,  I  accept  this  medal,  together  with  the  extraordinary 
honor  which  it  signifies,  and  the  opportunity  which  it  bespeaks  for 
continuing  in  the  job  of  trying  to  make  better  and  less  expensive 
motion  pictures  in  color.  . 


TECHNICOLOR  ADVENTURES  IN  CINEM ALAND* 
H.  T.  KALMUS** 


Summary. — An  account  of  some  of  the  highlights  in  the  history  of  the  development 
of  the  business  of  Technicolor  Motion  Picture  Corporation  primarily  from  the  poirt 
of  view  of  its  contact  with  motion  picture  producers,  distributors,  and  exhibitors; 
incidental  to  which  is  an  account  of  the  development  and  growth  of  the  various  Techni- 
color processes  from  a  semi-technical  point  of  view  but  with  special  reference  to  practi- 
cal application  in  the  motion  picture  industry. 

Webster  defines  adventure  as  chance  of  danger  or  loss;  the  encoun- 
tering of  risks;  a  bold  undertaking,  a  daring  feat;  a  remarkable  oc- 
currence or  experience,  a  stirring  incident;  a  mercantile  or  speculative 
enterprise  of  hazard;  a  venture.  The  excursions  of  Technicolor  into 
the  domain  of  the  producers,  distributors,  and  exhibitors  of  motion 
pictures  have  been  all  of  these. 

Technicolor  has  manufactured  and  shipped  prints  of  many  hun- 
dreds of  productions  (during  1937  alone  of  over  350  subjects  for  some 
fifty  different  customers  including  more  than  twenty  features)  and 
since  some  phase  of  adventure  usually  develops  during  the  photog- 
raphy or  printing  of  any  production,  it  is  clear  that  this  account 
does  not  pretend  to  be  complete. 

Nor  are  the  events  described  in  detail  necessarily  those  of  greatest 
importance.  The  writer  having  played  a  continuing  part  will  no 
doubt  unduly  emphasize  some  which  he  found  particularly  interesting, 
whereas  with  the  passage  of  time  others  only  lightly  touched  upon  or 
omitted  may  be  found  to  be  of  greater  significance.  However,  it  is 
hoped  that  this  paper  may  be  a  fitting  preliminary  to  a  more  ambi- 
tious one  which  I  have  been  asked  to  prepare,  reviewing  the  progress 
of  color  cinematography  over  the  past  quarter  of  a  century,  with 
special  reference  to  the  contributions  of  Technicolor. 

Early  in  the  development  of  any  color  process,  two  decisions  of 

*  Presented  at  the  Fall,  1938,  Meeting  at  Detroit,  Mich.,  received  October  28, 
1938. 

**  Technicolor  Motion  Picture  Corp.,  New  York,  N.  Y. 
564 


TECHNICOLOR  ADVENTURES  565 

policy  must  be  made:  first,  how  far  will  it  permit  departure  from 
standard  equipment  and  materials,  and,  second,  how  will  it  attempt  to 
divide  the  additional  requisites  of  recording  and  reproducing  color 
between  the  emulsion  maker,  the  photographic  and  laboratory  pro- 
cedure, and  the  exhibitor's  projection  machine.  Technicolor  as- 
sumed at  the  outset  that  special  cameras  and  special  projectors  were 
permissible,  provided  raw  film  of  standard  dimensions  were  employed. 

The  earliest  Technicolor  laboratory  was  built  within  a  railway  car. 
This  car  was  completely  equipped  with  a  photochemical  laboratory, 
darkrooms,  fire-proof  safes,  power  plant,  offices,  and  all  the  machinery 
and  apparatus  necessary  for  continuously  carrying  on  the  following 
processes  on  a  small  commercial  scale;  sensitizing,  testing,  perfo- 
rating, developing,  washing,  fixing  and  drying  negative;  printing, 
developing,  washing,  fixing  and  drying  positive ;  washing  and  condi- 
tioning air;  filtering  and  cooling  wash  water;  examining  and  splicing 
film;  and  making  control  measurements  and  tests.  In  1917  the  car 
was  rolled  over  the  railway  tracks  from  Boston,  Massachusetts,  where 
it  was  equipped,  to  Jacksonville,  Florida,  where  the  first  Technicolor 
adventure  in  feature  motion  picture  production  was  to  take  place. 
The  camera  was  the  single-lens,  beam-splitter,  two-component 
type,  without  the  refinements  which  came  later.  The  picture  was 
The  Gulf  Between,  with  Grace  Darmond  and  Niles  Welch  playing  the 
leads.  Technicolor  was  the  producer.  Dr.  D.  F.  Comstock,  Mr. 
W.  B.  Wescott,  Professor  E.  J.  Wall,  Mr.  C.  A.  (Doc)  Willat,  Mr. 
J.  A.  Ball,  Mrs.  Kalmus,  and  I  were  all  on  the  job.  The  process  was 
two-color,  additive,  standard  size  frame,  and  hence  demanded  a  mini- 
mum of  the  laboratory  procedure. 

During  the  progress  of  this  production,  February,  1917,  I  was  in- 
vited by  the  American  Institute  of  Mining  Engineers  to  deliver  a 
lecture  at  Aeolian  Hall,  New  York,  to  expound  the  marvels  of  the  new 
Technicolor  process  which  was  soon  to  be  launched  upon  the  public 
and  which  it  was  alleged  by  many  could  hardly  do  less  than  revolu- 
tionize their  favorite  form  of  entertainment. 

The  Gulf  Between  had  been  preceded  by  The  Glorious  Adventure,  a 
feature  picture  made  in  England  by  the  Kinemacolor  Process.  Since 
Kinemacolor  photographed  the  color  components  by  successive  ex- 
posure, it  was  nothing  for  a  horse  to  have  two  tails,  one  red  and  one 
green,  and  color  fringes  were  visible  whenever  there  was  rapid  motion. 
The  Technicolor  slogan  was  two  simultaneous  exposures  from  the 
same  point  of  view,  hence  geometrically  identical  components  and 


566  H.  T.  KALMUS  [j.  s.  M.  P.  E. 

no  fringes.  At  that  time  hundreds  of  thousands  were  being  spent  by 
others  trying  in  impossible  ways  to  beat  the  fringing  of  successive 
exposures  and  the  parallax  of  multiple  lenses. 

I  thought  the  Technicolor  inventors  and  engineers  had  a  practical 
solution,  commercial  at  least  temporarily,  so  I  marched  bravely  to 
the  platform  at  Aeolian  Hall.  It  was  a  great  lesson.  We  were,  of 
course,  introducing  the  color  by  projecting  through  two  apertures, 
each  with  a  color  filter,  bringing  the  two  components  into  register  on 
the  screen  by  means  of  a  thin  adjusting  glass  element.  Incidentally, 
Technicolor  had  to  invent  and  develop  a  horizontal  magnetically  con- 
trolled arc  which  gave  one-third  more  light  for  the  same  current  than 
the  then-standard  vertical  arcs  and  which  could  be  relied  upon  for 
constancy  of  position  of  the  source.  This  latter  was  vitally  impor- 
tant with  a  double  aperture.  During  my  lecture  something  happened 
to  the  adjusting  element  and,  in  spite  of  frantic  efforts  of  the  pro- 
jectionists, it  refused  to  adjust.  And  so  I  displayed  fringes  wider 
than  anybody  had  ever  before  seen.  Both  the  audience  and  the 
press  were  very  kind  but  it  didn't  help  my  immediate  dilemma  or 
afford  an  explanation  to  our  financial  angels. 

Arrangements  were  made  with  Messrs.  Klaw  and  Erlanger  to  ex- 
hibit The  Gulf  Between  by  routing  the  photoplay  one  week  each  in  a 
group  of  large  American  cities.  During  one  terrible  night  in  Buffalo 
I  decided  that  such  special  attachments  on  the  projector  required  an 
operator  who  was  a  cross  between  a  college  professor  and  an  acrobat, 
a  phrase  which  I  have  since  heard  repeated  many  times.  Techni- 
color then  and  there  abandoned  additive  processes  and  special  attach- 
ments on  the  projector. 

As  early  as  1918  Technicolor  had  in  mind  two  principal  methods  of 
attacking  the  color  problem.  Dr.  Leonard  T.  Troland,  who,  at  the 
time  of  his  death,  was  Director  of  Research  of  Technicolor  Motion 
Picture  Corporation,  had  done  some  important  pioneer  work  on  the 
Monopack  process.  Some  of  his  inventions  were  embodied  in  nu- 
merous patent  claims  which  have  been  issued  and  which  were  in- 
tended broadly  to  cover  the  multi-layer  method  both  for  taking  and 
printing.  The  other  Technicolor  attack  was  by  the  imbibition  method. 
Both  Monopack  and  imbibition  were  obviously  capable  of  ulti- 
mate development  into  multi-component  processes,  but  since  im- 
bibition seemed  to  load  more  of  the  problems  on  the  laboratory  and 
relatively  less  on  the  emulsion  maker,  we  pursued  it  with  the  greater 
vigor. 


Dec.,  1938]  TECHNICOLOR  ADVENTURES  567 

A  first  approximation  to  the  Technicolor  imbibition  method  con- 
sisted of  two  gelatin  reliefs  produced  upon  thin  celluloid  which  were 
glued  or  welded  together  back  to  back  .and  dyed  in  complementary 
colors.  Combined  with  the  Technicolor  two-component  cameras, 
this  method  provided  an  immediately  available  system  (1919-21) 
capable  of  yielding  two-component  subtractive  prints.  A  small 
laboratory  or  pilot  plant  was  built  in  the  basement  of  the  building  oc- 
cupied by  the  Technicolor  engineers,  Kalmus,  Comstock  &  Wescott, 
Inc.,  on  Brookline  Avenue,  Boston,  Mass. 

In  1920  Judge  William  Travers  Jerome  first  became  interested  in 
Technicolor;  he  brought  as  associates  the  late  Marcus  Loew,  Nicho- 
las M.  Schenck,  now  President  of  Loew's,  Inc.,  and  Joseph  M. 
Schenck,  now  Chairman  of  the  Board  of  Twentieth  Century  Fox,  Inc. 

Both  Joseph  and  Nicholas  Schenck  have  on  many  occasions  been 
most  helpful  to  Technicolor  by  giving  practical  advice  to  Judge 
Jerome  and  to  me,  but  at  no  time  more  so  than  when  it  was  decided 
to  produce  the  photoplay  which  was  later  called  The  Toll  of  the  Sea. 
This  was  the  first  Technicolor  production  by  the  subtractive  method. 
It  was  photographed  in  Hollywood  under  the  general  supervision  of 
Mr.  Joseph  M.  Schenck,  Chester  Franklin,  Director,  Anna  May 
Wong,  lead,  and  J.  A.  Ball,  Technicolor  cameraman. 

Mr.  Nicholas  Schenck  arranged  for  the  release  of  The  Toll  of  the 
Sea  by  Metro-Goldwyn-Mayer.  The  first  showing  was  given  at  the 
Rialto  Theater  in  New  York,  the  week  of  November  25,  1922.  Let- 
ters of  praise  were  received  from  Maxfield  Parrish,  Charles  Dana  Gib- 
son, and  other  artists.  But  because  of  insufficient  laboratory  ca- 
pacity we  were  not  able  to  supply  prints  fast  enough  to  follow  this  up 
immediately  and  not  until  1923  was  the  picture  generally  released  in 
the  United  States.  It  grossed  more  than  $250,000,  of  which  Techni- 
color received  approximately  $165,000. 

The  prints  of  The  Toll  of  the  Sea  were  manufactured  in  the  original 
pilot  plant  on  Brookline  Avenue,  at  a  manufacturing  cost  of  about  27 
cents  per  foot. 

Every  step  of  the  Technicolor  work  in  The  Toll  of  the  Sea  was  care- 
fully watched  by  the  executives  of  the  industry.  Rex  Ingram,  who 
was  in  the  midst  of  producing  Prisoner  of  Zenda,  wired  Mr.  Loew 
for  permission  to  scrap  everything  he  had  done  in  black  and  white  on 
that  picture  and  start  over  again  in  color.  D.  W.  Griffith  wanted 
to  produce  Faust  and  Douglas  Fairbanks  telephoned  about  producing 
a  feature. 


568  H.  T.  KALMUS  [J.  S.  M.  P.  E. 

Our  first  adventure  in  Hollywood  seemed  successful!  We  were 
told  that  with  prints  as  good  as  we  were  manufacturing  if  offered  at 
8  cents  per  foot  the  industry  would  rush  to  color. 

But,  thus  far  we  had  made  only  inserts  and  one  feature  produc- 
tion, The  Toll  of  the  Sea,  of  which  Technicolor  was  itself  the  pro- 
ducer. We  had  no  adequate  means  of  giving  rush  print  service  in 
Hollywood,  and  we  were  charging  20  cents  a  foot  for  release  prints. 
It  was  another  matter  to  convince  a  producer  to  employ  the  Techni- 
color company  to  photograph  and  make  prints  of  a  production  at  his 
expense  and  risk  and  under  the  conditions  which  prevailed  in  the  mo- 
tion picture  industry. 

Meanwhile  Technicolor  Plant  No.  2  was  being  built  in  Boston  in 
a  building  adjoining  the  one  containing  the  Pilot  Plant.  It  had  a 
capacity  of  about  one  million  feet  of  prints  per  month  and  cost  ap- 
proximately $300,000.  And  in  April,  1923,  the  late  C.  A.  Willat,  in 
charge,  J.  A.  Ball,  Technical  Director,  G.  A.  Cave,  Assistant  Techni- 
cal Director,  were  sent  from  Boston  to  establish  a  small  Technicolor 
laboratory  and  a  photographic  unit  in  Hollywood.  This  was  es- 
tablished in  a  building  in  Hollywood  rented  for  the  purpose. 

In  November,  1923,  Mr.  Jesse  L.  Lasky  and  I  finally  agreed  upon 
the  terms  of  a  contract  between  Technicolor  Motion  Picture  Corpora- 
tion and  Famous  Players  Lasky  Corporation  for  the  production  of 
The  Wanderer  of  the  Wasteland.  We  were  told  by  Mr.  Lasky  that 
they  had  appropriated  not  more  for  this  picture  than  they  would  have 
for  the  same  picture  in  black  and  white.  Also  that  the  time  schedule 
allowed  for  photographing  was  identical  with  what  it  would  have  been 
in  black  and  white.  The  photography  was  to  be  done  by  our  cameras 
in  the  hands  of  our  technical  staff,  but  following  a  budget  and  a  time 
schedule  laid  out  for  them  by  Famous  Players!  Rush  prints  and  the 
quality  of  negative  were  to  be  checked  by  them  each  day.  During 
the  six  weeks  of  photography  our  entire  staff  worked  from  early  morn- 
ing to  late  at  night,  including  Sundays  and  holidays.  At  one  time 
we  were  accumulating  negative  which  we  did  not  dare  to  develop 
because  of  inadequate  facilities  in  our  rented  laboratory.  A  few  of 
us  in  Technicolor  carried  the  terrorizing  thought  that  there  was  no 
positive  assurance  that  we  would  finally  obtain  commercial  negative, 
and  that  the  entire  Famous  Players  investment  might  be  lost.  How- 
ever, Mr.  Lasky  was  not  permitted  to  share  that  doubt.  His  con- 
fidence and  help  during  the  darkest  hours  were  really  marvelous  and 
finally  the  cut  negative  emerged  satisfactorily.  We  delivered  ap- 


Dec.,  1938]  TECHNICOLOR  ADVENTURES  569 

proximately  175  prints  which  were  shown  in  several  thousand  thea- 
ters over  the  country.  These  prints  were  billed  at  15  cents  a  foot, 
for  which  Technicolor  received  approximately  $135,000.  Some  of 
these  prints  were  made  in  the  pilot  plant,  but  more  of  them  were 
made  in  Plant  No.  2  which  was  now  being  run  by  operators  we  had 
trained. 

Nevertheless  there  were  reasons  why  we  could  not  obtain  a  volume 
of  business.  Every  producer  in  Hollywood  knew  that  the  first  im- 
portant production  by  the  Technicolor  process  under  actual  motion 
picture  conditions  and  not  controlled  by  the  Technicolor  company, 
had  just  been  completed  by  Famous  Players  Lasky  Corporation.  A 
considerable  group  of  producers  expressed  themselves  as  interested, 
but  were  waiting  to  see  the  outcome.  Another  group  believed  the 
process  to  be  practical  and  might  have  paid  our  then  price  of  1 5  cents 
a  foot,  but  considered  it  impracticable  to  send  the  daily  work  to  Bos- 
ton for  rush  prints. 

A  small  plant,  primarily  for  the  purpose  of  developing  negative, 
making  rush  prints,  and  providing  a  California  headquarters  was  in- 
stalled at  1006  North  Cole  Avenue,  Hollywood,  in  a  building  erected 
for  our  purposes.  A  large  part  of  the  equipment  was  built  by  our 
engineers  in  Boston  and  shipped  to  California.  The  installation 
was  ready  for  operation  about  the  middle  of  the  year  1924. 

Neither  The  Toll  of  the  Sea  nor  The  Wanderer  of  the  Wasteland,  nor 
any  of  the  inserts  made  until  the  middle  of  1924  had  given  us  experi- 
ence photographing  with  artificial  light.  We  were  therefore  very 
glad  to  obtain  an  order  for  an  insert  in  a  production  directed  by  Mr. 
George  Fitzmaurice,  called  Cytherea,  photographed  in  the  United 
Studios  lot  in  Hollywood,  giving  us  our  first  experience  in  photograph- 
ing an  interior  set  on  a  dark  stage.  Mr.  Fitzmaurice  was  delighted 
with  the  results. 

In  the  Fall  of  1924  we  had  six  men  and  four  cameras  working  in 
Rome  on  the  Metro -Gold  wyn-Mayer  production,  Ben  Hur. 

One  of  the  great  adventures  of  Technicolor  in  Cinemaland  and  a 
milestone  in  its  progress  was  in  the  photography,  print  manufac- 
ture, and  exhibition  of  Douglas  Fairbanks'  The  Black  Pirate.  Mr. 
Fairbanks  had  the  idea  that  the  screen  had  never  caught  and  re- 
flected the  real  spirit  of  piracy  as  one  finds  it  in  the  books  of  Robert 
Louis  Stevenson,  or  the  paintings  of  Howard  Pyle,  and  that  he  could 
catch  it  by  the  use  of  color.  He  said,  "This  ingredient  has  been 
tried  and  rejected  countless  times.  It  has  always  met  overwhelming 


570  H.  T.  KALMUS  [J.  s.  M.  P.  E. 

objections.  Not  only  has  the  process  of  color  motion  picture  pho- 
tography never  been  perfected,  but  there  has  been  a  grave  doubt 
whether,  even  if  properly  developed,  it  could  be  applied,  without 
detracting  more  than  it  added  to  motion  picture  technic.  The 
argument  has  been  that  it  would  tire  and  distract  the  eye,  take  at- 
tention from  acting,  and  facial  expression,  blur  and  confuse  the  ac- 
tion. In  short  it  has  been  felt  that  it  would  militate  against  the 
simplicity  and  directness  which  motion  pictures  derive  from  the  un- 
obtrusive black  and  white.  These  conventional  doubts  have  been 
entertained,  I  think,  because  no  one  has  taken  the  trouble  to  dis- 
sipate them.  A  similar  objection  was  raised,  no  doubt,  when  the 
innovation  of  scenery  was  introduced  on  the  English  stage — that  it 
would  distract  attention  from  the  actors.  Personally  I  could  not 
imagine  piracy  without  color.  ..." 

But  Mr.  Fairbanks'  attorneys  pointed  out  that  this  production 
would  cost  a  million  dollars,  and  asked  what  assurance  there  was 
that  Technicolor  would  be  able  to  deliver  prints,  much  less  satisfac- 
tory prints.  This  difficulty  was  finally  resolved  by  making  a  tri- 
partite agreement  in  which  the  engineering  firm  of  Kalmus,  Corn- 
stock  &  Wescott,  Inc.,  which  still  had  the  pilot  plant  in  the  base- 
ment of  its  building,  agreed  under  certain  conditions  that  it  would 
deliver  the  prints  in  case  Technicolor  company  failed.  There  was 
great  discussion  as  to  the  color  key  in  which  this  picture  would  be 
pitched.  We  made  test  prints  for  Mr.  Fairbanks  at  six  different  color 
levels,  from  a  level  with  slightly  more  color  than  black  and  white,  to 
the  most  garish  rendering  of  which  the  Technicolor  process  was  then 
capable.  Mr.  Fairbanks  set  to  work  on  the  shore  of  Catalina  Island 
and  off  that  shore  on  his  pirate  ship,  with  four  of  the  seven  Techni- 
color cameras  then  in  existence,  to  capture  moods  after  the  manner 
of  impressionistic  painting.  The  picture  was  released  through 
United  Artists  in  1925.  So  far  as  audience  reaction,  press  reviews,  and 
box-office  receipts  were  concerned,  it  was  a  triumph  from  the  start, 
but  for  the  Technicolor  company  it  was  a  terrible  headache. 

Technicolor  was  still  making  the  double-coated  cemented  together 
relief  prints,  so  that  the  red  and  green  images  were  not  quite  in  the 
same  plane,  and  the  pictures  didn't  project  too  sharply  on  the  screen. 
This  double-coated  film  is  considerably  thicker  than  ordinary  black  - 
and-  white  film,  with  emulsion  on  both  sides  which  tends  to  make  it 
cup  more  readily  and  scratch  more  noticeably  than  black-  and-  white 
film.  And  the  cupping  could  occur  in  either  direction,  more  or  less  at 


Dec.,  1938]  TECHNICOLOR  ADVENTURES  571 

random.  Judging  from  the  complaints,  at  each  such  change  in  the 
direction  of  cupping,  the  picture  would  jump  out  of  focus.  We  sent 
field  men  to  the  exchanges.  We  provided  these  men  with  a  supply 
of  new  prints  to  replace  the  cupped  ones  in  the  theaters,  in  order  that 
the  latter  might  be  shipped  back  to  our  laboratory  in  Boston  for  de- 
cupping.  The  newly  decupped  prints  were  temporarily  satisfactory; 
the  picture  was  a  great  success,  but  our  troubles  never  ended. 

It  had  been  clear  that  this  double-coated  process  was  at  best  but  a 
temporary  method,  and  the  work  of  developing  a  true  imbibition 
process  was  being  pressed  in  our  research  department. 

But  unfortunately  the  imbibition  process  was  not  ready  for  The 
Black  Pirate,  or  for  The  Wanderer  of  the  Wasteland. 

Early  in  1925  Mr.  Sydney  R.  Kent,  then  head  of  distribution  of 
Famous  Players  Lasky  Corporation,  said:  "We  have  concluded  not 
to  do  more  Technicolor  pictures  for  the  present,  for  two  reasons :  first, 
because  we  have  had  a  great  deal  of  trouble  in  our  exchanges  due  to 
the  fact  that  the  film  is  double-coated  and  consequently  scratches 
much  more  readily  than  black  and  white,  with  the  necessity  of  having 
to  order  more  replacements,  and  it  is  an  added  bother  to  our  opera- 
tors ;  and,  second,  because  the  cost  is  out  of  all  proportion  to  its  added 
value  to  us.  We  paid  $146,000  additional  for  Wanderer  prints. 
We  understand  that  you  need  volume  to  get  your  costs  down.  At 
an  8-cent  price  we  would  be  interested  to  talk  volume." 

Evidently  Technicolor  needed  the  single-coated  imbibition  prints 
and  volume  to  lower  the  price  to  meet  his  conditions. 

Meanwhile  Mr.  Nicholas  Schenck,  then  President  of  Loew's,  Inc., 
was  advising  us  to  produce  a  picture  ourselves,  to  prove  both  quality 
and  costs. 

And  so  in  1926-27  I  once  more  found  myself  explaining  to  the  di- 
rectors of  Technicolor  that  I  always  had  believed  and  still  believed 
very  thoroughly  in  the  ultimate  success  of  the  Technicolor  project, 
always  provided,  however,  that  it  was  recognized  by  all  the  Directors 
to  be  a  tremendously  difficult  undertaking  technically  and  one  which 
requires  business  sagacity  and  financial  endurance.  These  direc- 
tors, including  the  late  Wm.  Travers  Jerome,  the  late  Wm.  Hamlin 
Childs,  the  late  A.  W.  Erickson,  the  late  Wm.  H.  Coolidge,  the  late 
Thomas  W.  Slocum,  James  C.  Colgate,  Eversley  Childs,  and  Alfred 
Fritzsche,  had  many  earlier  reminders  of  the  necessity  of  financial 
endurance.  Prior  to  1926  over  two  and  one-half  million  dollars  had 
been  spent,  but  this  time  I  was  not  calling  for  money  for  cameras  and 


572  H.  T.  KALMUS  [j.  s.  M.  P.  E. 

printers,  for  imbibition  machines  and  research  salaries;  it  was  to  go 
into  production.  When  they  asked  me  what  I  knew  about  produc- 
tion, I  frankly  told  them  nothing,  but  at  least  I  could  start  from 
scratch  without  some  of  the  fixed  ideas  and  prejudices  concerning 
color  that  some  of  the  Hollywood  producers  seemed  to  have  accu- 
mulated. I  wanted  to  make  short  subjects,  not  primarily  to  make 
money  as  a  producer,  but  to  prove  to  the  industry  that  there  was 
nothing  mysterious  about  the  operation  of  Technicolor  cameras,  that 
the  transition  from  what  the  eye  saw  to  what  the  emulsion  recorded 
was  susceptible  of  reasonable  control  through  understanding,  that 
black  and  white  cameramen  could  easily  be  trained  to  light  for 
Technicolor  cameras,  that  talented  art  directors  could  readily  begin 
to  think  in  terms  of  color,  that  rush  prints  could  be  delivered 
promptly,  and  generally  that  the  job  could  be  done  efficiently  and 
economically,  utilizing  but  not  minutely  imitating  black-  and  white- 
experience. 

The  first  short  we  produced  was  a  story  of  the  creation  of  the 
American  flag,  an  episode  involving  George  Washington  and  Betsy 
Ross.  George  M.  Cohan  probably  never  produced  anything  more 
certain  of  applause  than  when  George  Washington  unfurled  the  first 
American  flag  in  glowing  color.  Another  subject  was  the  divorce 
episode  of  Napoleon  and  Josephine,  photographed  in  November, 
1927,  which  was  booked  all  over  the  world  as  a  companion  short  to 
Charlie  Chaplin's  then  tremendously  successful  production,  The 
Circus.  We  made  twelve  of  these  two-reelers,  an  experience  which 
established  the  fundamentals  of  our  studio  service  both  in  the  camera 
and  color  control  departments,  and  altogether  disclosed  the  answers 
to  a  multitude  of  practical  questions  which  have  served  us  no  end  since 
that  time. 

They  were  produced  economically  and  yet  we  were  continually 
praised  about  them  by  Metro  who  distributed  them.  In  my  opinion 
Technicolor  would  not  have  survived  without  the  experience  of  this 
series  of  short  subjects. 

Our  friends  and  customers  both  in  Hollywood  and  New  York 
praised  and  applauded  these  short  subjects,  but  they  were  only 
shorts.  Mr.  Nicholas  Schenck  advised  us  to  produce  a  feature  pro- 
duction which  Metro  would  distribute. 

I  had  been  much  impressed  with  a  production  called  The  Covered 
Wagon,  a  touching  love  story  with  the  epic  quality  of  slowly  and 
laboriously  conquering  a  continent.  Why  not  have  a  love  story  of 


Dec.,  1938]  TECHNICOLOR  ADVENTURES  573 

the  vikings  with  the  epic  quality  of  fighting  mutiny  and  storms  to 
conquer  an  ocean.  Jack  Cunningham,  recently  a  writer  and  asso- 
ciate producer  at  Paramount,  wrote  The  Covered  Wagon,  so  we  en- 
gaged him  to  write  The  Viking.  We  spent  $325,000  on  this  pro- 
duction and  got  our  full  money's  worth  of  experience  in  all  depart- 
ments. But  also  we  got  our  money  back.  The  late  Irving  Thai- 
berg,  who  was  always  our  friend  and  a  believer  in  Technicolor, 
thought  we  had  a  lot  of  production  for  that  amount  of  money,  and 
bought  it  for  Metro  by  reimbursing  our  cost  to  us. 

There  seemed  to  be  two  principal  troubles  with  The  Viking,  both 
of  which  I  suspected  but  without  certainty.  First,  it  came  out  among 
the  very  last  silent  pictures  in  1929  and,  second,  whiskers.  Leif 
Erickson,  the  viking  hero,  true  to  character,  had  a  long,  curling 
mustache,  whereas  American  audiences  prefer  their  lovers  smooth - 
shaven.  At  times  the  whole  screen  seemed  filled  with  viking  whisk- 
ers. But  the  picture  was  a  good  color  job  and  the  first  to  be  syn- 
chronized with  music  and  sound  effect. 

But  thus  far  we  had  only  isolated  feature  productions.  The  build- 
ing of  color  cameras  on  the  scale  they  exist  today,  the  building  of 
laboratories  of  sufficient  capacity  that  prints  could  be  made  cheaply 
enough  to  make  color  generally  available  could  not  be  carried  on  in 
terms  of  an  occasional  picture. 

We  brought  out  two-color  imbibition  prints  with  silver  sound  track 
in  1928.  The  advantages  in  respect  of  focus,  cupping,  scratching, 
size  of  reel,  and  cost  of  manufacture  were  immediate.  The  gelatin 
on  the  Technicolor  imbibition  film  is  harder  than  on  ordinary  black 
and  white,  and  through  the  years  there  is  substantial  evidence  that 
the  life  of  Technicolor  imbibition  prints  is  greater  than  that  of  ordi- 
nary black  and  white. 

By  early  1929  all  the  important  studios  in  Hollywood  had  become 
thoroughly  sound  conscious.  This  was  a  great  help  to  us  in  intro- 
ducing color.  Prior  to  that,  studio  executives  were  loath  to  permit 
any  change  whatsoever  in  their  established  method  of  photography 
and  production.  But  with  the  adoption  of  sound,  many  radical 
changes  became  necessary.  Technicolor  was  always  confronted  with 
objections  that  photographing  in  color  required  more  light,  different 
costumes,  a  knowledge  of  color  composition,  additional  time,  and  one 
or  the  other  of  these  points,  plus  the  added  forceful  argument  that  it 
cost  more  money,  made  it  difficult  for  us  to  get  started.  In  my  opin- 
ion the  turning  point  came  when  we  ourselves  produced  the  series  of 


574  H.  T.  KALMUS  [j.  s.  M.  P.  E. 

short  subjects.  By  entering  the  field  as  a  producer,  by  keeping  very 
careful  records  of  our  time  and  money  schedules,  and  by  openly  dis- 
cussing with  studio  executives  everything  that  we  were  doing  as  we 
went  along,  we  dissipated  most  of  the  prevailing  misinformation. 
Meanwhile  our  quality  was  improving;  our  costs  were  decreasing. 
Warner  Bros,  and  Metro-Goldwyn-Mayer  were  regularly  coming 
out  with  satisfactory  short  subjects  in  Technicolor,  and  two  inserts 
were  highly  successful,  namely,  Broadway  Melody  and  Desert  Song. 
Paramount  had  produced  a  successful  feature  length  picture  in  Tech- 
nicolor, Redskin.  The  studios  were  beginning  to  be  color  conscious. 

But  it  remained  for  Warner  Bros,  and  its  affiliated  company,  First 
National,  to  take  the  first  step  on  a  large  scale.  Mr.  J.  L.  Warner, 
with  foresight  and  courage,  signed  up  with  us  for  a  series  of  more 
than  twenty  features.  These  included  On  with  the  Show,  the  first 
all-talking  all  Technicolor  feature  picture,  and  Gold  Diggers  of  Broad- 
way, which  has  grossed  over  $3,500,000  and  which  still  ranks  high 
among  the  all-time  outstanding  box-office  attractions.  The  Techni- 
color mechanical  service  of  providing  and  maintaining  cameras  in 
good  working  order  and  of  delivering  rush  prints  on  time  was  well 
established.  Two  more  subtle  departments  of  service,  namely,  help- 
ing producers'  cameramen  to  learn  how  to  light  and  operate  to  advan- 
tage in  Technicolor,  and  consulting  and  advising  in  matters  of  color 
control,  were  being  demanded.  Cooperation  under  the  head  of  color 
control  was  ranging  all  the  way  from  deciding  the  details  of  the  color 
composition  of  sets,  choice  of  materials  and  costurres,  to  the  broad 
planning  and  preparation  of  a  picture  by  wiring  a  color  score  after  the 
manner  in  which  the  musical  score  is  written. 

As  evidence  of  the  increased  color-mindedness  throughout  the  in- 
dustry, Technicolor  had  contracts  for  the  ten  months  beginning 
March,  1929,  covering  the  photography  and  delivery  of  prints  of  the 
footage  equivalent  of  approximately  seventeeen  feature  length  pro- 
ductions. This  required  a  doubling  of  the  Hollywood  capacity  which 
was  accomplished  in  August,  1929.  For  the  year  1930  Technicolor 
had  closed  contracts  for  thirty-six  feature-length  productions  which 
would  call  for  some  12,000,000  linear  feet  of  negative  to  be  sensitized, 
photographed  and  developed  during  that  year  in  the  Hollywood 
plant,  and  a  print  capacity  of  approximately  60,000,000  feet. 

During  this  boom  period  of  1929  and  1930,  more  work  was  under- 
taken than  could  be  handled  satisfactorily.  The  producers  pressed 
us  to  the  degree  that  cameras  operated  day  and  night.  Laboratory 


Dec.,  1938]  TECHNICOLOR  ADVENTURES  575 

crews  worked  three  eight-hour  shifts.  Hundreds  of  new  men  were 
hastily  trained  to  do  work  which  properly  required  years  of  training. 
Many  pictures  were  made  which  I  counselled  against,  and  all  in  the 
face  of  the  fact  that  to  book  a  picture  in  our  crowded  schedules 
called  for  a  deposit  of  $25,000.  At  one  time  we  had  $1,600,000  of  such 
cash  payments. 

Among  the  features  photographed  and  released  during  this  period 
were:  Bride  of  the  Regiment,  Vivienne  Segal  (First  National); 
Bright  Lights,  Dorothy  Mackail  (First  National) ;  Doctor  X,  Lionel 
Atwill  and  Fay  Wray  (Warner  Bros.);  Fanny  Foley  Herself,  Edna 
May  Oliver  (RKO) ;  Fifty  Million  Frenchmen,  all-star  cast  (Warner 
Bros.);  Follow  Thru,  Charles  "Buddy"  Rogers  and  Nancy  Carroll 
(Paramount) ;  Gold  Diggers  of  Broadway,  all-star  cast  (Warner  Bros.) ; 
Golden  Dawn  (Warner  Bros.);  Hold  Everything,  Winnie  Lightner, 
Georges  Carpentier,  and  Joe  E.  Brown  (Warner  Bros.) ;  King  of  Jazz, 
Paul  Whiteman  (Universal);  Kiss  Me  Again  (First  National); 
Life  of  the  Party  (Warner  Bros.) ;  Mamba  (Tiffany  Productions)  ; 
Manhattan  Parade  (Warner  Bros.);  On  with  the  Show,  all-star  cast 
(Warner  Bros.) ;  Runaround  (RKO) ;  Show  of  Shows  (Warner  Bros.) ; 
Song  of  the  West,  John  Boles  and  Vivienne  Segal  (Warner  Bros.); 
Song  of  the  Flame,  Bernice  Clair  and  Alexander  Gray  (First  Na- 
tional) ;  Sweet  Kitty  Bellairs,  Claudia  Dell  and  Perry  Askam  (Warner 
Bros.);  The  Rogue  Song,  Lawrence  Tibbett  and  Catherine  Dale 
Owen  (Metro-Goldwyn-Mayer) ;  Sally,  Marilyn  Miller  (First  Na- 
tional) ;  The  Toast  of  the  Legion,  Bernice  Clair,  Walter  Pidgeon,  and 
Edward  Everett  Horton  (First  National);  The  Vagabond  King, 
Dennis  King,  Jeanette  MacDonald  (Paramount);  Under  a  Texas 
Moon,  Frank  Fay,  Noah  Beery,  Myrna  Loy,  and  Armida  (Warner 
Bros.) ;  Viennese  Nights,  all-star  cast  (Warner  Bros.) ;  Wax  Museum, 
Lionel  Atwill  (Warner  Bros.);  Woman  Hungry,  Sydney  Blackmer 
and  Lila  Lee  (First  National);  Whoopee,  Eddie  Cantor  (Samuel 
Goldwyn  and  Florenz  Ziegfeld). 

In  Warner's  Wax  Museum  and  Goldwyn 's  Whoopee  the  Techni- 
color two-component  process  may  have  reached  the  ultimate  that  is 
possible  with  two  components. 

By  reason  of  the  fact  in  Technicolor  of  complete  separation  of  the 
sound-track  technic  from  the  picture  technic,  the  necessity  (as 
in  black-and-white  procedure)  of  compromise  between  the  sound  and 
picture  quality  is  avoided  and  relatively  better  sound-track  should 
result.  The  first  to  take  advantage  of  this  was  Ted  Reed  who  was  in 


576  H.  T.  KALMUS  [j.  s.  M.  P.  E. 

charge  of  Mr.  Goldwyn's  sound  department  during  the  production  of 
Whoopee.  When  that  picture  was  shown  in  Hollywood  the  sound 
quality  elicited  much  favorable  comment  and  discussion  among  pro- 
ducers and  technicians. 

My  greatest  anxiety  at  the  time  was  that  there  might  be  thrust  upon 
the  public  productions  which  would  be  very  crude  in  color  composi- 
tion and  unfaithful  in  color  reproduction.  Our  own  color  control  de- 
partment was  doing  everything  possible  to  consult  with  and  advise 
directors,  authors,  art  directors,  wardrobe  heads,  paint  departments, 
and  others  in  the  studio,  and  this  department  was  being  expanded  as 
fast  as  practicable.  But  there  was  more  involved  than  questions  of 
composition  and  design.  There  were  the  limitations  of  the  process. 
As  early  as  May  29,  1929,  I  reported  to  our  directors:  "The  fact  that 
we  have  signed  this  large  volume  of  business  on  the  basis  of  our  pres- 
ent two-color  process  has  not  altered,  in  my  opinion,  the  fact  that 
the  quality  of  this  two-color  output  is  not  sufficiently  good  to  meet 
with  universal  approval,  and  hence  cannot  be  regarded  as  ultimate. 
I  feel  confident  that  the  short-comings  of  our  two-color  process  will 
be  aided  by  the  fact  that  they  are  combined  with  voice,  and  par- 
ticularly by  the  fact  that  the  work  includes  so  many  girl  and  music 
type  productions  like  Sally  with  Marilyn  Miller,  and  Paris  with  Irene 
Bordoni.  Also  this  combination  will  offer  a  very  considerable  nov- 
elty angle  for  a  time  which  is  always  important  in  the  amusement 
world.  Gradually,  however,  I  believe  the  public  will  come  to  realize 
that  these  two-color  pictures  do  not  represent  an  ultimate  natural 
color  process.  Consequently  I  feel  urgently  that  our  drive  to  put 
our  process  on  a  three-color  basis  as  soon  as  possible  should  not  in 
the  least  be  abated  because  of  our  success  in  getting  business  on  the 
two-color  basis.  This  three-color  work  is  moving  ahead  and  involves 
a  very  considerable  research  department  in  Hollywood  under  the  di- 
rection of  Mr.  J.  A.  Ball." 

This  premature  rush  to  color  was  doomed  to  failure  if  for  no  other 
reason  because  the  Technicolor  process  was  then  a  two-color  proc- 
ess. In  the  last  analysis  we  are  creating  and  selling  entertainment. 
The  play  is  the  thing.  You  cannot  make  a  poor  story  good  by  sound, 
by  color,  or  by  any  other  device  or  embellishment.  But  you  can 
make  a  good  story  better.  Broadway  has  a  terrible  struggle  each 
season  to  find  good  stories  or  plays  for  a  dozen  successes.  Hollywood 
is  trying  to  find  over  five  hundred.  They  don't  exist.  The  industry 


Dec.,  1938]  TECHNICOLOR  ADVENTURES  577 

needs  all  the  help  it  can  get,  all  the  showmanship  it  can  summon — 
it  needed  sound;  it  needs  color. 

But  color  must  be  good  enough  and  cheap  enough.  The  old  two- 
component  Technicolor  was  neither — hence  it  failed,  but  it  was  a  nec- 
essary step  to  present-day  Technicolor. 

During  the  rush  to  color,  Technicolor  had  not  only  its  own  short- 
comings to  contend  with,  but  also  a  surfeit  of  poor  stories  that  were 
to  be  saved  by  color,  and  a  monotony  of  musicals  more  or  less  on  the 
same  formula.  An  injustice  was  no  doubt  done  Technicolor  by  caus- 
ing it  thus  to  be  identified  so  largely  with  musical  and  period  pro- 
ductions. I  counselled  at  the  time  that  producers  were  no  doubt 
losing  an  opportunity  in  not  taking  advantage  of  the  fact  that  color 
can  be  used  to  intensify  dramatic  effect  and  bring  out  the  best  points 
of  personalities,  advantages  which  have  been  later  used  with  striking 
effectiveness. 

During  the  years  1929  and  1930  Technicolor  appropriated  over 
$3,000,000  for  plants,  equipment,  and  research  work,  which  increased 
its  plant  capacity  from  one  million  to  six  million  feet  of  two-com- 
ponent prints  a  month.  At  the  same  time  that  it  had  been  building 
those  plants  and  training  personnel  to  operate  them,  it  had  been 
filling  its  orders.  Such  conditions  were  not  conducive  to  the  high- 
est quality  product,  even  if  the  orders  had  been  normal.  The  fact 
that  this  rush  was  largely  forced  upon  Technicolor  by  the  producers 
wouldn't  help  in  the  slightest  degree  with  the  exhibitor  or  the  audi- 
ence, even  if  they  knew  of  it.  And  executives  who  were  glad  to  try 
to  work  it  out  with  us  gradually  over  a  period  of  time,  were  sud- 
denly confronted  with  the  necessity  for  drastic  curtailment  of  their 
own  budgets  because  of  a  sharp  drop  in  motion  picture  theater  at- 
tendance. At  the  peak  of  the  rush  Technicolor  had  twelve  hundred 
men  employed  with  a  payroll  of  approximately  $250,000  per  month, 
whereas  by  the  middle  of  1931  these  had  dropped  to  two  hundred 
thirty  men  and  approximately  $70,000.  In  the  middle  of  1931 
picture  production  in  Hollywood  was  at  an  extremely  low  ebb  and  the 
last  week  in  July  is  said  to  have  been  the  worst  week  for  theater  re- 
ceipts in  fifteen  years. 

During  1931  the  base  price  of  Technicolor  prints  was  reduced  from 
83/4  to  7  cents  per  foot. 

But  Technicolor  had  persisted  in  its  research  and  development 
work  so  that  by  May,  1932,  it  had  completed  the  building  of  its  first 
three-component  camera  and  had  one  unit  of  its  plant  equipped  to 


578  H.  T.  KALMUS  [j.  s.  M.  p.  E. 

handle  a  moderate  amount  of  three-color  printing.  The  difference 
between  this  three-component  process  and  the  previous  two-com- 
ponent process  was  truly  extraordinary.  Not  only  was  the  accuracy 
of  tone  and  color  reproduction  greatly  improved,  but  definition  was 
markedly  better. 

However,  we  could  not  offer  the  three-component  product  to  one 
customer  without  offering  it  to  all,  which  required  many  more 
cameras,  and  the  conversion  of  much  of  our  plant.  To  allow  time  for 
this  and  to  prove  the  process  beyond  any  doubt,  we  sought  first  to 
try  it  out  in  the  cartoon  field.  But  no  cartoonist  would  have  it. 
We  were  told  cartoons  were  good  enough  in  black  and  white,  and  that 
of  all  departments  of  production,  cartoons  could  least  afford  the  added 
expense.  Finally  Walt  Disney  tried  it  as  an  experiment  on  one  of 
his  "Silly  Symphonies."  This  first  attempt  was  the  delightful 
Flowers  and  Trees,  following  which  Disney  contracted  for  a  series. 
For  Christmas  1932  came  Santa's  Work  Shop,  the  following  Easter, 
Funny  Bunnies;  in  May,  1933,  came  Three  Little  Pigs,  which  made 
screen  history,  and  in  March,  1934,  Big  Bad  Wolf.  I  needn't  relate 
the  story  of  Disney's  extraordinary  success  with  Technicolor.  The 
"Silly  Symphonies"  in  Technicolor  surpassed  the  "Mickey  Mouses" 
in  black  and  white,  and  then  both  Mickies  and  Sillies  adopted  Techni- 
color. 

Both  the  Disney  Company  and  Technicolor  were  rather  under- 
sized at  birth  and  in  recent  years  both  have  grown  rapidly  in  im- 
portance. A  frequent  conversation  has  been  as  to  which  helped  the 
other  most.  Much  like  the  conversation  between  two  Irishmen  after 
a  considerable  session  at  the  bar:  "Yer  know,  Clancy,  when  I  was 
born  I  weighed  only  five  pounds."  "Yer  did,  and  did  yer  live?" 
"Did  I  live?  Yer  ought  to  see  me  now." 

What  Technicolor  needed  was  someone  to  prove  for  regular  pro- 
ductions, whether  short  subjects  or  features,  what  Disney  had  proved 
for  cartoons.  But  the  producers  asked:  "How  much  more  will  it 
cost  to  produce  a  feature  in  three-component  Technicolor  than  in 
black  and  white?"  This  question  is  always  with  us  and  it  seems  to 
me  the  answer  must  be  divided  into  two  parts;  the  added  cost  of 
prints,  negative  raw  stock,  rushes,  and  lighting  can  be  numerically 
calculated  and  requires  little  discussion.  But  then  there  are  the  less 
tangible  elements  about,  which  there  is  much  discussion.  I  have 
said  to  producers  and  directors  on  many  occasions:  "You  have  all' 
seen  Disney's  Funny  Bunnies;  you  remember  the  huge  rainbow 


Dec.,  1938]  TECHNICOLOR  ADVENTURES  579 

circling  across  the  screen  to  the  ground  and  you  remember  the 
Funny  Bunnies  drawing  the  color  of  the  rainbow  into  their  paint  pails 
and  splashing  the  Easter  eggs.  You  all^admit  that  it  was  marvelous 
entertainment.  Now  I  will  ask  you  how  much  more  did  it  cost  Mr. 
Disney  to  produce  that  entertainment  in  color  than  it  would  have  in 
black  and  white?"  The  answer  is,  of  course,  that  it  could  not  be 
done  at  any  cost  in  black  and  white,  and  I  think  that  points  to  the 
general  answer.  A  similar  analogy  can  be  drawn  with  respect  to  some 
part  of  almost  any  recent  Technicolor  feature. 

If  a  script  has  been  conceived,  planned,  and  written  for  black  and 
white,  it  should  not  be  done  at  all  in  color.  The  story  should  be 
chosen  and  the  scenario  written  with  color  in  mind  from  the  start,  so 
that  by  its  use  effects  are  obtained,  moods  created,  beauty  and  per- 
sonalities emphasized,  and  the  drama  enhanced.  Color  should  flow 
from  sequence  to  sequence,  supporting  and  giving  impulse  to  the 
drama,  becoming  an  integral  part  of  it,  and  not  something  super- 
added.  The  production  cost  question  should  be,  what  is  the  addi- 
tional cost  for  color  per  unit  of  entertainment  and  not  per  foot  of 
negative.  The  answer  is  that  it  needn't  necessarily  cost  any  more. 

In  1932  we  marked  our  base  print  price  down  from  7  cents  to  5l/2 
cents  a  foot. 

Early  in  1933  Mr.  Merian  C.  Cooper  and  Mr.  John  Hay  Whitney 
began  to  show  a  practical  interest  in  Technicolor.  After  thorough 
investigation  of  the  Technicolor  situation  by  Mr.  Whitney  and  his 
associates,  and  as  a  result  of  many  conferences,  a  contract  was  signed 
between  Technicolor  and  Pioneer  Pictures,  Inc.,  on  May  18,  1933, 
which  provided  for  the  production  of  eight  pictures,  superfeature  in 
character  and  especially  featuring  color.  There  were  some  condi- 
tional clauses,  among  others  a  provision  for  extensive  preliminary 
tests.  Certain  doubts  remained  in  the  minds  of  Whitney  and  his  as- 
sociates as  to  the  performance  cf  our  three-component  process  under 
certain  conditions.  Would  the  process  reproduce  the  various  shades 
of  green  in  woodland  and  jungle  ?  For  one  story  they  were  consider- 
ing a  lead  with  very  dark  coloring  and  black  hair.  Would  she  photo- 
graph satisfactorily  against  light  backgrounds?  For  another  story 
they  thought  of  placing  a  decided  blonde  in  the  leading  part;  how 
would  she  photograph  against  various  backgrounds?  What  about 
make-up?  What  about  the  visibility  of  extremely  small  figures  in 
the  distance?  An  exhaustive  sets  of  tests  were  made  with  results 
satisfactory  to  Mr.  Whitney  and  Mr.  Cooper. 


580  H.  T.  KALMUS  [j.  s.  M.  P.  E. 

Then  began  the  hunt  for  the  first  story  to  be  produced.  At  one 
time  Whitney  told  me  they  had  given  consideration  to  no  less  than 
two  hundred  stories. 

While  Mr.  Whitney  was  searching,  Pioneer  Pictures  made  a  very 
practical  and  complete  test  of  the  process  by  producing  the  picture 
La  Cucaracha.  This  short  subject  met  with  tremendous  success. 

La  Cucaracha,  together  with  ' 'Silly  Symphonies,"  caused  a  tre- 
mendous interest  in  three-component  Technicolor.  The  industry  was 
now  waiting  to  see  what  the  first  Whitney  feature  production  would 
be  like.  Meantime  Technicolor  business  was  improving.  Positive 
film  shipments  for  the  first  six  months  of  1933  were  double  what 
they  were  for  the  first  six  months  of  1932.  Appropriation  was  made 
to  increase  the  number  of  cameras  under  construction  from  three  to 
seven. 

The  first  test  of  the  three-component  process  on  a  very  large  set 
was  for  Twentieth  Century  Fox  on  the  closing  sequence  of  The  House 
of  Rothschild. 

Since  Whoopee  in  1930  Mr.  Goldwyn  and  I  had  talked  regularly 
each  year  about  another  picture  in  Technicolor,  so  that  on  one  oc- 
casion Eddie  Cantor  asked  me  if  I  were  coming  for  my  annual  ritual. 
This  time  it  was  the  closing  sequence  in  his  Cantor  picture,  Kid 
Millions,  which  was  another  important  early  three-component  in- 
sert. 

No  account  of  Technicolor  adventures  in  the  realm  of  producers 
would  be  complete  without  affectionate  mention  of  Mr.  Andrew  J. 
Callaghan.  He  was  a  Vice-President  of  the  company,  active  in  sales 
and  studio  contacts  through  our  most  troublous  times.  He  was 
Hollywood's  most  popular  man — loved  by  all — and  has  been  tre- 
mendously missed  by  everybody  in  Technicolor  since  his  death  in 
1934. 

Mr.  Whitney  and  his  Pioneer  Pictures  associates  finally  settled  on 
Becky  Sharp  as  their  first  production  of  the  series  of  eight.  Becky 
was  a  champion  for  hard  luck.  The  original  director,  Lowell  Sher- 
man, was  taken  ill  and  died  during  the  period  of  photographing.  He 
was  succeeded  by  Reuben  Mamoulian.  Unusual  difficulty  was  en- 
countered in  the  sound  recording  so  that  Mr.  Whitney  found  himself 
in  the  ironically  anomalous  position  of  having  produced  the  first 
three-component  Technicolor  feature,  of  having  surmounted  all  the 
hazards  of  color,  yet  being  in  difficulty  with  an  aspect  of  the  work 
which  he  had  naturally  taken  for  granted. 


Dec.,  1938]  TECHNICOLOR  ADVENTURES  581 

During  the  1935-36  season  we  were  manufacturing  in  the  neigh- 
borhood of  23/4  million  feet  of  prints  a  month,  which  included  a 
larger  volume  of  Warner  Bros,  short  subjects  than  ever  before  and 
about  forty  per  cent  of  all  Metro -Goldwyn-Mayer  short  subjects. 

A  very  interesting  and  important  adventure  in  the  history  of 
Technicolor  development  was  the  organization  of  a  British  affiliate, 
Technicolor,  Ltd.,  which  I  organized  as  a  subsidiary  of  Technicolor 
Motion  Picture  Corp.  and  later  developed  in  association  with  Sir 
Adrian  Baillie,  Mr.  Alexander  Korda,  and  The  Prudential  Assurance 
Company,  Ltd. 

The  first  Technicolor  feature  picture  photographed  in  England  was 
Wings  of  the  Morning,  a  race-track  story  which  has  had  very  successful 
distribution  throughout  the  world.  This  production  was  produced 
before  the  London  laboratory  was  built,  and  was  serviced  from 
Hollywood.  In  1936  the  British  laboratory  was  built  at  West  Dray- 
ton,  just  outside  of  London  where  it  is  now  regularly  operating  to  ser- 
vice British  made  productions  and  prints  of  American  made  produc- 
tions for  distribution  in  the  United  Kingdom.  Mr.  Alexander  Korda 
has  been  outspoken  in  his  enthusiasm  for  color,  as  evidenced  by  a  se- 
ries of  pictures  which  he  has  produced,  including  the  current  release 
Drums.  He  is  now  planning  an  all-Technicolor  series  of  pictures,  of 
which  the  first  is  The  Four  Feathers,  at  present  being  photographed  in 
the  Sudan. 

Since  Becky  Sharp  there  have  been  produced  at  Hollywood  and  in 
London  a  large  number  of  important  feature  productions  in  Techni- 
color, including:  Adventures  of  Robinhood,  Errol  Flyn,  Olivia  de 
Havilland  (Warner  Bros.) ;  A  Star  Is  Born,  Janet  Gaynor  and  Fred- 
ric  March  (Selznick  International  Pictures);  Drums,  Valerie  Hobson, 
Sabu,  Raymond  Masey  (London  Films  Productions) ;  Ebb  Tide,  Ray 
Milland,  Frances  Farmer  (Paramount);  Garden  of  Allah,  Marlene 
Dietrich,  Charles  Boyer,  Basil  Rathbone,  Joseph  Schildkraut  (Pio- 
neer Pictures) ;  God's  Country  and  the  Woman,  George  Brent,  Bev- 
erly Roberts  (Warner  Bros.);  Gold  Is  Where  You  Find  It,  George 
Brent,  Olivia  de  Havilland  (Warner  Bros.);  Goldwyn's  Follies,  all- 
star  cast  (Samuel  Goldwyn  Pictures,  Inc.) ;  Her  Jungle  Love,  Dor- 
othy Lamour,  Ray  Milland  (Paramount) ;  Men  with  Wings,  Ray 
Milland,  Louise  Campbell,  Fred  MacMurray  (Paramount) ;  Nothing 
Sacred,  Carole  Lombard,  Fredric  March  (Selznick  International 
Pictures);  Ramona,  Loretta  Young,  Don  Ameche  (Twentieth  Cen- 
tury Fox  Productions);  Sixty  Glorious  Years,  Anna  Neagle,  Anton 


582  H.  T.  KALMUS  [j.  s.  M.  P.  E. 

Walbrook  (Herbert  Wilcox);  Snow  White  and  the  Seven  Dwarfs, 
Walt  Disney  (RKO  Pictures,  Inc.);  Trail  of  the  Lonesome  Pine, 
Sylvia  Sidney,  Fred  MacMurray,  Henry  Fonda  (Walter  Wanger 
Productions);  Tom  Sawyer,  Tommy  Kelly,  Anne  Gillis  (Selznick 
International  Pictures) ;  Valley  of  the  Giants,  Claire  Trevor,  Wayne 
Morris  (Warner  Bros.);  Vogues  of  1938,  Joan  Bennett,  Warner  Bax- 
ter (Walter  Wanger  Productions). 

Generally  speaking,  these  pictures  have  been  extraordinarily  well 
received,  some  of  them  having  broken  attendance  records  in  many 
parts  of  the  world.  Thus  Technicolor  has  met  the  second  great  rush 
into  color  with  steadily  improving  quality  of  its  product  and  a  broad- 
ening range  of  service.  It  is  the  purpose  of  Technicolor,  during  the 
time  that  prints  of  any  picture  are  being  manufactured  in  its  plant, 
to  hold  the  laboratory  open  for  and  at  the  disposal  of  the  customer 
as  if  it  were  his  own.  His  representative  may  inspect  each  of  his 
prints  and  any  changes  suggested  will  be  undertaken  if  practicable. 
To  do  this  he  simply  moves  into  the  inspection  room  where  each 
print  before  shipment  is  compared  by  simultaneous  projection  with  a 
standard  print  approved  by  the  customer  for  the  purpose. 

William  Wellman  who  has  directed  more  three-component  Tech- 
nicolor pictures  than  any  other  individual,  all  of  them  successes, 
namely,  A  Star  Is  Born,  Nothing  Sacred,  and  Men  with  Wings,  has 
said  repeatedly  of  Technicolor  photography  that  he  takes  it  in  his 
stride,  at  substantially  the  same  number  of  setups  per  day  as  black  and 
white.  It  is  noteworthy  that  most  of  the  camera  work  is  now  done 
by  cameramen  in  the  direct  employ  of  the  studios. 

Broadly  considered,  this  recent  array  of  feature  pictures  is  of  such 
a  late  date  that  it  is  too  early  to  render  a  verdict  based  upon  any  sort 
of  generalization  with  respect  to  them. 

Looking  ahead,  Technicolor  has  contracts  for  about  forty  feature- 
length  productions  spread  among  most  of  the  outstanding  producers, 
constituting  a  very  substantial  volume  of  business.  Among  these 
there  are  now  either  being  photographed  or  in  preparation  the  follow- 
ing: Dodge  City,  Errol  Flynn,  Olivia  de  Havilland  (Warner  Bros.); 
Gone  with  the  Wind,  Clark  Gable  (Selznick  International  Pictures) ; 
Heart  of  the  North,  Dick  Foran,  Gloria  Dickson  (Warner  Bros.); 
Jesse  James,  Tyrone  Power,  Henry  Fonda,  Nancy  Kelly  (Twentieth 
Century  Fox);  Kentucky,  Loretta  Young,  Richard  Greene,  Walter 
Brennan  (Twentieth  Century  Fox) ;  Little  Princess,  Shirley  Temple, 
Richard  Greene,  Anita  Louise  (Twentieth  Century  Fox) ;  Northwest 


Dec.,  1938]  TECHNICOLOR  ADVENTURES  583 

Passage,  Robert  Taylor,  Spencer  Tracy  (Loew's,  Inc.);  Sweethearts, 
Jeannette  MacDonald,  Nelson  Eddy,  Frank  Morgan,  Ray  Bolger 
(Loew's,  Inc.) ;  The  Light  That  Failed,-  Ray  Milland  (Paramount) ; 
The  Mikado,  all-star  (G.  &  S.  Productions,  Ltd.);  The  Thief  of  Bag- 
dad (London  Films  Productions) ;  The  Wizard  of  Oz,  Judy  Garland, 
Jack  Haley,  Bert  Lahr,  Ray  Bolger  (Loew's,  Inc.);  and  a  second 
feature-length  production  is  being  prepared  by  Walt  Disney  Enter- 
prises, Inc. 

To  meet  this  growing  volume  of  business  Technicolor  many  months 
ago  appropriated  some  $1,500,000  to  increase  the  number  of  its  cam- 
eras and  to  double  its  plant  capacity.  This  expansion  program  is 
now  well  on  its  way  to  completion. 

I  have  thus  passed  over  rapidly  the  matter  of  eighteen  pictures  to 
be  produced  in  Technicolor  during  the  last  part  of  this  year  and  the 
first  six  months  of  next  year,  although  they  will  probably  represent 
an  investment  of  some  fifteen  million  dollars. 

The  foreign  situation  is  becoming  increasingly  difficult.  Sales  to 
Germany,  Spain,  Japan,  and  China  have  practically  ceased,  and  in 
many  other  foreign  countries  they  are  below  normal.  The  Italian 
Government  controls  the  entire  distribution  of  films  in  Italy,  which 
probably  means  that  everything  possible  will  be  done  to  distribute 
Italian-made  pictures  at  the  expense  of  English  and  American-made 
pictures.  To  cope  with  the  various  regulations  of  censorship,  the 
various  languages  requiring  either  superimposed  titles  or  dubbing 
with  new  sound-track,  has  for  years  been  difficult  enough,  but  with 
the  more  recent  quota  laws,  import  duties,  exchange  difficulties,  and 
especially  in  the  face  of  the  impossibility  of  getting  money  out  of 
several  foreign  countries,  to  continue  in  the  motion  picture  business 
there  means  adventures  in  other  businesses,  possibly  including  bank- 
ing and  politics.  The  establishment  of  Technicolor  laboratories  at 
various  points  over  the  world  is  a  practical  necessity  and  despite  all 
these  difficulties  definite  progress  is  being  made. 

About  a  year  ago  Technicolor  established  a  department  to  contact 
exhibitors  directly.  Its  representatives  travel  over  the  country  to 
call  upon  exchange  managers,  theater  managers,  and  projectionists. 
The  purpose  has  been  to  study  projection  and  screen  conditions  at 
the  theater;  to  advise  how  to  get  the  best  results  with  Technicolor 
prints,  to  listen  to  complaints  and  establish  good  will,  and  particularly 
to  obtain  projectionist,  manager,  and  audience  reactions  to  produc- 
tions in  Technicolor.  The  results  have  been  most  gratifying;  we 


584  H.  T.  KALMUS  [j.  s.  M.  P.  E. 

have  found  that  the  public  reaction  to  Technicolor  pictures  is  ex- 
tremely favorable  and  that  exhibitors  throughout  the  country  are 
realizing  more  and  more  that  Technicolor  has  great  box-office  value. 

In  the  letter  from  Dr.  Goldsmith,  suggesting  for  himself  and  Mr. 
Crab  tree,  that  I  write  this  paper,  he  said,  "I  believe  it  would  be  of 
particular  interest  to  the  engineers  and  the  industry  if  you  cared  to 
indicate  how  you  happened  to  cling  so  tenaciously  to  these  develop- 
ments through  the  'dark  ages'  when  color  motion  pictures  were  not 
so  well  appreciated."  All  I  have  said  points  to  the  answer;  it  was 
marvelously  interesting;  it  was  great  fun;  we  couldn't  let  anybody 
down,  neither  customers,  employees,  stockholders,  nor  directors. 
But  there  was  something  else  too;  there  was  always  something  just 
ahead,  a  plan  for  tomorrow,  something  exciting  to  be  finished — yes, 
and  something  more  to  be  finished  after  that;  and  I  am  willing  to 
predict  that  it  won't  be  finished  for  many  years  yet.  The  type  of 
film  which  will  be  standard  for  natural  color  pictures  ten  years  hence 
may  not  yet  have  emerged.  I  predict  that  within  two  years  Techni- 
color will  have  done  away  with  special  cameras  and  be  regularly  em- 
ploying single  strips  of  negative  through  any  standard  motion  picture 
camera  and  that  within  two  months  for  special  purposes  and  within 
six  months  for  more  general  purposes  it  will  be  offering  to  its  cus- 
tomers a  negative  for  use  in  its  present  cameras  with  from  three  to 
four  times  the  speed  of  its  present  negative.  That's  why  we  cling  so 
tenaciously;  there's  always  something  ahead;  there  always  will  be; 
our  pride  is  enlisted;  it's  our  job. 

DISCUSSION 

MR.  CRABTREE:  I  have  been  greatly  impressed  by  the  way  in  which  color  de- 
velops the  loveliness  of  the  ladies,  especially  the  blondes  and  the  redheads.  Are 
the  producers  sold  on  the  fact,  and  do  they  make  screen  tests  of  potential  stars  in 
both  color  and  black  and  white? 

DR.  KALMUS:  The  program  of  testing  is  always  with  us.  There  has  been  no 
end  of  tests,  both  in  black  and  white  and  in  color,  for  comparative  purposes. 
Relatively  few  are  being  made  now;  many  producers  think  they  are  not  necessary. 

MR.  CRABTREE:  I  have  been  wondering  whether  the  usual  methods  of  insert- 
ing backgrounds  are  being  used  with  Technicolor.  Were  there  very  many  back- 
ground shots  in  Men  with  Wings? 

DR.  KALMUS  :     We  do  projection  background  work  regularly. 

MR.  CRABTREE:     Is  it  as  flexible  as  with  black  and  white? 

DR.  KALMUS:     Not  quite,  but  sufficiently  flexible  to  be  very  practicable. 

MR.  WOLF:  I  understand  Technicolor  will  be  available  in  a  single  film  for 
use  in  standard  cameras.  Will  the  processing  be  difficult  or  will  it  be  as  simple 
as  with  black  and  white? 


Dec.,  1938]  TECHNICOLOR  ADVENTURES  585 

DR.  KALMUS:  That  is  getting  into  a  realm  I  am  avoiding  for  the  present. 
However,  I  think  it  will  be  some  time  before  the  processing  will  be  as  simple  as 
black-and-white,  if  ever.  The  program  as  we  have  it  outlined  will  be  simple  and 
practicable  as  compared  with  the  programs  weliave  been  through  before. 

MR.  KELLOGG:  When  you  have  a  two-color  system,  do  you  leave  some  silver 
in  the  film  in  order  to  get  some  black  in  addition  to  what  you  get  from  the  dyes? 

DR.  KALMUS:  The  two-component  system  was  strictly  two-component. 
The  present  system  is  really  four-component — the  three  components  ordinarily 
thought  of  as  the  color  components,  and  black. 

MR.  THOMAS:  Have  you  obtained  any  data  of  value,  from  the  projection 
standpoint,  from  the  questionnaires  sent  out  with  the  prints  of  Goldwyn  Follies? 

MR.  RACKETT:  We  have  received  valuable  information  from  the  projection- 
ists' comments  on  the  cards  sent  to  theaters  in  advance  of  the  showing  of  Techni- 
color pictures. 

The  comments  may  be  divided  into  two  classes:  first,  those  referring  to  the 
physical  condition  of  the  film,  which  have  occasioned  our  making  minor  changes 
in  the  visibility  of  instruction  titles  and  changeover  cue  marks ;  the  second,  relat- 
ing to  the  density  and  color  values  of  prints,  which  are  a  little  more  difficult  to 
classify  as  they  have  to  be  interpreted  in  connection  with  data  from  our  field  divi- 
sion relating  to  projection  equipment. 

Most  theaters  are  equipped  with  high-intensity  arcs  which  produce  a  screen 
image  that  is  slightly  bluish.  Technicolor  prints  are  balanced  to  yield  a  neutral 
image  on  such  a  screen. 

Small  projection  units  equipped  with  Mazda  light  produce  a  screen  image  that 
is  slightly  orange.  When  a  print  balanced  for  a  high-intensity  arc  is  projected  by 
a  Mazda  light  the  screen  result  will  be  slightly  orange. 

When  we  are  establishing  the  density  and  color  balance  of  a  feature  picture,  we 
make  a  series  of  prints  and  usually  arrange  to  view  these  with  the  producer  of  the 
picture  in  a  number  of  first-run  theaters,  as  far  as  time  permits.  We  then  com- 
pare a  number  of  prints  in  a  room  where  we  can  project  simultaneously  on  matched 
screens  as  many  as  six  prints  of  the  same  reel.  We  get  a  comparison  of  such  fine- 
ness that  we  have  not  been  able  to  find  quantitative  methods  of  measuring  the 
differences. 

All  the  data,  including  the  important  and  welcome  comments  of  the  projection- 
ists on  the  print  comment  cards  attached  to  the  print  suggestion  booklets,  are  very 
helpful  in  establishing  the  final  results. 

MR.  GRIFFIN:  How  quickly  is  the  rush  print  available  in  the  three-component 
process  after  the  negatives  leave  the  camera? 

DR.  KALMUS:     Regular  twenty-four  hour  service. 


A  METHOD  FOR  DETERMINING  THE  SCANNING  LOSS 
IN  SOUND  OPTICAL  SYSTEMS* 

E.  D.  COOK**  AND  V.  C.  HALLt 

Summary. — The  usual  methods  of  evaluating  the  frequency  characteristic  of 
sound  records  have  been  satisfactory  for  the  determination  of  the  required  correction 
for  overall  losses.  However,  the  losses  due  to  aperture  and  optical  effects  are  not 
known  with  sufficient  precision  to  permit  an  inferior  limit  to  be  assigned  to  film  loss 
only. 

The  method  described  was  chosen  in  connection  with  a  high-fidelity  development  and 
consists  of  comparing  direct  measurements  made  on  images  formed  by  contact  print- 
ing a  geometrically  shaped  test-object  on  the  film  with  measurements  of  frequency 
records  made  using  the  recorder  optical  system.  While  the  results  obtained  cannot  be 
applied  generally  as  yet,  due  to  the  difficulty  of  correcting  for  variations  in  slit  il- 
lumination, and  for  different  gammas,  the  method  is  capable  of  segregating  film  loss 
from  other  losses  for  the  specific  conditions  under  which  the  test  is  conducted. 

In  the  early  development  of  the  high-fidelity  system,  considerable 
compensation  was  employed  in  recording  to  overcome  the  effect  of 
high-frequency  losses.  Technical  disagreements  over  the  amount  of 
correction  required  were  encountered  almost  at  once.  Part  of  the 
difficulty  was  due  to  the  variations  in  film  characteristics  obtained 
by  different  laboratories.  Measurements  of  film  losses  were  reported 
that  disagreed  among  themselves.  The  need  for  precise  methods  for 
the  measurement  of  these  losses  was  evident  and  this  was  not  dis- 
pelled even  by  the  eventual  agreement  on  overall  recording  losses. 

Since  artistic  achievements  are  dependent  in  part,  at  least,  on 
technical  improvements,  it  was  desirable  to  establish,  if  possible,  the 
inferior  limit  for  film  loss,  for,  as  more  knowledge  became  available 
concerning  these  losses,  it  seemed  logical  that  means  for  reducing 
high-frequency  compensation  might  be  devised.  This  would  re- 
lease for  useful  recording  a  portion  of  the  amplitude  range  otherwise 
employed  merely  to  overcome  losses. 

*  Presented  at  the  Spring,  1938,  Meeting  at  Washington,  D.  C.;  received 
Aug.  12,  1938. 

**  General  Electric  Co.,  Schenectady,  N.  Y.,  formerly  RCA  Manufacturing 
Co.,  Camden,  N.  J. 

t  Eastman  Kodak  Co.,  Rochester,  N.  Y. 
586 


DETERMINING  SCANNING  Loss  587 

For  these  reasons,  it  was  felt  desirable  to  examine  other  methods  of 
determining  the  frequency  loss  due  to  the  film  alone,  and  that  these 
methods  should  be  as  divorced  as  possible  from  optical  systems  and 
apertures  even  though  the  test  conditions  were  somewhat  different 
from  those  of  actual  recording.  It  seemed  probable  at  that  time 
that  much  remained  to  be  said  concerning  the  effect  of  the  optical 
system  on  losses  ascribed  to  the  emulsion.  A  method  independent 
of  the  recording  optical  system  would  offer  a  useful  means  of  experi- 
mentally determining  the  magnitude  of  the  combined  losses  caused 
by  the  optical  system.  For  want  of  a  better  designation,  the  com- 
bined losses  due  to  the  optical  system  will  be  called  scanning 
losses. 

Two  general  methods  of  steady-state  analysis  are  available  for 
film  measurements:  one  is  static,  while  the  other  is  dynamic.  As 
is  implied,  in  the  first  method  a  sinusoidal  exposure  is  made,  usually 
on  a  small  sample,  and  the  result  is  analyzed  by  the  methods  of 
harmonic  analysis.  In  the  second  method,  sinusoidal  recordings  at 
various  frequencies  throughout  the  desired  spectrum  are  made  and 
the  record,  analyzed  by  a  densitometer  or  from  the  output  of  a  re- 
producer whose  characteristics  are  known,  is  employed  to  give  the 
desired  information.  Each  method  has  advantages  for  certain  prob- 
lems and,  similarly,  each  has  its  faults. 

For  example:  In  the  dynamic  method,  aperture  distortion  and 
reduction  of  image  contrast  due  to  lens  flare  and  other  stray  light  in 
recording,  are  too  imperfectly  known  to  permit  the  correct  portion  of 
the  total  loss  to  be  assigned  to  the  film,  while  in  the  static  method,  it 
is  essential  to  determine  that  no  significant  error  is  introduced  into 
results  intended  for  application  to  recording  conditions  by  the  failure 
to  employ  an  equivalent  exposure  time;  that  is,  the  failure  of  the 
reciprocity  law,  or  from  failure  to  have  the  recording  light  preserve 
the  same  angles  of  incidence  as  are  employed  in  direct  recording  when 
a  recording  mask  is  used  to  provide  the  wave-shape.  This  might 
introduce  errors  if  the  results  were  used  in  the  determination  of  the 
overall  losses  for  a  system  under  usual  operating  conditions.  In 
evaluating  the  film  loss  by  the  dynamic  method,  it  would  also  be 
necessary  to  provide  sufficient  constancy  of  film  motion  in  recording 
as  well  as  in  reproducing  to  insure  accuracy  and  uniformity  in  the 
result.  The  oscillator  wave-shape  would  have  to  be  adequately  free 
from  harmonics;  amplifiers,  galvanometers,  etc.,  should  have  linear 
response,  while  optical  system  images  should  have  uniform  illumina- 


588  E.  D.  COOK  AND  V.  C.  HALL  [j.  s.  M.  p.  E. 

tion  and  the  influence  of  such  effects  as  chromatic  and  spherical  aber- 
rations would  have  to  be  known. 

In  the  static  method,  there  is  a  choice  of  analyzing  separate  sam- 
ples of  different  wavelengths  or  of  employing  a  complex  wave-shape 
from  which  the  amplitudes  of  the  various  frequencies  are  determined 
by  the  method  of  harmonic  analysis.  In  the  first  alternative,  the 
number  of  samples  needed  for  analysis,  in  order  to  insure  the  accuracy 
and  uniformity  of  the  result,  would  be  quite  large;  whereas,  in  the 
latter,  measurement  errors  due  to  any  increased  steepness  of  wave- 
front  resulting  from  the  superposed  frequencies  would  have  to  be 
guarded  against.  Likewise  another  possible  measurement  error 
arises  from  the  necessity  of  taking  differences  between  a  measured 
quantity  and  the  applied  value  of  that  frequency  if  the  amplitude  of 
the  latter  is  allowed  to  become  small.  The  general  agreement  of  a 
reasonable  number  of  results  in  either  method  would  be  required  as 
a  safeguard  from  accidental  error.  In  spite  of  the  conditions  for 
reciprocity  and  collimation  of  exposure,  the  static  method  is  especially 
attractive  for  film  characteristics,  since  all  aperture  and  optical  sys- 
tem losses  can  be  practically  eliminated.  It  is  evident  that  by  proper 
comparison  between  the  two  methods,  scanning  losses  may  be  deter- 
mined. The  results  of  some  of  the  preliminary  work  with  the  static 
method  will  be  given.  These  are  not  intended  for  use  in  an  accurate 
determination  of  film  or  scanning  losses,  but  are  given  merely  to  il- 
lustrate what  information  is  obtained  by  this  method.  Further 
work  must  be  done  to  define  accurately  the  losses  mentioned. 

The  tests  were  developed  from  the  mathematical  viewpoint  rather 
than  the  one  mentioned  above.  It  is  the  property  of  a  linear  system 
having  constant  coefficients,  that  the  "steady-state"  behavior  is  in- 
dicated by  its  "transient  response."  However,  in  the  mathematical 
case,  a  second  "transient"  at  a  later  "time"  coordinate  would  not 
affect  the  "response"  at  a  previous  "time,"  whereas,  in  film  work,  the 
"time"  coordinate  is  transformed  into  a  "distance"  coordinate  by  the 
film  motion  and  a  sort  of  "adjacency"  effect,  which  causes  the  "trans- 
ient" to  extend  in  both  directions,  is  known  to  exist.  Therefore,  it 
was  concluded  that  the  simple  expedient  of  exposing  a  film  to  the 
correct  degree  on  one  side  of  a  straight-edged  mask  (which  prevented 
exposure  everywhere  else)  and  analyzing  the  growth  of  density  at  the 
transition,  should  be  replaced  by  some  other  process,  preferably  a 
periodic  one,  in  which  wave-shape  changes  would  include  the  "ad- 
jacency" effect  and  reveal  losses  in  frequency  response.  Such  an 


Dec.,  1938]  DETERMINING  SCANNING  LOSS  589 

exposing  process  is  found  in  the  stationary  exposure  of  a  square  wave- 
shape. Composed,  as  it  is,  strictly  of  the  odd  harmonics,  it  is  im- 
possible to  change  its  square  wave-form-  by  any  operator  which  raises 
it  to  a  power,  integral  or  fractional,  or  by  adding  or  subtracting 
various  combinations  of  this  operation.  This  property  is  especially 
useful  in  electrical  circuits,  since  even  a  rectifier  does  not  affect  the 
inherent  "squareness"  of  the  resultant  wave;  that  property  can  only 
be  affected  by  the  variation  of  frequency  selectivity  of  the  circuit. 

For  practical  work,  a  wave  of  moderate  frequency  would  preserve 
much  of  its  "squareness"  if  the  transmission  were  constant  only  over 
the  essential  range  of  audio  frequencies.  The  loss  of  amplitude  of 
odd  harmonics  during  transmission  results  in  the  creation  of  even 
harmonics  only  in  the  presence  of  non-linearity;  i.  e.,  if  the  harmonics 
modulate  one  another.  It  has  been  a  fundamental  assumption  that 
the  film  is  sufficiently  "linear"  to  permit  superposition  of  stimuli 
without  cross-product  or  modulation  terms.  The  correctness  of  this 
assumption  was  tested  to  a  reasonable  degree  of  accuracy  before 
these  experiments  were  begun.  The  results  found  by  Baker  and 
Robinson1  for  variable-amplitude  recording  also  show  the  assumption 
well  warranted,  at  least  to  the  order  of  approximately  one  per  cent 
over  the  density  range  found  satisfactory  for  commercial  sound  rec- 
ords. It  was  concluded,  therefore,  that  any  departure  from  "square- 
ness" in  the  resultant  wave-shape  of  records  falling  in  this  density 
range  could  be  safely  attributed  to  change  of  amplitude  of  harmonics, 
viewing  the  whole  process  as  a  stimulus  acting  through  an  operating 
function  to  produce  the  resultant  wave  of  density.  It  is  interesting 
to  observe  that  a  100-per  cent  modulated  square- wave  record  made 
by  amplitude  recording  would  be  indistinguishable  from  one  made  by 
density  recording. 

The  physical  reasoning  applying  to  images  made  under  conditions 
of  minimum  distortion  is  apparently  much  simpler.  If  the  system -is 
sufficiently  linear,  it  is  merely  necessary  to  employ  an  adequate  num- 
ber of  frequencies  of  known  amplitudes  simultaneously.  Then,  if 
cross-product  terms  do  not  exist,  it  is  convenient  to  choose  only  the 
odd  harmonics  having  assurance  that  the  amplitude  of  any  harmonic 
has  not  been  altered  to  a  significant  degree  by  the  interaction  of  any 
two  different  frequencies  through  cross-product  terms  of  any 
order. 

The  amplitude  of  the  harmonics  in  a  square  wave  of  height  A  may 
be  obtained  from  equation  1. 


590  E.  D.  COOK  AND  V.  C.  HALL  [j.  s.  M.  P.  E. 

n  =  oo 

A  A    \     >  1 

y  =  —    )     -  sin  nwt  (/) 

TT    /   ^  n 
n  =  1 

where  n  —  1,  3,  5,  etc.  .  .  . 

This  particular  wave-shape  has  mechanical  advantages  in  con- 
structing the  test-object  to  be  used  as  a  mask.  This  offsets  to  a 
large  degree  the  difficulty  due  to  the  decreasing  amplitude  of  the 
higher  order  harmonics. 

In  common  with  all  experimental  work,  these  results  are  valid  for 
conditions  of  the  tests.  The  difficulty  of  exposing  the  sample  film 
under  conditions  comparable  to  those  used  in  the  dynamic  method 
resulted  in  the  choice  of  the  conditions  employed  for  these  tests. 
Therefore,  the  film  loss  indicated  may  not  be  applied  generally  except 
to  these  conditions.  However,  consistent  differences  between  this 
method  and  the  measurements  made  on  frequency  records  using 
usual  recording  equipment  may,  for  comparable  conditions,  be  re- 
garded as  a  scanning  loss.  It  would  be  incorrect  to  ascribe  such  extra 
losses  to  the  film  since  they  would  be  the  result  of  circumstances  not 
common  to  the  two  methods  of  test,  and  if  sufficient  care  has  been 
used  in  regard  to  unnecessary  faults,  such  as  lack  of  sufficient  speed 
constancy,  etc.,  in  the  dynamic  method,  these  circumstances  are 
limited  to  the  optical  systems.  It  may  be  entirely  correct  to  say  that 
present-day  technic  knows  no  way  to  improve  scanning  conditions 
and  therefore  obtain  lower  overall  losses,  but  it  is  not  logically  cor- 
rect to  assign  the  excess  losses  to  the  film.  For  example,  assuming 
that  lens  flare  has  been  reduced  to  the  absolute  minimum  that  modern 
skill  can  attain,  some  flare  still  exists  and  causes  a  reduction  in  con- 
trast in  the  optical  image.  Methods  which  do  not  involve  an  optical 
system  should  therefore  show  lower  losses  under  conditions  otherwise 
equivalent  to  methods  which  do  employ  optical  systems.  The  dif- 
ferences in  these  losses  are  logically  chargeable  as  scanning  losses, 
this  being  the  only  difference.  In  fact,  if  two  records  are,  in  general, 
to  have  the  same  frequency  response,  special  care  would  have  to  be 
exercised  to  avoid  all  serious  optical  differences,  since  exposing  stimuli 
of  the  same  total  amount  but  varying  durations  or  varying  degrees  of 
collimation  of  light,  could  hardly  be  expected  to  produce  films  having 
the  same  frequency  response.  The  effect  of  a  reduction  of  contrast 
between  an  object  and  its  image  due  to  an  optical  system  has  been 
mentioned,  but  it  must  be  noted  that  any  change  in  final  contrast, 
whether  due  to  the  characteristics  of  the  optical  system  or  those  of 


Dec.,  1938]  DETERMINING  SCANNING  LOSS  591 

the  film,  affects  the  scanning  losses  obtained.  For  this  reason,  the 
scanning  losses  obtained  under  one  set  of  conditions  should  not  be 
applied,  without  evidence  of  their  validity,  to  an  entirely  different 
set  of  conditions.  Thus,  a  film  of  high  contrast,  which  would  tend 
to  minimize  the  effect  of  lens  flare,  would  produce  lower  scanning 
losses  than  would  be  the  case  for  a  film  of  lower  contrast  where  the 
density  developed  due  to  exposure  to  low  level  illumination,  such  as 
lens  flare,  would  be  greater. 

While  the  ultimate  or  complete  segregation  of  the  various  losses  in 
the  frequency-response  graph  would  require  further  and  extended 
research,  nevertheless  the  results  obtained  so  far  by  the  square-wave 
method  of  analysis  show  how  remarkably  faithful  present-day  film 
can  reproduce  an  event,  such  as  the  recording  of  high-frequency  sine 
waves,  if  proper  conditions  are  provided. 

The  square-wave  test-objects  were  prepared  by  the  Bausch  &  Lomb 
Optical  Co.  to  have  equivalent  wavelengths  corresponding  to  100, 
1000,  and  5000  cycles  per  second,  and  were  accurately  of  the  same 
amplitude.  These  were  analyzed  and  found  to  possess  the  distribu- 
tion of  harmonics  shown  in  Table  I.  The  deviations  from  the 
theoretical  values  required  by  equation  1  are  seen  to  be  small. 

TABLE  I 

Freq.  Percentage  Amplitude  of  Harmonic 

1  2345  6789  10 

100  100  0  0.8  33.1  0.2  19.5  0.5  14.0  0.5  10.8  0.4 
1000  100.0  2.7  32.8  3.0  19.2  3.0  14.1  3.0  10.1  2.8 
5000  100.0  6.1  32.4  6.2  17.8  6.2*  11.1*  5.8*  7.5*  7.2* 

*  Corrected  for  the  aperture  aiid  recording  galvanometer  losses  of  the  micro- 
densitometer. 

The  test-objects  themselves  consisted  of  three  blocks  of  glass  10 
mm.  by  20  mm.  by  7  mm.  thick  with  the  square- wave  forms  ruled  on 
a  silvered  surface.  Three  complete  cycles  were  ruled  in  each  test- 
object,  the  amplitudes  and  edges  being  held  to  tolerances  of  approxi- 
mately ±0.001  mm.  Small  pinholes,  lack  of  squareness  in  the 
corners,  and  nicks  in  the  ruled  edge  led  to  a  total  inaccuracy  of  some- 
what more  than  this  value,  but,  since  the  wavelength  of  the  5000- 
cycle  unit  was  0.092  mm.,  it  can  be  seen  that  the  limit  of  error  in  the 
ninth  harmonic  (X  =  0.010  mm.)  would  be  of  the  order  of  10  per  cent, 
while  at  longer  wavelengths,  the  errors  would  be  entirely  negligible 
because  of  other  variations.  The  appearance  of  the  test-objects  is 


592 


E.  D.  COOK  AND  V.  C.  HALL 


[J.  S.  M.  P.  E. 


illustrated  in  Fig.  1,  which  is  a  print  of  the  1000-cycle  test-object. 
At  the  magnification  shown,  a  departure  from  straightness  of  the 
edges  or  lack  of  squareness  at  the  corners  sufficient  to  have  appreci- 
able effect  at  frequencies  ten  times  the  fundamental  would  be  easily 
discernible. 

The  three  test-objects  were  mounted  in  a  frame  arranged  with  a 
pressure-pad  arrangement  to  hold  35-mm. 
film  in  close  contact  with  the  silvered  sur- 
faces. This  made  up  a  printing  frame 
which  was  mounted  about  3  feet  from  a 
lamp  house  equipped  with  a  shutter.  Suffi- 
cient neutral  absorption  was  interposed  to 
adjust  the  exposure  to  about  10  seconds 
for  Eastman  emulsion  1357.  While  the  ex- 
posures made  in  this  way,  of  course,  do  not 
compare  in  time  with  sound  recording  ex- 
posures, no  data  on  variations  of  image 
quality  with  intensity  are  available.  It  is 
probable,  however,  that  no  great  change  in 
the  characteristics  of  an  image  of  micro- 
scopic size  would  occur  without  some  cor- 
responding change  in  the  macroscopic  qualities,  such  as  gamma  and 
rate  of  development.  Over  the  range  of  intensities  encountered  here, 
the  primary  change  in  film  emulsion  characteristics  is  that  of  sensi- 


Fic.l.  Print  of  1000- 
cycle  per  second  silvered 
test-object. 


FIG.  2.     Microdensitometer  trace  of  1000-cycle  square  wave-form 
negative. 

tivity  variation,  so  that  .no  considerable  change  in  image  quality 
would  be  expected  between  the  two  sets  of  exposures,  except  that 
attributable  to  the  difference  in  optical  systems. 


Dec.,  1938] 


DETERMINING  SCANNING  Loss 


593 


DN«  NEGATIVE  OENSIT' 


1.0 
.9 
.8 
.7 

I- 


',&KX> 

FIGS.   3-5.     Relative   response   of   negatives   made 
by  square- wave  mask  for  various  densities. 


594  E.  D.  COOK  AND  V.  C.  HALL  [j.  s.  M.  P.  E. 

The  exposures  were  made  on  12-inch  strips  of  35-mm.  film  de- 
veloped by  machine,  with  sufficient  agitation  to  insure  even  develop- 
ment.2 Microphotometric  traces  of  the  images  were  made  and  en- 
larged to  a  wavelength  of  40  cm.  to  enable  analysis  to  be  carried  out 
on  a  Henrici  type  harmonic  analyzer.3  4  A  comparison  of  the  ampli- 
tude of  any  harmonic  with  the  theoretical  value  given  by  equation  1 
then  indicates  the  loss  due  to  the  film  under  the  experimental  con- 
ditions under  consideration.  A  correction  was  made  in  each  case 
for  the  deviation  of  the  test-object  from  the  theoretically  correct 
value,  the  final  result  being  a  frequency-response  curve  with  an  ex- 
perimental point  for  each  odd  harmonic  up  to  the  ninth,  since  this  is 
the  highest  harmonic  it  was  possible  to  read.  Since  the  data  ob- 
tained from  analysis  of  the  records  made  with  1000-cycle  per  second 
fundamental  amplitude  are  the  most  useful,  only  these  values  are 
presented.  A  print  of  the  microdensitometer  trace  obtained  from 
the  image  of  the  1000-cycle  test-object  having  a  density  of  1.08  is 
shown  as  Fig.  2.  The  small  irregularities  at  the  top  and  bottom  of 
the  wave  are  due  to  the  fact  that  in  ruling  the  test-objects  the  en- 
graving tool  cuts  up  to  the  line  on  each  stroke,  thus  inevitably  leaving 
a  somewhat  jagged  line  when  magnified  to  this  extent.  The  slope  of 
the  nearly  vertical  part  of  the  line  and  the  sharpness  of  the  corners 
are  the  only  factors  influencing  the  value  of  harmonics  up  to  the 
tenth,  however,  so  these  unevennesses  cause  no  measurable  error. 

The  negative  test  data  for  Eastman  emulsion  No.  1357  are  shown 
as  frequency-response  graphs  for  a  range  of  negative  densities  from 
0.66  to  2.26  in  Figs.  3-7.  These  curves  have  been  corrected  for  the 
loss  of  the  test -object.  It  is  seen  that  the  frequency-response  does 
not  show  severe  high-frequency  losses  even  at  quite  low  negative 
densities.  High  negative  densities  seem  to  produce  more  serious 
losses.  This  might  have  been  expected  but  it  is  probably  not  so  well 
recognized  that  any  set  of  exposure  conditions  would  result  in  the  low 
losses  shown  at  high  frequencies,  particularly  for  the  best  negative 
density  conditions. 

The  square-wave  analysis  for  this  emulsion  yields  results  which  cor- 
respond to  those  of  dynamic  tests  in  regard  to  the  range  of  negative 
densities  which  provide  the  best  frequency  response.  That  the  range 
is  broad  is  as  might  be  expected;  actually  it  varies  from  about  0.8 
to  1.4  density  with  a  maximum  at  about  1.25.  However,  the  choice 
of  recording  density  can  riot  be  made  on  the  basis  of  frequency- 
response  alone,  since  this  need  not  correspond  with  maximum  volume 


Dec.,  1938] 


DETERMINING  SCANNING  Loss 


595 


minimum  noise,  or  minimum  distortion  conditions  for  either  negative 
or  print.  It  has  been  shown  that  random  hiss  decreases  with  nega- 
tive density,5  hence  a  compromise  must  be  made  between  the  con- 
ditions for  minimum  loss  and  minimum  noise.  A  choice  of  recording 
density  of  between  1.4  to  1.5  has  been  previously  made  for  this  emul- 


f, 

.6 
.7 
6 
.9 


if: 


FIGS.    6-7.     Relative   response   of    negatives    made 
by  square- wave  mask  for  various  densities. 


sion  for  white-light  exposures  and  it  is  seen  that  these  conditions  do 
riot  represent  a  serious  compromise  with  conditions  for  minimum  film 
losses. 

A  comparison  between  the  negative  losses  as  obtained  from  micro- 
densitometer  measurements  of  a  recording  made  on  a  PR- 18  recorder 


596 


E.  D.  COOK  AND  V.  C.  HALL 


[J.  S  M.  P.  E. 


and  a  contact  negative  made  from  a  square-wave  mask  on  Eastman 
emulsion  1357  is  shown  in  Fig.  8.  The  samples  were  developed  to  a 
gamma  of  2.1  and  had  a  density  of  1.50  diffuse.  Because  of  the  fail- 
ure of  the  law  of  reciprocity,  it  is  probable  that  this  does  not  exactly 
portray  the  recording  scanning  loss,  but  it  seems  reasonable  that  the 
values  shown  are  not  in  error  by  more  than  5  per  cent. 


- 


T)|  MADE  ON  RECORQER 


FIG.  8.  Comparison  of  frequency  response  of 
negatives  on  Eastman  emulsion  1357  for  density 
1.5,  gamma  2.1. 

The  negatives  of  various  densities  obtained  from  the  square-wave 
test-objects  were  contact  printed  onto  Eastman  positive  film,  type 
1301,  and  developed  in  D-16  developer  to  a  gamma  of  2.0.  These 
prints,  which  had  densities  ranging  from  0.2  less  than  to  0.2  greater 
than  the  density  of  the  negative,  were  similarly  analyzed  by  the 
microdensitometer  and  the  harmonic  analyzer.  The  results  are 
shown  by  the  curves  in  Figs.  9-16.  These  curves  have  been  cor- 
rected for  the  loss  of  the  test-object.  It  is  seen  that  in  every  case, 
for  negative  densities  less  than  about  1.8,  the  loss  of  high-frequency 
response  in  the  print  exceeded  that  of  the  negative.  In  most  cases, 
the  response  was  less  than  the  product  of  the  negative  percentage 
response  by  itself.  The  exceptions  were  all  at  the  higher  negative 
densities  at  which  the  prints  showed  a  response  approximately  equal 
to  that  of  the  negative. 

It  is  thought  that  this  is  evidence  of  the  scattering  of  light  by  the 
negative  with  a  consequent  loss  of  contrast  in  the  print.  At  the 
higher  negative  densities,  the  "filling-in"  of  the  clear  portion  of  the 


Dec.,  1938] 


DETERMINING  SCANNING  Loss 


597 


1.0 
.9 

.8 
.7 

V* 

i  •* 

S'4 


0N»  NEGATIVE  DENSIT 


Dp  •  PRINT  DENSITY 


1OOOO 


bJ  .3 

> 
t  1.0 


'iSooo 


FIGS.  9-11.     Relative  response  of  print  made  from 
square-wave  mask  negative  on  emulsion  1301. 


598 


E.  D.  COOK  AND  V.  C.  HALL 


[J.  S.  M.  P.  E. 


7 '.oooo 


45676 


FIGS.  12-14.     Relative  response  of  print  made  from 
square-wave  mask  negative  on  emulsion  1301. 


Dec.,  1938] 


DETERMINING  SCANNING  Loss 


599 


negative  was  probably  compensated  in  the  print,  resulting  in  no 
material  increase  in  high-frequency  losses.  Since  these  densities 
are  beyond  the  range  for  best  general- performance,  the  results  are  of 
lesser  consequence  in  this  work  than  those  at  the  lower  densities. 


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U) 

L 

«O 

UN 

^ 

^ 

Dp 

2  2( 

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\ 

^ 

> 

0 

DP 

• 

2.4< 

3 

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\1 

s. 

3 

Ul 

X 

DP 

. 

246 

} 

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S\ 

.       ^  ^ 

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O 

FIGS.  15-16.     Relative  response  of  print  made  from 
square-wave  mask  negative  on  emulsion  1301. 


It  might  seem  that,  because  of  the  relatively  high  printing  loss  ob- 
served, the  possible  small  film  loss,  which  might  be  achieved  in  re- 
cording if  scanning  losses  were  reduced  or  entirely  eliminated,  would 
be  of  small  consequence.  This  conclusion  does  not  follow  from  the 
data  shown,  for  an  inferior  limit  of  film  loss  for  emulsion  1301  has  not 
been  given,  and  even  if  it  were  assumed  that  the  difference  between 


600 


E.  D.  COOK  AND  V.  C.  HALL 


[J.  S.  M.  P.  E. 


the  negative  loss  and  print  loss  is  all  ascribable  to  the  positive  film, 
the  use  of  a  different  type  of  negative  emulsion  might  change  the 
printing  conditions  for  minimum  distortion  and  cross-modulation 
products  to  a  value  of  print  density  which  would  show  considerably 
less  loss  ascribable  to  the  positive  film. 

In  Fig.  17,  a  comparison  is  shown  between  a  contact  print  of  den- 
sity 1.50  and  gamma  2.05  made  on  emulsion  1301  from  a  recorded 
negative  of  density  1.50  and  gamma  2.05  on  emulsion  1357  and  a  con- 
tact print  of  density  1.52  and  gamma  2.0  made  on  emulsion  1301 
from  a  square-wave  negative  of  density  1.55  and  gamma  2.2  made 
on  emulsion  1357.  The  losses  in  both  cases  have  increased  over  the 
corresponding  losses  shown  in  Fig.  8  for  the  negative  records,  but, 


Q  PRINl 


©PRIN 


OF  RECORC  -0  IE 


FIG.  17.  Comparison  of  frequency  response  of 
prints  made  from  recorded  negative  and  square-wave 
negative. 


while  the  printing  loss  for  the  sound  record  has  an  increased  loss  of 
1.4  db.,  the  square-wave  negative  has  an  increase  of  4.4  db.  Since,  as 
stated  above,  no  absolute  measurements  on  1301  -type  film  were  made, 
the  cause  of  this  differential  can  not  be  determined. 


CONCLUSION 


A  comparison  of  the  results  shown  in  the  curves  of  Fig.  8  and  Fig. 
17  indicates  that  at  10,000  cps.  there  is  a  scanning  loss  due  to  the  re- 
corder optical  system  of  7.2  db.  for  records  made  under  what  are  con- 
sidered satisfactory  white-light  recording  conditions  for  type  1357 


Dec.,  1938]  DETERMINING  SCANNING  LOSS  601 

sound-recording  negative,  and  4.2  db.  as  the  overall  scanning  loss 
when  these  negatives  are  printed  onto  type  1301  film. 

The  losses  ascribable  to  the  optical  system  are  the  result  of  light 
falling  on  the  film  outside  the  area  defined  by  the  slit  image.  The 
photographic  effect  of  this  extraneous  light  will  depend,  of  course,  on 
the  contrast  to  which  the  film  is  developed,  so  a  complete  understand- 
ing of  the  way  in  which  the  image  fails  must  await  the  analysis  of 
data  obtained  under  a  wide  variety  of  conditions. 

Since  the  modulation  loss  at  10,000  cycles  per  second  of  1357-type 
sound-recording  film  may  be  as  low  as  1  to  2  db.  under  favorable  ex- 
posure and  development  conditions,  it  is  probable  that  the  correspond- 
ing "static"  loss  for  records  made  on  recently  introduced  fine-grain 
high-contrast  sound-recording  emulsions  will  be  as  low  as  1/2  db.  If 
this  is  found  to  be  true,  then  the  dynamic  losses  found  on  high- 
frequency  sound  records  made  under  the  best  exposure  and  develop- 
ment conditions  can  be  considered  almost  entirely  as  scanning  losses, 
and  practical  experiments  on  sound-recording  optical  systems  can 
be  analyzed  on  the  basis  of  negligible  loss  attributable  to  the  film 
itself.  Since  part  of  the  reduction  in  scanning  loss  of  these  emulsions 
is  due  to  the  higher  gammas  to  which  they  are  developed,  thus  re- 
ducing the  photographic  effect  of  extraneous  light  surrounding  the 
slit  image,  a  study  of  the  relationship  between  development  and 
scanning  losses  may  make  it  possible  to  evaluate  the  effect  of  flare  in 
the  optical  system  more  accurately. 

In  conclusion  it  is  desired  to  acknowledge  the  sponsorship  of  Mr. 
M.  C.  Batsel  of  RCA  Mfg.  Co.,  whose  interest  in  film  and  scanning 
losses  stimulated  the  authors  to  devise  and  investigate  the  possi- 
bilities of  this  method. 

REFERENCES 

1  BAKER,  J.  O.,  AND  ROBINSON,  D.  H.:     "Modulated  High-Frequency  Re- 
cording as  a  Means  of  Determining  Conditions  for  Optimal  Processing,"  /.  Soc. 
Mot.  Pict.  Eng.,  XXX-Qan.,  1938),  No.  1,  p.  3. 

2  JONES,  L.  A.,  RUSSELL,  M.  E.,  AND  BEACHAM,  H.  R.:     "A  Developing  Ma- 
chine for  Sensitometric  Work,"  /.  Soc.  Mot.  Pict.  Eng.,  XXVIII  (Jan.,  1937),  No. 
l.p.73. 

3  SANDVIK,  O.,  AND  HALL,  V.  C.:     "Wave-Form  Analysis  of  Variable-Density 
Sound-Records,"  /.  Soc.  Mot.  Pict.  Eng.,  XIX  (Oct.,  1932),  No.  4,  p.  346. 

*  SANDVIK,  O.,  HALL,  V.  C.,  AND  STREIFFERT,  J.:  "Wave-Form  Analysis  of 
Variable-Width  Sound-Records,"  /.  Soc.  Mot.  Pict.  Eng.,  XXI  (Oct.,  1933),  No.  4, 
p.  323. 

5  SANDVIK,  O.,  HALL,  V.  C.,  AND  GRIMWOOD,  W.  K.:     "Further  Investigation 


602  E.  D.  COOK  AND  V.  C.  HALL  [j.  s.  M.  P.  E. 

of  Ground-Noise  in  Photographic  Sound-Records,"  J.  Soc.  Mot.  Pict.  E«g.,XXII 
(Feb.,  1934),  No.  2,  p.  83. 

DISCUSSION 

MR.  CARLSON:  As  I  understood  the  procedure  for  determining  the  final  re- 
sponse, a  scanning  beam  was  projected  on  the  film  and  the  response  measured 
through  the  film? 

MR.  COOK:     In  the  square-wave  test  method? 

MR.  CARLSON:     In  the  dynamic  method. 

MR.  COOK:  The  normal  recording  process  would  be  used  just  as  if  a  sound 
record  were  to  be  made,  except  that  the  galvanometer  would  be  excited  by  means 
of  an  oscillator. 

MR.  CARLSON:  Have  you  any  information  as  to  the  uniformity  in  either  the 
recording  or  reproducing  beam  ? 

MR.  COOK:  That  is  rather  difficult  to  remember.  I  think  that  in  practice,  the 
deviation  in  the  better  optical  systems  is  of  the  order  of  15  per  cent  from  a  uni- 
form illumination  as  the  beam  is  traversed  from  one  side  to  the  other. 

MR.  CARLSON:  How  much  of  the  total  loss,  then,  would  you  attribute  to  lack 
of  uniformity  within  the  scanning  beam  itself,  and  due  to,  as  you  stated,  scattered 
light  from  the  system? 

MR.  COOK:  I  should  attribute  most  of  the  losses,  as  discussed  in  the  paper,  to 
scanning  losses.  Non-uniform  illumination  would  produce  a  non-linearity  which 
would  cause  an  amplitude  loss  in  proportion  to  the  amount  permitted.  In  this 
case,  amplitude  losses  from  this  cause  were  not  as  serious  as  the  other  losses  dis- 
cussed. A  very  definite  indication  of  that  was  seen  in  the  data  for  the  prints  as 
presented  in  Fig.  17.  In  this  case,  the  losses  were  found  to  be  very  much  greater 
than  was  the  case  for  the  negatives  obtained  by  the  use  of  the  square-wave  mask 
in  a  field  of  uniform  illumination.  It  is  significant  that  non-uniform  illumination 
did  not  exist  during  the  printing  operation,  while  scattered  light  was  known  to  be 
present. 

While  in  practice,  every  known  improvement  should  be  made,  the  amount  of 
this  form  of  variation  of  illumination  present  in  the  better  forms  of  optical  sys- 
tems may  be  regarded,  at  least  for  present  purposes,  as  a  second  order  effect,  which 
would  become  relatively  more  important  as  the  primary  losses  are  further  reduced. 
I  believe  that  test  data  may  be  found  in  the  literature  substantiating  this  view- 
point. 

MR.  KELLOGG:  I  would  be  interested  to  have  Mr.  Cook  express  his  idea  as  to 
whether,  of  the  two  methods  that  have  been  in  considerable  use  for  testing  of  film 
losses,  namely,  the  modulated  steady  tone  and  the  square  wave,  he  feels  that  one 
is  a  closer  approximation  to  actual  recording  conditions  than  the  other.  I  can 
conceive  of  one  being  defendable  as  against  the  other  on  the  score  of  being  a 
closer  approximation  to  the  waves  you  actually  had  to  record. 

MR.  COOK:  If  I  understand  Mr.  Kellogg  correctly,  one  of  the  methods  men- 
tioned is  dynamic  and  the  other  is  static.  I  believe  my  position  would  be  some- 
thing like  this:  the  choice  will  depend  upon  what  one  wishes  to  find  out.  For 
example,  if  one  wishes  to  determine  experimentally  what  the  scanning  losses,  as 
defined  in  the  paper,  might  be  under  a  particular  set  of  conditions,  I  am  of  the 


Dec.,  1938]  DETERMINING  SCANNING  LOSS  603 

opinion  that  the  static,  square-wave  method  would  be  much  superior;  in  fact,  I 
do  not  see  how  the  other  method  may  be  employed  in  this  particular  problem 
and  still  yield  results  having  sufficient  exactness.  If,  however,  an  experimentally 
obtained  number  is  desired  to  express  the  percentage  of  the  scanning  loss  due  to 
the  aperture  alone  from  a  standpoint  of  light  translation  through  a  shaded  geo- 
metrical trace,  I  think  that  in  all  probability  one  is  forced  to  employ  the  dynamic 
method.  However,  he  must  be  prepared  to  face  the  necessity  of  knowing  some- 
thing about  the  mechanics  by  which  that  loss  occurs,  and  I  confess  I  know  no  way 
of  determining  that  with  the  desired  precision.  I  do  not  know  whether  this 
exactly  answers  Mr.  Kellogg's  question  or  not. 

MR.  KELLOGG  :  Not  entirely.  I  am  thinking  about  the  spectrum  of  the  square 
wave  that  you  are  employing.  For  example,  if  you  start  with  a  500-cycle  wave, 
the  amplitude  of  the  successive  harmonics  (which  will  be  at  500-cycle  intervals) 
goes  down  inversely  as  the  frequency.  How  nearly  would  that  represent  the  dis- 
tribution of  amplitudes  in  sound  as  actually  recorded?  The  square  wave  is  not 
in  exact  imitation,  and  neither  is  the  steady  tone. 

MR.  COOK:  Well,  that  is  rather  difficult,  because  not  only  the  subject  matter 
but  the  level  of  the  sound  to  be  recorded  varies  widely.  In  order  for  a  variation 
in  applied  amplitude  to  effect  these  losses,  it  would  be  necessary  for  some  con- 
siderable non-linearity  to  exist  in  the  recording  medium.  I  think  it  is  well  es- 
tablished that  for  the  conditions  used  in  practice,  no  evidence  of  sufficient  non- 
linearity  has  been  found.  However,  I  believe  that  analyses  have  been  published 
which  show  that  the  amplitudes  of  the  higher  frequencies  in  speech  and  music  are 
in  general  materially  reduced  as  the  frequency  is  increased,  and  as  a  crude  ap- 
proximation, the  reduction  varies  from  inversely  with  the  frequency  to  some 
higher  rate  of  decrease.  The  square-wave  method  of  analysis  has  harmonics 
whose  amplitudes  decrease  inversely  with  the  frequency.  Of  course,  in  applying 
a  test  wave  to  a  galvanometer  one  may  choose  any  amplitude  desired  but  there 
are  other  circumstances  which  follow  with  the  use  of  recording  optical  systems 
in  experimental  work.  As  has  been  mentioned,  one  of  these  is  lens  flare.  With 
the  presence  of  this  difficulty,  I  do  not  know  how  to  experimentally  determine 
the  aperture  and  optical  system  losses  accurately  enough  to  segregate  those  losses 
due  solely  to  the  film.  Since  one  determines  the  overall  losses  very  accurately  by 
the  dynamic  method,  it  has  been  made  a  necessary  companion  of  the  static, 
square- wave  method  in  this  work. 


THE  USE  OF  PHOTOELECTRIC  EXPOSURE-METERS  IN 
THE  HOLLYWOOD  STUDIOS* 

W.  STULL** 


Summary. — The  use  of  photoelectric  exposure-meters  by  Hollywood  studio  camera- 
men is  definitely  increasing.  Such  meters  are  universally  employed  on  Technicolor 
productions,  and  are  also  employed  by  an  increasing  majority  of  studio  cinematog- 
raphers  for  monochrome  exterior  scenes.  In  general,  cameramen  consider  conven- 
tional types  of  photoelectric  meters  unsuitable  for  use  on  interior  scenes.  For  use 
under  studio  interior  lighting  a  meter  of  especial  precision  in  the  low-brightness  range 
is  necessary  and  a  direct-reading,  rather  than  a  reflection-reading,  type  would  be  pre- 
ferred by  many.  In  the  opinion  of  many  leading  cameramen,  a  photometer  read- 
ing directly  in  foot-candles,  rather  than  an  exposure-meter  reading  in  photographic 
exposure  units,  would  be  preferable  for  this  usage. 

The  employment  of  photoelectric  exposure-meters  by  the  camera- 
men in  the  Hollywood  studios  is  definitely  increasing;  however  their 
use  is  by  no  means  universal.  In  fact,  the  camera  profession  is  di- 
vided into  two  argumentative  camps,  about  equally  divided,  according 
as  they  favor  or  condemn  these  meters. 

A  great  deal  of  enthusiasm  is  notable  among  the  proponents  of 
each  view.  The  non-users  of  meters,  especially,  bristle  with  indigna- 
tion at  the  mention  of  such  mechanical  aids.  Their  typical  reaction 
is  much  like  that  of  the  late  director  Richard  Boleslawsky  when,  in 
directing  a  Technicolor  production,  he  found  the  camera  crew  religi- 
ously using  a  photoelectric  meter. 

"Why  waste  time  on  such  foolishness,"  he  asked,  "a  real  camera- 
man doesn't  need  anything  like  that.  Why,  so-and-so,  who  photo- 
graphed my  last  picture  would  only  need  to  smell  a  strip  of  film  to 
know  all  about  it  and  how  to  shoot  it!" 

The  irony  of  the  situation  is  best  appreciated  when  one  knows  that 
the  man  named  happens  to  be  one  of  the  most  enthusiastic  users  of 
photoelectric  meters! 


*  Received  April  28,  1938. 
**  Hollywood,  Calif. 
604 


PHOTOELECTRIC  EXPOSURE-METERS  605 

Among  the  cinematographers  photographing  black-and-white 
productions,  the  use  of  photoelectric  exposure-meters  is  almost 
wholly  restricted  to  the  making  of  exterior  scenes,  for  several  reasons. 
The  majority  of  these  cinematographers  state  that  all  factors  of  in- 
terior lighting  are  so  familiar  and  so  completely  under  control  that 
there  is  little  need  for  other  aid.  There  is  much  to  support  this  con- 
tention. Until  the  very  recent  introduction  of  the  new  super-speed 
films,  the  technic  of  studio  interior  cinematography  differed  consid- 
erably from  that  in  many  other  photographic  fields.  Lenses  are  al- 
most invariably  used  at  their  maximum  apertures,  ranging  from 
f/2.7  to//2.3.  The  lighting  is  therefore  built  up  to  a  fairly  standard 
level,  so  familiar  that  it  can  well  be  determined  visually.  Further, 
individual  lighting  technic  varies  enormously,  according  to  the  indi- 
vidual's methods  of  balancing  illumination.  So  far  as  the  writer  is 
aware,  no  scientific  survey  of  this  situation  has  ever  been  made; 
but  based  upon  his  own  observation  over  a  period  of  many  years,  he 
would  say  that  there  is  a  difference  of  more  than  200  per  cent  between 
the  extremes  of  illumination  that  would  be  used  by  equally  capable 
low-level  and  high-level  "lighters"  to  obtain  comparable  results  with 
identical  film  and  processing.  Another  very  important  factor  is 
that  many  cameramen,  including  many  who  use  the  device  enthusi- 
astically on  exterior  scenes,  feel  that  no  meter  at  present  available 
has  sufficient  sensitivity  in  the  low  intensities  to  prove  a  satisfactory 
guide  for  their  work  on  the  stage. 

But  if  such  meters  are  not  used  extensively  in  filming  interior  scenes, 
they  are  used  quite  extensively  whenever  a  company  works  outdoors 
or  on  location.  Not  less  than  half  of  the  more  noted  cinematogra- 
phers employ  these  devices  under  such  conditions.  Many  follow 
their  meters  religiously. 

The  methods  of  using  the  meters  vary  with  the  individual.  Re- 
cently when  discussing  the  problem  with  three  equally  distinguished 
members  of  the  profession,  the  writer  found  three  quite  different  meth- 
ods of  using  the  meter.  Perhaps  the  most  popular  technic  is  to  posi- 
tion the  meter  according  to  the  angular  field  of  the  lens  used.  Thus 
in  making  a  long-shot,  for  which  a  40-mm.  or  50-mm.  lens  is  most 
frequently  employed,  the  reading  is  taken  with  the  meter  at  the 
camera  position.  For  closer  shots— two -shots,  waist  and  knee- 
length  figures,  etc. — the  meter  is  read  approximately  halfway  between 
the  actor  and  the  camera,  which  for  such  shots  uses  a  75-mm.  lens. 
For  close-ups,  made  often  with  a  4-inch  lens,  the  reading  is  taken 


606  W.  STULL  [j.  S.  M.  P.  E. 

with  the  meter  about  a  third  of  the  way  irom  the  actor  to  the 
camera. 

Other  outstanding  cinematographers  prefer  the  so-called  "bright- 
ness-range" method,  taking  separate  readings  of  extremes  of  shadow 
and  highlight  and  averaging  the  results,  or  using  the  shadow  readings 
as  guides  in  building  up  the  illumination,  either  with  reflectors  or 
booster  lights,  to  a  known  minimum-exposure  level. 

Such  readings  are  in  almost  all  cases  taken  after  the  lighting  has 
been  balanced  visually,  after  which  any  minor  changes  suggested  by 
the  meter  readings  are  made.  This  appears  to  be  the  most  eco- 
nomical of  time. 

Those  who  use  the  photoelectric  meter  are  almost  invariably  highly 
enthusiastic  over  its  value.  One  cinematographer  recently  told  the 
writer  of  a  scene  in  which  he  filmed  a  number  outdoors,  under  trees, 
with  six  cameras  photographing  two  singers,  simultaneously  from 
different  angles.  By  the  use  of  his  meter  he  was  able  to  adjust  the 
lighting  and  exposure  so  accurately  that  all  six  negatives  printed  on 
the  same  printer  light. 

Another  one  told  of  how  he  had  been  unexpectedly  assigned  to  a 
production,  replacing  a  colleague.  Here  again  his  meter  helped  him 
overcome  great  extremes  of  lighting  that  had  proved  troublesome  for 
his  predecessor. 

He  mentioned  also  another  production,  in  which  he  had  photo- 
graphed the  dramatic  action,  while  another  man  had  filmed  the  back- 
ground scenes.  Both  had  used  meters,  and  the  two  portions  of  the 
film  matched  so  perfectly  as  to  quality,  exposure,  and  negative  den- 
sity that  the  studio  heads  expressed  extreme  amazement. 

The  Weston  and  General  Electric  are  the  only  types  of  meters  used. 
The  latter  has  been  available  for  so  short  a  time,  however,  that  while 
several  of  them  are  in  use,  it  may  be  said  that  the  Weston  is  the  only 
type  in  widespread  use  in  this  field.  Almost  without  exception,  the 
older  model  617  is  the  favorite,  due  to  its  greater  sensitivity  range  and 
to  a  general  feeling  that  it  is  the  most  dependable. 

The  considerably  narrower  angle  scanned  by  the  newer  types  of 
meter  is  considered  a  definite  advantage,  but  not  as  yet  enough  to 
overcome  the  preference  for  the  older  type.  The  ideal  instrument 
would  in  the  opinion  of  virtually  all  cinematographers  be  one  the 
scanning  angle  of  which  was  identical  with  that  of  the  lenses  most 
commonly  used,  notably  the  50-mm.  lens  which  covers  a  horizontal 


Dec.,  1938]  PHOTOELECTRIC  EXPOSURE-METERS  607 

angle  of  25  degrees,  and  the  40-mm.  lens,  now  used  almost  as  fre- 
quently, which  covers  an  angle  of  30  degrees. 

A  universally  desired  adjunct  to  the  ideal  meter  would  be  a  hood  or 
sunshade  which  would  screen  from  the  cell  not  only  the  undesired  rays 
from  the  sky,  etc.,  but  also  reflected  light  from  large  adjacent  areas  of 
light-colored  walls,  sea,  sand,  pavement,  etc.,  which  ordinarily  intro- 
duce a  definite  element  of  error  into  the  meter  readings.  Several 
cinematographers  habitually  take  their  meter  readings  holding  the 
meter  in  the  matte  box  of  their  camera.  Others,  like  the  writer,  hold 
the  meter  in  such  a  way  that  the  over-folded  fingers  of  both  hands 
form  a  sunshade  for  the  cell.  A  few  cinematographers  have  had 
special  sunshades  made  for  their  meters.  Some  form  of  sunshade  is 
probably  more  generally  desired  than  any  other  single  feature. 

Almost  equally  desired  is  greater  sensitivity  in  the  low-intensity 
light  ranges,  so  that  the  meter  could  be  used  for  interior  cinema- 
tography under  artificial  lighting.  A  meter  that  could  be  used  inter- 
changeably for  both  direct  and  reflection  readings  would  also  be  wel- 
comed. 

There  is,  in  addition,  a  very  general  opinion  among  the  leading 
carreramen  that  the  successful  meter  for  professional  use  must  be  of 
the  direct-reading,  rather  than  the  reflection  type.  For  this  purpose 
(interior  scenes)  many  cinematographers  would  definitely  prefer  a 
meter  reading  directly  in  foot-candles,  rather  than  in  terms  of  photo- 
graphic exposures.  In  their  work,  they  point  out,  camera  exposure 
settings  are  virtually  fixed:  the  actual  problem  is  that  of  building 
light-intensities  to  known  levels,  dependent  upon  the  effect  desired, 
and  securing  a  fairly  constant  balance  between  highlight,  shadow,  and 
half-tone  areas.  A  multirange  photometer,  comparable  perhaps  to 
the  Weston  model  614  but  coordinated  to  panchromatic  sensitivity 
and  with  a  cell  mounted  on  an  extension  cable,  would  be  more  useful 
for  this  than  the  conventional  exposure  meter. 

The  photocell  meters  now  in  use  have  proved  remarkably  durable. 
Many  cinematographers  make  it  a  point  to  have  their  meters  tested 
either  at  the  completion  of  each  production  or  immediately  prior  to 
the  start  of  each  new  film.  Very  few  have  found  reason  for  more  than 
occasional  routine  repairs  and  adjustments.  This  record  may  be 
partly  due  to  the  fact  that  when  in  use  these  meters  are  not  as  a  rule 
carried  in  accessory  kits,  and  thus  subject  to  rough  handling,  but 
almost  invariably  are  carried  upon  the  person  of  either  the  chief 
cinematographer  or  his  operative  (second)  cinematographer.  In 


W.  STULL  [j.  s.  M.  P.  E. 

some  cases  the  writer  has  known  both  of  these  individuals  to  carry  and 
use  their  own  meters,  carefully  checking  the  readings  of  the  two  in- 
struments against  each  other. 

It  may  be  mentioned  in  this  connection  that  all  the  meters  used  in 
monochrome  cinematography  are  the  personal  property  of  the  cine- 
matographers  who  use  them.  While  camera  equipment  itself  is  now 
almost  invariably  the  property  of  the  studio,  photoelectric  meters, 
despite  their  growing  popularity,  have  not  as  yet  been  incorporated 
as  official  parts  of  the  camera  outfits.  It  is  definitely  a  tribute  to 
the  practical  worth  of  these  meters  that  so  many  cinematographers 
have  spent  their  own  money  to  obtain  them. 

The  most  notable  use  of  photoelectric  meters  in  Hollywood  is 
of  course  their  application  in  Technicolor  cinematography.  In  this 
they  have  for  some  years  been  universally  used.  The  practice  goes 
back  to  the  introduction  of  the  three-color  Technicolor  process  in 
1934,  although  some  experimental  use  of  the  device  was  made  prior 
to  that,  in  the  latter  days  of  Technicolor's  former  two-color  process. 
For  the  past  four  years,  however,  photocell  photometers  have  been  a 
standard  part  of  every  Technicolor  camera  outfit,  and  their  use 
a  standard  part  of  regulation  procedure. 

The  meter  used  on  Technicolor  sets  is  the  standard  Weston  "studio 
model"  603  meter.  In  this  application  the  meter  cells  are  usually 
fitted  with  special  filters  compensating  their  color-sensitivity  to  a 
close  approximation  of  the  visual  color-sensitivity  curve.  The  meters 
are  invariably  used  for  direct  reading,  never  for  reflection  readings. 
The  standard  procedure  is  to  take  three  meter  readings  from  ap- 
proximately the  position  of  the  principal  actor  in  the  scene.  The 
meter  is  held  level,  and  one  reading  is  taken  with  the  cells  facing  di- 
rectly toward  the  camera  and  two  other  readings  facing  45  degrees 
to  the  right  and  45  degrees  to  the  left. 

Until  quite  recently,  such  readings  were  taken  for  every  camera 
set-up,  and  whenever  any  important  change  was  made  in  lighting 
between  takes  of  the  same  scene.  These  readings  were  carefully  re- 
corded and  the  information  filed  for  future  reference.  This  proce- 
dure served  a  double  purpose :  In  the  first  place,  it  gave  the  cine- 
matographer  valuable  help  in  keeping  his  illumination  reasonably 
within  the  range  of  film  sensitivity  and  processing  limitations.  Sec- 
ond, and  of  even  greater  importance,  the  existence  of  such  records  ma- 
terially helped  the  mastery  of  a  process  that  was  new  and  relatively 
unexplored. 


Dec.,  1938]  PHOTOELECTRIC  EXPOSURE-METERS  609 

In  some  quarters  it  has  been  believed  that  this  use  of  photometers 
in  Technicolor  photography  was  done  to  insure  that  the  cinematog- 
rapher  adhered  to  rigidly  set-up  lighting  formulas.  Such  was  not 
the  case.  The  rumor  probably  originated  by  a  misinterpretation  of 
the  natural  fact  that  the  Technicolor  laboratory  required  reasonable 
adherence  to  a  normal  standard  of  illumination  if  normal  negatives 
and  print-quality  were  to  be  had.  No  attempt  was  at  any  time  made 
to  use  this  procedure  to  dictate  the  balancing  of  lighting.  This  was 
always  left  to  the  discretion  of  the  cinematographer  in  charge.  The 
matter  of  effect-lighting  was  also  left  to  the  individual's  judgment. 

The  technic  of  the  Technicolor  process  has  by  now  become  fairly 
well  established.  Sufficient  Technicolor  productions  have  been  made 
to  give  the  Technicolor  staff  cinematographers  a  practical  knowledge 
of  the  lighting  limitations  of  the  process,  comparable  to  the  general 
knowledge  of  similar  limitations  in  monochrome  cinematography. 
Therefore  the  use  of  the  photronic  meters  is  by  no  means  so  exten- 
sive as  it  necessarily  was  while  the  knowledge  of  the  process  was  being 
amassed.  The  meters  are  still  used,  and  their  readings  still  recorded ; 
but  the  meters  are  now  used  more  as  a  guide  to  the  cinematographer, 
as  a  supplement  to  his  judgment,  than  as  a  measure  of  performance. 
The  records  of  the  readings  are  also  proving  of  considerable  value  in 
instances  where  scenes  must  for  any  reason  be  retaken  or  amplified 
after  considerable  lapses  of  time.  Thus  while  meter  readings  are  not 
now  so  generally  taken  on  every  camera  set-up,  readings  are  still  taken 
of  key  scenes  on  any  set  or  sequence,  thus  affording  a  guide  in  match- 
ing the  scenes  in  the  event  of  retakes  or  added  scenes.  Such  readings 
are  generally  taken,  as  well,  for  future  guidance,  in  scenes  calling  for 
effect-lightings,  and  the  like. 

The  value  of  these  records  can  hardly  be  overestimated.  Several 
Technicolor  cinematographers  have  commented  to  the  writer  on 
the  assistance  they  have  received  from  these  records  in  instances 
where,  perhaps,  one  man  had  commenced  a  production,  or  possibly 
made  preliminary,  pre-production  photographic  tests  of  unusual  con- 
ditions, and  had  been  replaced  during  actual  production  by  another 
cameraman.  The  records  made  possible  a  much  better  continuity 
of  photographic  treatment  and  quality  than  could  otherwise  have  been 
possible. 

The  maintenance  of  these  meters  has  of  course  been  given  careful 
attention.  All  the  meters  used  by  Technicolor  camera  crews  are 
subjected  to  weekly  inspection  and  to  tests  against  standard  meters 


610  W.  STULL 

and  illuminometers.  Any  irregularities  are  immediately  remedied. 
In  general  these  instruments  appear  to  have  made  a  very  good  record 
of  durability  in  service  usage. 

Technicolor's  use  of  photoelectric  meters  is  having  a  marked  in- 
fluence on  the  use  of  such  devices  by  monochrome  cinematographers. 
An  increasing  number  of  cinematographers  directly  in  the  employ 
of  the  major  studios,  and  heretofore  active  in  making  only  black-and- 
white  productions,  are  being  assigned  either  to  photographing  Tech- 
nicolor productions  in  the  studios  of  their  employers,  or  to  studying 
Technicolor  with  a  view  to  such  future  assignments.  These  men  are 
almost  universally  gaining  a  new  respect  for  the  value  of  photronic 
meters.  When  they  return  to  their  routine  work  of  filming  black- 
and-white  productions,  many  of  them  obtain  their  own  meters  and 
adapt  the  technic  to  monochrome  cinematography.  In  at  least  one 
instance,  a  cinematographer  after  completing  his  first  Technicolor 
production  had  the  Technicolor  engineers  adapt  a  standard  meter 
to  his  requirements. 

It  may  therefore  be  said  that  the  use  of  photoelectric  exposure 
meters  is  becoming  more  general  in  the  Hollywood  studios,  and  is 
universal  in  natural-color  cinematography.  It  is  almost  certain 
that  within  a  relatively  short  time  the  use  of  these  instruments  will 
have  become  universal  for  black-and-white  exterior  scenes.  The 
trend  of  opinion  is  that  only  the  introduction  of  a  completely  satisfac- 
tory professional  meter  is  needed  to  make  the  use  of  these  instru- 
ments equally  universal  in  interior  cinematography. 


THE  STABILITY  OF  THE  VISCOSE  TYPE  OF 
OZAPHANE  PHOTOGRAPHIC  FILM* 


A.  M.  SOOKNE  AND  C.  G.  WEBER** 

Summary. —  Viscose  Ozaphane,  a  new  type  of  film  with  a  base  of  regenerated  cellu- 
lose sheeting,  and  having  certain  advantages  for  record  use,  was  tested  to  determine  its 
comparative  stability.  Its  stability  was  compared  with  that  of  cellulose  nitrate,  and 
also  with  that  of  cellulose  acetate,  which  is  widely  used  for  slide-films  and  which  has 
been  found  to  be  a  very  stable  material  for  preserving  records  in  libraries.  The  viscose 
type  of  film  apparently  is  not  suitable  for  permanent  records,  but  does  appear  to  have 
properties  to  recommend  its  use  for  reading-room  copies  that  can  be  replaced  when  they 
become  unserviceable.  The  stability  was  determined  by  measuring  changes  in  the 
chemical  and  physical  properties  under  accelerated  aging.  The  changes  observed 
were  increase  in  acidity  and  copper  number,  and  decrease  in  viscosity,  weight,  and 
flexibility. 

CONTENTS 

I.     Introduction. 
II.     Determination  of  stability  by  accelerated  aging. 

III.  Effects  of  accelerated  aging. 

(1)  Loss  of  folding  endurance. 

(2)  Loss  of  weight. 

(,?)  Increase  in  acidity. 

(4)  Increase  in  copper  number. 

(5)  Decrease  in  viscosity. 

IV.  Summary  and  conclusions. 

(I)     INTRODUCTION 

Viscose  Ozaphane,  a  relatively  new  type  of  motion  picture  film, 
was  investigated  with  reference  to  its  suitability  for  use  as  a  record 
material.  In  this  new  type  of  film,  a  light-sensitive  dye  incorpo- 
rated within  the  base  performs  the  function  of  the  emulsion  coating 
on  the  conventional  type  of  film  now  in  use.  The  film  tested  had  a 
base  of  transparent,  viscose  sheeting  about  0.002  inch  in  thickness, 
plasticized  with  glycerin  to  obtain  greater  flexibility.  The  new  type 

*  Presented  at  the  Fall,  1938,  Meeting  at  Detroit,  Mich.;  received  October 3, 
1938. 

**  National  Bureau  of  Standards,  Washington,  D.  C. 

611 


612  A.  M.  SOOKNE  AND  C.  G.  WEBER          [j.  s.  M.  P.  E. 

of  film  is  of  particular  interest  for  record  purposes  for  several  reasons. 
It  is  grainless,  gives  high  contrast,  is  slow-burning,  the  image  is  not 
readily  damaged  by  scratching,  and  the  film  is  only  one-third  as  thick 
as  the  films  of  the  emulsion  type.  The  cellulose  acetate  film  now  used 
for  record  purposes  has  been  found  in  previous  studies1  to  be  a  very 
stable  material  when  properly  made2  and  properly  processed  photo- 
graphically. The  purpose  of  this  study  was  to  determine  the  relative 
stability  of  this  type  of  Ozaphane  film. 

(II)     DETERMINATION  OF  STABILITY  BY  ACCELERATED  AGING 

The  stability  of  the  new  type  of  film  was  determined  by  measuring 
changes  in  its  chemical  and  physical  properties  under  accelerated 
aging.  The  accelerated  aging  treatment  used  was  the  same  as  that 
previously  employed  in  evaluating  acetate  and  nitrate  films,  namely, 
that  of  heating  in  dry  air  at  100°C.  This  test  had  formerly  been 
found  suitable  for  paper.3-4  Loss  of  flexibility  of  papers  and  films, 
measured  by  a  folding  endurance  test,  is  the  most  significant  property 
because  the  flexibility  is  most  sensitive  to  changes  produced  by  de- 
terioration. Measurements  of  the  loss  of  weight  on  heating  were  also 
made.  Other  tests  consisted  in  determining  the  decrease  in  viscosity 
of  solutions  of  the  film,  and  increase  in  the  copper  number  and  in 
acidity  measured  as  pH.  To  assist  in  interpretation  of  the  results, 
data  previously5  obtained  for  acetate  and  nitrate  films  under  com- 
parable aging  treatments  are  included  in  the  graphs  for  purposes  of 
comparison. 

(HI)  EFFECTS  OF  ACCELERATED  AGING 

(1)  Loss  of  Folding  Endurance. — The  Schopper  folding  endurance 
tester,  which  is  an  instrument  widely  used  for  determining  the  folding 
endurance  of  paper,  was  used  to  measure  the  effects  of  aging  on  the 
flexibility  of  the  film.  Results  of  tests  with  the  M.  I.  T.  folder  in- 
dicated that  it  was  unsatisfactory  because  of  excessive  stretching  of 
the  specimens  under  test;  and  the  film  was  found  to  be  too  thin  to  be 
tested  successfully  in  the  Pfund  tester,  which  had  been  used  for  ace- 
tate and  nitrate  films.  All  folding  tests  on  the  Ozaphane  film  were 
made  under  constant  atmospheric  conditions  of  50  per  cent  relative 
humidity  and  75°F,  the  conditioning  time  being  24  hours  for  all 
specimens.  The  standard  humidity  of  65  per  cent  was  not  selected 
because  stretching  of  the  specimens  under  test  was  troublesome  at 
that  humidity.  Control  and  aged  specimens  were  conditioned  and 


Dec.,  1938] 


OZAPHANE  PHOTOGRAPHIC  FILM 


613 


tested  under  identical  conditions,  and  all  specimens  were  humidi- 
fied by  adsorption  to  avoid  variations  attributable  to  hysteresis  in 
moisture  sorption. 

The  effects  of  oven-aging  on  the  folding  endurance  of  Ozaphane  as 
compared  to  acetate-  and  nitrate-base  films  are  shown  graphically  in 


•ACETATE   FILM  (AV«  *  BRANDS) 

O  SENSITIZED  VI  (COM     f  ILM(»V8  t   SHAKOS) 
ONITKATE     FILM    (»V8   S  •RAND*) 


TIME  OF  AOINO  IN  DAYS     (100* C) 


FIG.  1.  (Upper}  Effect  of  oven-aging  upon  flexibility 
of  viscose  Ozaphane  film  as  compared  to  effects  of  similar 
treatment  of  acetate  and  nitrate  film. 

FIG.  2.  (Lower)  Loss  of  weight  during  oven-aging  of 
viscose.  Ozaphane,  acetate,  and  nitrate  films. 


Fig.  1.  The  results  show  a  more  rapid  loss  of  flexibility  under  the 
heat  test  for  Ozaphane  than  for  the  acetate-base  film.  It  was, 
however,  much  more  resistant  than  the  nitrate-base  film.  After 
30  days  of  oven-aging,  the  acetate  retained  approximately  67  per 


614 


A.  M.  SOOKNE  AND  C.  G.  WEBER 


[J.  S.  M.  P.  E. 


cent  of  the  original  strength  while  Ozaphane  retained  only  13  per 
cent.  None  of  the  nitrate  film  retained  any  measurable  folding  en- 
durance after  15  days  of  heating. 


•  ACETATE     FILM  CAV6  3  BRANDS) 

«  SENSITIZED    VISCOSE    FILM 
O  UNSENSITIZED   VISCOSE    FILM 
O  NITRATE     FILM  (AVQ   3  BRANDS) 


TIMEOFAOINS  IN   DAYS      (100*  C> 


FIG.  3.  (Upper}  Effect  of  oven-aging  upon  acidity  of 
record  films. 

FIG.  4.  (Lower)  Change  of  copper  number  during 
oven-aging;  viscose  Ozaphane  and  acetate  films. 


(2)  Loss  of  Weight. — Oven-aging  caused  losses  of  weight  for  all 
types  of  films.  However,  the  Ozaphane  type  showed  only  slight 
losses  even  for  extended  periods  of  heating.  Fig.  2  shows  loss  in 
weight  for  Ozaphane,  acetate,  and  nitrate  films.  The  relatively 


Dec.,  1938]  OZAPHANE  PHOTOGRAPHIC  FlLM  615 

rapid  initial  decrease  for  acetate  and  nitrate  films  was  probably  caused 
by  loss  of  residual  solvents  and  plasticizers.  On  further  heating  the 
nitrate  continued  to  lose  appreciably  through  the  escape  of  gaseous 
products  of  decomposition.  The  slight  loss  for  Ozaphane  was 
apparently  plasticizer  with  possibly  a  little  dye.  All  weighings 
were  made  after  conditioning  at  65  per  cent  relative  humidity  and 
70°F. 

(3)  Increase  in  Acidity. — Chemical  degradation  of  cellulosic  ma- 
terials is  often  accompanied  by  increased  acidity.     The  changes  in 
acidity  of  Ozaphane  with  aging  were  followed  by  means  of  pH  deter- 
minations.    The  method  used  consisted  in  heating  1  gram  of  the 
ground  material  in  100  milliliters  of  distilled  water  of  pH  6.0  to  7.0 
for  ]  hour  in  a  steam  bath,  then  measuring  the  pH  of  the  extract  with 
a  glass  electrode.     The  results  obtained  on  both  sensitized  and  un- 
sensitized  Ozaphane  are  shown  in  Fig.  3,  which  includes  also  data 
on  aqueous  acetone  solutions  of  acetate-  and  nitrate-base  film  for 
purposes   of   comparison.     The    unsensitized    Ozaphane    showed   a 
gradual  increase  in  acidity  with  aging;  however,  the  pYL  value  was  5.4, 
which  is  moderate,  after  30  days.     The  unsensitized  film  was  inter- 
mediate in  this  respect  between  the  acetate,  which  showed  no  mea- 
surable increase  in  acidity,  and  the  nitrate,  the  acidity  of  which  in- 
creased   markedly    on    aging.     Sensitized    Ozaphane    showed    little 
change  of  pH  after  one  day  of  heating,  possibly  because  of  buffering 
action  of  the  dye  in  the  film,  some  of  which  went  into  solution  during 
extraction. 

(4)  Increase  in  Copper  Number. — The  copper  number  of  cellulose 
is  defined  as  the  number  of  grams  of  copper  reduced  from  the  cupric 
to  the  cuprous  state  by  100  grams  of  the  material  under  defined  con- 
ditions.    An  increase  of  copper  number  is  accepted  as  indicative  of 
degradation  of  a  cellulosic  material ;  hence,  the  rate  of  increase  during 
accelerated  aging  is  considered  a  measure  of  stability.     Fig.  4  shows 
the  effects  of  accelerated  aging  on  the  copper  number  of  unsensitized 
Ozaphane  film  and  acetate-base  film.     The  tests  were  made  in  ac- 
cordance with  the  official  method  of  the  Technical  Association  of  the 
Pulp  and  Paper  Industry.6     Unsensitized  Ozaphane  was  used  for  the 
copper  number  determinations  to  avoid  errors  introduced  by  the 
reducing  effect  of  the  dye   in   the   sensitized  film.     Although   the 
copper  number  for  unaged  acetate-base  film  is  relatively  high,  it 
changes  very  slowly  on  aging,  the  increase  being  10  per  cent  for  30 
days  of  aging.     The  increase  for  Ozaphane  was  200  per  cent  for  the 


616  A.  M.  SOOKNE  AND  C.  G.  WEBER         [j.  s.  M.  P.  E. 

same  treatment,  which  indicates  definitely  poorer  stability  under 
oven-aging. 

(5)  Decrease  in  Viscosity. — Data  on  the  viscosity  of  solutions  of 
cellulosic  films  provide  the  most  reliable  measure  of  their  chemical 
degradation.  According  to  Staudinger7  the  specific  viscosity  of 
long-chain  molecules  is  directly  proportional  to  the  molecular  weight, 
for  dilute  solutions  of  equal  concentration.  Molecular  breakdown 
should  therefore  be  accompanied  by  a  proportional  decrease  in  spe- 
cific viscosity.  Clibbens  and  Ridge8  have  shown  that  decreases  in 
strength  of  cotton  fibers  produced  by  a  variety  of  reagents  are  ac- 
companied by  corresponding  decreases  in  the  viscosities  of  their 
solutions. 

The  effects  of  accelerated  aging  on  the  viscosity  of  Ozaphane  were 
determined  by  measuring  the  viscosities  of  solutions  before  and 
after  various  aging  periods.  The  procedure  used  was  that  recom- 
mended by  the  British  Fabrics  Research  Committee9  and  described 
by  Clibbens  and  Little,10  except  that  the  concentration  of  ammonia 
in  the  standard  cuprammonium  solvent  was  240  grams  per  liter  as 
recommended  by  Clibbens  and  Geake.11  The  measurements  were 
made  at  21  =*=  0.05°C,  using  solutions  containing  2  grams  of  dry 
Ozaphane  per  100  milliliters  of  solution.  Hill  and  Weber12  deter- 
mined the  viscosities  of  acetate  and  nitrate  films  by  using  acetone 
solutions  containing  1  gram  of  film  per  100  milliliters  of  solution. 
Acetone  could  not  be  used  for  Ozaphane  because  it  is  not  a  solvent 
for  cellophane. 

Fig.  5  is  a  graphic  comparison  of  the  retention  of  viscosities  of 
acetate,  Ozaphane,  and  nitrate  films.  The  acetate  retained  more 
than  90  per  cent  of  its  original  specific  viscosity  after  30  days  of 
aging,  while  the  Ozaphane  films  retained  less  than  60  per  cent,  and 
the  nitrate  6  per  cent.  Here  again  the  Ozaphane  is  intermediate  in 
chemical  stability  between  the  stable  acetate-base  and  unstable 
nitrate-base  film. 

(IV)     SUMMARY  AND  CONCLUSIONS 

The  data  indicate  that  the  Ozaphane  type  of  film  having  a  viscose 
base  is  definitely  inferior  to  good  acetate  film  as  regards  stability 
under  accelerated  aging.  It  is  not  suitable  for  permanent  records  but 
apparently  it  has  sufficient  stability  for  positives  for  reading-room 
use.  Its  stability  is  comparable  to  that  of  ordinary  sulfite  wood- 
fiber  papers  which  are  known  to  last  25  years  or  longer  under  or- 


Dec.,  1938] 


OZAPHANE  PHOTOGRAPHIC  FILM 


617 


dinary  conditions  if  they  are  well  made.  Since  the  reading-room 
copies  that  are  in  use  will  doubtless  become  largely  unserviceable 
from  mechanical  wear  in  less  than  25  years,  greater  stability  for 
that  purpose  does  not  appear  essential.  The  Ozaphane  type  of  film 
has  certain  advantages  for  use  as  positives :  it  is  grainless,  gives  high 
contrast,  is  only  one-third  as  thick  as  acetate,  and  has  no  emulsion 
to  become  scratched  during  projection  and  handling. 

Although  the  viscose-base  film  apparently  is  not  sufficiently  stable 
for  permanent  records,  it  is  not  designed  for  use  where  the  highest 
permanence  is  required.  Negative  films  are  in  reality  the  master 
records,  and  the  dyes  employed  at  present  in  Ozaphane  are  too  slow 
to  permit  its  use  for  original  photographs. 


•  ACETATE     FILM  CAVO  3  BRANDS) 

scose  FILM   CAVO 

9UNSENSITIZED   VISCOSE    FILM 

ONITRATE   FILM  uvo  3  BRANDS) 


TIME  OF  AOINO  IN  DAYS    UOO»C> 


FIG.  5.     Effect  of  Oven-aging  upon  viscosity  of  viscose 
Ozaphane,  acetate,  and  nitrate  films. 

It  is  quite  possible  that  the  stability  of  the  Ozaphane  type  of  film 
can  be  improved  by  using  for  a  base  a  sheeting  having  higher  initial 
purity.  It  is  understood  that  a  film  of  this  kind  has  recently  been 
developed  and  investigation  of  it  is  planned  as  a  further  part  of  this 
work. 

REFERENCES 

1  HILL,  J.  R.,  AND  WEBER,  C.  G.:     "Stability  of  Motion-Picture  Films  as  De- 
termined by  Accelerated  Aging,"  /.  Research  Nat.  Bur.  Standards,  17 (Dec.,  1936), 
p.  871,  RP  950. 

2  HILL,  J.  R.,  AND  WEBER,  C.  G. :     "Evaluation  of  Motion-Picture  Film  for 
Permanent  Records,"  Nat.  Bur.  Standards  Misc.  Pub.,  M158  (July,  1937). 

3  RASCH,  R.  H. :     "A  Study  of  Purified  Wood  Fibers  as  a  Paper  Making  Ma- 
terial," Bur.  Standards  J.  Research,  3  (Sept.,  1929),  p.  476,  RP107. 


618  A.  M.  SOOKNE  AND  C.  G.  WEBER 

*  RASCH,  R.  H.,  AND  STONE,  G.  O. :  "Estimating  Stability  of  Paper  by  Heat- 
ing," Paper  Trade  J.,  95  (July,  1932),  p.  28. 

6  HILL,  J.  R.,  AND  WEBER,  C.  G. :  "Stability  of  Motion-Picture  Films  as  De- 
termined by  Accelerated  Aging,"  /.  Research  Nat.  Bur.  Standards,  17  (Dec.,  1936), 
p.  871,  RP950. 

6  "Copper  Number  of  Paper,"  TAPPI  Standard  T430m,  Tech.  Assn.  Pulp  & 
Paper  Industry. 

7  STAUDINGER,    H.:      "Die    Hochmolecularen    Organischen    Verbindungen" 
(Berlin),  1932. 

8  CLIBBENS,  D.  A.,  AND  RIDGE,  B.  P.:     'The  Tensile  Strength  and  Fluidity 
of  Chemically  Modified  Cotton,"  J.  Text.  Inst.,  19  (1928),  p.  389T. 

9  "The  Viscosity  of  Cellulose  Solutions,"  Fabrics  Research  Committee  Dept.  Sci. 
and  Ind.  Research  (London),  1932. 

10  CLIBBENS,  D.  A.,  AND  LITTLE,  A.  H.:     "The  Measurement  of  Fluidity  (or 
Viscosity)  of  Cotton  in  Cuprammonium  Solution,"  /.  Text.  Inst.,  27  (Dec.,  1936), 
p.  285T. 

11  CLIBBENS,  D.  A.,  AND  GEAKE,  A.:     "The  Measurement  of  the  Fluidity  of 
Cotton  in  Cuprammonium  Solution,"  /.  Text.  Inst.,  19  (1928),  p.  77T. 

12  HILL,  J.  R.,  AND  WEBER,  C.  G.:     "Stability  of  Motion-Picture  Films  as 
Determined  by  Accelerated  Aging,"  /.  Research  Nat.  Bur.  Standards,  17  (Dec., 
1936),  p.  871,  RP950. 


Note. — Since  completion  of  the  study  reported  above  the  National 
Bureau  of  Standards  has  made  a  similar  study  of  Ozaphane  film  com- 
posed of  cellulose  acetate.  When  this  film  was  heated  for  72  hours  at 
100°C,  the  base  was  found  to  be  as  stable  as  that  of  the  emulsion  type 
of  film;  it  compared  favorably  with  the  best  grades  of  permanent- 
record  papers.  As  far  as  the  stability  of  the  base  is  concerned,  the 
suitability  of  the  acetate  Ozaphane  film  for  permanent  records  can 
be  determined  as  suggested  for  the  emulsion  type  in  the  Bureau  Mis- 
cellaneous Publication  Ml 58,  "Evaluation  of  Motion-Picture  Film 
for  Permanent  Records,"  except  that  it  is  not  necessary  to  test  for 
sodium  hypochlorite  or  for  cellulose  nitrate,  and  a  M.  1.  T.  folding 
endurance  tester  should  be  used  instead  of  the  Schopper.  Film 
having  a  M.  I.  T.  folding  endurance  of  not  less  than  150  double  folds 
at  a  tension  of  500  grams,  and  relative  humidity  of  50  per  cent,  should 
be  satisfactory.  There  was  practically  no  fading  of  the  image  under 
the  heat  test.  On  exposure  to  carbon-arc  light  for  48  hours  the  image 
faded  somewhat  but  retained  good  legibility. 


REPORT  OF  THE  STANDARDS  COMMITTEE* 


Summary. — Semiannual  report  of  the  Committee.  The  present  report  deals  with 
(1)  cores  for  35-mm.  and  16-mm.  motion  picture  film;  (2)  sound-track  dimensions; 
(3)  16-mm.  sound-film  sprocket;  (4)  definition  of  safety  film;  (5)  reduction  ratio  for 
35-mm.  to  16-mm.;  (6)  universal  perforation;  and  (7)  "variable-area"  vs.  variable- 
width. 

The  principal  items  under  consideration  by  the  Standards  Com- 
mittee at  the  present  time  are  as  follows : 

(1)  Cores  for  35-Mm.  and  16-Mm.  Motion  Picture  Film. — Drawings 
for  cores  with  dimensions  and  tolerances  for  35-mm.  and  16-mm.  film 
have  been  given  initial  and  final  approval  by  the  Standards  Com- 
mittee and  are  being  published  in  an  early  issue  of  the  JOURNAL. 
There  are  two  questions  in  regard  to  these  drawings  on  which  there 
has  been  some  debate : 

In  the  first  place,  the  tolerances  adopted  have  been  fairly  large; 
for  example,  the  recommended  hole  size  for  the  35-mm.  core  is 
1.012  to  1.028  inches,  whereas  the  maximum  diameter  for  the  shaft 
is  1.000  inch.  This  gives  a  possible  clearance  of  0.028  inch  between 
the  shaft  and  the  inside  of  the  core.  It  was  the  consensus,  however, 
that  this  clearance  made  na  practical  difference  and  that  a  range  of 
values  was  necessary  in  order  to  permit  different  manufacturers  to 
use  the  various  plastics  and  other  materials  that  they  find  satisfac- 
tory. 

The  second  question  involved  is  the  question  of  standardizing  two 
types  of  cores,  viz.,  the  so-called  positive  core  and  the  so-called  nega- 
tive core.  The  positive  core  has  a  keyway  and  is  intended  to  fit  on  a 
round  shaft  with  a  key  or  stud  to  keep  the  core  from  revolving  on  the 
shaft.  The  second  type  of  core,  or  the  so-called  negative  core,  is  in- 
tended to  fit  on  a  shaft  having  a  keyway.  This  type  of  core,  there- 
fore, has  a  key  molded  into  the  core  and,  consequently,  will  not  go 
over  the  round  shaft.  In  adopting  as  standard  only  the  so-called 
positive  core,  the  Standards  Committee  realizes  that  for  some  time 
to  come  the  negative  cores  will  be  used,  and  that  possibly  the  change 

*  Presented  at  the  Fall,  1938,  Meeting  at  Detroit,  Mich.;  received  Nov.  11, 
1938. 

619 


620  STANDARDS  COMMITTEE  [J.  S.  M.  P.  E. 

to  the  positive  type  of  core  may  never  occur.  However,  the  film 
manufacturers  and  some  of  the  apparatus  producers  believe  it  would 
be  of  benefit  to  the  trade  if  a  single  type  of  core  could  be  used,  and 
for  that  reason  the  single  standard  has  been  adopted. 

(2)  Sound-Track  Dimensions. — A   thorough   study  of   the   best 
dimensions  for  the  35 -mm.  sound-track  is  being  made  by  a  committee 
of  the  Academy  of  Motion  Picture  Arts  &  Sciences.     Our  Committee 
is,  therefore,  waiting  until  the  Academy  committee  has  announced  its 
findings  before  taking  any  action  on  this  matter. 

(3)  16-Mm.  Sound-Film  Sprocket. — A  preliminary  drawing  has 
been  given  initial  approval  and  has  been  sent  out  to  the  various  mem- 
bers of  the  Standards  Committee  and  to  various  manufacturers  for 
criticism.     The   principles   involved  in   handling   singly  perforated 
film  are  somewhat  different  from  those  used  in  handling  doubly  per- 
forated film.     For  example,  with  16-mm.  sound-film,  it  is  common 
practice  to  have  the  sprocket-teeth  entirely  fill  the  holes,  at  least  in 
the  lateral  dimension,  and  guiding  of  the  film  in  the  picture  gate  by 
means  of  the  sprocket-holes  is  almost  universal.     If  such  guiding  is 
used,  the  sprocket-teeth  must  be  rounded  with  a  radius  of  curvature 
greater  than  that  used  for  the  film,  or  inevitably  damage  will  result. 
It  is  the  opinion  of  some  that  it  is  too  early  to  standardize  on  sprockets 
for   16-mm.  sound-film  and  that  correct  sprocket  design  depends 
entirely  upon  the  design  of  the  projector  on  which  it  is  to  be  used. 

(4)  Definition  of  Safety  Film. — The  Standards  Committee  has 
given  initial  approval  to  the  definition  and  specification  of  safety 
film  recommended  for  adoption  at  a  meeting  of  the  International 
Standards  Association  at  Berlin  on  June  28,   1938.     Inasmuch  as 
there  are  rather  important  differences  of  opinion  with  regard  to  the 
advisability  of  approving  this  definition,  it  is  included  herewith  in  full 
in  order  that  we  may  have  a  fuller  discussion : 

Definition. 

Safety  film  means  a  film  that  is  slow-burning  and  difficult  to  ignite. 

A  film  is  called  slow-burning  if  its  burning  time  for  a  piece  of  film  of  30  cm. 
takes  more  than  45  seconds .  For  films  having  a  thickness  of  less  than  0 .08  mm . ,  the 
burning  time  must  be  more  than  30  seconds.  The  burning  time  is  determined 
according  to  paragraph  a. 

A  film  is  termed  difficult  to  ignite  if  it  does  not  ignite  at  300  °C  within  10 
minutes. 

Safety  film  must  contain  not  more  than  0.36  per  cent  of  nitrate  nitrogen. 

Testing  Method. 

(a)     Testing  of  Burning  Time. 


Dec.,  1938]  STANDARDS  COMMITTEE  621 

(1)  The  film  is  freed  from  emulsion  in  warm  water  and  is  dried  in  open  air 
at  18°  to  22°C  and  40  to  50  per  cent  relative  humidity  for  12  hours. 

(2)  The  sample  to  be  tested  shall  be  35  cm.  long,  and  a  mark  provided  5 
cm.  from  the  top. 

(5)  The  sample  to  be  tested  shall  be  hung  horizontally  edgewise  between 
two  stretched  wires,  if  it  have  two  rows  of  perforations.  The  wires  shall  be 
threaded  through  the  holes  at  intervals  not  greater  than  32  mm.  and  in  such  a 
way  that  the  used  holes  are  displaced  against  each  other.  The  wire  shall  not 
be  thicker  than  0.5  mm. 

(4)  The  burning  time  is  calculated  from  the  moment  when  the  flame  reaches 
the  mark  until  the  sample  is  fully  burned.  This  time  shall  be  determined  in 
three  tests,  immediately  after  drying,  in  a  room  free  from  air  currents.  No 
test  shall  give  a  burning  time  less  than  the  fixed  minimum. 

Marking. 

Safety  film  that  conies  up  to  these  conditions  may  be  marked  Safety  Film  but 
only  in  connection  with  the  name  or  the  trade-mark  of  the  manufacturer. 

The  determination  of  inflammability  is  reserved  for  a  later  meeting  of  ISA 
Committee  36. 

The  above  definition  and  testing  procedure  constitute  essentially 
the  old  Lehman  burning  test,  with  an  additional  specification  as  to 
the  maximum  amount  of  cellulose  nitrate.  This  agrees  with  the 
minimum  amount  in  the  listings  of  the  Underwriters'  Laboratory,  but 
is  about  half  as  great  as  the  maximum  amount  in  their  listing. 

(5)  Reduction  Ratio  for  35-Mm.  to  16-Mm. — This  question  is  in 
the  hands  of  a  sub -committee  under  the  Chairmanship  of  J.  A. 
Maurer.     The  committee  has  not  yet  reported  its  findings. 

(6)  Universal  Perforation. — The  question  of  a  universal  perfora- 
tion with  the  basic  dimensions  of  the  Bell  &  Howell  and  with  the 
general  shape  of  the  positive  perforation  is  still  under  study.     A  re- 
port by  P.  Arnold,  Chairman  of  the  sub-committee  on  this  subject,  is 
expected  soon. 

(7)  "Variable-Area"    vs.    "Variable- Width. "—The    question    of 
standardizing  the  term  variable-area  or  variable-width  as  the  definitive 
name  of  one  kind  of  sound-track  has  been  referred  to  the  Standards 
Committee  by  the  editors  of  the  JOURNAL.     Letters  were  mailed  to 
all  the  members  of  the  Standards  Committee  asking  the  following 
questions : 

(1)  Whether  or  not  the  Society  should  standardize  on  one  or  the  other  of  these 
terms. 

(2)  Whether  in  their  opinion  one  term  was  more  desirable  than  the  other. 
(5)     Whether  in  their  neighborhood  one  term  was  in  wider  use  than  the  other 

erm. 


622  STANDARDS  COMMITTEE 

The  replies  were  approximately  2  to  1  in  favor  of  the  term  variable- 
area  principally  because  that  is  the  term  in  common  use,  although 
quite  a  number  of  the  members  indicated  their  belief  that  the  term 
variable-width  was  somewhat  more  technically  correct.  A  little  over 
a  majority  of  the  members  who  replied  were  in  favor  of  establishing  a 
standard. 

The  letters  indicated  great  diversity  of  points  of  view,  depending 
mainly  upon  the  connections  of  the  members — whether  the  matter 
was  looked  at  from  the  point  of  view  of  the  film  or  of  the  recording 
method.  It  was  pointed  out  that  in  the  November,  1931,  issue  of  the 
JOURNAL,  both  terms  were  listed  in  the  "Glossary  of  Technical  Terms 
Used  in  the  Motion  Picture  Industry,"  and  that,  although  the  term 
variable-width  may  have  been  preferred  editorial  practice  of  the 
Society,  nevertheless  the  two  terms  were  synonymous. 

The  motion  was  made,  seconded,  and  unanimously  approved,  that 
in  the  next  report  of  the  Standards  Committee  it  be  stated  that  the 
Standards  Committee  had  canvassed  the  situation  and  had  found 
that  the  term  variable-area  is  more  generally  used  than  the  term 
variable-width,  but,  however,  that  the  two  terms  should  be  regarded 
as  synonymous,  as  indicated  by  the  Glossary  of  November,  1931. 

E.  K.  CARVER,  Chairman 

P.  H.  ARNOLD  C.  L.  FARRAND  T.  NAGASE 

F.  C.  BADGLEY  G.  FRIEDL,  JR.  N.  F.  OAKLEY 

M.  C.  BATSEL  H.  N.  GRIFFIN  G.  F.  RACKETT 

L.  N.  BUSCH  A.  C.  HARDY  W.  B.  RAYTON 

A.  COTTET  L.  B.  HOFFMAN  C.  N.  REIFSTECK 

L.  W.  DAVEE  R.  C.  HUBBARD  H.  RUBIN 

A.  C.  DOWNES  E.  HUSE  O.  SANDVIK 

J.  A.  DUBRAY  C.  L.  LOOTENS  J.  L.  SPENCE 

P.  H.  EVANS  K.  F.  MORGAN  J.  VAN  BREUKELEN 

R.  E.  FARNHAM  I.  D.  WRATTEN 


REPORT  OF  MEMBERSHIP  AND  SUBSCRIPTION 
COMMITTEE* 

In  the  report  of  the  Committee  presented  last  spring  the  prediction 
was  made  that  if  business  conditions  improved  the  Society's  member- 
ship would  number  1400  by  the  end  of  this  year.  Actually  the  influx 
of  new  members  during  the  past  six  months  has  been  such  that  we 
should  have  far  surpassed  this  figure  had  it  not  been  for  the  large 
number  of  delinquent  members. 

On  April  15th  the  membership  was  1333,  the  largest  in  the  history 
of  the  Society.  Since  then  we  have  added  121  members,  which 
should  have  brought  the  figure  up  to  1454,  another  new  high.  Un- 
fortunately, however,  since  April  15th,  125  members  have  become 
delinquent  and  a  few  have  resigned,  with  the  result  that  the  net 
membership  as  of  September  30th  was  1309. 

While  the  reinstatement  of  delinquent  members  is  not  the  function 
of  the  Membership  Committee,  the  matter  of  delinquencies  is  of 
chief  concern  to  us  because  our  upward  climb  is  thus  impeded.  Our 
sincere  hope  is  that  before  the  end  of  this  year  a  very  substantial 
number  of  those  now  delinquent  will  have  come  back  into  the  fold. 

As  of  September  30,  1938,  totals  were  as  follows:  6  Honorary 
Members,  138  Fellows,  361  Active  Members,  and  804  Associates, 
making  a  net  total  of  1309.  Seven  applications,  6  Active  and  1 
Fellow,  are  pending. 

Our  loss  in  subscriptions  during  the  same  period  has  been  on  about 
the  same  scale  as  our  membership  delinquencies.  On  April  15th 
we  had  a  total  of  422  subscriptions.  Since  then  32  have  been  added. 
However,  87  were  lost  during  the  same  period. 

Perhaps  the  pronounced  recession  period  through  which  we  have 
just  passed  has  been  responsible  in  whole  or  in  part  for  the  member- 
ship delinquencies  and  subscription  losses  just  referred  to,  and  now 
that  brighter  skies  are  ahead,  we  shall  regain  the  ground  lost. 

E.  R.  GEIB,  Chairman 


*  Presented  at  the  Fall,  1938,  Meeting  at  Detroit,  Mich.;  received  October  31, 
1938. 

623 


CURRENT   LITERATURE   OF  INTEREST   TO   THE   MOTION   PICTURE 

ENGINEER 


The  editors  present  for  convenient  reference  a  list  of  articles  dealing  with  subjects 
cognate  to  motion  picture  engineering  published  in  a  number  of  selected  journals. 
Photostatic  copies  may  be  obtained  from  the  Library  of  Congress,  Washington,  D.  C., 
or  from  the  New  York  Public  Library,  New  York,  N.  Y.  Micro  copies  of  articles 
in  magazines  that  are  available  may  be  obtained  from  the  Bibliofilm  Service,  Depart- 
ment of  Agriculture,  Washington,  D.  C. 


American  Cinematographer 

19  (Sept.,  1938),  No.  9 
Dr.  Carter  Answers  Vital  Queries  Regarding  Metal  Film 

Development  (pp.  356-359). 
Erpi  Introduces  Sound  Recorder  for  Professional  16-Mm. 

Film  Men  (p.  364). 

Abrams  Builds  Plane  and  Camera  for  Aerial  Photo- 
graphic Mapping  (p.  370). 

Electronics 

11  (Sept.,  1938),  No.  9 

A  Sound  Illusion  Pre-Amplifier  (pp.  14-15). 
Combination  Tones  in  Non-Linear  Systems  (pp.  20-21). 
A  Laboratory  Television  Receiver — III  (pp.  22-25). 
Magnetic  Recording  (pp.  30-32). 

International  Photographer 

10  (Sept.,  1938),  No.  8 
New  Eastman  Films  (p.  1) 
M-R  Introduces  Duarc  (pp.  1-2). 
New  Canady  Recorder  (p.  6). 
Theatre  Sound  Optical  Systems  (pp.  25-27). 

International  Projectionist 

13  (Sept.,  1938),  No.  9 

Common  Causes  of  Breakdown  in  Theatre  Sound  Sys- 
tems (pp.  7-8,  10,  30). 

Emergency    Measures    Applicable    to    Motor    Control 
Failure  (pp.  11-14). 

Notes  on  Time-Lag  in  Gas-Filled  Photo-Electric  Cells 
(pp.  14-15). 

Notes  on  SMPE  16-Mm.  Test-Films  (p.  15). 

The  Theory  of  Commutation.     II  (pp.  16-19). 


624 


R.  W.  CARTER 


C.  F.  SHEAFFER 
F.  MASSA 

D.  G.  FINK 
S.  J.  BEGUN 


C.  N.  BATSEL 

A.  NADELL 
L.  BORGESON 
A.  M.  SKELLETT 

Engineering     Dept., 
National  Carbon  Co. 


CURRENT  LITERATURE 


625 


Craft    Opinion   on   Reverse    Prints   Sharply    Divided; 

Exchanges  Hit  (pp.  28-29). 
Push-Pull  Recording  and  Reproduction:     The  What, 

Why  and  How  (pp.  20-22).  F.  T.  JAMEY 

Kinematograph  Weekly 

259  (Sept.  22,  1938),  No.  1640 
Light  Intensity  and  Colour  Films  (p.  39).  R.  H.  CRICKS 

Kinotechnik 

20  (Sept.,  1938),  No.  9 

Ozaphantonfilm  (Ozaphane  Sound-Film)  (pp.  232-237).     A.  NARATH 
Der    Stereoskopische    Film    (Stereoscopic    Film)    (pp. 

237-238).  W.  THORNER 

Die  Bedeutung  des  stereoskopischen  Bildwurfes  beim 
Film  (Importance  of  Stereoscopic  Projection  for  Film) 
(pp.  238-240).  W.  PISTOR 

Motion  Picture  Herald 

132  (Sept.  24,  1938),  No.  13 

Cosmocolor,  New  Two- Color  Process  Is  Demonstrated 
(p.  24). 

La  Technique  Cinematographique 

9  (Aug.,  1938),  No.  92 

L'enregistrement  Sonore  sur  Bandes  Reduites  et  sur 
Papier  (Recording  Sound  on  Reduced  Strips  and  on 
Paper)  (pp.  1241-1242).  R.  HARDY 

Normes  des  Emissions  de  Television  (Television  Stand- 
ards) (p.  1242). 


PROGRAM 
FALL,  1938,  CONVENTION,  DETROIT,  MICH.,  HOTEL  STATLER 

(.4 s  actually  followed  in  the  Sessions} 
MONDAY,  OCTOBER  31,  1938 

9:00  a.m.     Registration. 
10:00  a.m.    Business  and  General  Session. 

Opening  remarks  by  President  S.  K.  Wolf. 

Report  of  the  Convention  Committee;  W.  C.  Kunzmann,  Conven- 
tion Vice-President. 

Report  of  the  Membership  Committee;    E.  R.  Geib,  Chairman. 
Election  of  Officers. 

"Underwater  Cinematography;"  E.  R.  F.  Johnson,  Mechanical 
Improvements  Corp.,  Moorestown,  N.  J.  (Demonstration.} 

"The  Spectroheliokinematograph;"  R.  R.  McMath,  McMath- 
Hulbert  Observatory,  University  of  Michigan,  Ann  Arbor,  Mich. 
(Demonstration.} 

"The  Future  of  Commercial  Motion  Pictures;"  F.  J.  Herman,  Jam 
Handy  Picture  Service,  Inc.,  Detroit,  Mich. 

"Oskar  Messter — German  Pioneer;"   H.  Traub,  Berlin,  Germany. 
12:30  p.m.    Informal  Luncheon. 

Addresses  by: 

Hon.  Richard  W.  Reading,  Mayor  of  Detroit,  Mich. 

Mr.  Jamison  Handy,  President  of  Jam  Handy  Corporation,  Detroit, 
Mich. 

Mr.  George  W.  Trendle,  President,  United  Detroit  Theaters  Corpora- 
tion, Detroit,  Mich. 

2:00  p.m.     Sound  Session. 

"Some  Practical  Accessories  for  Motion  Picture  Sound  Recording;" 
R.  O.  Strock,  Eastern  Service  Studios,  Long  Island  City,  N.  Y. 

"Improving  the  Fidelity  of  Disk  Records  for  Direct  Playback;" 
H.  J.  Hasbrouck,  Jr.,  RCA  Manufacturing  Co.,  Inc.,  Camden, 
N.  J.  (Demonstration.} 

Report  of  the  Standards  Committee. 

Society  Business. 
626 


CONVENTION  PROGRAM  627 

"Characteristics  of  Film-Reproducing  Systems;"  F.  Durst  and  E.  J. 
Shortt,  International  Projector  Corp.,  New  York,  N.  Y. 

"Some  Production  Aspects  of  Binaural  Recording  for  Sound  Motion 
Pictures;"  W.  H.  Offenhauser,  Jr.,  New  York,  N.  Y.,  and  J.  J. 
Israel,  Brooklyn,  N.  Y.  (Demonstration.} 

"Unidirectional  Microphone  Technic;"  J.  P.  Livadary,  Columbia 
Pictures  Corp.,  Ltd.,  Hollywood,  Calif.,  and  M.  Rettinger,  RCA 
Manufacturing  Co.,  Inc.,  Los  Angeles,  Calif. 

8:00  p.m.     Motion  Picture  Program. 

Showing  of  recent  feature  motion  pictures  and  short  subjects. 

TUESDAY,  NOVEMBER  1,  1938 

9:30  a.m.     General  Session. 

"A  Machine  for  Artificial  Reverberation;"  S.  K.  Wolf,  Acoustic 
Consultants,  Inc.,  New  York,  N.  Y. 

"A  Motion  Picture -Dubbing  and  Scoring  Stage;"  C.  L.  Lootens,  Re- 
public Productions,  Inc.,  North  Hollywood,  Calif.,  M.  Rettinger, 
RCA  Manufacturing  Co.,  Inc.,  Hollywood,  Calif.,  and  D.  J.  Bloom- 
berg, Republic  Productions,  Inc.,  North  Hollywood,  Calif. 

"Some  of  the  Problems  Ahead  in  Television;"  I.  J.  Kaar,  General 
Electric  Co.,  Bridgeport,  Conn. 

"Some  Television  Problems  from  the  Motion  Picture  Standpoint;" 
G.  L.  Beers,  E.  W.  Engstrom,  and  I.  G.  Maloff,  RCA  Manufac- 
turing Co.,  Inc.,  Camden,  N.  J.  (Demonstration.) 

2 :00  p.m.    Laboratory  Session. 

"Some  General  Characteristics  of  Chromium-Nickel-Iron  Alloys  as 
Corrosion-Resisting  Materials;"  F.  L.  LaQue,  International 
Nickel  Co.,  Inc.,  New  York,  N.  Y. 

"A  Color-Temperature  Meter;"  E.  M.  Lowry,  Kodak  Research 
Laboratories,  Rochester,  N.  Y. 

"Technicolor  Adventures  in  Cinemaland;"  H.  T.  Kalmus,  Tech- 
color  Motion  Picture  Corp.,  Hollywood,  Calif. 

"Chemical  Analysis  of  an  MQ  Developer;"  R.  M.  Evans  and  W.  T. 
Hanson,  Jr.,  Kodak  Research  Laboratories,  Rochester,  N.  Y. 

"Opacimeter  Used  in  Chemical  Analysis;"  R.  M.  Evans  and  G.  P. 
Silberstein,  Kodak  Research  Laboratories,  Rochester,  N.  Y. 

"Latest  Developments  in  Variable-Area  Processing;"  A.  C.  Blaney, 
RCA  Manufacturing  Co.,  Inc.,  Los  Angeles,  Calif.,  and  G.  M. 
Best,  Warner  Bros.  Pictures,  Inc.,  Burbank,  Calif.  (Demonstra- 
tion.) 


628  CONVENTION  PROGRAM  [j.  s.  M.  P.  E. 

7:30  p.m.     Semi- Annual  Banquet. 

Introduction  of  Officers- Elect. 
Presentation  of  Journal  Award. 
Presentation  of  SMPE  Progress  Medal. 
Entertainment  and  dancing. 

WEDNESDAY,  NOVEMBER  2,  1938 

9:30  a.m.     Studio-Lighting-Theater  Session. 

"The  Evolution  of  Arc  Broadside  Lighting  Equipment;"  P.  Mole, 
Mole-Richardson  Co.,  Hollywood,  Calif. 

Report  of  the  Studio  Lighting  Committee;  C.  W.  Handley,  Chair- 
man. 

"The  Lighting  of  Theater  Interiors;"  F.  M.  Falge,  General  Electric 
Company,  Cleveland,  Ohio.  (Demonstration.)  Discussion  led  by 
L.  A.  Jones  and  B.  Schlanger. 

Report  of  the  Projection  Practice  Committee;  H.  Rubin,  Chairman. 

"Coordinating  Acoustics  and  Architecture  in  the  Design  of  the 
Motion  Picture  Theater;"  C.  C.  Potwin,  Electrical  Research 
Products,  Inc.,  New  York,  N.  Y.,  and  B.  Schlanger,  New  York, 
N.  Y. 

"The  Copper  Sulfide  Rectifier  as  a  Source  of  Power  for  the  Pro- 
jection Arc;"  C.  A.  Kotterman,  P.  H.  Mallory  &  Co.,  Indianapolis, 
Ind. 

2:00  p.m.     16-Mm.  and  General  Session. 

"A  16-Mm.  Studio  Recorder;"  R.  W.  Benfer,  Electrical  Research 
Products,  Inc.,  New  York,  N.  Y.  (Demonstration.) 

"A  Super  Sound  and  Picture  Printer;"  O.  B.  Depue,  Burton  Holmes 
Films,  Inc.,  Chicago,  111. 

"A  New  16-Mm.  Developing  Machine;"  J.  M.  Blaney,  Cinanda- 
graph  Corp.,  Stanford,  Conn. 

"New  Sound  Recording  Equipment;"  D.  R.  Canady  and  V.  A. 
Welman,  Canady  Sound  Appliance  Co.,  Cleveland,  Ohio. 

"The  Evaluation  of  Motion  Picture  Films  by  Semimicro  Testing;" 
J.  E.  Gibson  and  C.  G.  Weber,  National  Bureau  of  Standards, 
Washington,  D.  C. 

"The  Stability  of  -the  Viscose  Type  of  Ozaphane  Photographic 
Film;"  A.  M.  Sookne  and  C.  G.  Weber,  National  Bureau  of 
Standards,  Washington,  D.  C. 

"A  Silent  Wind  Machine  for  the  Production  Stage;"  F.  G.  Albin, 
United  Artists  Studio  Corp.,  Hollywood,  Calif. 


Dec.,  1938]  CONVENTION  PROGRAM  629 

"Independent  Drive  for  Camera  in  the  A-c.  Interlock  Motor  Sys- 
tem;" F.  G.  Albin,  United  Artists  Studio  Corp.,  Hollywood,  Calif. 

"A  Semi- Automatic  Follow-Focus  Device;"  J.  Arnold,  M-G-M 
Studio,  Culver  City,  Calif. 

"A  New  Single-System  Recording  Attachment  for  Standard  35-Mm. 
Cameras;"  A.  Reeves,  Art  Reeves  Motion  Picture  Equipment  Co., 
Hollywood,  Calif. 


SOCIETY  ANNOUNCEMENTS 


OFFICERS  FOR  1939 

Election  of  officers  and  governors  of  the  Society  for  1939  was  completed  at  the 
Detroit  Convention  on  October  31st.  The  results  of  the  election  are  given  on 
page  557  of  this  issue  of  the  JOURNAL. 

ATLANTIC  COAST  SECTION 

On  November  18th,  in  the  North  Ballroom  of  the  Hotel  New  Yorker,  New  York, 
N.  Y.,  two  papers  on  the  subject  of  television,  originally  presented  at  the  Detroit 
Convention,  were  re-presented,  namely, 

"The  Road  Ahead  for  Television,"  by  I.  J.  Kaar,  General  Electric  Company, 
Bridgeport,  Conn. 

"Some  Television  Problems  from  the  Motion  Picture  Standpoint,"  by  G.  L. 
Beers,  E.  W.  Engstrom,  and  I.  G.  Mallof,  RCA  Manufacturing  Company,  Cam- 
den,  N.  J. 

The  two  papers  aroused  considerable  interest  and  elicited  much  discussion. 
Plans  for  future  meetings  of  the  Section  include  papers  by  F.  C.  Gilbert  on 
motion  picture  theater  equipment  servicing  (December) ;  E.  Epstean  on  the  con- 
tributions of  Daguerre,  on  the  occasion  of  the  centenary  of  Daguerre's  announce- 
ments of  his  work  to  the  French  Academy  of  Science  (January);  E.  I.  Sponable 
on  newsreel  recording  (February);  and  W.  B.  Rayton  on  projection  lenses 
(March). 

MID-WEST  SECTION 

At  a  meeting  held  at  the  Bell  &  Howell  Laboratory,  Chicago,  111.,  on  October 
25th,  W.  D.  Myers  of  the  National  Theater  Supply  Company  presented  a  paper 
on  "A  New  Theater  Sound  System." 

Following  the  paper,  the  film  "High  Lights  and  Shadows,"  an  industrial  motion 
picture  film  of  the  Eastman  Kodak  Company,  was  presented. 

SPRING  1939  CONVENTION 

The  Spring,  1939,  Convention  will  be  held  at  Hollywood,  Calif.,  with  head- 
quarters at  the  Hotel  Roosevelt,  April  17th  to  21st,  inclusive.  Members  are 
urged  to  bear  the  dates  in  mind  so  that  they  may  make  their  plans  in  advance 
for  attending  the  Convention.  It  is  suggested  that  vacations  may  be  combined 
with  the  trip  to  the  Coast. 

NEW  AMENDMENTS 

At  the  Detroit  Convention  on  October  31st,  a  number  of  proposed  amendments 
of  the  Constitution  and  By-Laws  were  acted  upon  by  the  Society  in  session.  The 
630 


SOCIETY  ANNOUNCEMENTS  631 

ensuing  paragraphs  give  the  substance  of  the  amendments  and  are  followed  by 
the  amendments  in  their  exact  original  and  new  wordings,  for  comparison. 

CONSTITUTION 

Article  IV,  Officers 

It  is  proposed  that  the  term  of  office  of  the  Executive  Vice-President  be  extended  to 
two  years,  in  view  of  the  fact  that  the  terms  of  all  the  other  vice-presidents  are  two  years. 

Original  wording: 

The  officers  of  the  Society  shall  be  a  President,  a  Past-President,  an  Executive 
Vice-President,  an  Engineering  Vice-President,  an  Editorial  Vice-President,  a 
Financial  Vice-President,  a  Convention  Vice-President,  a  Secretary,  and  a  Trea- 
surer. 

The  term  of  office  of  the  President  and  Past-President  shall  be  two  years;  of 
the  Engineering,  Editorial,  Financial,  and  Convention  Vice-Presidents,  two  years; 
and  of  the  Executive  Vice-President,  Secretary,  and  Treasurer,  one  year.  Of  the 
Engineering,  Editorial,  Financial,  and  Convention  Vice-Presidents,  two  shall  be 
elected  alternately  each  year  or  until  their  successors  are  chosen.  The  Presi- 
dent shall  not  be  immediately  eligible  to  succeed  himself  in  office. 

Proposed  wording: 

The  officers  of  the  Society  shall  be  a  President,  a  Past-President,  an  Executive 
Vice-President,  an  Engineering  Vice-President,  an  Editorial  Vice-President,  a 
Financial  Vice-President,  a  Convention  Vice-President,  a  Secretary,  and  a 
Treasurer. 

The  term  of  office  of  the  President,  the  Past-President,  the  Executive  Vice- 
President,  the  Engineering  Vice-President,  the  Editorial  Vice-President,  the 
Financial  Vice-President,  and  the  Convention  Vice-President  shall  be  two  years, 
and  the  Secretary  and  the  Treasurer  one  year.  Of  the  Engineering,  Editorial, 
Financial,  and  Convention  Vice-Presidents,  two  shall  be  elected  alternately  each 
year,  or  until  their  successors  are  chosen.  The  President  shall  not  be  immedi- 
ately eligible  to  succeed  himself  in  office. 

(This  amendment  is  to  be  voted  upon  by  the  voting  membership  of  the  Society  by 
letter  ballot.  Ballots,  and  a  complete  transcript  of  the  discussion  on  this  proposal  at 
the  Convention,  will  be  mailed  to  the  voting  membership  in  the  near  future.) 

The  following  By-Laws  were  approved  at  the  Convention  in  accordance  with  the 
existing  procedure  for  amending  the  By-Laws,  and  are  therefore  now  in  effect: 

BY-LAW  I 
Membership 

Fellow  membership  may  no  longer  be  applied  for. 

Original  wording: 

Sec.  2. — All  applications  for  membership  or  transfer  shall  be  made  on  blank 
forms  provided  for  the  purpose,  shall  give  a  complete  record  of  the  applicant's 
education  and  experience. 


632  SOCIETY  ANNOUNCEMENTS  [j.  s.  M.  P.  E. 

New  wording: 

Sec.  2. — All  applications  for  membership  or  transfer,  except  for  Honorary  or 
Fellow  membership,  shall  be  made  on  blank  forms  provided  for  the  purpose,  and 
shall  give  a  complete  record  of  the  applicant's  education  and  experience.  Honor- 
ary and  Fellow  membership  may  not  be  applied  for. 

Fellow  membership  will  be  granted  by  the  Board  of  Governors.  A  Committee  on 
Fellow  membership  will  be  established  to  recommend  periodically  to  the  Board  of 
Governors  the  names  of  those  eligible  for  elevation  to  the  grade  of  Fellow. 

Original  wording: 

Sec.  3  (b). — Applicants  for  the  grade  of  Fellow  shall  give  as  reference  at  least 
three  Fellows  in  good  standing.  Applicants  shall  be  elected  to  membership  by 
the  approval  of  at  least  three-fourths  of  the  Board  of  Governors. 

New  wording: 

Sec.  3  (b). — Fellow  membership  may  be  granted  upon  recommendation  of  at 
least  three-fourths  of  the  Board  of  Governors. 

BY-LAW  II 
Officers 

Hitherto,  holding  office  in  the  Society  has  been  restricted  to  Honorary  and  Fellow 
members.  The  new  amendment  extends  the  privilege  to  Active  members. 

Original  wording: 

Sec.  1. — An  officer  or  governor  shall  be  an  Honorary  member,  a  Fellow,  or  an 
Active  member.  After  January  1,  1935,  Active  members  shall  not  be  eligible  to 
hold  national  office  in  the  Society. 

New  wording: 

Sec.  1. — An  officer  or  governor  shall  be  an  Honorary,  a  Fellow,  or  Active  mem- 
ber. 

BY-LAW  VII 

Dues  and  Indebtedness 

Dues  beginning  January  1,  1939,  will  be  $15  for  Fellows  and  Active  members,  and 
$7. 50  for  Associate  members.  At  present  the  dues  are  $20  for  Fellows,  $10  for  Active 
members,  and  $6  for  Associate  members. 

Original  wording: 

Sec.  1.— The  annual  dues  shall  be  twenty  dollars  ($20)  for  Fellows,  ten  dollars 
($10)  for  Active  members,  and  six  dollars  ($6)  for  Associate  members,  payable 
on  or  before  January  1st  of  each-year.  Current  or  first  year's  dues  for  new  mem- 
bers, dating  from  the  notification  of  acceptance  in  the  Society,  shall  be  prorated 
on  a  monthly  basis.  Five  dollars  of  these  dues  shall  apply  for  annual  subscrip- 
tion to  the  publication.  No  admission  fee  will  be  required  in  any  grade  of  mem- 
bership. 


Dec.,  1938]  SOCIETY  ANNOUNCEMENTS  633 

New  wording: 

Sec.  1. — The  annual  dues  shall  be  fifteen  dollars  ($15)  for  Fellows  and  Active 
members  and  seven  dollars  and  fifty  cents  ($7.50)  for  Associate  members,  payable 
on  or  before  January  1st  of  each  year.  Current  or  first  year's  dues  for  new  mem- 
bers, dating  from  the  notification  of  acceptance  in  the  Society,  shall  be  prorated 
on  a  monthly  basis.  Five  dollars  of  these  dues  shall  apply  for  annual  subscription 
to  the  publication.  No  admission  fee  will  be  required  for  any  grade  of  member- 
ship. 

This  By-Law  describes  the  procedure  to  be  followed  in  case  of  delinquent  members. 
The  original  wording  permitted  retaining  delinquent  members  on  the  mailing  list  of 
the  JOURNAL  for  six  months;  the  new  wording  reduces  this  to  four  months. 

Original  wording: 

Sec.  4. — Members  shall  be  considered  delinquent  whose  dues  remain  unpaid 
for  four  months.  Members  who  are  in  arrears  of  dues  for  30  days  after  notice 
of  such  delinquence,  mailed  to  their  last  address  of  record,  shall  have  their  names 
posted  at  the  Society's  headquarters,  which  shall  be  the  General  Office,  and  notices 
of  such  action  mailed  to  them.  Two  months  after  becoming  delinquent,  mem- 
bers shall  be  dropped  from  the  rolls  if  non-payment  is  continued. 

New  wording: 

Sec.  4. — Members  shall  be  considered  delinquent  whose  annual  dues  for  the 
year  remain  unpaid  on  February  1st.  The  first  notice  of  delinquency  shall  be 
mailed  February  1st.  The  second  notice  of  delinquency  shall  be  mailed,  if  neces- 
sary, on  March  1st,  and  shall  include  a  statement  that  the  member's  name  will  be 
moved  from  the  mailing  list  for  the  JOURNAL  and  other  publications  of  the  Society 
before  the  mailing  of  the  April  issue  of  the  JOURNAL.  Members  who  are  in  arrears 
of  dues  on  June  1st,  after  two  notices  of  such  delinquency  have  been  mailed  to 
their  last  address  of  record,  shall  be  notified  their  names  have  been  removed 
from  the  mailing  list  and  shall  be  warned  that  unless  remittance  is  received  on 
or  before  August  1st,  their  names  shall  be  submitted  to  the  Board  of  Governors 
for  action  at  the  next  meeting.  Back  issues  of  the  JOURNAL  shall  be  sent,  if  avail- 
able, to  members  whose  dues  have  been  paid  prior  to  August  1st. 

Delinquent  members  may  be  dropped  from  the  rolls  by  action  of  the  Board  of  Gov- 
ernors. Members  dropped  from  the  rolls  for  non-payment  of  dues  may  resume  mem- 
bership in  the  Society  only  by  applying  as  new  members. 

Original  wording: 

Sec.  5. — Any  member  may  be  suspended  or  expelled  for  cause  by  a  majority 
vote  of  the  entire  Board  of  Governors;  provided  he  shall  be  given  notice  and  a 
copy  in  writing  of  the  charges  preferred  against  him,  and  shall  be  afforded  oppor- 
tunity to  be  heard  ten  days  prior  to  such  action. 

New  wording: 

Sec.  5  (a). — Members  whose  dues  remain  unpaid  on  October  1st  may  be  dropped 
from  the  rolls  of  the  Society  by  majority  vote  and  action  of  the  Board,  or  the 
Board  may  take  such  action  as  it  sees  fit. 


634  SOCIETY  ANNOUNCEMENTS  (J.  S.  M.  p.  E. 

(6)  Anyone  who  has  been  dropped  from  the  rolls  of  the  Society  for  non-pay- 
ment of  dues  shall,  in  the  event  of  his  application  for  reinstatement,  be  considered 
as  a  new  member. 

(c)  Any  member  may  be  suspended  or  expelled  for  cause  by  a  majority  vote 
of  the  entire  Board  of  Governors;  provided  he  shall  be  given  notice  and  a  copy 
in  writing  of  the  charges  preferred  against  him,  and  shall  be  afforded  oppor- 
tunity to  be  heard  ten  days  prior  to  such  action. 


BY-LAW  XI 

Amendments 

A  new  procedure  is  established  for  amending  the  By-Laws  in  case  no  quorum  is 
obtainable  at  a  Convention  of  the  Society,  in  which  case  proposed  amendments  may 
be  validated  by  vote  of  the  Board  of  Governors. 

Original  wording: 

Sec.  1. — These  By-Laws  may  be  amended  at  any  regular  meeting  of  the 
Society  by  a  two-thirds  vote  by  ballot  of  the  members  present  at  the  meeting,  a 
quorum  being  present,  either  on  the  recommendation  of  the  Board  of  Governors 
or  by  a  recommendation  of  the  Board  of  Governors  signed  by  any  ten  members 
of  Active  or  higher  grade. 

New  wording: 

Sec.  1. — These  By-Laws  may  be  amended  at  any  regular  meeting  of  the  So- 
ciety by  the  affirmative  vote  of  two-thirds  of  the  membership  present  at  a  meet- 
ing who  are  eligible  to  vote  thereon,  a  quorum  being  present,  either  on  the  recom- 
mendation of  the  Board  of  Governors  or  by  a  recommendation  to  the  Board 
of  Governors  signed  by  any  ten  members  of  active  or  higher  grade,  provided  that 
the  proposed  amendment  or  amendments  shall  have  been  published  in  the  Jour- 
nal of  the  Society,  in  the  issue  next  preceding  the  date  of  the  stated  business  meet- 
ing of  the  Society,  at  which  the  amendment  or  amendments  are  to  be  acted  upon. 

Sec.  2. — In  the  event  that  no  quorum  of  the  voting  membership  is  present  at 
the  time  of  the  meeting  referred  to  in  Sec.  1,  the  amendment  or  amendments  shall 
be  referred  for  action  to  the  Board  of  Governors.  The  proposed  amendment  or 
amendments  then  become  a  part  of  the  By-Laws  upon  receiving  the  affirmative 
vote  of  three-quarters  of  the  Board  of  Governors. 

ADMISSIONS  COMMITTEE 

At  a  recent  meeting  of  the  Admissions  Committee  at  the  General  Office  of  the 
Society,  the  following  applicants  for  membership  were  admitted  to  the  Associate 
grade: 

ALLA,  R.  BATTLE,  G.  H. 

38  Avenue  des  Champs  Elysees,  Canadian  National  Carbon  Co.,  Ltd., 

Paris,  France.  805  Davenport  Rd., 

Toronto,  Canada. 


Dec.,  1938] 


SOCIETY  ANNOUNCEMENTS 


635 


BENHAM,  H.  J. 

616  Keith  Building, 

Cleveland,  O. 
BLUHME,  A.  B. 

646  N.  Lotus  Ave., 
Chicago,  111. 

BOSTELMANN,  T.  A. 

3315  Olive  St., 

St.  Louis,  Mo. 
COAR,  R.  J. 

1421  Massachusetts  Ave.,  N.  W., 

Washington,  D.  C. 
COOK,  J.  A. 

4956  Thekla  Ave., 

St.  Louis,  Mo. 
DOWNS,  G.  W.,  JR. 
6900  McKinley  Ave., 
Los  Angeles,  Calif. 
EAGLES,  J.  P. 

16-22  Australia  St., 
Camperdown,  N.  S.  W., 

Australia. 
GLEASON,  J.  P. 

Movietone  News,  Inc., 
1118  So.  Michigan  Ave., 

Chicago,  III. 
GUNSBURG-SHICK,  H. 

National  Theater  Supply  Co., 
1560  Broadway, 

New  York,  N.  Y. 
HOTINE,  W. 
%  Films,  Inc., 
330  West  42d  St., 

New  York,  N.  Y. 
ISRAEL,  J.  J. 
•     1598  East  28th  St., 
Brooklyn,  N.  Y. 
JONES,  R.  W. 

100  Broadview  Ave., 
New  Rochelle,  N.  Y. 

LlPPERT,  O. 

7002  Sheridan  Rd., 
Chicago,  III. 

In  addition,  the  following  applicants  have  been  admitted  by  vote  of  the  Board 
of  Governors  to  the  Active  grade: 


MARTIN,  S.  M. 

Miller  Broadcasting  System, 
113  West  57th  St., 

New  York,  N.  Y. 
MORRIS,  R.  M. 

22  Mountainview  Rd., 
Millburn,  N.  J. 

MULLER,  R. 

Rome,  via  Guitinio  Sella  20. 

Italy. 

MURUA,  A.  P. 
Campichuelo  553, 

Argentina. 
NAPOLETANO,  T. 
3910  French  Rd., 
Detroit,  Mich. 
PACE,  G.  C. 

3134  Elliott  Ave., 

Dayton,  O. 
PAI,  B.  K. 

Lamington  Rd., 

Bombay  4,  India. 
ROSENBERG,  T. 
1560  Broadway, 

New  York,  N.  Y. 
STOWELL,  T.  C. 

Department  of  Health, 
State  of  New  York, 

Albany,  N.  Y. 
TICKES,  S. 

4927  N.  Lawndale, 

Chicago,  111. 
WALTER,  E. 

Rua  Sao  Pedro  268, 
Coixa  Postal  849, 

Rio  de  Janeiro,  Brazil 
WHEELWRIGHT,  G.  W.  SRD. 
Polaroid  Corporation, 
285  Columbus  Ave., 
Boston,  Mass. 


BOUTELLEAU,  C. 

296,  Rue  Lecourse, 
Paris  XV8,  France 


EDMONDS,  A.  L. 
4248  Deenan  Blvd., 
Los  Angeles,  Calif. 


BACK  NUMBERS  OF  THE  TRANSACTIONS  AND  JOURNALS 

Prior  to  January,  1930,  the  Transactions  of  the  Society  were  published  quar- 
terly. A  limited  number  of  these  Transactions  are  still  available  and  will  be 
sold  at  the  prices  listed  below.  Those  who  wish  to  avail  themselves  of  the  op- 
portunity of  acquiring  these  back  numbers  should  do  so  quickly,  as  the  supply 
will  soon  be  exhausted,  especially  of  the  earlier  numbers.  It  will  be  impossible 
to  secure  them  later  on  as  they  will  not  be  reprinted. 

No.      Price  No.      Price  No.      Price 

1920     10       $1.00  (21       $1.25  i HOT/ 29       $1.25 


1921     12         1.00  iQ25\ 


1922     15         1.00 


22 

23  1 

24  1.25 


1927 


20         1.25 


1.25  0,     '          1928 


0, 

Zb     L.Zb 


1926  26    1.25 


33  2.50 

34  2.50 

35  2.50 


36        2.50 

27        1.25  Q7        o  nn 

1 28         1.25  1929  {  3?        3;°° 


Beginning  with  the  January,  1930,  issue,  the  JOURNAL  of  the  Society  has  been 
issued  monthly,  in  two  volumes  per  year,  of  six  issues  each.  Back  numbers  of 
all  issues  are  available  at  the  price  of  $1.00  each,  a  complete  yearly  issue  totalling 
$12.00.  Single  copies  of  the  current  issue  may  be  obtained  for  $1.00  each. 
Orders  for  back  numbers  of  Transactions  and  JOURNALS  should  be  placed  through 
the  General  Office  of  the  Society  and  should  be  accompanied  by  check  or 
money-order. 

SOCIETY  SUPPLIES 

The  following  are  available  from  the  General  Office  of  the  Society,  at  the  prices 
noted.  Orders  should  be  accompanied  by  remittances. 

Aims  and  Accomplishments. — An  index  of  the  Transactions  from  October, 
1916,  to  December,  1929,  containing  summaries  of  all  articles,  and  author  and 
classified  indexes.  One  dollar  each. 

Journal  Index. — An  index  of  the  JOURNAL  from  January,  1930,  to  December, 
1935,  containing  author  and  classified  indexes.  One  dollar  each. 

SMPE  Standards. — The  revised  edition  of  the  SMPE  Standards  and  Recom- 
mended Practice  was  published  in  the  March,  1938,  issue  of  the  JOURNAL,  copies* 
of  which  may  be  obtained  for  one  dollar  each. 

Membership  Certificates. — Engrossed,  for  framing,  containing  member's  name, 
grade  of  membership,  and  date  of  admission.  One  dollar  each. 

Lapel  Buttons. — The  insignia  of  the  Society,  gold  filled,  with  safety  screw  back. 
One  dollar  each. 

Journal  Binders. — Black  fabrikoid  binders,  lettered  in  gold,  holding  a  year's 
issue  of  the  JOURNAL.  Two  dollars  each.  Member's  name  and  the  volume 
number  lettered  in  gold  upon  the  backbone  at  an  additional  charge  of  fifty  cents 
each. 

Test- Films. — See  advertisement  in  this  issue  of  the  JOURNAL 


JOURNAL 

OF  THE  SOCIETY  OF 

MOTION  PICTURE  ENGINEERS 


AUTHOR  AND  CLASSIFIED 
INDEXES 

VOLUME  XXXI 
JULY-DECEMBER,  1938 


AUTHOR  INDEX,  VOLUME  XXXI 

JULY  TO  DECEMBER,  1938 


Author 


AALBERG,  J.  O. 

(and  STEWART,  J.  G.) 
ALTMAN,  F.  E. 

(and  McLEOD,  J.  H.) 
ARNOLD,  P.  H. 

BACH,  W. 

(and  MAURER,  J.  A.) 
BAKER,  J.  O. 

BAKER,  T.  T. 
BAMFORD,  H.  S. 
BOON,  J.  L. 
CARLSON,  F.  E. 

COOK,  E.  D. 

(and  HALL,  V.  C.) 
CRANE,  G.  R. 

DEVRY,  H.  A. 

DIMMICK,  G.  L. 
(and  SACHTLEBEN,  L.  T.) 

EVANS,  R.  M. 


FARNHAM,  R.  E. 

(and  NOEL,  E.  B.) 
FRAYNE,  J.  G. 

(and  SILENT,  H.  C.) 
FRIEDL,  G.,  JR. 
GARITY,  W.  E. 

(and  MCFADDEN,  W.  C.) 
638 


Issue  Page 

Application    of    Non-Linear    Volume 

Characteristics  to  Dialog  Recording    Sept.    248 

An  Optical  System  for  the  Reproduc- 
tion of  Sound  from  35-Mm.  Film  July  36 

Problems  in  the  Use    of    Ultra-Speed 

Negative  Film  Sept.    307 

The  Shrinkage  of  Acetate-Base  Motion 

Picture  Films  July       15 

Processing  of  Ultraviolet  Recordings  on 

Panchromatic  Films  July       28 

Negative-Positive    Technic    with    the 

Dufaycolor  Process  Sept.    240 

A  Non-Intermittent  Projector  for  Tele- 
vision Film  Transmission  Nov.  453 

Some  Unusual  Adaptations  of  16-Mm. 

Equipment  for  Special  Purposes  Oct.     386 

A  Higher-Efficiency  Condensing  Sys- 
tem for  Picture  Projectors  Aug.  187 

A  Method  for  Determining  the  Scan- 
ning Losses  in  Sound  Optical  Systems  Dec.  586 

Variable  Matte  Control  (Squeeze 
Track)  for  Variable- Density  Re- 
cording Nov.  531 

A  Basically  New  Framing  Device  for 

35-Mm.  Projectors  Sept.    319 

An  Ultraviolet  Push-Pull  Recording 
Optical  System  for  Newsreel 
Cameras  July  87 

A  Color  Densitometer  for  Subtractive 

Processes  Aug.     194 

Maintenance  of  a  Developer  by  Con- 
tinuous Replenishment  Sept.    273 
A  Water-Cooled  Quartz  Mercury  Arc        Sept.    221 

Push-Pull  Recording  with  the  Light- 
Valve  July       46 
A  New  Sound  System                                 Nov.     511 
The  Multiplane  Camera  Crane  for  Ani-     Aug.     144 
mation  Photography 


INDEX 


639 


Author 
HALL,  V.  C. 

(and  COOK,  E.  D.) 
HARDY,  A.  C. 

HOPPER,  F.  L. 

HOUCK,  R.  C. 

(and  SHEPPARD,  S.  E.) 
HUNT,  F.  L. 
HUNT,  F.  V. 

(and  PIERCE,  J.  A.) 
IVES,  C.  E. 

IVES,  H.  E. 

KALMUS,  H.  T. 
KIMBALL,  H.  R. 

LENARD,  A. 
LEWIS,  L.  L. 

(and  WERT,  C.  M.) 
MACADAM,  D.  L. 

MANDERFELD,  E.  C. 


MAURER,  J.  A. 

(and  OFFENHAUSER,  W.  H.) 
MAURER,  J.  A. 

(and  BACH,  W.) 
MCFADDEN,  W.  C. 

(and  GARITY,  W.  E.) 
MCLEOD,  J.  H. 

(and  ALTMAN,  F.  E.) 
MERCEY,  A.  A. 

MILLER,  W.  C. 

NOEL,  E.  B. 

(and  FARNHAM,  R.  E.) 
OFFENHAUSER,  W.  H. 

(and  MAURER,  J.  A.) 
PHILLIPS,  E.  S. 


PIERCE,  J.  A. 
(and  HUNT,  F.  V.) 


Issue  Page 

A  Method  for  Determining  the  Scan- 
ning Losses  in  Sound  Optical  Systems  Dec.  586 

The  Theory  of  Three-Color  Photog- 
raphy Oct.  331 

Electrical  Networks  for  Sound  Re- 
cording Nov.  443 

The  Influence  of  pH  on  Washing  Films 

after  Processing  July  67 

Sound  Pictures  in  Auditory  Perspective     Oct.     351 

Distortion  in  Sound  Reproduction  from 

Phonograph  Records  Aug.  157 

An  Improved  Roller  Type  Developing 

Rack  with  Stationary  Drive  Oct.  393 

The  Transmission  of  Motion  Pictures 

over  a  Coaxial  Cable  Sept.  256 

Technicolor  Adventures  in  Cinemaland     Dec.     564 

Application  of  Electrical  Networks  to 

Sound  Recording  and  Reproducing  Oct.  358 

A  Novel  Surgical  Filming  Stand  Oct.     413 

Sound-Stages  and  Their  Relation  to 

Air-Conditioning  Sept.  287 

The  Fundamentals  of  Color  Measure- 
ment Oct.  343 

Permanent  -  Magnet  Four  -  Ribbon 
Light- Valve  for  Portable  Push-Pull 
Recording  Sept.  315 

A  Criticism  of  the  Proposed  Standards 

for  16-Mm.  Sound-Film  July  3 

The  Shrinkage  of  Acetate-Base  Motion 

Picture  Films  July  15 

The  Multiplane  Camera  Crane  for 

Animation  Photography  Aug.  144 

An  Optical  System  for  the  Reproduc- 
tion of  Sound  from  35-Mm.  Film  July  36 

Documentary  Film  Study — a  Supple- 
mentary Aid  to  Public  Relations  July  82 

A  Technic  for  Testing  Photographic 

Lenses  Nov.  472 

A  Water-Cooled  Quartz  Mercury  Arc         Sept.    221 

A  Criticism  of  the  Proposed  Standards 

for  16-Mm.  Sound-Film  July  3 

Problems  Involved  in  Full-Color  Re- 
production of  Growing  Chick 
Embryo  July  75 

Distortion  in  Sound  Reproduction  from 

Phonograph  Records  Aug.  157 


640 


INDEX 


Author 
ROBBINS,  J.  E. 

SACHTLEBEN,  L.  T. 

(and  DIMMICK,  G.  L.) 
SCOVILLE,  R.  R. 

SHEPPARD,  S.  E. 

(and  HOUCK,  R.  C.) 
SILENT,  H.  C. 

(and  FRAYNE,  J.  G.) 
SOOKNE,  A.  M. 

(and  WEBER,  C.  G.) 
SPENCE,  J.  L. 
STEWART,  J.  G. 

(and  AALBERG,  J.  O.) 
STULL,  W. 

TASKER,  H.  G. 
TOWNSLEY,  M.  G. 

(and  ZUBER,  J.  G.) 
WEBER,  C.  G. 

(and  SOOKNE,  A.  M.) 
WELLMAN,  H.  C. 
WERT,  C.  M. 

(and  LEWIS,  L.  L.) 
ZUBER,  J.  G. 

(and  TOWNSLEY,  M.  G.) 


Issue  Page 

Silent  Gasoline  Engine  Propelled 

Apparatus  Nov.  462 

An  Ultraviolet  Push-Pull  Recording 

Optical  System  for  Newsreel  Cameras  July  87 

Overload  Limiters  for  the  Protection  of 

Modulating  Devices  July  93 

The  Influence  of  />H  on  Washing  Films 

after  Processing  July  67 

Push-Pull  Recording  with  the  Light- 
Valve  July  46 

The  Stability  of  the  Viscose  Type  of 

Ozaphane  Photographic  Film  Dec.  611 

An  Improved  Editing  Machine  Nov.    539 

Application  of  Non-Linear  Volume 

Characteristics  to  Dialog  Recording  Sept.  248 

The  Use  of  Photoelectric  Exposure- 
Meters  in  the  Hollywood  Studios  Dec.  604 

Multiple-Channel  Recording  Oct.     381 

A  Continuous  Optical  Reduction  Sound 

Printer  Oct.  405 

The  Stability  of  the  Viscose  Type  of 

Ozaphone  Photographic  Film  Dec.  611 

A  New  16-Mm.  Projector  Oct.     410 

Sound-Stages  and  Their  Relation  to 

Air-Conditioning  Sept.  287 

A  Continuous  Optical  Reduction  Sound 

Printer  Oct.  405 


CLASSIFIED  INDEX,  VOLUME  XXXI 
JULY  TO  DECEMBER,  1938 

Addresses 

Proceedings  of  the  Semi-Annual  Banquet  at  the  Fall  Convention  at  Detroit, 
Mich.,  No.  6  (Dec.),  p.  551. 

Air-Conditioning 

Sound-Stages  and  Their  Relation  to  Air-Conditioning,  C.  M.  Wert  and  L.  L. 
Lewis,  No.  3  (Sept.),  p.  287. 

Animation 

The  Multiplane  Camera  Crane  for  Animation  Photography,  W.  E.  Garity  and 
W.  C.  McFadden,  No.  2  (Aug.),  p.  144. 

Apparatus 

An  Ultraviolet  Push-Pull  Recording  Optical  System  for  Newsreel  Cameras, 

G.  L.  Dimmick  and  L.  T.  Sachtleben,  No.  1  (July),  p.  87. 
Overload  Limiters  for  the  Protection  of  Modulating  Devices,  R.  R.  Scoville, 

No.  1  (July),  p.  93. 
The  Multiplane  Camera  Crane  for  Animation  Photography,  W.  E.  Garity  and 

W.  C.  McFadden,  No.  2  (Aug.),  p.  144. 
A  Color  Densitometer  for  Subtractive  Processes,  R.  M.  Evans,  No.  2  (Aug.), 

p.  194. 
Problems  in  the  Use  of  Ultra-Speed  Negative  Film,  P.  H.  Arnold,  No.  3  (Sept.), 

p.  307. 

Permanent-Magnet  Four-Ribbon  Light- Valve  for  Portable  Push-Pull  Record- 
ing, E.  C.  Manderfeld,  No.  3  (Sept.),  p.  315. 
A  Basically  New  Framing  Device  for  35-Mm.  Projectors,  H.  A.  DeVry,  No.  3 

(Sept.),  p.  319. 
An  Improved  Roller  Type  Developing  Rack  with  Stationary  Drive,  C.  E. 

Ives,  No.  4  (Oct.),  p.  393. 
A  Continuous  Optical  Reduction  Sound  Printer,  M.  G.  Townsley  and  J.  G. 

Zuber,  No.  4  (Oct.),  p.  405. 

A  New  16-Mm.  Projector,  H.  C.  Wellman,  No.  4  (Oct.),  p.  410. 
A  Novel  Surgical  Filming  Stand,  A.  Lenard,  No.  4  (Oct.),  p.  413. 
Silent  Gasoline-Engine  Propelled  Apparatus,  J.  E.  Robbins,  No.  5  (Nov.), 

p.  462. 

A  New  Sound  System,  G.  Fried!,  Jr.,  No.  5  (Nov.),  p.  511. 
Variable  Matte  Control  (Squeeze  Track)  for  Variable-Density  Recording,  G.  R. 

Crane,  No.  5  (Nov.),  p.  531. 
An  Improved  Editing  Machine,  J.  L.  Spence,  No.  5  (Nov.),  p.  539. 

Archives 

Documentary  Film  Study — a  Supplementary  Aid  to  Public  Relations,  A.  A. 
Mercey,  No.  1  (July),  p.  82. 

641 


642  INDEX  [j.  s.  M.  p  .E. 

Applied  Motion  Picture  Photography 

Problems  Involved  in  Full-Color  Reproduction  of  Growing  Chick  Embryo, 

E.  S.  Phillips,  No.  1  (July),  p.  75. 
Some  Unusual  Adaptations  of  16-Mm.  Equipment  for  Special  Purposes,  J.  L. 

Boon,  No.  4  (Oct.),  p.  386. 
A  Novel  Surgical  Filming  Stand,  A.  Lenard,  No.  4  (Oct.),  p.  413. 

Arcs 

A  Water-Cooled  Quartz  Mercury  Arc,  E.  B.  Noel  and  R.  E.  Farnham,  No. 
3  (Sept.),  p.  221. 

Auditory  Perspective 

Sound  Pictures  in  Auditory  Perspective,  F.  L.  Hunt,  No.  4  (Oct.),  p.  351. 

Coaxial  Cable 

The  Transmission  of  Motion  Pictures  Over  a  Coaxial  Cable,  H.  E.  Ives,  No.  3 
(Sept.),  p.  256. 

Color  Cinematography 

A  Color  Densitometer  for  Subtractive  Processes,  R.  M.  Evans,  No.  2  (Aug.), 

p.  194. 
Negative-Positive  Technic  with  the  Dufaycolor  Process,  T.  T.  Baker,  No.  3 

(Sept.),  p.  240. 

The  Theory  of  Three-Color  Photography,  A.  C.  Hardy,  No.  4  (Oct.),  p.  331. 
The  Fundamentals  of  Color  Measurement,  D.  L.  MacAdam,  No.  4  (Oct.),  p. 

343. 
Problems  Involved  hi  Full-Color  Reproduction  of  Growing  Chick  Embryo,  E. 

S.  Phillips,  No.  1  (July),  p.  75. 

Committee  Reports 

Membership 

No.  6  (Dec.),  p.  623.      Report. 
Standards 

No.  1  (July),  p.  65.        Report 
No.  6  (Dec.),  p.  623.      Report. 
Progress 

No.  2  (Aug.),  p.  109.      Progress  in  the  Motion  Picture  Industry. 
Papers 

No.  2  (Aug.),  p.  202.      Report. 
Projection  Practice 

No.  5  (Nov.),  p.  480.     Projection  Room  Plans. 

No.  5  (Nov.),  P-  498.  Proposed  Revision  of  Regulations  of  the  National 
Board  of  Fire  Underwriters  for  Nitrocellulose 
Motion  Picture  Film  as  Pertaining  to  Projection 
Rooms. 

Constitution  and  By-Laws 
Amendments,  No.  6  (Dec.),  p'.  630. 

Densitometers 

A  Color  Densitometer  for  Subtractive  Processes,  R.  M.  Evans,  No.  2  (Aug.), 
p.  194. 


Dec.,  1938]  INDEX  643 

Development,  Photographic 

Maintenance  of  a  Developer  by  Continuous  Replenishment,  R.  M.  Evans,  No. 

3  (Sept.),  p.  273. 
An  Improved  Roller  Type  Developing  Rack  with  Stationary  Drive,  C.  E.  Ives, 

No.  4  (Oct.),  p.  393. 

Disk  Recording 

Distortion  in  Sound  Reproduction  from  Phonograph  Records,  J.  A.  Pierce  and 
F.  V.  Hunt,  No.  2  (Aug.),  p.  157. 

Documentary  Films 

Documentary  Film  Study — a  Supplementary  Aid  to  Public  Relations,  A.  A. 
Mercey,  No.  1  (July),  p.  82. 

Editing 

An  Improved  Editing  Machine,  J.  L.  Spence,  No.  5  (Nov.),  p.  539. 

Educational  Motion  Pictures 

Documentary  Film  Study — a  Supplementary  Aid  to  Public  Relations,  A.  A. 
Mercey,  No.  1  (July),  p.  82. 

Emulsions 

Problems  in  the  Use  of  Ultra-Speed  Negative  Film,  P.  H.  Arnold,  No.  3  (Sept.), 
307. 

Exposure 

The  Use  of  Photoelectric  Exposure-Meters  in  the  Hollywood  Studios,  W.  Stull, 
No.  6  (Dec.),  p.  604. 

Film,  Photographic  Characteristics 

Problems  in  the  Use  of  Ultra-Speed  Negative  Film,  P.  H.  Arnold,  No.  3  (Sept.), 
p.  307. 

Film,  Physical  Characteristics 

The  Shrinkage  of  Acetate-Base  Motion  Picture  Films,  J.  A.  Maurer  and  W. 

Bach,  No.  1  (July),  p.  15. 

The  Stability  of  the  Viscose  Type  of  Ozaphane  Photographic  Film,  A.  M. 
Sookne  and  C.  G.  Weber,  No.  6  (Dec.),  p.  611. 

Fire  Regulations 

Proposed  Revision  of  Regulations  of  the  National  Board  of  Fire  Underwriters 
for  Nitrocellulose  Motion  Picture  Film  as  Pertaining  to  Projection  Rooms, 
No.  5  (Nov.),  p.  498. 

General 

Problems  Involved  in  Full-Color  Reproduction  of  Growing  Chick  Embryo, 

E.  S.  Phillips,  No.  1  (July),  p.  75. 
Progress  in  the  Motion  Picture  Industry — Report  of  the  Progress  Committee, 

No.  2  (Aug.),  p.  109. 

Report  of  the  Papers  Committee,  No.  2  (Aug.),  p.  202. 
Proceedings  of  the  Semi-Annual  Banquet  at  the  Fall  Convention  at  Detroit, 

Mich.,  No.  6  (Dec.),  p.  551. 


644  INDEX  [j.  s.  M.  P.  E. 

Technicolor  Adventures  in  Cinemaland,  H.  T.  Kalmus,  No.  6  (Dec.),  p.  564. 

Illumination 

A  Water-Cooled  Quartz  Mercury  Arc,  E.  B.  Noel  and  R.  E.  Farnham,  No.  3 
(Sept.),  p.  221. 

Index 

Author  Index,  No.  6  (Dec.),  p.  638. 
Classified  Index,  No.  6  (Dec.),  p.  641. 

Instruments 

The  Use  of  Photoelectric  Exposure-Meters  in  the  Hollywood  Studios,  W.  Stull, 
No.  6  (Dec.),  p.  604. 

Journal  Award 

Proceedings  of  the  Semi-Annual  Banquet  at  the  Fall  Convention  at  Detroit, 
Mich.,  No.  6  (Dec.),  p.  551. 

Lenses  (See  Optics) 
Lighting 

A  Water-Cooled  Quartz  Mercury  Arc,  E.  B.  Noel  and  R.  E.  Farnham,  No.  3 
(Sept.),  p.  221. 

Light-Valves 

Push-Pull  Recording  with  the  Light-Valve,  J.  G.  Frayne  and  H.  C.  Silent,  No. 
1  (July),  p.  46. 

Permanent-Magnet  Four-Ribbon  Light- Valve  for  Portable  Push-Pull  Record- 
ing, E.  C.  Manderfeld,  No.  3  (Sept.),  p.  315. 

Non-Intermittent  Projection 

A  Non-Intermittent  Projector  for  Television  Film  Transmission,  H.  S.  Bamford 
No.  5  (Nov.),  p.  453. 

Obituary 

Norman  McClintock,  No.  4  (Oct.),  p.  438. 

Officers  and  Governors  of  the  Society 

On  the  reverse  of  the  Contents  Page  of  each  issue  of  the  JOURNAL. 

Optical  Systems 

An  Optical  System  for  the  Reproduction  of  Sound  from  35-Mm.  Film,  J.  H 

McLeod  and  F.  E.  Altman,  No.  1  (July),  p.  36. 
An  Ultraviolet  Push-Pull  Recording  Optical  System  for  Newsreel  Cameras 

G.  L.  Dimmick  and  L.  T.  Sachtleben,  No.  1  (July),  p.  87. 
A  Higher-Efficiency  Condensing  System  for  Picture  Projectors,  F.  E.  Carlson, 

No.  2  (Aug.),  p.  187. 

Optics 

A  Technic  for  Testing  Photographic  Lenses,  W.  C.  Miller,  No.  5  (Nov.),  p.  472. 

Ozaphane 

The  Stability  of  the  Viscose  Type  of  Ozaphane  Photographic  Film,  A.  M 
Sookne  and  C.  G.  Weber,  No.  6  (Dec.),  p.  611. 


Dec.,  1938]  INDEX  645 

Photography 

The  Use  of  Photoelectric  Exposure-Meters  in  the  Hollywood  Studios,  W.  Stull, 
No.  6  (Dec.),  p.  604. 

Portable  Equipment 

Silent  Gasoline  Engine  Propelled  Apparatus,  J.  E.  Robbins,  No.  5  (Nov.),  p. 
462. 

Printing 

A  Continuous  Optical-Reduction  Sound  Printer,  M.  G.  Townsley  and  J.  G. 
Zuber,  No.  4  (Oct.),  p.  405. 

Processing 

Processing  of  Ultraviolet  Recordings  on  Panchromatic  Films,  J.  O.  Baker,  No. 

1  (July),  p.  28. 
The  Influence  of  pH  on  Washing  Films  after  Processing,  S.  E.  Sheppard  and 

R.  C.  Houck,  No.  1  (July),  p.  67. 
Maintenance  of  a  Developer  by  Continuous  Replenishment,  R.  M.Evans,  No.  3 

(Sept.),  p.  273. 
An  Improved  Roller  Type  Developing  Rack  with  Stationary  Drive,  C.  E.  Ives, 

No.  4  (Oct.),  p.  393.  4 

Progress 

Progress  in  the  Motion  Picture  Industry — Report  of  the  Progress  Committee, 
No.  2  (Aug.),  p.  109. 

Progress  Award 

Proceedings  of  the  Semi-Annual  Baaiquet  at  the  Fall  Convention  at  Detroit, 
Mich.,  No.  6  (Dec.),  p.  551. 

Projection 

Projection  Room  Plans,  No.  5  (Nov.),  p.  480. 

Proposed  Revision  of  Regulations  of  the  National  Board  of  Fire  Underwriters 

for  Nitrocellulose  Motion  Picture  Film  as  Pertaining  to  Projection  Rooms, 

No.  5  (Nov.),  p.  498. 

Projectors 

A  Higher-Efficiency  Condensing  System  for  Picture  Projectors,  F.  E.  Carlson, 
No.  2  (Aug.),  p.  187. 

A  Basically  New  Framing  Device  for  35-Mm.  Projectors,  H.  A.  DeVry,  No.  3 
(Sept.),  p.  319. 

A  New  16-Mm.  Projector,  H.  C.  Wellman,  No.  4  (Oct.),  p.  410. 

A  Non-Intermittent  Projector  for  Television  Film  Transmission,  H.  S.  Barn- 
ford,  No.  5  (Nov.),  p.  453. 

Sixteen-Mm. 

A  Criticism  of  the  Proposed  Standards  for  16-Mm.  Sound-Film,  J.  A.  Maurer 

and  W.  H.  Offenhauser,  No.  1  (July),  p.  3. 
The  Shrinkage  of  Acetate-Base  Motion  Picture  Films,  J.  A.  Maurer  and  W. 

Bach,  No.  1  (July),  p.  15. 


646  INDEX  [j.  s.  M.  P.  E. 

Some  Unusual  Adaptations  of  16-Mm.  Equipment  for  Special  Purposes,  J.  L. 

Boon,  No.  4  (Oct.),  p.  386. 
A  New  16-Mm.  Projector,  H.  C.  Wellman,  No.  4  (Oct.),  p.  410. 

Sound  Recording 

Processing  of  Ultraviolet  Recordings  on  Panchromatic  Films,  J.  O.  Baker,  No. 

1  (July),  p.  28. 
Push-Pull  Recording  with  the  Light- Valve,  J.  G.  Frayne  and  H.  C.  Silent,  No. 

1  (July),  p.  46. 
An  Ultraviolet  Push-Pull  Recording  Optical  System  for  Newsreel  Cameras, 

G.  L.  Dimmick  and  L.  T.  Sachtleben,  No.  1  (July),  p.  87. 
Overload  Limiters  for  the  Protection  of  Modulating  Devices,  R.  R.  Scoville. 

No.  1  (July),  p.  93. 
Distortion  in  Sound  Reproduction  from  Phonograph  Records,  J.  A.  Pierce  and 

F.  V.  Hunt,  No.  2  (Aug.),  p.  157. 

Application  of  Non-Linear  Volume  Characteristics  to  Dialog  Recording,  J.  O. 
Aalberg  and  J.  G.  Stewart,  No.  3  (Sept.),  p.  248. 

Permanent-Magnet  Four-Ribbon  Light- Valve  for  Portable  Push-Pull  Record- 
ing, E.  C.  Manderfeld,  No.  3  (Sept.),  p.  315. 

Application  of  Electrical  Networks  to  Sound  Recording  and  Reproducing,  H. 
R.  Kimball,  No.  4  (Oct.),  p.  358. 

Electrical  Networks  for  Sound  Recording,  F.  L.  Hopper,  No.  5  (Nov.),  p.  443. 
•  Variable  Matte  Control  (Squeeze  Track)  for  Variable- Density  Recording, 

G.  R.  Crane,  No.  5  (Nov.),  p.  531. 

A  Method  for  Determining  the  Scanning  Losses  in  Sound  Optical  Systems, 

E.  D.  Cook  and  V.  C.  Hall,  No.  6  (Dec.),  p.  586. 

I 

Sound  Reproduction 

An  Optical  System  for  the  Reproduction  of  Sound  from  35-Mm.  Film,  J.  H. 

McLeod  and  F.  E.  Altman,  No.  1  (July),  p.  36. 
Distortion  in  Sound  Reproduction  from  Phonograph  Records,  J.  A.  Pierce  and 

F.  V.  Hunt,  No.  2  (Aug.),  p.  157. 

Sound  Pictures  in  Auditory  Perspective,  F.  L.  Hunt,  No.  4  (Oct.),  p.  351. 
Application  of  Electrical  Networks  to  Sound  Recording  and  Reproducing, 

H.  R.  Kimball,  No.  4  (Oct.),  p.  358. 

Multiple-Channel  Recording,  H.  G.  Tasker,  No.  4  (Oct.),  p.  381. 
A  Continuous  Optical  Reduction  Sound  Printer,  M.  G.  Townsley  and        G. 

Zubef,  No.  4  (Oct.),  p.  405. 
A  New  Sound  System,  G.  Friedl,  Jr.,  No.  5  (Nov.),  p.  511. 

Standards 

A  Criticism  of  the  Proposed  Standards  for  16-Mm.  Sound-Film,  J.  A.  Mauiet 

and  W.  H.  Offenhauser,  No.  1  (July),  p.  3. 
Report  of  the  Standards  Committee,  No.  1  (July),  p.  65. 

Studio  Equipment 

The  Multiplane  Camera  Crane  for  Animation  Photography,  W.  E.  Garity  and 

W.  C.  McFadden,  No.  2  (Aug.),  p.  144. 
Sound-Stages  and  Their  Relation  to  Air-Conditioning,  C.  M.  Wert  and  L.  L. 

Lewis  No.  3  (Sept.),  p.  287. 


Dec.,  1938]  INDEX  647 

Technicolor 

Technicolor  Adventures  in  Cinemaland,  H.  T.  Kalmus,  No.  6  (Dec.),  p.  564. 

Television 

The  Transmission  of  Motion  Pictures  over  a  Coaxial  Cable,  H.  E.  Ives,  No.  3 

(Sept.),  p.  256. 
A  Non-Intermittent  Projector  for  Television  Film  Transmission,  H.  S.  Bamford, 

No.  5  (Nov.),  p.  453. 

Theater  Design 

Projection  Room  Plans,  No.  5  (Nov.),  p.  480. 

Proposed  Revision  of  Regulations  of  the  National  Board  of  Fire  Underwriters 
for  Nitrocellulose  Motion  Picture  Film  as  Pertaining  to  Projection  Rooms, 
No.  5  (Nov.),  p.  498. 

'transmission  of  Pictures 

The  Transmission  of  Motion  Pictures  over  a  Coaxial  Cable,  H.  E.  Ives,  No.  3 
(Sept.),  p.  256. 

A  Non-Intermittent  Projector  for  Television  Film  Transmission,  H.  S.  Bam- 
ford, No.  5  (Nov.),  p.  453. 

Trick  Photography 

The  Multiplane  Camera  Crane  for  Animation  Photography,  W.  E.  Garity  and 
W.  C.  McFadden,  No.  2  (Aug.),  p.  144. 

Washing  Motion  Picture  Film 

The  Influence  of  />H  on  Washing  Films  after  Processing,  S.  E.  Sheppard  and 
R.  C.  Houck,  No.  1  (July),  p.  67. 


S.M.P.E.  TEST-FILMS 


These  films  have  been  prepared  under  the  supervision  of  the  Projection 
Practice  Committee  of  the  Society  of  Motion  Picture  Engineers,  and  are 
designed  to  be  used  in  theaters,  review  rooms,  exchanges,  laboratories, 
factories,  and  the  like  for  testing  the  performance  of  projectors. 

Only  complete  reels,  as  described  below,  are  available  (no  short  sections 
or  single  frequencies).  The  prices  given  include  shipping  charges  to  all 
points  within  the  United  States;  shipping  charges  to  other  countries  are 
additional. 


35-Mm.  Visual  Film 

Approximately  500  feet  long,  consisting  of  special  targets  with  the  aid 
of  which  travel-ghost,  marginal  and  radial  lens  aberrations,  definition, 
picture  jump,  and  film  weave  may  be  detected  and  corrected. 

Price  $37.50  each. 

16-Mm.  Sound-Film 

Approximately  400  feet  long,  consisting  of  recordings  of  several  speak- 
ing voices,  piano,  and  orchestra;  buzz-track;  fixed  frequencies  for  focus- 
ing sound  optical  system;  fixed  frequencies  at  constant  level,  for  de- 
termining reproducer  characteristics,  frequency  range,  flutter,  sound- 
track adjustment,  60-  or  96-cycle  modulation,  etc. 

The  recorded  frequency  range  of  the  voice  and  music  extends  to  6000 
cps.;  the  constant-amplitude  frequencies  are  in  11  steps  from  50  cps.  to 
6000  cps. 

Price  $25.00  each. 

16-Mm.  Visual  Film 

An  optical  reduction  of  the  35-mm.  visual  test-film,  identical  as  to 
contents  and  approximately  400  feet  long. 

Price  $25.00  each. 


SOCIETY  OF  MOTION  PICTURE  ENGINEERS 

HOTEL  PENNSYLVANIA 

NEW  YORK,  N.  Y.