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Full text of "The development and uses of high speed photography / Bowen W. Shaw."


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MAKSTLaND BETA CHAPTER 
TAU Bi^TA PI 

THE DEVELOPMENT AND USES OP HIGH SPSiJ) PHOTOGRAPHY 

BOWEN W. SHAW 



SUMMARY 

This paper deals with the development of speed in pho- 
tography from the latter part of the nineteenth century up to 
the present time . 

The material is divided into two parts, the first dealing 
with the mecnanica-± of obtaining very short exposures, and the 
last part with the development of speed pnotography through the 
use of flashes of light of very short duration. 

The applications of each camera are dealt with in the dis- 
cussion of the camera. 



















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THE BBVBLCPMENT AMD USES OF HIGH SPEED PHOTOGRAPHY 

During the past fifty /ears photography has developed from an un- 
reliable to/ to an integral part of engineering ana r-e»eaT"bh-. There are sev- 
eral reasons for this growth. First, there is the laot that a photograph 
furnishes a permanent record of a large number of details without requiring 
the time neoessary to maKe a detailed drawing. Seconal/, a photograph proper- 
ly made records things as they actually are as against the eye which tanas to 
observe ouiy those things which the eye is directed to look for by the mind. 
Thirdly, a photograph of a moving object shows dearly the position oi the 
ob^eot at an instant of time (sometimes less than one millionth of a seoond 
in duration) , whereas the eye sees only a blur oi continuous motion. In this 
paper the latter subject will be discussed, that is, tue development oi speed 
in photography. 

There are four factors which limit the shortness of the exposure 
in a oaniera. They are the speed of the lens; the intensity and quality of the 
light on the subject; the spaed of the emulsion on the ixlm; and a method of 
exposing the rilm for a very short period of time. In the very early experi- 
mental days of photography the emulsion and the lens w*e so slow that exposures 
of several seconds or minutes were required and obtaining a suitable meoham- 
jfecal shutter was not a prooiem. However toward the latter part of the nine- 
teenth century the emulsions and the lenses were improved to such an extent 
that the ordinary mechanical shutter became useless for very high speed wori. 

TYPES JF MECHANICAL SHUTTERS 

Mechanical shutters may De divided into two general o las s if i cations; 
those whioh operate at or near the optical center 01 the camera; ana those 
which operate near the focal plane oi the camera. Eaoh of these ty^es has its 
own advantages and disadvantages. 



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The shutter whioh operates at the optical oenter of the lenses is 
advantageous in tht-t all portions of the plate or sensitive lilnt are exposed 
through the saiae periou oi time* However as this type operates by having an 
opening in a flat piece of metal move across the film or by causing two or 
more leaves to move outward exposing the iilm and then inward dosing oil the 
light, at high speeds the camera is not operating at full aperture throughout 
the exposure and hence the effective speed of the lens is less than indicated. 

In the focal plane type oi shutter the plate is exposed by allow- 
ing a pieoe of metal or cloth containing a narrow slit to move rapidly across 
the film a short distance in front oi it. The exposure may oe oontroled by 
varying the width 01 the slot and the speed with which it travels across the 
plate. A high speea ana a narrow slot will give a short exposure, and con- 
versely a low s^eea and a wide slot will cause the exposure to be relatively 
long. For instance, if the slot has a width oi one tenth oi an inch and trav- 
els at a s^eed of fifty inohes per second every point on the plate will be 
exposed for a period of one -five hundredth or a second. Ihis camera has the 
advantage that the camera is operating at the same aperture throughout the 
exposure. However all of the portions oi the plate are not exposed at tlie 
same instant and ii the subject is moving rapidly its image will be distorted. 
In the case cited aoove the exposure was one-iive hundredth oi a second but 
if the plate were seven inches long one side of the plate woula be exposed 
fourteen-hundredths of a seconc alter the other siae . 

DAYLIGHT PH0TU3RAPHY «ITH A MECHANICAL SHUTTER 

One of the first means oi' obtaining photographs oi very short dur- 
ation by a mechanical shutter was perfected by Charles Francis Jensins who 
began his experiments in IdsG. In these experiments Jenkins located a number 
of lenses on the periphery 02 a wheel. The image irom the leos was reilected 
oy a prism onto a strip ji moving film and the lenses moved at a speod such 



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that the velocity of the i'ilci and the tangential velocity ox the lens as It 
passed the prism ware the same. Due to this the image was stationary with 
respeot to the iilm ana the exposure was nepenoent on the speed of the revolv- 
ing wheel. There existed a very slight blur in the negative caused by the iaet 
that the lens moved in an aro rather than in a straight line. However with a 
wheel of fairly large uiaraater this effect was negligible. 

with tiiis camera JenJtins was ubie to obtain up to three thousand two hun- 
dred images per seoond with exposures of as little as one-twenty thousandth of 
a seoona. The camera was valuaole in Lhat it took a series of pictures oi rap- 
idly moving objects such as projectiles rather than one single picture as is 
the case with, some of the methods to he treated later. Another aavantage j&E 
*as the fact that the camera wat, complete in itself ana no special laboratory 
conditions such as special lighting or spars discharges were necessary to 
obtain a series of photographs. Due to tno nuture ol the camera it has a 
splenaid rati a 01 time oi exposure to time oi operation, as it taices three 
thousand two hundred pictures a secona ana each exposure is one -twenty thou- 
sandth oi tt second the total time of exposure is sixteen-hunaredths oi a sec- 
ond per secjna. 

Another type of daylight oamerta was uevised in l~yl7 in Germany 
which is in reality a modified moving picture camera. The shutter of the ord- 
inary moving picture oamera is a circular metal uisc with a slot cut in it as 
shown in Figure 1 * - The film is stationary while the slot is in iront oi the 
film and the film is being exposed. During the interval when the lilm is not 

being exposed it is advanced one irame. The numoer oi pictures ta^en ana the 

Of i 

exposure given each pijture is ^seatr-oled- by the speed with which the disc 

revolves. 7he regular value is sixteen irames per second, however this is not 

suitable lor photographing projectiles, ana even ii the speed is boosted to 

one hunured and twenty irames per second the results are not satisfactory. 

At this speed oontinuous operation is not Batisiaotory and even if it were the 



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that the velocity of the film and the tangential velocity oi the lens as It 
passed the prism were the same. Due to this the image was stationary with 
respect to the lilm and the exposure was Dependent on the speed of the revolv- 
ing wheel. There existed a very slight blur in the negative caused by the; iact 
that the lens moved in an aro rather than la a straight line. However with a 
wheel oi jiairly large diameter this effect was negligible. 

„ith tiiis camera Jen&ins was able to obtain up to three thousand two hun- 
dred images per second with exposures of as little as one-twenty thousandth of 
a second. The camera was valuaole in that it took a series of pictures ot rap- 
idly moving objeots auoh as projectiles rather than one single picture as is 
the case with some of the methods to be treated later. Another advantage 
w as the fact that the camera wat, complete in itself ana no special laboratory 
conditions such as special lighting or spar^ discharges were necessary to 
obtain a series oi photographs. Due to the nature oi the camera it has a 
splendid ratio oi time oi exposure to time 01 operation, as it ta*ces three 
thousand two hundred pictures a second ana each exposure is one-twenty thou- 
sandth of a second the total time of exposure is six teen -hundredths of a sec- 
ond per seeona. 

Another type of daylight camera was aevised in iyl7 in derinany 
which is in reality a modified moving pioture camera. The shutter of the ord- 
inary moving picture oamera is a circular metal disc with a slot cut in it as 
shown in Figure 1 • The I'iLn is stationary while the slot is in iront oi the 
^ilm and the film is being exposed. During the interval when the iilm is not 
being exposed it is advanced one irame. The numoer oi pictures ta^en ana the 
exposure given each pioture is controled by the speed with which the diso 
revolves. The regular value is sixteen iraraes per seeona. However this is not 
suitable lor photographing projectiles, ana even ii the speed is ooostea to 
ona hunared and twenty irames per second the results are not satisfactory. 

At this speed oontinuous operation is not satisfactory and even if it were the 





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projeotile Is blurred and the interval oetween frames is so great that the 
projectile might pass entirely through the field of the camera while the 
shutter is closed. Because of this the shutter was changed to the type 
shown in Figure 2 in which the single opening is replaced by three narrower 
ones . When this type is used three exposures are made on eaoh frame thus 
giving the relative position of the projectile at three instants as shown in 
Figure 3. This facilitates the calculation of the trajectory of the shell 
and any deviation of the axis of the shell from its path at that instant* 
With this type of shutter the projectile may be photographed three times 
while it is in the field of the camera and the distance between the suoce sk- 
ive positions of the shell may be no greater than twioe its length* 

When it is desired to obtain pictures with a phase difference 
less than in the oase above the camera is modified further so that the shutter 
is as it appears in Figure 4* Each of these four staggered slots is behind 
a separate lens, and in operation four pictures are made across the width of 
of the film with a phase difference of one - twelve thousandth of a second. 
Figure 5 illustrates the type of picture which is obtained by this system 
and it may be seen that the projeotile moves very little between the sucoe st- 
rive pictures. 

This camera is especially useful in obtaining pictures of large 
projectiles in flight, as suoh pictures oould hardly be made in a laboratory 
under controlled light. In order for the shell to be distinct it should be 
photographed against a brilliant background suoh as the sky or snow. 

Still another method of stopping a rapidly moving objeot was de- 
vised by H. R. Curtis, W. H. Wadleigh. and A. H. Sellman in 1924. A diagram 
of their camera is shown in Figure 6. The film drum contains one loop of 
film on the surface and the film drum rotates at suoh a speed that the surfaoe 
of the film on whioh the Image is east is moving in the same direction and 




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at tha same speed that the Image ia moving* The fooal plane shutter is 
another cylinder which fits closely over the film drum and contains narrow 
slots parallel to the axis* The shutter revolves in the opposite direotion 
from the image and at a speed several times as great* Sinoe the film is 
moving at the same speed that the image is moving, the linage is stationary 
with respaot to the film. The slot passing in front of the lenses control* 
the length of the exposure* The faot that the image is stationary on the 
film means that a longer exposure may be obtained without blurring than oould 
be obtained if the image were moving* Of course the approximate velocity 
of the moving object must be known in order to adjust the speed of the film 
drum* 

The main shutter is placed behind the lens for the purpose of 
exposing the film at the proper instant and then closing the aperture after 
one complete revolution of the film drum. When it ia desired to make a 
series of pictures with a very short time interval in between them, the 
camera is modified by replacing the single lens by a number of lenses and 
the single slot in the fooal plane shutter by the same number of staggered 
slots, as shown in Figure 7a. If five lenses are used the camera will take 
five times as many pictures in a given length of time, and there will be five 
rows of pictures around the film as shown In Figure 7b* 

The field in whioh this oamera might be used would be rather 
specialized as the velooity of tha subject must be known and the motion must 
be in a straight line* Like the above cameras it requires no speoial light- 
ing conditions, and may be used under natural light. The features of the 
oamera make it especially useful in work with projectiles. Mith It it is 
possible to study the yaw of tha projectile, its velooity, the speed of ro- 
tation, and the blast. 

A method similar to that above was developed in France in 1932. 



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In this camera 35 millimeter film ran through the camera In the manner that 

it does in an ordinary moving picture camera except that the film mores 

continuous 1/ through the camera rather than stopping at each frame • The 

7 

focal plane shutter is of the same type shown in Figure 3, there being a 
large number of rows of slots rather than Just one. When the oaaera was 
made with four concentric rows of slots there were four lenses, and four 
rows of images were formed on the film staggered similarly to the pictures 
shown in Figure Ta* The Individual pictures are quite small , the space 
ordinarily occupied by one image contains 12 smaller ones. By varying the 
speed of the shutter, up to 12,000 piotures a second may be obtained* This 
oamera was used in France largely for the purpose of studying the flight of 
inseots* 

Despite these accomplishments in mechanically controlled photography 
it is still difficult to obtain a fair sized clear picture of a rapidly moving 
object at the precise position that the picture is wanted. In order to gat 
the subject at a certain point it is necessary to photograph It in a whole 
series of positions. 

THE DEVELOPMENT CF LIGHT CONTROIBD PHOTOGRAPHY 

Over fifty years ago it occurred to experimenters in photography that 
a plate might be exposed to light by leaving the oamera In a dark room with 
its shutter open and then flashing a light off and on in the room* The 
length of the exposure would then be the length of time that the light re- 
mained on. 

ELECTRIC SPARK PHOTOGRAPHY 

In 1393 C. V. Boys delivered a talk telling of his accomplishments in 
the field of spark photography. He had patterned his apparatus somewhat 
after that of Professor E- Mach's. The eleotrioal circuit of Professor 
Maoh's apparatus consisted of two spark gaps and a oondenser in series. 




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One of the spark gaps was located on a point In the path 01 the projectile 
end the other was looated in front of a lens so that its light would be 
oonoentrated on the projectile. On the other side of the first spark gap 
was the camera focused on the first spark gap. The condenser would be 
charged to such an extent that the voltage would be almost enough to cause 
a spark to jump the two gaps* Then with the shutter of the camera open the 
gun would be fired* The bullet reaching the spark gap in its path would 
short circuit It and cause a spark to jump the second gap thus giving a 
brilliant light of a short duration. The flash of light would accomplish the 
same result as a shutter being oppenned for the same length of time, and the 
bullet would be photographed. 

Boys' apparatus is shown in Figure 3* It consisted of a condenser 
constructed from a square foot of tinfoil placed on either side of a piece of 
glass, in series with two spark gaps E and E* * G f is a small capacity ijeydon 
jar. S is another spark gap in the path of the bullet and the dotted line 
represents a string wetted with calcium chloride. The system is charged 
until both of the spark gaps are about to break down and the gun is fired. 
When the bullet short circuits the gap S. The voltage is able to break down 
the gap B*. 'with this gap broken down the large condenser oan now discharge 
through E oausing a brilliant spark lasting about one millionth of a second. 
Very little of the charge goes through S as the condenser C is quite small 
and the string is practically a non-conductor during the discharge. The 
spark generated at E being small casts a sharp shadow of the bullet on the 
plate. 

With this apparatus Boys conducted a series of experiments to 
determine just how the apparatus should be constructed to obtain the maximum 
illumination with a minimum duration* 

The original apparatus was set up with ordinary wire for the conneot- 



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iotis and the spark tips at E made of magna slum. The projectile was travel- 
ing 2,100 feat per seoond and the spark lasted long enough for the projectile 
to travel half an inoh, blurring the image on the negative. Upon investi- 
gation it was found that while the main spark lasted one millionth of a second, 
the magnesium tips glowed for about seven millionths of a seoond. it was 
oonoludad that a less volatile metal suoh as platinum should be used at the 
spark gap and this substitution was made. It * as found that the time of dis- 
charge could be materially reduced by replacing the wires carrying the main 
discharge by heavy bands of copper made as short as possible. With these 
changes made it was found that the whole spark was extinct in less than one 
millionth of a second, and the first blaie which supplies most of the light 
was extinot in less than one ten millionth of a second* The bullet traveled 
one four hundredth of an inoh in this time . 

While the images obtained by this method are shadows they are re- 
markably olear as the source of light is small and the time is very short. 
The Images show the projectile, the wires whioh initiate the discharge and 
In the case of projectiles moving over eleven hundred feet per second the air 
waves set up at the nose and tail of the bullet are clearly visible. 

Today this apparatus has changed somewhat into several specialized 
types of apparatus* 

Prank S. tfyle, a student at the Massachusetts Institute of Technology 
in Cambridge constructed a high speed camera which represents one of these 
types. His apparatus uses one hundred and ten volt alternating current step 
lng it up to 3,000 volts, and then converting it into direct current. A bank 
of oondensers is charged with this currant. This charge is discharged through 
a tube filled with krypton at the same Instant that a high voltage is passed 
through a spark ooil into a wire around the tube. The eleotrioal oharge 
passing through the gas oauses a five million oandlepower flash whioh lasts 



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only one-fifty thousandth of a seoond* The light may be timed either by an 
eleotrioal contact or by the impulse from a miorophone plaoed near the source 
of a sound connected with the motion to be photographed* When the miorophone 
was used Wyle was able to delay the flash by moving the miorophone away from 
the source of the sound* 

On the following pages some of the results obtained with the camera 
are illustrated* Figure 9 illustrates the set-dip used in investigating a 
defect in the operation of a drop hammer* The drop hammer was forming a 
duralumin air scoop for an airplane and part of the metal was torn away* 
Examination of the photographs showed the oause and it was corrected. 

Figure 10 shows how a fine stream of milk appears when photographed by 
this method* 

In Figure 11 at the top one sees a bullet which has passed through 
two glass bulbs and is about to pass through a third. At the bottom the 
action of a light bulb on being struck by a hammer is shown. 

A variation of this apparatus was constructed by Francis Behn Riggs, 
Jr. of Harvard University and an example of its work is shown in Figure 12* 
The three pictures show the bullet about to enter the bulb, entering it. and 
leaving the bulb* The bullet was from a forty-five caliber revolver and was 
traveling at a speed of eight hundred feet per second when photographed* 

Perhaps the most recent and complete apparatus is that constructed 
by K. V. Germeshauser, H. JS. Grier, and Harold Eugene Bd gar ton of the Massa- 
chusetts Institute of Technology* In this apparatus the film moves contin- 
uously through the camera and the light source is similar to that used in the 
stroboscope. The camera is known as a strobosoope oamera* The light 
flashes on and off 6.000 times a second and each flash lasts for one -hundred til Thavsctfi^ 
of a second* It is the most complex of the apparatus which has been mentioned 
so far, indeed one whole room is occupied by apparatus concerned with pro- 



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duoing the suddenly released high voltages whioh produce the photographio 
sparks* The camera is linked to the stroboscope and runs at closely regu- 
lated speeds so that aooe la ration and velocity may be measured on the films. 

The instrument is extremely useful in clocking projectiles, 
whirling engines and propellers, and other meohanioal devices. The strobo- 
scope camera is used in studying the dangerous shiver of high speed maohlnes 
and is even used in medioine to study action of high spaed micro-organisms* 

JCNOLUSItHS 

Several types of cameras have been discussed, but each has its 
field in which it Is extremely useful. The mechanical cameras which are 
able to take plotures in natural light cannot be replaced by the ones using 
artificial light* ill the other hand if a series of clear plotures of 
rapidly moving objeots which oan be photographed in a laboratory are desired 
the stroboscope camera is the logical one to use* For very high speed pro- 
jectiles it might be best to use Boys* apparatus whloh has an exposure time 
of less than one millionth of a second. 

The value of this high speed photography oan not be over emphasised* 
The illustrations show but a few of its uses* Whenever it is desired to 
study fractures, deformation, or motion occurring at high speeds the camera 
is the most effective and reliable means of conducting this study. 



BIBLIOGRAPHY 

Baker, Thomas Thorne, The Klngc otn of the Game ra . London; Bell & Sons Ltd., 
1934. 

Boys, J. V., "Spar* photographs oi" Flying Bullets," Nature . XLVII (March, 
1893), pp 415-421, 4*0-446. 

i&gnan, A., "Glnematographie Juaqufe 12,000 Vues Par Second," Actualities 
boientii'jques et Indus triallas . (.1932) . 

Mueller, Grover J., "Stop Action Photographs';" Popular Soienoe Monthly , Vol. 
134 No. 1, pp 80-83. 

Von Jles, Hildebrand P., "Motion Pictures of Projectiles in Plight in Day- 
light or by Artifioial Light," Journal of the pnitea States Artillery. 48 
(1917), 91ff. 

"A Camera for studying Projectiles in Plight," Teohnolo^io Pap.ers of t he Bar- 
r'fau of Sfondards . No. 22o, Vol. 18, (1924). 
•Photo Amateur Snaps Bullet Striding Lamp," Moaern Meohanix. iXX (April, 1933), 
p56» 

Soiance . Vol. 89 Ho. 2299 (1939), p 156. 

"Stroboscope Photography," Spientjiio Monthly . 1LVI Ho. 5 (1939), p. 455. 
£img. (January, 1939), p. 97.