A Practical Guide to Binocular Collimation

A Practical Guide to Binocular Collimation was first published in

the Micro Miscellanea newsletters No 64 (2006) and No 65 (2007)

of the Manchester Microscopical and Natural History Society.

Revised in 2008
All rights reserved by the author.

Author

Many years ago, in the mid 1990's I received a phone call from a member
of a Microscopical Society who was an acquaintance of mine; it was a plea
for help, "Ron... a friend is in dire straits, he has given his binocular head a
very bad knock putting it out of collimation. As you have recently offered
assistance in our 'Sales and Wants' can you help him?" After a brief
exchange I said that I would, so the following Sunday saw my tools and I
travelling to the outskirts of a small local town to meet the troubled
microscopist.

Knocking on his door I was greeted by an old age pensioner who appeared
to be in a state of stress; he told me he lived on his own, and his only
enjoyment was his beloved microscopy. It was also obvious that he had seen
better times, for his microscope was a very expensive piece of kit. He told me
he had contacted the manufacturer about his binocular head, but the price
quoted was far beyond his present means.

On examining the head, I found the prisms were still intact and in place,
but at the base of one eyepiece tube was a 'scuff mark and its mount
appeared to have moved slightly under impact. On a scale of difficulty its
collimation would be called "A Now't Job" in Yorkshire and, with the type of
microscope he had, the time taken would be less than a couple of minutes. So
to have a little fun I asked the gentleman for a cup of coffee or tea while I
worked.

When he returned a few minutes later he saw my closed toolbox and his
face dropped, "tis beyond repair then" he said, "No, it's back in commission"
I replied with a grin. In disbelief he sat at his microscope and the tension that
had gripped him since I arrived drained away. Taking my leave after refusing
payment (I owed his friend a favour), I was pleasantly surprised the following
week, to receive a nice box of slides in the post from him.

My point of writing this practical guide on collimation is to help amateur
microscopists who may one day find themselves in similar traumatic
circumstances to the above, and in response to a number of kind requests
from members of the PMS and Manchester society. Unfortunately, today we
live in a country with very little optical expertise, our 'Great Microscope
Houses' which in times past provided a pool of skilled Service Engineers are

alas no more; as a result microscopists are often thrown on their own
resources when their microscopes require collimation. A more mundane
factor of course is cost; third party charges for head collimation can be quite
astronomical and in some cases can run to three or four figures, yet the
adjustment of binocular collimation is not some mystic art practised by
modern day Wizards, any microscopist with common sense and simple
equipment can do it. A little basic background information on collimation
errors may not come amiss.

The three main errors of collimation are Dipvergence, Divergence, and
Convergence. Figure 1 shows only dipvergence, (enforced Hyperphoria of
one eye) as divergence and convergence are self-explanatory. These faults are
undesirable deviations of the optical axes in a binocular microscope, which
can occur if the microscope is subject to physical shock, user interference, or
just plain old-fashioned wear and tear. Furthermore, such errors are relevant
to microscopes with either convergent or parallel eyepiece tubes; fortunately,
the image at the point of focus, as represented in Figure 3, is correct for both
types when in collimation.

Another less common error; is rotation of an optical axis as it passes
through a prism which has been disturbed, known generally as Prism rotation
(see Figure 2) it is mostly found in binocular heads that use three point fixing
of the prism mounts. Furthermore, this is usually caused by the user/owner
attempting to adjust the collimation without the necessary knowledge or
means of checking their work.

One common question I am often asked is "How can one tell if any
collimation errors exist in a microscope?"... Well, one test experts
recommended is to focus on the edge of a glass slide, then slowly withdraw
one's head from the microscope eyepieces until the single image separates
into two. The line formed by the edge of the slide must continue to be
straight through both eyepieces. Any errors such as dipvergence or prism
rotation will appear as in Figures 1 and 2. Unfortunately, this test is of no
value in detecting divergence or convergence. In addition, if any error exists
in the vertical location of the testers eyes, (One or two millimetres is not
uncommon), this will almost certainly void the check for dipvergence.

A far better test is one that I use after working on a microscopes
collimation; it makes use of a spread slide of Deep Sea Soundings, although

any slide of fine Sand or Foraminifera is suitable. How I use this will be
explained later.

Another question asked is. . . "What is adjusted when recollimating a
binocular head?". . . The answer is, that in most microscopes one has the
option of moving an eyepiece tube, prism, or a first-surface mirror; the first
method [moving an eyepiece tube] is of course to be preferred as no error
such as rotation of the optical axis is introduced.

Moving on, many independent Contract Service Engineers correct any
problem of collimation on site, and you may adopt their method as described
here (two axes qualified collimation). The collimation tools you require are
surprisingly few; a lOx eyepiece with a cross-line graticule, a Centring slide
with cross-lines, and of course a variety of screwdrivers, star drives, and
small Allen (Hex) keys.

The procedure for adjusting the collimation of a binocular head is as
follows :-

Step 1. With both eyepieces removed from the head, put a straight edge
across the eyepiece tubes and adjust them to the same height (use
a depth gauge on convergent tubes). Also set the interpupillary
distance to 65 mm, as an average setting will balance out any
wear, in addition it is of benefit to Siedentopf heads as it can
help reduce their collimation 'run out'.

Step 2. Put the lOx eyepiece (with cross-line graticule) into the left
hand eyepiece tube.

Step 3. Place the Centring slide on the stage, then select the lOx
objective and bring the slide cross-lines to focus.

Step 4. Now with the mechanical stage adjust the position of the
Centring slide cross-lines, until they appear to contact the
eyepiece cross-lines as in Figure 3. Note, do not superimpose

the eyepiece cross-lines ... we require greater accuracy than the
thickness of most Centring slide cross-lines (as seen at lOOx).

Step 5. Next, remove the lOx eyepiece and put it in the right hand

eyepiece tube, ensuring the eyepiece orientation is the same, (my
eyepiece has a pointer that indicates the 180-degree position of
the graticule). Additionally do not disturb the adjustments you
have made previously.

Step 6. Looking through the eyepiece you will now see any error of

collimation, for it is immediately apparent in the relative position
of the two sets of cross lines.

Repeat steps 1 to 6 until you are quite satisfied that the error you see is not
false, then take a piece of paper, and draw what you see through the eyepiece,
try and be as accurate as possible. This is done purely as a safeguard in case
of problems and you need to go back to your starting position. When you
have completed the above record move on to Step 7.

Step 7. Now the right hand eyepiece tube, prism or mirror, after first
slackening off the retaining screws, may be moved into
collimation, constantly checking progress through the lOx
eyepiece as the adjustment is made. When collimation is
achieved the result should appear identical to Figure 3 in both
eyepiece tubes.

Pleases note: the collimation of many binocular heads can be adjusted
from either side but, for the sake of convention, I have chosen the right side.
If you are left-handed, you may change the start procedure, commence with
the right eyepiece, and adjust the left eyepiece tube or prism... However,
with some heads such as the Lomo Ay- 12 the left eyepiece tube is the only
one that can be adjusted. Likewise, mirror type heads also have restrictions
i.e. adjustment is on the right side. Also, please keep in mind the aim is to
only 'tweak' the settings, and not cause major disruption to the optical
system. Furthermore the method described, although adequate for use in the
'field', cannot compare with the ease of using an optical collimator, but then
again neither can the cost, a collimator can run to many thousands of pounds
(or dollars).

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Figure 1.
Dipvergence

Figure 2.
Prism Rotation

Figure 3.
Eyepiece

Cross Lines

Centring
Slide

Cross Lines

Image as seen in both eyepiece
tubes when correctly ColHmated

Before trying one's hand at adjusting collimation it is very important that
due notice is taken of the following advice, for it will help prevent anyone
'getting out of their depth' :-

1. Do not attempt to adjust the collimation of your binocular head
without the necessary tools, although it may appear to be collimated

it can still cause eyestrain. Small collimation errors can be 'insidious'.

2. Only adjust a Siedentopf prism as a last resort and only then when you
are quite sure, the microscope manufacturer has not provided any other
means.

3. If you have to adjust a prism or mirror to collimate, do not move any
others at that time . If you fail to achieve collimation, see four below.

4. If after moving the eyepiece tube, prism or mirror you cannot achieve
collimation return them to the starting position (refer to your record)
then work on the other side of the binocular head.

5. Beware! Some manufacturers in the past have used shims under the
prism-mounts.

6. When working on a binocular head, try not to use an excessive amount
of adjustment on any one side, for this can lead to other problems of
collimation.

7. When you have moved the eyepiece tube, prism, or mirror into position,

be very careful re-tightening the screws; tighten each a little at a time
constantly checking progress through the lOx eyepiece, as it is very
easy to undo your work.

8. If when conducting the recommended slide test the images appear to
have the same angle of prism rotation in both eyepiece tubes, the cause
is unlikely to be the head. This condition is typical of an out-of-square
mechanical stage.

9. Only undertake collimation if you are confident of your ability in
matters mechanical, dexterity is the order of the day and any hand
tremors are a "No No". If you have an old binocular head, practice
on that to discover if this type of work is for you.

10. Last but not least use common sense ^Don't fix it if it's not broken'
... you can make matters a lot worse. This is especially the case with
older microscopes, sometimes their original collimation left a lot to be
desired.

The following photographs and advice are just a few selected examples to
give those contemplating such work a source of reference:-

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Photo 1.

Carl Zeiss Head ...Type Siedentopf.

Adjust right side eyepiece tube.

Comments. Slacken screws and slide eyepiece tube into collimation.

Difficulty level. . .Easy and straight forward.

Carl Zeiss
Head

( Siedentopf)

Photo 2.

Nikon Trinocular Head . . .Type Siedentopf.
Adjust left eyepiece tube.

Comments. With this type of head the right eyepiece is rotated by a metal
band under a fibre cover, so try to avoid working on the right or you may also
have to adjust the said band as well. Note the two-collimation screws may
be very tight and sealed with a drop of epoxy resin, so it is most important a
good fitting screwdriver is used; as you may have to give it a short sharp rap
to break the seal on each of the screws (not with a 7 lb hammer please).
Difficulty level. . . Easy, but the above screws can make one's heart rate
increase.

Nikon Trinocular Head

( Siedentopf )

a - Collimation
Screws

Photo 2.

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Photo 3.

Olympus Head. . .Type Jentsch.

Adjust right side eyepiece tube. (Prism underneath is attached to the tube)
Comments. First remove bridge plate between eyepiece tubes, and then
remove focus ring of right eyepiece (grub screws require an Allen key). Next
remove the right cover plate (one small screw on top and two underneath).
The collimation adjusting screws (Four) are now revealed. When
reassembling after collimation set the left eyepiece tube to say 65, adjust right
tube with a straight edge to same height and set that eyepiece ring to 65 then
tighten the screws, but make sure you have put the cover plate on first.
Difficulty level. . .Easy, but more work is involved.

Collimation
Screws

Photo 3.

Olympus Head

( Jentsch)

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Photo 4.

Gillett & Silbert Head... Type Siedentopf.

Adjust right side eyepiece tube.

Comments. This head is pure delight to work on; the bridge construction

even provides good access for cleaning the prisms. A much-underrated

design.

Difficulty level. . .Easy and straight forward.

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Photo 5.

Vickers (Patholette) . . . Type Siedentopf.
Adjust right side eyepiece tube.

Comments. Adjustment is by screws that bear on cone fittings, which are part
of the eyepieces tubes. Slacken off screws (c) in ball housing and remove
prism frame, at the base of the cover plates are counter sunk screws remove
the right one (b) and slide the plate down, replace head assembly applying
pressure to compress internal spring and fix with frame screw (c). The three
adjustment screws (a) are below the top plate. Note the range of adjustment
is limited before a collimation screw prevents the cover sliding back on.
Difficulty level... Not hard but more work what's more take care with the
screwdriver do not damage the prism.

a

Vickers Patholette Head

( Siedentopf)

Stripped ready for
Collimating

a - Collimation
Screws

b - Prism Cover
Screw

Prism

c - Frame

Screw

Photo 5.

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Photo 6.

Vickers M15 Head... Type Jentsch.

Adjustment by moving a prism. . .Adjust right side.

Comments. This head requires either a skeleton housing jig or two pillar

screws to hold the head far enough away to adjust the selected prism.

Commence work by removing the two Chrome knobs, some models have

flush fitting plugs which require a double pin tool to remove; next centre the

holes in the top plates, and remove the left and right screws to release the

prism assembly, there are three screws to each prism mount for adjusting the

collimation, but again take care with the screwdriver do not damage the

prisms.

Vickers Ml 5
Head

( Jentsch)

Photo 6.

a - Collimation
Screws

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Difficulty level. . .Can be a pain for the novice and the expert alike, a great
deal of work is involved and at times can get quite frustrating, especially if it
has been badly serviced by Mr. Fix-it. Also check the eyepiece slideways for
wear; if you can rock the eyepiece tubes then collimation will be next to
impossible. If you are still not put off and intend to proceed, be careful of
prism rotation it is easily caused with the three point fixing. Furthermore, do
not interfere with the centre Swan cube mount.

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Photo 7.

Carl Zeiss Head. . .Type Jentsch.

Adjust right side eyepiece tube.

Comments. Slacken screws and slide eyepiece tube into collimation.

Difficulty level. . .Easy and straight forward.

Carl Zeiss
Head

( Jentsch)

a - Collimation Screws

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Photo 8.

Lomo Ay- 12... Type Siedentopf .

Adjust left side eyepiece tube.

Comments. Remove six screws holding the left Prism cover, then slacken

three screws (a) under top plate, and slide eyepiece tube into collimation.

Difficulty level... Easy, Should present no problems but once again the

warning is; take care with the screwdriver do not damage the prism.

LOMO
Ay-12Head

( Siedentopf)

Stripped ready
a for Collimation

a - Collimation Screws

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Photo 9.

Carl Zeiss (Mirror) Head... Type Siedentopf.
Adjust mirror on right side.

Comments. With this head, Zeiss has made provision for the collimation to
be adjusted using two screws bearing on a first surface angled mirror in the
right eyepiece box. If you look under this box you will see two small plastic
plugs, remove these (thumb nail only please) to gain access to the said
screws. Now, when you sit facing the microscope the screw in the top hole
adjusts Dipvergence, and the screw in the bottom hole Divergence and
Convergence.

Photo 9

Caps

A 1 Adjusts Dipvergence

A 2 Adjusts Divergence & Convergence

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Use your screwdriver with care, a fraction of a turn has a noticeable effect,
which of course you will see as you observe the collimation progress through
the 10 X (cross line) eyepiece. Please note, the side cover plate was only
removed (as shown in Photo 9) to display the mirror that is moved by these
screws during the collimation process, and it is not a requirement when
adjusting the binocular head. In addition, do not forget to replace the plastic
plugs when you have finished.
Difficulty level. . .Easy and straight forward.

Testing your handy work.

When you have completed the collimation process, your handy work needs to
be crosschecked but in a different way, (using 'blink comparison'). The
following test is very searching, take a spread slide like I mentioned earlier
(fine sand, forams etc) and focus the slide using a lOx objective (4x if the
sand or forams are coarse) and a matched pair of lOx eyepieces. Then study
the edge of the field diaphragms in each eyepiece, looking North, East, South
and West, and noting where the subject matter is bisected, if the sight picture
in your binocular head is identical in both eyepieces when you 'blink'
between the two, then you have achieved collimation. If not rotate, the
eyepieces to check they are not introducing errors for they may not be
matched pairs, (although with today's manufacturing it is seldom a problem).
If the collimation is still out, go back to step one because you have not been
as careful as you thought! ...Not to worry try again, you will get better with
practice.

Finally, if you have taken care when performing the systematic
instructions your resulting accuracy of collimation will equal the original
manufacturer's tolerances. Oh and by the way, welcome to the world of
D.I.Y. microscope servicing.

Addendum

After the above article was published by the Manchester Microscopical and
Natural History Society I received a great many e-mails asking "could I
recommend a few books for further reading on the subject of binocular
collimation"... Well, I am afraid that was quite a tall order for information is
sparse to say the least. In the nineteen fifties, one G. D. Hanna, California

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Academy of Sciences, San Francisco, wrote an excellent article in a Scientific
American publication entitled The Overhaul and Adjustment of Binoculars'.
Even though Hanna did not cover binocular microscopes as such, that said,
his article was still of great value in the respect of collimation and allied
topics.

So, other than the above and an occasional paragraph or two found in
microscope service manuals, as far as I am aware there are no in depth guides
to collimation for microscopists or anyone else. Unfortunately, this is one-
subject that most authors writing on microscope construction appear to avoid
like the plague. In fact, there exists a fog of silence surrounding binocular
microscope collimation, which I hope this article has helped blow away.

Ron Green, Rotherham, England.
28**^ November 2008

Disclaimer

Any person or persons undertaking collimation adjustment of any
microscope do so entirely at their own risk. The author accepts no
liability for financial loss, damage or injury caused by following any
advice or instructions given or implied in this article.

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The author would hke to thank the organisers of the

Internet Archive Library for the invaluable service

they provide for historical research.

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