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Full text of "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:- 



8 



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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