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Zorki lens mount shims
Old 06-11-2019   #1
NovaXeros
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Zorki lens mount shims

Hi all,

I'm about ready to throw my Zorki in the bin, and all because I cannot for love-nor-money figure out how to shim the lens mount to 28.8mm.

I know the theory about it, and can measure within 0.02mm, but it's those damned shims - the ones I have are too thick, or too thin and not the right size to double up because then it's too thick and ARGHH.

There has to be an easier way - surely.

Does anyone know any way of making shims/shimming a Zorki 1 lens mount to bring it in line with 28.80mm? Is there a particular material best for this? A trick? A tip? Anything, just to help me keep what little hair (and sanity) I have left!

Thanks
G
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Old 06-11-2019   #2
Ko.Fe.
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Use paper. It has different thickness. Notepads, business cards, printing plane paper and waxed paper.
This is what was in use originally. Waxed paper.
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Old 06-11-2019   #3
NovaXeros
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Many thanks for the reply - an odd follow up question then, if I may?

How best to cut the shims out of the paper? Any attempt to cut the same shape as the original shims results in paper that is either jagged and catches down the side of the mount, or too flimsy upon piercing "holes" in for the screws to go through the mount and the shell.

Also: follow up follow up question - what's the deal with lenses becoming difficult to focus when I shim the mount? It's like it's bending the mounting ring and causing the ring to "compress" the lens, but it's the only way I can get even close to 28.80mm at all four corners of the film gate.

Man, this Zorki will be the death of me; I've successfully changes both curtains, cleaned and refreshed the springs inside the rollers, confirmed accurate shutter speeds, but the LENS MOUNT.....
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Old 06-11-2019   #4
Livesteamer
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Can you check the film plane for flatness? Is there any chance either the body casting or the lens mount ring is warped or out of flat? Shims do not have to be the shape of the lens mount. Simple washer shaped shims should work. You might want to make a punch the size of the screws to help make the holes. Being patient and thoughtful is your best tool. You've come a long way, you can work this out. Good Luck. Joe
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Old 06-11-2019   #5
Sarcophilus Harrisii
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Select the combination you have that is over size by the smallest dimension, then use a flat surface (Ie. the surface plate you presumably have, if you're measuring the lens register and correcting parallelism) and some abrasive paper to reduce a shim thickness until it achieves the necessary dimension.
Cheers
Brett
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Old 06-11-2019   #6
farlymac
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Like Brett says, a hole punch works wonders. Also, try installing a disk of the material sized to just cover the mount, tighten down the mount ring, then use an Exacto blade to cut out the center.


After that, do a check for flatness.



As for material, most of them I've seen have been card stock or thinner. Thicker card stock will compress more, so use the thinnest you can find. Or go to a machine shop, and buy some brass shimming stock. That way you can get whatever size combination you need to achieve the proper thickness.


PF
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Old 06-12-2019   #7
NovaXeros
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Thanks very much for all the replies, I'm going to give this another try tonight and will update with results/loss of hair/etc.

I must admit though, I'm confused at the mention of a hole punch, both in regards to making one and using one - presumably this would be to punch holes in the made shims for the screws to go through? A traditional office hole punch would no doubt make holes too big though, right?
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Old 06-12-2019   #8
wolves3012
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Quote:
Originally Posted by NovaXeros View Post
Also: follow up follow up question - what's the deal with lenses becoming difficult to focus when I shim the mount? It's like it's bending the mounting ring and causing the ring to 'compress' the lens, but it's the only way I can get even close to 28.80mm at all four corners of the film gate.
Make sure you tighten the mount screws in a diagonal pattern (X-shaped), otherwise you will distort the mount. Best done in stages, nip them up lightly first, then go around in several stages. Tighten each stage to the same force, as near as you can judge. If you need too much force, your shim must be too thick because you're trying to compress it.
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Old 06-12-2019   #9
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Hole punches are not hard to make. If you have a lathe then use steel rod, drill down the center of the size needed and then turn an angle on the end of the rod to create a sharp edge. If no lathe then find a hobby shop that sells brass tubing and flat stock. Select a tube with an interior diameter of the size needed for the hole then use a file to file around the end carefully, creating a sharp edge. Steel is better but even brass should work on paper especially if you rotate it a bit while pushing down. Good Luck, Joe
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Old 06-12-2019   #10
NovaXeros
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Many thanks to all who posted with tips, I took all of your ideas and put them to practice, and by jove it worked!

I think I only started pulling on my beard for a few minutes whilst I toiled over why some shims I measured at 0.2mm only changed the lens register distance by 0.1mm when applied. Still a mystery, but I just binned that material and used waxed paper instead.

As a final question, and not one that will affect this Zorki repair (as it's now done), just how critical really is the whole +/- 0.02mm accuracy requirement? Given that film isnt perfectly flat, wouldn't the curvature of the film have a bigger impact than the 0.02mm?

Many thanks for all your help - now I've got to calibrate the rangefinder, which is always a joy on these things....
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Old 06-12-2019   #11
Sarcophilus Harrisii
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I would take it seriously. It's not the only variable involved. As you say, film is not perfectly flat; lenses are rarely perfectly optically centred etc. (There's no such thing as perfection, of course, anything which measures perfect inevitably ceases to be so when examined under a higher resolution regime). The point is if various tolerances stack up or are exceeded sub-standard performance is the result. That means controlling the dimensions you may reasonably manage.
Cheers
Brett
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Old 06-12-2019   #12
Ko.Fe.
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I never bothered to measure and deal with this. My FED-2 lens passport is saying it is 28.87...
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Old 06-18-2019   #13
Murray Kelly
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The lens mounts I have dismantled have had a crumbly yellow shim. I suspect the assembler has a selection of paper shims (pre-punched) and selects one that can be screwed down with the 4 screws to compress the paper to the exact tolerance. To keep it set there is the problem. Rigidity is maintained by wicking in some shellac in alcohol drop by drop and that is why the shim looks brittle and yellow.
My Zorkii 4 had another problem only this method fixed. The mount was slightly wedge shaped and it was impossible to have the 28.8mm register at all points of the film plane. Thick soft paper did the trick.
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