Contax/Kiev RF flange focal distance

I'm restoring a couple bodies and on one of them, though I attempted to be careful, I think all the shims that may have been between the lens mount and body ended up rattling around the body before I had a chance to note their locations.

Kiev survival site has a good writeup on this that seems relevant: https://web.archive.org/web/2019081.../public/rpnchbck/camera working distance.html where he measures 35.00mm as the nominal focal distance (measured from the front face of the outer bayonet), but some other resources online quote the nominal distance as 35.85mm. I have a couple other bodies that (hopefully) haven't had their shims mangled which I can check against but still waiting on my depth gauge to show up in the mail.

Wondering if anyone else has ever taken precise measurements of this and attempted to re-shim, if so what measurements did you end up using?. Regardless of what I pick I'll probably be double checking any micrometer measurements with the collimator (using the marked-glass-plate on the film plane and slr-with-long-lens approach since I don't actually have an autocollimator)

I think I recall reading that one or another brand of Contax-mount RF camera (Kiev or Canon?) had a different flange depth and one had to shim either lens collars or the outer flange to get it to focus correctly with other brand lenses. This might be what you're seeing with a difference of .85 mm.

I will tell you that based on film results, my Kiev 2 is dead on with all four of the Soviet lenses I have for it (two 50 mm, one 35 mm, and a 135 mm), so collimating with a known good Soviet lens should be the final confirmation.

My Jupiter-8 and Jupiter-11 are very accurate on my Kiev-4. The Jupiter-3 wouldn't be a good candidate for testing as it has a lot of focus shift.

loccdor said:

The Jupiter-3 wouldn't be a good candidate for testing as it has a lot of focus shift.

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I haven't noticed that with mine, but I haven't used it much -- 135 isn't one of my favorite focal length for 35 mm film. Rather be 85 or 185+ (and the latter probably isn't a great choice for an RF camera).

Donald Qualls said:

I haven't noticed that with mine, but I haven't used it much -- 135 isn't one of my favorite focal length for 35 mm film. Rather be 85 or 185+ (and the latter probably isn't a great choice for an RF camera).

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The Jupiter-3 is the 50mm f/1.5, the 135mm is the Jupiter-11.

At minimum focus distance, wide open, my Jupiter-3 was focused about 6 inches too close. For every stop-down, that would reduce by maybe 1.5 inches. At 5.6 the focus was fine.

Contax RF 34.85-back registry
Kiev-2 (-4) 34,85-back registry
Nikon RF have the same, but different gear ration of lens focusing. So equivalent only infinity

loccdor said:

At minimum focus distance, wide open, my Jupiter-3 was focused about 6 inches too close. For every stop-down, that would reduce by maybe 1.5 inches. At 5.6 the focus was fine.

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Ah, I've shot a bunch of film with the Jupiter 3 I have (50 mm f/1.5, right?) and never noticed that, but I don't shoot a lot of close-ups. The close shots I've done were with my 50 mm f/2 Jupiter 8 that came with my (not working right) Kiev 4.

Focus shift seems like a bad thing for an RF camera lens, though, especially the fastest one available that you'll be tempted to use wide open to hand hold in low light...

Just wanted to circle back:
Measured 3 different bodies with a depth micrometer and 34.85mm seems to be the ticket (not 35). My depth mic setup is probably not ideal so my confidence is not extreme, but all my bodies seem to measure within .02mm of 34.85. Based on some helicoid measurements I'd guess that error is on the order of 1 inch at the minimum focus distance, so really only ever going to be noticeable wide open with a normal or longer lens.

For reference, I measured by setting the helicoid to infinity and using a small piece of glass that fits up against the film gate (actually the same piece of glass I made to use as a collimation target for 35mm cameras). Glass is generally pretty dang flat and I figured that'd give me better reliability than a piece of film on the pressure plate.

hospadar said:

Glass is generally pretty dang flat

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Modern float glass will typically be less than .01 mm across a piece the size of a desk picture frame. Not flat by optical standards (and optical flat will be out by less than a hundredth of that figure), but flatter than you can measure with a depth mic.

Donald Qualls said:

I think I recall reading that one or another brand of Contax-mount RF camera (Kiev or Canon?) had a different flange depth and one had to shim either lens collars or the outer flange to get it to focus correctly with other brand lenses. This might be what you're seeing with a difference of .85 mm.

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This is based on camera lore not my personal measurement, but it's well-attested lore:

- Contax RF and Kiev RF are consistent, but Nikon RF is slightly different (physical lens mount is similar, focusing is a little off). As additional evidence, there are some Nikon-made RF lenses that have a small "C" marked on the barrel to indicate they are set up to focus with Contax, not Nikon. This little "C" is pretty small and would be easy to miss. Also, Henry Scherer, the Contax repairman, has a webpage where he described measuring the Contax-Nikon difference in lens register, but I have not been able to understand his description of his method.

- In the M39 world, Leica and Japanese Leica copies (Canon, Nicca, Yashica, etc) are the same, but Soviet RF such as FED and Zorki are slightly different from Leica.

It's confusing because the similarities are swapped between the two systems: in one system the Soviet models match the German camera and the Japanese models don't, and in the other system it's the reverse.