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Zeiss 85mm f1.2 Contax/Yashica problems!

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I have a Zeiss 85mm f1.2 (50th anniversary) lens which originally had a Contax/Yashica mount. When I bought the lens it came with an Aaton mount. I want to install an EF conversion mount which I bought from Simmod, but it requires the original C/Y mount to be present, in order for it to attach to and I guess sit at the right height for flange distance etc. I've tinkered with making a shim/spacer out of a Canon lens cap, but it's not exactly as good as a nice machined metal part. And it requires me to find longer screws..

Anyway, my questions would be:

1) What is the correct distance from rear element of this lens to sensor/film plane?

2) Is there a way to source a C/Y mount for this particular lens? (Note it's quite a bit wider at the base than many potential "donor" contax lenses, I know because I've already destroyed a 50mm f1.7 *sorry)

3) Do spec sheets, blueprints, technical data or papers exist in a public domain for this particular lens?

4) Could someone please point me in the direction of a good resource for understanding how the C/Y mechanism works? I seem to have begun my lens *home servicing journey on a rather expensive lens, and I'm pulling a few too many hairs out with anxiety...

Many thanks and hello!

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That’s a rather expensive lens to be tinkering with. If you’re not at least a proficient DIY lens repairer I would send it to a professional rather than potentially damage it.

The back focus distance is usually set with a collimator or lens projector, not measured by hand, and should be set to within a tenth of a mm if you want to even roughly have the focus scale line up, or have the lens reach infinity focus. Proper back focus depth is usually set to within hundredths of a mm. You can roughly estimate it by just holding the lens against a piece of paper and forming an image of something like clouds (nearly infinity). It will change depending on the subject distance.

I’ve never found any technical information on these lenses. They are at least several decades old now. Zeiss can possibly supply you with names of companies that specialise in their legacy lenses, or just find a local lens repair facility that knows Contax C/Y lenses. They are the ones most likely to have spare mounts or know how to convert the lens safely. Otherwise you’d probably just need to find a damaged/junk version of the lens to get the mount. I’m not familiar enough with the series to tell you if the 85mm shares the same mount with any other focal lengths.

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Since you are trying to reconstruct the lens to as-new spec, you're going to need an experienced tech who has the parts to spare. In the UK, I'd try CRR Luton first. That is a very low-production and high dollar lens, so there won't be much in the way of spare parts, if any. You can't simply swap in the mount, linkage, and aperture ring from a lens which would physically fit over the rear element, as those are all lens-specific. You can see this in the difference between a pair of 50mm lenses, one f/1.7 and the other f/1.4. They may physically fit each other but the aperture rate of movement is different between the two. In a nutshell, the only parts which fit the 85/1.2 are those from another 85/1.2. 

Good luck!

Phil Forrest

Edited by Philip Forrest
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