I have a Contax Zeiss Distagon 28mm that I acquired two weeks ago. I ordered the K mount conversion from Leitax which just arrived. Though about doing it myself, but I just did not want to take the chance of my butchering such a nice lens, so I am going to send it to Eric.
As far as adapters, there is nothing I could find. The lens came with a C/Y to M42 adapter, however that is to mount an M42 lens on a Contax camera. I'v found nothing for the other way around. So for these lenses it appears that a physical conversion is the only option.
I do believe that for certain lenses (for instance that are on the Leitax list) acquired at reasonable prices - that this route should be a reasonable path. For instance the Contax Zeiss Distagon T* 28mm f2.8 is suppose to be a wonderful lens. Zeiss sells it in the ZK mount (Pentax K) for about $1,300 (and it a f2 as opposed to a f2.8). So a $100 conversion should result is a very nice lens. The gentleman I acquired it from had a large set of wonderful images, and was reducing his collection of Contax glass.
So, I figure that in a week or so - I hopefully should have the lens back and some images to compare with my 31 Ltd. I am really hoping for this set of the 31 and 28 providing the glass for a lot of wonderful images far into the future.
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Edit - My wife had told me that the mount arrived - it turned out to be the M42 to K mount adapter that I ordered from Pentax. The C/Y to K mount conversion kit wound up in US Customs for 11 weeks (the holidays, the Post Office told me). So now Eric has it and is converting it - as I did not want to botch the job. Hopefully, I should have it within a week or so....
Edit 2 - I now have had the converted lens for about a month or so. Its the equal of the FA 31 Ltd - but only manual - aperture and focusing (like a K or M lens). Its sharper and its "character" is a bit different -
not worse or bad. It handles contrast and colors slightly differently - very pleasing to me. My total cost is 1/3 that of either a new FA 31 Ltd or Zeiss 28/2 ZK, and it the equal of either of them - just more "manual".