Great idea. I love the Zeiss glass but am not too fond of the Kyocera bodies.
I looked into that adapter and, as I remember, it imposes limitations. Possibly you have to use the lenses in stop-down mode? Anyay, I sadly discarded the idea for myself.
To use Contax/Yashica mount lenses on a Canon EOS camera body, the adapter has to incorporate a thin negative element to correct for the extra extension so as to restore infinity focus. This works as a weak tele-converter and will indeed have a certain impact on the absolute image quality, If it is possible to use a plain adapter to fit Brand X lenses to a Brand Y camera without the need for such optical makeshift, I have no problem with that, otherwise I would not be at all keen to do so.
I asked Stephen Gandy specifically about infinity focus just recently, and he assured me that it does indeed work. I don't think he'd say that without believing it, and he's definitely one of the greatest photographic gearhead cobblers out there in the world. Likewise Zörk promises infinity focus, and I doubt they're throw away their optical reuptation for the sake of an obscure $200 part.
Stop-down restrictions, yeah. But sturdier, sharper, and easier for manual focus than the Canon equivalents (for the 50mm and 28mm lengths, they're rated by photodo as sharper than Canon, Nikon, or Leica -- pretty consistent with my experience with the G2 and (long ago) RTS).
(In fact when I started processing the first roll shot with my G2, I could see the extra "snap" right there on the negatives, before they were even dry, as compared to my Canon-lens negs in the same batch.)
Canon FD lenses on Canon EOS -- yeah, those won't focus to infinity. Canon made a camera that can use most everyone's lenses but their own. Go figure.
The Contax/Yashica lens to Canon EOS camera adapter without negative glass sure looks like a relatively new development; I was only aware of the one by Kenko which has the negative element.
On the same note, I have two adapters with negative elements for using Minolta manual focus lens on autofocus camera, one offers no automation and seems to carry no maker's mark, only "Adapter MD/Maxxum", which seems to be easy enough to use even with no automation coupling. The other is a Sigma 1.6X converter which not only offers diaphragm automation couplings but autofocus as well; I have contacted Sigma but they couldn't be bothered to send me a manual so I am not sure how to use it either with a Minolta lens or even a M42 lens via a Minolta P-Adapter. Any thoughts on that?
I have two adaptors namely Pentacon Six to Mamiya 645 and Pentacon Six to Canon FD. I use the P6/Mamiya adaptor less these days because I have a nice range of Mamiya lenses that cover my needs. I got the P6/Canon with a view to doing some bird photograpy because I have a 300mm F4 Sonnar and a 180mm f2.8 Sonnar.
Re: FD-EOS, I use 35mm mostly for bird photography, so almost exclusively with long lenses, so when I found a good deal on an original FD-EOS converter (only works with 200mm and longer due to protruding lens elements and acts as a 1.2X converter) I bought one. I also picked up a rare Tamron Adaptall mount for EOS, since I have a couple of those lenses as well. I'm confident that my F-1N will be good for another 20 years at least, but somewhere along the line, I can see looking into a digital body, and I don't want to get stuck having to replace my FD teles with EO$ versions.
I also have an FD-Bronica S adapter for macro, that Frank Marshman made for me for about $50. In the macro range, FD lenses like the 35/2.8 Macrophoto and Tamron SP 90/2.5 cover 6x6 with no problem and are really sharp.
Went through an M42 phase, but didn't find any really unusual lenses that I really liked and didn't have perfectly good FD counterparts. I still have the adapters though, just in case something comes along.
I wrote a piece on lens adaptations for usefilm.com, which you can read here:
My favorite 35mm adaptation has been the Ektar 100/3.5 Medalist lens, for which I cobbled together an FD adapter. It's a Heliar type that's great for portraits. You can read about that one here on Bob Monaghan's site, which has lots of info on lens hacking, particularly for classic Bronicas: