Mr. Joshua Daniels was kind enough to email me the following description of the Zoerkendoerfer adapter that fits Contax manual-focus lenses onto Canon EOS-series film and digital camera bodies. Here is what Mr. Daniels wrote, paraphrased slightly:
Our adapter essentially allows you to focus a Contax lens throughout its normal range, from infinity to close up, to operate the diaphragm in manual mode, and to perform metering functions. We have not tested the adapter on every EOS body, but my understanding is that at least averaging and spot TTL metering are possible with most if not all models, although at shooting aperture. You can also make use of aperture priority AE, although again at shooting aperture.
Canon engineers had the good sense to design the EOS system with a relatively small registry (film plane-to-flange distance). As a result, you can use other manufacturers' lenses (e.g., Contax, Leica, Nikon) on the EOS body, providing the adapter is sufficiently thin and precisely made.
Zoerkendoerfer's Contax adapter attaches to the Contax lens, then must be positioned (lining up the mounting dot with an alignment mark), and then locked onto the lens with an allen head hex screw. The reason for attaching this way is that the adapter must be quite thin, and this left no room for a locking mechanism. It takes less than a minute to attach or remove the adapter, but it is not as fast as bayonetting the lens into place. Some professionals who have purchased this adapter prefer to buy a couple of them so they are not switching adapters each time they change Contax lenses.
The Contax lenses and adapter work extremely well on the digital bodies, particularly because the Contax lenses are so good, and especially so from center to 3/4 out.
I can contact our German office for more-specific detail or to field any technical questions that I'm unable to address. They continually test our products with a wide range of cameras, given that our specialty is tilt, shift, macro, and adapter accessories that interoperate with multiple systems.
I don't know if the user group is aware of our Contax G mount Heliar, but this may also be of interest to Contax owners.