I use mine with several Contax 645 items.
The fit from Adapter to Leica S2 is perfect, as with Leica S lenses – no issues.
The fit to Contax 645 lenses and extension tubes is very tight.
My 13mm extension tube will lock after some use of the adapter tightly into place.
My 80/2 Planar will not lock when normally attached.
After using the adapter now for about one week, I can attach the 80mm when twisting tightly and it will lock into place sometimes.
As the extension tubes didn’t lock the first times, I attached them but will now more or less lock, I will look into this for a while and see, if regular use with lens changes will “wear in” the adapter.
Honestly, I did expect the adapter to work flawlessly for the price, Leica is asking for it.
Should it mechanically wear in, it will be fine though.
When comparing the locking mechanism of the Leica adapter and the Contax extension tubes, the locking pin of the Leica adapter does not sit as precisely in position, as the Contax locking pin in the extension tube does.
Measurement wise, both are within ±0.03mm in Ø, while the Contax pin measures Ø 1.97mm and the Leica locking pin is slightly smaller (so it is likely not an issue of a locking pin, that is too large in diameter).
I have another issue though with the operation of the Leica “S-Adapter C”:
I have to nailed the exact behaviour down until now, as I was busy shooting and did little testing, but I have to regularly unmount the adapter from the camera body, as the camera (Leica S2 with latest firmware version 1.0.4.2) will “forget” the mounted lens.
When this happens, all lens information will be forgotten and not displayed anymore on the info display.
It will also no aperture information be displayed in the viewfinder and the camera behaves as if no lens is attached at all.
So far, I have found during operation, that it is possibly linked to the camera forgetting the mounted lens during standby/ sleep mode, as the issue disappeared during a day of shooting, while deliberately preventing the camera from going into standby mode.
I have to test further though to verify.
As my S2 body suffers from a dead OLED display, I will probably ship the adapter with the body to Leica on the next occasion and have this behaviour checked out.
Please share if you experience similar issues of camera bodies, that “forget” the attached lens, when using one of the “intelligent” Leica-S adapters.
Btw – I love, using the Carl Zeiss lenses on the S2 so much, that I have shopped around for some of the interesting Contax 645 glass – such a great glass to have next to the S lenses, both in focal length options and in different imaging character!