It's amazing what 0.5mm will do to the focus of a lens. The difference between a Nikon S-mount lens working on an adapter, and a Zeiss lens working.
This LTM adapter is pretty amazing. It is thin, but I've had it on/off 10 times already. I'm thinking of leaving it on a Canon 7. Manually selected framelines, metal curtains, and the meter. And I have two of them.
Just to add: the back-focus for the M42 mount is much greater than the 28.8mm that these lenses are designed for.
But I did get a Zeiss-Jena preset 50/2.8 Tessar in M-42 mount transplanted into LTM, using the focus mount from an I-61L/D.
RF COupled, collimated for the Leica. On the Canon 7, wide-open.