Hi,
Tolerances my be less of a problem than suggested by many. Adding an extra mount introduces extra opportunity for error, but those errors are always alignment errors. In real world subjects are not aligned very well with the sensor. Where you focus you get excellent sharpness even with a system out of alignment.
So I would suggest that lens alignment problems are in part a test chart only problem. Or if you are shooting a brick wall, how do you know the camera is aligned with the wall?
The real issue may rather be that all lenses are not created equal. Some of the Leica lenses are excellent, but I am pretty sure that many are not so perfect and some may be tricky. With Biogon type lenses there is an additional issue that the optical package on the sensors introduces astigmatism, this was one of the reasons Leica used such a weak IR filter on the M8. On the M9 they went for a thicker filter.
The Hartblei HCam is often used with a Mirex TS adapter and I understand that combo produces excellent images.
Best regards
Erik
I'm afraid people using the high resolution A7R will be disappointed when using their beloved old Leica and Contax wideangles with an adapter. Tolerances are extremely tight here. I'm curious on people actually testing this and reporting.