, I still use a 1950's Agfa (aka Ansco in the States) rangefinder and (having owned a rangefinder more than 30 years) I do understand the rf technique and limitations pretty thoroughly.
All Leica M (from M2 to M9) are manual focusing cameras.... All Voigtlaender, ZE, ZF ZF.2, ZK and ZM lenses are manual focusing too. The field curvature of fast lenses is intrinsically pronounced so you either need to pre-compensate or live with poor focus from focus and recompose. Your final alternative is to focus on your subject and crop the image - but that reduces the camera's effective resolution to something like 11 megapixels. (purely an estimate based on the rule of thirds costing you 1/6 of your field in each direction.)
My comment that Leica has corrupted the M-bayonet specification.....Finally - I would like to address the comment on retrofocus designs for lenses degrading performance.
An Agfa/Ansco range finder camera from the 50's can hardly be qualified as a good well built range finder camera. It has fixed lens and the range finder accuracy and operation is way below Leica camera of the sametime.
Any lens that will fit the Lieca M is manual focusing by right. That is why I did not mention the Voigtlander and the Ziess ZM are manual focusing. As for the curvature of field for the lens., No auto focusing can correct them.
That is another reason why the Leica lenses are more expensive. Leica trys to minimize them by excellent design and tight manufacturing control.
If M9 can use The Lieca M lenses all the the back to the 50's, I still cannot see why the M9 has corrupted the M mount. If the other brand cannot work properly, it it is the other guy's problem .You are old enough to use an Agfa camera from the 50's. Do you remember why the Nikon range finder lens will not work right with the Ziess Contax?? Even both mounts are identical??
I have never mention that retrofocus degrade the lens performance. i just mention that It is easier to design short lens for range finder than for DSLR. FYI, even leica is using retrofocus design for their 24mm and 21mm M mount lenses.
The M9 is using offet micro lens to try to minimize the effect of the short back focus of the lens. on top of that there is soft ware correction built-in the M9 also.
Please rememder that quality and price is not a liner relationship. It is exponental. Juts look at the price of D1 and the price of a Rebel. Is D1 nearly 10 times better than the Rebel???