Yes I understand that Leica M is a rangefinder system, which allows for different optical designs that SLR mounts. (Rear element protruding further into the body, etc) Which does not necassarily mean that this particular design is dependent on those factors, and impossible to port to F-mount. For instance, that Voigtländer 15mm you mention is also available in Nikon F-mount.
And how about that Zeiss Contax 15mm? Could that be a place to start?





