[Digitalis]

Sensor reflections are also a much bigger problem with today's short-registration-distance mirrorless cameras, especially when the lens design places the rear element quite close to the sensor.

Leica M mount managed to side step this issue by having a more modest registration distance: Leica M = 27.80mm Vs SONY's E mount = 18mm. Leica didn't really expect anyone to want any lenses wider than 24mm* as we know, lenses with focal lengths that go too far below the lens mount registration distance are a headache for lens designers.


* Leica does make a not-quite-a-zoom Tri-elmar 16-18-21mm f/4 ASPH and did make a Elmar 18mm f/3.8 ASPH superwide.