The Sony A7 and A7r are starting to look promising as a full frame M-mount option if Ricoh doesn't come to the party. Anecdotal reports suggest that lenses from 28 upwards work fairly well, with 35 and up working with almost no vignetting or coloured edges. For lenses 28mm and wider, it seems that extreme retrofocus lens designs may suffer at bit. I love my GXR-M, and have been shooting more with it recently, but a full frame option with focus peaking and similar upgrades would only add to our choices.
I have the A7 now. After quick tests of all my M-mount lenses:
- Color Skopar 21, 28, Ultron 28/2, Nokton 50/1.5 LTM ::
unacceptable
- Color Skopar 35, 50 ::
satisfactory
- Nokton 40/1.4 MC, M-Rokkor 40/2, M-Rokkor 90/4, Hektor 135/4.5 ::
good
On the other hand, all my Leica R lenses (24, 50/2, 50/1.4, 90/2, 135/2.8, 180/2.8) and Nikkor SLR lenses (50/1.2, 55/3.5, 85/1.8, 105/2.8) work very well with it. I have yet to see how the Nikkor 18 and Elmarit-R 19 mm lenses do, but I expect well.
From other tests done on various forums around the net, I'd say that the A7/A7r are excellent bodies for nearly all SLR lenses but only for a small percentage of RF mount lenses.
I consider the A7 a sort of "one-body-fits-all" SLR replacement.
G