So, I've been playing around with an A7 (the non-R version) and M glass. I don't have any native mount lenses, and I'm using a Novoflex adapter.
Couple of quick thoughts.
a) I've been getting pretty systematical, pretty severe underexposure. I'd say a good stop, stop and a half. Anyone else run into the issue ?
b) the RX1 (non-R) would appear to be sharper than the A7 + summicron IV combo. As a tool, I like the RX1 MUCH more, if only because it's totally silent. I'd like it even more if they'd thought of adding a sensor cleaning system in it, because dust DOES get to the sensor, and then you need to send it out for service, which just sucks.
c) the elmarit 21 pre-asph vignettes very heavily (at 5.6, not like I'm trying to split hairs here). I'm not certain if it's the adapter, or the sensor, or the lens, but it's a good couple of stops. It of course also goes purple on the sides, as has been reported elsewhere. I'm sure it could be monetised and made into an Instagram effect, or something. Color shift doesn't seem to be too, too bad with the pre-asph elmarit 24 and 28s, but I haven't done things like shoot a white piece of paper with them.
d) it's nice to be able to take that Leica glass out of the closet without getting hit with the dentist tax.
I've got to say I'm really liking both the RX1 and the A7, although both feel, for lack of a better term, half-assed in terms of the demographic they seem to be trying to reach. It's little things, really - uncompressed RAW (whether or not it makes an actual difference in the end) options would be nice on both the RX1 and the A7. Being able to choose file naming would be as well, if only because it makes things easier to handle for people who have more than one of their cameras. Spending money on a bit of absorbent foam for the A7 would have been a sweet touch, too...