Re: Fun with the A7/7R
1) I'm not speaking of SLR like registers, which are most located between 44-48mm. I spoke explicitly of picking a flange distance a little lower than the film rangefinders (aka something lower than the Leica Ms or the PenF mounts which need only 28mm). But instead of 17.5mm Sony could have taken a flange of say 25mm and a wider mount : this would have eased the question of the light rays falling too steep at the corners.
2) With a 25mm flange you can still keep the flexibility to adapt most lenses; you may even get more flexibility, if wide angle legacy RF lenses performs better than is the case now.
3) Sony/Zeiss may not have so much flexibility for the design of new lenses if they want to keep the main advantage of the A7/A7r : aka smaller size and lower weight. A slightly deeper flange distance would have eased correction of retrofocus lenses too.
4) Yes, the system is new, I'm waiting to see what they will produce in the wide angle department with curiosity. The 35mm has very good reputation. Let's see what they will achieve in the 21-24-28mm range.
1- To allow clean adaptation of an M-mount lens, 2-3mm difference in mount register is not enough IMO. 10mm is good.
FourThirds*SLR was designed with the ideal relationship in flange diameter to sensor diagonal in mind for an f/1.4 lens. Micro-FourThirds preserved that relationship—going to a shorter mount register allowed the flange diameter to shrink, maintaining the same section presentation to the sensor. Sony's E-mount on APS-C format was larger than needed, causing the lenses to be larger than needed. For FF format, the same mount is a smaller diameter than ideal, which complicates ideal lens design somewhat. A deeper register would need an even bigger diameter mounting flange for the oblong 2:3 format.
2- There would be ZERO difference in the performance of older RF lenses if you made the camera's mount register deeper ... the lens still needs to sit at the ~28mm distance from the sensor, whether you set that with a deeper body or a tube. The incident angle of light rays to the sensor has to do with the optical design, not the mount register, for an existing lens designed for an existing mount register.
3- Same as above. Existing lenses designed for an even deeper mount register get no benefit at all from having a deeper mount register. New lenses get a lot of benefit from having a shallower mount register to work with.
Hopefully they'll come up with some nice new lenses for the A7/A7r. Not that it matters much to me - I have 24 to 180 mm lenses all of which I've proven work just beautifully on the A7 now. Really don't need anything else, although a 16-19mm might be fun.
I guess at some point I'll have to test them on the A7r.
G