25.07.2015 - Today I had the chance to get my hands on the upcoming and extremely promising Sony A7R II and I would like to share some information that may not all have been adressed so far.
Of course the new 42.4 MP BSI (back side illuminated) sensor is the biggest improvement, providing higher resolution with a well balanced sensivity that may have been increased as well compared to the A7R - I would estimate an advantage of about 0.5 stops. In the past 1,5 years there was a lot of discussion all around the internet about disappointing results with symmetrically designed legacy wide angle lenses especially with M-mount lenses from Leica, Zeiss and Voigtlander. Most articles came to vague conclusions, many of them ignoring that there were also quite well working lenses like the Leica WATE (3D-Kraft was the first site reporting positive results for that lens).
The new BSI sensor design not only gives more light to each photo diode, it also brings these diodes closer to the surface which means less light fall off for oblique projected rays of light. As they also get closer to the bayer filter pattern, my assumption is that this sensor will produce far less color shift towards the borders.
In order to prove my assumption, I tested the A7RII with the most extremely designed ultra wide angle lens that I know at the moment: The ZEISS Hologon T* 8/16 (originally designed for Contax G cameras). If you want to know more about this optical oddity, I recommend to take a look at this article: http://www.thephoblographer.com/2013/10/12/the-top-five-most-extreme-wide-angle-lenses-ever-built