Sony sensor causes massive field curvature to 28mm Biogon. I was planning to use this lens only for square format but using A7 (A7r is worse for field curvature) and f/11 it's possible to generate 1280px wide photos. Viewing fullscreen (2560x1600) or print is of course not possible.
Field curvature is much "milder" with A7 compared to A7r, top left crop: http://www.zeissimages.com/photo.php?link=http ://www.zeissimages.com/gallery/686/U686I1397163571.SEQ.0.jpg
The branch gets to focus due to field curvature, in A7r the focus on corners would be >10m/30ft in this kind of situation.
