DO NOT USE LEICA. USE ZEISS ONLY.
I own the A7R. Surprisingly, the Sony 28-70 kit lens is very good. For legacy lenses, I have used the Zeiss ContaxG/45 lens and the Leica Summicron/50 with the A7R (using the Shogun adapter, and manual everything). The Zeiss produces far superior images with the A7R. No colour shifts whatsoever; excellent colour, contrast, sharpness, dynamic range. The Leica produces weird colours, degraded images, and requires a great amount of postpro to correct. Ken Rockwell documents this on his site. KR blames the A7 for the weird colours, but in fact the problem is the Leica lens. Thus, I would avoid Leica lenses with the A7R and USE ZEISS ONLY.
Bumping an old thread - does anyone have both the CV 12mm and CV 15mm lenses that they can compare on the A7 for performance? I know there's heavy vignetting with both lenses that I'll have to correct in post, but I'm interested in center and edge sharpness, as well as distortion (beyond the obvious you'd expect with a 12-15mm lens).
What about size/ergonomics when shooting? Obviously the 12mm is larger, but I am having a hard time estimating size in hand on the Internet