With the NEX7 you come up with a rough composition, hit the front button that takes you into manual focus, quickly move the "enlargement square" to the subjects face and the camera zooms in. Now you're looking at one small section of the frame, enlarged. Focus the lens, tap the shutter button and you're back to the whole composition. Shoot the picture.
With the Sonnar wide open I was getting more in focus shots with the Sony than the M9. No question the M9 was quicker to focus, just not as accurate.
This is with the Sony NEX7 wide open on the Zeiss Sonnar 50mm f1.5. I'm not saying it's a good photo, but this is the classic look of the Sonnar lens. Subject is sharp, but not as sharp as they would be with a Planar lens, but the depth of field and sharpness drop of quickly and some people like the resulting bokeh. I'm not sure it would really look that different with another lens design I'll have to try it. One thing for sure.... people like the Sonnar lenses even with their finicky issues.
When you stop down to f5.6 you get more sharpness but less of a signature look, which is why people buy the Sonnar.
Again, this one is wide open on the NEX7.
I sell the Zeiss Sonnar 50mm f1.5 at my retail store for rangefinder gear.