Upload & Sell: Off
I just did this comparison for my purposes, but I thought others might be interested in this as well. I recently sold my xpro1 and bought an nex 7. I had conceded that the Contax G 21mm wasn't going to work out well with the 7, but I decided to test it with the Adobe flat field plug in anyway. I was surprised that it actually looked pretty good after conversion so I decided to test it against two SLR lenses that I had planned on using occasionally with the 7. Here's what was tested:
Contax G 21mm
Canon FD 20mm f2.8
Nikon 20mm f2.8 AIS
All shots were taken at f8. White balance was manually adjusted to get them close (flat field plugin really changes the WB).
Here's my standard test image
Center 100% crops
Here they all look pretty good. Keep in mind this is a long way away for a wide angle. I'd rank them:
Here's a crop about half way out from center. I chose this spot because CA performance really shows up here.
The G shows just a hint of CA, but much less than the other two. In this sample I'd rank them:
Last crop is from the left edge.
This one surprised me. While they are all soft, the G21 performs the best. I'll leave it up to you to decide whether this is good, good enough, or inadequate for your uses. I just thought it was interesting since prevailing wisdom is that retrofocus wide angle lenses will perform better with the NEX 7. The G did of course require "cornerfix" but with the lightroom plugin, this is pretty painless.
Here's the before and after on the G21 image:
Next, I will have to compare the results between the 7 and 5n to determine how I will actually use this lens. I planned on having it permanently mounted to the 5n, but now I think it's at least useable on the 7 and certainly better than either of these SLR options.