The Canon FD 20mm 2.8 is an affordable wideangle lens (around $200 mid 2015) which performs well on the Alpha 7. I have owned and used my copy for more than a year now and wanted to share my experience with you.
All ratings are based on my experience with these lenses on my fullframe Sony Alpha 7.
Minolta MD FISH-EYE Rokkor 16mm 1:2.8 (3-3.5/5)
f/2.8: The center is excellent, and most of the image sharp enough, midframe sharpness is actually lower than near corner sharpness wile the far corners are unsharp. Vignetting is surprisingly low.
f/5.6: noticeably better than f/4, most of the image is very sharp, only the far corners are unsharp
f/11: very good sharpness across the frame. Flare resistance is average and CA pronounced.
A rather heavy lens with integrated filters and lens hood. Built quality is excellent
Fisheye lenses are very hard to master, I wasn’t really succesfull at it. But this is a good lens, so good in fact that it also came in Leica R-mount and the same optical design is still used by the current Sony 2.8/16 Fisheye.
There is a younger MD version which is supposedly not as good.