Bought a red ring version for canon for about 230$ used.First thing I noticed is that 14mm on a full frame is considerably wider than 10mm on a crop.At f2.8 my copy is not usable. The sharpness gets much better at f4.
Decent sharpness when stopped down, dramatically wide on a ff
Inaccurate focus scale. It seems the lens barrel "breathes", giving you sharpness inconsistency from shot to shot