There are three versions of this lens. I am testing version two. It is sharp wide open with excellent contrast. Contrast and sharpness are excellent across the entire frame at all apertures. There is some vignetting from f2.5 - f4. Fringing can be seen in high contrast areas at f2.5. Distortion is very low. Colors are accurate. It has a long fous throw which allows for precise focusing. Focus dampening is smooth and precise. Aperture settings click at full stops from f2.5 thru f16. This lens is noticeably better than the Rokkor SG 28mm f3.5 and the MD 28mm f2.8.