07-09-2013, 03:07 AM
Hi Frank, some of the old lenses have aberrations in the center as they are not optimized for the light reflected from the sensor. Check Tom Hogan's website, he explains it in more technical terms... I don't have the exact link, sorry. I used to rent this lens before, but never notice the issue. My impressions are that the lens is sharp at f 2.8, but it shows purple fringing, which is quite visible.