I purchased a used Mamiya 35mm AF lens for my 645AFDIII about 18 months ago and failed to test lens as well as I should have when it arrived. While zooming in 100% on an image recently I noticed what looked like a small focus smear in the center 20% area of the lens. I sent the lens to Capture Integration who sent it to Mamiya/Phase One service in Japan. Prognosis is that there is fungus growth on one of the lens elements. Since I keep all my equipment in environmentally good/dry conditions and since no other lenses have issues I can only guess the lens had this issue when I purchased it. A word of caution for all to test new and used equipment rigorously when you take possession.