Greetings, I've noticed with my 12-40mm Pro lens that the best shots (most sharpness) come when I'm about 100 feet from the subject, shooting at or near 35mm. I can't yet find an optimum distance with my 75mm lens, if there is one. Usually shoot about 1/320 sec. and above and have tried near, medium and far distances. Just can't get a sharp image, even on tripod. Beginning to wonder if I have a bad copy of this lens. Or maybe it's just operator error! Any advice appreciated.