I use a diopter correction eyepiece on my F3, as I hate wearing glasses myself. I often wear sunglasses, and I just tip these up onto my head when I shoot. To make focusing easier, I use a Beattie intense screen, which is brighter, and allows for precise focus. I often shoot fast telephotos (300/2.8-400/5.6) which have a very shallow depth of field even very far out, and I can focus with a decent amount of precision.