hummm. i used diopter lenses for years before i realize they waz absolutelky useless for my astigmatism. I've a really bad vision from the right eye (-9.5) and a really good one from the left (more than 12,25), in some cases my left eye weakens and my vision falls; this means that many times my own eyes dof and distance evaluation distorts... to not mention when my left eye simply gives up and all blurs =) Not funny ... when i was younger (8-9 yo) my vision with the right eye was really better and for some times i've tried dioptic correction lenses but i was forced to use glasses anyway to shot. The Diopter lenses cannot correct an astigmatic issue as zhounder said. The trick is to choose tha most comfortable glasses (with really light mount) and an High Eyepoint camera. Most of the recent SLR cameras of middle-high and high level has an HP pentaprism. some old ones can be refitted if the body has an interchangeable pentaprism (a Nikon F3, for example, has an HP pentaprism as an option; Nikon F5 has an HP pentaprism for itself... and F100 too i think). I dunno what kind of camera you have... a great help can come from your camera's focal screen... for example i've always used as a reference my Nikkormat stygmometer to be sure of the focus when my eye was tired. A nice solution (if you have enough money) is buy a telemeter camera... focus is a lot easier coz you see 2 images and you have to make them surmount to have the right focus on the scene...