Yea, I'd go with Michelle's suggestion. Try them out in a store. Each manufacturer has a different formula for figuring out which diopter you need. However, someone correct me if I'm wrong, Diopters are meant to be used -with- your eyeglasses or contacts. Diopters aren't like glasses that compensate for things like myopia or astigmatism. They compensate for the difference between seeing normally (with your glasses/contacts) and seeing through the camera. I think that's right, since all the diopter formulas I've ever seen took your prescription and subtracted some number from it to get the diopter you'd need. -=>Donald