This may be old news, but I discovered that all rear-projection TV's contain a fresnel lens that is the size of the screen. As an added bonus, most also contain a first-surface mirror. (Handy for situations when you have a very short throw but want to use a projector). Anyway, I am planning on getting hold of a fresnel tonight, and am wondering what the size rule of thumb is - should the lens be the exact same size as the screen?
