For a class, I need to design a basic overhead projector. I know a little bit about optics from an algebra based physics class I took a while back, but I don't remember most of the specifics, such as what kinds of lenses flip objects before and after their focal points. I'm also not sure what effect the directional mirror will have on the image. Here's what I've got so far, we get bonus points the more detail we are able to put in so I'm going to toss in some calculus dealing with the reflective properties of a parabola rotated about it's axis. I'll have a concave mirror in the bottom, the mirror's dimensions will be provided by rotating a parabola around it's axis. A light source will be located at it's focal point, according to what I remember from physics and my calc book, this will direct the light parallel to the axis of the parabola. At the top of the base I'll have a fresnel lens. This will angle the light to a focal point. At the head of the device I'll have a plano convex lens, rounded side down to collect the light and convert it back to parallel before striking the mirror and going on to the screen. Sound right so far? My question is, do I want the focal point of the first lens to be between the lenses or past the second lens? Also, I'm having a hard time visualizing what effect the mirror is going to have on the image, turn it upside down? make it backward? Thanks for any help.