Optics demonstrations with an overhead projector

The idea for these demonstrations occurred when while preparing a demonstration for a course, I realized that I was reinventing the overhead projector. Because the projector is so readily available, I undertook to see how much could be done with it using additional inexpensive and readily available materials. No fundamental novelty is claimed, since projectors have been around for at least 300 years, and people have probably tried most everything. Moreover, most of these demonstrations are variations on classics that can be done in many ways. The purposes of this work are to point out just how much can be done so easily on the projector, to provide guidance in optimizing the demonstrations, and to provide information on vendors and useful materials. Most important, I hope to encourage people to do demonstrations. The projector is obviously ideal for many demonstrations of human vision, but I have not undertaken these, leaving them to specialists in the field.