How do you make an opaque projector, or epidioscope, at home?

Question

I remember seeing one at a science fair once and have heard of other people making them. Is it hard? Does anyone have directions on how to do it?

Answer 1

It isn't hard. The question has come up here before.
You need a very bright light, a front surface mirror, a fairly large and long focal length lens (to gather as much light as possible from a fair distance above the paper to avoid distortion and a box to hold the lens and mirror at the top and cover the paper via an opening in the bottom. A place like Edmund Optical on the web will probably have some surplus lens units they will say are suitable for projectors.
If you can set the thing up silly and not for an audience, you can save the front surface mirror by mounting the lens pointing at the paper (like a camera and film) and putting the image on the ceiling or tacking the paper inside the box (hard with a book) and laying the box on its side to put the image on the wall.
The purpose of the mirror is to turn the image from straight off the page to one side, so it is mounted at a 45° angle and the lens looks at the paper through the mirror. Front surface avoids extra reflections, raises the cost and makes it prone to damaging fingerprints.