Find a large box. Size is only important to give room for a pinhole that’s not obstructed by your head or your camera.
Cut a small hole near the center of the short side.
Set your camera lens face down near the edge and draw an outline around your lens.
Cut out that hole. You’ll use that for your lens or your eye.
Pop a little pinhole in the center of a small piece of aluminum foil. Use a pin to make that hole. The cleaner and rounder the hole is- the sharper your viewing will be. Don’t dig around – a tiny, pure hole is what we want. Tape the foil over your centered hole.
Tape a piece of paper inside the box opposite of your pinhole. This is your projector screen.
I’ll use a sheet of nice bright white photo paper.
Seal up the box, being sure to tape up all the corners. you won’t want any stray light to pollute your projection.
Bigger boxes make for a larger projection. Bigger boxes mean that the projection is farther from your eye. No matter what size box, the image will visibly look the same to you.