I've made a pinhole from a Nikon 35mm body by taking the backing paper from 120 film, taping it over the lens opening in the body and punching a hole in it with a pin. I used 400 speed film and made exposures of 2-5 seconds in sunlight and it worked. Body caps work fine too if you happen to have one, but if not, improvise -- it's more fun experimenting anyway. Have a good time!