The other day I created a pinhole camera from an old Russian SLR I found at a market. It was quite easy to convert. It's just a matter of removing all the stuff from inside so you're left with a shell. The results are really interesting, just going round my garden taking exposures of different lengths to see what happens, but I think the whole that I drilled through the lens cap needs to be ever so slightly bigger. I think too big will let too much light in. I'll play around with it and see. I want to see what happens with colour film too, but I think I need to sort out the size of the pin hole first.