I'm toying with building my own medium format camera. It would be designed to shoot long exposure shots, so I don't actually need a very good shutter with it. And since there's no way I can do stuff quickly, I'm figuring that I can just make it simple with no mechanical or electronic automation. A lot of it can be forced to work with sufficent amounts of duct tape, no? A camera's just a light tight box with a lens on one side. First, what do I do about a pressure plate and film feed mechanism? Is this something I can build myself, or is it best to hack up an existing camera to make it? My mental picture is to put the spools recessed behind the pressure plate such that the film is forced between the pressure plate and some rails on top and bottom. To feed on one side, I guess I can use a one-way ratchet, but how much tension do I need to keep on the other side to have a flat film plane? Second, focusing mechanisms... I'm figuring that my lens options are to scrounge either medium format or large format lenses and mount them against a lens board. If I use a medium format lens, most of 'em have a focusing helical that I can use, so I can scale focus off of another camera as long as I get the correct registration distance. But if I use a large format lens, what do I do? Is it possible to derive from an arbitrary lens what the focusing scale would be based on known paramaters? How hard would it be to make the necessary light seals so that I could use it as a view camera without getting light leaks?