I've built a 5"x7" sliding box camera from black foamcore, which uses a foamcore sandwich film holder; since I only made 1 holder, it's essentially a 1-shot camera. But I can use a regular sized changing bag in the field, since the entire camera doesn't have to go inside the bag, only the holder.
The film holder is a sandwich of 4 layers of 1/4" foamcore, with a foamcore darkslide that is designed to stay in the side slot of the holder; you pull it out to a preset stop point, and the darkslide maintains a light-tight seal against the body of the camera. It also has a removable view screen, built to the same size and thickness as the film holder, but which uses a thin sheet of clear plastic, which has been sanded down on one side; it works remarkably well for previewing the scene.
There is a remarkably good resource for camera-building ideas, the George Eastman online collection, at this link.
Here's an example of a sliding box plate camera from their collection, who's general concept I used as inspiration for my foamcore camera. I used an old sheet of plywood for the bottom plate, to which the front half of the camera body is permanently affixed. The front half needs to be the larger of the two halves of the nesting boxes. The back half nests inside the front half, such that any light leaking through the seal won't shine directly onto the film. You'll notice that the back half of the box rests on the bottom platform as it slides, such that it will stay sufficiently aligned with the front box to prevent light leaks. This is an especially important feature to incorporate in your camera if you expect to be extending the boxes out near the limit of their nesting, where there is minimal contact between the side walls; you want the bottom platform to support the rear half, preventing it from further movement.
If you line the inside of the box with black adhesive craft felt (from stores like Hobby Lobby or Michael's) it'll totally dampen any light reflections. The black felt is also a good material to use on the side walls of the box halves, where they slide together, providing for a light-tight but dynamic seal.
PS: My avatar was a self-portrait onto Efke's direct positive paper using this camera. I was using a 150mm binocular lens as the taking lens, nearly wide open around F/4.5, with a simple lens cap shutter.
Last edited by Joe VanCleave; 08-29-2009 at 01:23 PM. Click to view previous post history.