I just had an idea after seeing something in the Make blog about re-using antique lenses with new cameras. I'm not linking to it. I can't even believe they took apart such a beautiful old Zeiss. Nicole had one that she got in Germany, but alas, it got "lost" in the mail. Anyway, I think it might be better to go about this in the other direction.
The Zeiss and a lot of other old cameras use medium format film. The film is 6 cm wide and the part exposed by the camera can be 4.5 cm or 6 or some other sizes. This means that any medium format camera can fit in a thin addition of 4.5 x 6cm or larger. So instead of taking apart a beautiful old film camera, why not disassemble a digital camera?
My first thoughts on how to do this are that I would want to avoid modifying the holding camera. So in order to signal to my digital module that it's time to take a picture, I would use a light sensor as a switch. The shutter opens, the sensor says, "ooh, light!" and snaps a photo.
That doesn't leave much time for light metering inside the electronic bits. Would this work as a DIY project?
I bet somebody already did this. I just stumbled across a whole bunch of stuff at bamboo cargo bikes tonight. Duuuude, I totally wanted to do that.