Originally posted by unixrevolution ...And why does the digital portion need to know exactly when the shutter is opening or closing? Film doesn't.
Ummm...film sort of does. On most 35mm cameras, the shutter will not fire until the film has been advanced.
There is a complex series of events that happen with a digital camera's electronics when an exposure occurs. Assuming that the sensor is "hot on", the shutter open part is not an issue unless you are using live-view. The problem comes after the shutter closes. The sensor "state" must be captured to a temporary memory buffer for image processing and the sensor re-initialized for the next exposure. On legacy film cameras, there is no wire or connection to provide the information on when this should be done. Medium format digital backs have proprietary contacts to communicate with the camera or do so using a cable to the PC flash sync (perhaps a good solution here) or tapping via cable into existing data connections on the camera body.
Oh...and one other issue regarding a digital back adapter for 35mm film cameras. There is little standardization, even within a brand or camera series, on the size and shape of these backs. Remember, they must fit perfectly to be light-tight. Any digital solution would have to be a kit that cannibalizes an existing back.
Steve