Interesting. Do you know how the backs are controlled? My guess would be that either they use X-synch from the lens to signal the back when capture should commence, or they totally bypass the shutter system of the camera and use their own 'virtual' shutter.
Supposing there's no signal from the camera available. And since it's not a full frame sensor. You have the physical place for an additional optical sensor that could detect when the shutter starts moving.
cheers, caveman
