When the trigger button is depressed, a crank rod is pulled by a biasing spring in a first direction from a first to a second position triggering the shutter in the process, and an associated crankwheel drives a gear segment coupled thereto to an angular position engaging a motor-driven transmission, which latter then drives the gear segment, crankwheel and thereby the crank rod in an opposite second direction back to first position, the crank rod resetting the shutter in the process, whereupon the gear segment reaches an angular position once more disengaged from the film-transport motor. A switch-control lever coupled to a perforation feeler keeps a motor-energize switch closed until the feeler enters a film perforation, but a switch-control lever redundantly keeps the motor-energize switch closed under the camming action of the crank rod, whereby if film is present in the camera motor energization terminates when the feeler enters a perforation, whereas if film is not present then, for demonstration purposes, the same operations are performed, but with motor energization terminating in dependence upon crank rod position.