Abstract: A motor driving the shutter of a motion-picture camera is intermittently energizable under the control of two time-constant networks triggering respective pulse generators of the one-shot type, the first time-constant network including a photoresistor to measure an exposure interval dependent upon luminous intensity, the second time-constant network being adjustable to establish a selected recurrence period. With the shutter arrested in an unblocking position at the start of an operating cycle, which coincides with the beginning of an exposure interval, a pulse from the first generator releases the shutter for movement into a blocking position until a pulse from the second generator restarts the cycle by letting the shutter return to its unblocking position.