when a stepping motor is used as a driving source for a shutter device , if the stepping motor loses synchronization because of variations in load during driving or the like , it becomes unable to rotate a driving ring at that time , and this disables an exposure operation . in a first zone where a driven member is driven , but a light shielding member remains in a closed state or an open state , the motor drives the driven member in open - loop driving mode . in a second zone where the driven member is driven , and thus the light shielding member moves to the closed state or the open state , the motor drives the driven member in feed - back driving mode .