A shutter mechanism, employed in a camera, is provided having a pair of blade members pivoted about a point. The blade members are moved between a position where the light path is completely shielded and another position where light is allowed to pass through. Each of the blade members has a gear portion, and gear members transmit a driving force from a pulse motor to the gear portions to move the blade members toward and away from each other. Further, the width of the pulses to be applied to the motor is varied corresponding to the revolution of the motor, and the phase of the pulse is temporarily reversed corresponding to certain aperture values. Furthermore, a reverse rotation pulse is applied to the motor at the end of the revolution of the motor for preventing the motor from overrunning. When the blade members are moved to form the opening corresponding to a predetermined aperture value, another pulse is applied to the motor for the period of time corresponding to exposure time in order to hold the opening for the period of time.

A program shutter for automatic exposure control including a forwardly/reversibly rotatable step motor for opening and closing a shutter to effect automatic exposure in the control circuit for controlling the operation of the step motor. The control circuit includes stored predetermined shutter mechanism characteristic values. The reversible stepping motor varies the lens aperture in response to a pulsed lens control signal generated by the control circuit. The corresponding value associated with each pulse is varied to be synchronized with and dependent on the shutter mechanism characteristic values and correspondingly varies the rotational power of the reversible stepping motor to overcome detrimental inherent shutter mechanism characteristics and to increase the response efficiency of the shutter.