A program shutter has a plurality of shutter sectors driven in opening and closing directions by a reversible stepping motor to define a lens aperture during an exposure operation. An arithmetic circuit calculates an exposure amount corresponding to the brightness of the object being photographed, and a counting circuit outputs a pulse count corresponding to the number of steps through which the stepping motor should be rotated based on the calculated exposure amount. A pulse circuit produces driving pulses equal in number to the number of steps determined by the counting circuit, and a time circuit determines the ON/OFF periods of the driving pulses based on the calculated exposure amount. The driving pulses are applied to the stepping motor through a driving circuit to accordingly drive the shutter sectors in the opening and closing directions during the exposure operation.
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.
An optical apparatus includes a light quantity adjusting member arranged to vary a quantity of light when the member is moved, a stepping motor arranged to drive the light quantity adjusting member, a luminance detecting part for detecting the luminance of a shooting object on the basis of the quantity of light obtained through the light quantity adjusting member, and a control circuit for driving and controlling the stepping motor in such a way as to make a difference between the luminance of the object detected by the luminance detecting part and a target luminance value smaller, the control circuit being arranged to change the driving speed of the stepping motor to be lowered when the object luminance comes near to the target luminance value.
