Title: Program-controlled shutter

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Abstract: The invention discloses a program-controlled shutter of the type in which, in response to the brightness of a subject, an electronic control circuit controls the motions of a stepping motor so that a plurality of shutter blades coupled thereto may be opened to define a desired aperture, for a time interval, depending upon the brightness of the subject. The control circuit includes a pulse generator, a circuit for determining the number of pulses to be applied to the stepping motor in response to the brightness of the subject so that the shutter blades may be opened to define an aperture optimum for that brightness, a time constant circuit for determining the exposure time; that is, the time interval from the time when the shutter blades begin to open to the time when they are closed again as a function of the aperture defined depending upon the brightness of the subject, a circuit for changing the time constant of the time constant circuit depending upon the opening pulses applied to the stepping motor, a circuit for causing the stepping motor to close the shutter blades after they are opened to define the desired aperture, a circuit for resetting the above circuits immediately after the shutter blades are closed again, and a circuit for selectively connecting the above circuits to a power supply.


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