A shutter is rotatably mounted in a housing for opening and closing a shutter aperture in the housing. The shutter is coupled to a drive unit for unidirectionally rotating the shutter with the same velocity profile to open and close the shutter aperture during each exposure period. This drive unit includes a drive motor and a control circuit having a source of position and velocity reference data and a feedback control loop configurable for either position or velocity control of the shutter as determined by a control command.