Abstract: Variation in the width of the shutter opening in a motion picture film copying machine is rapidly effected to control the amount of light passed through the shutter for transmission of the image from the master film onto the blank sensitized film running in registry therewith. Such rapid change in size of the opening in the shutter is effected by presetting the predetermined fixed extent of opening or closing of the opposed shutter halves in advance and shifting these halves to the scheduled predetermined position on signal from a sensor associated with the moving master film strip.