Abstract: A dynamic shutter mechanism for use with a still or motion video camera which is operable at variable shutter speeds to capture high speed events. The shutter mechanism includes a pair of apertured shutter discs which are independently driven by separate motors. Phase lock loop control circuits lock the speed and phase of each disc to the vertical and horizontal sync rates of the video camera. The video signal produced by the video camera produces a control signal which is indicative of the intensity of light of a captured scene. The control signal controls the speed of the shutter mechanism by changing the relative rotational position of the shutters and consequently the relative exposure aperture. In a preferred shutter mechanism the shutter discs are mounted coaxially and are driven by coaxial disc motors.