Abstract: A motion picture projector substantially free of picture jump comprises a gate assembly having a projection aperture and a light source for projecting light through the aperture and focusing lens and onto a screen. The film is intermittently advanced through the gate assembly by an intermittent sprocket which is intermittently rotated by a modified Geneva mechanism. The Geneva mechanism comprises a star wheel having a plurality of radially extending slots separated by curved surfaces. A rotating cam has a ring which slidably engages the curved surface of the star wheel and a pin which engages the slots as the cam rotates, rotating the star wheel a fraction of a rotation for each full rotation of the cam. The cam has a tension area adjacent the pin and a relief area remote from the pin. The tension area engages the curved surfaces of the star wheel closely, preventing backward rotation.

Abstract: A projection screen including a rectangular film having a back surface, a front surface and a periphery, a support frame and chamber connected to the periphery of the film for defining the shape of the periphery of the film, a device for creating a pressure differential between the front surface and the back surface of the film, a sensor for sensing the position of the film and indirectly sense the pressure differential on the film and a controller for controlling the device for creating the pressure differential in response to the sensor such that the position of the film is a predetermined position as a result of some pressure differential whereby the shape of the film is set by the shape of the frame which is connected to the periphery of the film and by the predetermined position of the film resulting from the pressure differential.