A Rotating Lens System for Cine Projection with Continuous Film Transport

Abstract

As a point of departure, the two main methods of film transport in projection systems — intermittent and continuous — are discussed. Their basic conditions and the functions of the shutter are described. With continuous film transport, the projected image must continuously be shifted at the same frame rate as the film and in the opposite direction to its movement in order to obtain a perfectly stable image on the screen. The principle involved is called optical motion compensation. Moving, rotating, or oscillating prisms, mirrors, and lens rings may be used as optical compensators. A brief history of such devices is given. Many of these produced a so-called roving error which arises because a reference point on the film having a fixed position within the frame may not appear absolutely stationary on the screen during all phases of motion compensation. An analytical consideration of the elements and parameters that cause roving error is undertaken. The conclusion is reached that in a motion compensator consisting of a rotating ring of object lenses, the introduction of a certain amount of image distortion — by means of appropriate lens design — may compensate for the roving error and yield a steady image, free from blur.