Abstract: In one system configuration the size of the horizontal sweep of light valve projection apparatus is regulated from two pulses, one at the start of the sweep and one nominally in the second half of the sweep, wherein the reference signal for determining the regulation pulses is obtained from one of two oscillators. A first keyed voltage controlled oscillator is used as a reference source when color is considered to be a more critical feature and a second free running oscillator is used as a reference source when horizontal size is considered to be a more critical feature, such as when a plurality of side-by-side registered images from a corresponding plurality of projectors are desired. Provision is included for fine adjustment of the horizontal size and frequency of the first oscillator for color control. Operator inputs may be received through an information interface.