Abstract: An electro-optical light scanning system using a modulated laser illumination source directed upon a multifaceted rotating polygonal mirror or polygon. The mirrored facets reflect the impinging light toward a moving photoreceptor and forms a raster of scan lines as the photoreceptor moves. The system incorporates sensing optics and closed loop electronics for correcting inaccuracies in the position of the reflected light resulting from deflects in the angular relationship between the plane of the facets and that of the rotating axis of the polygon. Such correction is accomplished through use of selectively located reflective and transparent surfaces wherein location of the impinging light may be determined.