Synchronizing light beam detector

Abstract

A synchronizing light beam detecting apparatus is provided in a light scanning system, such as a laser printer, which includes a light source for emitting a light beam, a polygonal mirror driven to rotate for deflecting the light beam over a predetermined angle repetitively, and a f.theta. lens for focusing the deflected beam along a predetermined imaginary scanning line. The detector includes a cylindrical lens for receiving the light beam passing through the f.theta. lens and picked up at a predetermined position and a detector surface for receiving the light beam passing through the cylindrical lens. A conjugate relation is established between the light beam deflecting point at the polygonal mirror and the detector surface so that the effect of inclination of a mirror surface of the polygonal mirror is cancelled. The detector surface is so located that the light beam is formed thereon only by the image-forming action of the f.theta. lens so that the effect of differences in the beam deflecting point at the polygonal mirror from one mirror surface to another is advantageously cancelled.

Dependencies are inferred from the claim text.