LIGHT BEAM SCANNING OPTICAL SYSTEM

PURPOSE:To make correction of the scan speed difference (distort abberation) and a correction of the image surface curvature in aux. scanning direction using a simple optical configuration without provision of ftheta lens, and obtain a good distortion characteristic and good image surface flatness over a wide picture angle. CONSTITUTION:An optical system according to the invention is composed of a semiconductor laser 1, a collimator lens 6, a polygonal mirror 10, No.1 spherical surface mirror 20 which is convex, and No.2 spherical surface mirror 25 which is concave. A light flux emitted from the semiconductor laser 1 is scanned over the reflex surface 10a of the polygonal mirror 10 rotating in the direction of arrow (a), reflected by the convex surface of the No.1 spherical surface mirror 20 and tone convex surface of the No.2 spherical surface mirror 25, and condensed on a photo-sensitive element 30. Because of sphericalness of the surfaces of the two mirrors 20, the image surface curvatures in the main scanning direction and aux. scanning direction are canceled, and the scan speed difference (distort abberation) is also corrected.