Patent ID: 7433095

Claim:
A reflective scanning optical system for dynamically deflecting a laser beam emitted from a light source by each reflecting surface of a polygon mirror revolving at a constant angular speed and thereby scanning the laser beam on a scan target surface at a constant speed in a main scanning direction via an imaging optical system including a curved mirror for reflecting the dynamically deflected laser beam and an anamorphic lens on which the laser beam reflected by the curved mirror is incident, the laser beam being incident upon each reflecting surface of the revolving polygon mirror and the reflecting surface of the curved mirror at specific angles in an auxiliary scanning direction which is orthogonal to the main scanning direction, wherein the reflecting surface of the curved mirror has positive power in the main scanning direction, wherein the anamorphic lens has positive refractive power in the auxiliary scanning direction, and wherein at least one lens surface of the anamorphic lens is formed as a rotationally asymmetric surface on which slope and curvature of a line of intersection of the lens surface and a plane parallel to an auxiliary scanning cross section, as a plane containing an optical surface reference axis of the lens surface and parallel to the auxiliary scanning direction, change as the plane gets further from the auxiliary scanning cross section in the main scanning direction so that magnification of the imaging optical system in the auxiliary scanning direction for the laser beam will be constant regardless of the angle of deflection by the revolving polygon mirror.