Patent ID: 6954222

Claim:
A manufacturing method of a scanning optical system including a light source for emitting a laser beam, a polygon mirror for scanning the laser beam in a main scanning direction by reflecting the laser beam with reflecting surfaces while revolving around its central axis in a fixed direction, and an imaging optical system including a plurality of lens surfaces for converging the laser beam reflected and scanned by the polygon mirror on a target surface, the method comprising: determining whether a following conditions (1) is satisfied: H /2>|2 βD ( D−Rz 1 )/ Rz 1 | (1) where, “H” denotes a width of each reflecting surface of the polygon mirror in an auxiliary scanning direction perpendicular to the main scanning direction, “β” denotes an incident angle [radian] of the laser beam on the reflecting surface of the polygon mirror in the auxiliary scanning direction, “D” denotes a distance between the reflecting surface of the polygon mirror and a first lens surface at the front end of the imaging optical system, and “Rz 1 ” denotes a radius of curvature of the first lens surface in the auxiliary scanning direction; and forming anti-reflection coating on the first lens surface only when the condition is satisfied.