Optical scanning system and image forming apparatus employing same for electrophoto graphically forming images

摘要

An optical scanning system includes a first lens for receiving a light beam from a light source and allowing the light beam to pass therethrough, and a polygon mirror having at least one reflection surface for deflecting the light beam from the first lens by reflecting the light beam on the reflection surface thereof. A second lens is provided for receiving the light beam from the polygon mirror and focusing the light beam on a first plane to be scanned. The second lens has a first surface facing toward the polygon mirror and a second surface facing toward the first plane. The first surface is of a toric shape defined by rotating, about an axis of symmetry lying in a second plane which contains an optical axis of the second lens and is parallel to a first direction in which scanning takes place, a curve lying in the second plane and having a center of curvature on the optical axis, while the second surface is of a toric aspherical shape defined by a surface-generating profile equation in which terms have respective orders equal to or greater than a fourth order with respect to the first direction. The first and second surfaces of the second lens have radii of curvature R1 and R4, respectively, in the first direction as measured from the polygon mirror along the optical axis. The radii of curvature R1 and R4 have a relationship given by |R4|<|R1|.