Patent ID: 8068265

Claim:
In an optical scanner having a source of a light beam, a rotatable polygonal mirror for deflecting the light beam and an imaging lens system for focusing the light beam deflected by said polygonal minor to form a beam spot on a surface to be scanned, wherein the light beam is incident on the polygonal mirror in a direction inclined relative to an optical axis of said imaging lens system in the main scanning plane, the improvement wherein said imaging lens system comprises a plurality of surfaces having curvatures in a sub-scanning direction which vary continuously along a main scanning direction over an effective area of said imaging lens system and independently of curvatures in the main scanning direction, and wherein the curvatures in the sub-scanning direction are non-symmetrical along a main scanning direction with respect to a sub-scanning plane including the optical axis, and wherein the curvatures in the main and sub-scanning directions are rotationally non-symmetrical with respect to an optical axis of said imaging lens system.