| 摘要 |
A scanning and image forming lens system in an optical scanning apparatus optical scans a surface to be scanned by deflecting a luminous flux emitted from a light source in a direction corresponding to a main scanning direction via an optical deflector at equiangular velocity. The scanning image forming lens system transmits the luminous flux deflected by the optical deflector so as to condense the luminous flux into an optical beam spot on the surface to be scanned and to scan the surface to be scanned with the optical beam spot. The scanning image forming lens system includes one or more image forming optical elements including at least one lens. At least one lens surface of the at least one lens of the scanning image forming lens system has a non-arc shape in a sub scanning cross section. The non-arc shape changes according to a position in a direction that is substantially perpendicular to the sub scanning cross section such that a positional deviation of the optical beam waist of the deflected luminous flux from the surface to be scanned at each position in the direction perpendicular to the sub scanning cross section, which is caused by a paraxial curvature of field of the scanning image forming lens system in a sub scanning direction, is corrected.
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