Patent ID: 6130768
Filing Date: 2000-10-10
Classification: G02B

Abstract:
A scanning image forming lens in an optical scanning apparatus for optically scanning a surface to be scanned at a constant velocity by deflecting a luminous flux formed as a linear image in a direction corresponding to a main scanning direction via an optical deflector having a deflecting reflective plane located near where the linear image if formed so as to transmit the deflected luminous flux through the scanning image forming lens and to condense the deflected luminous flux on the surface to be scanned as a light spot, the scanning image forming lens comprising:a first lens located at a side of the optical deflector, the first lens being a positive meniscus lens with a concave surface facing toward the optical deflector and having a co-axial aspherical shape at both surfaces thereof; anda second lens located at a side of the surface to be scanned, the second lens having an optical axis and being symmetrical relative to the optical axis, the second lens having a non-arc shape in the deflected plane at least at one surface of the second lens, and the at least one surface of the second lens having the non-arc shape being shaped such that a radius of curvature in a sub scanning cross-section changes in a direction corresponding to the main scanning direction such that a curvature center line plotting a curvature center in the sub scanning cross-section of the at least one lens surface in the direction corresponding to the main scanning direction is a curve which is different from the non-arc shape in the deflected plane, and at least one surface of the second lens has a concave shape in the sub scanning cross-section.