Patent ID: 7639412

Claim:
An optical scanning apparatus comprising: a light-source unit; an incident optical system for directing light beams emitted from the light-source unit to a deflecting unit; and an imaging optical system for guiding the light beams deflected from the deflecting unit to a surface to be scanned, wherein the direction of the light beams emitted from the light-source unit and entering a deflection plane of the deflecting unit is inclined with respect to the deflection plane in the sub-scanning section, and wherein the imaging optical system comprises a toric lens whose power in the main scanning direction is different from that in the sub-scanning direction; and in which the toric lens has a first toric surface and a second toric surface, the curvature centers of the meridians of the first toric surface of the toric lens connected to form a curved line are located in a common plane Ha, the curvature centers of the meridians of the second toric surface connected to form a curved line are not located in a common plane, the generatrix of the second toric surface of the toric lens formed by connecting the vertexes of the meridians in every area of the second toric surface is curved in the sub-scanning direction, and the degree of curvature ΔA of a generatrix of the second toric surface satisfies the following conditions: 0 ≦ΔA ≦ 1 (mm) Δ A =|Z max − Z min|(mm), where Zmax and Zmin indicate the maximum value and the minimum value, respectively, of the central positions of the curvature radii of the meridians of the second toric surface in the Z direction when the point of intersection of the optical axis of the second toric surface and the curved surface of the lens is defined as the origin, and an axis orthogonal to the optical axis in the sub-scanning section is defined as the Z axis, and the curvature radii R of the meridians of the second toric surface, over the entire area of the lens of use, are in the following range: 22 mm< R <-11 mm.