Optical scanning apparatus and scanning image forming lens

Abstract

An optical scanning apparatus includes a light source for outputting light, a first lens system arranged to receive the light output from the light source and to transmit a light flux therefrom, an optical deflector arranged to receive the light flux from the first lens system and having a deflecting reflective plane to deflect the light flux from a surface therefrom and a second lens system arranged to receive the light flux deflected from the optical deflector and to condense the deflected luminous flux into an optical beam spot on a surface to be scanned so as to form images having image heights, the luminous flux condensed by the second lens system into the optical beam spot including an optical beam waist. The second lens system has a scanning and image forming element including at least one surface including a plurality of portions each having a non-arc shape in a sub-scanning direction such that at least two of the non-arc shapes are different from each other and such that an effective writing width W and a width Fs of the sub-scanned image-surface curvature located within the effective writing width satisfies the condition Fs/W<0.005. Alternatively, the second lens system includes a scanning and image forming element including at least one surface including a plurality of portions each having a non-arc shape in a sub-scanning direction such that at least one lens surface is a sub non-circular arc surface and a shape in a sub-scanning cross section of the sub non-arc circular shape is a non-arc shape and the non-arc shape changes in accordance with a position of the sub-scanning cross section in the main scanning direction.

Dependencies are inferred from the claim text.