Patent ID: 7557974

Claim:
An optical scanning apparatus, comprising: a light source unit; an incident optical system for guiding a light beam emitted from the light source unit to a deflecting unit; and an imaging optical system for imaging the light beam deflected by the deflecting unit onto a surface to be scanned, wherein the following conditions are satisfied, 0.85≦ W/ 2 L , and 0.4< Sd/L< 0.9, where W (mm) represents an effective scanning width on the surface to be scanned, L (mm) represents an interval in an optical axis direction of the imaging optical system between a deflecting surface of the deflecting unit and the surface to be scanned and Sd (mm) represents an interval between the deflecting surface of the deflecting unit and a natural convergent point, wherein the imaging optical system is constituted by a single imaging optical element LR, and wherein a scanning field angle region changes from a region in which |θ 1 |<|θ 3 | and |θ 2 |<|θ 3 | are satisfied to a region in which |θ 1 |>|θ 3 | and |θ 2 |>|θ 3 | are satisfied as an absolute value of the scanning field angle (|θ 1 |) increases, where in a main scanning cross section and for a finite scanning field angle θ 1 (deg.) (|θ 1 |>0), θ 2 (deg.) represents an angle formed between a principal ray of a light beam incident on the imaging optical element LR and an optical axis of the imaging optical system and θ 3 (deg.) represents an angle formed between a principal ray of a light beam emitted from the imaging optical element LR and the optical axis of the imaging optical system.