Patent ID: 7889408

Claim:
An optical scanning apparatus, comprising: a light source unit; a deflection unit for deflecting a light beam (Ray 1 ) emitted from the light source unit for scanning; and an imaging optical system for imaging, on a surface to be scanned, the light beam (Ray 1 ) deflected by a deflecting surface of the deflection unit, wherein the imaging optical system comprises, in an optical path in the following order from a side of the deflection unit: an imaging optical element (G 1 ); a first reflecting mirror (M 1 ); and a second reflecting mirror (M 2 ), wherein the second reflecting minor (M 2 ) is disposed, within a sub-scanning section, between the deflection unit and the imaging optical element (G 1 ) in a direction of an optical axis of the imaging optical system, and wherein the second reflecting minor (M 2 ) and the imaging optical element (G 1 ) overlap each other in a sub-scanning direction within the sub-scanning section, and the following conditional expression (1) is satisfied: A ⁢ ⁢ TAN ⁡ [ { 0.55 × h - L ⁢ ⁢ 2 × tan ⁡ ( α ) - σ } L ⁢ ⁢ 2 - L ⁢ ⁢ 1 ] < θ < A ⁢ ⁢ TAN ⁡ [ { h - L ⁢ ⁢ 2 × tan ⁡ ( α ) - σ } L ⁢ ⁢ 2 - L ⁢ ⁢ 1 ] ( 1 ) where α denotes an oblique incident angle of a principal ray of the light beam (Ray 1 ) in the sub-scanning direction, which enters the deflecting surface of the deflection unit from a direction oblique to the optical axis of the imaging optical system within the sub-scanning section; L 1 (mm) denotes an interval in the optical axis direction of the imaging optical system, between a deflection-for-scanning point O and an optical surface on the surface-to-be-scanned side of the imaging optical element (G 1 ), L 2 (mm) denotes an interval in the optical axis direction of the imaging optical system, between the deflection-for-scanning point O and a reflection point P of the first reflecting minor (M 1 ); h (mm) denotes a length of the imaging optical element (G 1 ) in the sub-scanning direction; σ (mm) denotes an interval in the sub-scanning direction between the deflection-for-scanning point O and a profile center C of the imaging optical element (G 1 ); and θ (degree) denotes an angle, in the sub-scanning direction, between the principal ray of the light beam (Ray 1 ) reflected by a reflection surface of the first reflecting mirror (M 1 ) and a plane perpendicular to a rotational axis of the deflection unit.