Patent ID: 7304777

Claim:
An optical scanning apparatus having light source unit, a light deflector having a plurality of deflection surfaces, an incidence optical system for causing a light beam emitted from the light source unit to be incident on the deflection surface of the light deflector in a converged state with a light beam width wider than the width of the deflection surface in a main scanning section, and an imaging optical system for imaging the light beam reflected by the light deflector on a surface to be scanned, wherein the following condition is satisfied: ( 1 - Sk f ) ⁢ δ ⁢ ⁢ L ⁡ [ sin ⁡ ( α 2 - β 2 ) + cos ⁡ ( α 2 - β 2 ) ⁢ tan ⁢ ⁢ β ] < 25.4 3 ⁢ N M where f is the focal length of the imaging optical system in a main scanning direction, Sk is the distance in the main scanning section from the rear side principal plane position of the imaging optical system to an imaging point at which the converged light beam is imaged by the imaging optical system, α is an angle in the main scanning section formed by the optical axis of the imaging optical system and the principal ray of the light beam incident on the light deflector, β is an angle in the main scanning section formed by the optical axis of the imaging optical system and the principal ray of the light beam reflected at any angle by the light deflector, δL is the unevenness amount of the distances, defined in the main scanning section, from the rotation center of the light deflector to the plurality of deflection surfaces, and N M is the number of pixels per one inch in the main scanning direction on the surface to be scanned determined from the resolution of an image in the main scanning direction.