| 摘要 |
An optical scanning apparatus includes: a rotational polygonal mirror on the the side of which a plurality of reflecting surfaces are provided, the reflecting surfaces deflecting a beam of incident light in the primary scanning direction at a substantially equal angular velocity; a first optical system for forming a beam of light sent from the light source into an image long in the primary scanning direction in such a manner that the formed image strides over the plurality of deflecting surfaces; and an f theta lens for converging the beam of light deflected on the deflecting surface at a position close to the surface of the photoreceptor drum so that a spot of light irradiated on the photoreceptor drum can be moved at a substantially equal speed. In the optical scanning apparatus, the angles alpha and beta satisfy the following expression: (cos (( beta + alpha ) DIVIDED 2)) DIVIDED (cos (( beta - alpha ) DIVIDED 2))>/=0.75where alpha is the maximum deflection angle of the deflection luminous flux with respect to the optical axis of the f theta lens, and beta is an angle formed between the optical axis of the first optical system projected in the subsidiary scanning direction and the optical axis.
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