Patent ID: 8711457

Claim:
An optical scanner comprising: a light source that emits a light; a deflecting unit that deflects and scans the light in a main scanning direction; a shielding rib disposed near the deflecting unit and between the light source and the deflecting unit, the shielding rib being formed with a first aperture that allows the passage of the light from the light source while restricting a width of the light; and a scanning optical system that forms images on a photosensitive surface of a photosensitive member with the light deflected and scanned by the deflecting unit; wherein: the deflecting unit includes a polygon mirror having a plurality of reflecting surfaces that reflect the light from the light source, the polygon mirror rotating around a rotational axis; and the light source, the scanning optical system, and the polygon mirror are arranged such that the light from the light source that is incident on the polygon minor is reflected from a first one of the reflecting surfaces of the polygon mirror other than a second one of the reflecting surfaces that is oriented orthogonal to an optical path of the incident light, and that the reflected light forms an image on the photosensitive surface; the scanning optical system includes an fθ lens that converts the light deflected and scanned by the deflecting unit into a light scanned at a constant speed over the photosensitive surface; and the light source, the scanning optical system, and the polygon mirror are arranged to satisfy the equation: α/2 +W /(2 *f )−2 π/N> 0 wherein: α is an angle formed by an optical path of the light from the light source to a point of reflection on the reflecting surface of the polygon mirror and a straight line connecting the point of reflection with a center point in the main scanning direction of an effective scanning region in which the light is scanned over the photosensitive surface; W is ½ the width of the effective scanning region in the main scanning direction; f is a focal length of the fθ lens; and N is the number of reflecting surfaces.