Patent ID: 8400699

Claim:
An optical scanning device, comprising: light source means; deflecting means; an input optical system configured to direct a light beam from said light source means onto said deflecting means; and an imaging optical system configured to image a light beam scanningly deflected by a deflecting surface of said deflecting means, upon a scan surface to be scanned, wherein, in a sub-scan section, a light beam directed from said input optical system toward the deflecting surface of said deflecting means is incident thereon at a finite angle with respect to a plane which is orthogonal to a rotational axis of said deflecting means, wherein said imaging optical system includes at least one molded imaging lens, wherein a shape within a sagittal section of at least one lens surface, of lens surfaces of said at least one imaging lens, is non-arcuate, and a sagittal curvature in a light beam passage region has an extreme value, and wherein, when N denotes a value which is obtainable by converting a difference between the sagittal curvature at a passage position of a principal ray of a light beam and the sagittal curvature at a central position of the lens surface, into a Newton number with respect to a 3 mm width, within the sagittal section, the shape of said at least one lens surface of said imaging lens in the sagittal section satisfies a condition 0.7 <N< 10 over the whole region in a main-scan direction in which the light beam passes.