Patent ID: 7561319

Claim:
An optical scanning device, comprising: a light source device; a rotary polygonal mirror having a plurality of deflecting surfaces configured to scanningly deflect a light beam emitted from a light emitting member of said light source device; an input optical system configured to direct the light beam emitted from the light emitting member of said light source device to a deflecting surface of said rotary polygonal mirror; and an imaging optical system configured to image the light beam scanningly deflected by the deflection surface of said rotary polygonal mirror, on a scan surface to be scanned; wherein in a sub-scan section the deflecting surface of said rotary polygonal mirror and the scan surface are placed in a conjugate relationship with each other, wherein in a main scan section the light beam incident on the deflecting surface of said rotary polygonal mirror has a beam width narrower than a width of the deflecting surface of said rotary polygonal mirror, wherein said imaging optical system includes at least one imaging optical element and wherein at least one optical surface of said at least one imaging optical element has a shape in the sub-scan section which shape comprises a non-arcuate shape including an aspherical coefficient of quartic or higher order, wherein the aspherical coefficient of quartic or higher order changes in the main-scan direction and from a scan central portion of the imaging optical element to a scan end portion of the imaging optical element, wherein, in the non-arcuate shape of the imaging optical element in the sub-scan section and at the scan central portion in the main-scan direction, an absolute value of a curvature radius at an end portion of the imaging optical element in the sub-scan direction is larger than an absolute value of a curvature radius at a central portion of the imaging optical element in the sub-scan direction, and wherein, in the non-arcuate shape of the imaging optical element in the sub-scan section and at the scan end portion in the main-scan direction, an absolute value of the curvature radius at the end portion of the imaging optical element in the sub-scan direction is smaller than the absolute value of the curvature radius at the central portion of the imaging optical element in the sub-scan direction.