Patent ID: 8217980
Filing Date: 2012-07-10
Classification: G02B,G03G

Abstract:
1. A multi-beam optical scanning device, comprising: light source means; deflecting means configured to scanningly deflect a plurality of light beams emitted from said light source means; and an imaging optical system configured to image a plurality of light beams scanningly deflected by a deflecting surface of said deflecting means, upon a photosensitive drum, wherein each of a plurality of light beams incident on an imaging optical element of imaging optical elements constituting said imaging optical system, which imaging optical element has a largest positive power in a sub-scan direction among the imaging optical elements, is deviated in one direction along the sub-scan direction relative to an optical axis of the imaging optical element having a largest positive power in the sub-scan direction, and the plurality of light beams, when they pass through the imaging optical element having a largest positive power in the sub-scan direction, pass through positions which are spaced apart from each other in the sub-scan direction; wherein at least one surface of the imaging optical element having a largest positive power in the sub-scan direction has a curvature in the sub-scan direction which curvature changes from an axial position toward an abaxial position; wherein when, among the plurality of light beams passing through the imaging optical element having a largest positive power in the sub-scan direction, a light beam which passes through a position furthermost in the sub-scan direction from a meridional of the imaging optical element having a largest positive power in the sub-scan direction is incident on said photosensitive drum, an incidence angle thereof in the sub-scan direction with respect to a surface normal of said photosensitive drum becomes smallest as compared with the other light beam or beams, and wherein, where a maximum angle in a main-scan direction as the plurality of light beams pass through said imaging optical system and incident on said photosensitive drum is denoted by α, a mean of incidence angles in the sub-scan direction as the plurality of light beams are incident with respect to a surface normal of said photosensitive drum is denoted by θ is satisfied.