Patent ID: 8217980

Claim:
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 0 , a pixel density is denoted by DPI, an amount of jitter in the main-scan direction caused, when the plurality of light beams pass through the imaging optical element, by the passage of the plurality of light beams through positions which are spaced apart from each other in the sub-scan direction is denoted by ΔJ (mm), a relation  Δ ⁢ ⁢ J × DPI 25.4 + sin ⁢ ⁢ θ 0 ⁢ tan ⁢ ⁢ α  ≤ 0.1 is satisfied.