Patent ID: 7283287

Claim:
A light scanning unit comprising: an optical deflecting element for deflecting a plurality of beams emitted from a light source having a plurality of light outgoing portions; and a scanning optics for focusing the plurality of deflected beams on a to-be-scanned surface and scanning the to-be-scanned surface with the plurality of deflected beams; wherein: the plurality of light outgoing portions belonging to the light source are arrayed substantially on one straight line, and the straight line is inclined with respect to a plane where the plurality of beams emitted from the plurality of light outgoing portions are deflected to scan; a coupling optics for forming the beams emitted from the light source into parallel beams, a cylindrical lens having a positive power and having a generatrix in a direction substantially perpendicular to the plane where the beams are deflected to scan, and a spherical lens having a positive power are disposed in an optical path between the light source and the optical deflecting element in order of increasing distance from the light source; an aperture for limiting diameters of the beams is disposed in a posterior focal plane of the coupling optics; the cylindrical lens and the spherical lens form an afocal system in the plane where the beams are deflected to scan, and the aperture and the optical deflecting element are disposed in a conjugate relationship in the plane where the beams are deflected to scan; an anterior focal plane of the spherical lens and the to-be-scanned surface are disposed in a conjugate relationship in the plane where the beams are deflected to scan; and the following expression is satisfied: M t ≦D/δγ (1) when δ designates a diameter of the aperture in a direction perpendicular to the plane where the beams are deflected to scan, D designates a diffraction diameter of each beam focused on the to-be-scanned surface and scanning the to-be-scanned surface, γ designates an angle between the generatrix of the cylindrical lens and a direction perpendicular to the plane where the beams are deflected to scan, and M t designates a conjugate magnification from the anterior focal plane of the spherical lens to the to-be-scanned surface in the plane where the beams are deflected to scan.