Patent ID: 6734890
Filing Date: 2004-05-11
Classification: B41J,G02B

Abstract:
A scanning optical system that emits a plurality of beams to a plurality of surfaces to be scanned, respectively, comprising:a light source that emits a plurality of beams; a polygonal mirror that is rotated to deflect the plurality of beams simultaneously to scan in a main scanning direction, the plurality of beams incident on said polygonal mirror being inclined with respect to each other in an auxiliary scanning direction which is perpendicular to the main scanning direction; an imaging optical system that converges the plurality of beams deflected by said polygonal mirror on the plurality of surfaces to be scanned, respectively, said imaging optical system including a front lens group and a plurality of rear lens groups, all the beams deflected by said polygonal mirror being incident on said front lens group, the plurality of beams passed through said front lens group respectively pass through said plurality of rear lens groups, each of said plurality of rear lens groups being configured to have a shape which is designed in accordance with an angle of a beam incident thereon with respect to an optical axis of said front lens group, wherein each of said plurality of rear lens groups has at least one refraction surface which is expressed by a predetermined mathematical expression, each of said plurality of rear lens groups being configured such that a reference axis of the at least one refraction surface is displaced with respect to a center of a shape of the at least one refraction surface so that shifting amounts of positions where the beams incident on the respective at least one refraction surfaces of said plurality of rear lens groups with respect to the reference axes of the refraction surfaces are different from each other.