Scanning optical system

A scanning optical system for emitting a plurality of beams scanning in a main scanning direction, comprising:

• a light source that emits the plurality of beams;
• a polygonal mirror that rotates and deflects the plurality of beams to scan in the main scanning direction within a predetermined scanning range;
• and
• an imaging optical system that converges the plurality of beams deflected by said polygonal mirror to form the plurality of beam spots on surfaces to be scanned, said plurality of beam spots scanning in the main scanning direction on the surfaces to be scanned, wherein said imaging optical system has:
• a scanning lens group;
• and
• a plurality of compensation lenses which are provided for the plurality of beams, respectively, and are provided on the surfaces side with respect to said scanning lens group, said compensation lenses compensating for curvature of field,
• wherein said light source is arranged such that the plurality of beams emitted by said light source are incident on the polygonal mirror from the outside of the predetermined scanning range in the main scanning direction and are incident on said polygonal mirror with the plurality of beams being inclined in an auxiliary scanning direction with respect to a plane perpendicular to a rotational axis of said polygonal mirror, the auxiliary scanning direction being perpendicular to the main scanning direction,
• wherein at least one surface of said scanning lens group has a first anamorphic surface, power of said first anamorphic surface in the auxiliary scanning direction is distributed asymmetrically in the main scanning direction with respect to an optical axis of said scanning lens group,
• wherein power of each surface of said compensation lenses in the auxiliary scanning direction is distributed symmetrically with respect to a center position of said each surface.