Patent ID: 7375869

Claim:
A scanning optical system, comprising: a light source configured to emit a plurality of beams; a deflecting device configured to deflect the plurality of beams simultaneously to scan in a main scanning direction; and an imaging optical system configured to converge the plurality of beams on a plurality of target surfaces to form a plurality of beam spots scanning on the plurality of target surfaces, respectively, wherein the imaging optical system includes: a first lens comprising a single lens element arranged on a common optical path along which the plurality of beams deflected by the deflecting device proceed; and a diffractive lens structure formed on a target surface side surface of the first lens, wherein a base curve of the lens surface on which the diffractive lens structure is formed has a rotational symmetry axis extending in the main scanning direction, the curvature of the lens surface taken along the main scanning direction and the curvature taken along an auxiliary scanning direction are different from each other; and wherein the base curve on which the diffractive lens structure is formed is a toric surface, of which a shape along the auxiliary scanning direction is convex on a deflection device side.