Patent ID: 6956686

Claim:
A scanning optical system for emitting at least one beam scanning in a main scanning direction, comprising: a light source that emits at least one beam; an anamorphic optical element that converges the at least one beam emitted by said light source in an auxiliary scanning direction which is perpendicular to the main scanning direction; a polygonal mirror that rotates and deflects the at least one beam emerged from said anamorphic optical element to scan in the main scanning direction; an imaging optical system that converges the at least one beam deflected by said polygonal mirror to form at least one beam spot on a surface to be scanned, said at least one beam spot scanning in the main scanning direction on the surface to be scanned, wherein said imaging optical system has: a scanning lens; and a compensation lens provided on the surface side with respect to said scanning lens, said compensation lens compensating for curvature of field, wherein all surfaces of said scanning lens are rotationally symmetrical, and wherein said compensation lens has at least one aspherical surface, a cross section of said aspherical surface in the auxiliary scanning direction being asymmetrical with respect to the optical axis thereof, a SAG amount defining said at least one surface being expressed by a two-dimensional polynomial.