Scanning optical system

A laser beam printer employing a scanning optical system for emitting at least one beam scanning in a main scanning direction,

• said scanning optical system 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 said scanning lens having at least one convex surface that has a toric surface having a stronger power in the auxiliary scanning direction than in the main scanning direction,
• wherein one surface of said compensation lens has an anamorphic aspherical surface, said anamorphic aspherical surface being defined as a surface whose radius of curvature in the auxiliary scanning direction at a point spaced from the optical axis thereof is determined independently from a cross-sectional shape thereof along the main scanning direction, said anamorphic aspherical surface satisfying a condition:
• −1.1<rz2/rz1<−0.3,
• wherein, rz1 represents a radius of curvature of said toric surface in the auxiliary scanning direction and rz2 represents a radius of curvature of said anamorphic surface in the auxiliary scanning direction.