Patent ID: 7215354

Claim:
A scanning optical system condensing a beam deflected by an optical deflector so as to form a beam spot on a surface to be scanned, comprising two lenses, wherein: a lens on the side of optical deflector thereof has a negative refracting power in sub-scanning direction; a lens on the side of surface to be scanned thereof has a positive refracting power in the sub-scanning direction; and at least one lens surface of the lens surfaces of said two lenses is such that a shape in a sub-scanning direction thereof is a non-arc shape, and said at least one lens surface has a non-coaxial surface, wherein: at least two lens surfaces such that a curvature in a sub-scanning section varies in main scanning direction are formed in different lenses; at least one surface of said at least two lens surfaces is such that change in the main scanning direction of a curvature in a sub-scanning section thereof is asymmetrical; and said optical system is such that a lateral magnification β 2 in the sub-scanning direction at a central height and a lateral magnification β h in the sub-scanning direction at any image height satisfy the following condition (2) 0.93<|β h /β 2 |<1.07. (2)