Patent ID: 6933961

Claim:
An optical scanning system, comprising: a first optical system that converges a light beam emitted from a light source at least in a main scanning direction; a second optical system that focuses the light beam converged by the first optical system on a deflection surface of a deflector in a sub-scanning direction; and a third optical system that spottily focuses the light beam deflected by the deflector on a surface to be scanned and causes the light beani to scan the surface to be scanned with a constant velocity, wherein the third optical system comprises a first lens of which an entrance surface and an exit surface have rotational symmetries, and a second lens of which an entrance surface has a rotational symmetry and an exit surface has a rotational asymmetry, and wherein the optical scanning system satisfies an inequality 0.9<(Le×cos θ)/Lc <1.1, where Lc is a distance from the exit surface of the second lens to the surface to be scanned in a center of a scanning line, Le is a distance from the exit surface of the second lens to the surface to be scanned at a start and an end of the scanning line, and θ is an angle formed by a laser beam at an end of the scanning line and a perpendicular line of the surface to be scanned.