Patent ID: 8314824

Claim:
An optical scanning apparatus, comprising: a light source unit; an incident optical system that allows a light beam emitted from the light source unit to enter to deflecting unit; and an imaging optical system that images the light beam deflected by the deflecting unit for scanning on a surface to be scanned, wherein the incident optical system comprises: a first optical system that converts the light beam emitted from the light source unit into parallel light beam; and a second optical system that guides the light beam emitted from the first optical system onto a deflection surface of the deflecting unit, wherein the first optical system comprises in order from the light source unit: a first optical element having a positive power and being of rotational symmetry; and a second optical element having a positive power with rotation symmetry, wherein the light source unit is disposed at a position which is on the first optical element side of a front focus position of the first optical element, wherein the light source unit and the first optical element are integrally formed, wherein the second optical system comprises a third optical element having a power in a sub-scanning direction, and wherein the following conditions are satisfied, 0.04≦Φ2/Φ≦0.10, Δ ds≦ 0.2×Δ dm , and 5≦(β m/βs ) 2 ≦15, where Φ2 represents a power of the second optical element; Φ represents a power of the first optical system in a main scanning direction; βm represents a magnification of entire system within a main scanning section; βs represents a magnification of the entire system in a sub-scanning section; and Δdm and Δds represent focus movement amounts within the main and sub-scanning sections on the surface to be scanned, respectively, when the second optical element is moved in the optical axis direction.