Patent ID: 8149477

Claim:
An optical scanning apparatus comprising: a light emitting unit; a deflecting unit having a deflecting surface; an incidence optical system configured to cause a light beam emitted from the light emitting unit incident on the deflecting unit; an imaging optical system including a transmissive imaging optical element that forms an image of a light beam on a surface to be scanned, the light beam being subjected to scanning and deflected by the deflecting surface of the deflecting unit, with the transmissive imaging optical element having a first transmitting surface, a second transmitting surface, a third transmitting surface, and a fourth transmitting surface; and a reflective optical element disposed in an optical path between the deflecting unit and the transmissive imaging optical element, the reflective optical element having a reflecting surface, wherein, after the light beam subjected to scanning and deflected by the deflecting surface of the deflecting unit passes through the transmissive imaging optical element in order of the first transmitting surface and the second transmitting surface and then reflected at the reflecting surface of the reflective optical element, the light beam re-passes through the transmissive imaging optical element in order of the third transmitting surface and the fourth transmitting surface, and wherein the following condition is satisfied: L 2×tan(2α)>( w 1 +w 2)/2 0<α<20 where L 2 is a length in millimeters of an optical path from the first transmitting surface to the reflecting surface, α is an angle in degrees between a normal to the reflecting surface and a normal to the deflecting surface in a sub-scanning section, w 1 is a width in millimeters of the light beam in a sub-scanning direction at the first transmitting surface, and w 2 is a width in millimeters of the light beam in the sub-scanning direction at the fourth transmitting surface.