Patent ID: 8755094

Claim:
An optical scanning apparatus comprising: a light source that outputs a light beam; an optical member though which the light beam passes; a deflector that deflects the light beam such that the light beam that has passed through the optical member moves on a photosensitive member in a predetermined direction; a first light splitting unit that splits the light beam from the deflector into a plurality of light beams in the movement direction of the light beam on the photosensitive member; a second light splitting unit that splits the light beam from the deflector into a plurality of light beams in a direction orthogonal to the movement direction; a detection unit that detects the plurality of light beams split by the first light splitting unit and the plurality of light beams split by the second light splitting unit; a shift amount determination unit that determines, from image forming positions on the detection unit of the plurality of light beams split by the first light splitting unit, an amount of focus shift which is an amount of shift relative to a target diameter of a spot diameter of the light beams in the movement direction and an amount of image forming position shift which is an amount of shift relative to a target position of the image forming positions of the light beams in the movement direction, and determines, from the image forming positions on the detection unit of the plurality of light beams split by the second light splitting unit, the amount of focus shift and the amount of image forming position shift in the direction orthogonal to the movement direction; and a movement unit that moves the optical member in an optical axis direction of the light beam by an amount of movement corresponding to the amount of focus shift in the movement direction and the amount of focus shift in the direction orthogonal to the movement direction.