| 摘要 |
PURPOSE:To correct beam spot positional error without using a cylinder face lens and a toric face lens by controlling the direction of a beam incident on a deflector to cancel positional error relating to the deflection plane of the deflector according to output signals of a detector that detect beam spot position on the scanning plane. CONSTITUTION:An optical system controlled by making a collimator lens eccentric consists of a light source 1, a collimator lens 2, a polygon mirror 3, an f-theta lens 4 and a photosensitive face 5, and a light source spot image is scanned when a deflector 3 is rotated. In this case, if the deflection plane 3a is slanted by epsilon, the spot position on the photosensitive face deviates by DELTA' (when focal length of the f-theta lens if f, DELTA'=f tan 2epsilon). This is detected by a spot position signal by a photo-electric conversion element in the trigger face on the photosensitive face, and the collimator lens 2 is made to eccentric (shifting in a plane at right angles to the optical axis) and the direction of incidence on the deflector 3 is controlled. Thereby, deviation of spot position is corrected. |
