| 摘要 |
PURPOSE:To correct the surface inclination of a rotary polygon mirror and to reduce an irregularity of scanning lines and to obtain excellent images by providing a means which varies the diameter size of a light beam, incident on an image forming lens, at right angles to its scanning direction and a means which shifts a cylindrical lens in fitting position in directions of an optical axis. CONSTITUTION:A variable aperture stop 19 is arranged between a collimator lens 3 and a beam shaping device 4 and the cylindrical lens 8 is allowed to move in the direction of the optical axis (Z axis). When the variable aperture stop 19 is so positioned that its aperture width is maximum, a beam projected from the beam shaping device 4 has the largest diameter. The largest beam spot is therefore obtain the scanned surface of a photosensitive drum 7, and the cylindrical lens 8 and photosensitive drum 7 are so arranged that their current gap is shorter than the focal length (f) of the cylindrical lens 8 and a deviation dz in image formation position due to the curvature of field of the cylindrical lens is uniformed to overall scanning width.
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