| 摘要 |
PROBLEM TO BE SOLVED: To obtain an image of high definition without causing variation in the linear speed of moving a light beam or expansion of aberrations by providing an image formation optical system with optical characteristics of right-left symmetry about a main scanning direction, and aligning the center line of the deflection angle of the scanning direction of the light beam with the center of symmetry of the image formation optical system. SOLUTION: An image forming lens 12 images a laser beam deflected by a deflector 10 on a photosensitive drum 3, and has F.arecinθcharacteristics so that the scanning line of the laser beam moves on the photosensitive drum 3 at a nearly equal speed in the main scanning direction. And, the light beam reflected by an optical deflecting element 9 needs to have a position of incidence on an F.arecinθlens properly adjusted, namely, an adjustment part 20 is provided which adjusts the center line of the light deflection angle of scanning within an effective range of image information to a position on the symmetrical surface of an image forming element. Consequently, an image of good quality is obtained and the permissible range of the precision of the deflection angular speed that the deflector 10 needs to have can be increased.
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