| 摘要 |
An optical beam scanning device 21 includes a pre-deflection optical system 40 for adjusting a laser beam L emitted from a semiconductor laser element 41 so as to be focused as a line image longitudinally extending in a direction corresponding to a main scanning direction, a polygon mirror 50 for scanning a photosensitive drum 23 with the laser beam L, and an imaging optical system 60 for focusing the laser beam L scanned by the polygon mirror 50 on the photosensitive drum 23 . The imaging optical system 60 includes one or a plurality of lenses, and is formed so as to satisfy Lc/Le>=2.2, where a light passage distance through the inside of the lens when scanning the center of an image region is denoted as Lc and a light passage distance through the inside of the lens when scanning the end of the image region is denoted as Le. The imaging optical system 60 may include a plastic lens composed of one lens or a plastic lens along with a glass lens.
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