| 摘要 |
PROBLEM TO BE SOLVED: To prevent the curvature of a field from occurring without spoiling the degree of freedom for arranging a photosensitive drum in an over-field type scanning optical system. SOLUTION: By inserting a plate mirror 9 in an over-field type image forming optical system 5 including an fθlens 7 and a cylindrical mirror 8, the bending angleθof the mirror 8 is formed to be the acute angle being <=30 deg. so as to prevent the deterioration of image quality such as the curvature of the field from occurring. Thus, the degree of freedom for arranging the photosensitive drum 6 is enhanced in comparison with the case that the image is directly formed on the drum 6 from the mirror 8.
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