| 摘要 |
PROBLEM TO BE SOLVED: To surely suppress changes in a scanning position caused by changes in the position of the plane of a rotating polygon mirror at applying of an oblique incident optical system to allow a light beam to enter the rotating polygon mirror at a prescribed angle both in a main scanning direction and in the subscanning direction. SOLUTION: The device has an x-z plane which includes a center axis (z) of a second imaging optical system 34 and an axis (x) perpendicular to the center axis (z) and to a rotation axis (T), the y-z plane including the axis (y) perpendicular to the x-z plane and the center axis (z), an angleαformed by an incident beam (a) and the center axis (z) in the x-z plane, an angleβformed by the incident beam (a) and the center axis (z) in the y-z plane, the maximum scanning angleθm by the rotating polygon mirror 20, lateral magnitude M of the imaging optical system in the sub-scanning direction, a difference S in the position of the plane of the rotating polygon mirror 20, and a distance L of the scanning lines in the sub-scanning direction on the plane to be scanned. The size of each element is determined so as to satisfy the condition 2SMtanβ/ cos(α/2+θm/2)<=L/5. |
