| 摘要 |
An f theta scanning lens arrangement, arranged from a polygonal mirror side to an imaging surface side, including a first, second, third, and fourth lens with having negative, positive, positive, and negative power, respectively, in the main scanning and subscanning directions is provided. The ratio of the focal length in the main scanning direction of the fourth lens versus the focal length in the main scanning direction of the entire f theta lens is selected to simultaneously minimize astigmatism, field curvature, and linearity error. Further, the ratio of the focal length in a subscanning direction of the first lens versus the focal length in the subscanning direction of the second lens is selected to minimize curving of scanning lines displaced from the optical axis.
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