| 摘要 |
An f theta scanning lens, 5 used in a scanning optical system of a laser printer, comprises, in order from a polygonal mirror 2 side to an imaging surface 4 side, first 5a, second 5b, third 5c, and fourth 5d lenses having negative, positive, positive, and negative power, respectively, in both the main scanning and subscanning directions. The focal length (f4) of the main scanning direction of the fourth lens versus the focal length (f) of the entire f theta lens may simultaneously minimize astigmatism, field curvature, and linearity error. Further, the focal length of a subscanning direction of the first lens (f1z) versus the second lens (f2z) may minimize curving of scanning lines displaced from the optical axis. <IMAGE>
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