| 摘要 |
PROBLEM TO BE SOLVED: To provide a scanning lens coping with two wavelengths by which excellent image-forming performance is obtained in the two different designed wavelengths. SOLUTION: Luminous flux from a semiconductor laser 10 is reflected and deflected by a polygon mirror 14 and forms a spot on a scanning object surface 40 through an fθlens 20 and a correcting lens 30. The fθlens 20 is constituted of 1st and 2nd lenses 21 and 22, and the surface of the 1st lens 21 on the mirror 14 side is a diffraction surface 21a where diffraction lens structure is formed. The diffraction surface is designed to satisfy the following condition (1), whereby magnification chromatic aberration is corrected in terms of the 1st and the 2nd wavelengths different from each other. (1) 9.0<fd/f<17.0, where fd is the focal distance of the diffraction lens structure, and (f) is the focal distance of the whole including the diffraction lens structure and the diffraction lens.
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