| 摘要 |
An optical scanning unit that includes a first optical device that forms collimated light from light radiated from a light source, a second optical device that focuses the collimated light onto a deflector, and an imaging optical device that focuses light deflected by the deflector onto an exposure object. The optical scanning unit further includes a refraction unit and a diffraction unit, and the power of the refraction unit is &phgr;r, the power of the diffraction unit is &phgr;d, and the ratio &phgr;r/&phgr;d is such that 0.5<&phgr;r/&phgr;d<1.3.
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