| 摘要 |
PROBLEM TO BE SOLVED: To obtain a compact scanning optical device suitable for high definition printing by appropriately setting a lens shape of an f&thetas; lens.SOLUTION: The multi-beam scanning optical device includes a rotary polygon mirror for deflecting a plurality of luminous fluxes emitted from light source means, in a main scanning direction by a deflecting surface thereof and an imaging optical system for imaging, on a scanned surface, the plurality of luminous fluxes deflected by the deflecting surface of the rotary polygon mirror, and the deflecting surface and the scanned surface have an optically conjugate relation in a sub-scanning direction vertical to the main scanning direction. The imaging optical system includes two lenses, and curvatures in the sub-scanning direction of at least two lens surfaces of the two lenses are continuously changed outward from on axes to suppress variation of the F number in the sub-scanning direction due to an image height of luminous fluxes impinging on the scanned surface. |
