| 摘要 |
As has been described above, this invention can achieve a scanning optical device and color image forming apparatus in which a refraction element and diffraction element are used as the scanning optical element of a scanning optical device, the powers of the refraction element and diffraction element are set such that an imaging position deviation in the main scanning direction caused by a wavelength variation along with the environmental fluctuation of the scanning optical device and an imaging position deviation caused by the refractive index variation of the material of the scanning optical element are set to opposite directions at the two ends of an effective image region (effective scanning region), thereby reducing an imaging position deviation caused by an environmental fluctuation, and at the same time an imaging position deviation caused by a wavelength variation not accompanied by any environmental fluctuation is also set to a desired value or less, thereby implementing a scanning optical device resistant to a wavelength fluctuation or environmental fluctuation, and in which images are recorded on a plurality of image carriers (photosensitive drums) using a plurality of scanning optical devices, thereby implementing with a simple arrangement at low cost a color image forming apparatus which is almost free from misregistration between colors caused by a wavelength fluctuation or environmental fluctuation and almost free from density nonuniformity between colors.
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