Scanning optical device and image forming apparatus

Abstract

A scanning optical device and color image forming apparatus use a refraction element and diffraction element as the scanning optical element of a scanning optical device, the powers of the refraction element and diffraction element being 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). This reduces imaging position deviation caused by an environmental fluctuation, and limits imaging position deviation caused by a wavelength variation not accompanied by any environmental fluctuation. By this means it is possible with a simple arrangement at low cost to prevent color image misregistration between colors caused by a wavelength fluctuation or environmental fluctuation and largely to avoid density nonuniformity between colors.

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