| 摘要 |
A temperature of a scanning optical system is different from a temperature of a light source when an optical scanning device is in operation, and when the both temperatures are assumed to be equal, a diffractive surface of a diffractive optical element is set according to a magnitude relationship between both temperatures when the optical scanning device is in operation such that a deviation amount of an in-focus position of the light flux by the diffractive optical element becomes larger or smaller than a deviation amount for canceling a deviation amount of an in-focus position of the light flux by the scanning optical system.
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