| 摘要 |
In a multi-beam scanning optical system, when at least three light fluxes emitted from a light source having at least three light-emitting points are deflected and reflected on a deflection unit and guided to a surface to be scanned by a scanning optical unit, at least three light fluxes are entered into a deflection surface of the deflection unit at irregular angles within a main-scanning section and entered into the surface to be scanned at an angle within a sub-scanning section, and provided that a variation in lengths of scanning lines which is caused when each of the at least three light fluxes is entered into the surface to be scanned at an angle within the sub-scanning section is represented as DeltaY 1 , a variation in lengths of scanning lines which is caused when each of the at least three light fluxes is allowed to enter as a non-parallel light flux to the deflection surface within the main-scanning section is represented as DeltaY 2 , and a variation in lengths of scanning lines which is caused from a difference of wavelength between at least two of the at least three light fluxes is represented as DeltaY 3 , values of DeltaY 1 , DeltaY 2 , and DeltaY 3 are set so as to satisfy |DeltaY 1 +DeltaY 2 +DeltaY 31 <|DeltaY 1|.
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