Patent ID: 7843482

Claim:
A multi-beam optical scanning device, comprising: a plurality of light sources; a deflection unit that deflects a plurality of light beams from the light sources; a first optical system that directs the light beams from the light sources to the deflection unit; and a second optical system that guides the light beams deflected by the deflection unit to a scanning surface, wherein the first optical system includes a first lens having a diffracting surface and formed from a resin, the second optical system includes at least one optical element formed from a resin, the plurality of the light beams pass through the first optical system and the second optical system, and assuming that in the first optical system, a change of a position of a main-scanning beam waist caused by power variation of a refractive portion, when a wavelength of one of the light sources increases by 1 nm, is represented by Δm′ 1 , and a change of a position of the main-scanning beam waist caused by power variation of a diffractive portion, when a wavelength of one of the light sources increases by 1 nm, is represented by Δm′ 2 , in the second optical system, a change of a position of a main-scanning beam waist caused by power variation, when a wavelength of one of the light sources increases by 1 nm, is represented by Δm′ 3 , and a depth of a diameter of the main scanning beam on the scanning surface is represented by Wm, the following relation is satisfied: |Δm′1+Δm′2+Δm′3|<Wm/2.