| 摘要 |
A first optical system guides a light beam from a light source to an optical deflector, and a second optical system converges the light beam deflected by the optical deflector on a surface to be scanned. The first optical system includes at least one resin lens having a diffractive surface. The second optical system includes at least one resin optical element. A beam diameter depth in a main scanning direction, Wm, that can have a maximum intensity of 1/e<SUP>2</SUP>, satisfies conditions <?in-line-formulae description="In-line Formulae" end="lead"?>Deltam1+Deltam2+Deltam3-Deltad1x(f2/f1)<SUP>2</SUP><WM/40 (1) <?in-line-formulae description="In-line Formulae" end="tail"?> <?in-line-formulae description="In-line Formulae" end="lead"?>Deltad1>0 and Deltam2<0. (2) <?in-line-formulae description="In-line Formulae" end="tail"?>
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