To enable a scanning with high resolution and also at a wide view angle while keeping a plane tilt compensation function by providing a scanning lens with an aspherical lens and making its aspherical face to be continuously increased asymmetrically to scanning center so that the reflection face of a rotary polygon mirror and the scanning face becomes a conjugate relation in a subscanning direction.
The scanning lens (Fθ lens) 1 is constituted of a 1st lens provided with lens faces 11 and 12 on both sides of itself with an axis of rotation symmetry, and a 2nd lens provided with a flat, or spherical lens face 13 and a lens face 14 being asymmetry to the axis of rotation on both sides of itself. Such the aspherical face is used as the aspherical face 14 of the scanning lens 1, that the curvature radius of the principal axis is different from that of the sub axis, simultaneously, the curvature radius of the tub axis is increased as it is off-axis, and also, the aspherical face provided with a shape asymmetry to the scanning center (in an (x) direction). Thus, the curvature of field generated on the photoreceptor drum surface 15 in the subscanning direction due to the oblique entrance of the laser beam 100 to the rotary polygon mirror 10 and the shift of the reflection surface 40 of the rotary polygon mirror 10 is compensated.
SAITO SUSUMU
TSUNODA YOSHITO
MORIYAMA SHIGEO
MOCHIZUKI KENJI
HITACHI KOKI KK