| 摘要 |
PROBLEM TO BE SOLVED: To excellently compensate fθcharacteristics of a scanning and image forming lens, curvature of image surface in the horizontal and vertical scanning directions, and unevenness of a beam diameter over the entire effective scanning area. SOLUTION: This lens is constituted by arranging 1st-3rd groups in order from the side of an optical deflector 3 to the side of a scanned surface 8 has an fθfunction in the horizontal scanning corresponding direction, and the 1st group is a 1st lens 5 which has a concave spherical surface concave to the side of a deflecting and reflecting surface 4, a plane on the side of a scanned surface 8, and negative refracting power, the 2nd group is a 2nd lens 6 which has a concave cylinder surface with curvature only in the vertical scanning orresonding direction on the side of the deflecting and reflecting surface 4, a convex spherical surface on the side of the scanned surface 8, and positive refracting power in the horizontal scanning corresponding direction and is anamorphic having negative refracting power in the vertical scanning corresponding direction, and the 3rd group is a 3rd lens 7 which has a plane on the side of the deflecting and reflecting surface 4 and a toric surface on the side of the scanned surface 8 and is anamorphic having large positive refracting power in the vertical scanning corresponding direction. |
