| 摘要 |
PROBLEM TO BE SOLVED: To realize a high performance and inexpensive fθlens by using a plastic lens having a low refractive index consisting of a single lens. SOLUTION: A light beam outgoing from a laser light source 1 is guided onto a rotary polygon mirror 5 through an optical system, and is guided onto a surface 7 to be scanned through the fθlens 6 after it is reflected and deflected by the rotary polygon mirror 5 to be optical scanned on the surface 7 to be scanned. The fθlens 6 is constituted of a sheet of plastic fθlens 6. The fθlens 6 is constituted so that the optical axial vicinity of the main scan direction in a deflection surface is made a both side aspherical shape being a both convex shape, and the sub-scan direction in the direction vertical to the deflection surface is made a meniscus shape turning a concave surface in the deflective direction, and at least one surface in the curvature of the sub-scan direction is made so that the radius of curvature is changed asymmetrically continuously for the center of the fθlens 6. |
