| 摘要 |
PURPOSE:To provide a scanning optical system capable of correcting the collapse of an image surface in both main and sub scan directions independently. CONSTITUTION:This system is provided with a semiconductor laser 10, a collimator lens 11, an anamorphic convergence lens 12, a ploygonal mirror 10, and an f-theta lens 40 as a scan lens, and the f-theta lens 40 is comprised by arranging three lenses; a first lens 41 provided with a concave spherical surface and a concave cylindrical surface with power in the sub scan direction and which corrects image collapse in the main scan, a second lens 42 with two spherical surfaces that is a positive meniscus lens whose concave surface is directed to the polygonal mirror side, and a third lens 43 provided with a flat surface and a convex toric surface with more power in the sub scan direction and which corrects the image collapse in the sub scan direction sequentially from a the polygonal mirror side, and also, this system is provided with such feature that conditions L>0, 2f, 0.1<=D<=0.5 can be satisfied setting distance from a reference deflecting point to a scan lens 30 as L, a focal distance in the main scan direction of the scan lens as (f), and the diameter of the inscribing circle of the polygonal mirror 30 as D. |
