| 摘要 |
PURPOSE:To improve an ftheta characteristic by setting up the focal distances or the like of lenses having positive and negative power values respectively to a prescribed relation on the side of a polarizing means for condensing polarized beams on a scanning image surface. CONSTITUTION:In a covex lens 3 having positive power and convex surfaces on both the sides and a meniscus lens 4 having negative power, the radiuses of curvature of respective refractive surfaces of the lenses are defined as r1-r4 from the side close to an incident pupil 1 and distances between respective refractive surfaces are defined as d1-d3 in the order close to the pupil 1. In addition, the distance from the pupil 1 to the lens 3, the focal distance of the whole image forming lens system and the focal distance of the lens 3 are defined as d0, (f) and f1 respectively. Under said definition, the scanning device is constituted so that the conditions of the formula I are satisfied. |
