| 摘要 |
PURPOSE:To hold down the deviation from a prescribed distortion to + or -0.5% throughout a scan area and obtain the image flatness and the other optical characteristic sufficiently well by constituting a specific lens system where the first lens is a negative lens and the second lens is a positive lens. CONSTITUTION:The first lens 10 is a negative lens, and the second lens 12 is a positive lens, and an entrance pupil P is provided in the front of the lens system. This lens system satisfied conditions of inequalities (I)-(IV) where (f) is the focal length of the whole of the system and f1 is the focal length of the first lens 10 and r1-r4 are radiuses of curvature of lens faces in order from the entrance pupil side and d1-d3 are lengths between lens faces in order from the entrance pupil side. The inequality (I) is the condition concerning the distortion especially, and the inequality (II) prescribes the power of the first lens, and the inequality (III) prescribes the shape of the first lens, and the inequality (IV) is the condition concerning the flatness of the image surface and the distortion especially. |
