| 摘要 |
PURPOSE:To stabilize a value of MTF with regard to the whole scanning sur face by providing an entrance pupil on the object side of a lens system constitut ed of two groups and two pieces having two lenses of negative and positive from the object side, and making this optical system satisfy a prescribed condi tion. CONSTITUTION:This lens system is constituted of two groups and two pieces, and the first lens and the second lens from an object side are a negative lens and a positive lens, respectively. Also, an entrance pupil is provided in front of this lens system. This optical system is made to satisfy conditions of an expression I - an expression IV. In this regard, in the expressions, (f), r1-r4, and d1-d3 denote a focal distance of the whole system, radiuses of curvature of each surface of lenses in order from the pupil side, and thickness of the lens surface and an interval of the lens surface in order of the pupil side, respec tively. |
