| 摘要 |
PROBLEM TO BE SOLVED: To provide a reading lens which is bright, whose aperture efficiency is about 100% to a periphery part, which excellently corrects the curvature of field, restrains comatic flare and has high contrast from vicinity on axis to the outermost periphery in a high spatial frequency area, and to provide an image reading lens unit, an image reader and an image forming apparatus. SOLUTION: The reading lens is composed of: a first group comprising a first positive lens; a second group obtained by cementing a second positive lens and a third negative lens and having negative refractive power; a third group obtained by cementing a fourth negative lens and a fifth positive lens and having negative refractive power; and a fourth group comprising a sixth positive lens in order from an object side, and has a diaphragm between the second group and the third group. The Abbe number of at least one of the positive lenses is≥60, and the reading lens satisfies conditions; (1) -0.0075<δθgd convex -δθgd concave<-0.001, (2) -0.02<n convex - n concave<0.02 and (3) 19.5<νconvex -νconcave<22.0. COPYRIGHT: (C)2007,JPO&INPIT
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