| 摘要 |
PROBLEM TO BE SOLVED: To provide a wide-viewing-angle inexpensive image reading lens having simple constitution of four spherical lenses, satisfactorily correcting aberrations and achieving a reader made small in size and light in weight. SOLUTION: The image reading lens is constituted of: a first meniscus lens L1 turning its convex surface to an object side and having positive refractive power; a second biconcave lens L2 having negative refractive power; a diaphragm; a third biconvex lens L3 having positive refractive power; and a fourth meniscus lens L4 turning its convex surface to an image forming surface side and having negative refractive power in order from the object side to the image forming side, and constituted to satisfy following conditional expressions. (1) 0.05<D1/f<0.08, (2) 0.015<D2/f<0.022, (3) 0.3<D6/f<0.4 and (4) 0.03<D7/f<0.09, provided that f is the focal length of the lens entire system, D1 is the center thickness of the first lens L1, D2 is an air distance between the first lens L1 and the second lens L2, D6 is the center thickness of the third lens L3, and D7 is an air distance between the third lens L3 and the fourth lens L4. COPYRIGHT: (C)2007,JPO&INPIT
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