| 摘要 |
PROBLEM TO BE SOLVED: To provide a photographic lens made compact without increasing the number of lenses. SOLUTION: A lens system is constituted of an aperture diaphragm 4, a 1st lens 1, a 2nd lens 2 and a 3rd lens 3 in order from an object side. The 1st lens 1 is a biconvex lens, the 2nd lens 2 is a meniscus lens whose object side is concave and which has negative refractive power, and the 3rd lens 3 is a meniscus lens whose object side is convex and which has positive refractive power, and the lens system for which resin material is used satisfies following conditions (1) 1.5<f/f1<2.0, (2) -2.0<f/f2<-0.8, (3) 0.5<f/f3<0.8, (4) -1.0<f/(f1×f2)<-0.7, (5)ν1-ν2>15 and (6) 2.5<f/D1<3.0. Provided that (f) is the focal distance of the lens system, f1 is the focal distance of the 1st lens 1, f2 is the focal distance of the 2nd lens 2, f3 is the focal distance of the 3rd lens 3,ν1 is the Abbe number of the 1st lens 1,ν2 is the Abbe number of the 2nd lens 2, and D1 is the center thickness of the 1st lens 1. COPYRIGHT: (C)2006,JPO&NCIPI
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