| 摘要 |
PROBLEM TO BE SOLVED: To provide a small-sized and compact imaging lens comprising three groups of four lenses, which can be adapted to a mega-order high pixel device. SOLUTION: An imaging lens 10 has; a first lens group I (consisting of a first lens 1) which has a convex directed to the object side and has a positive power; a second lens group II (consisting of a concave lens 2 and a convex lens 3) which has a concave directed to the object side and has a positive power; and a third lens group III (consisting of a fourth lens 4) having a negative power. Lens surfaces 4a and 4b of the fourth lens 4 are aspherical surfaces together, and the imaging lens 10 satisfies 0.6<Σd<F<1.2, 0.8<Nd5/Nd4<1.2, and 1.4<νd5/νd4<2.5 wherein; F is the resultant focal length of an entire lens system;Σd is an interval on an optical axis between the object-side lens surface of the first lens and the image surface-side lens surface of the fourth lens; Nd4 is the refractive index of the second lens; Nd5 is the refractive index of the third lens;νd4 is the Abbe's number of the second lens; andνd5 is the Abbe's number of the third lens. COPYRIGHT: (C)2005,JPO&NCIPI
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