| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical device capable of coping with a large angle of view exceeding 180°by a small number of lenses, achieving a projection system (isometric projection or stereoscopic projection or the like) in which compressibility on the periphery is small by positively utilizing a resin lens, restraining shift of focus caused by temperature change, and made inexpensive, compact and suitable for an imaging lens. SOLUTION: A front group I comprises a first negative lens being a meniscus lens the object side of which is convex and a second negative lens. A rear group II comprises a third positive biconvex lens, an aperture diaphragm S, a fourth negative lens and a fifth positive biconvex lens. The first lens is a glass lens and the second lens 2 is a resin aspherical lens. When it is assumed that the focal distance of an entire system is f, the focal distance of the first lens is f1; the focal distance of the second lens is f2; the focal distance of the front group is fI; the average Abbe number of the third lens and the fourth lens is va, and the average Abbe number of the other lenses is vb; the optical device satisfies -2.4<fI/f<-1.55, 0.15<f2/f1<0.35, va<29 and vb>50. COPYRIGHT: (C)2007,JPO&INPIT
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