| 摘要 |
PROBLEM TO BE SOLVED: To provide a zoom lens that is a lens system composed of five groups, has a wide angle of view, is telecentric, and has a small F-number and a sufficient long back-focus, and to provide a projection device using the zoom lens. SOLUTION: The zoom lens is composed of five groups of negative, negative, positive, positive, positive powers. Specifically, it is composed of, in order from the enlargement side: the first lens group G1 having the negative refracting power that is fixed when a magnification is changed and used for focusing; the second lens group G2, third lens group G3 and fourth lens group G4 which are moved; and the fifth lens group G5 having the positive refracting power that is fixed when a magnification is changed. The zoom lens satisfies the following conditional formulas: (1) 0.3<G2t/fw<0.8, (2) 0.3<G3t/fw<0.8, (3) 0.3<G4t/fw<0.8, in which fw is the focal distance of the entire lens system at a wide angle end, G2t is the distance of the movement of the second lens group between the wide angle end and telephoto end, G3t is the distance of the movement of the third lens group between the wide angle end and telephoto end, G4 is the distance of the movement of the fourth lens between the wide angle end and telephoto end. COPYRIGHT: (C)2006,JPO&NCIPI
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