| 摘要 |
<P>PROBLEM TO BE SOLVED: To achieve a new zoom lens for projection in which brightness is not changed in accordance with variable magnification while it has a high variable magnification ratio, and which is suitable even to image projection to a large-sized screen in a movie theater or the like. <P>SOLUTION: In order from the expansion side, first to sixth lens groups G1 to G6 are arranged; an aperture diaphragm S is fixedly provided in the sixth lens group G6; the first and second lens groups G1, G2 have negative refractive power; the third and fourth lens groups G3, G4 have positive refractive power; the fifth lens group G5 has negative refractive power, and the sixth lens group G6 has positive refractive power, respectively. Upon variable magnification, the first to fifth lens groups are displaced; the aperture diaphragm and the sixth lens group are fixed; the back focus of the whole system, FB, and the focal distance in the wide angle end of the whole system, Fw, satisfy condition, (1) 2.5<FB/Fw<2.8, and in the reduction side, the constitution is made telecentric. <P>COPYRIGHT: (C)2011,JPO&INPIT |
