| 摘要 |
PROBLEM TO BE SOLVED: To provide a compact bright zoom lens. SOLUTION: The zoom lens has a first negative lens group, a second positive lens group and a third positive lens group. When zooming from the wide angle end to the telephotographic end is performed, the first lens group is moved from an object side to an image surface side and then, to the object side, the second lens group is monotonously moved from the image surface side to the object side and the third lens group is moved from the object side to the image surface side monotonously or nonlinearly orbitly. The second lens group includes five lenses composed of three positive lenses 3, 4 and 7 and two negative lenses 5 and 6 and a cemented lens obtained by cementing one positive lens 4 and one negative lens 5. The focal length at the wide angle end fw, the entire length of a lens system at the wide angle end TLw, the moving amount of the second lens group from the wide angle end to the telephotographic end MA, the focal length of the second lens group fG2 and the aperture of an aperture diaphragm SDD satisfy the following expression: 4.5≤TLw/fw≤7.5, 1.3≤MA/fw≤2.3 and fG2/SDD<2.2. Thus, the compact bright zoom lens of FNo≤2.2 can be provided. COPYRIGHT: (C)2008,JPO&INPIT
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