| 摘要 |
PROBLEM TO BE SOLVED: To make a lens system compact at the photographing and collapsing time while favorably maintaining high resolution of the lens system in a small-sized three-group zoom lens whose variable power ratio is threefold or more. SOLUTION: The lens system is composed of three groups of lenses which are negative, positive, and positive in order from an object side. When varying the power, a 1st group G<SB>1</SB>is moved to relatively approach to a 2nd group G<SB>2</SB>, and this G<SB>2</SB>is monotonously moved to the object side, and a 3rd lens group G<SB>3</SB>is moved so that the moving locus is a convex arc to the object side. The G<SB>3</SB>is moved to the object side at the time of focusing. Moreover, the G<SB>1</SB>consists of, in order from the object side, a negative 1st lens L<SB>1</SB>facing a concave surface of a large curvature to the image side and a positive meniscus form 2nd lens L<SB>2</SB>of which at least one surface is made aspherical and the convex surface of a large curvature is faced to the object side. Moreover, the lens system satisfies the conditional expressions (1) and (2); 2.0<¾f<SB>1</SB>¾/f<SB>W</SB><2.6 (1), 0.41<F<SB>2</SB>/f<SB>3</SB><0.50 (2), however, f<SB>W</SB>represents a focal length of the whole system at the wide angle end, and f<SB>1</SB>represents a focal length of the 1st lens group. COPYRIGHT: (C)2006,JPO&NCIPI
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