| 摘要 |
PROBLEM TO BE SOLVED: To provide a compact and wide-angle variable power optical system capable of obtaining a large aperture ratio while finely maintaining optical performance by effectively using an aspherical lens and allowed to be used for both of a visible area and a near infrared area. SOLUTION: The power variable optical system is constituted so that a negative first lens group G<SB>1</SB>, a diaphram 1 and a positive second lens group G<SB>2</SB>are successively arrayed from the object side, power variation is performed by moving the second lens group G<SB>2</SB>to the object side on an optical axis in accordance with separation from a wide angle end to a telephoto end and the movement of an image surface due to variable power operation is corrected by moving the first lens group G<SB>1</SB>to the image forming surface side. The second lens group G<SB>2</SB>has two single lenses consisting of a first lens L2-1 having positive refractive power and forming an aspherical surface on at least one surface and a second lens L2-2 having positive refractive power and forming convex faces on both the surfaces which are successively arrayed from the object side and satisfies the following conditions (1) to (3). Namely nd21>1.55...(1), vd22>68...(2) and 1.0<¾f2/f1¾<1.8...(3). Provided that the nd21 is a refractive index of the first lens L2-1 in the second lens group about a line d, the vd22 is the Abbe number of the second lens L2-2 in the second lens group about the line d, the f1 is the focal distance of the first lens group, and the f2 expresses the focal distance of the second lens group. COPYRIGHT: (C)2006,JPO&NCIPI
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