| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide a variable power optical system which achieves reduction in cost while realizing a small size, a wide angle, a large aperture ratio and high imaging performance. <P>SOLUTION: The variable power optical system has a first lens group G1 having negative refractive power and a second lens group G2 having a diaphragm and positive refractive power in order from an object side, and varies power by changing an interspace between the first lens group G1 and the second lens group G2 in a direction of an optical axis. The diaphragm is fixed relative to an image surface when the power is varied. The first lens group G1 has a biconcave lens L1 and a positive lens L2 the convex face of which is oriented on the object side in order from the object side. The second lens group G2 has a biconvex lens L3, a biconcave lens L4 and a positive lens L5 in the order from the object side. If the focal length of the biconcave lens L1 of the first lens group G1 is expressed by f1 and the focal length of the whole system at a wide-angle end is expressed by fw, the variable power optical system satisfies a conditional expression (1):-2.9<f1/fw<-2.0. <P>COPYRIGHT: (C)2012,JPO&INPIT |
