| 摘要 |
PROBLEM TO BE SOLVED: To provide a zoom optical system having a wide field of view at the maximum telescoping and a large magnification ratio, and an imaging device using it. SOLUTION: The zoom optical system has a first positive refractive power lens group G1, a second negative refractive power lens group G2, a third positive refractive power lens group G3, and a fourth positive refractive power lens group G4, all arranged in this order from the object side. A brightness diaphragm S is positioned between the second lens group G2 and the fourth lens group G4. When changing the magnification; at least the first lens group G1, the second lens group G2, and the third lens group G3 move to change the spaces between those groups. The first lens group G1 is composed of at most two lenses L1<SB>1</SB>, L1<SB>2</SB>. The second lens group G2 is composed of a 1st negative lens L2<SB>1</SB>having an image side surface of a curvature larger than the surface facing the object, an air space, a 2nd negative lens L2<SB>2</SB>having an image side surface of a curvature larger than the surface facing the object, an air space, and a positive lens L2<SB>3</SB>having the object side surface of a curvature larger than the image side surface, all arranged in this order from the object side. The 2nd negative lens L2<SB>2</SB>is made to satisfy the conditional expression: -0.7<f2/r23<0.05, where r23 is the curvature radius of the object side surface of the above 2nd negative lens, and f2 the focal length of the above second lens group. COPYRIGHT: (C)2006,JPO&NCIPI |
