| 摘要 |
Disposing from an object side in the order of a positive first lens group which is fixed at the time of zooming, a negative second lens group which is moved at the time of zooming, an aperture stop, a positive third lens group which is fixed at the time of zooming, and a fourth lens group which is moved along the optical axis at the time of zooming to correct a change in image plane position arising from the zooming for focusing. When a refractive index of the third group first lens with respect to d-line, a focal length of the third group, and focal lengths of the overall lens system at a wide angle end and a telephoto end are taken as Nd31, f3, fw, and ft respectively, conditional expressions (1): 1.77<Nd31 and (2): 0.8<f3/(fw�ft)1/2<1.6 are simultaneously satisfied. |
