| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an optical system capable of effectively reducing generation of flare and ghost due to reflection from a lens surface while favorably correcting chromatic aberration fluctuation when focusing. <P>SOLUTION: This optical system comprises, in order from an object side towards an image side, a first lens group of positive refractive power, an aperture stop, and a second lens group, the first lens group includes a first 1a lens group of positive refractive power and a first 1b lens group of negative refractive power that moves on an optical axis in focusing, and the first 1b lens group comprises a first 1b positive lens of positive refractive power, and a first 1b negative lens of negative refractive power. When the Abbe number of a material of the first 1b positive lens and a partial dispersion ratio of the material thereof are νdbp and θgFbp respectively, the first 1b positive lens satisfies the following expression: 0.02<θgFbp-0.6438+0.0016821×νdbp<0.10, and both the first lens group and the second lens group include lens surfaces formed by a wet process. <P>COPYRIGHT: (C)2012,JPO&INPIT |
