| 摘要 |
<P>PROBLEM TO BE SOLVED: To provide an imaging optical system that is advantageous in sound isolation and dust prevention, that can easily have a small size in a radial direction, and that can easily secure optical performance, and provide an image pickup device including the imaging optical system. <P>SOLUTION: An imaging optical system comprises in the order from an object side to an image plane side a first lens group G1 with positive refractive power, a second lens group G2 with positive or negative refractive power, a third lens group G3 with positive refractive power, and a brightness diaphragm S disposed between an object side plane of the first lens group and an object side plane of the second lens group. A lens of the first lens group that is the closest to the object side and a lens of the third lens group that is the closest to the image side are normally fixed. When focusing is performed from a long distance to a short distance, the optical axis of only the second lens group is moved. The third lens group includes with air interval on the largest axis in the third lens group, a front sub lens group G3F with positive refractive power disposed on the object side and a rear sub lens group G3R with negative refractive power disposed on the image side. <P>COPYRIGHT: (C)2012,JPO&INPIT |
