Patent ID: 9411139
Filing Date: 2016-08-09
CPC Classification: G02B

Claim Text:
1. An imaging optical system comprising a first lens group of positive lenses, a second lens group of negative lenses, and a third lens group of positive lenses in order from an object side, wherein focusing on a nearby object is performed by moving the entire second lens group along an optical axis toward an image side, and the following conditional expressions (1) to (5) are satisfied: where FL represents a focal length of the entire system, 1Gr_Fl represents a focal length of the first lens group, 2Gr_Fl represents a focal length of the second lens group, 3Gr_Fl represents a focal length of the third lens group, 1Gr_R_nop represents a distance from the outermost surface of the first lens group on the object side to a rear principal point of the first lens group, 1Gr_Thi represents a total length of the first lens group, 2Gr_R_nop represents a distance from the outermost surface of the second lens group on the object side to a rear principal point of the second lens group, and 2Gr_Thi represents a total length of the second lens group.