US 12,228,713 B2
Variable magnification optical system, optical apparatus, and method for producing variable magnification optical system
Takeshi Umeda, Fujisawa (JP)
Assigned to Nikon Corporation, Tokyo (JP)
Filed by Nikon Corporation, Tokyo (JP)
Filed on Sep. 13, 2023, as Appl. No. 18/367,995.
Application 18/367,995 is a continuation of application No. 17/535,915, filed on Nov. 26, 2021, granted, now 11,789,245.
Application 17/535,915 is a continuation of application No. 16/645,564, granted, now 11,231,566, issued on Jan. 25, 2022, previously published as PCT/JP2017/032696, filed on Sep. 11, 2017.
Prior Publication US 2024/0077709 A1, Mar. 7, 2024
Int. Cl. G02B 15/14 (2006.01)
CPC G02B 15/144105 (2019.08) [G02B 15/145105 (2019.08); G02B 15/145121 (2019.08); G02B 15/1461 (2019.08)] 21 Claims
OG exemplary drawing
 
1. A variable magnification optical system comprising, in order from an object side, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, and a rear lens group comprising at least one lens group;
upon varying a magnification, distances between adjacent lens groups being varied;
said rear lens group having negative refractive power in a wide angle end state;
the number of positive lenses in said first lens group being one;
said third lens group or said rear lens group comprising a focusing lens group which is moved upon carrying out focusing; and
the following conditional expressions being satisfied:
2.00<f1/fw<8.000
0.400<BFw/fw<1.300
1.100<βFw<2.500
where f1 denotes a focal length of said first lens group, fw denotes a focal length of said variable magnification optical system in the wide angle end state, BFw denotes a back focus of said variable magnification optical system in the wide angle end state, and βFw denotes a transverse magnification of said focusing lens group in the wide angle end state.