Patent ID: 11933951
Assignee: NIKON CORPORATION
Field: nan (nan)
Classification: CPC nan | IPC G

Claim 13:
14. A method for manufacturing a variable magnification optical system which comprises, 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 having positive refractive power;
the method comprising the following steps:
constructing such that the rear lens group comprises, in order from the object side, a fourth lens group having positive refractive power and a fifth lens group having negative refractive power;
constructing such that, upon varying a magnification, a distance between the first lens group and the second lens group is varied, a distance between the second lens group and the third lens group is varied, a distance between the third lens group and the fourth lens group is varied, and a distance between the fourth lens group and the fifth lens group is varied;
constructing such that the rear lens group comprises a focusing lens group which is moved upon carrying out focusing; and
constructing such that the fifth lens group consists of one lens component constituted by a single lens or a cemented lens composed of a plurality of lenses cemented together,
the method further comprising one of the following steps (A), (B), and (C):
(A) satisfying the following conditional expressions:

4.00<f1/fw<6.500

0.100<BFw/fw<1.00

−3.000<f5/f3<−0.500, (B) satisfying the following conditional expressions:

2.00<f1/fw<6.500

0.100<BFw/fw<0.91

−3.000<f5/f3<−0.500

(C) constructing such that the rear lens group further comprises a sixth lens group having negative refractive power adjacent to the image side of the fifth lens group, and
satisfying the following conditional expressions:

4.00<f1/fw<6.500

0.100<BFw/fw<1.00

where f1 denotes a focal length of the first lens group, fw denotes a focal length of the variable magnification optical system in a wide angle end state, BFw denotes a back focus of the variable magnification optical system in the wide angle end state, f3 denotes a focal length of the third lens group, and f5 denotes a focal length of the fifth lens group.