# US 2025/0155693 A1 · Variable magnification optical system, optical apparatus, and method for producing variable magnification optical system

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- Number: US 2025/0155693 A1
- Document ID: US20250155693A1
- Status: Published application
- Kind: A1
- Application number: 19/026,324
- Filed: 2025-01-16
- Published: 2025-05-15
- Earliest claimed: 2020-03-08
- Assignees: Nikon Corporation
- Applicants: Nikon Corporation
- Inventors: Takeshi Umeda
- Web page: https://patentgrep.com/patent/US20250155693A1

## CPC

- G02B 15/145113: {arranged +-++-}
- G02B 15/144113: {arranged +-++}
- G02B 15/1461: {the first group being positive}
- G02B 13/18: with lenses having one or more non-spherical faces, e.g. for reducing geometrical aberration {(G02B13/002 takes precedence)}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

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 having positive refractive power; upon varying a magnification, a distance between the first lens group and the second lens group being varied, a distance between the second lens group and the third lens group being varied, and a distance between the third lens group and the rear lens group being varied; the rear lens group comprising a focusing lens group which is moved upon carrying out focusing from an infinitely distant object to a closely distant object; and predetermined conditional expression(s) being satisfied, thereby various aberrations being corrected superbly.

## Claims

### Claim at position 1

1-14. (canceled)

### Claim 15

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 having positive refractive power;
upon varying a magnification, a distance between said first lens group and said second lens group being varied, a distance between said second lens group and said third lens group being varied, and a distance between said third lens group and said rear lens group being varied;
said rear lens group comprising a focusing lens group which is moved upon carrying out focusing; and
the following conditional expressions being satisfied:
2.
<
f
⁢
1
/
fw
<
8.
0.1
<
BFw
/
fw
<
1.
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, and BFw denotes a back focus of said variable magnification optical system in the wide angle end state.

### Claim 16 (depends on 15)

A variable magnification optical system according to claim 15, wherein
the following conditional expression is satisfied:
-
1
.
0
⁢
0
<
f
⁢
3
⁢
f
/
f
⁢
3
⁢
r
<
-
0.05
where f3r denotes a focal length of a most image plane side negative lens component in said third lens group, and f3f denotes a composite focal length of lens components disposed on a side which is closer to the object than said most image side negative lens component, in said third lens group.

### Claim 17 (depends on 15)

A variable magnification optical system according to claim 15, wherein
the following conditional expression is satisfied:
0.04
<
β
⁢
Fw
<
0.8
where βFw denotes transverse magnification of the focusing lens group in the wide angle end state.

### Claim 18 (depends on 15)

A variable magnification optical system according to claim 15, wherein
the rear lens group comprises a fourth lens group having positive refractive power, and a fifth lens group having negative refractive power, and
the following conditional expression is satisfied:
-
3
.
0
⁢
0
⁢
0
<
f
⁢
5
/
f
⁢
3
<
-
0
.
5
⁢
0
⁢
0
where f3 denotes a focal length of the third lens group, and f5 denotes a focal length of the fifth lens group.

### Claim 19 (depends on 18)

A variable magnification optical system according to claim 18, wherein
said fourth lens group comprises said focusing lens group.

### Claim 20 (depends on 15)

A variable magnification optical system according to claim 15, wherein
the following conditional expression is satisfied:
4.
<
f
⁢
1
/
f
⁢
1
⁢
Rw
<
9.
where f1 denotes a focal length of the first lens group, and f1Rw denotes a composite focal length of lens groups in the wide angle end state disposed on the side which is closer to the image plane than the first lens group.

### Claim 21 (depends on 15)

A variable magnification optical system according to claim 15, wherein
the following conditional expression is satisfied:
nd3fp<1.800
where nd3fp denotes refractive index of a lens having the largest refractive index in the third lens group.

### Claim 22 (depends on 15)

A variable magnification optical system according to claim 15, wherein
the following conditional expression is satisfied:
50.000<νd3p
where νd3p denotes Abbe's number of a lens having the smallest Abbe's number in the third lens group.

### Claim 23 (depends on 15)

A variable magnification optical system according to claim 15, wherein
the following conditional expression is satisfied:
0.5
<
1
/
β
⁢
Rw
<
1.
where βRw denotes a transverse magnification of a lens group disposed at the most image plane side in the wide angle end state.

### Claim 24 (depends on 15)

A variable magnification optical system according to claim 15, wherein
the following conditional expression is satisfied:
0.5
<
f
⁢
2
⁢
fn
/
f
⁢
2
<
1.1
where f2fn denotes a focal length of a most object side lens component in the second lens group, and f2 denotes a focal length of the second lens group.

### Claim 25 (depends on 15)

A variable magnification optical system according to claim 15, wherein
the following conditional expression is satisfied:
0.3
<
fF
/
ft
<
1.4
where fF denotes a focal length of the focusing lens group, and ft denotes a focal length of the variable magnification optical system in the telephoto end state.

### Claim 26 (depends on 15)

A variable magnification optical system according to claim 15, wherein
the following conditional expression is satisfied:
40.
o
<
ω
⁢
w
<
85.
o
where ωw denotes a half angle of view of the variable magnification optical system in the telephoto end state.

### Claim 27 (depends on 15)

A variable magnification optical system according to claim 15, wherein
the rear lens group is composed of, in order from an object side, a fourth lens group having negative refractive power, and a fifth lens group having positive refractive power,
upon varying a magnification, a distance between said fourth lens group and said fifth lens group is varied,
said first lens group comprises, in order from the object side, a negative lens and a positive lens,
said second lens group comprises, in order from the object side, a negative lens, a negative lens and a positive lens,
said third lens group comprises a positive lens disposed at the most object side and a positive lens disposed at the most image plane side,
said fourth lens group comprises, in order from the object side, a negative lens and a positive lens, and
said fifth lens group comprises a positive lens disposed at the most object side and a positive lens disposed at the most image plane side.

### Claim 28 (depends on 15)

An optical apparatus comprising a variable magnification optical system according to claim 15.