# US 12,000,998 B2 · Magnification-variable optical system, optical apparatus, and method for manufacturing magnification-variable optical system

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- Number: US 12,000,998 B2
- Document ID: US12000998B2
- Status: Granted
- Kind: B2
- Application number: 17/431,707
- Filed: 2019-12-20
- Published: 2022-05-12
- Granted: 2024-06-04
- Earliest claimed: 2019-02-22
- Assignees: Nikon Corporation
- Applicants: Nikon Corporation
- Inventors: Fumiaki Ohtake; Azuna Nonaka
- Web page: https://patentgrep.com/patent/US12000998B2

## CPC

- G02B 15/1425: {the first group being negative}
- G02B 15/145523: {arranged -++-+}
- G02B 3/04: with continuous faces that are rotationally symmetrical but deviate from a true sphere {, e.g. so called "aspheric" lenses}
- G02B 15/143507: {arranged -++}
- G02B 15/144507: {arranged -++-}
- G02B 15/145515: {arranged -+++-}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

A magnification-variable optical system having a small size, a wide angle of view, and high optical performance, an optical apparatus including the magnification-variable optical system, and a method for manufacturing the magnification-variable optical system are provided. A magnification-variable optical system ZL used for an optical apparatus such as a camera 1 includes a first lens group G1 having a negative refractive power and including at least two lenses, and a rear group GR including at least one lens group disposed on an image side of the first lens group G1, and is configured so that a distance between lens groups adjacent to each other changes at magnification change and a condition expressed by predetermined condition expressions is satisfied.

## Claims

### Claim 1

A magnification-variable optical system comprising:
a first lens group having negative refractive power and including, sequentially from an object side, a negative lens, a negative lens, a negative lens, and a positive lens; and
a rear group including at least one lens group disposed on an image side of the first lens group, wherein
a distance between lens groups adjacent to each other changes at magnification change,
all lens groups move in an optical axis direction at magnification change, and
the following conditional expressions are satisfied:
80.00<v1n
1.05<nL2/nL1
where
v1n: Abbe number of a medium of at least one negative lens included in the first lens group at a d line,
nL1: refractive index of a medium of a lens at a d line, the lens being closest to an object side in the first lens group, and
nL2: refractive index of a medium of another lens at a d line, the lens being second closest to the object side in the first lens group.

### Claim 2 (depends on 1)

The magnification-variable optical system according to claim 1, wherein the following conditional expression is satisfied:
N1n≤4
where
N1n: number of negative lenses included in the first lens group.

### Claim 3 (depends on 1)

The magnification-variable optical system according to claim 1, wherein the following conditional expression is satisfied:
100.00°<2ωw
where
2ωw: full angle of view of the magnification-variable optical system in a wide-angle state.

### Claim 4 (depends on 1)

The magnification-variable optical system according to claim 1, wherein the following conditional expression is satisfied:
nL1<1.70
where
nL1: refractive index of a medium of a lens at a d line, the lens being closest to an object side in the first lens group.

### Claim 5 (depends on 1)

The magnification-variable optical system according to claim 1, wherein the following conditional expression is satisfied:
1.20<Bfw/fw<4.00
where
fw: focal length of the magnification-variable optical system in a wide-angle state, and
Bfw: back focus of the magnification-variable optical system in the wide-angle state.

### Claim 6 (depends on 1)

The magnification-variable optical system according to claim 1, wherein the following conditional expression is satisfied:
0.40<STLw/TLw<0.70
where
TLw: total length of the magnification-variable optical system in a wide-angle state, and
STLw: distance on an optical axis from a lens surface closest to an object side to an aperture stop in the magnification-variable optical system in the wide-angle state.

### Claim 7 (depends on 1)

The magnification-variable optical system according to claim 1, wherein the following conditional expression is satisfied:
1.00<(−f1)/fw<2.00
where
fw: focal length of the magnification-variable optical system in a wide-angle state, and
f1: focal length of the first lens group.

### Claim 8 (depends on 1)

The magnification-variable optical system according to claim 1, wherein the following conditional expression is satisfied:
0.65<(−f1)/ft<1.20
where
ft: focal length of the magnification-variable optical system in a telephoto end state, and
f1: focal length of the first lens group.

### Claim 9 (depends on 1)

The magnification-variable optical system according to claim 1, wherein the following conditional expression is satisfied:
1.00<fL1/f1<2.00
where
f1: focal length of the first lens group, and
fL1: focal length of a lens closest to the object side in the first lens group.

### Claim 10 (depends on 1)

The magnification-variable optical system according to claim 1, wherein the following conditional expression is satisfied:
1.00<fL2/f1<4.00
where
f1: focal length of the first lens group, and
fL2: focal length of a lens second closest to the object side in the first lens group.

### Claim 11 (depends on 1)

The magnification-variable optical system according to claim 1, wherein the following conditional expression is satisfied:
3.50<TLw/Bfw<8.00
where
Bfw: back focus of the magnification-variable optical system in a wide-angle state, and
TLw: total length of the magnification-variable optical system in the wide-angle state.

### Claim 12 (depends on 1)

The magnification-variable optical system according to claim 1, wherein the following conditional expression is satisfied:
−4.00<(L1r2+L1r1)/(L1r2−L1r1)<−0.50
where
L1r1: radius of curvature of a lens surface of a lens closest to the object side in the first lens group, the lens surface being on the object side, and
L1r2: radius of curvature of a lens surface of the lens closest to the object side in the first lens group, the lens surface being on an image side.

### Claim 13 (depends on 1)

The magnification-variable optical system according to claim 1, wherein the following conditional expression is satisfied:
−4.00<(L2r2+L2r1)/(L2r2−L2r1)<−0.50
where
L2r1: radius of curvature of a lens surface of a lens second closest to the object side in the first lens group, the lens surface being on the object side, and
L2r2: radius of curvature of a lens surface of the lens second closest to the object side in the first lens group, the lens surface being on an image side.

### Claim 14 (depends on 1)

The magnification-variable optical system according to claim 1, wherein the following conditional expression is satisfied:
−0.80<(L3r2+L3r1)/(L3r2−L3r1)<0.80
where
L3r1: radius of curvature of a lens surface of a lens third closest to the object side in the first lens group, the lens surface being on the object side, and
L3r2: radius of curvature of a lens surface of the lens third closest to the object side in the first lens group, the lens surface being on an image side.

### Claim 15 (depends on 1)

The magnification-variable optical system according to claim 1, wherein part of the rear group moves to an image side upon focusing from an infinite distance object to a close distance object.

### Claim 16 (depends on 1)

The magnification-variable optical system according to claim 1, wherein the rear group includes one or more aspheric surfaces.

### Claim 17 (depends on 1)

The magnification-variable optical system according to claim 1, wherein the rear group includes one or more lenses that satisfy the following conditional expression:
66.50<vr
where
vr: Abbe number of a medium of the respective lens included in the rear group at a d line.

### Claim 18 (depends on 1)

The magnification-variable optical system according to claim 1, wherein the rear group has positive refractive power.

### Claim 19 (depends on 1)

The magnification-variable optical system according to claim 1, wherein the following conditional expression is satisfied:
Fnow<4.20
where
Fnow: maximum aperture of the magnification-variable optical system in a state of focusing at infinity in a wide-angle state.

### Claim 20 (depends on 1)

The magnification-variable optical system according to claim 1, wherein the following conditional expression is satisfied:
Fnot<6.00
where
Fnot: maximum aperture of the magnification-variable optical system in a state of focusing at infinity in a telephoto end state.

### Claim 21 (depends on 1)

The magnification-variable optical system according to claim 1, further comprising a filter on an object side of the first lens group.

### Claim 22 (depends on 1)

An optical apparatus comprising the magnification-variable optical system according to claim 1.

### Claim 23

A magnification-variable optical system comprising:
a first lens group having negative refractive power and including, sequentially from an object side, a negative lens, a negative lens, a negative lens, and a positive lens; and
a rear group including at least one lens group disposed on an image side of the first lens group, wherein
a distance between lens groups adjacent to each other changes at magnification change,
all lens groups move in an optical axis direction at magnification change, and
the following conditional expressions are satisfied:
100.00 mm2<fw×(−f1)/Fnow<165.00 mm2
N1n≤3
100.00°<2ωw
where
fw: focal length of the magnification-variable optical system in a wide-angle state,
f1: focal length of the first lens group,
Fnow: maximum aperture of the magnification-variable optical system in a state of focusing at infinity in the wide-angle state,
N1n: number of negative lenses included in the first lens group, and
2ωw: full angle of view of the magnification-variable optical system in the wide-angle state.

### Claim 24

A method for manufacturing a magnification-variable optical system including a first lens group and a rear group, the first lens group having negative refractive power and including, sequentially from an object side, a negative lens, a negative lens, a negative lens, and a positive lens, the rear group including at least one lens group disposed on an image side of the first lens group, the method for manufacturing the magnification-variable optical system comprising:
disposing the lens groups so that a distance between lens groups adjacent to each other changes at magnification change;
disposing the lens groups so that all lens groups move in an optical axis direction at magnification change; and
further comprising one of the following features A or B,
the feature A comprising,
satisfying the following conditional expressions:
80.00<v1n
1.05<nL2/nL1
where
v1n: Abbe number of a medium of at least one negative lens included in the first lens group at a d line,
nL1: refractive index of a medium of a lens at a d line, the lens being closest to an object side in the first lens group, and
nL2: refractive index of a medium of another lens at a d line, the lens being second closest to the object side in the first lens group,
the feature B comprising,
satisfying the following conditional expressions:
100.00 mm2<fw×(−f1)/Fnow<1/65.00 mm2
N1n≤3
100.00° <2ωw
where
fw: focal length of the magnification-variable optical system in a wide-angle state,
f1: focal length of the first lens group,
Fnow: maximum aperture of the magnification-variable optical system in a state of focusing at infinity in the wide-angle state,
N1n: number of negative lenses included in the first lens group, and
2ωw: full angle of view of the magnification-variable optical system in the wide-angle state.