# US 10,481,370 B2 · Optical system, optical apparatus, and method for manufacturing the optical system

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- Number: US 10,481,370 B2
- Document ID: US10481370B2
- Status: Granted
- Kind: B2
- Application number: 14/426,754
- Filed: 2014-02-13
- Published: 2015-08-27
- Granted: 2019-11-19
- Earliest claimed: 2013-02-19
- Assignees: Nikon Corporation
- Applicants: Nikon Corporation
- Inventors: Keigo Koida; Atsushi Suzuki
- Web page: https://patentgrep.com/patent/US10481370B2

## CPC

- G02B 13/04: Reversed telephoto objectives
- G02B 7/021: {for more than one lens}
- G02B 13/18: with lenses having one or more non-spherical faces, e.g. for reducing geometrical aberration {(G02B13/002 takes precedence)}
- Y10T 29/49826: Assembling or joining
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- Y10T: TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

## Abstract

An optical system has, in order from an object: a first lens having negative refractive power; a second lens having positive refractive power; a third lens having positive refractive power; a fourth lens having negative refractive power; a fifth lens having negative refractive power; and a sixth lens having positive refractive power, wherein the following conditional expression (1) is satisfied: 1.52<L3R1/f3 - - - (1), where L3R1 denotes a radius of curvature of an object side lens surface of the third lens L3, and f3 denotes a focal length of the third lens L3.

## Claims

### Claim 1

A fixed focal length optical system, comprising a continuous series of six lenses consisting of, in order from an object, consecutively:
a first lens having negative refractive power;
a second lens having positive refractive power;
a third lens having positive refractive power;
a fourth lens having negative refractive power;
a fifth lens having negative refractive power; and
a sixth lens having positive refractive power, and
the following conditional expression being satisfied:
0.88<L4R2/f
where L4R2 denotes a radius of curvature of an image side surface of the fourth lens, and f denotes a focal length of the total lens system, and
wherein
the following conditional expression is satisfied:
−1.000<(L5R1+L4R2)/(L5R1−L4R2)<−0.310
where L5R1 denotes a radius of curvature of an object side surface of the fifth lens,
wherein the first lens is a negative meniscus lens closest to the object and has a concave surface facing the image, and wherein the continuous series of six lenses is devoid of lens elements between successive lenses of the series.

### Claim 2 (depends on 1)

The fixed focal length optical system according to claim 1, wherein
the following conditional expression is satisfied:
L3f/f<0.56
where L3f denotes a focal length of the third lens.

### Claim 3 (depends on 1)

The fixed focal length optical system according to claim 1, wherein
the first lens is a negative meniscus lens having a concave surface facing the image.

### Claim 4 (depends on 1)

The fixed focal length optical system according to claim 1, wherein
an image side surface of the lens located closest to the image is aspherical.

### Claim 5 (depends on 1)

An optical apparatus including the fixed focal length optical system according to claim 1.

### Claim 6 (depends on 1)

The fixed focal length optical system according to claim 1, wherein
the following conditional expressions are satisfied:
1.820≤L3R1/f3
where L3R1 denotes a radius of curvature of an object side lens surface of the third lens, and f3 denotes a focal length of the third lens
0.10<n3−n4<0.30
where n3 denotes a refractive index of a material of the third lens at the d-line, and n4 denotes a refractive index of a material of the fourth lens at the d-line
1.00<Σd/f<1.30
where Σd denotes a distance on the optical axis from a lens surface closest to the object to a lens surface closest to the image in the optical system, and f denotes a focal length of the total lens system
or
the following conditional expressions are satisfied:
0.88<L4R2/f
where L4R2 denotes a radius of curvature of an image side surface of the fourth lens, and f denotes a focal length of the total lens system
−1.000<(L5R1+L4R2)/(L5R1−L4R2)<−0.310
where L5R1 denotes a radius of curvature of an object side surface of the fifth lens
L3f/f<0.56
where L3f denotes a focal length of the third lens.

### Claim 7 (depends on 1)

The fixed focal length optical system according to claim 1, wherein
the fifth lens is a concave lens or a negative meniscus lens having a concave surface facing the object.

### Claim 8

A method for manufacturing a fixed focal length optical system including a continuous series of six lenses consisting of, in order from an object, consecutively, a first lens having negative refractive power, a second lens having positive refractive power, a third lens having positive refractive power, a fourth lens having negative refractive power, a fifth lens having negative refractive power, and a sixth lens having positive refractive power,
the method comprising assembling each lens in a lens barrel so as to satisfy the following conditional expression:
0.88<L4R2/f
where L4R2 denotes a radius of curvature of an image side surface of the fourth lens, and f denotes a focal length of the total lens system,
wherein
the following conditional expression is satisfied:
−1.000 <(L5R1+L4R2)/(L5R1−L4R2)<−0.310
where L5R1 denotes a radius of curvature of an object side surface of the fifth lens, and
wherein the first lens is a negative meniscus lens closest to the object and has a concave surface facing the image, and wherein the continuous series of six lenses is devoid of lens elements between successive lenses of the series.

### Claim 9

A fixed focal length optical system, comprising a continuous series of six lenses consisting of, in order from an object, consecutively:
a first lens having negative refractive power;
a second lens having positive refractive power;
a third lens having positive refractive power;
a fourth lens having negative refractive power;
a fifth lens having negative refractive power; and
a sixth lens having positive refractive power, and
the following conditional expressions being satisfied:
1.52<L3R1/f3
−1.000 <(L5R1+L4R2)/(L5R1−L4R2)<−0.310
where L3R1 denotes a radius of curvature of an object side lens surface of the third lens,
f3 denotes a focal length of the third lens, and
L5R1 denotes a radius of curvature of an object side surface of the fifth lens, and
L4R2 denotes a radius of curvature of an image side surface of the fourth lens,
wherein the first lens is a negative meniscus lens closest to the object and has a concave surface facing the image,
wherein the continuous series of six lenses is devoid of lens elements between successive lenses of the series, and
wherein the fifth lens is a bi-concave lens or a negative lens having a concave surface facing the object.

### Claim 10 (depends on 9)

The fixed focal length optical system according to claim 9, wherein
the third lens and the fourth lens constitute a cemented lens, and satisfy the following conditional expression:
0.10<n3−n4<0.30
where n3 denotes a refractive index of a material of the third lens at the d-line, and n4 denotes a refractive index of a material of the fourth lens at the d-line.

### Claim 11 (depends on 9)

The fixed focal length optical system according to claim 9, wherein
the second lens is a positive meniscus lens having a convex surface facing the object.

### Claim 12 (depends on 9)

The fixed focal length optical system according to claim 9, wherein
the following conditional expression is satisfied:
1.00<Σd/f<1.30
where Σd denotes a distance on the optical axis from a lens surface closest to the object to a lens surface closest to the image in the optical system, and f denotes a focal length of the total lens system.

### Claim 13 (depends on 9)

The fixed focal length optical system according to claim 9, wherein
a lens surface closest to the image is aspherical.

### Claim 14 (depends on 9)

An optical apparatus including the fixed focal length optical system according to claim 9.

### Claim 15

A method for manufacturing a fixed focal length optical system including a continuous series of six lenses consisting of, in order from an object, consecutively, a first lens having negative refractive power, a second lens having positive refractive power, a third lens having positive refractive power, a fourth lens having negative refractive power, a fifth lens having negative refractive power, and a sixth lens having positive refractive power,
the method comprising assembling each lens in a lens barrel so as to satisfy the following conditional expressions:
1.52<L3R1/ f3
−1.000 <(L5R1+L4R2)/(L5R1−L4R2)<−0.310
where L3R1 denotes a radius of curvature of an object side lens surface of the third lens,
f3 denotes a focal length of the third lens,
L5R1 denotes a radius of curvature of an object side surface of the fifth lens, and
L4R2 denotes a radius of curvature of an image side surface of the fourth lens,
wherein the first lens is a negative meniscus lens closest to the object and has a concave surface facing the image,
wherein the continuous series of six lenses is devoid of lens elements between successive lenses of the series, and
wherein the fifth lens is a bi-concave lens or a negative lens having a concave surface facing the object.

### Claim 16

A fixed focal length optical system, comprising a continuous series of six lenses consisting of, in order from an object, consecutively:
a first lens having negative refractive power;
a second lens having positive refractive power;
a third lens having positive refractive power;
a fourth lens having negative refractive power;
a fifth lens having negative refractive power; and
a sixth lens having positive refractive power, and
the following conditional expressions being satisfied:
1.52<L3R1/f3
0.88<L4R2/f
where L3R1 denotes a radius of curvature of an object side lens surface of the third lens,
f3 denotes a focal length of the third lens,
L4R2 denotes a radius of curvature of an image side surface of the fourth lens, and
f denotes a focal length of the total lens system,
wherein the first lens is a negative meniscus lens closest to the object and has a concave surface facing the image,
wherein the continuous series of six lenses is devoid of lens elements between successive lenses of the series, and
wherein the fifth lens is a bi-concave lens or a negative lens having a concave surface facing the object.

### Claim 17 (depends on 16)

The fixed focal length optical system according to claim 16, wherein
the third lens and the fourth lens constitute a cemented lens, and satisfy the following conditional expression:
0.10<n3−n4<0.30
where n3 denotes a refractive index of a material of the third lens at the d-line, and n4 denotes a refractive index of a material of the fourth lens at the d-line.

### Claim 18 (depends on 16)

The fixed focal length optical system according to claim 16, wherein
the second lens is a positive meniscus lens having a convex surface facing the object.

### Claim 19 (depends on 16)

The fixed focal length optical system according to claim 16, wherein
the following conditional expression is satisfied:
1.00<Σd/f<1.30
where Σd denotes a distance on the optical axis from a lens surface closest to the object to a lens surface closest to the image in the optical system, and f denotes the focal length of the total lens system.

### Claim 20 (depends on 16)

The fixed focal length optical system according to claim 16, wherein
a lens surface closest to the image is aspherical.

### Claim 21 (depends on 16)

An optical apparatus including the fixed focal length optical system according to claim 16.

### Claim 22

A method for manufacturing a fixed focal length optical system including a continuous series of six lenses consisting of, in order from an object, consecutively, a first lens having negative refractive power, a second lens having positive refractive power, a third lens having positive refractive power, a fourth lens having negative refractive power, a fifth lens having negative refractive power, and a sixth lens having positive refractive power,
the method comprising assembling each lens in a lens barrel so as to satisfy the following conditional expressions:
1.52<L3R1/f3
0.88<L4R2/f
where L3R1 denotes a radius of curvature of an object side lens surface of the third lens,
f3 denotes a focal length of the third lens,
L4R2 denotes a radius of curvature of an image side surface of the fourth lens, and
f denotes a focal length of the total lens system,
wherein the first lens is a negative meniscus lens closest to the object and has a concave surface facing the image,
wherein the continuous series of six lenses is devoid of lens elements between successive lenses of the series, and
wherein the fifth lens is a bi-concave lens or a negative lens having a concave surface facing the object.