# US 8,786,956 B2 · Zoom lens system, imaging optical device, and digital appliance

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 8,786,956 B2
- Document ID: US8786956B2
- Status: Granted
- Kind: B2
- Application number: 13/773,111
- Filed: 2013-02-21
- Published: 2013-08-22
- Granted: 2014-07-22
- Earliest claimed: 2012-02-21
- Assignees: Konica Minolta Advanced Layers, Inc.
- Applicants: Yoshihito Souma; Yasushi Yamamoto
- Inventors: Yoshihito Souma; Yasushi Yamamoto
- Web page: https://patentgrep.com/patent/US8786956B2

## CPC

- G02B 15/144511: {arranged -+-+}
- G02B 15/14: by axial movement of one or more lenses or groups of lenses relative to the image plane for continuously varying the equivalent focal length of the objective
- G02B 15/177: having a negative front lens or group of lenses
- G02B 13/009: {having zoom function}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

A zoom lens system is composed of negative, positive, negative, and positive lens groups, of which at least the first to third move during zooming. During zooming from the wide-angle end to the telephoto end, the distance between the first and second lens groups decreases, the distance between the second and third lens groups varies, and the distance between the third and fourth lens groups increases. The conditional formulae 1.0≦|f2/f1|≦1.5 and 2.0≦|f4/f1|≦5.0 are fulfilled (f1, f2, and f4 representing the focal lengths of the first, second, and fourth lens groups).

## Claims

### Claim 1

A zoom lens system comprising, from an object side, a first lens group having a negative optical power, a second lens group having a positive optical power, a third lens group having a negative optical power, and a fourth lens group having a positive optical power, the zoom lens system achieving zooming by varying distances between the lens groups, wherein
during zooming, at least the first to third lens groups move individually,
during zooming from a wide-angle end to a telephoto end, the distance between the first and second lens groups decreases, the distance between the second and third lens groups varies, and the distance between the third and fourth lens groups increases, and
Conditional Formulae (1) and (2) below are fulfilled:
1.0≦|f2/f1|≦1.5 (1)
2.0≦|f4/f1|≦5.0 (2)
where
f1 represents a focal length of the first lens group;
f2 represents a focal length of the second lens group; and
f4 represents a focal length of the fourth lens group.

### Claim 2 (depends on 1)

The zoom lens system according to claim 1, wherein
an aperture stop that moves together with the second lens group during zooming is provided to an object side of or within the second lens group,
a cemented lens element formed by cementing together a negative lens element having a strong concave surface on an image side and a biconvex lens element is arranged within the second lens group, to an image side of the aperture stop, and
a material of the biconvex lens element fulfills Conditional Formula (3) below:
ΔPgF≧0.015 (3)
where
ΔPgF=PgF−αgF−βgF×νd;
PgF=(ng−nF)/(nF−nC);
ng represents a refractive index for a g-line;
nF represents a refractive index for an F-line;
nC represents a refractive index for a C-line;
αgF=0.6483;
βgF=−0.0018; and
νd represents an Abbe number of the lens material.

### Claim 3 (depends on 2)

The zoom lens system according to claim 2, wherein
materials of the lens elements composing the cemented lens element fulfill Conditional Formula (4) below
nn−np≧0.25 (4)
where
nn represents a refractive index of the negative lens element for the d-line; and
np represents a refractive index of the biconvex lens element for the d-line.

### Claim 4 (depends on 1)

The zoom lens system according to claim 1, wherein
a negative meniscus lens element that fulfills Conditional Formula (5) below is arranged in the third lens group:
1.0≦(R1+R2)/(R1−R2)≦3.5 (5)
where
R1 represents a radius of curvature of an object-side surface of the negative meniscus lens element; and;
R2 represents a radius of curvature of an image-side surface of the negative meniscus lens element.

### Claim 5 (depends on 1)

The zoom lens system according to claim 1, wherein
focusing is achieved by moving the third lens group, and
Conditional Formula (6) below is fulfilled:
1.2≦β3t≦4.0 (6)
where
β3t represents a paraxial lateral magnification at the telephoto end.

### Claim 6 (depends on 1)

The zoom lens system according to claim 1, wherein
an aperture stop that moves together with the second lens group during zooming is provided to an object side of or within the second lens group,
the second lens group has at least one air gap inside,
when the second lens group is divided into two lens groups located to opposite sides of a largest air gap within the second lens group, with the object-side lens group referred to as a 2a-th lens group and the image-side lens group referred to as a 2b-th lens group,
the 2a-th lens group has a positive optical power,
the aperture stop is arranged to an object side of the 2b-th lens group,
a surface concave to the object side is arranged at a most object-side position in the 2b-th lens group, and
Conditional Formula (7) below is fulfilled:
−5.0≦R2b/Ds≦−1.0 (7)
where
R2b represents a radius of curvature of the concave surface; and
Ds represents a distance from the aperture stop to a vertex of the concave surface along the optical axis.

### Claim 7 (depends on 6)

The zoom lens system according to claim 6, wherein
Conditional Formula (8) is fulfilled:
0.9≦f2a/f2≦1.4 (8)
where
f2a represents a focal length of the 2a-th lens group; and
f2 represents a focal length of the second lens group.

### Claim 8 (depends on 1)

The zoom lens system according to claim 1, wherein
the zoom lens system is an interchangeable lens for a mirrorless camera.

### Claim 9 (depends on 2)

The zoom lens system according to claim 2, wherein
a negative meniscus lens element that fulfills Conditional Formula (5) below is arranged in the third lens group:
1.0≦(R1+R2)/(R1−R2)≦3.5 (5)
where
R1 represents a radius of curvature of an object-side surface of the negative meniscus lens element; and;
R2 represents a radius of curvature of an image-side surface of the negative meniscus lens element.

### Claim 10 (depends on 2)

The zoom lens system according to claim 2, wherein
focusing is achieved by moving the third lens group, and
Conditional Formula (6) below is fulfilled:
1.2≦β3t≦4.0 (6)
where
β3t represents a paraxial lateral magnification at the telephoto end.

### Claim 11 (depends on 2)

The zoom lens system according to claim 2, wherein
an aperture stop that moves together with the second lens group during zooming is provided to an object side of or within the second lens group,
the second lens group has at least one air gap inside,
when the second lens group is divided into two lens groups located to opposite sides of a largest air gap within the second lens group, with the object-side lens group referred to as a 2a-th lens group and the image-side lens group referred to as a 2b-th lens group,
the 2a-th lens group has a positive optical power,
the aperture stop is arranged to an object side of the 2b-th lens group,
a surface concave to the object side is arranged at a most object-side position in the 2b-th lens group, and
Conditional Formula (7) below is fulfilled:
−5.0≦R2b/Ds≦−1.0 (7)
where
R2b represents a radius of curvature of the concave surface; and
Ds represents a distance from the aperture stop to a vertex of the concave surface along the optical axis.

### Claim 12 (depends on 11)

The zoom lens system according to claim 11, wherein
Conditional Formula (8) is fulfilled:
0.9≦f2a/f2≦1.4 (8)
where
f2a represents a focal length of the 2a-th lens group; and
f2 represents a focal length of the second lens group.

### Claim 13 (depends on 3)

The zoom lens system according to claim 3, wherein
a negative meniscus lens element that fulfills Conditional Formula (5) below is arranged in the third lens group:
1.0≦(R1+R2)/(R1−R2)≦3.5 (5)
where
R1 represents a radius of curvature of an object-side surface of the negative meniscus lens element; and;
R2 represents a radius of curvature of an image-side surface of the negative meniscus lens element.

### Claim 14 (depends on 3)

The zoom lens system according to claim 3, wherein
focusing is achieved by moving the third lens group, and
Conditional Formula (6) below is fulfilled:
1.2≦β3t≦4.0 (6)
where
β3t represents a paraxial lateral magnification at the telephoto end.

### Claim 15 (depends on 3)

The zoom lens system according to claim 3, wherein
an aperture stop that moves together with the second lens group during zooming is provided to an object side of or within the second lens group,
the second lens group has at least one air gap inside,
when the second lens group is divided into two lens groups located to opposite sides of a largest air gap within the second lens group, with the object-side lens group referred to as a 2a-th lens group and the image-side lens group referred to as a 2b-th lens group,
the 2a-th lens group has a positive optical power,
the aperture stop is arranged to an object side of the 2b-th lens group,
a surface concave to the object side is arranged at a most object-side position in the 2b-th lens group, and
Conditional Formula (7) below is fulfilled:
−5.0≦R2b/Ds≦−1.0 (7)
where
R2b represents a radius of curvature of the concave surface; and
Ds represents a distance from the aperture stop to a vertex of the concave surface along the optical axis.

### Claim 16 (depends on 15)

The zoom lens system according to claim 15, wherein
Conditional Formula (8) is fulfilled:
0.9≦f2a/f2≦1.4 (8)
where
f2a represents a focal length of the 2a-th lens group; and
f2 represents a focal length of the second lens group.

### Claim 17

An imaging optical device comprising an image sensor for converting an optical image formed on a light-sensing surface into an electrical signal and a zoom lens system provided such that an optical image of a subject is formed on a light-sensing surface of the image sensor, wherein
the zoom lens system comprises, from an object side, a first lens group having a negative optical power, a second lens group having a positive optical power, a third lens group having a negative optical power, and a fourth lens group having a positive optical power, the zoom lens system achieving zooming by varying distances between the lens groups, wherein during zooming, at least the first to third lens groups move individually; during zooming from a wide-angle end to a telephoto end, the distance between the first and second lens groups decreases, the distance between the second and third lens groups varies, and the distance between the third and fourth lens groups increases; and Conditional Formulae (1) and (2) below are fulfilled:
1.0≦|f2/f1|≦1.5 (1)
2.0≦|f4/f1|≦5.0 (2)
where
f1 represents a focal length of the first lens group;
f2 represents a focal length of the second lens group; and
f4 represents a focal length of the fourth lens group.

### Claim 18 (depends on 17)

The imaging optical device according to claim 17, wherein in the zoom lens system,
an aperture stop that moves together with the second lens group during zooming is provided to an object side of or within the second lens group,
a cemented lens element formed by cementing together a negative lens element having a strong concave surface on an image side and a biconvex lens element is arranged within the second lens group, to an image side of the aperture stop, and
a material of the biconvex lens element fulfills Conditional Formula (3) below:
ΔPgF≧0.015 (3)
where
ΔPgF=PgF−αgF−βgF×νd;
PgF=(ng−nF)/(nF−nC);
ng represents a refractive index for a g-line,
nF represents a refractive index for an F-line,
nC represents a refractive index for a C-line,
αgF=0.6483;
PgF=−0.0018; and
νd represents an Abbe number of the lens material.

### Claim 19

A digital appliance comprising an imaging optical device so as to be additionally equipped with at least one of a function of shooting a still image of a subject and a function of shooting a moving image of a subject, wherein
the imaging optical device comprises:
an image sensor for converting an optical image formed on a light-sensing surface into an electrical signal; and
a zoom lens system provided such that an optical image of a subject is formed on a light-sensing surface of the image sensor,
the zoom lens system comprises, from an object side, a first lens group having a negative optical power, a second lens group having a positive optical power, a third lens group having a negative optical power, and a fourth lens group having a positive optical power, the zoom lens system achieving zooming by varying distances between the lens groups, wherein during zooming, at least the first to third lens groups move individually; during zooming from a wide-angle end to a telephoto end, the distance between the first and second lens groups decreases, the distance between the second and third lens groups varies, and the distance between the third and fourth lens groups increases; and Conditional Formulae (1) and (2) below are fulfilled:
1.0≦|f2/f1|≦1.5 (1)
2.0≦|f4/f1|≦5.0 (2)
where
f1 represents a focal length of the first lens group;
f2 represents a focal length of the second lens group; and
f4 represents a focal length of the fourth lens group.

### Claim 20 (depends on 19)

The digital appliance according to claim 19, wherein in the zoom lens system,
an aperture stop that moves together with the second lens group during zooming is provided to an object side of or within the second lens group,
a cemented lens element formed by cementing together a negative lens element having a strong concave surface on an image side and a biconvex lens element is arranged within the second lens group, to an image side of the aperture stop, and
a material of the biconvex lens element fulfills Conditional Formula (3) below:
ΔPgF≧0.015 (3)
where
ΔPgF=PgF−αgF−βgF×νd;
PgF=(ng−nF)/(nF−nC);
ng represents a refractive index for a g-line,
nF represents a refractive index for an F-line,
nC represents a refractive index for a C-line,
αgF=0.6483;
βgF=−0.0018; and
νd represents an Abbe number of the lens material.