# US 10,310,241 B2 · Zoom lens system

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- Number: US 10,310,241 B2
- Document ID: US10310241B2
- Status: Granted
- Kind: B2
- Application number: 15/422,777
- Filed: 2017-02-02
- Published: 2017-08-31
- Granted: 2019-06-04
- Earliest claimed: 2016-02-29
- Assignees: Ricoh Imaging Company, Ltd.
- Applicants: Ricoh Imaging Company, Ltd.
- Inventors: Tomoya Koga
- Web page: https://patentgrep.com/patent/US10310241B2

## CPC

- G02B 15/1421: {the first group being positive}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

A zoom lens system includes a positive first lens group, and a rear lens group behind the first lens group, in that order from the object side. The first lens group includes at least one positive single lens element, a negative meniscus lens element having a convex surface on the object side, and at least one positive lens element, in that order from the object side. A distance between the first lens group and the rear lens group increases upon zooming from the short to long focal length extremities. The following conditions (1) and (2) are satisfied: fG1/fn<−1.50 (1), and 65<νpave (2), wherein fG1 designates the focal length of the first lens group, fn designates the focal length of the negative meniscus lens element, and νpave designates the average value of the Abbe numbers with respect to the d-line of the positive lens elements.

## Claims

### Claim 1

A zoom lens system comprising a positive first lens group, and a subsequent rear lens group provided subsequently behind said first lens group, in that order from an object side,
wherein said first lens group includes at least one positive single lens element, a negative meniscus lens element having a convex surface on the object side, and at least one positive lens element, in that order from the object side,
wherein a distance between said first lens group and said subsequent rear lens group increases upon zooming from a short focal length extremity to a long focal length extremity, and
wherein the following conditions (1) and (2) are satisfied:
fG1/fn<−1.50 (1), and
65<νpave (2), wherein
fG1 designates a focal length of the first lens group,
fn designates a focal length of the negative meniscus lens element that is provided within the first lens group, and
νpave designates an average value of Abbe numbers with respect to a d-line of positive lens elements that are provided within the first lens group.

### Claim 2 (depends on 1)

The zoom lens system according to claim 1, wherein said subsequent rear lens group comprises at least one negative lens group, and wherein a negative nth lens group that is provided closest to the object side within said subsequent rear lens group includes a negative lens element that is provided closest to the object side within said negative nth lens group.

### Claim 3 (depends on 1)

The zoom lens system according to claim 1, wherein said subsequent rear lens group comprises at least one negative lens group, and wherein the following condition (3) is satisfied:
fG1/fGn<−0.70 (3), wherein
fG1 designates the focal length of the first lens group, and
fGn designates a focal length of said negative nth lens group that is provided closest to the object side within said subsequent rear lens group.

### Claim 4 (depends on 1)

The zoom lens system according to claim 1, wherein the following condition (4) is satisfied:
1.650<nn (4), wherein
nn designates a refractive index with respect to the d-line of the negative meniscus lens element that is provided within the first lens group.

### Claim 5 (depends on 1)

The zoom lens system according to claim 1, wherein the following condition (5) is satisfied:
1.40<fG1/R1p<3.30 (5), wherein
fG1 designates the focal length of the first lens group, and
R1p designates a paraxial radius of curvature of the surface closest to the object side on the first lens group.

### Claim 6 (depends on 1)

The zoom lens system according to claim 1, wherein the following condition (6) is satisfied:
1.30<(R1n+R2n)/(R1n−R2n) (6), wherein
R1n designates a paraxial radius of curvature of the surface on the object side of the negative meniscus lens element provided within the first lens group, and
R2n designates a paraxial radius of curvature of the surface on an image side of the negative meniscus lens element provided within the first lens group.

### Claim 7 (depends on 1)

The zoom lens system according to claim 1, wherein said subsequent rear lens group comprises at least one negative lens group, and wherein a negative nth lens group that is provided closest to the object side within said subsequent rear lens group includes a negative lens element that is provided closest to the object side within said negative nth lens group, and wherein the following condition (7) is satisfied:
fGn/R2Gn<−1.10 (7), wherein
fGn designates a focal length of said negative nth lens group that is provided closest to the object side within said subsequent rear lens group, and
R2Gn designates a paraxial radius of curvature of the surface on an image side of the negative lens element that is provided closest to the object side within said nth lens group.

### Claim 8 (depends on 1)

The zoom lens system according to claim 1, wherein said subsequent rear lens group comprises at least one negative lens group, and wherein a negative nth lens group that is provided closest to the object side within said subsequent rear lens group includes a negative lens element and a positive lens element, in that order from the object side.

### Claim 9 (depends on 1)

The zoom lens system according to claim 1, wherein said subsequent rear lens group comprises at least one negative lens group, and wherein a negative nth lens group that is provided closest to the object side within said subsequent rear lens group includes a negative lens element provided closest to an image side within said negative nth lens group.

### Claim 10 (depends on 9)

The zoom lens system according to claim 9, wherein said negative lens element that is provided closest to the image side, within said negative nth lens group, includes a concave surface on the object side, wherein the following condition (8) is satisfied:
29<νGn (8), wherein
νGn designates an Abbe number with respect to a d-line of the negative lens element that is provided closest to the image side within the nth lens group.

### Claim 11 (depends on 1)

The zoom lens system according to claim 1, wherein said subsequent rear lens group comprises at least one negative lens group, and wherein a negative nth lens group that is provided closest to the object side within said subsequent rear lens group comprises a negative second lens group provided immediately behind said first lens group on an image side thereof.

### Claim 12 (depends on 1)

The zoom lens system according to claim 1, wherein the following condition (9) is satisfied:
θgFn−(0.6440−0.001682×νn)<0 (9), wherein
νn designates an Abbe number with respect to a d-line of the negative meniscus lens element provided within said first lens group,
θgFn designates a partial dispersion ratio at a short wavelength side of the negative meniscus lens element provided within the first lens group,
θgF=(ng−nF)/(nF−nC),
ng designates a refractive index at a g-line,
nF designates the refractive index at a F-line, and
nC designates the refractive index at a C-line.

### Claim 13 (depends on 1)

The zoom lens system according to claim 1, wherein the following condition (10) is satisfied:
34<νn (10), wherein
νn designates an Abbe number with respect to a d-line of the negative meniscus lens element provided within said first lens group.

### Claim 14 (depends on 1)

The zoom lens system according to claim 1, wherein the following condition (11) is satisfied:
2.40<fG1/R2n (11), wherein
fG1 designates the focal length of said first lens group, and
R2n designates a paraxial radius of curvature of the surface on an image side of the negative meniscus lens element provided within the first lens group.

### Claim 15 (depends on 1)

The zoom lens system according to claim 1, wherein the following condition (12) is satisfied:
4.00<fG1/1Gd<13.00 (12), wherein
fG1 designates the focal length of the first lens group, and
1Gd designates a distance along an optical axis from a surface closest to the object side on the first lens group to the surface closest to an image side on the first lens group.

### Claim 16 (depends on 1)

The zoom lens system according to claim 1, wherein the following condition (13) is satisfied:
0.80<fG1/fw (13), wherein
fG1 designates the focal length of said first lens group, and
fw designates a focal length of the entire said zoom lens system at the short focal length extremity.

### Claim 17 (depends on 1)

The zoom lens system according to claim 1, wherein the following condition (14) is satisfied:
0.60<fG1/(fw×ft)1/2 (14), wherein
fG1 designates the focal length of said first lens group,
fw designates a focal length of the entire said zoom lens system at the short focal length extremity, and
ft designates a focal length of the entire said zoom lens system at the long focal length extremity.

### Claim 18 (depends on 1)

The zoom lens system according to claim 1, wherein a positive meniscus lens element having a convex surface on the object side is provided immediately in front on the object side of the negative meniscus lens element that is provided within said first lens group.

### Claim 19 (depends on 1)

The zoom lens system according to claim 1, wherein one or two positive lens elements are provided on an image side of the negative meniscus lens element that is provided within said first lens group.

### Claim 20 (depends on 1)

The zoom lens system according to claim 1, wherein said first lens group is configured to move toward the object side upon zooming from the short focal length extremity to the long focal length extremity.