# US 11,994,745 B2 · Optical system and imaging device

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- Number: US 11,994,745 B2
- Document ID: US11994745B2
- Status: Granted
- Kind: B2
- Application number: 17/479,480
- Filed: 2021-09-20
- Published: 2022-06-02
- Granted: 2024-05-28
- Earliest claimed: 2020-11-30
- Assignees: Tamron Co., Ltd.
- Applicants: Tamron Co., Ltd.
- Inventors: Toshiya Segawa; Yuki Mori; Hirofumi Tabata
- Web page: https://patentgrep.com/patent/US11994745B2

## CPC

- G02B 9/60: having five components only
- G02B 7/04: with mechanism for focusing or varying magnification
- G02B 27/0025: {for optical correction, e.g. distorsion, aberration}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

There is provided: an optical system including a focus lens group having positive refractive power and configured to move along an optical axis when focusing from an infinite-distance object to a short-distance object, and satisfying predetermined conditional expressions; and an imaging device including the optical system. The focus lens group includes a lens subgroup A, an aperture stop, and a lens subgroup B in order from the object side. The lens subgroup A includes a negative lens, a positive lens, and a positive lens in order from the image side. The lens subgroup B includes a negative lens and a positive lens in order from the object side.

## Claims

### Claim 1

An optical system comprising:
a focus lens group having positive refractive power and configured to move along an optical axis when focusing from an infinite-distance object to a short-distance object, wherein
the focus lens group includes a lens subgroup A, an aperture stop, and a lens subgroup B in order from an object side,
the lens subgroup A includes a negative lens, a positive lens, and a positive lens in order from an image side,
the lens subgroup B includes a negative lens and a positive lens in order from the object side, and
the optical system satisfies following conditional expressions:
θct≥0.800 (1)
vd≤55 (2)
nd_pave<1.75 (3)
vd_pave>50 (4)
where
θct is a partial dispersion ratio from a C line to a t line of the negative lens in the part B group,
the partial dispersion ratio θct from the C line to the t line is defined by a following expression:
θct=(nC−nt)/(nF−nC)
nC is a refractive index on the C line,
nt is a refractive index on the t line,
nF is a refractive index on an F line,
vd is an Abbe number on a d line of the negative lens in the part B group,
nd_pave is an average value of refractive indices on the d line of all positive lenses disposed in the lens subgroup B, and
vd_pave is an average value of Abbe numbers on the d line of all positive lenses disposed in the lens subgroup B.

### Claim 2 (depends on 1)

The optical system according to claim 1 that satisfies a following conditional expression:
−0.007<0.00558×vd_n+0.531−θct_n<0.000 (5)
where
vd_n is an Abbe number on the d line of the negative lens disposed on the most object side in the lens subgroup B, and
θct_n is a partial dispersion ratio regarding the C line and the t line of the negative lens disposed on the most object side in the lens subgroup B.

### Claim 3 (depends on 1)

The optical system according to claim 1, wherein the lens subgroup A includes at least one positive lens that satisfies a following conditional expression:
0.623<θgF_p (8)
where
θgF_p is a partial dispersion ratio regarding a g line and the F line of the positive lens, and
a partial dispersion ratio egF from the g line to the F line is defined by a following expression:
θgF=(ng−nF)/(nF−nC)
ng is a refractive index on the g line.

### Claim 4 (depends on 1)

The optical system according to claim 1 that satisfies a following conditional expression:
1.50<Fa/F<6.00 (9)
where
Fa is a focal length on the d line of the lens subgroup A, and
F is a focal length on the d line of the optical system.

### Claim 5 (depends on 1)

The optical system according to claim 1, wherein a surface on the most image side of the lens subgroup A is concave with respect to the aperture stop, and a surface on the most object side of the lens subgroup B is concave with respect to the aperture stop.

### Claim 6 (depends on 1)

The optical system according to claim 1, further comprising a fixed lens group fixed in an optical axis direction when focusing from an infinite-distance object to a short-distance object on the object side of the focus lens group, wherein
the fixed lens group includes a negative lens and a positive lens in order from the object side.

### Claim 7 (depends on 1)

An imaging device comprising: the optical system according to claim 1; and an image sensor configured to convert an optical image formed by the optical system on the image side of the optical system into an electrical signal.

### Claim 8 (depends on 1)

The optical system according to claim 1, wherein the lens subgroup B includes at least four lenses.

### Claim 9 (depends on 1)

The optical system according to claim 1, wherein the lens subgroup B includes at least two cemented lenses.