# US 12,007,539 B2 · Projection lens system and image projection device

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- Number: US 12,007,539 B2
- Document ID: US12007539B2
- Status: Granted
- Kind: B2
- Application number: 17/113,376
- Filed: 2020-12-07
- Published: 2021-04-22
- Granted: 2024-06-11
- Earliest claimed: 2018-09-28
- Assignees: Panasonic Intellectual Property Management Co., Ltd.
- Applicants: Panasonic Intellectual Property Management Co., Ltd.
- Inventors: Takuya Imaoka
- Web page: https://patentgrep.com/patent/US12007539B2

## CPC

- G02B 15/143105: {arranged +-+}
- G03B 21/00: Projectors or projection-type viewers; Accessories therefor (devices for changing pictures G03B23/00)
- G02B 13/16: for use in conjunction with image converters or intensifiers {, or for use with projectors, e.g. objectives for projection TV}
- G02B 15/16: with interdependent non-linearly related movements between one lens or lens group, and another lens or lens group (G02B15/22 takes precedence)
- G03B 21/142: {Adjusting of projection optics}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G03B: APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR (optical parts of such apparatus G02B; photosensitive materials or processes for photographic purposes G03C; apparatus for processing exposed photographic materials G03D)

## Abstract

A projection lens system is a projection lens system including a plurality of lens groups, the plurality of lens groups each including one or more lenses and moving such that an interval between the lens groups changes during a zooming action, the projection lens system including a first lens group disposed closest to a magnification side, the first lens group having positive power, wherein the first lens group includes one negative lens satisfying 0.0005<Δpgfn<0.01 and 32<vdn<45.

## Claims

### Claim 1

A projection lens system comprising a plurality of lens groups, the plurality of lens groups each including one or more lenses and moving such that an interval between the lens groups changes during a zooming action,
the projection lens system comprising a first lens group disposed closest to a magnification side, the first lens group having positive power,
wherein the first lens group includes one negative lens satisfying following conditions (1) and (2):
0.0005<Δpgfn<0.01 (1)
32<vdn<45 (2)
where Δpgfn=(ngn−nfn)/(nfn−ncn)−(−2.20599×10−3×vdn+6.69612×10−1),
vdn is Abbe number of the negative lens,
ngn is a refractive index of the negative lens to g-line,
nfn is a refractive index of the negative lens to F-line, and
ncn is a refractive index of the negative lens to C-line,
the projection lens system further comprising: a second lens group disposed closer to a reduction side of the first lens group, the second lens group having negative power; and
a third lens group disposed closer to a reduction side of the second lens group, the third lens group having positive power,
wherein a lens of the second lens group disposed closest to the magnification side has positive power.

### Claim 2 (depends on 1)

The projection lens system according to claim 1, satisfying the following condition (3):
0.8<|fn/f1|<1.5 (3)
where fn is a focal length of the negative lens, and
f1 is a focal length of the first lens group.

### Claim 3 (depends on 1)

The projection lens system according to claim 1, satisfying the following condition (4):
1.0<f1/ft<2.0 (4)
where
ft is a focal length when a projection distance of an entire system at a telephoto end is infinity, and
f1 is a focal length of the first lens group.

### Claim 4 (depends on 1)

The projection lens system according to claim 1, wherein the first lens group includes at least one positive lens, and satisfies following condition (5):
dn1/dt<−4.5×10−6 (5)
where dn1/dt is a relative refractive index-temperature coefficient of a material of the positive lens of the first lens group at normal temperature, which is 20° C. to 30° C., based on a refractive index of the positive lens to d-line.

### Claim 5 (depends on 1)

The projection lens system according to claim 1, satisfying the following condition (6):
0.2<|f2/ft|<0.7 (6)
where f2 is a focal length of the second lens group.

### Claim 6 (depends on 1)

The projection lens system according to claim 1, satisfying the following condition (7):
0.3<f3/ft<1.0 (7)
where f3 is a focal length of the third lens group.

### Claim 7 (depends on 1)

The projection lens system according to claim 1, wherein the lens of the second lens group disposed closest to the magnification side satisfies following conditional expressions:
0.0005<Δpgfp<0.01 (8)
32<vdp<45 (9)
where Δpgfp=(ngp−nfp)/(nfp−ncp)−(−2.20599×10−3×vdp+6.69612×10−1),
vdp is Abbe number of the lens of the second lens group disposed closest to the magnification side,
ngp is a refractive index for g-line, of the lens of the second lens group disposed closest to the magnification side,
nfp is a refractive index for F-line, of the lens of the second lens group disposed closest to the magnification side, and
ncp is a refractive index for C-line, of the lens of the second lens group disposed closest to the magnification side.

### Claim 8 (depends on 1)

The projection lens system according to claim 1, wherein the third lens group includes at least five positive lenses of that satisfy following condition:
dn3/dt<−4.5×10−6(10)
where dn3/dt is a relative refractive index-temperature coefficient of a material of the positive lens of the third lens group at normal temperature, which is 20° C. to 30° C., based on a refractive index of the positive lens to d-line.

### Claim 9 (depends on 1)

The projection lens system according to claim 1, wherein the first lens group includes the negative lens having negative power, a first positive lens having positive power, and a second positive lens having positive power which are arranged in order from the magnification side.

### Claim 10 (depends on 1)

An image projection device comprising:
the projection lens system according to claim 1; and
an image forming element to generate an image to be projected onto a screen.