# US 9,753,261 B2 · Projection lens and projection-type display apparatus

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

- Number: US 9,753,261 B2
- Document ID: US9753261B2
- Status: Granted
- Kind: B2
- Application number: 14/660,963
- Filed: 2015-03-18
- Published: 2015-09-24
- Granted: 2017-09-05
- Earliest claimed: 2014-03-20
- Assignees: FUJIFILM Corporation
- Applicants: FUJIFILM Corporation
- Inventors: Chikara Yamamoto
- Web page: https://patentgrep.com/patent/US9753261B2

## CPC

- G02B 13/16: for use in conjunction with image converters or intensifiers {, or for use with projectors, e.g. objectives for projection TV}
- G02B 13/02: Telephoto objectives, i.e. systems of the type + - in which the distance from the front vertex to the image plane is less than the equivalent focal length
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

A projection lens consists essentially of a first lens group having positive refractive power and a second lens group having positive refractive power in this order from a magnification side. A surface closest to a reduction side in the first lens group is convex. The second lens group consists of two single lenses each having positive refractive power, and in each of which a surface having a smaller absolute value faces the reduction side. Further, the following conditional expressions (1) through (4) are satisfied: |R1b/R1f|≦0.5 (1); |R2b/R2f|≦0.6 (2); |Δ/f2|≦0.3 (3) and d2/f2≦0.4 (4).

## Claims

### Claim 1

A projection lens consisting essentially of:
a first lens group having positive refractive power; and
a second lens group having positive refractive power in this order from a magnification side,
wherein a surface closest to a reduction side in the first lens group is convex, and
wherein the second lens group consists of two single lenses each having positive refractive power, and in each of which a surface having a smaller absolute value of a curvature radius faces the reduction side, and
wherein the following conditional expressions (1) through (4) are satisfied:
|R1b/R1f|≦0.5 (1);
|R2b/R2f|≦0.6 (2);
|Δ/f2|≦0.3 (3); and
d2/f2≦0.4 (4), where
R1b: a curvature radius of a reduction-side surface of the positive lens located toward the magnification side in the second lens group,
R1f: a curvature radius of a magnification-side surface of the positive lens located toward the magnification side in the second lens group,
R2b: a curvature radius of a reduction-side surface of the positive lens located toward the reduction side in the second lens group,
R2f: a curvature radius of a magnification-side surface of the positive lens located toward the reduction side in the second lens group,
Δ: a distance between a lens surface closest to the reduction side in the first lens group and a magnification-side focal position of the second lens group,
f2: a focal length of the whole second lens group, and
d2: the total length of the second lens group.

### Claim 2 (depends on 1)

The projection lens, as defined in claim 1, wherein the following conditional expressions (5) and (6) are satisfied:
0.0≦R1b/R1f≦0.5 (5); and
−0.6≦R2b/R2f≦0.4 (6).

### Claim 3 (depends on 2)

The projection lens, as defined in claim 2, wherein the following conditional expression (5-1) is satisfied:
0.1≦R1b/R1f≦0.5 (5-1).

### Claim 4 (depends on 2)

The projection lens, as defined in claim 2, wherein the following conditional expression (6-1) is satisfied:
−0.5≦R2b/R2f≦0.3 (6-1).

### Claim 5 (depends on 1)

The projection lens, as defined in claim 1, wherein the following conditional expression (7) is satisfied:
R1f/R2f≦0.6 (7).

### Claim 6 (depends on 1)

The projection lens, as defined in claim 1, wherein the following conditional expression (8) is satisfied:
0.9≦f2/f≦3.5 (8), where
f: a focal length of an entire system.

### Claim 7 (depends on 1)

The projection lens, as defined in claim 1, wherein the following conditional expression (9) is satisfied:
0.2≦dd/l≦0.5 (9), where
dd: a distance between the first lens group and the second lens group, and
l: the total length of an entire system.

### Claim 8 (depends on 1)

The projection lens, as defined in claim 1, wherein the following conditional expression (10) is satisfied:
Bf/f≦0.35 (10), where
Bf: a back focus of an entire system, and
f: a focal length of the entire system.

### Claim 9 (depends on 1)

The projection lens, as defined in claim 1, wherein the following conditional expression (11) is satisfied:
1.7≦N2 (11), where
N2: a refractive index of each lens constituting the second lens group.

### Claim 10 (depends on 1)

The projection lens, as defined in claim 1, wherein the first lens group consists essentially of:
a first lens having positive refractive power;
a second lens having negative refractive power;
a third lens having negative refractive power;
a fourth lens having positive refractive power;
a fifth lens having positive refractive power; and
a sixth lens having positive refractive power in this order from the magnification side.

### Claim 11 (depends on 10)

The projection lens, as defined in claim 10, wherein the third lens and the fourth lens are cemented together.

### Claim 12 (depends on 1)

The projection lens, as defined in claim 1, wherein the following conditional expression (4-1) is satisfied:
d2/f2≦0.3 (4-1).

### Claim 13 (depends on 1)

The projection lens, as defined in claim 1, wherein the following conditional expression (7-1) is satisfied:
−3.0≦R1f/R2f≦0.5 (7-1).

### Claim 14 (depends on 1)

The projection lens, as defined in claim 1, wherein the following conditional expression (8-1) is satisfied:
1.2≦f2/f≦3.0 (8-1), where
f: a focal length of an entire system.

### Claim 15 (depends on 1)

A projection-type display apparatus comprising:
a light source;
a light valve, which light from the light source enters; and
the projection lens as defined in claim 1, as a projection lens that projects an optical image formed by light that has been optically modulated by the light valve onto a screen,
wherein also the light entering the light valve passes through the second lens group before the light enters the light valve.