# US 2017/0285451 A1 · Projection optical system and image projector

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- Number: US 2017/0285451 A1
- Document ID: US20170285451A1
- Status: Published application
- Kind: A1
- Application number: 15/464,585
- Filed: 2017-03-21
- Published: 2017-10-05
- Earliest claimed: 2016-03-30
- Assignees: Panasonic Intellectual Property Management Co., Ltd.
- Applicants: Panasonic Intellectual Property Management Co., Ltd.
- Inventors: Tsuneo UCHIDA; Katsu YAMADA
- Web page: https://patentgrep.com/patent/US20170285451A1

## CPC

- G03B 21/147: {Optical correction of image distortions, e.g. keystone}
- G02B 13/16: for use in conjunction with image converters or intensifiers {, or for use with projectors, e.g. objectives for projection TV}
- G02B 13/18: with lenses having one or more non-spherical faces, e.g. for reducing geometrical aberration {(G02B13/002 takes precedence)}
- G02B 17/08: Catadioptric systems {(used in non-imaging applications G02B19/00)}
- G02B 17/0852: {having a field corrector only}
- G03B 21/28: Reflectors in projection beam {(in illumination beam G03B21/2066)}
- 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)
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS

## Abstract

A projection optical system of the present disclosure projects onto a projection surface (screen) an image ray bundle formed on an image display element, and includes a transmissive optical system that is positioned on a side of an emission surface of the image display element and has positive power, and a reflective optical system including at least one mirror for reflecting, toward the projection surface, light rays emitted from the transmissive optical system. The transmissive optical system includes an aperture stop, at least one positive lens disposed closer to the image display element than the aperture stop is, a first positive meniscus-shaped lens, a negative lens, and a second positive meniscus-shaped lens with the first and second positive lenses and the negative lens being closer to the projection surface than the aperture stop is. The first and second positive lenses are disposed with the negative lens being disposed therebetween so that their respective concave surfaces face each other. During focusing, a spacing between the first positive lens and the negative lens and a spacing between the second positive lens and the negative lens remain unchanged.

## Claims

### Claim 1

A projection optical system for projecting onto a projection surface an image ray bundle formed on an image display element,
the projection optical system comprising:
a transmissive optical system positioned on a side of an emission surface of the image display element, the transmissive optical system having positive power; and
a reflective optical system including at least one mirror for reflecting, toward the projection surface, light rays emitted from the transmissive optical system,
wherein
the transmissive optical system includes:
an aperture stop;
at least one positive lens disposed closer to the image display element than the aperture stop is;
a first positive lens having a meniscus shape, the first positive lens being disposed closer to the projection surface than the aperture stop is;
a negative lens disposed closer to the projection surface than the aperture stop is; and
a second positive lens having a meniscus shape, the second positive lens being disposed closer to the projection surface than the aperture stop is,
the first positive lens and the second positive lens are disposed so that a concave surface of the first positive lens and a concave surface the second positive lens face each other,
the negative lens is disposed between the first positive lens and the second positive lens, and
during focusing, a spacing between the first positive lens and the negative lens and a spacing between the second positive lens and the negative lens remain unchanged.

### Claim 2 (depends on 1)

The projection optical system according to claim 1, wherein
an incident surface and an emission surface of the negative lens are concave.

### Claim 3 (depends on 1)

The projection optical system according to claim 1, wherein
the negative lens has an aspheric shape.

### Claim 4 (depends on 3)

The projection optical system according to claim 3, wherein
the shape of the negative lens is such that curvature reduces radially away from a center of the negative lens.

### Claim 5 (depends on 1)

The projection optical system according to claim 1, wherein
of the first positive lens and the second positive lens, a lens closer to the image display element satisfies the following condition (1):
1<|(R2+R1)/(R2−R1)|<10 (1)
where R1 is a radius of curvature of a surface of the lens disposed closer to the image display element, and R2 is a radius of curvature of an opposite surface of the lens disposed closer to the image display element.

### Claim 6 (depends on 1)

The projection optical system according to claim 1, wherein
at least one of the first positive lens and the second positive lens has an aspheric shape.

### Claim 7 (depends on 1)

The projection optical system according to claim 1, wherein
the transmissive optical system further includes a negative low-dispersion lens disposed closer to the projection surface than the aperture stop is.

### Claim 8 (depends on 1)

The projection optical system according to claim 1, wherein
the transmissive optical system further includes a meniscus-shaped lens group including the first positive lens and the second positive lens, and
a lens of the meniscus-shaped lens group, the lens having a largest thickness deviation ratio in the meniscus-shaped lens group, is disposed closer to the projection surface than the negative lens is.

### Claim 9 (depends on 1)

The projection optical system according to claim 1, wherein
an intermediate image is formed between the transmissive optical system and the projection surface.

### Claim 10

An image projector for projecting an image ray bundle onto a projection surface,
the image projector comprising:
an image display element that forms the image ray bundle; and
a projection optical system that includes
a transmissive optical system positioned on a side of an emission surface of the image display element, the transmissive optical system having positive power, and
a reflective optical system including at least one mirror for reflecting, toward the projection surface, light rays emitted from the transmissive optical system,
wherein
the transmissive optical system includes:
an aperture stop;
at least one positive lens disposed closer to the image display element than the aperture stop is;
a first positive lens having a meniscus shape, the first positive lens being disposed closer to the projection surface than the aperture stop is;
a negative lens disposed closer to the projection surface than the aperture stop is; and
a second positive lens having a meniscus shape, the second positive lens being disposed closer to the projection surface than the aperture stop is,
the first positive lens and the second positive lens are disposed so that a concave surface of the first positive lens and a concave surface of the second positive lens face each other,
the negative lens is disposed between the first positive lens and the second positive lens, and
during focusing, a spacing between the first positive lens and the negative lens and a spacing between the second positive lens and the negative lens remain unchanged.