# US 7,466,368 B2 · Image projection apparatus and adjusting method used for the same

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- Number: US 7,466,368 B2
- Document ID: US7466368B2
- Status: Granted
- Kind: B2
- Application number: 11/228,605
- Filed: 2005-09-16
- Published: 2006-03-30
- Granted: 2008-12-16
- Earliest claimed: 2004-09-17
- Assignees: Canon Kabushiki Kaisha
- Inventors: Atsushi Okuyama; Makoto Takahashi
- Web page: https://patentgrep.com/patent/US7466368B2

## CPC

- H04N 9/3105: {for displaying all colours simultaneously, e.g. by using two or more electronic spatial light modulators (simultaneous projection in colour photography G03B33/10; beam splitting or combining systems per se G02B27/10)}
- H04N 9/315: {Modulator illumination systems (general applications of lighting devices F21V; general optical systems G02B; lamp houses for projectors not peculiar to the presence of an electronic spatial light modulator G03B21/20)}
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

An image projection apparatus includes a first reflection type liquid crystal display device for modulating and reflecting red light, a second reflection type liquid crystal display device for modulating and reflecting green light, a third reflection type liquid crystal display device for modulating and reflecting blue light, the image projection apparatus projecting colored light made of the red, green and blue lights from the first to third reflection type liquid crystal display devices, a first 1/4 wave plate provided on an optical path of the red light, a second 1/4 wave plate provided on an optical path of the green light, and a third 1/4 wave plate provided on an optical path of the blue light, a direction of a fast axis of the third 1/4 wave plate being different from a direction that minimizes leakage light of the blue light.

## Claims

### Claim 1

An image projection apparatus comprising:
a first reflection type liquid crystal display device for modulating and reflecting red light;
a second reflection type liquid crystal display device for modulating and reflecting green light;
a third reflection type liquid crystal display device for modulating and reflecting blue light, said image projection apparatus projecting colored light made of the red, green and blue lights from said first to third reflection type liquid crystal display devices;
a first 1/4 wave plate provided on an optical path of the red light;
a second 1/4 wave plate provided on an optical path of the green light; and
a third 1/4 wave plate provided on an optical path of the blue light, a direction of a fast axis of the third 1/4 wave plate being different from a direction that minimizes leakage light of the blue light.

### Claim 2 (depends on 1)

An image projection apparatus according to claim 1, wherein a direction of a fast axis of the third 1/4 phase plate is shifted by 1° or greater from a direction of a fast axis which minimizes the leakage light of the blue light.

### Claim 3 (depends on 1)

An image projection apparatus according to claim 1, wherein a direction of a fast axis of the third 1/4 phase plate is shifted by 2.5° or greater from a direction of a fast axis which minimizes the leakage light of the blue light.

### Claim 4 (depends on 1)

An image projection apparatus according to claim 1, wherein an angle is within 5° between a direction of a fast axis of the third 1/4 phase plate and a direction of a fast axis which minimizes the leakage light of the blue light.

### Claim 5 (depends on 1)

An image projection apparatus according to claim 1, wherein a fast axis of the third 1/4 phase plate has a rotational angle different from that of the first 1/4 phase plate.

### Claim 6 (depends on 1)

An image projection apparatus according to claim 1, wherein a slow axis of the third 1/4 phase plate has a rotational angle different from that of the first 1/4 phase plate.

### Claim 7 (depends on 1)

An image projection apparatus according to claim 1, further comprising;
a projection optical system for synthesizing and projecting optical paths from the first to third reflection type liquid crystal display devices; and
a polarization beam splitter for introducing light from a light source to the first to third reflection type liquid crystal display devices, and for the light reflected on the first reflection type liquid crystal display device to said projection optical system.

### Claim 8 (depends on 1)

An image projection apparatus according to claim 1, wherein an angle is within 1° between each of directions of fast axes of the first and second 1/4 phase plates and a corresponding one of the directions that minimize the leakage lights of the red and green lights.

### Claim 9 (depends on 1)

An image projection apparatus according to claim 1, wherein where a first fast-axis angle is defined as an angle between a direction of a fast axis of the first 1/4 phase plate and a direction of a fast axis that minimizes leakage light of the red light, a second fast-axis angle is defined as an angle between a direction of a fast axis of the second 1/4 phase plate and a direction of a fast axis that minimizes leakage light of the green light, and a third fast-axis angle is defined as an angle between a direction of a fast axis of the third 1/4 phase plate and a direction of a fast axis that minimizes the leakage light of the blue light, the third fast-axis angle is greater than each of the first and second fast-axis angles.