JPH05181107A - Video device for liquid crystal image - Google Patents

Abstract

(57) [Abstract] [Purpose] A video device that separates the screen image of a liquid crystal panel into image lights of three primary colors by four dichroic mirrors, and then synthesizes and displays the image lights. The purpose is to obtain accurate image quality. [Structure] A blue reflection dichroic mirror 60 having a characteristic of reflecting a wavelength of 500 nm or more, and about 500 to 60
The second red reflection dichroic mirror 61, 62 having a characteristic of reflecting a wavelength of about 550 nm or more is optically provided between the green reflection dichroic mirror 63 having a characteristic of reflecting a band wavelength of 0 nm and the characteristic. The red reflected dichroic mirror on one side is reflected by the red reflected dichroic mirror on the other side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video device such as a liquid crystal video projector and a liquid crystal projection television, and more particularly to a video device using a dichroic mirror.

[0002]

2. Description of the Related Art A conventional liquid crystal video projector of this type is shown in FIG. 1 is a light source for projecting white light, 2,
DMs 3, 4 and 5 reflect light in a specific wavelength range, transmit light in other wavelength ranges, and separate color light by wavelength.
(Dichroic mirror), 6, 7 and 8 are liquid crystal panels,
Reference numerals 9, 10, 11 are condenser lenses, 12 and 13 are total reflection mirrors, and 14 is a projection lens.

The above-mentioned four DMs 2, 3, 4 and 5 have the characteristic of separating the white light from the light source 1 into the three primary colors of blue, green and red. And the characteristic is determined as follows. The white light from the light source 1 is extracted in the visible light range (about 400 nm to 800 nm) using a bandpass filter or the like, and the chromaticities of blue, green, and red are almost the same as the chromaticities of the three primary colors specified by NTSC. Determine the wavelength range. As a result, for example, color light blue ≈500 nm or less, color light green ≈50
Assuming 0 to 550 nm and color light red≈600 nm or more, the characteristics of the four DMs 2, 3, 4, and 5 are determined based on this wavelength.

First, DM-5 is a DM- that reflects the color light red.
Define as R. That is, the cutoff wavelength, which is the separation point between the wavelength of reflected light and the wavelength of transmitted light, is 600 nm.
The DM-R having the characteristics shown in FIG. Next, DM3 and 4 are set to DM-G that reflects the green color light.
That is, a DM- having two cutoff wavelengths, a cutoff wavelength on the short wavelength side of 500 nm and a cutoff wavelength on the long wavelength side of 550 nm is provided.
Let G. And DM- which reflects colored light blue in DM2
B. That is, the DM-B is provided with the characteristics of FIG. 4C in which the cutoff wavelength is 500 nm. And
The above-mentioned four DMs 2, 3, 4, and 5 are arranged as shown in FIG.

In the projector described above, the white light emitted from the light source 1 is first reflected by the colored light blue by the DM 2. This colored light blue is totally reflected by the total reflection mirror 12, condensed by the condenser lens 9, and enters the liquid crystal panel 6. Then, the blue image light that has passed through DM4 and DM5 enters the projection lens 14. The light transmitted through DM2 is reflected by DM3 in the color light green. This green color light is condensed by the condenser lens 10 and enters the liquid crystal panel 7.
Then, it becomes green image light and is reflected by DM4 and D
The light transmitted through M5 enters the projection lens 14. DM2
And the light transmitted through DM3 become red color light and the condenser lens 1
The light is condensed at 1 and enters the liquid crystal panel 8. The red image light is totally reflected by the total reflection mirror 13, and the light reflected by the DM 5 enters the projection lens 14. Then, each image light becomes a combined light and is screened from the projection lens 14.
Projected onto the screen.

[0006]

The image projected by the above projector contains intermediate colors,
There is a problem that the image quality is deteriorated. That is, taking the color light blue as an example, the color light blue is reflected by the DM2, but at this time, only the color light blue is not completely reflected and selected. Generally, the transmittance in the DM transmission band is about 90% on average, and it is difficult to increase the transmittance beyond this. Therefore, about 10% of the non-selected wavelength light of about 500 nm or more is included in the wavelength light reflected by DM2.
The degree is included.

The color light blue containing this non-selective wavelength is subsequently D
About 50 in DM4 by passing through M4 and DM5
The light of non-selective wavelength in the range of 0 nm to 550 nm is also D
The light of non-selective wavelength of about 600 nm or more is reflected by M5, respectively, but the light of non-selective wavelength in the band of about 550 nm to 600 nm remains, and this appears as a colored light yellow in the projected image. Further, similarly to the above, for the colored light red, colored light cyan, which is an intermediate color between the colored light blue and the colored light green, appears. The inclusion of such an intermediate color results in image light having a poor color tone, leading to a reduction in projected image quality.

In view of the above problems, it is an object of the present invention to develop a liquid crystal image display device capable of preventing light leakage and maintaining an image with good color tone.

[0009]

In order to achieve the above object, the present invention has a first dichroic mirror for reflecting light from a light source to separate a first color light. A first optical system that transmits the third and fourth dichroic mirrors and guides it to a light projecting lens, and a second optical system that reflects the light transmitted through the first dichroic mirrors and separates the second color light.
It has a dichroic mirror of
A second optical system which is reflected by the dichroic mirror of and transmits the fourth dichroic mirror to lead to the light projecting lens;
The light transmitted through the first and second dichroic mirrors is converted into the fourth light.
And a third optical system that guides the third color light to the light projecting lens by being reflected by the dichroic mirror, and the liquid crystal images of the liquid crystal members arranged in each optical system are separated into three primary color lights and then combined. In a video device for a liquid crystal image to be displayed as a video, a dichroic mirror of either the first or the fourth
Is provided with a predetermined wavelength band for reflecting light, and the other dichroic mirror has a cutoff wavelength on the short wavelength side of the above wavelength band or a cut for switching from reflection to transmission on the wavelength side longer than this cutoff wavelength. An image device is proposed in which an off-wavelength is set, and cutoff wavelengths within the wavelength band are set for the second and third dichroic mirrors.

[0010]

In the image device constructed as described above, the light from the light source is first reflected by the first dichroic mirror to select light having a wavelength of, for example, 500 nm or less, and the selected wavelength light is selected by the third dichroic mirror. By passing through the negative dichroic mirror and the fourth dichroic mirror, light having a wavelength of 500 nm or less, that is, colored light blue, which contains almost no other colored light, is obtained. (First optical system)

After passing through the first dichroic mirror,
For example, light having a wavelength of 500 nm or more is reflected and selected, for example, light having a wavelength of 550 nm or more by the second dichroic mirror. The selected wavelength light is the third dichroic mirror having the same characteristics as the second dichroic mirror, and the wavelength light of 550 nm or more is reflected and selected.
It is a light having a wavelength of, for example, 550 nm or more, which hardly contains other color light. Then, this selected wavelength becomes, for example, light having a wavelength of 600 nm or more, that is, color light red by passing through the fourth dichroic mirror. (Second optical system)

The light transmitted through the first dichroic mirror and the second dichroic mirror contains almost no other color light, for example, light having a band wavelength of 500 nm to 550 nm, that is, color light green. (Third optical system) From this, blue separated by each dichroic mirror,
The green and red color lights become pure color lights that do not include intermediate colors, and the liquid crystal image is displayed by these pure color lights. Further, the same effect can be obtained when the first dichroic mirror and the fourth dichroic mirror are replaced among the arrangement configuration of the four dichroic mirrors described above.

[0013]

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an optical system diagram of a liquid crystal video projector embodying the present invention, and FIG. 2 is a characteristic diagram of a dichroic mirror provided in this projector.

This projector, like the conventional example, has a light source 50, three liquid crystal panels 51, 52 and 53, a condenser lens 54 provided corresponding to each liquid crystal panel 51, 52 and 53,
55, 56, two total reflection mirrors 57, 58, a projection lens 59, and four dichroic mirrors (hereinafter, D
60, 61, 62, 63. DM6 out of four DM60, 61, 62, 63
0 as the first DM, blue reflection DM-B that selectively reflects colored light blue, DM 61 and 62 as second and third DMs, and red reflection DM-R that selectively reflects colored light red, D
M63 is assigned as a fourth DM and is assigned as a green reflection DM-G that selectively reflects the color light green.

The above-mentioned blue reflection DM60 and red reflection D
M61, 62 and green reflection DM63 are shown in FIGS. 2 (A) and (B).
It has the unique characteristics shown in (C), and the characteristics are determined as follows.

White light from the light source 50 is extracted in the visible light range (about 380 to 780 nm) using a bandpass filter or the like, and the chromaticity of colored light blue, colored light red, and colored light green is defined by NTSC. A wavelength that substantially matches the chromaticity of blue, colored light red, and colored light green is determined. As a result, color light blue ≈ 500 nm or less,
Color light red ≈ 600 nm or more, color light green ≈ 500 to 550 nm
Below, based on this, blue reflection DM60, red reflection DM
The characteristics of 61, 62 and the green reflection DM 63 are determined.

In the case of the red reflection DMs 61 and 62, the limit wavelength (λR) on the short wavelength side in the color light red is longer than the limit wavelength (λG ₁ ) on the long wavelength side in the color light green, that is, in FIG. When λR> λG ₁ in A) and (B), the red reflection DMs 61 and 62 have a cutoff wavelength λG ₁ which is a separation point between the wavelength of reflected light and the wavelength of transmitted light, and λR <λG ₁ , The cutoff wavelength is λ
As R, the characteristics of the red reflection DMs 61 and 62 are determined. The characteristics obtained in this procedure are the characteristics shown in FIG.

In the case of the green reflection DM 63, the cutoff wavelength on the long wavelength side and the cutoff wavelength on the short wavelength side are determined. The cutoff wavelength on the long wavelength side is λR when λG ₁ <λR. , ΛG ₁ > λR, λG ₁ is set. Further, the cutoff wavelength on the short wavelength side is a case where the short wavelength side limit wavelength (λG ₂ ) in the color light green is longer than the long wavelength side limit wavelength (λB) in the color light blue, that is,
If λG ₂ > λB, then λB; if λG ₂ ≦ λB, then λB
And G _2. The characteristics shown in FIG. 2B are obtained by this procedure.

For the blue reflection DM60, λB <λG ₂
For the the .lambda.G _2, in the case of .lambda.B ≧ .lambda.G ₂ to a cutoff wavelength .lambda.B. The characteristics obtained in this procedure are shown in FIG.

In the above projector, the light source 50
From the white light projected from the first, the color light blue is selected by first reflecting the light of the wavelength of about 500 nm or less by the blue reflection DM 60. The selected color light blue is reflected by the total reflection mirror 57, condensed by the condenser lens 54, and incident on the liquid crystal panel 51. Then, it becomes blue image light, passes through the red reflection DM 62 and the green reflection DM 63, and enters the projection lens 59.

When the color light blue is selected by the blue reflection DM 60, the wavelengths of the color light red and the color light green are also included due to light leakage. That is, the transmittance of the dichroic mirror is about 90% on average, and it is difficult to increase the transmittance any more. Therefore, among the colored light blue reflected by the blue reflection DM 60, the non-selected wavelength of the blue reflection DM 60 is included. That is, about 10% of the combined wavelengths of the colored light red and the colored light green are included. However, when this color light blue passes through the red reflection DM 62, light having a wavelength of about 550 nm or more is reflected, and further, when passing through the green reflection DM 63, light having a wavelength of about 500 to 600 nm is reflected. Therefore, the final pure color light blue is about 500 nm or less.

About 500 transmitted through the blue reflection DM 60
As for the light having a wavelength of nm or more, the red reflection DM 61 then reflects the light having a wavelength of about 550 nm or more to select the color light red. The selected color light red wavelength is condensed by the condensing lens 55, enters the liquid crystal panel 52, becomes red image light, is reflected again by the red reflection DM 62, passes through the green reflection DM 63, and is projected through the projection lens 59. Incident on.

When the above-described colored light red is also reflected and selected by the red reflection DM 61, the wavelength of the colored light green is included due to light leakage. However, the color light red is reflected again by the red reflection DM 62 that selects and reflects the same wavelength light, so that the wavelength light of the color light green has a light leakage of 10% out of 10%, that is, 1%. Then, the light having a wavelength of about 600 nm or more is transmitted by passing through the green reflection DM 63, and becomes almost pure colored light red.

The light transmitted through the blue reflection DM 60 and the red reflection DM 61 becomes light having a wavelength in the range of about 500 nm to 550 nm, becomes almost pure colored green light, is condensed by the condenser lens 56, and enters the liquid crystal panel 53. Then, it becomes green image light, which is reflected by the total reflection mirror 58, further reflected and selected by the green reflection DM 63, and enters the projection lens 59.

Since the red, blue, and green color lights selected in this way contain almost no intermediate color, the composite image projected onto the screen from the projection lens 59 has a good color tone.
The image quality is highly accurate. It should be noted that, in the above-mentioned embodiment, even if the blue reflection DM 60 and the green reflection DM 63 are interchanged and arranged, the same effect as in the above-mentioned embodiment can be obtained.

Further, although the front projection type liquid crystal video projector has been described in the above embodiment, the same can be applied to the rear projection type liquid crystal projection television or the like.

[0027]

As described above, according to the image device of the present invention, since the lights of the three primary colors are separated into the color lights without including the intermediate colors, the formed image has a good color tone and the image quality is high. It becomes a video device that can obtain.

[Brief description of drawings]

FIG. 1 is an optical system diagram of a liquid crystal video projector embodying the present invention.

FIG. 2 is a characteristic diagram of red, green and blue reflection dichroic mirrors provided in the projector, (A) is a characteristic diagram of a red reflection dichroic mirror, and (B) is a characteristic diagram of a green reflection dichroic mirror; (C) is a characteristic diagram of a blue reflection dichroic mirror.

FIG. 3 is an optical system diagram of a liquid crystal video projector shown as a conventional example.

FIG. 4 is a characteristic diagram of blue, green and red reflection dichroic mirrors provided in a projector of a conventional example, (A) is a characteristic diagram of red reflection dichroic mirrors, and (B) is a characteristic of green reflection dichroic mirrors. FIG. 1C is a characteristic diagram of the blue reflection dichroic mirror.

[Explanation of symbols]

 50 light source 51, 52, 53 liquid crystal panel 54, 55, 56 condenser lens 57, 58 total reflection mirror 59 projection lens 60 blue reflection DM 61, 62 red reflection DM 63 green reflection DM

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication H04N 5/74 A 9068-5C 9/31 C 8943-5C

Claims (1)

[Claims] 1. A first dichroic mirror for reflecting light from a light source to separate a first color light, the first color light being transmitted through a third dichroic mirror and a fourth dichroic mirror. It has a first optical system that guides it to the lens and a second dichroic mirror that reflects the light that has passed through the first dichroic mirror and separates the second color light. The second optical system that reflects the light from the mirror and transmits the fourth dichroic mirror and guides it to the projection lens, and the light that has passed through the first and second dichroic mirrors is reflected by the fourth dichroic mirror. And a third optical system for guiding the third color light to the light projecting lens, and a liquid crystal image imaging device for separating the liquid crystal images of the liquid crystal members arranged in each optical system into the three primary color lights and then synthesizing the images. At
One of the first and fourth dichroic mirrors is provided with a predetermined wavelength band for reflecting light, and the other dichroic mirror has a cut-off wavelength on the short wavelength side of this wavelength band or this cut-off wavelength. A cutoff wavelength for switching from reflection to transmission is set on a wavelength side longer than the wavelength, and a cutoff wavelength within the above wavelength bandwidth is set for the second and third dichroic mirrors. Video equipment.