JPH0682744A - Liquid crystal projector - Google Patents

Abstract

PURPOSE:To vary the thickness of a glass base in a plurality of dichroic filters arranged on synthetic optical systems for synthesizing each color light, shift the positions of stray lights generated by the respective dichroic filters, and prevent the increase in intensity caused by the superposition of the projected stray lights. CONSTITUTION:A liquid crystal projector is provided with a spectral optical system 14 for dividing the light from a light source 12 into a plurality of color lights; an image display means 15 consisting of a plurality of liquid crystal display panels 24-26 for displaying an image corresponding to each divided color; a synthetic optical system 16 having a plurality of dichroic filters 28, 29 for synthesizing the light illuminated by each color light and transmitted by each liquid crystal panel; and a projector lens 18 for projecting the synthesized light to a screen 19. The thicknesses of glass bases 28a, 29a of at least two dichroic filters in the synthetic optical system are differed to each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal projector in which light carrying an image illuminating a plurality of liquid crystal display panels is combined by a dichroic filter and projected by a projection lens.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal projector for projecting a magnified image is generally an image for displaying an image corresponding to each color by splitting light from a light source into a plurality of colors by a spectroscopic optical system. The liquid crystal display panel of the display means is illuminated, and light carrying an image transmitted through each liquid crystal display panel is combined by a plurality of dichroic filters of a combining optical system,
It is provided in a configuration for projecting on a screen via a projection lens.

Further, the dichroic filter which constitutes the above-mentioned synthesizing optical system selectively reflects and transmits colors on the surface on which the dichroic coat is applied, and synthesizes images from a plurality of liquid crystal display panels as one color image. . On the other hand, the surface not coated with the dichroic coating is coated with an antireflection coating to suppress reflection as much as possible. The reflectance of an ordinary antireflection coating (multilayer) is about 0.2 to 2% in the visible wavelength range.

[0004]

However, in the conventional dichroic filter of the synthetic optical system in the liquid crystal projector as described above, although a plurality of glass substrates are arranged, the glass substrates are formed to have the same thickness. There is a problem that stray light overlaps with each other and the intensity is high, and the light is recognized in a projected image and deteriorates the image quality.

That is, referring to FIG. 3, an example of the image combining optical system by the two dichroic filters 41 and 42 will be explained. For example, the red image light 1 is incident on the first dichroic filter 41 and its surface is Dichroic coat
It is reflected by 41b, is incident on the second dichroic filter 42, is reflected by the dichroic coat 42b on the surface thereof, and is projected. On the other hand, the light 2 of the green image is incident on the back side of the first dichroic filter 41, passes through the glass substrate 41a and the dichroic coat 41b from the antireflection coat 41c thereof, and is combined with the light 1 of the red image. And the blue image light 3 is incident on the back side of the second dichroic filter 42, passes through the glass substrate 42a and the dichroic coat 42b from the antireflection coat 42c thereof, and then passes through the first dichroic filter 42. It is combined with the light 4 from 41 to obtain a combined light 5 for projection.

Then, the first dichroic filter 41
Dichroic coat out of light 1 of red image incident on
Of the light 2 transmitted through 41b and the light 2 of the green image incident from the antireflection coating 41c, the light reflected by the dichroic coating 41b is converted into the light amount by the antireflection coating 41c on the opposite side.
0.2 to 2% is reflected, and a part of the light is again transmitted through the dichroic coat 41b and is incident on the second dichroic filter 42 as stray light 4a for the light 4 combined by the first dichroic filter 41.

The first dichroic filter
When the light 4 combined in 41 is incident on the second dichroic filter 5, a part of the light transmitted through the dichroic coat 42b and the antireflection coat 42 as described above.
Of the light 3 of the blue image incident from c, the light reflected by the dichroic coat 42b passes through the glass substrate 42a, is reflected by the antireflection coat 42c on the opposite side, and part of the light passes through the dichroic coat 42b again. , The stray light 5a for the light 5 combined by the second dichroic filter 42 is incident on a projection lens (not shown), and the stray light 4a from the first dichroic filter 4a coincides with the stray light 5a. It is synthesized.

The stray light described above is generated by both dichroic filters 4
The 1,42 glass substrates 41a, 42a have the same thickness, and the stray light 4a due to the first dichroic filter 41 and the stray light 5a due to the second dichroic filter are formed at the same position, and both are overlapped to increase the light amount. , The intensity exceeds the threshold that is projected on the same position on the screen and is recognized as stray light, which may lead to deterioration of image quality and blurring.
In particular, in a bright and dark image having a bright line in a dark background portion, stray light may be projected on the dark portion and may be remarkable.

Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide a liquid crystal projector capable of obtaining a high-quality image by reducing the intensity of stray light by the dichroic filter so that the stray light is not recognized. It is what

[0010]

In order to achieve the above object, a liquid crystal projector of the present invention comprises a spectroscopic optical system that disperses light from a light source into a plurality of color lights, and a plurality of devices that display images corresponding to each of the disperse colors. Image display means by a liquid crystal display panel, a combining optical system having a plurality of dichroic filters that combine lights that are illuminated by the respective color lights and transmitted through the respective liquid crystal display panels, and a projection lens that projects the combined lights onto a screen. And at least two of the composite optical systems
The glass substrates of the dichroic filters are made different in thickness.

[0011]

In the liquid crystal projector as described above, even if stray light occurs due to a part of the light that should originally be reflected or transmitted through the dichroic coat in each dichroic filter of the composite optical system being transmitted or reflected, a plurality of dichroic Since the thickness of the glass substrate of the filter is different, the stray light generation position in each dichroic filter is different based on this difference in thickness, and each stray light is also displaced when projected onto the screen. The intensity is low without overlapping and does not reach the threshold value, and a good projection image can be obtained without being recognized as stray light.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of an optical system of a liquid crystal projector.

The liquid crystal projector 10 includes a spectroscopic optical system 14 for separating the light from the light source 12 into a plurality of color lights, an image display means 15 for displaying an image corresponding to each of the separated colors, and an image illuminated by the respective color lights. A combining optical system 16 for combining the light carrying the image transmitted through the display means 15 and a projection lens 18 for projecting the combined light onto a screen 19 are provided.

The spectroscopic optical system 14 comprises two dichroic filters 21 and 22 for splitting the light emitted from the light source 12 into three colors of blue, green and red, and a total reflection mirror 23 for changing the optical path. There is. That is, the first dichroic filter 21
The green light G is reflected and dispersed by the second dichroic filter 21, the red light R is reflected by the second dichroic filter 22, and the blue light B is transmitted to be separated into three colors. It is a thing.

Further, the image display means 15 has three liquid crystal display panels 24, 2 for displaying images corresponding to respective colors of blue, red and green.
5, 26 are provided respectively in the optical paths of the color lights dispersed by the spectroscopic optical system 14, and are transmitted and illuminated by the respective color lights.

On the other hand, the combining optical system 16 combines an optical path changing total reflection mirror 27 and two dichroic filters 28, 29 for combining the three components of light in the convergent optical path from the light source 12 to the projection lens 18. It has and. That is, the first dichroic filter 28 combines the light reflected by the filter 28 and transmitted through the red liquid crystal display panel 25 with the light transmitted through the filter 28 and transmitted through the green liquid crystal display panel 26. And is further reflected by the second dichroic filter 29.
The red / green light combined by the dichroic filter 28 and the light transmitted through the blue liquid crystal display panel 27 that has passed through the filter 29 are combined, and the light that has been combined by the second dichroic filter 29 It is enlarged and projected on the screen 19 by the projection lens 18.

The two dichroic filters 28, 29 in the synthetic optical system 16 as described above are configured so that the glass substrates have different thicknesses. That is, the dichroic filters 28 and 29 are, as shown in FIG.
The dichroic coats 28b and 29b that selectively reflect and transmit colored light are provided on one surface of the glass substrates 28a and 29a, and the antireflection coatings 28c and 29c are provided on the opposite surface. The thickness of the glass substrate 28a of the first dichroic filter 28 is smaller than that of the glass substrate 29a of the second dichroic filter 29.

Due to the difference in the thickness of the glass substrates 28a and 29a of the dichroic filters 28 and 29 in the synthetic optical system 16, the position of stray light projected on the screen 19 is separated to reduce the intensity. The operation will be described with reference to FIG.

First, the dichroic filters 28, 29
In the synthesis by, the light 1 of the red image is incident on the first dichroic filter 28 and reflected by the dichroic coat 28b on its surface, and is incident on the second dichroic filter 29 and reflected by the dichroic coat 29b on its surface and projected. To be done. On the other hand, the light 2 of the green image is the first
Is incident on the back side of the dichroic filter 28, passes through the glass substrate 28a and the dichroic coat 28b from the antireflection coat 28c, becomes the light 4 combined with the light 1 of the red image, and further the light 3 of the blue image. Second above
Is incident on the rear side of the dichroic filter 29, passes through the glass substrate 29a and the dichroic coat 29b from the antireflection coat 29c thereof, and is combined with the light 4 from the first dichroic filter 28 to form a combined light 5 for projection. I will get it.

In the combination of the above lights, of the red image light 1 incident on the first dichroic filter 28, the light transmitted through the dichroic coat 28b and the green image light 2 incident on the antireflection coat 28c are dichroic coats. Of the light reflected by 28b, 0.2 to 2% of the light amount is reflected by the antireflection coating 28c on the opposite side, a part of which is transmitted through the dichroic coat 28b again, and is mixed by the first dichroic filter 28. Is incident on the second dichroic filter 29 as stray light 4a for the second dichroic filter 29b.
It is reflected as the first stray light 5a with respect to the light 5 combined in (1).

Further, the light 4 combined by the first dichroic filter 28 is incident on the second dichroic filter 5 and a part of the light transmitted through the dichroic coat 29b and the antireflection coat 29c. Of the light 3 in the blue image, the light reflected by the dichroic coat 29b passes through the glass substrate 29a and the antireflection coat on the opposite side.
Reflected at 29c, part of it again dichroic coat
The second stray light 5b is generated as the second stray light 5b transmitted through the second dichroic filter 29 and transmitted through the second dichroic filter 29.

However, the stray light 5a, 5b is different in the thickness of the glass substrates 28a, 29a of both dichroic filters 28, 29, and the stray light 5a by the first dichroic filter 28 and the stray light 5b by the second dichroic filter 28 are different. They are formed separately at different positions, and their respective intensities are so small that they are not recognized as stray light when projected on the screen.

The dichroic filters 28 and 29 of the synthetic optical system 16 are made of the glass substrate because of the astigmatism.
28a and 29a are formed to have a thickness of about 1 to 2 mm. In this case, the difference between the glass substrates 28a and 29a is 0.3 mm or more, for example, 0.5 mm, to reduce stray light. Although the effect was confirmed, this is the liquid crystal projector 10
Of the thickness, the type of projection image, the coat structure of the dichroic filter, etc., and the actual difference in thickness is appropriately set.

[0024]

According to the liquid crystal projector of the present invention, the positions of the stray light generated by the dichroic filters can be separated by making the glass substrates of the dichroic filters of the synthetic optical system different in thickness. , The intensity of each projected stray light is reduced so that the intensity does not exceed the recognizable threshold value, and a clear projected image can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an optical system of a liquid crystal projector according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing generation of stray light by a dichroic filter of the synthetic optical system of FIG.

FIG. 3 is an explanatory diagram showing generation of stray light by a dichroic filter of a synthetic optical system of a liquid crystal projector according to a conventional technique.

[Explanation of symbols]

 10 Liquid crystal projector 12 Light source 14 Spectral optical system 15 Image display means 16 Composite optical system 18 Projection lens 19 Screen 24-26 Liquid crystal display panel 28,29 Dichroic filter 28a, 28b Glass substrate

Claims (1)

[Claims] 1. A spectroscopic optical system that disperses light from a light source into a plurality of color lights, image display means by a plurality of liquid crystal display panels that displays images corresponding to each of the disperse colors, and illumination by each of the color lights. In a liquid crystal projector including a combining optical system having a plurality of dichroic filters for combining the light transmitted through each liquid crystal display panel, and a projection lens for projecting the combined light onto a screen, at least two of the combining optical systems are provided. A liquid crystal projector characterized in that the glass substrates of the dichroic filters have different thicknesses.