JPH08271876A - Liquid crystal video projector - Google Patents

Abstract

PURPOSE: To equally set the optical path length of three primary color light beams arranging the optical system of a liquid crystal video projector nearly symmetrically. CONSTITUTION: A 1st dichroic mirror 102, a 4th reflection mirror 117, a green light liquid crystal display panel 107, a dichroic prism 105 and a projection lens 111 are positioned in a line aligned with the advancing direction of light 103 from a light source 101; and 1st and 3rd reflection mirrors 114 and 116, and 2nd and 5th reflection mirrors 115 and 118 are arranged to be linearly symmetric with the above-mentioned line as the axis of symmetry; then the optical path of red light R and the optical path of blue light B are formed to be linearly symmetric each other. Since green light G irradiates a liquid crystal display panel 107 positioned on the front side of the prism 105 by the 4th reflection mirror 117, the arrangement of the respective mirrors is nearly symmetric as the entire optical system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention separates light from a light source into three primary color lights using a color separation optical system, guides each of these primary color lights to a liquid crystal display panel, and modulates the brightness using a video signal. The present invention relates to a liquid crystal video projector that synthesizes by a dichroic prism and magnifies and projects the synthesized light onto a predetermined screen. More specifically, the present invention relates to an improvement in a mirror arrangement configuration of a color separation optical system including a dichroic mirror and a reflection mirror.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal video projector in which color-separated three primary color lights are modulated by a predetermined video signal using a liquid crystal display panel, the modulated lights are combined by a dichroic prism, and then enlarged and projected on a predetermined screen. Is widely known.

In such a liquid crystal video projector, a color composed of two dichroic mirrors and a plurality of reflection mirrors is provided for separating light from a light source into three primary color lights and guiding each primary color light to a corresponding liquid crystal display panel. Equipped with a separation optical system.

By the way, conventionally, in such a color separation optical system, since the optical path lengths of the primary color lights from the light source to the liquid crystal display panels are not all set equal,
The intensity distributions of the primary color lights do not match on the screen, causing color unevenness in the projected image, which causes deterioration of the image quality of the projected image.

Under these circumstances, in recent years, a liquid crystal video projector having a color separation optical system as shown in FIG. 4 has been disclosed in order to set the optical path lengths of the respective primary color lights to be equal (Japanese Patent Laid-Open No. Hei 5). No. 107658).

That is, to explain this prior art with reference to FIG. 4, first, the light from the light source 1 is separated by the first dichroic mirror 2 into the first primary color light R and the remaining primary color light. The first primary color light R is reflected at a right angle by the first dichroic mirror 2, and then the first reflection mirror 1
3, the second reflection mirror 14 and the third reflection mirror 15 sequentially make a right-angle reflection, and enter the first liquid crystal display panel 4.

On the other hand, the remaining primary color light is reflected at a right angle by the fourth reflecting mirror 16 and then separated into the second primary color light G and the third primary color light B by the second dichroic mirror 6.
The second primary color light G is reflected at a right angle by the second dichroic mirror 6. The second primary color light G is a fifth reflection mirror arranged on the back surface of the first reflection mirror 13.
The light is reflected at a right angle at 17 and enters the second liquid crystal display panel 7.
Further, the third primary color light B is reflected at a right angle by the sixth reflection mirror 18 and enters the third liquid crystal display panel 10. After that, the primary color lights transmitted through the respective liquid crystal display panels 4, 7, 10 are combined by the dichroic prism 5, and the combined primary color lights are enlarged and projected on the screen 12 by the projection lens 11.

In this prior art, two dichroic mirrors 2, 6 and six reflective mirrors 13, 14, 15, 1 are used.
Since 6, 17, 18 are arranged as described above and the optical path lengths of the primary color lights R, G, B from the light source 1 to the liquid crystal display panels 4, 7, 10 are set equal to each other, It is possible to avoid the occurrence of color unevenness.

[0009]

Generally, from the standpoint of an engineer, in designing a liquid crystal video projector, it is sensuously practical to arrange the mirrors so that the mirrors are arranged substantially symmetrically. There is a circumstance that it is easy to handle in terms of calculation.

Further, if the mirrors are arranged so as to be substantially symmetrical, the work of assembling the optical system becomes easy, and the arrangement when the optical system is incorporated into the case becomes easy.

However, in the above-mentioned prior art, the arrangement of each mirror constituting the optical system is asymmetrical,
It has been desired to develop a liquid crystal video projector in which the arrangement of each mirror is substantially symmetrical.

The present invention has been made in view of the above circumstances, and the mirrors of the optical system are arranged in a substantially symmetrical manner.
An object of the present invention is to provide a liquid crystal video projector in which the optical path lengths of the three primary color lights can be set equal to each other.

[0013]

A first liquid crystal video projector according to the present invention separates light from a light source into three primary color lights and irradiates a liquid crystal display panel corresponding to each primary color light, and the respective liquid crystal displays are displayed. In the panel, each of the primary color lights is brightness-modulated by a video signal corresponding to the primary color light, and these modulated primary color lights are combined by a dichroic prism.
In a liquid crystal video projector for enlarging and projecting the combined three primary color lights on a predetermined screen, one of the lights from the light source is leftward and the other is rightward with respect to the traveling direction of the light. A first dichroic mirror that separates the first primary color light and the remaining primary color light, and the first primary color light that is reflected by the first dichroic mirror in either the left or right direction is reflected in the forward direction. A first reflecting mirror, a second reflecting mirror that reflects the remaining primary color light reflected in the other direction to the left or right by the first dichroic mirror, and a second reflecting mirror. The remaining primary color light reflected in the forward direction is reflected by the second primary color light in the one direction, and the third primary color light is transmitted in the forward direction by the second primary color light and the second primary color light. A second dichroic mirror that splits into three primary color lights and the first primary color light reflected by the first reflecting mirror are reflected in the other direction, and the first dichroic prism near the side surface of the dichroic prism on the other direction side. A third reflection mirror, which is positioned and irradiates the liquid crystal display panel corresponding to the first primary color light, reflects the second primary color light reflected by the second dichroic mirror in the forward direction to form the dichroic prism. A fourth reflection mirror, which is located near the front side surface of the second side and irradiates the liquid crystal display panel corresponding to the second primary color light, and the third primary color light transmitted through the second dichroic mirror in the one direction. A fifth reflecting mirror which reflects and irradiates the liquid crystal display panel corresponding to the third primary color light located near the side surface of the dichroic prism on the one direction side. Wherein the first dichroic mirror, the fourth reflecting mirror,
The liquid crystal display panel corresponding to the second primary color light and the dichroic prism are located on a substantially straight line, and the straight line is a symmetry axis, and the first reflecting mirror, the second reflecting mirror, and the third reflecting mirror. The mirror and the fifth reflecting mirror are arranged symmetrically with respect to each other.
In addition, the optical paths of the three primary color lights are configured to be substantially equal to each other.

The second liquid crystal video projector of the present invention separates the light from the light source into three primary color lights and irradiates the liquid crystal display panels corresponding to the respective primary color lights, and in each of these liquid crystal display panels, In a liquid crystal video projector, the primary color light is brightness-modulated by a video signal corresponding to the primary color light, the modulated primary color lights are combined by a dichroic prism, and the combined three primary color lights are enlarged and projected on a predetermined screen. , The light from the light source is reflected upward in the traveling direction of the first primary color light, and the remaining primary color light is transmitted in the forward direction to transmit the first primary color light and the remaining primary color light. The first dichroic mirror for separating the primary color light and the remaining primary color light are used to reflect the second primary color light to the left and the third primary color light to the right. The second dichroic mirror that separates the second primary color light and the third primary color light, and the first primary color light that is reflected upward by the first dichroic mirror is above the second dichroic mirror. A first reflecting mirror that reflects the first primary color light in a forward direction so that the first primary color light passes therethrough, and a second reflection mirror that reflects the first primary color light that passes above the second dichroic mirror in a downward direction. A reflection mirror, a third reflection mirror for reflecting the second primary color light reflected leftward by the second dichroic mirror in a forward direction, and a right reflection reflected by the second dichroic mirror A fourth reflecting mirror that reflects the third primary color light in the forward direction and the first primary color light that is reflected by the second reflecting mirror in the forward direction, and the dike Situated in front of the vicinity of the side surface of the Ikkupurizumu, fifth reflecting mirror for irradiating the liquid crystal display panel corresponding to the first primary color light, the third
The second primary color light reflected by the reflecting mirror of the second reflection mirror is reflected to the right to irradiate the liquid crystal display panel corresponding to the second primary color light located near the left side surface of the dichroic prism. Corresponding to the third primary color light, which is located near the right side surface of the dichroic prism by reflecting the third primary color light reflected by the second reflection mirror and the fourth reflection mirror in the left direction. A seventh reflection mirror for irradiating a liquid crystal display panel, the first dichroic mirror, the second dichroic mirror, the fifth reflection mirror, the liquid crystal display panel corresponding to the first primary color light, and The dichroic prism is located on a substantially straight line, and the straight line is a symmetry axis, and the third reflecting mirror and the fourth reflecting mirror;
And the sixth reflection mirror and the seventh reflection mirror are arranged symmetrically to each other, and the optical path lengths of the three primary color lights are substantially equal to each other. It is what

The "forward direction", the "upward direction", and the "left-right direction" are relative directions to the traveling direction of the light from the light source when the optical system is arranged in a predetermined state. It is a convenient expression shown.

[0016]

According to the first liquid crystal video projector of the present invention, two dichroic mirrors and a plurality of reflection mirrors are used, and the light from the light source is converted into the first primary color light and the first primary color light by the first dichroic mirror. The other primary color light is separated into left and right, and the remaining primary color light is further separated into the second primary color light and the third primary color light by the second dichroic mirror, and the first primary color light is separated by the two reflecting mirrors. An optical path leading to either the left or right direction of the dichroic prism,
The third primary color light is constructed by two reflecting mirrors so that the optical path for guiding the light to the left or right of the dichroic prism is line-symmetrical to each other, and the second primary color light is reflected by the dichroic prism. Since it is configured to irradiate the front side of, the mirrors can be formed so that the arrangement of the mirrors is substantially symmetrical in the entire optical system.

According to the second liquid crystal video projector of the present invention, two dichroic mirrors and a plurality of reflection mirrors are used, and the light from the light source is directed upward by the first dichroic mirror. Is reflected by the first primary color light and the remaining primary color light is separated in the forward direction, and the remaining primary color light is separated by the second dichroic mirror. Light and third
Separated by reflecting the primary color light of each to the left and right,
The optical path that guides the second primary color light to the left of the dichroic prism using two reflection mirrors and the optical path that guides the third primary color light to the right of the dichroic prism using two reflection mirrors are line-symmetrical to each other. In addition, since the first primary color light is configured so as to bypass the second dichroic mirror upward by the three reflecting mirrors and to be irradiated to the front side of the dichroic prism, the entire optical system. Can be formed so that the arrangement of the mirrors is symmetrical.

As described above, according to the two liquid crystal video projectors constructed as described above, the arrangement of the mirrors of the optical system is formed to be substantially symmetrical, so that the optical path in the optical system can be sensed. The optical design is facilitated because it is easy to understand and the specific design numerical value can be easily calculated.

Also, in the manufacturing process of incorporating the optical system in a predetermined case, since the optical system is symmetrical, it is generally easy to secure a space.

Further, according to the two liquid crystal video projectors constructed as described above, since the optical path lengths of the three primary color lights are made substantially equal to each other, the occurrence of color unevenness in the projected image on the screen is prevented. It is possible to

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic view showing a liquid crystal video projector according to the first embodiment of the present invention. The liquid crystal video projector shown in FIG. 1 includes a light source 101 and first and second dichroic mirrors 102, 10 for separating light of three primary colors.
6, the first, second, third, fourth and fifth total reflection mirrors 114, 115, 116, 117 and 118, and the first, second and blue light liquid crystal display panels 104, 107 and 110. Dichroic prism 105 for combining three primary color lights and projection lens
It is mainly composed of 111 and.

The light source 101 is a high brightness white light source such as a halogen lamp or a metal halide lamp, and its output light 103 is made into a parallel light flux by an optical system (not shown).

A UV / IR cut filter for cutting ultraviolet light and infrared light is usually arranged on the light emission side of the light source 101, and cooling means for cooling the light source 101 and its vicinity by air cooling or the like. Is provided.

The first dichroic mirror 102 comprises a red light reflecting mirror 102a and a green / blue light reflecting mirror 102b which are orthogonal to each other in a cross shape, and the second dichroic mirror 106 is green. The light-reflecting mirror is formed by forming a dichroic film made of a dielectric multilayer film having a spectral characteristic as a mirror that reflects light of a predetermined primary color on each glass substrate.

Further, three liquid crystal display panels 104, 107,
Each of 110 is composed of a twisted nematic (TN) type liquid crystal display element, displays an image in accordance with a corresponding image signal from a liquid crystal driver (not shown), and modulates the intensity of each incident primary color light.

Further, the dichroic prism 105 is
It is formed by joining four right-angled prisms, and two orthogonally joined surfaces are provided with a dichroic film composed of a dielectric multilayer film having spectral characteristics as a red light reflection mirror and a blue light reflection mirror, respectively. And red, blue,
It is possible to combine the three primary color lights of green into one light beam of white light.

The projection lens 111 is so constructed as to project the combined three-primary-color light on a screen arranged at a predetermined distance, and a full-color image can be enlarged and projected on this screen.

Further, in the liquid crystal video projector of the present embodiment, each optical member is arranged on one plane as shown in FIG. 1, and the first dichroic mirror 102 and the fourth reflection member 102 are provided. Mirror 117, LCD panel for green light 107, dichroic prism 105 and projection lens
111 is located on a straight line that coincides with the traveling direction of the light 103 from the light source 101, and this straight line is the axis of symmetry,
114, a third reflecting mirror 116, and a second reflecting mirror
115 and the fifth reflection mirror 118 are arranged so as to be line-symmetrical to each other, and the optical path of the red light R and the optical path of the blue light B are formed to be line-symmetrical to each other. Moreover, the green light G is separated from the blue light B by the second dichroic mirror 106, and is radiated to the green light liquid crystal display panel 107 located in front of the dichroic prism 105 by the fourth reflecting mirror 117. Because
The optical system as a whole is configured so that the respective mirrors and the like are arranged in line symmetry.

The operation of the liquid crystal video projector configured as described above will be described below.

Light (white light) 103 output from the light source 101
Is separated into red light R and the remaining primary color light by the first dichroic mirror 102. The first dichroic mirror 102 is a combination of the dichroic mirror 102a having the spectral characteristic of reflecting the red light R and the dichroic mirror 102b having the spectral characteristic of reflecting the green light G / blue light B as described above. Therefore, the red light R is reflected to the light 103 in the left-right direction, and the remaining primary color light is reflected to the right-right direction.

The first total reflection mirror 114 receives the red light R reflected by the first dichroic mirror 102 at an incident angle of 45.
Make it incident at ° and reflect at right angles.
The second total reflection mirror 115 makes the red light R reflected by the first total reflection mirror 114 incident at an incident angle of 45 ° and reflects it in the direction of the liquid crystal display panel 104 for red light which is the right angle direction. It is distributed.

On the other hand, the remaining primary color light reflected rightward by the first dichroic mirror 102 to the right is reflected at a right angle by the second total reflection mirror 116, and the green light G and the blue light are reflected by the second dichroic mirror 106. Separated into B.

The second dichroic mirror 106 is
As described above, it has a spectral characteristic of reflecting the green light G, and since it is arranged so that its incident angle is 45 ° with respect to the remaining primary color light, it reflects the green light G at a right angle, The blue light B is transmitted.

The green light G reflected by the second dichroic mirror 106 is reflected at a right angle by the third total reflection mirror 117 and guided to the liquid crystal display panel 107 for green light, while passing through the second dichroic mirror 106. The blue light B is reflected at a right angle by the fourth total reflection mirror 118 and guided to the blue light liquid crystal display panel 110.

In this way, the corresponding liquid crystal display panel
The respective primary color lights R, G, B incident on the 104, 107, 110 are brightness-modulated by the video signals corresponding to the primary color lights R, G, B in the liquid crystal display panels 104, 107, 110, and thereafter, The dichroic mirror 105 combines the light into a single white light, which is enlarged by the projection lens 111 and projected on a predetermined screen. As a result, the image displayed on each of the liquid crystal display panels 104, 107 and 110 is projected as a full color image on the screen.

FIG. 1 shows the distance on the optical axis between the optical members in the apparatus of this embodiment. That is, the distance between the first dichroic mirror 102 and the first total reflection mirror 114 is 50 mm, the distance between the first total reflection mirror 114 and the second total reflection mirror 115 is 85 mm, and the second total reflection mirror 115. And the liquid crystal display panel for red light 104 is 20 mm, the distance between the first dichroic mirror 102 and the third total reflection mirror 116 is 50 mm, and the third total reflection mirror 116 is between the second dichroic mirror 106. The distance is 35 mm, and the distance between the second dichroic mirror 106 and the fourth total reflection mirror 117 is 50 m.
m, 4th total reflection mirror 117 and green light liquid crystal display panel 1
The distance between 07 is 20mm and the second dichroic mirror 106
And the distance between the fifth total reflection mirror 118 and the fifth total reflection mirror 118 is 50 mm, and the distance between the fifth total reflection mirror 118 and the liquid crystal display panel 110 for blue light is
It is set to 20 mm. Thereby, the optical path length of the red light R from the first dichroic mirror 102 to the liquid crystal display panel 104 for red light, the optical path length of the green light G from the first dichroic mirror 102 to the liquid crystal display panel 107 for green light, and the first The optical path length of the blue light B from the dichroic mirror 102 to the blue light liquid crystal display panel 110 is 155 mm, which is the same length.

Next, a liquid crystal video projector according to a second embodiment of the present invention will be described with reference to FIGS. 2 and 3.
The numbers attached to the optical members in FIGS. 2 and 3 are the first.
In the following description, the description of the optical members similar to those of the first embodiment device will be omitted.

The device of the second embodiment differs from the device of the first embodiment in the spectral characteristics of the first dichroic mirror 202 and the second dichroic mirror 206 and the optical path of the green light G.

That is, the first dichroic mirror 202 has a spectral characteristic of reflecting the green light G and transmitting the red light R and the blue light B.
It reflects only the green light R of the white light 203 from the above and transmits the remaining primary color light.

In addition, the second dichroic mirror 206
Is the same as the first dichroic mirror 102 of the apparatus of the first embodiment described above.
6b is combined in a cross shape.

The dichroic mirror 206a has a spectral characteristic of reflecting the red light R and transmitting the blue light B, and the dichroic mirror 206b has a spectral characteristic of reflecting the blue light B and transmitting the red light R. Is configured to have.

The optical path of the green light G in the device of the second embodiment is, as shown in FIG. 3, a first dichroic mirror 202, a first reflecting mirror 208, and a second reflecting mirror.
209 and the third reflection mirror 217, which is an optical path to the liquid crystal display panel 207 for green light, and each of these reflection mirrors 20
It is formed so as to be reflected at a right angle by 8, 209 and 217 and to detour above the second dichroic mirror 206.

By thus forming the optical path of the green light G in three dimensions, the mirror arrangement of the optical system can be made completely symmetrical as shown in FIG.

Similar to FIG. 1, FIG. 2 shows the distance on the optical axis between the optical members in the apparatus of the second embodiment. That is, the distance between the first dichroic mirror 202 and the first total reflection mirror 208 is 50 mm, the distance between the first total reflection mirror 208 and the second total reflection mirror 209 is 60 mm, and the second total reflection mirror 209. The distance between the third total reflection mirror 217 and the third total reflection mirror 217 is 50 mm, the distance between the third total reflection mirror 217 and the liquid crystal display panel 207 for green light is 20 mm, and the distance between the first dichroic mirror 202 and the second dichroic mirror 206. Distance is 30
mm, the distance between the second dichroic mirror 206 and the fourth total reflection mirror 214 is 50 mm, the distance between the fourth total reflection mirror 214 and the fifth total reflection mirror 215 is 80 mm, and the fifth total reflection mirror 215 And the distance between the red liquid crystal display panel 204 is 20 m
m, the distance between the second dichroic mirror 206 and the sixth total reflection mirror 216 is 50 mm, the distance between the sixth total reflection mirror 216 and the seventh total reflection mirror 218 is 80 mm, and the seventh total reflection mirror 218 And the distance between the LCD panel for blue light 210 and 20 mm
Is set to Thus, the optical path length of the green light G from the first dichroic mirror 202 to the liquid crystal display panel 207 for green light, the optical path length of the red light R from the first dichroic mirror 202 to the liquid crystal display panel 204 for red light, and the first The optical path length of the blue light G from the dichroic mirror 202 to the liquid crystal display panel 210 for blue light is 180 mm, which is the same length.

The liquid crystal video projector of the present invention is not limited to the above-mentioned embodiment, and various modifications can be made.

For example, the distance between the optical members is not limited to that in the above embodiment.

The optical paths of the red, blue, and green lights can be interchanged by changing the spectral characteristics of the dichroic mirror. Also, the light reflection direction of each mirror does not necessarily have to be a right angle direction and can take various other angles, but the optical paths of the two primary color lights incident from both side surfaces of the dichroic prism should be line-symmetrical to each other. Must be set.

Further, although the total reflection mirror is used as the reflection mirror in the above embodiment, it is also possible to replace a part of the reflection mirror with a half mirror and adjust the light amount between the primary color lights.

[Brief description of drawings]

FIG. 1 is a plan view showing a liquid crystal video projector according to a first embodiment of the invention.

FIG. 2 is a plan view showing a liquid crystal video projector according to a second embodiment of the present invention.

FIG. 3 is a side view showing a part of the liquid crystal video projector according to the embodiment shown in FIG.

FIG. 4 is a schematic view showing a conventional liquid crystal video projector.

[Explanation of symbols]

1, 101, 201 Light source 103, 203 Light 2, 6, 102, 106, 202, 206 Dichroic mirror 13, 14, 15, 16, 17, 18, 114, 115, 116, 117, 11
8, 208, 209, 214, 215, 216, 217, 218 Reflecting mirror (total reflecting mirror) 4, 7, 10, 104, 107, 110, 204, 207, 210
Liquid crystal display panel 5,105,205 Dichroic prism 11,111,211 Projection lens 12 Screen

Claims (2)

[Claims] 1. A light source separates light into three primary color lights and irradiates the liquid crystal display panels corresponding to the respective primary color lights, and in each of these liquid crystal display panels, the respective primary color lights are image signals corresponding to the primary color lights. In the liquid crystal video projector, in which the modulated primary colors are combined by a dichroic prism, and the combined three primary colors are enlarged and projected on a predetermined screen, One of them is reflected to the left and the other is reflected to the right with respect to the traveling direction.
A first dichroic mirror that separates the primary color light and the remaining primary color light, and a first dichroic mirror that reflects the first primary color light reflected in either the left or right direction by the first dichroic mirror in the forward direction. A reflection mirror; a second reflection mirror that reflects the remaining primary color light reflected in the left or right direction by the first dichroic mirror to the other direction; and a second reflection mirror that reflects the remaining primary color light to the front direction. The remaining primary color light that has been reflected reflects the second primary color light in the one direction, and transmits the third primary color light in the front direction to form the second primary color light and the third primary color light. A second dichroic mirror that separates the first primary color light reflected by the first reflecting mirror is reflected in the other direction, and is positioned near a side surface of the dichroic prism on the other direction side. A third reflection mirror that irradiates the liquid crystal display panel corresponding to the first primary color light, and the second primary color light reflected by the second dichroic mirror are reflected in the forward direction, so that the dichroic prism A fourth reflection mirror located near the front side surface and illuminating the liquid crystal display panel corresponding to the second primary color light, and a third primary color light transmitted through the second dichroic mirror are reflected in the one direction. At least, a fifth reflecting mirror for irradiating the liquid crystal display panel corresponding to the third primary color light located near the side surface on the one direction side of the dichroic prism, the first dichroic mirror, the first dichroic mirror, No. 4 reflection mirror, the liquid crystal display panel corresponding to the second primary color light, and the dichroic prism are located on a substantially straight line, and the straight line is used as an axis of symmetry. The first reflection mirror and the second reflection mirror, and the third reflection mirror and the fifth reflection mirror are arranged symmetrically with respect to each other, and the optical path lengths of the three primary color lights are A liquid crystal video projector, wherein the liquid crystal video projectors are configured to be substantially equal to each other. 2. The light from the light source is split into three primary color lights and applied to the liquid crystal display panels corresponding to the respective primary color lights, and in each of these liquid crystal display panels, the respective primary color lights are image signals corresponding to the primary color lights. In the liquid crystal video projector, the light from the light source is first modulated by the luminance modulation, the modulated primary color lights are combined by a dichroic prism, and the combined three primary color lights are enlarged and projected on a predetermined screen. A first dichroic mirror that separates the first primary color light and the remaining primary color light by reflecting the primary color light upward with respect to the traveling direction of the light and transmitting the remaining primary color light in the front direction. A second primary color light is reflected to the left and a third primary color light is reflected to the right to separate the remaining primary color light into the second primary color light and the third primary color light. 2's The first primary color light reflected upward by the icroic mirror and the first dichroic mirror is reflected in the forward direction so that the first primary color light passes above the second dichroic mirror. A first reflecting mirror and a second reflecting mirror that reflects downward the first primary color light that has passed above the second dichroic mirror; and a second reflecting mirror that is reflected leftward by the second dichroic mirror. A third reflecting mirror for reflecting the second primary color light in the forward direction, and a fourth reflecting mirror for reflecting the third primary color light reflected in the right direction by the second dichroic mirror in the forward direction Is located near the front side surface of the dichroic prism by reflecting the first primary color light reflected by the second reflecting mirror in a forward direction. A fifth reflection mirror for irradiating the liquid crystal display panel corresponding to the first primary color light and the second primary color light reflected by the third reflection mirror are reflected in the right direction, and the left side of the dichroic prism is reflected. A sixth reflection mirror, which is located near the side surface and irradiates the liquid crystal display panel corresponding to the second primary color light, and the third primary color light reflected by the fourth reflection mirror are reflected to the left. And a seventh reflecting mirror located near the right side surface of the dichroic prism for illuminating the liquid crystal display panel corresponding to the third primary color light, the first dichroic mirror and the second dichroic The mirror, the fifth reflection mirror, the liquid crystal display panel corresponding to the first primary color light, and the dichroic prism are located on a substantially straight line, and this straight line The third reflection mirror and the fourth reflection mirror, and the sixth reflection mirror and the seventh reflection mirror are arranged symmetrically with respect to each other as axes of symmetry, and the three primary color lights A liquid crystal video projector, characterized in that the optical path lengths thereof are substantially equal to each other.