JP2647019B2 - LCD projector - Google Patents

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, and more particularly to an optical arrangement for obtaining a uniform contrast ratio at a halftone of a projection screen in order to enhance the quality of the projection screen.

[0002]

2. Description of the Related Art In recent years, since a large screen can be easily displayed, light is irradiated from behind a transmissive liquid crystal panel 20 by a light source 10 as shown in FIG. Liquid crystal projectors are attracting attention. This liquid crystal projector has the advantage that the problem of viewing angle dependence is unlikely to occur because the direction of light incident on the liquid crystal panel is constant compared to the direct-view type, in which light incident on the liquid crystal panel is viewed directly from various directions. Have been.

However, the viewing angle characteristic described above exists in the liquid crystal panel itself. In particular, the peak angle of the contrast in the vertical direction shifts by the applied voltage, and the maximum contrast value also changes. For this reason, there has been a problem that the contrast and the color are not uniform inside the projection screen. In the liquid crystal projector shown in FIG. 4, care is taken to reduce the influence of the viewing angle dependence of the liquid crystal panel while using the same components as the projector shown in FIG.
Specifically, as disclosed in Japanese Patent Application Laid-Open No. 2-5082, a light source is installed so that the light axis of the light source enters the liquid crystal panel 20 at an angle of the maximum contrast angle, and the light source is generated due to the viewing angle dependency. This reduces the unevenness of the contrast and color of the projected screen.

[0004]

However, in a conventional liquid crystal projector, a condenser lens is provided on the light source side of the liquid crystal panel in order to reduce the aperture of the projection lens as much as possible, and the light is converged on the liquid crystal panel. In the liquid crystal projector having this configuration, the angle of light incident on the liquid crystal panel is different in the liquid crystal panel as shown in FIG. Therefore, the condenser lens reduces the illumination light of the liquid crystal panel, so that the light incident angle changes in the liquid crystal panel surface, especially in the vertical direction, which has a large viewing angle dependence, and the contrast on the projection screen is not uniform in the plane. There was a problem. The above is specifically described with reference to the drawings. A liquid crystal projector having the configuration shown in FIG. 4 employs a liquid crystal panel having a viewing angle dependency shown in FIG. 2 and receives light from an upper viewing angle of 1 °, which is the optimum viewing angle, and receives an angle of ± 3 ° by a condenser lens. The aperture was stopped down (specifically, a condenser lens having a focal length of 440 mm was used). In this case, when the maximum contrast display, that is, when the blackest screen is displayed, the uniformity of the contrast is high, and the contrast is 1 at the center of the screen.
28 : 1, contrast 110 : 1 at the top and bottom of the screen
And the contrast difference in the screen was about 1.2 times. However, when displaying a halftone, the contrast at the center of the screen is 75: 1 (the contrast peak value is 100: 1).
When displaying, the contrast is about 10 at the top on the projection screen.
0: 1 and 50: 1 at the bottom, resulting in a contrast difference of about 2 times. The projection screen is often displayed in the halftone rather than the blackest display, and the display of the halftone is important for the image quality, and it is necessary to emphasize the halftone for the uniformity of the contrast. Is done. As described above, the uneven contrast in the halftone is the biggest problem as the deterioration of the image quality. In addition, three liquid crystal panels are used, and red, green, and blue
In a liquid crystal projector of a type that performs color display by separating and synthesizing the primary colors, there is also a problem that color unevenness occurs in a halftone.

It is therefore an object of the present invention to provide a liquid crystal projector in which the contrast non-uniformity caused by the viewing angle dependency is reduced.

Another object of the present invention is to provide a light incident angle control method that controls the angle of incident light with respect to a liquid crystal panel in a liquid crystal projector and contributes to reduction of non-uniformity of contrast generated due to viewing angle dependency. is there.

[0007]

According to the present invention, there is provided a transmission type liquid crystal panel that transmits light emitted from a light source and converts it into image light, a projection lens for enlarging and projecting the image light, the liquid crystal panel and the liquid crystal panel. In a liquid crystal projector including a condenser lens disposed between the light source and the light source, the optimal viewing angle θ ₁ representing the contrast peak angle at the time of maximum contrast in the vertical direction of the liquid crystal panel and the contrast peak value are 10
0: the light from the light source is incident on the liquid crystal panel at an intermediate angle between the viewing angle best angle theta ₂ which represents the contrast peak angle at 1, and the light to narrow the upper and lower ends of the liquid crystal panel by the condenser lens Is set to at most about (θ ₂ −θ ₁ ) / 2, thereby obtaining a liquid crystal projector.

Further, according to the present invention, a transmission type liquid crystal panel that transmits light emitted from a light source and converts the light into image light, a projection lens that enlarges and projects the image light, and a liquid crystal panel between the liquid crystal panel and the light source. In a light incident angle control method for controlling an angle of incident light with respect to the liquid crystal panel in a liquid crystal projector including a condenser lens disposed therein, an optimum viewing angle θ ₁ representing a contrast peak angle at the time of maximum contrast in a vertical direction of the liquid crystal panel. a contrast peak value 100: the light from the light source at an intermediate angle of view angle best angle theta ₂ which represents the contrast peak angle at 1 is incident on the liquid crystal panel, and, and below the liquid crystal panel by the condenser lens A light incident angle control method is characterized in that the angle of the light converged to the end is at most about (θ ₂ −θ ₁ ) / 2.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. The configuration of the liquid crystal projector according to the embodiment of the present invention is the same as the configuration of the conventionally known projector shown in FIG. As the transmissive liquid crystal panel 20, a type 3 (display diagonal size: 76.2 cm) having a viewing angle characteristic shown in FIG. 2 was used. From FIG. 2, the optimum viewing angle θ ₁ of this liquid crystal panel is about 1 ° in the upward direction,
The best viewing angle θ _{2 with a} contrast ratio of 100 is about 5 ° in the upward direction. A 150 W metal halide lamp was used as the light source 10, and although not shown in FIG. 4, a reflecting mirror having a focal length of 13 mm and a diameter of 100 mm was set behind the lamp to make the light substantially parallel. Light from this light source,
The liquid crystal panel 20 has an upward direction 3 which is halfway between θ ₂ and θ _1.
Injected with ゜. Further, a condenser lens 40 having a focal length of about 650 mm was placed 10 mm away from the light source side of the liquid crystal panel. The method of calculating the angle of light ψ focused on the upper and lower ends of the liquid crystal panel by this condenser lens is based on the vertical dimension V of the liquid crystal panel display section, the focal length f of the condenser lens, and the distance d between the condenser lens and the liquid crystal panel.
V / 2 (fd). Thereby, the aperture angle of the condenser lens at the upper and lower ends of the liquid crystal panel 20 was set to approximately 2 °. Further, the projection lens 50 is arranged so that the optical axis of the light transmitted through the liquid crystal panel 2 passes through the lens pupil.

In the liquid crystal projector having the above configuration, when a display is performed with a contrast peak value of 100: 1, the contrast at the top of the screen is about 100: 1, the contrast at the bottom of the screen is 75: 1, and the contrast difference is about 1: 1. 0.3 times as much. Further, at the maximum contrast, the contrast was about 130: 1 at the lower part of the screen and 110: 1 at the upper part of the screen, and the contrast difference was about 1.2 times. As described above, in the present embodiment, the contrast difference at the halftone and the contrast difference at the time of the maximum contrast display are 1.
The contrast can be reduced by a factor of 2 to 1.3, and the uniformity of the contrast in the screen is improved.

In particular, as compared with a device using the same liquid crystal panel shown in FIG. 2 and having a conventionally known incident angle of 1 ° and a converging angle of ± 3 ° with a condenser lens, the incident angle is 3 °.
{Circle around (2)} In the apparatus having a configuration in which the aperture angle is set to ± 2 ° by the condenser lens, the uniformity of the halftone (contrast in the vicinity of the projection screen contrast 100) is improved.
What had a difference of twice was reduced to about 1.3 times. Accordingly, the image quality of the projection screen has been improved.

In this embodiment, a liquid crystal projector that performs display on a single panel has been described as an example. However, three liquid crystal panels are used to separate and combine three primary colors of red, green, and blue to perform color display. A liquid crystal projector of the type also has the effect of uniformity of contrast. Further, in this type of liquid crystal projector, the deterioration of the uniformity of the contrast also causes the occurrence of color unevenness due to the non-uniform brightness of the three primary colors.

[0013]

As described above, according to the present invention,
The non-uniformity of the contrast generated due to the viewing angle dependency can be reduced, and the improvement of the image quality of the projection screen can be expected.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an effect of the present invention.

FIG. 2 is a diagram showing a change in contrast depending on an incident angle of light incident on a liquid crystal panel.

FIG. 3 is a schematic diagram illustrating an example of a configuration of a conventional liquid crystal projector.

FIG. 4 is a schematic diagram showing another example of the configuration of a conventional liquid crystal projector.

[Explanation of symbols]

 Reference Signs List 10 light source 20 liquid crystal panel 30 screen 40 condenser lens 50 projection lens

Claims (4)

(57) [Claims] 1. A transmissive liquid crystal panel that transmits light emitted from a light source and converts the light into image light, a projection lens that enlarges and projects the image light, and a condenser lens that is disposed between the liquid crystal panel and the light source. And an optimal viewing angle θ ₁ representing a contrast peak angle at the time of maximum contrast in the vertical direction of the liquid crystal panel and a viewing angle best angle θ ₂ representing a contrast peak angle at a contrast peak value of 100: 1. The light from the light source is incident on the liquid crystal panel at an intermediate angle of the above, and the angle of the light narrowed down to the upper and lower ends of the liquid crystal panel by the condenser lens is at most about (θ ₂ −θ ₁ ) / 2. A liquid crystal projector characterized by the above-mentioned. 2. The liquid crystal projector according to claim ₁ , wherein an incident angle of light incident on said liquid crystal panel is set to a value substantially at the center between said optimum viewing angle θ ₁ and said optimum viewing angle θ ₂ . 3. The liquid crystal projector according to claim ₁ , wherein an incident angle of light incident on the liquid crystal panel is set near a central value between the optimum viewing angle θ ₁ and the optimum viewing angle θ ₂ . 4. A transmissive liquid crystal panel that transmits light emitted from a light source and converts the light into image light, a projection lens that enlarges and projects the image light, and a condenser lens that is disposed between the liquid crystal panel and the light source. In a light incident angle control method for controlling an angle of incident light with respect to the liquid crystal panel in a liquid crystal projector, the optimal viewing angle θ ₁ and the contrast peak value representing the contrast peak angle at the time of maximum contrast in the vertical direction of the liquid crystal panel are adjusted. 100: applying light from the light source to the liquid crystal panel at an intermediate angle of view angle best angle theta ₂ which represents the contrast peak angle at 1,
Further, the angle of the light converged on the upper and lower ends of the liquid crystal panel by the condenser lens is at most about (θ ₂ −θ ₁ ) /
2. A method for controlling a light incident angle, the method comprising: