JPH0353236A - Rear type video projector - Google Patents

Abstract

PURPOSE:To obtain as image without the irregularity of color by separately image-modulating the luminous fluxed of red, green and blue by the use of three liquid crystal panels, synthesizing the image with the aid of wavelength selective transmission film so that a single optical axis is attained and projecting it on a light transmissive screen. CONSTITUTION:Light emitted from a light source lamp 101 is condensed by a lamp reflector 102 and the condensed light is separated to three primary colors such as blue, green and red by a color separation and illuminating optical system constituted of a blue separation dichroic mirror 301 and a green separation dichroic mirror 302 which are the wavelength selective transmission film and three increasable reflection mirrors 303. Thereafter, the liquid crystal panel 411 for blue color, the liquid crystal panel 412 for green color and the liquid crystal panel 413 for red color are irradiated with the light. The three primary colors which are image-modulated by the three liquid crystal panels are synthesized to be the image by a dichroic prism 312. The light which is synthesized to be the image by the prism 312 is projected to the light transmission type screen 309 by a projecting lens 308. Thus, the image without the irregularity of color is obtained on the screen.

Description

[Detailed description of the invention] [Industrial application fields] The present invention relates to a rear type video projector.

[Prior Art] A conventional rear-type video projector uses a CRT for the light source and image modulation, uses a three-tube system to increase the amount of light, and performs image synthesis on the screen. Therefore, a three-optical axis system is adopted.

[Problem to be solved by the invention] However, because the conventional rear-type video projector uses a three-optical axis system, the red, green, and blue optical axes are different from each other with respect to the screen, and some parts of the screen are relative to each other. The angle of incidence changes. Furthermore, since the screen has directivity for transmitted light, there is a problem in that color unevenness is likely to occur on the screen. In addition, even if an attempt is made to obtain a single optical axis by combining images using a wavelength-selective transmissive film to avoid this problem, CRT projection tubes have a diagonal of more than 5 inches in order to increase the amount of light. This is not practical because it requires a large wavelength-selective transmission film and is expensive.

Therefore, in order to solve these problems, the present invention uses three small liquid crystal panels of 5 inches or less to separately image-modulate the red, green, and blue light beams, and uses a selectively transparent thin film to create an image. The objective is to obtain an image without color unevenness on the screen by projecting the light onto a light-transmitting screen using a single optical axis.

[Means for Solving the Problems] A rear video projector of the present invention includes at least a light source lamp, an illumination optical system, a liquid crystal panel, a projection optical system, and a light transmission screen. It is characterized in that the blue light beam is image-modulated separately using three liquid crystal panels, the images are combined using a wavelength-selective transmission film to form a single optical axis, and the images are projected onto a light-transmitting screen.

Hereinafter, the details of the present invention will be shown by examples.

[Example] Example 1 FIG. 1 is an example of a rear type projector using the liquid crystal of the present invention.

Light generated by the light source lamp 101 is focused by a lamp reflector 102. The condensed light is divided into blue, blue, and blue by a color separation and illumination optical system consisting of a blue separation dichroic mirror 301 and a green separation dichroic mirror 302, which are wavelength-selective transmission films, and three reflection-enhancing mirrors 303. After the light is separated into the three primary colors of green and red, it is irradiated onto a blue liquid crystal panel 411, a green liquid crystal panel 412, and a red liquid crystal panel 413.

The three primary colors image-modulated by the three liquid crystal panels are combined into an image by a dichroic prism 312.

The dichroic prism is formed of a blue reflective dichroic film 321 and a red reflective dichroic film 322, which are wavelength-selective transmission films, intersecting each other in a diagonal direction.

The light image synthesized by the dichroic prism 312 is transmitted to the light transmission screen 3 by the projection lens 308.
Projected on 09.

FIG. 2 is a schematic diagram when light enters, passes through, and exits a transmissive screen in a single-optical-axis video projector using liquid crystal.

Red light 11, green light 12,
Blue light 13 is incident. 309 has a directional characteristic in order to obtain screen gain, and the light incident there is diffused with a certain directionality. Diffused red light 21,
Since the green light diffused light 22 and the blue light diffused light 23 have a single optical axis, they completely overlap. Therefore, color unevenness does not occur when viewed from the viewpoint 60.

In FIG. 2, 11, 12, and 13 are shown sliding for convenience, but since they are a single optical axis, they should originally overlap.

Comparative Example 1 FIG. 3 is a block diagram of a standard CRTS tube type video projector. CRT as a light source and image modulation
I use three of them, corresponding to the three colors of red, green, and blue. CRT
Projection tubes have a larger light intensity loss due to the projection optical system than direct viewing tubes, so the brightness on the screen cannot be obtained unless the brightness is significantly increased. The phosphor screen generates a tremendous amount of heat to drive the gun. Therefore, extreme miniaturization like direct viewing tubes is difficult.
A diagonal of 5 inches or more is normal.

For this reason, if an attempt is made to realize a single optical axis optical system, a large wavelength-selective transmission film is required, which is expensive and is therefore impractical. Currently, a three-axis projection optical system shown in FIG. 3 is often used. Images obtained on the fluorescent screens of the red CRT projection tube 121, green CRT projection tube 122, and blue CRT projection tube 123 are projected onto a transmission screen 309 by a red projection lens 131, a green projection lens 132, and a blue projection lens 133. Projected. At this time, the red light optical axis l51
, green light optical axis 152, and blue light optical axis 153 are not on the same axis.

FIG. 4 is a schematic diagram when light enters, passes through, and exits a transmission screen in a multi-optical axis video projector using a CRT projection tube.

Red light 11, green light 12,
Blue light 13 is incident. 309 as mentioned in Example 1
The light incident on it is diffused with a certain directionality. Red diffused light 21, green diffused light 22, blue diffused light 23
are diffused along their respective optical axes.

Therefore, the intensity of each color light when viewed from the viewpoint 60 is
The colors are red light 31, green light 32, and blue light 33, and although the incident intensity is the same, the outgoing intensity varies among the colors. Therefore, color unevenness occurs.

[Effects of the Invention] As described above, according to the present invention, in a rear video projector, red, green, and blue light beams are image-modulated separately using three liquid crystal panels, and wavelength-selective transmission is achieved. By combining images using a film to form a single optical axis and projecting the images onto a light-transmitting screen, we were able to obtain an image without color unevenness on the screen.

[Brief explanation of drawings]

Figure 1 is a diagram of a liquid crystal video projector. 101 Light source lamp 102 Lamp reflector 301 Blue separation dichroic mirror 302 Green separation dichroic mirror 303 Reflection increasing mirror 308 Projection lens 309 Light transmission screen 312 Dichroic prism 321 Blue reflection dichroic film 322 Red reflection dichroic film 411 Blue liquid crystal panel 412 Green color Liquid crystal panel 413 Red liquid crystal panel FIG. 2 is a schematic diagram when a single optical axis light passes through the screen. 11 Red light 12 Green light 13 Blue light 21 Diffusion of red light 22 Diffusion of green light 23 Diffusion of blue light 60 Viewpoint 309 Light transmission type screen Figure 3 is a diagram of a three-tube CRT projection tube video projector. 2l 22 2 3 31 32 Red CRT projection tube Green CRT projection tube Blue CRT projection tube Red projection lens Green projection lens 1 3 3 1 5 1 1 5 2 1 53 309 Blue projection lens Red optical axis Green optical axis Blue light optical axis transmission type screen FIG. 4 is a schematic diagram when double optical axis light is transmitted through the screen. 11 Red light 12 Green light 13 Blue light 21 Diffusion of red light 22 Diffusion of green light 23 Diffusion of blue light 31 Intensity of red light 32 Intensity of green light 33 Intensity of blue light 60 Viewpoint 309 Light-transmissive screen Figure 2 Figure 3

Claims (1)

[Claims] (1) In a rear video projector that consists of at least a light source lamp, an illumination optical system, a liquid crystal panel, a projection optical system, and a light transmission screen, red, green, and blue light beams are separated using three liquid crystal panels. A rear-type video projector characterized by modulating images, combining the images into a single optical axis using a wavelength-selective transmission film, and projecting the images onto a light-transmitting screen.