JPS61121583A - Projection television - Google Patents

Abstract

PURPOSE:To prevent unnecessary light occurrence due to reflection by providing a light absorbing layer to absorb green and blue, at the projecting lens mirror for a red projection cathode ray tube (CRT) and a light absorbing layer to absorb green and red, at the projecting lens mirror for a blue projection CRT. CONSTITUTION:At a built-in mirror 3-1 of the projection lens for a red projection CRT, a light absorbing layer to absorb green and blue, and red selecting transmission layers 9 and 9' are provided. Namely, a dichroic mirror is adopted. At such a case, a light absorbing layer 9' may be partially installed at the mirror 3-1 according to the inclination of the mirror 3-1. In the same manner as above-mentioned concerning the built-in mirror of the projecting lens for a blue projection CRT which is not shown in the figure, a green and red light absorbing layer is installed. A curve (a) shows a light emitting distribution of the red projection CRT and a curve (b) shows a transmission ratio of a light absorbing layers 9 and 9'. A curve (d) shows a transmission ratio of the light absorbing layer installed at the built-in mirror of the projecting lens for the blue projection CRT.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a projection television, and particularly to a projection television in which an optical path turning mirror is devised to provide a high-contrast image.

[Background of the invention]

Most projection TVs are red or green.

Images from three blue projection cathode ray tubes are magnified by projection lenses installed in front of each tube, and a large, powerful image is projected onto the screen. Compactness of the set is also an important factor, and to solve this problem, VC1 to 3 reflecting mirrors are placed in the optical path between the projection lens and the screen to turn the optical path. As a means to further enhance the effect, there is also a projection lens in which a small mirror (hereinafter referred to as a built-in mirror) is provided in the lens barrel of the projection lens. FIG. 4 is a cross-sectional view of essential parts of such a projector-in-one television, and FIG. 5 shows the projection type cathode ray tube and projection lens shown in FIG.

Red, green, blue projection type cathode ray tube 1-1゜+-2,1-
Projection lenses 2-1.2-2.2-3 on the front of 3 respectively.
is provided to project a composite film on a screen 6. Built-in mirror 3- in the lens barrel of projection lens 2-1゜2-2.2-3
1°5-2.3-3, the optical path is first bent, and the reflecting mirrors 4 and 5 are also bent to reduce the height and depth of the set and make it compact.

Such conventional products still have the following points to be improved. FIG. 5 is a diagram for explaining in an easy-to-understand manner how unnecessary light is generated due to reflection, where 8 is a test pattern and 7 is an image caused by unnecessary light. That is, when a bright pattern 8 is projected on the screen 6 in a dark environment, an image 7 of unnecessary light appears above it. As shown in Fig. 4, when the pattern 8 is projected, it is reflected off the inner surface 6-1 of the screen 6, jumps into the built-in mirror 5-1.3-2°5-3, and then returns to the screen 6-1. Returning to , I 7 appears due to unnecessary light. If such unnecessary light is present, the contrast will drop significantly and the clarity of the projector and television will deteriorate.

Furthermore, although the mirror arrangement of such conventional projector TVs has been made more compact, the disadvantages mentioned above also occur.

In particular, if there are a large number of mirrors, they interact with each other and cause unnecessary light to be generated. Conventionally, measures have been taken to solve such unnecessary light by arranging mirrors, but compactness has always been given priority, and therefore, the unnecessary light has often been left unsolved.

As a countermeasure, it is possible to make the inner surface of the screen rough to scatter light or to color the screen to reduce reflection, but both are undesirable as they lead to a decrease in the degree of resolution and brightness.

Incidentally, a related device K of this type is, for example, Utility Model Application Laid-Open No. 56-155572.

[Purpose of the invention]

An object of the present invention is to improve the conventional technology and provide a projection television with high contrast (and therefore high clarity). Therefore, the present invention provides a means for reducing unnecessary light by maintaining compactness while keeping the arrangement of mirrors as is.

That is, by providing the built-in mirror with a light absorption layer that absorbs unnecessary light, generation of unnecessary light due to reflection is prevented.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

As shown in FIG. 1, the built-in mirror 5-1 of the red projection cathode ray tube projection lens has a light absorption layer that absorbs green and blue light, or
A red selectively permeable layer (e.g. multilayer thin film) 9.9'' is provided.

That is, it is made into a dichroic mirror. In this case, depending on the inclination of the built-in mirror 3-1, the built-in mirror 5-1 may be partially provided with a light absorption layer of 9°. ``The built-in mirror 3-5 of the projection lens for the red projection cathode ray tube is also provided with green and red light absorbing layers in the same manner as described above.

In Figure 2, a shows the luminescence distribution of a red projection type cathode ray tube,
Good shows the transmittance curve of the light absorption layer 9, 9°. Also the third
In the figure, C shows the light emission distribution of the blue cathode ray tube, and d shows the transmittance curve of the light absorption layer 7 provided in the built-in mirror 5-3 of the projection lens for the blue projection type cathode ray tube.

In this case, the arrangement angles of the built-in mirrors 3-1.5-2, 3-3 vary depending on the set structure, but the image 7 caused by the unnecessary light described above is caused by the pattern 8 being projected onto a limited area on the screen 6. It may not occur only when the light is emitted, and in such cases there is no need to provide a light absorption layer on the entire reflective surface of the built-in mirror 5-1.3-2.5-5 (see Figure 4 (6)). (The effect is the same even if it is provided partially.)

Furthermore, depending on the relative angle between the built-in mirror and the screen, the built-in mirror 5-2 of the projection lens 2-2 for a green projection CRT may also generate an image of unnecessary red or blue light. A light absorption layer that absorbs red and blue light is also formed on the built-in mirror of the projection lens.

〔Effect of the invention〕

According to the present invention, among the built-in mirrors that individually reflect and return the images of red, green, and blue projection type cathode ray tubes, the built-in mirror of the projection lens for red projection type cathode ray tubes has a light absorption layer that absorbs green and blue. Since the built-in mirror of the projection lens for the blue projection type CRT is provided with a light absorption layer that absorbs green and red, the unnecessary light reflected from the back surface 6-1 of the screen is further reflected by the built-in mirror and onto the screen. Since it is possible to prevent unnecessary light from appearing on the screen, the contrast can be improved and a clear image can be obtained.

In addition, there is no need to limit the angles of the above-mentioned reflecting mirrors, including the built-in mirror, just to prevent the above-mentioned unnecessary light from reflecting me, and the compactness of the set is not hindered.
It also has the effect of allowing more freedom in the design of the set.

In terms of cost, we still use an expensive surface reflection type for the built-in mirror, so there is almost no problem in replacing it with a guichroic mirror.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing the formation of a light absorption layer on a built-in mirror according to the present invention, and FIGS. 2 and 3 show the transmittance curves of the light absorption layer used in the present invention and the emission distribution of each projection type cathode ray tube. Also shown are graphs, Figure 4 is a sectional view of the main parts of a projector according to the prior art, Figure 5 is an explanatory diagram showing in particular the projection type cathode ray tube and projection lens, and Figure 6 is a diagram showing the main parts of a conventional projector screen. FIG. 3 is an explanatory diagram illustrating an image caused by unnecessary light. s-1, s-2, 5-s=Built-in mirror, 6: Screen; 6-1... Screen inner surface i7--image by unnecessary ff1K; 9, 9'... Light absorption layer.

Claims (1)

[Claims] 1) A projection television in which images from three red, green, and blue projection cathode ray tubes are magnified by three projection lenses each having a built-in optical path folding mirror and projected onto a screen. Of the built-in mirrors, the mirror of the projection lens for a red projection type cathode ray tube is provided with a light absorption layer that absorbs green and blue, and the mirror of the projection lens for a blue projection type cathode ray tube is provided with a light absorption layer that absorbs green and blue.
A projection television characterized in that a light absorption layer that absorbs red color is formed on each of the projection televisions. 2) A projection television according to claim 1, characterized in that a light absorption layer that absorbs red and blue light is formed on the mirror of the projection lens for a green projection cathode ray tube.