JPH055748Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] This invention projects images projected by three projection tubes of red, green, and blue onto a screen using a projection lens; The present invention relates to a rear projection television in which a projected image is viewed from the side opposite to the projection side of the screen.

[Conventional technology]

Conventionally, rear projection televisions are configured so that the image projected onto a projection tube (CRT) is projected onto a screen using a projection lens, and the projected image is viewed from the opposite side of the projection tube. .

Generally, this type of rear projection TV is equipped with a Fresnel lens in front of the screen, which is a concentric collection of discontinuous lenses. This suppresses the occurrence of the net spot phenomenon where the screen becomes bright.

In addition, the above screen uses a lenticular screen in which semicylindrical lenticular lenses are usually arranged horizontally at a pitch of about 1.0 to 1.5 mm. I try to make the directional characteristics uniform.

Figures 7 and 8 illustrate the focal length of the Fresnel lens in relation to the brightness of the screen image, where 1 is the projection tube, 2 is the projection lens, and 3 is the focal length of the Fresnel lens.
is a Fresnel lens, and 4 is a lenticular screen.

The broken line 5 in FIGS. 7 and 8 is a virtual lens surface of the Fresnel lens 3. In FIG.

First, FIG. 7 shows the case where a short-focus Fresnel lens is used, and since almost all the light emitted from the screen 4 reaches the eyes 6, the brightness of the image becomes high.
Also, the surrounding area becomes brighter. Its characteristics are shown by curve A in FIG. However, in this case, as shown in FIG. 10, three projection tubes 1R, 1G, and 1B that emit red, green, and blue light are actually located as shown in the diagram, so As shown, color unevenness occurs at the four corners of the screen.

In other words, as shown in Figure 10, the R light (red light) is strongly bent in the left corner and does not match the bending angle of the B light (blue light), so the upper left and lower left are blue components. becomes stronger, and even if a white raster signal is output on the projection tube, the entire screen will not become uniformly white, and the upper left and lower left will be in a state where cyan, which is a combination of blue and green, is emphasized. Furthermore, for the same reason, in the upper right and lower right, the yellow component, which is a combination of red and green, is emphasized.

Figure 8 shows the case where a long focus Fresnel lens is used. In this case, all the light emitted from the periphery of the screen does not reach the eye 6, so the brightness decreases as shown by curve B in Figure 9, and the peripheral Since the brightness also decreases, the light collection rate decreases.

As mentioned above, shortening the focal length of the Fresnel lens to make the screen brighter will cause color unevenness on the screen, and increasing the focal length of the Fresnel lens to prevent this will reduce the brightness of the entire screen. , a contradictory result arises in that the image quality appears poor.

[Purpose of this invention]

The present invention improves the Fresnel lens in rear projection televisions that use three projection tubes (red, green, and blue), eliminates the contradictory drawbacks of the conventional ones, and improves the brightness of the screen. The purpose is to prevent color unevenness from occurring at the corners of the screen.

[Example of the present invention]

FIG. 1 shows an embodiment of the present invention,
Each part indicated by reference numerals 1 to 6 corresponds to those shown in FIGS. 7 and 8.

The Fresnel lens 3 in FIG. 1 is constructed such that the focal length at the periphery of the lens becomes longer as it goes toward the periphery, compared to the focal length at the center of the lens. In the case of Fig. 1, the focal length of the Fresnel lens is divided into three parts, and the focal length at the center of the lens is f ₁ , the focal length at the middle part around it is f ₂ , and the focal length at the periphery is f 1 . When is set to f ₃ , the configuration is such that the relationship f ₁ < f ₂ < f ₃ holds.

The virtual lens surface of the Fresnel lens in this case is shown in Figure 2, where the seam between the focal length f ₁ part and the focal length f ₂ part, and the joint between the focal length f ₂ part and the focal length f The seams with part ₃ are constructed so that they are continuous and smooth.
As is well known, a Fresnel lens is a collection of discontinuous lenses, so it can be easily configured to smoothly change the focal point f in this manner.

Figure 3 shows the lens shape when each lens surface with focal lengths f ₁ , f ₂ , and f ₃ is broken down into a model.
These have the function of condensing light towards the viewer from a macroscopic perspective.

The example explained above shows the case where the focal length is divided into 3 as a Fresnel lens, but the number of divisions is 2.
You can set more than one, up to infinity.

In the examples shown in FIGS. 1 and 2, the focal length of the peripheral portion of the Fresnel lens is longer than that of the center, so as shown in FIG. projection tube 1
Among the rays from R and 1B, the bending angle of the rays incident on the periphery of the Fresnel lens 3 is smaller than that shown in FIG. 10, and as a result, when a white raster is produced, the angle shown in FIG. In this way, the screen 4 can be a uniform white screen without any color shift. In this case, the brightness distribution above and below the screen becomes like curve C in FIG. 9, and good results can be obtained as a whole.

FIG. 6 shows the present invention applied to a single screen in which a Fresnel lens and a lenticular screen are integrally formed. In the case of a single screen like this example, if the angle of view θ is large, vignetting occurs in the periphery and the brightness in the periphery decreases significantly, which is a major drawback.However, when the present invention is used, Since the prism angle of the peripheral Fresnel lens becomes smaller, vignetting is reduced, and the drawback of reduced peripheral brightness can be overcome.

In this case as well, the occurrence of color unevenness around the screen can be eliminated, as in the case of two screens.

[Effect of idea]

As explained above, according to the present invention, red, green,
A rear projection system in which the image projected by three blue projection tubes is projected onto a screen using a projection lens, and the image projected onto the screen is viewed from the opposite side of the screen from the projection side. In Yon TV, the focal length of the Fresnel lens, in which the discontinuous lenses installed on the screen are assembled in a concentric circle, is larger at the periphery than at the center of the Fresnel lens.
It is possible to prevent color unevenness at the corners of the screen from occurring without reducing the brightness on the screen.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of an embodiment of the present invention, Fig. 2 is a cross section showing a virtual lens surface of a Fresnel lens in the embodiment, and Fig. 3 is a cross section showing a schematic exploded state of the virtual lens of Fig. 2. 4 is a diagram illustrating the action of the Fresnel lens in the embodiment with regard to light from the red and blue projection tubes among the three projection tubes, and FIG. 5 is a front view showing the state of the screen in the embodiment. Fig. 6 is a block diagram showing another embodiment of the present invention, Figs. 7 and 8 are block diagrams using short focus and long focus Fresnel lenses, respectively, and Fig. 9 shows the position on the screen. A characteristic diagram showing the relationship between brightness, Figure 10 is a configuration diagram of a conventional rear projection television equipped with three projection tubes, and Figure 11 is a front view showing what appears on the screen with the configuration shown in Figure 10. It is. 1... Projection tube, 2... Projection lens, 3... Fresnel lens, 4... Lenticular screen,
1R...Red light emitting projection tube, 1G...Green light emitting projection tube,
1B... Blue emitting projection tube.

Claims (1)

[Claims for Utility Model Registration] An image projected by three projection tubes of red, green, and blue is projected onto a screen by a projection lens, and the image projected on this screen is the projection side of the screen. is a rear projection television that is viewed from the opposite side, the screen is equipped with a Fresnel lens, the Fresnel lens is a collection of discontinuous lenses concentrically, and the center of the Fresnel lens is A rear projection television characterized in that f ₁ < f ₂ , where f ₁ is the focal length of the outer part and f ₂ is the focal length of the outer part.