JPH043044A - Rear projection television - Google Patents

Abstract

PURPOSE:To prevent the generation of unequal colors on a screen by setting the condensing distance of a Fresnel lens larger on the periphery than at the center and changing the offset quantity of the lenses on the front and rear surfaces of a lenticular sheet so as to have at least >=1 inflection points in the graph of the change rate thereof. CONSTITUTION:The condensing distance of the Fresnel lens B constituting the screen of the rear projection television is set larger on the periphery than at the center and the offset quantity of the lenses on the front and rear surfaces of the lenticular sheet A is changed so as to have at least >=1 inflection points in the graph of the change rate thereof. Namely, the Fresnel lens B is formed to have multifocuses and the condensing distance in the peripheral part is set longer than at the center to adjust the incident angle on the lenticular sheet A. The offset quantity of the lenses 1, 2 on both surfaces of the lenticular sheet A is set at the offset quantity shown in the graph C having the two inflection points from the center to the periphery. The exit light from the Fresnel lens B can prevent the unequal colors arising from the loss of the color balance by a difference of the projected light from red and blue projecting tubes in the incident angle on the Fresnel lens B in this way.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention comprises a projection tube and a screen that receives projection light projected from the projection tube, and an image projected onto the screen is transmitted to the projection tube. This invention relates to an improvement to a rear projection television that can be viewed from the opposite side.

[Conventional technology]

Generally, in this type of rear projection television, three projection tubes with red, green, and blue light emitting surfaces are arranged in a row, and the image of each projection tube is superimposed on the screen by a projection lens. be projected.

The screen on which this image is projected is viewed from the projection tube side using a Fresnel lens, which has lenses formed concentrically so that the cross section has a sawtooth shape. It is composed of a lenticular sheet with cylindrical lenses formed on both the front and back sides.

The Fresnel lens suppresses the brightness development in which the center of the screen caused by the projection lens becomes brighter than other parts.

In addition, the lenticular sheet has a diffusing material mixed inside, and has the function of forming an image on this surface, diffusing light in the horizontal direction and widening the horizontal field of view.

In this way, in an abrogation television, the projection light that passes through the Fresnel lens and enters the lenticular sheet is projected onto the lenticular sheet A at a point X away from the center of the screen in FIG. 4, as shown in FIG. The light is incident on the back surface of the lens 1 at an angle of θ.

As shown in FIG. 6, this incident angle θ increases as X increases from the center.

Due to this angle of incidence θ, it is necessary to shift the optical axis of the lens 1 on the back side and the optical axis of the lens 20 on the front side, and as the angle of incidence θ increases, it becomes necessary to increase the amount of shift Δ.

The shift amount Δ is expressed as Δ= D become.

θ of tan θ in this equation is determined by the projection light from the central projection tube, which is the green projection tube.

In addition, in FIG. 5, 3 is a portion called a black stripe that does not transmit light.

[Problem to be solved by the invention]

In recent years, it has been desired to make this type of projection television thinner, but in order to achieve such a thinner profile, it is necessary to shorten the optical path from the projection tube to the screen.

When the optical path is shortened in this way, the difference in the angle of incidence from the red and blue projection tubes on both sides to the lenticular sheet becomes large.

However, the amount of shift of lenses 1.2 on both sides of the lenticular sheet is determined with respect to green, and red and blue are treated as parallel, so the difference in incidence angle on the right and left of the screen causes distortion. This results in color unevenness.

In other words, when projecting white with three color projection tubes, the blue projection tube side will have a yellowish color due to the combined light of blue and green, and the red projection tube side will have a yellowish color due to the combined light of red and green. The drawback is that the color becomes a certain cyanide-tinged color.

[Purpose of the invention]

An object of the present invention is to solve the above-mentioned problems in conventional rear projection televisions, and to provide a rear projection television that has a color balance of 1 and does not deteriorate color shift even if the optical path is shortened due to thinning. do.

[Summary of the invention]

The present invention relates to a means for a rear projection television to achieve the above-mentioned object, in which the condensing distance of the Fresnel lens constituting the screen of the rear projection television is made larger at the periphery than at the center, and the front and back surfaces of the lenticular sheet are The offset amount of the lens is changed so that the graph of the amount of change has at least an inflection point for use.

C Embodiment of the Invention] Next, an example of the implementation of the present invention will be described with reference to FIGS. 1 to 3.

In Figure 3, the Fresnel lens B into which the projection light from the green projection tube is incident is emitted onto the lenticular sheet A, and the lenses 1°2 on both sides of the lenticular sheet A are connected to the Fresnel lens B.
A state in which an offset amount Δ is provided corresponding to the output angle θ is shown.

In the same figure, 3 is the lens 2 of the lenticular sheet A.
It shows black stripes placed between them that do not transmit light.

The Fresnel lens B prevents the projection lens from brightening the center of the screen and causing a hot spot phenomenon.

However, with the recent increase in the visibility and resolution of rear projection televisions, there is a tendency for the viewpoint to move closer to the screen.

When the viewpoint approaches the screen, the hot spot phenomenon appears at the outgoing angle θ due to the condensing distance of the Fresnel lens B shown by the dotted line in Fig. A true band phenomenon occurs in which a bright band appears in the horizontal direction.

To prevent this and increase the angle of incidence θ to the lenticular sheet A
In order to adjust, Fresnel lens B is made multifocal,
The light collection distance at the periphery is longer than that at the center.

As a result, the outgoing angle θ from the Fresnel lens B, that is, the incident angle θ of the lenticular sheet A changes as shown by the solid line in FIG. 2 from the center to the periphery.

In this example, the dimensions of the screen are 40 inches, which is about 600 inches high and about 800 inches wide. It is set for light.

By configuring the Fresnel lens B in this manner, in the case of the above embodiment, even if the viewpoint is 3 m from the screen, the true band from the viewpoint is expanded to approximately 600 m above and below, and it is no longer perceived as a hot hand. .

In this case, the focusing distance at the center, which was conventionally 8 to 20 m, has been shortened to about 5 m, and the distance of light convergence at the center has been shortened to approximately 5 m, and
This prevents color unevenness around the edges.

When the Fresnel lens B is configured in this way, the incidence of red and blue projected light on the conventional lenticular sheet shown by the dotted line in FIG. Due to the difference in angle θ, color balance is disrupted, and color unevenness occurs at positions away from the center.

Therefore, in the above embodiment, the offset amount Δ of the double-sided lenses 1 and 2 is expressed as a graph with two inflection points as shown by the solid line in FIG. 2 during 400 fl from the center to the periphery. The offset amount Δ is set as shown.

With such a lenticular sheet A, the output light θ from the Fresnel lens B can be prevented from color unevenness due to color imbalance caused by the difference in the incident angle of the projection light from the red and blue projection tubes to the Fresnel lens B. It is.

The above embodiment is for a so-called 40-inch rear projection television, but the solid lines in FIGS. 1 and 2 may change depending on the length of the optical path, the size of the screen, etc. However, the graph in Figure 1 must have an inflection point in its use.

〔Effect of the invention〕

The present invention aims to reduce the distance from the projection tube to the screen by using a Fresnel lens or lenticular sheet to make the product thinner. and color shift.

Therefore, it is possible to obtain a thin glue ablation television with good color balance and color shift, and to reduce restrictions on the installation space.

Moreover, even when viewed from a position close to the screen, this tendency does not change, and the hot band phenomenon does not occur.

[Brief explanation of the drawing]

FIG. 1 shows an example of a diagram of changes in the amount of offset of the lenticular sheet of the present invention, FIG. 2 shows an example of a diagram of changes in the output angle of a Fresnel lens, and FIG. 3 is an explanation of FIGS. 1 and 2. Figure 4 is a front view of the screen, Figure 5 is an explanatory diagram of the amount of offset, Figure 6 is a diagram of changes in the output angle to the lenticular sheet by a conventional reflex lens, Figure 7 is the offset angle of the lenticular sheet. It is a change diagram of quantity. A... Lenticular sheet, B... Fresnel lens, 1.2... Lens. V 曵zu・ra4 bait fart place (mml fig. 2 fig.

Claims (1)

[Claims] A rear projection television comprising a projection tube and a screen that receives projection light projected from the projection tube, the image projected on the screen being viewed from the opposite side of the projection by the projection tube, A Fresnel lens and a lenticular sheet are sequentially arranged on the screen from the projection tube side, and the condensing distance of the Fresnel lens is made larger at the periphery than at the center, and the optical axes of the lenses on the front and back surfaces of the lenticular sheet extend to the periphery. The rear projection television is characterized in that the offset amount changes with at least an inflection point in use in a graph of the relationship between the offset amount and the distance from the center of the lenticular sheet.