JPH0627922B2 - Rear projection tv - Google Patents

Description

Description: TECHNICAL FIELD The present invention includes a projection tube and a screen for receiving projection light projected from the projection tube, and an image projected on the screen is projected by the projection tube. It is related to the improvement of the rear projection TV that can be viewed from the opposite side.

[Conventional technology]

Generally, in this type of rear projection television, three projection tubes having red, green, and blue light emitting surfaces are arranged in a line, and the images of the projection tubes are projected on the screen by a projection lens. To be done.

The screen on which this image is projected is a Fresnel lens in which lenses are concentrically formed so as to have a sawtooth cross-section from the projection tube side, the arrangement direction (generally horizontal) of the projection tubes, and the vertical direction (generally vertical). Direction), a lenticular sheet having cylindrical lenses formed on both sides.

The Fresnel lens suppresses the hot spot phenomenon in which the central part of the screen by the projection lens becomes brighter than other parts.

Further, the lenticular sheet has a diffusing material mixed therein and has a function of forming an image on this surface, and diffuses light in the horizontal direction to widen the horizontal visual field.

In such a rear projection television, the projection light that passes through the Fresnel lens and is incident on the lenticular sheet is at a point x away from the center of the screen in FIG. 4, as shown in FIG. It is incident on the backside lens 1 at an angle of θ.

This incident angle θ increases as x increases from the center, as shown in FIG.

It is necessary to shift the optical axis of the lens 1 on the back surface side and the optical axis of the lens 2 on the front surface side by this incident angle θ, and it is necessary to increase the shift amount Δ as the incident angle θ increases.

The shift amount Δ is roughly ΔDtanθ, where D is the thickness between the lenses 1 and 2 and θ is the incident angle of the projection light from the green projection tube, which is the central projection tube, as shown in FIG. The obtained shift amount Δ becomes as shown in FIG. 7 as x increases.

The outline here is that the red and blue projection tubes are actually on both sides of the green projection tube and the incident angle is different from that of green, and the actual light amount balance is different due to the difference in the refractive index depending on the wavelength. Because it is necessary to decide while taking.

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

[Problems to be Solved by the Invention]

In recent years, it has been desired to reduce the thickness of this type of rear projection television, but in order to achieve the reduction in thickness, the optical path from the projection tube to the screen must be shortened.

When the optical path is shortened in this way, the difference in the incident angles from the red and blue projection tubes, which are the projection tubes on both sides, to the lenticular sheet becomes large.

However, the shift amounts of the lenses 1 and 2 on both sides of the lenticular sheet are determined with respect to green, and red and blue are treated as parallel ones. Therefore, the right and left sides of the screen are distorted due to the difference in incident angle. This causes color unevenness.

That is, when white projection is performed with a three-color projection tube, a yellowish color due to the combined light of blue and green appears on the side of the blue projection tube, and a combined light of red and green appears on the side of the red projection tube. There is a drawback that it becomes a certain cyanish color.

[Object of the Invention]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems in conventional rear projection televisions, and to provide a rear projection television that does not deteriorate in color balance and color shift even when the optical path is shortened by thinning. .

[Outline of Invention]

The present invention relates to means of a rear projection television for achieving the above-mentioned object, wherein the converging distance of the Fresnel lens constituting the screen of the rear projection television is made larger in the periphery than from the center, and the front and back surfaces of the lenticular sheet are The offset amount of the lens is changed so as to have at least one inflection point in the graph of the change amount.

Example of Invention

Next, an example of implementation of the present invention will be described with reference to FIGS.

In FIG. 3, the Fresnel lens B on which the projection light of the green projection tube is incident is emitted to the lenticular sheet A, and the lenses 1 and 2 on both sides of the lenticular sheet A are Fresnel lens B.
A state in which an offset amount Δ is provided in correspondence with the emission angle θ of is shown.

In the figure, 3 is the lens 2 of the lenticular sheet A.
A black stripe that does not transmit light is provided between them.

The Fresnel lens B prevents the hot spot phenomenon from occurring due to the central portion of the screen being brightened by the projection lens.

However, the viewpoint tends to be closer to the screen due to the increase in the brightness and resolution of the rear projection television.

When the viewpoint approaches the screen, the hot spot phenomenon appears at the exit angle θ due to the focusing distance of the Fresnel lens B shown by the dotted line in FIG. 2 so far, and this hot spot is horizontal with the diffusion material of the lenticular sheet. A hot band phenomenon occurs in which a bright band appears in the horizontal direction by being diffused in the direction.

This is prevented, and the incident angle θ on the lenticular sheet A is
In order to adjust the
The light collecting distance in the peripheral portion is longer than that in the center.

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

In this embodiment, the size of the screen is projected to a size of 40 inches with a height of about 600 mm and a width of about 800 mm, and the incident angle θ is the same as the projection light of the green projection tube. It has been set for.

By constructing the Fresnel lens B in this way, in the case of the above embodiment, even when the viewpoint is 3 m from the screen, the hot band from the viewpoint is expanded to about 600 mm in the vertical direction, and it is not considered as a hot band. .

In this case, the condensing distance at the central portion was reduced from about 8 to 20 m in the past to about 5 m and the Fresnel lens B
This prevents uneven color around.

When the Fresnel lens B is configured in this way, if the offset amounts Δ of the lenses 1 and 2 on both sides of the conventional lenticular sheet A shown by the dotted line in FIG. Due to the difference in the angle θ, the color balance is lost, and color unevenness occurs at positions away from the center.

Therefore, the offset amount Δ of the lenses 1 and 2 on both sides is a graph having two inflection points as shown by the solid line in FIG. The offset amount Δ shown is set.

With such a lenticular sheet A, the emitted light θ from the Fresnel lens B can prevent color unevenness due to a color balance failure due to a difference in incident angle of the projection light from the red and blue projection tubes to the Fresnel lens B. Is.

The above embodiment is for a rear projection television called 40 inches, but the solid lines in FIGS. 1 and 2 are changed depending on the length of the optical path, the size of the screen, etc. However, the graph of FIG. 1 must have one or more inflection points.

〔The invention's effect〕

As described above, the present invention uses a Fresnel lens and a lenticular sheet to shorten the distance from the projection tube to the screen, and when the product is made thinner, the color balance that is derived from other than the center of the screen is obtained. There is no deterioration of color shift.

Therefore, a thin rear projection TV with good color balance and color shift can be obtained, and restrictions on the installation space can be reduced.

Moreover, even when viewed from a place near the screen, this tendency remains unchanged, and the hot band phenomenon does not occur.

[Brief description of drawings]

FIG. 1 shows an example of a change diagram of the offset amount of the lenticular sheet of the present invention, FIG. 2 shows an example of a change diagram of the exit angle of the Fresnel lens, and FIG. 3 is an explanation of FIGS. 1 and 2. Fig. 4, Fig. 4 is a front view of the screen, Fig. 5 is an explanatory diagram of the offset amount, Fig. 6 is a diagram showing the change of the emission angle to the lenticular sheet by the conventional Fresnel lens, and Fig. 7 is a change of the offset amount of the lenticular sheet. It is a figure. A: Lenticular sheet, B: Fresnel lens,
1,2 ... Lens.

Claims (1)

[Claims] 1. A projection tube and a screen for receiving projection light projected from the projection tube, wherein an image projected on the screen is viewed from the side opposite to the projection side of the projection tube. On rear projection TV,
Fresnel lens on the screen from the projection tube side,
A lenticular sheet is arranged, the condensing distance of the Fresnel lens is increased from the center to the periphery, and the optical axes of the lenses on the front and back surfaces of the lenticular sheet are shifted toward the periphery, and the offset amount is the offset amount. A rear projection television characterized in that it changes with at least one inflection point in the graph of the relationship between the distance from the center of the lenticular sheet and the center of the lenticular sheet.