JPH047987A - Rear projection television - Google Patents

Abstract

PURPOSE:To improve a hot band by setting the converging distance of a Fresnel lens within the range of width in the vertical direction of a screen to a value satisfying a specified formula. CONSTITUTION:When the distance from the emission pupil 2a of a projection lens to the Fresnel lens 1 is set to (a) meters and the converging distance of the Fresnel lens 1 is set to (b) meters, the converging distance of the Fresnel lens 1 within the range of the vertical width of a screen 4 is set to satisfy the inequality (a)X(b)<=5.5. Thus, a hot spot 5 obtains the same dimension as the vertical dimension of the Fresnel lens 1 shown by a full line in the figure. Therefore, the hot spot 5 is enlarged horizontally on a lenticular sheet and the picture of the hot band is enlarged to the full longitudinal dimension. Thus, the picture is not viewed as the hot band.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention includes a projection tube, a projection lens that projects onto a screen of the projection tube, and a screen on which an image projected by the projection lens is projected. , the image projected on the screen,
This invention relates to an improvement in a rear projection television that is viewed from the side opposite to the projection tube.

[Conventional technology]

As shown in Figure 9, the projection lens used in conventional rear projection televisions of this type appears circular (SO) when viewed from the axis of the lens, but when viewed from an oblique direction θ, it looks like a cat's eye. It seems.

This is due to the vignetting of the projection lens, and this causes a hot spot phenomenon in which the Fresnel lens becomes brighter from the center and darker at the periphery than the center.

In order to improve this hot spot, a diffusing agent is mixed into the lenticular lens, which diffuses it vertically to make it less noticeable, and at the same time, the lens effect widens the field of view horizontally.

However, it has not been possible to achieve sufficient diffusion in the vertical direction using only the lenticular lens.

Therefore, even when viewed from a position that is about 8 times the screen distance, which was conventionally considered a common viewing distance, the hot spot or the hot spot remained as a hot band expanded in the horizontal direction.

The condensing distance of the Fresnel lens was set to 8 to 20 m.

Until now, there have been no restrictions on the central part of this Fresnel lens, and in the peripheral part, out of the three projection tubes lined up, color unevenness occurs due to the difference in reflectance between the red and blue projection tubes on both sides. Therefore, as shown in FIG. 5, in some cases the light collecting distance b2 at the peripheral part is made larger than the light collecting distance b2 at the central part.

In addition, the symbol a in the same figure indicates the distance from the Fresnel lens 1 to the projection lens 2.
The distance to the exit pupil of , 3 indicates the projection tube.

[Problem to be solved by the invention]

However, in recent years, due to improvements in the resolution of rear projection televisions and the brightness of their screens, it has become common to view images at a viewing distance of about five times the vertical dimension of the screen.

On the other hand, rear projection televisions are also required to be thinner in actual size in order to reduce the installation space and shorten the viewing distance as described above.

If this depth dimension is made thinner, the distance from the projection tube to the screen must also be reduced.

For example, if the distance from the exit pupil of the projection lens to the Fresnel lens is set to 0.8 m on an ablation television with a screen size of 40 inches, about 600 meters long and about 800 meters wide, the Fresnel lens will The optical distance is approximately 20m.

If this is viewed from t3m, which is five times the vertical dimension of the screen, the situation will be as shown by the dotted line in FIG. is approximately 60% of the vertical dimension of the screen 4, as shown by the dotted line in FIG.

This hot spot 5 is horizontally diffused by the lenticular sheet and is visualized as a horizontally bright hot band.

Conventionally, countermeasures against such hot bands include increasing the amount of diffusion material mixed into the lenticular sheet, and as shown in FIGS. It has been considered to provide a vertical wrench 7 between the Fresnel lens 1 and the lenticular sheet 6 to increase the diffusivity in the vertical direction.

If we take this method of increasing vertical diffusivity,
The relationship between vertical viewing angle and brightness is shown in Figure 8, as the viewing angle θ in the vertical direction to the screen 4 changes, the brightness Br changes as shown in A before the increase in diffusivity. This results in a state like B. As is clear from this, although there is an effect of improving the hot band, the brightness of the screen is reduced.

The vertical viewing angle does not change significantly because the height of the eye at which the screen is viewed does not change significantly, and the brightness of the screen decreases.

[Purpose of the invention]

An object of the present invention is to solve the above-mentioned hot band problems caused by thinning of conventional rear projection televisions and shortening of viewing distance without impairing the brightness of the screen.

[Summary of the invention]

The present invention relates to means for a rear projection television to achieve the above-mentioned object, in which the distance from the exit pupil of the projection lens to the Fresnel lens is 3 meters, and the condensing distance of the Fresnel lens is 5 meters. The condensing distance of the Fresnel lens is within the range of a×b≦5.
By satisfying 5, the purpose is achieved.

[Embodiments of the invention]

Next, a first embodiment of the present invention will be described with reference to FIGS. 1 and 2.

This embodiment is for a rear projection television having a screen size of approximately 600 meters in height and approximately 800 meters in width, which is referred to as a screen size of 40 inches.

The Fresnel lens 1 used in this example has a refractive index n
−1,525, and the distance a from the exit pupil 2a of the projection lens 2 to the Fresnel lens l is set to 0.8 m.

At this time, if the condensing path Mb of the Fresnel lens 1 is formed to be 6.44 m, axb=5.15, which is a value of 5.5 or less.

At this time, if you look at this screen 4 from a position 3 m from the screen 4, the hot spot 5 will be as shown by the solid line in Fig. 1 and as shown in Fig. 2 due to the relationship between distances a and b. The vertical dimension of the Fresnel lens 1 is approximately 600 fl.

Therefore, this hot spot 5 is horizontally diffused by the lenticular sheet and becomes a real hand from the entire screen, so that it is not seen as a hot hand.

On the other hand, in the conventional example shown by the dotted line in the figure, aX b
= 15.8, and when the value is 5.5 or more, a hot band with a hot spot of 60% of the vertical dimension of the screen appears as described above.

Next, a second embodiment will be explained with reference to FIGS. 3 and 4.

This embodiment is for an ablation television with a reduced screen size of 76011 called 50 inches and a screen size of approximately 1000 m in width.

The Fresnel lens 1 used in this example has a refractive index n
=1.525, and the distance a from the exit pupil 2a of the projection lens 2 to the Fresnel lens 1 is set to 1 m.

At this time, by forming the condensing distance of the Fresnel lens 1 to 4.8 m, a x b = 4.8, which is less than the specified value of 5.5 of the present invention.

When this is viewed from a position 3 m from the screen 4, it becomes the state shown by the solid line in Figure 3, and the true spot 5 is expanded to cover the entire length of the screen 4, as shown by the solid line in Figure 4, and the lenticular sheet allows the true spot to be Even so,
Since they are formed all over the screen, they cannot be seen as a real band.

In this example, if a Fresnel lens 1 with a condensing distance of 6.8 m is used, a×b=5.3, and 5.
When the value becomes 5 or more, the state shown by the dotted line in FIG. 3 occurs, and the true spot 5 appears on about 60% of the vertical dimension of the screen 4, as shown by the dotted line in FIG.

Therefore, the hot band that spreads this horizontally is
It appears in 60% of the vertical dimension of the screen, resulting in a loss of image quality.

Although each of the above embodiments has been described for a three-tube type rear projection television, it is also effective for a single-tube type or liquid crystal type rear projection television.

〔Effect of the invention〕

By making the depth dimension thinner like soft soil, the distance between the exit pupil of the projection lens and the Fresnel lens becomes shorter, and this can be seen from a short distance of about 3 to 5 times the vertical dimension of the screen. Even if the hot hand is enlarged to fill the vertical dimension of the screen, it is not perceived as a real band.

Furthermore, compared to a method that diffuses the real spot in the vertical direction, the brightness of the screen does not decrease.

Therefore, even if a rear projection television, which has a reduced depth and increased flexibility in installation location, is viewed from a close distance, the image quality will not be impaired.

[Brief explanation of drawings]

Figures 1 and 3 are explanatory diagrams of each embodiment of the present invention and the visual perception of the true spot of a conventional Fresnel lens. Figures 2 and 4 are the sizes of the true spots appearing on the same Fresnel lens. 5 is an explanatory diagram of an example of a conventional Fresnel lens, FIGS. 6 and 7 are oblique views of vertical wrench installation, and FIG. 8 is a diagram of change in screen gain according to the above. 1... Fresnel lens, 2... Projection lens, 2a.
...Exit pupil, 3...Projection tube, 4...Screen, 5
... Hosotosbo 7th, 6... Lenticular sheet.

Claims (1)

[Claims] The device includes a projection tube, a projection lens that projects the screen of the projection tube, and a screen on which the image projected by the projection lens is projected, and the image projected on the screen is viewed from the opposite side of the projection tube. In the rear projection television, the screen has a Fresnel lens and a lenticular sheet arranged in order from the projection tube side, where the distance from the Fresnel lens to the exit pupil of the projection lens is a meter, and the condensing distance of the Fresnel lens is b meters. A rear projection television, characterized in that the condensing distance of the Fresnel lens within the vertical width of the screen satisfies a×b≦5.5.