JPH06102583A - Transmission type screen - Google Patents

Abstract

PURPOSE:To restrain ghost caused by multiple reflection in a Fresnel lens without making a viewing distance longer by dispersing light absorbing material in the Fresnel lens. CONSTITUTION:The light absorbing material 26 is dispersed in the Fresnel lens 18 of a transmission type screen. It is good to uniformly disperse the material 26 in the lens 18 or disperse it in a belt shape, or it is possible to stick a light absorbing film to the lens 18. Light made incident on the lens 18 is refracted or reflected on a prism surface on an exiting side, and a path through which the light reflected on the prism surface passes is much longer than a path through which the refracted light passes, so that the reflected light is much more attenuated than the light refracted on the prism. Therefore, though the light refracted on the prism surface is somewhat attenuated, almost all the light quantity is normally projected from the lens 18 so as to form a desired image, but the reflected light is absorbed by the material 26 while it is propagated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmissive screen usable as a rear screen of a rear projection display device.

[0002]

2. Description of the Related Art In recent years, a rear projection display device using a liquid crystal panel as a light valve has been developed. In the rear projection display device, the image light spatially modulated by the light valve is enlarged and projected on the rear screen by the projection lens,
The viewer is looking at the screen from the opposite side of the projection lens. Therefore, the image light passes through the screen,
The viewer will see the transmitted light.

Such a transmissive screen has a structure in which a Fresnel lens, a diffusion plate and a lenticular lens are stacked. Of these, the Fresnel lens is equipped with a lens unit consisting of concentric prisms, and the diffused light projected from the projection lens is made to enter the diffuser plate as a light beam that is parallel or converges with the optical axis. It determines the viewing angle of the direction. The viewing angle set at this time is the same in both the horizontal and vertical directions,
Generally, the horizontal viewing angle needs to be wider than the vertical viewing angle. Therefore, the lenticular lens is used to diffuse the light beam emitted from the diffuser plate in the horizontal direction again, thereby expanding the degree of diffusion in the horizontal direction.

[0004]

Such a rear projection display device has been conventionally used for a television, and a viewer has been viewing the screen at a position relatively far from the screen. For example, in the case of a television, the viewing distance is about 6 to 8 times the height of the screen, and the prism surface 2a of the prism 2 is
The slope of (Fig. 5) was correspondingly relatively small. However, in recent years, it has been required to use a rear projection display device that can save space as compared with a conventional CRT display device as a display of a CAD or a workstation. However, in the display used for CAD and workstations, the viewing distance is at most about twice the height of the screen due to its usage, and therefore the focal length of the Fresnel lens 1 is significantly shortened. That is, that is, the inclination of the prism surface 2a on the surface of the Fresnel lens needs to be greatly inclined in order to largely bend the incident light.

At this time, the component reflected on the prism surface 2a becomes a problem. That is, the light incident on the Fresnel lens is refracted and reflected on the prism surface 2a. Of these, the refracted light is emitted as normal output light L _o , but one of the reflected light is reflected light L _R.
Is repeatedly reflected in the Fresnel lens, and is emitted from another position different from the predetermined emission position. The intensity of the reflected light L _R depends on the incident angle of the light ray on the prism surface 2a, and is determined by the inclination of the prism surface 2a when the angle of the incident light ray is constant. Therefore, the reflected light L _R is increased by inclining the prism surface 2a largely in order to shorten the viewing distance. If the intensity of the reflected light L _R is low, it will not be visually recognized, but as the intensity becomes high, it will be visually recognized, and this will be a ghost and the display quality will be significantly impaired. Conventionally, there is no method of extinguishing this ghost other than reducing the light amount of the reflected light L _R by extending the focal length of the Fresnel lens. In this case as well, the viewing distance becomes long, and it is common for CAD, workstations, etc. There was a problem that the brightness unevenness on the screen increased in the use state.

An object of the present invention is to provide a transmissive screen capable of suppressing a ghost due to multiple reflection in a Fresnel lens without increasing the viewing distance.

[0007]

The transmission screen according to the present invention is characterized in that it includes a Fresnel lens 18, and a light absorbing material 26 is dispersed in the Fresnel lens 18. The light absorbing material 26 may be uniformly dispersed in the Fresnel lens 18, the light absorbing material 26 may be dispersed in a band shape in the Fresnel lens 18, or the light absorbing film 30 may be attached to the Fresnel lens 18. It can also be.

[0008]

In the above structure, the light incident on the Fresnel lens is refracted and reflected by the prism surface on the exit side. At this time, the path through which the light reflected on the prism surface travels is sufficiently longer than the path through which the refracting light travels, and thus is greatly attenuated as compared with the light refracting at the prism. Therefore, although the light refracted on the prism surface is attenuated to some extent, almost the entire amount of light normally exits from the Fresnel lens to form a desired image. However, if one of the reflected lights propagates as it is, it causes a ghost, but in the present invention, since it is absorbed during the propagation by the light absorbing material dispersed in the Fresnel lens, it becomes large when it is emitted from the Fresnel lens. It is attenuated and does not cause a ghost.

[0009]

FIG. 2 is a diagram showing an example of a rear projection display device. This rear projection display device includes a light source 10, a liquid crystal panel 12, a projection lens 14, and a screen 16. In addition to this, another member may be inserted. For example, a condenser lens or the like may be arranged in front of the liquid crystal panel 12. In this rear projection display device, the image light spatially modulated by the liquid crystal panel 12 is projected by the projection lens 14
Thus, the image is enlarged and projected on the screen 16. The projection lens 14 projects the diffused light toward the screen 16 as indicated by the arrow.

The screen 16 has a Fresnel lens 18
The diffuser plate 20 and the lenticular lens 22 are stacked. Of these, the Fresnel lens 18
The divergent light projected from the projection lens 14 is incident on the diffusion plate as a light beam that is parallel to or converges with respect to the optical axis to determine the horizontal / vertical viewing angle. The lenticular lens 22 diffuses the light rays emitted from the diffusion plate 20 in the horizontal direction again, thereby setting the horizontal viewing angle to be wide independently of the vertical viewing angle.

FIG. 1 shows a first embodiment of the present invention and is a partially enlarged view of the Fresnel lens 18 of FIG. The light incident side of the Fresnel lens 18 is a flat surface, and the light emitting side of the Fresnel lens 18 is a lens portion including a minute prism 24. Prism 24
Has a prism surface 24a inclined with respect to the incident plane.
The inclination of each prism surface 24a changes according to the distance from the center of the Fresnel lens 18, and among the diffused light from the projection lens 14, peripheral light is largely refracted and central light is refracted small. (Fig. 2).

In this embodiment, the Fresnel lens 1
Absorbing material 26 is uniformly dispersed in 8. The Fresnel lens 18 is made of a transparent plate such as acrylic resin, and has a light absorbing material 2
6 is diffused in the acrylic resin. The light absorbing material 26 is made of a black pigment or a black dye and has a light absorption rate of 15% (transmittance of 85%).

In FIG. 1, the incident light L _I enters the Fresnel lens 18, passes through the Fresnel lens 18, and reaches the prism surface 24a. This light is refracted and reflected on the prism surface 24a. Light refracted at the prism surface 24a is emitted as a normal outgoing light L _O, diffusion plate 20
And an image is formed through the lenticular lens 22. The reflected light L _R reflected on the prism surface 24a undergoes multiple reflection in the Fresnel lens 18, and is emitted from a position different from the predetermined emission position of the Fresnel lens 18.

In the present invention, since the Fresnel lens 18 has the light absorbing material 26 dispersed therein, the prism surface 24a.
The light reflected at is absorbed by the light absorbing material 26 during its propagation, and the amount of light emitted from the emission side of the Fresnel lens 18 again decreases. Therefore, even if the viewing distance is small, it does not cause a ghost. Since the distance between the incident surface of the Fresnel lens 18 and the prism surface 24a, which is the exit surface, is quite small, the absorption of the light traveling between them is small, and the light absorption rate is 15% (transmittance of 85% as described above). %). Therefore, the ratio of the emitted light L _O, which passes through the Fresnel lens 18 and is normally emitted, is attenuated by the light absorbing material 26 is considerably small, and there is no practical problem. On the other hand, since the light reflected on the prism surface 24a propagates in the Fresnel lens 18 for a long process (about 10 times as much as normal light), the attenuation rate becomes 80% or more, and even if it is emitted from the prism surface 24a. No ghost was visible. Within the scope of the present invention, it is not necessary to limit the light absorptivity to 15%, and the light absorptance can be changed according to the thickness of the Fresnel lens 18 and the angle of the prism surface 24a.

FIG. 3 is a diagram showing a second embodiment of the present invention. The light incident side of the Fresnel lens 18 is a flat surface, and the light emitting side of the Fresnel lens 18 is a lens portion including a minute prism 24. The prism 24 has a prism surface 24a inclined with respect to the incident plane. In this embodiment, the Fresnel lens 18 has the light absorbing material 26 dispersed in a band shape. The light absorbing material 26 made of black pigment or black dye is a transparent resin plate material 2
8 is a plate material 2 which is diffused and dispersed with the light absorbing material 26.
8 is arranged parallel to the incident surface of the Fresnel lens 18.
The operation is similar to that of the first embodiment.

FIG. 4 is a diagram showing a third embodiment of the present invention. In this embodiment, the Fresnel lens 18 has a light absorbing film 30.
It is configured to be stuck together. The light absorption film 30 is made of a resin layer in which the light absorption material 26 is dispersed. Alternatively, the light absorbing film 30 is composed of a material layer that absorbs light by itself. Light absorbing film 30
Is attached to a transparent plate member 32, which is attached to the Fresnel lens 18. This structure also has the same operation as that of the first embodiment. Further, according to this configuration, the Fresnel lens 18 can be used without any change.

[0017]

As described above, according to the present invention,
In a transmissive screen, it is possible to reliably prevent ghosts due to multiple reflections in the Fresnel lens, which is a problem when the viewing distance is short, and this greatly contributes to improving the performance of the display device.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a rear projection display device.

FIG. 3 is a diagram showing a second embodiment of the present invention.

FIG. 4 is a diagram showing a third embodiment of the present invention.

FIG. 5 is a diagram illustrating a problem of the conventional technique.

[Explanation of reference numerals] 16 ... Screen 18 ... Fresnel lens 20 ... Diffuser 22 ... Lenticular lens 26 ... Absorbing material 30 ... Absorbing film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuya Hamada 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (72) Inventor Yoshinori Tanaka, 1015, Kamedotachu, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited

Claims (4)

[Claims] 1. A transmissive screen comprising a Fresnel lens (18) in which a light absorbing material (26) is dispersed. 2. The light absorbing material (26) is a Fresnel lens (1).
8. The transmissive screen according to claim 1, wherein the transmissive screen is evenly dispersed within 8). 3. The light absorbing material (26) is a Fresnel lens (1).
8. The transmissive screen according to claim 1, wherein the transmissive screen is dispersed in a strip shape within 8). 4. A transmissive screen comprising a Fresnel lens (18) and a light-absorbing film (30) attached to the Fresnel lens.