JPS626201B2 - - Google Patents

Abstract

PURPOSE:To prevent the formation of spectral light strips which are likely to be produced at peripheral parts when a Fresnel lens sheet is used for a transmission type screen and enhance the quality of reproduced plane images by forming the rising faces of the Fresnel lens into polyhedral constitution so that the respective angles of intersection of the plural faces differ each other. CONSTITUTION:The rising faces 10 of a Fresnel lens 1 are formed into polyhedral constitution in such a manner that the respective angles 16 of intersection of the plural faces differ each other. Then, when the Fresnel lens is used for a renticular lens sheet as a constituting element for a transmission type screen, a rear projection television device combined with a diffusion layer, etc., the images are well visible when viewed from diagonally, too.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a Fresnel lens sheet that is a component of a transmissive screen used as a display section of a slide projector, rear projection television device, or the like.

Conventionally, when a projection light beam is incident on a Fresnel lens sheet, the projection light beam that has entered the rising surface of the Fresnel lens of this Fresnel lens sheet is repeatedly refracted and reflected in this Fresnel lens sheet, and then is reflected in an unnecessary direction in a certain direction. Emitting it as a light beam sometimes caused a significant deterioration in the quality of the reproduced image.

An object of the present invention is to emit light rays that are unnecessarily emitted in a specific direction in a wide range of unspecified directions by forming the rising surface of the Fresnel lens in a multifaceted configuration, thereby improving the quality of reproduced images. The goal is to significantly improve the decline.

Hereinafter, the Fresnel lens sheet of the present invention will be explained in detail using the drawings. Note that the same components are given the same reference numerals.

FIG. 1 shows an example of a rear projection television apparatus 4 using a transmission screen consisting of a Fresnel lens sheet 1, a lenticular lens sheet 2, and a diffusion layer 3. In this device, a projected light beam 6 from a projector 5 is reproduced as an image on this transmission screen and observed by an observer 7. The Fresnel lens sheet 1 is used to condense the projected light beam 6 from the projector 5 toward the viewer 7 and to improve the light utilization efficiency.

Generally, in order to reduce the size of a rear projection television device, the distance between the projector and the transmission screen is shortened. However, the exit angle 8 of the projected light rays projected from the projector and directed toward the periphery of the transmissive screen with respect to the optical axis increases as the device is made smaller, and as shown in FIG. The projected light ray 6 that enters the lens is divided into one that enters the Fresnel lens surface 9 and one that enters the rising surface 10 of the Fresnel lens, and is then refracted. As the exit angle increases, the rising surface 1 of the latter Fresnel lens increases.
The ratio of the incident light beam 6 to 0 becomes large, and the projection light beam 6 incident to the rising surface 10 of the Fresnel lens gradually comes to influence the reproduced image.

According to experiments conducted by the inventors, when a transmissive screen is observed obliquely as shown in FIG. A spectral light band was observed along with the reproduced image at the periphery of the screen, and it was observed that the quality of the reproduced image was significantly degraded.

When we analyzed the cause of this, we found that the projected light ray 6 that entered the Fresnel lens rising surface 10 was repeatedly refracted and reflected in the Fresnel lens sheet 1, and finally became the emitted light ray 12, as shown in Figure 4. However, it has become clear that this can be observed as a spectral light band due to the combination of the lenticular sheet and the diffusion layer as a transmission screen. Furthermore, this emitted light ray 1 is defined as a spectroscopic light band.
2 is observed because the refractive index of the vinyl chloride resin or acrylic resin, which is the material of the Fresnel lens sheet 1, differs depending on the wavelength of the light, and when the light is finally incident on the plane 14 facing the Fresnel lens surface of the Fresnel lens sheet 1. It has also become clear that this is caused by the fact that the incident angle 13 differs for each wavelength of light, and that the critical angle of total reflection also differs for each wavelength of light.

FIG. 5 shows an embodiment of the present invention constructed based on the above study results. In this embodiment, the Fresnel lens rising surface 10 is composed of three surfaces.
The projected light ray 6 from the projector that is incident on each surface is refracted in accordance with the angle of incidence with each surface, but the direction of each refracted light ray 15 differs depending on each surface of the Fresnel lens rising surface 10. This refracted ray 1
5 then travels around the optical path shown in FIG. It's on. Therefore, conventionally, since there are regular differences in the incident angle for each wavelength of light, the exit light 12
However, in the present invention, the angle of incidence differs for each wavelength of light, and also differs for each rising surface of each Fresnel lens as described above, so the regularity as in the past is not possible. is eliminated or reduced. As a result, the emitted light ray 12 has no spectroscopic elements, and the direction of the emitted light ray 12 becomes irregular, which would conventionally result in a significant deterioration of the quality of the reproduced image by unnecessarily emitting it in a specific direction. There will be no more.

It is better to have a large number of surfaces constituting the rising surface of the Fresnel lens, and better results can be obtained if the intersection angles 16 of the respective surfaces are also different from each other.

The above-mentioned surface structure can be formed by cutting directly into the vinyl chloride resin sheet or acrylic resin sheet, which is the material of the Fresnel lens sheet, with a cutting blade, or by cutting it into a mold when molding by a press method. This can be easily achieved by processing with a knife.

As described above, in a transmission screen that has a Fresnel lens sheet as one component, conventionally, the projected light beam incident on the rising surface of the Fresnel lens on the Fresnel lens sheet is refracted and reflected within the Fresnel lens sheet. According to the present invention, the emitted light rays are emitted irregularly over a wide range, and the light rays are non-spectroscopic. , it becomes possible to significantly reduce the influence on the reproduced image.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing how a Fresnel lens sheet is used as a component of a transmission screen in a rear projection television device.
Figure 2 shows how the projected light beam enters the Fresnel lens surface and the rising surface of the Fresnel lens when it enters the Fresnel lens sheet, and Figure 3 shows how the ray that enters the rising surface of the Fresnel lens exits in a specific direction. Figure 4 is a diagram showing the state in which the projected light beam incident on the rising surface of the Fresnel lens is refracted and reflected in the Fresnel lens sheet, and exits spectroscopically from the flat side of the Fresnel lens sheet.
FIG. 5 is a diagram showing the structure of an embodiment of the screen of the present invention and how projection light rays are incident on and refracted thereon. 1... Fresnel lens sheet, 6... Projected light beam, 10... Fresnel lens rising surface, 15...
Refracted ray, 16... angle of intersection of planes.

Claims (1)

[Scope of Claims] 1. A Fresnel lens sheet, characterized in that the Fresnel lens rising surface of the Fresnel lens has a multifaceted structure consisting of a plurality of surfaces. 2. The Fresnel lens sheet according to claim 1, wherein the plurality of surfaces constituting the rising surface of the Fresnel lens have mutually different intersection angles.