1. Field of the Invention
The present invention relates to a rear projection screen with a double sheet for use in projectors and projection televisions and more particularly, to a rear projection screen with a double sheet which is structured with a first sheet formed with a Fresnel lens and vertical lenticular lenses disposed on both surfaces of a first transparent sheet made of synthetic resin, and a second sheet formed with a horizontal grating disposed on one surface of a second transparent sheet made of synthetic resin and also formed with a horizontal grating or a fine mat surface layer and simultaneously a black striped layer disposed on the other surface of the second transparent sheet so that brightness and contrast of the screen are improved.
2. Description of the Prior Art
A conventional projection television is, as shown in FIG. 1, structured with a color picture tube 2 attached with a projection lens 3 maintained at a predetermined distance from a screen 1, and the screen 1 is formed with a Fresnel lens 4 disposed on a surface directing to the projection lens 3 and lenticular lenses 5 disposed on the opposite surface in various forms as shown in FIG. 2.
Diffusers such as SiO.sub.2, CaCO.sub.3, TiO.sub.3, BaSO.sub.4, ZnO, Al(OH).sub.3, and fine powdered glass are added to the interior of the screen 1, or a fine mat surface layer is formed on the surface of the screen 1, or else diffuser addition and fine mat surface layer formation are executed together.
The Fresnel lens 4 serves a field lens function for an image beam directed from the projection lens 3, thereby converging the image beam directed to the screen 1 toward an observer. At this moment, the directed image beam is diffused by the diffuser or fine mat surface layer during passing the screen 1. This diffusing degree depends on the control of density or thickness of the diffuser or fine mat surface layer. This is determined according to a desired vertical angle of a field view. A lenticular lens 5 serves as a function for further diffusing the directed image beam come out by diffusing according to the process as aforementioned into the desired horizontal angle of the field view toward horizontal direction, and the observer recognizes the directed image focusing on the screen 1 according to the process.
The conventional rear projection screen as aforementioned includes a loss of transmitted beam according to the surface reflection of the screen 1 but also it is added with loss of transmitted beam according to the backward reflection appeared by addition of the diffuser or formation of fine mat surface layer, whereby brightness of the entire screen 1 is decreased and since shapes of lenticulars are all same, difference of brightness at the corner and center of the screen 1 is increased to, thereby causing a decrease of brightness uniformity. It causes contrast decrease of screen image according to the external light.