Optical: systems and elements – Projection screen – Unitary sheet comprising plural refracting areas
Reexamination Certificate
2002-09-09
2003-08-05
Mahoney, Christopher (Department: 2851)
Optical: systems and elements
Projection screen
Unitary sheet comprising plural refracting areas
C359S742000
Reexamination Certificate
active
06603604
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection television and, more particularly, to a screen of a projection television having a high brightness.
2. Description of the Related Art
With the development of the information industry, there has been a need for an image display medium having a large screen. However, there is a technical limit in making a rectangular CRT of a television which has been a main conventional display device medium. Accordingly, to provide an image on a large screen, an image projection system in which a small CRT or LCD generates an image which is magnified by an optical lens to be projected on a large screen has been developed and widely used. The image projection system is known as a projection television or a video projector.
The image projection system can be divided into two types according to an image projecting method. One is a front projection system in which an image is directly projected on the front surface of a screen, and the other is a rear projection system in which an image is projected on the rear surface of a screen. The brightness of a display image of the rear projection system is much higher than that of the front projection system.
Referring to
FIG. 1
, a conventional projection television screen includes a Fresnel lens
11
for converting a divergent light beam from a projection lens (not shown) provided at a projection apparatus (not shown) into a parallel beam by receiving a light beam emitted from an image source (not shown) and deflecting the light beam so that an image is displayed at substantially uniform brightness throughout a wide viewing angle. A lenticular lens
12
is arranged close to the Fresnel lens
11
as a light spreading means for forming an image by spreading the parallel beam output from the Fresnel lens
11
. The lenticular lens
12
is formed of a plurality of lens elements
13
having a column shape and arranged consecutively. A screen protective panel (not shown), which is formed of an acryl material, is provided on the front surface of the lenticular lens
12
, that is, at the position facing a viewer. A protrusion
14
having a predetermined height is formed at a connection portion of each lens element at the front surface of the lenticular lens
12
contacting the rear surface of the screen protective panel, to absorb part of light divergently coming out of a bulged portion
13
a
of the lens element
13
. A black strip
14
a
is coated in black ink at the end portion of the protrusion
14
. Thus, the contrast of an image formed on the front surface of the lenticular lens
12
can be improved.
FIG. 2
is a cross sectional view of the Fresnel lens
11
shown in
FIG. 1
, vertically crossing the center of the Fresnel lens
11
. Referring to
FIG. 2
, the shape of a surface facing the lenticular lens
12
has a saw-toothed shape.
FIG. 3
shows a magnified portion of a circled portion A in FIG.
2
. Referring to
FIG. 3
, part of incident light, in particular a light beam
22
input at an angle greater than the critical angle of the total internal reflection of a sharp portion
20
of a sawtooth, cannot pass through the Fresnel lens
11
due to the total internal reflection. If the light cannot pass through the Fresnel lens
11
, and proceeds in a direction totally different from the originally set direction after the total internal reflection, it cannot be used in image projection.
In the above conventional screen, the efficiency of light passing is lowered due to loss of light at the Fresnel lens so that the entire brightness of the screen is lowered.
SUMMARY OF THE INVENTION
To solve the above-described problems, it is an aspect of the present invention to provide a projection television screen having a high brightness by minimizing loss of light due to the shape of the surface of the Fresnel lens.
To achieve the above aspect, there may be provided a screen of a projection television comprising a Fresnel lens for converting an incident light beam emitted from an image source into a parallel beam, a lenticular lens formed by sequentially arranging a plurality of lens elements having a column shape parallel to one another for forming an image from the parallel beam output from the Fresnel lens and spreading the formed image, and a protective panel installed on the front surface of the lenticular lens for protecting the lenticular lens. The Fresnel lens may comprise a base substrate and a lens unit contacting one side of the base substrate, patterns having a saw-toothed shape formed on a surface of the lens unit facing a lenticular lens, and a portion of each pattern corresponding to a sharp portion of a sawtooth may have a processed curved surface having a predetermined curvature.
In the present invention, the refractive indexes of the base substrate and the lens unit may be different from each other.
In the present invention, the curved surface may be a spherical surface or an aspherical surface.
Thus, by using the screen of the projection television according to the present invention, the brightness of the projection television can be improved and the brightness can be uniformly distributed throughout the entire screen.
REFERENCES:
patent: 6292295 (2001-09-01), Yamashita et al.
patent: 6407860 (2002-06-01), Funazaki et al.
Mahoney Christopher
Sughrue & Mion, PLLC
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