Optics: image projectors – Reflector
Reexamination Certificate
2002-12-04
2004-03-09
Adams, Russell (Department: 2851)
Optics: image projectors
Reflector
C359S726000
Reexamination Certificate
active
06702447
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates to a projection display system, and more particularly, to a projection display system capable of diminishing ghost images.
2. Description of the Prior Art
The rapid development of electro-optics technologies has made projection display devices become popular both in an office and at home. A projection display device projects images on a display, in the meantime, generating some blurs, such as ghost images. Ghost images downgrade the performance of projected images and consequently become a concern to design the projection display device.
Please refer to
FIG. 1
, which is a projection display system
10
according to the prior art The projection display system
10
comprises an illumination system
110
and an image system
120
. As far as the illumination system
110
is concerned, white light beams, emitted by a light source
111
and reflected from a reflector
112
, converge onto a color generator
113
, such as a color wheel. The color generator
113
comprises a series of red, green, and blue filters for transforming the white light beams into colored light beams. After leaving the color generator
113
, the colored light beams sequentially pass through a light-uniform device
114
, such as an integration rod or a lens array, and through an illumination lens set
115
and reach a reflection mirror
116
. The reflection mirror
116
reflects the colored light beams through a field lens
117
and finally onto a light valve
121
, such as a digital micro-mirror device (DMD). Reflected by the light valve
121
, the colored light beams, which are projected onto the light valve
121
, pass through the field lens
117
again. The colored light beams then penetrate through a projection lens
122
and project onto a screen
124
, composing the image system
120
.
The light valve
121
, which is mounted on a substrate, is formed with a plurality of pixel lenses disposed in a matrix, each pixel lens being capable of pivotably rotating around an axis within a range of 12 degrees. The pixel lenses reflect an incident light beam onto a region inside of the projection lens
122
and the incident light beam can project onto the screen
124
when the light valve
121
is in an ON-state. The pixel lenses reflect an incident light beam onto a region outside of the projection lens
122
and, of course, outside of the screen
124
when the light valve
121
is in an OFF-state.
However, not all the colored light beams will directly project from the light valve
121
onto the screen
124
. Please refer to
FIG. 2A
to
FIG. 2C
, which show light paths of ghost images of the projection display system
10
according to the prior art. As the light valve
121
is in the ON-state, the white light beams, emitted by the light source
111
will sequentially pass through the color generator
113
, the light-uniform device
114
, the illumination lens set
115
, the reflection mirror
116
, and the field lens
117
, and project onto the light valve
121
. The light valve
121
reflects the colored light beams onto the field lens
117
again and a first surface
1171
of the field lens
117
reflects the colored light beam back onto the light valve
121
, generating second reflection colored light beams. As shown in
FIG. 2A
to
FIG. 2C
, the light valve
121
still reflects the second reflection colored light beams through the projection lens
122
and onto the screen
124
, forming so-called ghost images
1241
. A corresponding focal point F located on a position near the light valve
121
and corresponding to the ghost images
1241
forms a virtual ghost-image light source
1211
, which is extended along a direction from the focal point F toward the light valve
121
. The virtual ghost-image light source
1211
projects colors light beams onto the screen
124
to generate the ghost images
1241
. The ghost images
1241
undoubtedly downgrade the performance of the projection display system
10
.
Please refer to
FIG. 3A
to
FIG. 3C
, which are schematic diagrams of a first projection display system capable of diminishing ghost images according to the prior art. In the first projection display system, a convex surface with a curvature radius R less than 50 mm is formed on a first surface
1172
of the field lens
117
. As the colored light beams project onto the light valve
121
and the light valve
121
reflects the colored light beams onto the field lens
117
, the convex surface reflects and focuses the reflected colored light beams to a focal point F
1
between the light valve
121
and the convex surface. The reflected colored light beams continue to travel toward the light valve
121
to form a light-spreading area
1212
. The light valve
121
reflects the reflected colored light beams onto the screen
124
through the projection lens
122
, forming spreading images
1242
and diminishing ghost images. The spreading images
1242
are not ghost images, but reduced contrast for the first projection display system.
Please refer to
FIG. 4A
to
FIG. 4C
, which are schematic diagrams of a second projection display system capable of diminishing ghost images according to the prior art. In the second projection display system, a convexo-concave surface with a curvature radius R less than 0 mm is formed on a first surface
1173
of the field lens
117
. As the colored light beams project onto the light valve
121
and the light valve
121
reflects the colored light beams onto the field lens
117
, the convexo-concave surface diverges the reflected colored light beams toward the light valve
121
to form a light-spreading area
1213
. The light-spreading area has a virtual focal point F
2
. The light valve
121
reflects the reflected colored light beams onto the screen
124
through the projection lens
122
, forming another spreading images
1243
. The spreading images
1243
are not ghost images either, but also reduced contrast for the second projection display system.
The above-mentioned prior art projection display systems solve the ghost images problem at the cost of contrast.
SUMMARY OF INVENTION
It is therefore an objective of the claimed invention to provide a projection display system that can effectively diminishing ghost images.
According to the claimed invention, the projection display system includes an illumination system and an image system. The projection display system has a light source for emitting at least one light beam, and a field lens having a first surface and a second surface opposite to the first surface, the first surface having at least one reflection area. The image system utilizes the field lens and a light valve mounted adjacent to the second surface of the field lens for reflecting the light beam emitted by the light source. The light beam reflected from the light valve to the interface reflecting area is further reflected to a region outside of the light valve by the reflection area.
It is an advantage of the claimed invention that a projection display system can diminish ghost images by using the field lens with appropriate curvature radius to reflect unwanted light beams to a region outside of the light valve of the projection display system.
REFERENCES:
patent: 4981352 (1991-01-01), Tejima et al.
patent: 5268775 (1993-12-01), Zeidler
patent: 6500378 (2002-12-01), Smith
patent: 6522453 (2003-02-01), Yoneyama
patent: 6557999 (2003-05-01), Shimizu
US 2003/0058414 A1.
Adams Russell
Coretronic Corporation
Nguyen Michelle
Winston Hsu
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