Illumination – Revolving
Reexamination Certificate
1998-12-23
2003-08-19
O'Shea, Sandra (Department: 2875)
Illumination
Revolving
C362S268000, C362S296040, C362S353000, C349S010000, C353S097000, C353S119000, C353S122000, C359S254000, C359S634000
Reexamination Certificate
active
06607280
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection apparatus and, more particularly, to a projection apparatus suitable for, e.g., a liquid crystal projector for projecting image information displayed on a light modulation element such as a monochrome liquid crystal, color liquid crystal (color liquid crystal panel), or the like for forming an image onto a screen in an enlarged scale.
2. Related Background Art
Conventionally, various liquid crystal projectors for projecting image information displayed on a liquid crystal panel, which is a light modulation element, onto a screen have been proposed.
FIG. 18
is a schematic view showing principal part of the optical system of a color liquid crystal projector using a reflection liquid crystal, which is proposed by Japanese Laid-Open Patent Application No. 6-265842. This optical system is called a Schlieren optical system.
Referring to
FIG. 18
, light emitted by a light source
1
is converted into nearly collimated light by a reflector
2
(parabolic mirror), is reflected by a mirror
3
, and is then focused to form a light source image near a reflection mirror
5
placed at the stop position of a projection optical system
13
. The light beam reflected by the reflection mirror
5
travels toward a plano-convex lens
7
, and is converted into collimated light by the plano-convex lens
7
. The collimated light is color separated into three, R, G, and B light beams by a cross dichroic prism
8
to respectively illuminate reflection liquid crystal panels
9
,
10
, and
11
for forming images of the respective colors (wavelength ranges).
The R, G, and B light beams modulated by the reflection liquid crystal panels
9
,
10
, and
11
are color-synthesized into full-color image light by the cross dichroic prism
8
again. The full-color image light is focused by the plano-convex lens
7
, passes through a stop
12
, and is then projected onto a screen
15
via the projection optical system
13
.
In each liquid crystal panel, for example, a polymer dispersed liquid crystal or polymer network liquid crystal is sealed. When white level is displayed, the liquid crystal becomes transparent to specularly reflect a light beam; when black level is displayed, the liquid crystal scatters and reflects (diffusely reflects) a light beam. The light beams which are reflected by the liquid crystal panels and color-synthesized by the cross dichroic prism
8
are focused at or in the vicinity of the position of the stop
12
of the projection optical system
13
. Most of the light beam reflected by each liquid crystal panel pass through the aperture of the stop
12
, and display white level on the screen
15
via the projection optical system
13
. However, little of the light scattered by the liquid crystal panel pass through the aperture of the stop
12
, thus displaying black level on the screen
15
.
In this way, image information is displayed using scattering of the liquid crystal, and is projected onto the screen via the projection optical system.
The above-mentioned stop
12
will be explained below with reference to FIG.
19
.
FIG. 19
shows the relationship between an aperture
12
a
of the stop
12
placed at the pupil position of the projection optical system (projection lens)
13
, and a light source image S′. A pupil
16
of the projection lens
13
has a semi-circular shape since its half portion is occupied by the reflection mirror
5
. The light source image S′ represents a mode in which the liquid crystal panel reflects an incoming light beam to display white. In case of the other mode in which the liquid crystal panel scatters an incoming light beam to display black, the light source image S′ becomes sufficiently larger than the aperture
12
a,
and only a part of the entire light beam pass through the aperture
12
a.
If the size of the aperture
12
a
is increased, the amount of light that reaches the screen
15
increases, and a bright projected image can be obtained. However, since the luminance of black level similarly rises, the contrast lowers. If the size of the aperture
12
a
is decreased, the contrast can be improved, but the projected image becomes dark. Thus, the brightness and contrast of the projected image normally have a trade-off relationship.
However, in the color liquid crystal projector shown in
FIG. 18
, even when an aperture
12
a
smaller than the light source image S′ is used to give priority to contrast over the brightness of the projected image, the contrast cannot be improved.
This problem will be explained using FIG.
19
. When the light source image S′ is classified into portions inside and outside the aperture
12
a,
only the former portion contributes to the brightness of the projected image when white is displayed on the liquid crystal panel. However, when black is displayed on the liquid crystal panel, since a light beam incident on the liquid crystal panel is scattered, both light beams focused inside and outside the aperture
12
a
are partially diffused and pass through the aperture
12
a
. Hence, the contrast lowers due to the presence of the latter light beam.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a projection apparatus suitable for a high-resolution liquid crystal projector such as a computer monitor, which can project image information with high contrast.
According to one aspect of the present invention, there is provided a projection apparatus which guides a light beam emitted by a light source to at least one light modulation element for forming an image, and projects the light beam coming from the light modulation element onto a screen or the like, by a projection lens wherein a stop is located at a position conjugate with an aperture of a stop of the projection lens to intercept a part of the light beam emitted by the light source.
According to another aspect of the present invention, there is provided a projection apparatus which guides a light beam emitted by a light source to at least one light modulation element for forming an image, and projects the light beam coming from the light modulation element onto a screen or the like, by a projection lens comprising: first optical means for forming an image of the light source as a first light source image; and second optical means for re-imaging the light beam coming from the light modulation element illuminated with light emanating from the first light source image at a position in the vicinity of an aperture of a stop of the projection lens as a second light source image, wherein a peripheral portion of the first light source image is intercepted by stop means located at a position conjugate with the stop of the projection lens.
According to still another aspect of the present invention, there is provided a projection apparatus, which has color-separation means for separating a white light beam emitted by a light source into a plurality of light beams corresponding to different wavelength ranges, optical means for guiding the plurality of light beams to a plurality of light modulation elements for forming images corresponding to the respective wavelength ranges, synthesizing means for synthesizing the light beams coming from the plurality of light modulation elements, and a projection lens for projecting the light beam synthesized by the synthesizing means onto a screen or the like, comprising: first optical means for forming images of the light source as first light source images; and second optical means for imaging light beams coming from the plurality of light modulation elements illuminated with light beams emanating from the first light source images to re-form second light source images of the light source at or in the vicinity of a stop position of the projection lens via the synthesizing means, wherein peripheral portions of the first light source images are intercepted by stop means located at a position conjugate with the stop position.
According to still another aspect of the present invention, there is prov
Koyama Osamu
Kurioka Yoshiaki
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