Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
1999-08-25
2001-04-03
Epps, Georgia (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S853000, C359S869000
Reexamination Certificate
active
06212013
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection type display apparatus used for video display, large-screen display, and so on.
2. Related Background Art
In recent years the variety of use of display apparatus has increased in the fields of image processing etc. and thus there are needs for display devices capable of implementing optimum chromatic purity, chromatic balance, illuminance, and so on according to their use.
FIG. 10
shows an example of the conventional projection type display apparatus.
In the figure, white light emitted from a light source unit
1
having a reflector
2
travels through fly-eye lenses
3
and
4
, a PS converter
5
, a condenser lens
6
, etc. and thereafter a dichroic mirror DM
1
as a first optical system transmits red band light R but reflects green and blue band light. Then the red band light transmitted by the dichroic mirror DM
1
is reflected by a total reflection mirror M
1
to change its optical path by 90° and it then travels through a field lens
7
R and a trimming filter TR into a red liquid-crystal display unit
8
R comprised of an image display element, in which the red band light is optically modulated according to an input signal. The light thus optically modulated is incident to a dichroic prism
9
for combining as a second optical system, and the dichroic prism
9
changes the optical path of the red light by 90° into a projection lens
10
.
On the other hand, among the green and blue band light reflected by the dichroic mirror DM
1
so as to change its optical path by 90°, the green band light G is reflected by another dichroic mirror DM
2
also acting as a first optical system to change its optical path by 90° and then it travels through a field lens
7
G and a trimming filter TG into a green liquid-crystal display unit
8
G comprised of an image display element, in which the green band light is optically modulated according to an input signal. The light thus optically modulated is incident to the dichroic prism for combining
9
and then into the projection lens
10
. Further, the blue band light B transmitted by the dichroic mirror DM
2
travels via a condenser lens
11
, a total reflection mirror M
2
, a relay lens
12
, a total reflection mirror M
3
, and a field lens
7
B into a blue liquid-crystal display unit
8
B comprised of an image display element, in which the blue band light is optically modulated according to an input signal. The light thus optically modulated is incident to the combining dichroic prism, and the dichroic prism
9
changes the optical path of the blue light by 90° into the projection lens
10
.
Then trichromatic light combined by the combining dichroic prism is projected by the projection lens
10
.
A light source of the light source unit
1
is normally selected from a halogen lamp, a metal halide lamp, UHP (available from Philips Inc.: registered trademark), and so on, the dichroic mirrors DM
1
and DM
2
have their spectral transmittances illustrated in FIG.
11
A and
FIG. 11B
, respectively, and the trimming filters TR and TG have their spectral transmittances as illustrated in FIG.
11
C and
FIG. 11D
, respectively.
In the conventional projection type display apparatus constructed as described above, where the contrast was sufficiently high in each of the liquid-crystal panels, the chromatic purity of the red band light was determined by the spectral property of the light-source light and the spectral transmittances of the dichroic mirror DM
1
and the trimming filter TR, the chromatic purity of the green band light was determined by the spectral property of the light-source light and the spectral transmittances of the dichroic mirrors DM
1
, DM
2
and the trimming filter TG, the chromatic purity of the blue band light was determined by the spectral property of the light-source light and the spectral transmittances of the dichroic mirrors DM
1
, DM
2
, and the optical elements were designed so as to gain the optimum chromatic balance and chromatic purity.
Incidentally, there are such various demands that bright display is required even with a penalty of size increase of the apparatus, that bright display is required even with a penalty of degradation of chromatic purity, that the chromatic purity is not required in a white/black mode, and so on, depending upon use purposes of the projection type display apparatus.
The convectional projection type display apparatus implemented the optimum chromatic balance and chromatic purity by cutting the light in the wavelength region of 570 nm to 600 nm in order to enhance the chromatic purity.
However, many lamps have a peak near 580 nm in their spectral distribution, and use of wavelengths near it contributes to increase of illuminance.
There is thus the known projection type display apparatus with a mechanism for putting a band cut filter as an optical element (DF) capable of varying the chromatic purity into or out of the optical path, which is described in Japanese Patent Application Laid-Open No. 7-72450.
This projection type display apparatus was a single device capable of implementing both brightness-priority display and color-reproduction-priority display, but it had a problem that in the color-reproduction-priority display the display became darker than necessary, because the band cut filter was likely to lower the transmittance even at the wavelengths necessary for the projection.
SUMMARY OF THE INVENTION
In view of the problem of the prior art example described above, an object of the present invention is to provide an improved projection type display apparatus capable of implementing both the brightness-priority display and color-reproduction-priority display by itself.
In order to accomplish the above object, the present invention adopts an optical element such as an edge filter for transmitting light in a region not less than a predetermined wavelength but intercepting light in the other region in the visible region or for transmitting light in a region not more than a predetermined wavelength but intercepting light in the other region in the visible region, for selectively carrying out the brightness-priority display and the color-reproduction-priority display in the projection display apparatus. The present invention can also be applied to the projection type display apparatus of various structures independently of types and the number of image display elements.
One aspect of the invention is characterized by a projection type display apparatus for separating light from a light source into a plurality of light beams of mutually different colors, guiding the light beams of the respective colors into corresponding pixel groups among a plurality of pixel groups, and projecting beams of the respective colors from the plurality of pixel groups, wherein purity of at least one color is made variable by use of an optical element for transmitting light in a region not less than a predetermined wavelength but intercepting light in the other region in the visible region or for transmitting light in a region not more than a predetermined wavelength but intercepting light in the other region in the visible region, and it can be constructed in such a form that the plurality of pixel groups are provided in a plurality of (normally three) image display elements different from each other or in such a form that the plurality of pixel groups are provided in a single image display element.
Another aspect of the invention is characterized by a projection type display apparatus for separating light from a light source into a plurality of light beams of mutually different colors, guiding the light beams of the respective colors into corresponding pixel groups among a plurality of pixel groups, and projecting beams of the respective colors from the plurality of pixel groups, wherein an optical element for enhancing purity of a predetermined color by transmitting light in a region not less than a predetermined wavelength but intercepting light in the other region in the visible region or by transmitting ligh
Kodama Hiroyuki
Okuyama Atsushi
Canon Kabushiki Kaisha
Epps Georgia
Lucas Michael A.
Morgan & Finnegan , LLP
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