Optics: image projectors – Composite projected image – Multicolor picture
Reexamination Certificate
2000-02-11
2003-02-04
Adams, Russell (Department: 2851)
Optics: image projectors
Composite projected image
Multicolor picture
C353S020000, C349S005000
Reexamination Certificate
active
06513934
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for projecting an image and an apparatus for observing an image and, more particularly, to those suitably applicable to liquid crystal projectors using a liquid crystal display element (liquid crystal panel) as an image display element and constructed to project an image obtained thereby through a projection lens, for example, onto a polarizing screen and to image observation systems constructed to permit observation of an enlarged and projected image from a screen of a computer, a picture of a video camera, or the like.
2. Related Background Art
A variety of proposals have been made heretofore as to the image projection devices (liquid crystal projectors) constructed to illuminate the liquid crystal panel with light from a light source, display an image on the liquid crystal panel, and enlarge and project an image based on transmitted or reflected light from the liquid crystal panel, through the projection lens onto the screen.
FIG. 17
is a schematic diagram of major part of a conventional image projection apparatus. In
FIG. 17
reference numeral
101
designates a white light source. Numeral
102
designates a reflector. Numeral
103
represents a visible-light-transmitting filter for removing the components of light except for the visible light.
Numeral
104
indicates an integrator for yielding a uniform illumination area, which is comprised of fly's eye lenses
104
a
,
104
b
each consisting of an array of lenses. Numeral
105
denotes an array of polarization converting elements for converting non-polarized light into linearly polarized light polarized in a predetermined direction of polarization, each element consisting of a polarization separating surface
105
a
, a reflecting surface
105
b
, and a half-wave plate
105
c
.
Numeral
106
represents a condenser lens. Numeral
107
designates a first dichroic mirror,
108
a second dichroic mirror, and
109
a
and
109
b
reflecting mirrors. Numeral
110
stands for a relay system for relaying the illumination light, which is comprised of relay lenses
110
a
,
110
b
and relay mirrors
110
c
,
110
d.
Symbols
111
r
,
111
g
, and
111
b
are condenser lenses for images (light beams) of the colors of R (Red), G (Green), and B (Blue), respectively. Symbols
112
r
,
112
g
, and
112
b
are image display elements for R, G, and B, respectively. Numeral
113
represents a cross dichroic prism DP for color composition. Numeral
114
stands for a projection lens.
The white light emitted from the white light source
101
is collected by the reflector
102
and then travels through the integrator
104
, the polarization converting element array
105
, and the condenser lens
106
. After that, the light is separated into the color beams of R, G, and B light by the dichroic mirrors
107
,
108
. The first color light (B in the figure) is guided via the reflecting mirror
109
b
and condenser lens
111
b
to the image display element
112
b
, the second color light (G in the figure) is guided via the condenser lens
111
g
to the image display element
112
g
, and the third color light (R in the figure) is guided via the relay system
110
and condenser lens
111
r
to the image display element
112
r.
The color beams of R, G, and B, traveling through the image display elements
112
b
,
112
g
, and
112
r
and modulated according to image signals, are then combined into one by the cross dichroic prism DP
113
, whereby the images displayed on the respective image display elements are enlarged and projected in a superimposed manner onto the screen (not illustrated) through the projection lens
114
. A discharge lamp such as a metal halide lamp, a mercury lamp, or the like is used as the white light source.
FIG. 18
shows an example of spectral distribution of the white light source
101
. From the white light having the continuous spectral distribution as illustrated, the dichroic mirrors DM
1
, DM
2
create the three color beams of R, G, and B, for example, having respective spectral distributions as illustrated in FIG.
19
.
In the conventional apparatus, these light beams are modulated by the respective image display elements
112
r
,
112
g
,
112
b
and thereafter combined by the cross dichroic prism DP. In order to avoid loss in light amount in the cross dichroic prism DP, dichroic films of the cross dichroic prism are designed so that light reflected thereby is s-polarized light components of red (R) and blue (B) while the light of green (G) transmitted by the dichroic films of the cross dichroic prism DP is a p-polarized light component.
The reason is that, from the characteristics of the dichroic films as illustrated in
FIG. 20
, a broader reflection band can be set in the case of the s-polarized light components being reflected by the dichroic films (BRs, RRs) and a broader transmission band can be set in the case of the p-polarized light component being transmitted by the dichroic films (GTp). This suppresses the loss of light amount in the dichroic prism due to the so-called incident angle characteristics of the dichroic films, which are variations in cut wavelengths of the dichroic films due to variations in angles of incidence of light to the dichroic films.
In order to realize this structure, where the polarization directions of the image beams emerging from the image display elements were as illustrated in
FIG. 21
, the apparatus was so constructed that a half-wave plate was placed in each of the three paths of the emergent beams and that the slow phase axis directions of the phase plates were set so as to make the polarization direction of G light perpendicular to the polarization direction of R and B light and so as to make the polarization direction of G light coincident with that of the p-polarized light with respect to the dichroic films of the dichroic prism DP.
In systems necessitating alignment of the polarization directions of projected light on the occasion of projection of image (for example, such as polarized image projection systems using the polarizing screen or stereoscopic image projection systems for projecting images for the right eye and for the left eye with beams having respective polarization directions different from each other), however, the polarization direction of G light has to be aligned with the polarization direction of R and B light by providing a polarizing means at an arbitrary position in the optical path from the dichroic prism to the polarizing screen or to the observer.
The reason is as follows. When the polarization direction of light reflected by the polarizing screen is set in parallel to the s-polarized light component of the dichroic prism, the color beam of green is absorbed. When the polarization direction of light reflected by the polarizing screen is set in parallel to the p-polarized light component of the dichroic prism, the color beams of red and blue are absorbed. This will result in failing to reproduce a correct color image.
It is then conceivable, for example, to convert the beams into the polarization directions inclined at 45° relative to the polarization direction SC of the screen by the half-wave plates as illustrated in
FIGS. 22A and 22B
, or to convert the polarized beams into circularly polarized light beams by quarter-wave plates as illustrated in
FIGS. 23A and 23B
.
FIG. 22A
shows the relationship between the polarization directions of the beams (R, B, and G beams) emerging from the dichroic prism and the slow phase axis direction of the phase plates (indicated by the dashed line), and
FIG. 22B
shows the relationship between the polarization directions of the projected beams and the transmission-axis direction of the polarizing screen.
FIG. 23A
shows the relationship between the polarization directions of the beams (R, B, and G beams) emerging from the dichroic prism and the slow phase axis direction of the phase plates (indicated by the dashed line), and
FIG. 23B
shows the relationship between the polarization directions of the pro
Adams Russell
Koval Melissa
Morgan & Finnegan L.L.P.
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