Optics: image projectors – Composite projected image – Multicolor picture
Reexamination Certificate
2001-02-14
2003-05-20
Gray, David M. (Department: 2851)
Optics: image projectors
Composite projected image
Multicolor picture
C353S034000, C353S037000, C349S008000, C349S018000, C359S558000
Reexamination Certificate
active
06565212
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection display apparatus, and an information processing system and image recording/reproducing system using the same and, more particularly, to a so-called multiple-plate type projection display apparatus using a plurality of image display elements.
2. Related Background Art
Attention has recently been paid to a projection display apparatus for enlarging and projecting a display image on the image display element of a liquid crystal panel or the like. Along with this trend, demands have arisen for further improvements in the image quality and brightness of the display image and reduction in the size and weight of the whole apparatus.
Projection display apparatuses are classified into a single-panel type apparatus using one liquid crystal panel and a multiple-panel type apparatus using a plurality of liquid crystal panels. Many projection display apparatuses aiming high image quality use three panels corresponding to red, green, and blue light components. A projection display apparatus using multiple, e.g., three liquid crystal panels will be described.
The arrangement of a general multiple-plate type projection display apparatus will be described with reference to FIG.
24
.
FIG. 24
shows an overview of an optical system
101
in the projection display apparatus. The optical system
101
of the projection display apparatus is mainly constituted by an illumination optical system
110
and projection optical system
102
. An image display element
105
(
105
a
to
105
c
) made up of liquid crystal panels or the like is illuminated by the illumination optical system
110
, and an image on the illuminated image display element
105
is formed on a screen
112
via the projection optical system
102
.
In the illumination optical system
110
, the image display element
105
is made up of the three, first, second, and third liquid crystal panels
105
a
,
105
b
, and
105
c
. These liquid crystal panels
105
a
,
105
b
, and
105
c
are transmission panels which are driven by an electric circuit (not shown) to display images to be projected.
The optical path and optical elements from the illumination optical system
110
to the screen
112
will be explained. In the illumination optical system
110
, a light source section
109
has a light source
109
a
for emitting white light, and a reflector
109
b
for collimating a ray from the light source
109
a
. An integrator section
108
increases the uniformity of illumination light, and is a fly-eye integrator in this case. The integrator section
108
sometimes comprises, e.g., a polarization conversion element for increasing the use efficiency of illumination light.
In the illumination optical system
110
, a color separation system
106
separates the optical path of white light from the light source
109
a
in units of wavelength regions, i.e., colors. For descriptive convenience, the color separation system
106
separates white light from the light source
109
a
into three representative wavelengths &lgr;
1
, &lgr;
2
, and &lgr;
3
. In practice, the respective optical paths correspond to red, green, and blue colors which respectively include the wavelengths &lgr;
1
, &lgr;
2
, and &lgr;
3
which respectively indicate the center of wavelength of the transmitting light or at which the respective transmittances become maximum.
In the color separation system
106
, a first dichroic mirror
106
a
has a function of transmitting only a light component with the wavelength &lgr;
1
out of white light from the light source
109
a
, and reflecting light components with the wavelengths &lgr;
2
and &lgr;
3
. The light component with the wavelength &lgr;
1
having passed through the first dichroic mirror
106
a
is deflected by a deflection means
107
to illuminate the first liquid crystal panel
105
a
via a lens. The light components with the wavelengths &lgr;
2
and &lgr;
3
reflected by the first dichroic mirror
106
a
are incident on a second dichroic mirror
106
b.
The second dichroic mirror
106
b
reflects the light component with the wavelength &lgr;
2
, and transmits the light component with the wavelength &lgr;
3
. The light component with the wavelength &lgr;
2
reflected by the second dichroic mirror
106
b
illuminates the second liquid crystal panel
105
b
via a lens. The light component with the wavelength &lgr;
3
having passed through the second dichroic mirror
106
b
illuminates the third liquid crystal panel
105
c
via the deflection means
107
and a relay system
111
including a plurality of lenses.
The projection optical system
102
comprises a cross prism (cross dichroic prism)
104
for color combination. The above-described transmission liquid crystal panels
105
a
to
105
c
are arranged near respective incident surfaces of the cross prism
104
. With this arrangement, the projection optical system
102
combines the optical paths of the light components with the wavelengths &lgr;
1
, &lgr;
2
, and &lgr;
3
. A projection lens
103
is arranged near the exit surface of the cross prism
104
. Images on the illuminated liquid crystal panels
105
a
,
105
b
, and
105
c
are projected on the screen
112
so as to overlap each other.
In the projection display apparatus having this arrangement, the illumination light components of the first, second, and third liquid crystal panels
105
a,
105
b
, and
105
c
are combined as an image by the cross prism
104
, projected via the projection lens
103
, and displayed on the screen
112
so as to overlap each other. In the projection display apparatus, therefore, pixels constituting the liquid crystal panels
105
a
to
105
c
must overlap each other, and aberrations of the optical system
101
, particularly chromatic aberration of magnification of the projection optical system
102
needs to be further reduced.
As for reduction in chromatic aberration, techniques of greatly reducing chromatic aberration by arranging a diffraction optical element in a refraction optical system are conventionally disclosed in Japanese Patent Application Laid-Open No. 06-194509 “Optical System Including Diffraction Optical Element, and Diffraction Optical Element”, Japanese Patent Application Laid-Open No. 08-043767 “Image Sensing Optical System”, Japanese Patent Application Laid-Open No. 10-213744, and the like.
FIGS. 25A and 25B
show the sections of optical systems disclosed in Japanese Patent Application Laid-Open Nos. 08-043767 and 10-213744, respectively.
FIG. 25A
shows an image sensing optical system for a telescope lens or the like. A surface r
3
of a parallel plate located closest to the object side is formed as the formation surface of a diffraction optical element to greatly reduce chromatic aberration without using any low or extra-low dispersion glass.
As shown in
FIG. 25B
, Japanese Patent Application Laid-Open No. 10-213744 discloses an optical system for a finite-distance zoom lens made up of a lens unit GR
1
having negative and positive meniscus lenses, and a lens unit GR
2
having a biconvex positive lens, stop (A), and negative and positive meniscus lenses. Diffraction optical elements are formed on surfaces (HOE) in
FIG. 25B
, i.e., a convex surface r
3
* of the positive meniscus lens of the lens unit GR
1
and a convex surface r
11
* of the positive meniscus lens of the lens unit GR
2
. This realizes a small number of lenses in the lens units GR
1
and GR
2
, a small-size zoom lens, and high performance.
Reduction in chromatic aberration is achieved in this case because the diffraction optical element has characteristics opposite to the dispersion of an optical glass having &ngr;d=about −3.453 in Abbe constant, and has high dispersion characteristics. The diffraction optical element is very thin because the grating structure exhibits these characteristics, and can downsize the optical system.
The diffraction optical element has these properties, can greatly improve optical performance, but must consider parasitic-diffracted light (stray light) gener
Kobayashi Shuichi
Nakai Takehiko
Cruz Magda
Gray David M.
Morgan & Finnegan L.L.P.
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