Optics: image projectors – Composite projected image – Multicolor picture
Reexamination Certificate
1999-12-21
2002-11-12
Adams, Russell (Department: 2851)
Optics: image projectors
Composite projected image
Multicolor picture
C353S030000, C353S033000
Reexamination Certificate
active
06478430
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an illumination apparatus and a projection apparatus having it and, more particularly, to the illumination apparatus that is compact and that can implement highly uniform illumination, which is suitably applicable, for example, to color liquid-crystal projectors of a three panel type.
2. Related Background Art
In recent years, the illumination apparatus in the field of liquid-crystal projectors employs an illumination system using a fly's eye lens or a rod type integrator in the optical path in order to realize high luminance and enhance uniformity of screen illuminance, and one of such apparatus is proposed, for example, in Japanese Patent Application Laid-Open No. 7-98479.
FIG. 10
is a sectional view of the major part of the illumination system in a conventional, color liquid-crystal projector of the three panel type. In
FIG. 10
, DM
1
designates a red-transmitting dichroic mirror. DM
2
denotes a blue-transmitting dichroic mirror. G
1
, G
2
, and G
3
represent lenses, these three lenses composing a blue-path relay lens group
76
B. RLCD indicates a liquid crystal display device for red only, GLCD that for green only, and BLCD that for blue only.
Rays from a light source
71
are reflected by a reflector
72
to be outgoing from the reflector
72
in the form of parallel rays. Then the rays are incident to a first lens array
73
to be separated into a plurality of beams by the first lens array
73
. The plurality of beams form a plurality of secondary light source images (which are images of the light source
71
) on a second lens array
74
. Light from each secondary light source image formed on the second lens array
74
is guided through a PBS element
75
to be subjected to polarization conversion. After that, the light travels via a condenser lens
76
, a trichromatic separation system (DM
1
, DM
2
), and a field lens
76
R or
76
G, or the relay lens group
76
B placed immediately before the liquid crystal display device (RLCD, GLCD, or BLCD), whereby an optical conjugate relation is maintained between the light entrance plane or the principal plane of each lens unit forming the first lens array
73
, and the liquid crystal display devices (i.e., the image on this plane of each unit lens is formed on the display devices), thereby realizing superimposed illumination in a rectangular shape matched with the shape of the liquid crystal display devices.
FIG. 10
showed the example of the illumination system using the lens arrays (
73
,
74
), but there is also another illumination system with the rod integrator contemplated. Specifically, the light from the light source
71
is made incident as convergent light to the rod so as to form a light source image on the light entrance plane of the rod, and a plurality of secondary light source images (images of the light source) are formed from the light source image formed on the light entrance plane, by total reflection on the side surfaces of the rod integrator and by a lens unit placed thereafter. After that, the light from each of the secondary light source images is guided through the PBS element to effect polarization conversion thereof. Then the light travels via the condenser lens
76
, the trichromatic separation system (DM
1
, DM
2
), and the field lens or the relay lens group placed immediately before each liquid crystal display device, whereby the aforementioned optical conjugate relation is maintained between the light exit plane of the rod integrator and the liquid crystal display devices, thereby realizing the superimposed illumination in the rectangular shape matched with the shape of the liquid crystal display devices.
In the illumination systems of the two types described above, where a cross dichroic prism
78
is used as a color composition system, the surfaces of the three-color liquid-crystal display devices, which are conjugate planes (i.e., planes in the optically conjugate relation, i.e., in the image forming relation) with a screen surface, need to be placed at nearly equal distance while being the length of the back focus of a projection lens
77
apart therefrom with the cross dichroic prism in between. At this time, only one out of the three color (R, G, B) beam paths having their respective wavelength zones different from each other is extended as illustrated in
FIG. 10
, when compared with the other two paths, and through the extended optical path the conjugate plane of the first lens array
73
or the light exit plane of the rod integrator is imaged on the liquid crystal display device, using the three relay lenses G
1
, G
2
, G
3
. This realizes the illumination effect equivalent to that by the two optical paths of the other colors.
However, since all the lenses G
1
, G
2
, G
3
of the relay lens system
76
B illustrated in
FIG. 10
are positive lenses, the image (image plane) of the conjugate plane of the first lens array
73
is curved.
As the weight and size of the liquid crystal projectors have been reduced in recent years, the refracting power of each lens, particularly, in the relay lens system had to be increased and this tended to make the curvature of field greater.
When the image plane is curved, the image is blurred, particularly, only in peripheral portions (four corners) of the illumination area on the liquid crystal display devices, as illustrated in FIG.
11
. This will cause nonuniformity of illuminance and thus result in color irregularity of the image projected onto the screen after composition of the three colors, which is not preferable.
SUMMARY OF THE INVENTION
An object of the present invention is, therefore, to provide an illumination apparatus and a projection apparatus without nonuniformity of illuminance in the illumination area or with acceptably little nonuniformity of illuminance if any.
An illumination apparatus according to one aspect of the present invention is an illumination apparatus for illuminating a surface to be illuminated, by use of light source means, secondary light source forming means for forming a plurality of secondary light sources from light emitted from the light source means, and a lens system for forming a conjugate plane conjugate with a light entrance plane or a vicinity plane thereof of the secondary light source forming means after a color separation system for separating light from the secondary light source forming means into three beams of mutually different wavelength regions, wherein a relay lens system is placed in a predetermined optical path out of three optical paths of the three beams color-separated and wherein the surface to be illuminated does not agree with a paraxial image plane of the conjugate plane formed by the relay lens system.
An illumination apparatus according to another aspect of the present invention is the illumination apparatus according to the above aspect wherein the surface to be illuminated, which does not agree with the paraxial image plane of said conjugate plane formed by said relay lens system, is located while being shifted to the light source side with respect to said paraxial image plane.
An illumination apparatus according to another aspect of the present invention is an illumination apparatus for illuminating a surface to be illuminated, by use of light source means, secondary light source forming means for forming a plurality of secondary light sources from light emitted from the light source means, and a lens system for forming a conjugate plane conjugate with a light entrance plane or a vicinity thereof of the secondary light source forming means after a color separation system for separating light from the secondary light source forming means into three beams of mutually different wavelength regions, wherein a relay lens system is placed in a predetermined optical path out of three optical paths of the three beams color-separated and wherein the surface to be illuminated lies at a position shifted from a position of a paraxial image plane to the center side of curvature of an image plane of the conju
Adams Russell
Fuller Roy
Morgan & Finnegan , LLP
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