Optics: image projectors – Light shield – mask – hood – or diaphragm
Reexamination Certificate
2003-04-04
2004-06-29
Dowling, William C. (Department: 2851)
Optics: image projectors
Light shield, mask, hood, or diaphragm
Reexamination Certificate
active
06755538
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection-type image display device (liquid crystal projector) wherein an image generated on a liquid crystal panel is projected in an enlarged manner on a projection face by a projection optical system (e.g., a projection lens).
2. Description of the Related Art
Conventionally, various types of techniques have been proposed relating to liquid crystal projectors for illuminating a liquid crystal panel (liquid crystal or liquid crystal display device) with light flux from a light source, modulating the light flux at the liquid crystal panel, and projecting on a screen in an enlarged manner an image based on transmitted light or reflected light emitted from the liquid crystal panel.
Liquid crystal panels often used for liquid crystal projectors normally comprise polarizing filters of polarizers or analyzers on the front and back of the liquid crystal layer. Polarizing filters have properties of transmitting particular polarized components of incident light, and shielding polarized components which have polarization direction orthogonal thereto.
Image display devices using liquid crystal (liquid crystal panels) generally are of a nature that the contrast changes in the event that the viewing angle (direction) from the center of the liquid crystal display screen changes, since properties of the liquid crystal result in viewing angle properties (viewing angle dependency) in the contrast (ratio between transmission and non-transmission of light).
Projecting an image on the screen using an image display device with a the liquid crystal panel having such viewing angle properties regarding contrast has caused irregularities in brightness depending on the viewing direction. Also, this has caused color irregularities with color liquid crystal projectors.
There are the following configurations designed as image display devices configured to make such irregularities inconspicuous. A first conventional image display device is a device which has a configuration for compressing the illumination light by an optical system corresponding to the form of the liquid crystal panel in order to prevent picking up light at portions wherein the viewing angle properties regarding contrast are poor, thereby increasing the f-number of the illumination optical system as viewed from the liquid crystal panel. Also, a second conventional image display device has been configured with a visual angle improving film for improving viewing angle properties regarding contrast of the liquid crystal panel between a polarizing plate and the liquid crystal panel, thereby making the color irregularities in black color display of the liquid crystal panel less conspicuous.
With the first image display device, there is the need to compress the illumination light emitted from the light source with an illumination optical system, in order to make the f-number (brightness) of the illumination optical system as viewed form the liquid crystal panel greater (darker). With a configuration using a fly-eye lens as the configuration for compressing illumination light with the illumination optical system, there is the need to make the size of the fly-eye lens at the side of the liquid crystal panel smaller than the fly-eye lens at the light source side. With this configuration, vignetting of the light source image due to the aperture stop of the polarization converter is great, causing problems in that the illumination efficiency drops, and the brightness of the image projected on the screen drops.
Also, with the second conventional image display device, there is a configuration wherein a visual angle improving film is placed between a polarizing plate and the liquid crystal panel. With this configuration, the spacing between the liquid crystal panel and the visual angle improving film, and the spacing between the visual angle improving film and the polarizing plate, become narrow. This makes for poorer passage of cooling air, resulting in difficulties in cooling the liquid crystal panel and polarizing plate. This has also resulted in the problem that the device becomes more complex, due to the use of the visual angle improving film.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a projection-type image display device with a new configuration, which reduces or eradicates the problem of visual angle dependency in the visual contrast of liquid crystal panels.
According to a first aspect of the present invention, a projector-type image display device comprises: a liquid crystal display device for forming an image; an illumination optical system for illuminating the liquid crystal display device with light from a light source; a projection optical system for projecting an image from the liquid crystal display device; and a diaphragm member disposed on at least one optical system of the illumination optical system and the projection optical system; wherein an aperture is formed in the diaphragm member; and wherein the aperture has a shape such that the f-numbers at a plurality of directions from the at least one optical system are different f-numbers, according to contrast properties of each direction of the liquid crystal display device.
According to a second aspect of the present invention, a projector-type image display device comprises: a plurality of liquid crystal display devices which each form images; an illumination optical system for dividing light from a light source into a plurality of different color lights, and illuminating each of the liquid crystal display devices with a matching color light; a color synthesizing optical system for synthesizing the images from each of the color lights from the plurality of liquid crystal display devices, the color synthesizing optical system comprising an odd-number reflection optical path wherein an image of a color light from one liquid crystal display device of the plurality of liquid crystal display devices reflects an odd number of times on an optical path leading from the one liquid crystal display device to a projection optical system; and an even-number reflection optical path wherein an image of a color light from another liquid crystal display device of the plurality of liquid crystal display devices is non-reflective or reflects an even number of times on an optical path leading from the another liquid crystal display device to a projection optical system; a projection optical system for projecting an image synthesized by the color synthesizing optical system; and a diaphragm member disposed on at least one optical system of the illumination optical system and the projection optical system; wherein an aperture is formed in the diaphragm member; and wherein the aperture has a shape such that the f-numbers at a plurality of directions from the at least one optical system are different f-numbers, according to contrast properties of each direction of the liquid crystal display device and the reflection optical path of the color synthesizing optical system.
The diaphragm member may be disposed at the illumination optical system, with the aperture of the diaphragm member having a shape such that a first f-number of the illumination optical system is greater than a second f-number of the illumination optical system, with the first f-number being an f-number of the illumination optical system in a direction matching the direction of the liquid crystal display device for first contrast properties, and with the second f-number being an f-number of the illumination optical system in a direction matching the direction of the liquid crystal display device for second contrast properties with contrast properties higher than the first contrast properties.
The diaphragm member may be disposed at the projection optical system, with the aperture of the diaphragm member having a shape such that a first f-number of the projection optical system is greater than a second f-number of the projection optical system, with the first f-number being an f-number of the projection optical syst
Canon Kabushiki Kaisha
Dowling William C.
Fitzpatrick ,Cella, Harper & Scinto
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