Optical: systems and elements – Projection screen
Reexamination Certificate
2000-08-02
2001-11-27
Adams, Russell (Department: 2851)
Optical: systems and elements
Projection screen
C359S449000, C359S452000, C359S479000, C353S007000, C353S074000
Reexamination Certificate
active
06323999
ABSTRACT:
This application is based on application No. H11-221017 filed in Japan on Aug. 4, 1999, the entire contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image display apparatus for displaying an image with a wide field of view, and is used in the field of providing images such as the field of virtual reality.
2. Description of the Prior Art
Recently, virtual reality providing imaginary images and enhancing the feeling of presence has become remarkably wide-spread, and image display apparatuses of various types have been developed for providing images with wide fields of view. As one of these image display apparatuses, there is an image display apparatus that projects an image, displayed on a display device, onto a screen with magnification of the image by a projection optical system. The apparatus can be used while being held by the observer's hands or mounted on the observer's head so that the screen is positioned in front of the observer's eyes. In this type of image display apparatus, it is necessary to apply light to the observer from all parts of the screen. Therefore, a screen having diffusive-reflectivity or retro-reflectivity is used.
In the case when a screen having diffusive-reflectivity is used, since the degree of light diffusion depends on the incident angle of light onto the screen, the quantity of light going from respective positions of the screen to the observer varies, so that the brightness of the image to be provided is apt to become uneven. In addition, since the projected light proceeds from the screen in all directions and the quantity of the light applied to the observer becomes small, it is inevitable that the brightness of the image observed is reduced. Furthermore, when images having parallax are provided to the left and right eyes to enhance the three-dimensional effect, a phenomenon that the light of the image for the left eye enters the right eye and the light for the right eye enters the left eye, that is, cross-talk arises. Therefore, it is necessary to provide special means for avoiding this.
On the other hand, if a screen having retro-reflectivity is used, light entering into any part of the screen is almost reflected toward each incident direction. Therefore, by projecting light from a direction of the observer's eyes toward the screen, it is possible to direct almost all of the projected light from any part of the screen to the observer's eyes. For this reason, it is possible to provide a bright image without uneven brightness and cross-talk. It is also possible to set the images for the left and right eyes to overlap each other on the screen.
However, in the screen having retro-reflectivity, the pupil diameter of the image provided for the observer, that is the diameter of the light beams expressing individual points of the image at the position of the eyes is defined by only the diameter of the exit pupil of a projection optical system and the distance between the screen and the eyes. Therefore, it is difficult to magnify the pupil diameter of the images for facilitating observation, and at the same time to miniaturize and lighten the apparatus so as to make the apparatus suitable to the mode of usage. For example, if the exit pupil of the projection optical system is made larger, the size and the weight of the projection optical system increase. If the distance between the eyes and screen is elongated, the apparatus inevitably becomes large.
In Japanese Laid-Open Patent Application No. H6-75303, a screen is proposed which is provided with a diffusing layer in front of a retro-reflective layer and has retro-reflectivity and diffusivity. If such a screen is used, the disadvantage of retro-reflectivity is compensated, since the light beams expressing individual points of an image are magnified by the diffusing layer. Therefore, it is expected that an image display apparatus which is small-sized and light-weight and provides an image with a large pupil diameter will be realized.
Man's field of view is large in the horizontal (left and right) direction and small in the vertical (up and down) direction. Nevertheless, in the screen described in the above-described patent application, the light beam is magnified isotropically by the diffusing layer. Hence, at least either excessive magnification in the vertical direction or insufficient magnification in the horizontal direction is caused. That is, if the light beam is magnified so as to meet the field of view in the horizontal direction, the image is excessively magnified beyond the field of view in the vertical direction. On the contrary, if the light beam is magnified so as to meet the field of view in the vertical direction, the image is insufficiently magnified below the field of view in the horizontal direction.
If the light beam is excessively magnified, the image provided becomes dark, and futile light without any probability of entering into eyes arises. If the light beam is insufficiently magnified, a situation arises where some part of the light expressing the image does not enter the eyes depending on the direction of the observer's eyes, i.e., the direction of line of sight. This causes eclipse, that is, partial dropouts of the image to be provided.
The phenomenon that the image to be provided becomes dark by excessive magnification of the light beam can be compensated by increasing the quantity of light in the display device displaying the image. However, doing so requires high performance of the display device itself or a light source illuminating the display device. Therefore, manufacturing cost of the apparatus is increased, and in addition, power consumption and running cost is also increased. Furthermore, when images with parallax are provided to the left and right eyes, excessive magnification of light beams results in cross-talk. In the screen described in the above-mentioned patent application, the extent to which the light beam is magnified by the diffusing layer is not considered.
SUMMARY OF THE INVENTION
In view of the above circumstances, an object of the present invention is to provide a small-sized and light-weight projection-type image display apparatus that displays on a screen a bright image free from eclipse and cross-talk.
In order to achieve the above-described object, according to one aspect of the present invention, an image display apparatus is provided with a screen having retro-reflectivity, an image display device displaying an image thereon, a projection optical system that projects light from the image display device and forms, on the screen, a magnified image of the image displayed on the image display device, and a beam magnifier located between the projection optical system and the screen so as to be close to the screen, the beam magnifier transmitting the light from the projection optical system, and magnifying light beams originating at individual points of the image display device and included in the light from the projection optical system, so that magnifications in two directions perpendicular to each other are different.
With the projection optical system, this image display apparatus forms on the screen a magnified image of the image displayed on the image display device and provides this magnified image to an observer. The screen has retro-reflectivity, and a beam magnifier transmitting the light from the projection optical system is located between the projection optical system and the screen. The observer can observe the image formed on the screen, by watching the screen through the beam magnifier from an angle of the light entering the screen from the projection optical system.
The beam magnifier magnifies the light beams, originating at individual points of the image display device and included in the light going from the projection optical system to the screen, and also magnifies the light beams reflected by the screen. Here, since the beam magnifier is located close to the screen, the light beams that pass through
Endo Takeshi
Ishibashi Kenji
Kasai Ichiro
Kobayashi Yasushi
Tanijiri Yasushi
Adams Russell
Cruz Magda
Minolta Co. , Ltd.
Sidley Austin Brown & Wood
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