Ultra-wide angle liquid crystal projector system

An ultra-wide angle liquid crystal projector system comprising a light source, a liquid crystal panel, a curved screen, and a projection lens for projecting in accordance with light emitted by the light source an image formed on the liquid crystal panel onto the curved screen. The projection lens has a curvature of field substantially conforming to the shape of the curved screen and an angle of projection of at least 120 degrees. The projection lens is disposed with respect to the curved screen so that a distance from an exit surface of the projection lens to the curved screen is less than 3 meters.

FIELD OF THE INVENTION 
The present invention relates to an ultra-wide angle liquid crystal 
projector system for projecting an image which has been formed on a liquid 
crystal panel by inputting a picture signal, such as a video signal to the 
panel, onto a screen on an enlarged scale. In particular, the invention is 
concerned with an ultra-wide angle liquid crystal projector system 
suitable for use of a game system or an audio-visual system, capable of 
affording images full of a sense of presence, and rich in variety of 
amusement. 
BACKGROUND OF THE INVENTION 
A conventional projector system for obtaining an image over a large screen 
using a liquid crystal, is described in Japanese Patent Laid Open No. 
159120/87. FIG. 2 is a schematic construction diagram of such a 
conventional liquid crystal projector system wherein light emitted from a 
light source 1 is condensed by a lens 2 and then an image formed on a 
liquid crystal panel 3 by the light beam from the lens 2 is projected 
enlargedly onto a screen 5 through a projection lens 4. This system 
enables a planer image as large as 100 inches in the length of a diagonal 
line. It is noted that the light source 1, lens 2, liquid crystal panel 3 
and projection lens 4 are generally contained in a single housing which 
also contains a cooling device and thereby heat and noise are generated in 
such housing. 
As a related conventional projector, there is known an all sky projector 
using a planetarium as a structural building, for example, such as that 
described on page 95 of Gendai Camera Shinsho No. 76--Introduction to the 
Science of Lens (Last Volume)--by Toshinobu Ogura (publisher: Asahi 
Sonorama Co.). Further, there is described a liquid crystal projector 
system using a fish-eye lens, in Japanese Patent Laid Open No. 80239/91. 
According to this technique, the fish-eye lens forms a part of the 
projector body and is disposed proximate to the head of the viewer 
whereby, the viewer is provided with more realistic images having a sense 
of presence. 
For obtaining an image over a large screen of 100 inches in diagonal length 
with the above-mentioned conventional liquid crystal projector systems, it 
is required to provide a sufficient projection distance on the order of 3 
to 4 meters from the projection lens 4 to the screen 5. Consequently, when 
the system is in use, it is necessary to provide a large space almost 
equal to one six-mat room of the Japanese standard measurement or 
approximately 10 m.sup.2. 
On the other hand, in order to use such a large screen projector system as 
a game system for the pleasure of many people, it is necessary to make the 
system into a compact system requiring only a small projection space which 
permits indoor installation as in a so-called game center. Besides, it is 
desired that the system permit one or more persons to enjoy it and that 
the system provide variety of amusement to many people through the 
transmission of many pieces of information. 
For an image viewer who plays a game, it is necessary to ensure an 
appropriate space and improve comfortableness so that the viewer does not 
have a sense of oppression or unpleasant feeling. In the case of an all 
sky projector used in a planetarium, for example, where a sufficient space 
for the viewer is ensured, since the planetarium is a structural building, 
such a projector system is not easy to manufacture industrially and 
requires a large amount of space not suitable for the game usage. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a liquid crystal 
projector system which permits a reduction of the necessary projection 
space, is suitable for industrial projection and can provide images having 
a sense of reality. 
It is another object of the present invention to provide a system which, in 
its projection space, ensures a user a comfortable space free from a sense 
of oppression or unpleasant feeling in the presence of a projector body, 
as well as a system rich in the variety of amusement through the 
transmission of many pieces of information to a user. 
According to the present invention, there is provided a liquid crystal 
projector system wherein there is used a projection lens, e.g. fish-eye 
lens, having a curvature of field approximately conforming to the shape of 
a curved screen and having an angle of projection of not smaller than 120 
degrees. Further, as the curved screen there is a used a dome-like screen, 
and the distance from the exit surface of the projection lens to the 
screen is set at about 0.3 to 2 meters, preferably 0.6 to 1.5 meters. 
According to a feature of the present invention, a back focal length of the 
projection lens in the direction of the liquid crystal panel is set at a 
value of 0.1 to 2.2 meters, preferably 0.2 to 1.2 meters and/or the angle 
between an optical axis of light emitted from the projection lens and a 
perpendicular line extending from the center of the screen, namely, the 
degree of decentering, is set at a value exceeding 20 degrees. 
In accordance with the other features of the present invention, the surface 
of the screen is provided with an autoluminous display element or a light 
transmitting display element and/or there is used a information projecting 
portion for projecting on the screen a new piece of information different 
from the image projected on the screen through the projection lens. 
In the ultra-wide angle liquid crystal projector system of the present 
invention, there is used a projection lens, e.g. fish-eye lens, having a 
curvature of field approximately conforming to the shape of the screen and 
having an angle of projection of not smaller than 120 degrees, and thus, 
the angle of projection is much wider than that of 35 to 45 degrees of the 
projection lens used in the conventional liquid crystal projector system, 
so by shortening the projection distance from the projection lens up to a 
large screen of 100 inches or more in the length of a diagonal line 
(aspect ratio 3:4, corresponding to a curved surface length of a dome-like 
screen), it is made possible to reduce the space occupied by the system 
during projection. Moreover, the use of projection lens permits the 
projection distance from the projection lens to the screen to be set at a 
value of not larger than 1.5 meters, whereby the overall system length can 
be made 3 meters or so. Such an ultra-wide angle liquid crystal projector 
system can be used for the pleasure of many people because it can be 
installed indoors as in a game center. Further, unlike structural 
buildings, the system can be constructed as a relatively small-sized 
system of about the size of a small-sized automobile, thus having 
industrial productivity. 
In the projector body extending from the light source to the liquid crystal 
panel, there are present both heat from the light source and noise 
generated from a cooler device for reducing the generated heat. If both 
the heat and noise are transmitted to the image viewer who plays a game, 
the viewer will have an unpleasant feeling. In view of this point, by 
making the back focus of the projection lens long so as to permit a 
construction wherein the projector body is positioned behind the viewer, 
it is made possible to provide a comfortable space not giving unpleasant 
feeling to the viewer. Moreover, by installing the projector body 
extending from the light source to the liquid crystal panel in such a 
manner that the angle between the optical axis of light emitted from the 
projection lens and the normal line extending from the center of the 
screen, namely, the degree of decentering, exceeds 20 degrees, it is also 
made possible to ensure a comfortable space not giving unpleasant feeling 
to the viewer who plays a game. 
Further, by adopting the construction wherein the screen surface is 
provided with an autoluminous display element or a light transmitting 
display element, and/or the construction including the foregoing 
information projecting portion, it becomes possible to provide the viewer 
with a new piece of information different from the image projected on the 
screen through the projection lens, and thus it is possible to realize a 
game system rich in variety of amusement. 
These and other objects, features and advantages of the present invention 
will become more readily apparent from the following detailed description 
when taken in conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a schematic diagram of a liquid crystal projector system 
according to an embodiment of the present invention wherein light from a 
light source 1 is condensed onto a liquid crystal panel 3 by means of a 
lens 2, allowing a picture signal fed to the panel 3 to be imaged on the 
panel and by way of a projection lens 6 projected onto a curved dome-like 
screen 7 on an enlarged scale. 
As the light source 1, there may be used, for example, a halogen lamp, 
xenon lamp or metal halide lamp, of which the metal halide lamp is now 
most suitable in point of luminous efficiency and service life. A 
reflecting mirror 8 for the light source 1 is used for effective 
utilization of the light emitted from the light source 1. For example, the 
shape of the reflecting mirror 8 is spherical, parabolic or elliptic, and 
it is configured so that the quantity of light incident on the lens 2 is 
as uniform as possible. 
The lens 2 receives the light emitted from the light source 1 and condenses 
the light in a picture plane size of the liquid crystal panel 3. In this 
embodiment, a Fresnel lens of narrow width is used as the lens 2, although 
it is not always necessary to use a Fresnel lens. The lens 2 may comprise 
plural lenses. A certain distance is required from the lens 2 to the light 
source 1 for ensuring a cooling effect utilizing the flow of air. The lens 
2 is formed of substantially transparent material such as glass or plastic 
material. In the light from the light source 1 there are included infrared 
light and ultraviolet light in addition to visible light, but the former 
two are not necessary in this system. In particular, infrared light acts 
as a heat source and exerts a bad influence on circuits, etc., so it is 
necessary to reduce the amount of infrared light. The lens 2 also 
functions to reduce such infrared light and ultraviolet light. As to 
infrared light and ultraviolet light, they can be reduced to a certain 
extent by using a cold mirror or a cold filter and an ultraviolet light 
cut-off filter in addition to the lens 2. Also, with respect to heat 
generated by infrared light, cooling can be effected by means of a cooling 
device such as a cooling fan or the like. 
The liquid crystal panel 3 is not specially limited if only it received the 
light from the light source 1 which has passed through the lens 2 and 
forms an image thereon. The panel may be, for example, configured as three 
panels separated in three colors RGB instead of a single liquid crystal 
panel 3. In this embodiment, the liquid crystal panel 3 is constituted by 
a single TFT liquid crystal panel of full color which permits high 
definition. It is desired that parallel rays of light be applied to the 
liquid crystal panel 3 which serves for diminishing the loss of light in 
the liquid crystal panel 3. The portion from the light source 1 and 
including the liquid crystal panel 3 is designated as a projector body 11 
and contained in a housing. In the projector body 11 there are included a 
circuit portion such as a drive circuit and a cooling device for the 
circuit. 
The projection lens 6, which is a fish-eye lens, for example, has a 
curvature of field approximately conforming to the screen shape curvature 
and has an angle of projection of not smaller than 120 degrees and may be 
contained in a housing separate from the projector body 11. It may 
comprise plural lenses. The curved dome-like screen 7 has a shape 
constituted by a portion of a solid of revolution of a curved line. By 
using the projection lens 6, e.g. fish-eye lens, having a curvature of 
field approximately conforming to the screen shape curvature and having an 
angle of projection of not smaller than 120 degrees, it is possible to 
obtain a wide projection angle 120 degrees or more and an image of a large 
picture plane (at least 100 inch diagonal length) can be obtained in a 
shorter distance than the distance (3 to 4 meters) from the conventional 
projection lens having a small projection angle up to the screen. 
Consequently, the space for enlarged projection can be made smaller, and 
hence, it is possible to diminish the space occupied by the system during 
projection. The large picture plane of 100 diagonal inches is here 
expressed for convenience sake as a picture plane having a diagonal line 
length of 100 inches and an aspect ratio of 3:4. Since the image is 
projected at a short distance and at a wide field angle (120 degrees or 
more) by the projection lens 6, the viewer can obtain a feeling of image 
reality at a short distance. Besides, the dome-like screen 7 gives the 
viewer a sense of oppression and that of distance which are based on the 
screen shape. As a result, this system permits the viewer to enjoy images 
having a sense of presence. 
FIGS. 3(A) and 3(b) are explanatory diagrams for providing a comparison 
between the projection distance from the projection lens to the screen in 
the conventional liquid crystal projector system and that from the 
projection lens to the dome-like screen in the liquid crystal projector 
system of the present invention. FIG. 3(A) shows the conventional system 
in which the distance L from the projection lens 4 to the screen 5 is 3 to 
4 meters, while FIG. 3(B) shows the system of the present invention in 
which, by using the projection lens 6 described above having the curvature 
of field conforming to the screen shape and a projection angle of at least 
120 degrees, an image over the same size of a picture plane as in the 
conventional system can be obtained at a projection distance L from the 
projection lens 6 to the dome-like screen 7 of 0.3 to 2 meters which is 
substantially shorter than that (3 to 4 meters) from the projection lens 
to the screen in the conventional system. 
In the case of a projector system installed indoors, it is desirable that 
the overall system length be within about 3 meters. Therefore, the 
projection distance L from the projection lens 6 to the dome-like screen 7 
is preferably not longer than 1.5 meters, taking into account both the 
required distance from the light source 1 to the projection lens 6 and the 
space which is necessary structurally. 
On the other hand, in the case where the projection angle is set as large 
as 180 degrees, the screen is made semispherical and the projection lens 
is positioned at the center of the sphere, the projection length L from 
the projection lens 6 to the dome-like screen 7 required for obtaining an 
image 100 inches or larger in the length of a diagonal line is 0.6 meter 
or longer. If the projection distance L is set smaller than 0.6 meters, 
the image on the screen will become smaller than 100 inches as a diagonal 
line length, thus deteriorating the sense of presence, although the system 
itself can be rendered compact. When projection is made at the same 
distance using both a projection lens having a projection angle of, about 
120 degrees, which is smaller than 180 degrees and a projection lens 
having a projection angle of 180 degrees, the image size on the screen is 
smaller in the use of the former projection lens, and hence, the sense of 
presence is deteriorated. Thus, in order to make the image on the screen 
larger, it is necessary to make the projection distance longer, that is, 
it is necessary that the projection distance L in the use of the 
projection lens having a projection angle of 120 degrees be made longer 
than 0.6 meters. It is preferable that the projection distance L from the 
projection lens 6 up to the dome-like screen 7 be in the range of 0.3 to 2 
meters, more preferably 0.6 to 1.5 meters. 
FIGS. 4(A) and 4(B) show a plan view and a side view, respectively, of a 
positional relation between viewers and a projector body of a liquid 
crystal projector system according to another embodiment of the present 
invention. These figures are representational and do not define the size 
of each portion thereon. Further, although the number of viewers shown in 
the figures is two, it may be one or several. 
In a projector body 11 extending from a light source 1 to a liquid crystal 
panel 3, there are present both heat generated from the light source and a 
cooling device for cooling the heat. Thus, there arise both heat from the 
light source and noise from the cooling device, etc. If the heat and noise 
are transmitted to viewers 12 who play a game, the viewers will have 
unpleasant feeling. In this embodiment, in order that the viewers 12 can 
play the game pleasantly, the projector body 11 is disposed in a position 
to the rear of the viewers 12. In this construction, a back focal length 
(BF) of a projection lens 6 is made longer according to the projection 
distance from the projection lens to the dome-like screen 7. The 
projection lens 6 may be arranged in a housing separate from and coupled 
to the projector body. 
However, the overall length of the system becomes longer with increase in 
back focal length (BF), so it is desirable that the spacing between the 
viewers 12 and the front of the projector body 11 be in the range of 0.1 
to 0.5 meters, preferably 0.2 to 0.3 meters. In the case where the viewers 
12 are positioned at a distance of 1 to 2 meters from the dome-like screen 
7, the projection distance L from the projection lens 6 up to the 
dome-like screen 7 is 0.3 to 2 meters and the spacing between the viewers 
12 and the projector body 11 is 0.1 to 0.5 meters, the back focal length 
(BF) of the projection lens 0.1 to 2.2 meters. When the viewers 12 are 
positioned at a distance of 1.5 meters from the dome-like screen 7, the 
projection distance L from the projection lens 6 up to the dome-like 
screen 7 os 0.6 to 1.5 meters and the spacing between the viewers 12 and 
the projector body 11 is 0.2 to 0.3 meters, the back focal length (BF) of 
the projection lens 6 is suitably in the range of 0.2 to 1.2 meters. 
In the case of a long back focal length (BF) of the projection lens 6, 
there may be used a relay lens, or the optical axis may be bent using a 
mirror or the like. By so bending the optical axis, it is made possible to 
reduce the space of the projecting portion from the light source 1 to the 
projection lens 6. 
When the image from the projection lens 6 is enlarged to a large picture 
plane of 100 diagonal inches or more and is projected on the dome-like 
screen 7, the picture element size of the image projected on the same 
screen depends on the number of picture elements in the liquid crystal 
panel 3. Therefore, even in the case of a liquid crystal panel having a 
coarse picture element pitch, if the panel size is large, it is possible 
to make the picture element pitch on the screen small in correspondence to 
a small magnification of enlargement from the liquid crystal panel to the 
dome-like screen 7. However, if light is incident in parallel form on the 
liquid crystal panel 3 when the panel size is made large, it is required 
that the incident aperture of the projection lens 6 be also made large. 
FIG. 5 is an explanatory diagram showing a positional relation between a 
projection lens and a dome-like screen in a liquid crystal projector 
system according to a further embodiment of the present invention. As to 
the positional relation between the projection lens 6 and the dome-like 
screen 7, the one shown in FIG. 1 is the best in point of projection, but 
since the lens-screen distance is as short as 0.6 to 1.5 meters, the 
projecting portion from the light source 1 to the projection lens 6 is 
sometimes an obstacle to the viewer. In this embodiment, in view of the 
point just mentioned, the angle A between an optical axis 61 of light 
emanating from the projection lens 6 and a perpendicular line 72 drawn 
from a screen center 71 of the dome-like screen 7, namely, the degree of 
decentering, is set at a value exceeding 20 degrees. In this case, the 
optical axis 61 need not pass through the screen center 71. Since the 
distance between the projection lens 6 and the dome-like screen 7 is as 
short as 0.6 to 1.5 meters and the depth of field of the projection lens 
6, e.g. fish-eye lens, is pan-focused, the image projected in the above 
state is in focus. In other words, the projecting portion from the light 
source 1 to the projection lens 6 need not be disposed directly in front 
of the screen, and hence, the projector body 11 from the light source 1 to 
the liquid crystal panel 3 can be disposed away from the viewers 12 who 
play a game. 
FIG. 6 is a diagram showing a principal portion of a liquid crystal 
projector system according to another embodiment of the present invention. 
This projector system comprises the ultra-wide angle liquid crystal 
projector system illustrated in FIG. 1, and a second information 
projecting portion 9. According to the projector system of this 
embodiment, score, characters such as information of a competitor in a 
competition type game, images and other pieces of information, are 
projected in a combined form on the screen, so that the system is rich in 
variety of amusement. 
The second information projecting portion 9 is not limited to a liquid 
crystal projector and may be a projection tube type, a video projector or 
a slide projector. The second information projecting portion 9 is disposed 
in a position where it is not an obstacle to the viewers. According to the 
present technical level, when the image on the liquid crystal panel 3 is 
projected enlargedly on the dome-like screen 7 of a large picture plane 
not smaller than 100 diagonal inches by using the projection lens 6, the 
picture element pitch on the screen becomes fairly coarse. Consequently, 
character information is difficult to read although this problem will be 
solved in the near future because of the recent tendency to a higher 
definition of liquid crystal panel. Therefore, if character information is 
projected on part of the screen using the second information projecting 
portion 9, even character information can be projected in a satisfactory 
manner because the projection magnification is not so large in comparison 
with the case where the image on the liquid crystal panel 3 is projected 
on an enlarged scale using the projection lens 6. 
FIGS. 7(A) and 7(B) show respectively a sectional view and a front view of 
a dome-like screen which is used in a liquid crystal projector system 
according to an embodiment of the present invention. In this embodiment, 
the surface of the dome-like screen 7 is provided with a dot-like light 
source 10. Plural dot-like light sources 10 may be provided, or a group of 
such dot-like sources may be provided. Such dot-like light sources may be 
provided throughout the entire surface of the screen 7. The dot-like light 
sources 10 are energized interlockedly with or independently of the image 
projected on the screen by the ultra-wide angle liquid crystal projector 
system, and by combining the image obtained on the screen by the 
ultra-wide angle liquid crystal projector system with other information 
obtained by the dot-like light sources 10, it is made possible to obtain 
strange images so far not obtainable by only the ultra-wide angle liquid 
projector system, thus affording a projector system rich in variety of 
amusement. Examples of the other information includes moving body 
information and a target information. 
From the standpoint of power consumption, life, cost, freedom of hue and 
response speed, light emitting diodes (LED) are preferred as the dot-like 
light sources 10, although any other suitable dot-like light sources than 
LEDs may be utilized. It is also possible to project character information 
on the screen using the dot-like light sources 10. In the case where the 
dot-like sources 10 are in the form of group or occupy the whole surface 
of the screen, the way of use richer in variety can be attained by using a 
liquid crystal for the display of color images in place of LEDs. 
Although the above description has referred to a game system, it is 
apparent that the present invention is also applicable to other 
apparatuses. Further, the invention may be embodied in other specific 
forms without departing from the spirit or essential characteristics 
thereof. The present embodiment is therefore to be considered in all 
respects as illustrative and not restrictive, the scope of the invention 
being indicated be the appended claims.