Near-infinity image display system

A near-infinity image display system (10) has a convex faceplate cathode ray tube (12) positioned with respect to a concave mirror (14) such that the cathode ray tube (12) is in front of the center of curvature (16) of the mirror (14) and so that the mirror (14) reflects a near-infinity image of the visual display surface to an eyepoint (20) of an observer located below and in front of the center of curvature (16) of the mirror (14) and below the cathode ray tube (12). The cathode ray tube (12) is positioned at a height above the eyepoint (20) of the observer so that it does not interrupt the vertical field of view (24) of the image reflected to the eyepoint (20) of an observer. The concave mirror (12) may be a spherical, ellipsoidal or toroidal mirror. A multiple-display system (30) may be used to create a mosaic reflected image. In the multiple-display system (30), the convex faceplates of cathode ray tubes ( 12) are placed side by side, and optimally spaced apart at an angle (35) to provide a near-infinity mosaic reflection to an eyepoint (20) of a single observer or eyepoints (40) and (42) of multiple observers. In the multiple-display system (30), multiple observers are spaced apart a distance (41) that optimizes independent viewing of the near-infinity image by each observer.

TECHNICAL FIELD OF THE INVENTION 
The present invention relates to an image display system, and more 
particularly to an image display system for projecting a near-infinity 
image to an observer. 
BACKGROUND OF THE INVENTION 
Systems which display images are used for many purposes. Sometimes the 
image is simply displayed and viewed directly, such as a cathode ray tube 
used as a television screen or computer display. A concern in viewing 
images from a cathode ray tube is the viewer's exposure to radiation from 
the screen of the device. Since the radiation is low-level radiation, 
exposure can be reduced by distancing a viewer from the screen. 
In another instance, it is often desirable to project to a viewer an image 
which is spatially realistic. For example, projecting images of landscape 
scenery to trainees in a flight simulator. Systems which produce an 
infinity or near-infinity image are used for this purpose. In such 
systems, the viewed image has usually been reflected and otherwise 
manipulated in some way. A problem with these systems is that they are 
complex because they use several components to produce the image to the 
viewer. A typical system may consist of a projector and projection screen, 
mirrors, beamsplitters, lenses and a final image viewing screen. The 
complexity of such a system is further increased by the numerous 
mechanisms needed to support and align the components. The complexity 
increases the cost of a system, and the more complex the system the more 
costly. In addition to the expense related to the number of components, 
some of the individual components are inherently costly. For example, a 
quality projector and screen display is relatively expensive, particularly 
when compared to an image-originating device such as a cathode ray tube. 
In general, quality optical items are expensive. Also, with respect to 
projection systems, the projector normally used has a shorter useful life 
than a CRT. The complexity of some systems also causes image abnormalities 
such as under illumination, lack of definition, lack of clarity, 
distortion and chromatic aberrations. Further, alignment of an image in a 
projector system which uses red, blue and green tubes is difficult. All of 
the problems outlined above may be exacerbated when a mosaic image is 
attempted. A mosaic image is a composite image of distinct displays. A 
display system which eliminates some of the components mentioned above 
would be simpler to construct, more compact, less expensive and capable of 
more easily providing a clear, distortion-free image. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a means for viewing a cathode 
ray tube while reducing a viewer's exposure to radiation therefrom. 
It is also an object of the invention provide a compact, inexpensive 
near-infinity image display system which produces a clear, distortion-free 
image. 
It is a further object of the invention to provide a compact, inexpensive 
near-infinity image display system which produces a clear, distortion-free 
mosaic image. 
According to a preferred embodiment of the present invention, a 
near-infinity image display system has a convex visual display surface 
positioned with respect to a concave mirror such that the convex visual 
display surface is in front of the center of curvature of the mirror and 
so that the mirror reflects a near-infinity image of the display surface 
to an eyepoint of an observer positioned below and in front of the center 
of curvature of the mirror and below the display surface. The convex 
visual display surface is preferably a faceplate of a cathode ray tube. 
The cathode ray tube is positioned at a height above the field of view of 
the image projected to the eyepoint of an observer so that it does not 
interfere therewith. The concave mirror may be a spherical, ellipsoidal or 
toroidal mirror. 
In another embodiment of the invention, a multiple-display system produces 
a mosaic reflected image. In the multiple-display system, visual display 
surfaces are placed side by side, and optimally spaced apart at angles to 
provide a desired mosaic near-infinity image to a single observer or to 
multiple observers. In the multiple-display system, multiple observers are 
optimally spaced apart so that each observer may independently view the 
near-infinity image. 
Other aspects, objects, features, and advantages of the present invention 
will become apparent to those skilled in the art upon reading the detailed 
description of preferred embodiments in conjunction with the accompanying 
drawings and appended claims.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION 
While the specification concludes with claims particularly pointing out and 
distinctly claiming the subject matter which is regarded as the present 
invention, the invention will now be described with reference to the 
following description of an embodiment taken in conjunction with the 
accompanying drawings. 
Standard display systems which project near-infinity, infinity or, in 
general, collimated images require at least one beamsplitter, perhaps at 
least one lens and, often, a backscreen and/or projector to fold the 
displayed image out of the line of vision of the observer and to remove 
aberrations and distortions from the image which are caused by routing the 
image out of the line of vision. In many cases, the image is ultimately 
projected upon and viewed from a projection screen after it has been 
manipulated. The present invention teaches the projection of a 
near-infinity image without the use of a beamsplitter, lens, backscreen or 
projector. The image to be viewed is not folded out of the line of vision 
or field of view of the observer. The invention accomplishes its objective 
by uniquely positioning a display surface and a concave mirror with 
respect to one another and relative to the position of an observer. 
Referring now to FIG. 1, therein is shown a schematic representation of a 
near-infinity image display system 10 according to a preferred embodiment 
of the present invention which projects a near-infinity image of a cathode 
ray tube display to an eyepoint of an observer. A concave mirror 14 is the 
reflecting medium. The mirror 14 may be spherical, ellipsoidal or 
toroidal. The mirror 14 has a center of curvature 16 and a radius of 
curvature 18 which is the distance from a normal to the mirror 14 to the 
center of curvature 16. A cathode ray tube 12, commonly referred to as a 
"CRT," is the visual display surface which provides the image reflected by 
the mirror 14. More specifically, the cathode ray tube 12 has a curved 
faceplate which is the visual display surface that is reflected. A cathode 
ray tube 12 is the preferred visual display mechanism because of its 
relatively low cost for a quality display and its ability to easily 
display a variety of high quality images. A curved faceplate CRT 12 is 
preferred over a flat faceplate because a flat faceplate produces very 
noticeable and problematic aberration and makes the image difficult to 
focus. The quality of the reflected image is optimized by utilizing a 
mirror 14 and CRT 12 faceplate combination wherein the radius of curvature 
18 of the mirror 14 is about two times the radius of curvature of the 
curved faceplate of the CRT 12. A perfect 1:2 ratio is difficult to 
achieve utilizing currently available CRT's but the closer the combination 
comes to this ratio the better the reflected image in terms of adequate 
illumination, clarity and chromatic trueness. 
In the preferred embodiment, the display image, that is, the faceplate of 
the CRT 12, is positioned in front of the center of curvature 16 of the 
mirror 14. The eyepoint 20 of the observer is positioned below and in 
front of the center of curvature 16 of the mirror 14 and below the CRT 12. 
This is the optimum position for viewing the near-infinity image 
reflected. As shown, the mirror 14 may be tilted slightly upwards so that 
the top of the CRT 12 faceplate is captured in the reflected image. The 
mirror 14 is optimally tilted to produce the best reflected image while 
maintaining an unobstructed field of view for the observer. The vertical 
field of view 24 of the observer from eyepoint 20 is illustrated as an arc 
inscribed by an angle. The CRT 12 is positioned at a height above the 
eyepoint 20 of an observer so that it does not interfere with or otherwise 
obstruct the vertical field of view 24. 
The system may be operated with a variety of CRT 12 curved faceplate, or 
curved screen, sizes. For example, diagonal screen sizes of 14, 19, 25, or 
35 inches, or even larger. A desired image size and field of view may be 
obtained by varying the size of CRT 12 faceplates, mirror 14 size and 
radius of curvature 18, and position of observer eyepoint 20. Another 
design parameter that may impact the selection process is the amount of 
space which the system occupies. The space which the mirror 14 occupies in 
vertical and horizontal planes is important in this context. The distance 
26 along a vertical axis which the mirror 14 extends is a space parameter 
to be considered. Referring momentarily to FIG. 2, a plan view of the 
schematic illustration, therein is illustrated another space parameter, 
namely, the distance 28 along a horizontal axis, that is, a straight 
horizontal line, over which the mirror 14 extends. As an example of 
applicable parameters, the CRT 12 may be a 19-inch curved faceplate 
monitor. To accommodate this CRT 12 faceplate, the mirror 14 may be a 
spherical, ellipsoidal or toroidal mirror having a radius of curvature 18 
of 40 to 50 inches and extending a horizontal distance 28 of about 24 to 
30 inches. The mirror 14 may also be sized to have a length such that the 
vertical distance 26 extended by the mirror would be about 16 to 20 inches 
upon proper tilting and alignment. Given the above parameters, the field 
of view angle 24 would be about 28 to 30 degrees for an observer optimally 
positioned in front of the center of curvature 16 of the mirror 14. 
Referring now to FIG. 3, a plan view of a schematic illustration of a 
multiple-display system 30 according to the invention, multiple CRT 
displays 12 are used. A side view of this arrangement would be very 
similar to the side view of the single display system discussed above. The 
multiple-display arrangement is especially useful to create a mosaic 
image. FIG. 3 illustrates three CRT's 12. This system is capable of 
accommodating two observers as illustrated by the eyepoint for a left 
observer 40 and the eyepoint for a right observer 42. Both of these 
eyepoints 40 and 42 are located in front of and below the center of 
curvature 16 of the mirror 14 and below the CRT's 12. The observers are 
separated at an optimal distance 41 with respect to one another so that 
each may independently receive the desired image at their respective 
eyepoints 40 and 42. The CRT's 12 are optimally spaced with respect to one 
another to achieve the desired blended mosaic. Each CRT 12 inscribes a 
horizontal field of view denoted by an angle 33 that contributes to the 
overall reflected image. Angular spacing 35 between the CRT's 12 allows 
the displays to be properly blended to achieve the desired imaging. The 
key elements remain the positioning of the CRT 12 in front of the center 
of curvature 16 of the mirror and the positioning of the observer or 
observers below and in front of the center of curvature 16 of the mirror 
and below the CRT 12. The elements of the system are arranged and adjusted 
to optimize a near-infinity image at the eyepoints 40 and 42. The vertical 
field of view for the multiple-display system would be the same as the 
vertical field of view 24 inscribed in the single-display system described 
above because the vertical alignment of the elements of the invention 
would be about the same. An example of parameters useful for the 
multiple-display embodiment shown would be the use of three CRT's 12 each 
having a 35-inch curved faceplate. The horizontal field of view 33 
inscribed by each CRT 12 of this size in the configuration shown is about 
34 to 36 degrees. The vertical field of view 24 would again be about 28 to 
30 degrees. A suitable sized mirror 34 is a spherical, ellipsoidal or 
toroidal mirror having a radius of curvature of about 70 to 75 inches. 
Using the center of curvature 16 of the mirror 34 as a reference point, an 
angular spacing 35 between mirrors 34 of about 5 to 6 degrees is suitable. 
The mirror 34 may also be sized to have a length such that the vertical 
distance 26 extended by the mirror would be about 30 to 34 inches upon 
proper tilting and alignment. A suitable spacing 41 between observer 
eyepoints 40 and 42 is about 21 to 22 inches. 
The invention has several advantages over other near-infinity or infinity 
display systems. In particular, the present invention has advantages over 
a system which uses a projector display. Commercially available cathode 
ray tubes are less expensive than projector displays. The tubes of a 
projector have a shorter useful life than a CRT. Alignment of an image 
using a CRT is much simpler than the alignment of an image using the red, 
blue and green tubes of a projection system. With respect to a system 
which employs the use of a backscreen, direct viewing of the CRT as taught 
by the invention eliminates the expense of a high quality backscreen and 
the problems inherent in achieving a uniform gain high quality diffusion 
coating on a backscreen. Although it is possible to project a CRT image 
onto a screen, direct viewing as taught by the invention yields a 
brighter, higher-contrast, clearer image without the problems of light 
transmission, backscatter, halation and hot spots common to backscreen 
diffusion surfaces. 
The display system 10 taught by the invention may be used for video display 
terminals for computer systems. The near-infinity image provided by the 
invention helps to eliminate eye strain and, because of the distance the 
observer is removed from the CRT itself, the system greatly reduces 
radiation exposure associated with direct, close viewing of video display 
terminals. The system of the invention is also suitable as a visual 
display in simulation training devices for aircraft, spacecraft, land and 
water vehicles. In addition, the system is suitable as visual display for 
arcade style game devices and for higher end interactive generator and 
video disc systems. The multiple-display system is particularly suitable 
for simulation and entertainment uses. 
As should be apparent from the foregoing specification, the invention is 
susceptible of being modified with various alterations and modifications 
which may differ from those which have been described in the preceding 
specification and description. Accordingly, the following claims are 
intended to cover all alterations and modifications which do not depart 
from the spirit and scope of the invention.