GB2076557A

GB2076557A - A Virtual Image Display Apparatus

Info

Publication number: GB2076557A
Application number: GB8017238A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1980-05-27
Filing date: 1980-05-27
Publication date: 1981-12-02
Also published as: GB2076557B

Abstract

A virtual image display device for alpha-numeric and pictorial information comprises a concave spherical mirror segment 14 which magnifies and reflects an image from an image source 11. The image source 11 is mounted between the focus 16b of the mirror and the said mirror and parallel to its optical axis 16a. The virtual image 16c thereby formed is visible to the viewer 29 in front of the mirror 14. In related embodiments, the concave mirror segment can be made partially reflective and placed in front of a camera lens to allow a camera to photograph through it. A planar mirror can also be included to fold the light path of the display and thereby reduce the size of the apparatus. <IMAGE>

Description

SPECIFICATION Virtual Image Display Apparatus Background of the Invention This invention is a device for displaying alpha numeric and pictorial information in an enlarged format. Such a device has utility as an advertising display panel, a prompting device, closed circuit television display or photographic projector. It can also be used in place of other apparatus commonly used for imaging texts and pictures.

Visible displays have been produced in the prior art by projecting an image, often termed a "real image," on a screen. Since the image is formed on the screen surface, its size is limited to that of the screen itself. This real image appears to grow smaller, and therefore, more difficult to see, as a viewer's distance from the screen increases. Real images on a screen are also degraded by ambient light.

Where visual information is produced for prompting purposes, the screen must display enough words for a performer to read his script comfortably. It is often difficult to use characters large enough so that they can be read from a distance and still fit on the small cathode ray screens currently in use. Moreover, such present day displays cannot be enlarged readily.

Airlines also use closed circuit television systems in their terminals to make flight information available to their passengers. These screens too must show so much information on a small area that they are difficult to read from a distance.

The present invention overcomes many of the difficulties with prior art devices by producing a magnified virtual image display. The virtual image, created by its concave mirror, is more readily shielded from ambient light than are real image displays. Unlike prior art devices employing flat mirrors, the curved virtual image apparatus can magnify its display so that it can be read at a distance. The degree of magnification can be varied readily if desired.

Another object of the present invention is to provide a means for viewing information in front of a photographic or television camera for prompting purposes. In this embodiment, the virtual image display apparatus will provide a script for a performer that he can read in a studio while he is looking directly at the camera.

Still another object of the present invention is to provide a prompting device which can be used outdoors or in the presence of high levels of ambient light.

Summary of the Invention A virtual image display apparatus according to the present invention comprises a concave mirror segment and an off axis image projection device directed at said mirror. Said information projection device may be a small television tube, or any other analogous form of illuminated image projecting device. The spherical mirror segment reflects the projected light and magnifies the projected image. Various embodiments are shown and described in which the information is projected through different optical configurations to achieve specific spatial and optical advantages.

Several types of mirrors are also disclosed for ues in the present invention.

Description of the Drawings In the accompanying drawings forming a part hereof, similar parts have been given identical reference numerals, in which drawings: Figure 1 is a somewhat diagrammatic side view, partially in section, of one complete embodiment of the present invention.

Figure 2 is a somewhat diagrammatic side view of another embodiment of the present invention.

Figure 3 is a somewhat isometric view, partially broken away, of another complete embodiment of the present invention useful for prompting.

Figure 4 is a diagrammatic view, partially in section, of the embodiment shown in Figure 3 illustrating the various light paths.

Figure 5 is a somewhat diagrammatic side view, partially in section, of still another embodiment of the present invention.

Figure 6 is a view similar to Figure 5 showing a further embodiment of the invention.

Detailed Description Referring to the drawings, and Figure 1 in particular, 10 indicates one complete -embodiment of a virtual image display device made in accordance with the present invention.

Said embodiment is particularly well suited for large format displays in airline terminals, train stations, and other places where information must be read easily at a distance.

The virtual image display device 10 comprises an information projection device 11, hereinafter referred to as an image source, and a curved mirror segment 14 to receive light from said projection device. The image, source illustrated at 11 is intended to depict a cathode ray tube 12, a thin film electroluminescent display, a liquid crystal display-rear or front illuminated, an illuminated film, a light emitting diode array, electroluminescent panel, filament lamp, gaseous plasma discharge cell or analogous unit. The image source 11 is mounted in an enclosure 13 and its image display face 30 is substantially normal to the optical axis 1 6a and is preferably shielded from ambient light by said enclosure.In the present embodiment, the image source 11 is suspended from the ceiling of a room, but other supports may be used to suit the location of the image source apparatus.

The image source 11 is directed at a concave spherical mirror segment as used herein is intended to mean a concave portion of a larger hemispherical mirror structure indicated by dashed lines 14a in Figure 1. Mirror segment 14 is held stationary at some predetermined distance below and in front of image source 11 as by bracket 15.

In the embodiment shown in Figure 1, mirror segment 14 is fully aluminized, preferably front surface. It magnifies the image received from the image source 11 and reflects it toward the viewers 29 located at some distance below and behind enclosures 13. The viewers 29 are represented by the schematic eye 29.

Every concave spherical mirror has a focus and an optical axis. Said focus is always located at some distance in front of the mirror and on its axis. Rays parallel and close to the optical axis directed at the surface of the concave mirror concerge near or at its focus. Any object placed between the focus and the concave mirror will appear to be magnified when viewed by one standing somewhere behind the focus. The closer the object is located to the focus, the more it will be magnified. The object reflected by the concave mirror will also appear to the viewer as if it is located somewhere behind the surface of the mirror itseif. This reflection is commonly called a virtual image.

In Figure 1, the optical axis of the mirror 1 4a is designated by the line 1 6a. The focus of mirror 1 4a is the point 1 6b. The image source 11 is positioned between said focus 1 6b and the mirror 1 4a to magnify its display. Mirror segment 14 is mounted below the axis 1 6a so that the display it reflects is not partially blocked from view by the image source 11 and its enclosure 13. Since image source 11 radiated light out over a wide angular range in front of it, it is possible for mirror segment 14 to be positioned below its own axis and yet reflect a portion of this light to the viewer 29. This reflected portion constitutes the desired display of the present invention.The light rays drawn in Figure 1 show how this so-called off axis projection technique picks up a portion of the light that image source 11 emits and reflects it toward the viewer 29. Said viewer sees the display from the image source 11 as an enlarged virtual image 1 6c appearing to exist behind mirror segment 14.

Figure 2 shows another embodiment of the present invention in which the virtual image display apparatus is used as a prompting device.

The viewer 29 may be at some distance in front of a movie or television camera 18 mounted upon a support 20. This schematic figure again shows a cathode ray tube 12 image source directing a display such as a script on to mirror segment 1 7.

Unlike mirror segment 14, used in the first embodiment of this invention, mirror segment 1 7 is only partially reflective. Mirror segment 1 7 is surfaced so that typically 70 to 80% of the incident light enters camera lens 19 after passing through said mirror segment 17. At the same time, mirror segment 17 allows 30 to 20% respectively of the light coming from the image source 11 to be reflected to the viewer 29. The placement of the image source 11 outside of the field of view of the recording camera (indicated by lines 1 2a) prevents said camera from receiving the display being projected by image source 11.

Image source 11 uses a sufficiently intense light so that the viewer 29 can still read the reflected display coming from the 20 to 30% of the light from the mirror segment 1 7. The remaining 70 to 80% of the light from image source 11 is wasted.

The 20 to 30 , decrease in brightness of the scene that camera 18 is recording, similarly, is not sufficient to disrupt its proper functioning.

Coating mirror segment 1 7 with silver, aluminum, or other reflective substances to reflect and transmit light in the above described manner is accomplished by techniques well known in the art and comprise no part of the present invention.

Figures 3 and 4 illustrate a third embodiment of the present invention. This embodiment if similar to Figure 1 except that the light path of the display reflected from mirror segment 14 is folded once before it is directed to the viewer 29. Folding the light path allows the components of the virtual image display apparatus 10 to be more closely arranged in front of a recording camera 1 8. A partially reflective planner mirror 22 is here used to fold the light path. The apparatus of Figure 3 is contained in a housing 23 having a top 24, bottom 25, spaced sides 26a and b, and back 27. The front of housing 23 is open.

Figure 4 shows the arrangement of each of the optical components in the embodiment of Figure 3. The image source 11 is again mounted with its image display face 30 substantially perpendicular to the optical acis 1 6a of soherical mirror segment 14. Image source 1 is placed inside the focus 1 6b of mirror segment 14 so that its display is magnified by said mirror A small baffle 21, mounted on one edge of the image source 11, prevents the viewer from being distracted by light radiating from the edge of the image source's display face 30.

Mirror segment 14 is mounted off its own optical axis 1 6a as described in previous embodiments. Image source 11 is also mounted off the axis 1 6a. Mirror segment 14 is fully reflective so that it transmits all the light it receives from source 11 toward planar mirror 22.

Planar mirror 22 is mounted in front of camera lens 1 9. Mirror 22 is coated to have its front surface partially reflective such as, for example, mirror segment 17 described in the second embodiment of this invention.

As noted above, the degree to which a spherical mirror will magnify an object placed before it depends upon its location: The closer the object is placed to the mirror's focus, the more the mirror will magnify its virtual image. Applying this principal to each of the three above described embodiments, it becomes apparent that moving the image source 11 toward focus 1 6b will increase the magnification of the virtual image display. Moving the source 11 away from the focus 1 6b decreases the size of the virtual image.

Experimentation shows that the image source 11 must be moved along a line which passes through the focus 1 6b of mirror segment 14, at an angle 0 with respect to axis 1 6a such that

where h equals the distance from the center of the image source's display face 30 normal 1 6a; f.l. equals the foval length of the mirror segment 14 (the distance from the optical center 1 6d of mirror segment 14 to point 1 6b as measured along axis 1 6a) and s equals the distance from the point 1 6e where line he intersects axis 1 6a to the center 1 6d of mirror segment 14 measured along axis 1 6a so that the virtual image of image source 11 in mirror segment 14 will stay at the same height above the optical axis mirror as the magnification is changed.

Image source 11 may be slidably carried by supports 1 a to move it along the line 11 b to change the magnification.

Figure 5 shows still another embodiment of the present invention. Here, a mirror segment 1 7 is mounted in front of camera lens 19, as it was in Figure 2 of the invention. An image source 11 is mounted above said mirror 17. A planar fully silvered mirror 22a is placed in front of image source 11 to receive its display and reflect it on to mirror segment 1 7. This folded light path embodiment like that of Figures 3 and 4, is particularly useful where excessive overhang of the recording camera 18 is undesirable for handling purposes.

Instead of using a partially reflective mirror in the various embodiments of this invention, a similar result can be achieved using a dichroic mirror, spherical or planar, in front of camera lens 19, in Figures 2 through 5. The dichroic mirror must be fashioned so that it will allow all but a narrow range of light frequencies to pass through it and be photographed by camera 18. A mirror could be coated, for example, so that it would reflect only a narrow range of intense greens of between 540 and 546 nanometers in wavelength. The image source 11 could be designed to emit light only at these frequencies.

The dichroic mirror would therefore reflect substantially all light coming from image source 11 to the viewer 29. The mirror would allow all other frequencies to pass through it, so the camera 1 8 located directly behind it would sense virtually full color. The operator could boost the sensitivity of camera 18 to greens within the spectrum from those reflected by the dichroic mirror to compensate for it and thereby record virtually full color.

In the embodiments described above, except those using both the planar and spherical mirrors, those skilled in the art will have no difficulty selecting and positioning mirrors to meet their needs. The parameters of the folded light path designs can also be worked out through experimentation or by applying the information set forth above and basic principles of optics. To facilitate building the most complex embodiment, however, the one set forth in Figures 3 and 4, an example of how the mirrors and image source might be designed and positioned in a prompter is here provided.

Example Assume a designer wishes to magnify a three by four inch image three and one half times without obscuring the + 1 50 field of view of the movie camera lens mounted directly behind his mirror segment. Experimentation shows that the cathode ray tube, or other image source, should be located with its closest edge six inches in front of the camera lens and six inches below its optical center. The cathode ray tube's screen should be tilted forward toward the viewer at an angle of 340 below the horizontal axis of the movie camera's lens.

The partially reflective planar mirror should be rectangular. It should measure 16" in width and 12" from top to bottom. The mirror should be inclined forward at its bottom at an angle of 63.50 from the horizontal. Its bottom should be parallel with the bottom of the housing. Its center should be located 2" in front of the camera lens.

The concave spherical mirror segment should also be rectangular. It should have a radius of curvature of 50" and should measure 11" from front to back and 16" from side to side. Its forward edge should be located about 9" above the center line of the camera lens. Its rear edge should be located 13" above the center line and 4 1/2" in front of the front of the camera lens.

It is within the purview of the present invention to substitute a convex front surface mirror segment 35 as shown in Figure 6 for the planar mirror 22a shown in Figure 5. The convex front surface mirror 35 will provide better off-axis imaging as the viewer moves from left to right of from up to down with respect to optical axis. The precise optics of the convex mirror 35 will vary in accordance with well known optical principles and need not be described, therein.

Having thus fully described the invention, what is desired to be secured and protected by Letters Patent is as follows:

Claims

1. A virtual image display apparatus comprising a mirror in the shape of a substantially concave segment of a hemisphere said spherical mirror having an optical axis and a focus, an image source means for said mirror segment, and an image display face on said image source disposed substantially perpendicular to said optical axis but located off said axis and substantially on the same side of the axis as the line of sight of an observer and between said focus and said mirror segment.

2. A virtual image display apparatus according to Claim 1 wherein said mirror segment is a partially reflective mirror.

3. A virtual image display apparatus according to Claim 1 wherein a partially reflective planar mirror is angularly positioned between said image source to receive light reflected by the mirror segment and direct it in a path across the optical axis of said mirror segment.

4. A virtual image display apparatus according to Claim 1 wherein a fully reflective mirror is placed substantially in front of said image source laterally displaced from the concave mirror segment and parallel to the light emitting image display face of said image source and wherein the said image display face is directed away from said mirror segment.

5. A virtual image display apparatus according to Claim 1 wherein said image source means is a cathode ray tube.

6. A virtual image display apparatus according to Claim 1 wherein said image source means is a this film cathode ray tube.

7. A virtual image display apparatus according to Claim 1 wherein said image source means is a liquid crystal display apparatus.

8. A virtual image display apparatus according to Claim 1 wherein said image source means is a light emitting diode array.

9. A virtual image display device according to Claim 1 wherein said image source means is an electroluminescent panel.

10. A virtual image display device according to Claim 1 wherein said image source means is a tungsten filament projector.

11. A virtual image display device according to Claim 1 wherein said image source means is a gaseous plasma discharge cell.

12. A virtual image display device according to Claim 1 wherein said image source is a back illuminated film or transparency.

13. A virtual image display device according to Claim 1 wherein said image source means is a front illuminated partially reflecting original.

14. A virtual image display apparatus according to any one of Claims 1 to 8, wherein said image source is a tungsten filament projector.

1 5. A virtual image display apparatus according to any one of Claims 1 to 8, wherein said image source is a gaseous plasma discharge cell.

1 6. A virtual image display apparatus according to any one of Claims 1 to 8, wherein said image source is a back illuminated film or transparency.

1 7. A virtual image display apparatus according to any one of Claims 1 to 8, wherein said image source is a front illuminated partially reflecting original.

1 8. A virtual image display apparatus according to any preceding Claim, wherein said image source is slidably carried by a support located between said mirror segment and said focus, whereby said image source may be moved so as to decrease or increase the degree to which its image is magnified by the virtual image display apparatus without changing the vertical position of the virtual image with respect to the mirror segment.

1 9. A virtual image display apparatus substantially as hereinbefore described with reference to the accompanying drawings.

14. A virtual image display device according to Claim 1 wherein said mirror segment is dichroic.

1 5. A virtual image display apparatus according to Claim 3 wherein said partially reflective planar mirror is dichroic.

1 6. A virtual image display apparatus according to Claim 1 wherein said image source is slidably carried by a support located between said mirror segment and said focus, whereby said image source may be moved so as to decrease or increase the degree to which its image is magnified by the virtual image display apparatus changing the vertical position of the virtual image with respect to the mirror segment.

1 7. A virtual image display apparatus according to Claim 4 in which the fully reflective mirror is a curved front surface mirror

18. A virtual image display apparatus according to Claim 4 in which the fully reflective mirror is a planar mirror.

New Claims or Amendments to Claims filed on 1 sot September 1981 .

Superseded Claims 1 and 5 to 18.

New or Amended Claims:

1. A virtual image display apparatus comprising a mirror in the shape of a substantially concave segment of a hemisphere, said spherical mirror having an optical axis and a focus, an image source for said mirror segment, and an image display face on said image source disposed substantially perpendicular to said optical axis but located off said axis and between said focus and said mirror segment, said mirror segment being located substantially on the same side of the said optical axis as the image source, whereby an observer positioned on the same side of the optical axis as the mirror segment and the image display face can observe a substantially distortion free image.

5. A virtual image display apparatus according to Claim 1 wherein said mirror segment is dichroic.

6. A virtual image display apparatus according to Claim 3 wherein said partially reflective planar mirror is dichroic.

7. A virtual image display apparatus according to Claim 4 in which the fully reflective mirror is a curved front surface mirror.

8. A virtual image display apparatus according to Claim 4 in which the fully reflective mirror is a planar mirror.

9. A virtual image display apparatus according to any preceding claim, wherein said image source is a cathode ray tube.

10. A virtual image display apparatus according to any one of Claims 1 to 8, wherein said image source is a thin film cathode ray tube.

11. A virtual image display apparatus according to any one of Claims 1 to 8, wherein said image source is a liquid crystal display apparatus.

12. A virtual image display apparatus according to any one of Claims 1 to 8, wherein said image source is a light emitting diode array.

1 3. A virtual image display apparatus according to any one of Claims 1 to 8, wherein said image source is an electroluminescent panel.