Wide-angle on-axis projection system
United States Patent Herndon 1 Apr. 29, 1975 WIDE-ANGLE ON-AXIS PROJECTION SYSTEM [75] Inventor: John W. Herndon, Orlando, Fla.  
 [73] Assignee: The United States of America as represented by the Secretary of the Navy, Washington, DC.  
 [22] Filed: Mar. 15, 1974 [21] Appl. No.: 451,635  
 {52] US. Cl. 353/12; 35/12 N; 350/294; 350/299; 353/28; 353/69; 353/79; 353/99 [51] Int. Cl. G03b 21/28; G09b 9/08; G02b 5/10 [581 Field of Search 353/11. l2. l3. 14, 28, 353/69, 79, 99. 122; 350/21, 293, 294. 299. 302; 35/12 N [56] References Cited UNITED STATES PATENTS 3,432.2l9 3/1969 Shcnket et al. 350/21 3.620.592 1l/l97l Freeman 353/99 Primary ExaminerRichard E. Aegerter Arr/stun! E.mminer-Steven L. Stephan Almrney, Agent. or FirmR. S. Sciascia; John W. Pease [57] ABSTRACT The invention provides a wide-angle common axis projection system wherein a reflector and a seethrough beam splitter reflector are combined with a projector means having a wide angle lens and a display screen of spherical shape to develop on-axis image projection for wide-angle display in relation to a viewers point located on the non-reflective side of the beam splitter reflector.  
 4 Claims, 2 Drawing Figures I WIDE-ANGLE ON-AXIS PROJECTION SYSTEM BACKGROUND OF THE INVENTION The invention is in the field of optics and is particularly useful in the field of visual aid training simulators.  
  There is a longstanding need in the field of image projection for wide-angle display systems, especially as applied to achieving visual simulation in the field of training devices. One such training device for which suitable visual techniques have been sought is a carrier landing simulator for aircraft. Various schemes which have been implemented or are under consideration include wide-angle systems using a plurality of projectors which achieve wide-angle display by contiguous smaller displays. Other systems use wide angle lenses but are off-axis. giving the image an improper perspective from the viewer&#39;s position.  
 SUMMARY OF THE INVENTION In accordance with the subject invention there is combined with a spherically shaped display screen and projector means having wide-angle lens, a reflector and a beam splitter reflector arranged to reflect the projected image on the display screen while providing an on-axis view ofthe scene from an observers position of view. The invention contemplates a conical shaped beam splitter reflector and a first reflector means which is horizontally circular and vertically dependent in curvature upon the intersection points of intersecting rays between the projector lens and the beam splitter reflector. Further, by selection a preferable 60 vertical im&#39; age, as picked up by a TV camera, is condensed to a 30 vertical field-of-view by the projection lens to reduce the size of the first reflector means. The on-axis feature is obtained by placing the beam splitter reflector in front of the viewer so that the optical axis of the image reflected to the display screen and the optical axis of the viewer are in coincidence (on-axis), the beam splitter reflector mediating the optical path between viewer and final viewing (i.e., display) screen.  
 BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a conceptual diagrammatic sketch of the invention applied, as one example. to an aircraft training device.  
  FIG. 2 is a diagrammatic view illustrating the principle of the reflecting rays and the elements of the system.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing, FIG. 1 shows, as an example of a device incorporating the invention, a visual aid simulator for aircraft training. Here, projector I is posi&#39; tioned so that an image is projected through a wideangle lens 2 to a first reflector means 3 shaped to receive the full wide-angle image and reflect it downward to the rear, reflector side, of a see-through beam splitter reflector 4. Reflector 4 then reflects the projected image to a spherical contoured display screen 5. Beam splitter reflector 4 is partially silvered in the manner of a one-way mirror, or otherwise surface treated, so as to reflect a substantial magnitude of the image light while, at the same time, providing the viewer 6 an adequate view, through beam splitter 4, of the displayed image on display screen 5. In the example of FIG. 1, the viewer would be a trainee in a simulator cockpit 7. Projector l, reflector 3, beam splitter reflector 4, display screen 5 and cockpit 7 are all mounted in fixed relationship and upon an associated device, as for example, a motion platform 8. Brackets 9, l0 and II indicate support means. In practice, more sophisicated means would be employed. Also in the example of FIG. I, the lens 2, reflector 3, beam splitter reflector 4 and screen 5 are configured for wide display. The vertical field of view in the preferred example is 60.  
  FIG. 2 illustrates the geometry of the system. In the preferred embodiment, the projection lens 2 is configured for 180 azimuth and 30 vertical field of view. The original scene vertical field of view is 60. The re duction to 30 in the projection lens 2 allows a smaller first reflection 3 to be utilized.  
  The first reflector means 3 has a vertical contour generated by means of connecting all points of intersection of corresponding ray paths from lens 2 and beam splitter reflector 4. For example, ray Al from lens 2 crosses ray A2 at point A. While in operation the projected ray follows a path, for instance, from lens 2 along Al to point A where it is reflected along A2 to point D on the beam splitter reflector 4 and from point D along A3 to the display screen 5.  
  The requirements are set up in reverse. The vertical field of view is selected. In the example shown in FIGS. I and 2, a 60 vertical angle was selected with 40 above the horizontal and 20 below, all measured from a point G corresponding to the viewer&#39;s eye position. Ray path A3, being so established, determines the angle of A2 with respect to the beam splitter reflector 4. Similarly, all ray paths from the screen 5 have corresponding ray paths reflecting from the reflection, i.e., the rear surface of beam splitter reflector 4 and result in points of intersection with their corresponding ray paths from lens 2. These defined intersection points determine the vertical contour of first reflector means 3.  
  The horizontal contour of first reflector means 3 is circular. The beam splitter reflector means 4 is a 45 conical section. Both reflector 3 and beam splitter reflector 4 are. in this example, made for 180 wide-angle coverage.  
  Attention is directed to the feature that with a suitable 360 projection head at the center of first reflector means 3 and with the contours shown in FIG. I generated for 360 instead of 180 as shown, a 360 projection system may be provided. Also, the system need not be limited by the vertical and horizontal fields-of-view used as an example herein.  
  It will also be appreciated from the above that the invention provides a continuous, spherical, wide-angle field of view in projection utilizing a special arrangement of reflectors and screen including a see-through reflection type beam splitter. It will be further appreciated that the final ray paths to the display screen 5 are identical to the viewers corresponding optical paths, thus achieving an on-axis wideangle projection system.  
  It is obvious in the light of the above teachings that modifications may be made in structure and arrangement without departing from the true spirit and scope of the invention, and it is intended that the appended claims relating to the invention be accorded as broad an interpretation as is consistent with the basic concepts herein taught.  
 What is claimed is:  
  I. A wide-angle common axis projecting and viewing display system comprising:  
  3 380,509 3 4 a. a difusing type display screen stantial magnitude of the image light while at the b. projector means having a wide-angle lens for prosame time providing the viewer from an adequate jecting image light rays, view, through said beam splitter reflector of the c. a first reflector means for receiving said rays image displayed on said display screen. d a see-through beam splitter reflector means being 5 3 App-drums according to l i 1 h i surfaced to provide a beam splitter effect and positioned to receive and reflect to said display screen said rays from said first reflector means while acting as a see-through window for a viewer monitor a. said display screen is a spherical segment b said first reflector means is circular in horizontal contour,  
 c. said beam splitter reflector is a 45 degree conical i ng said display screen along line of sight paths 1() Sect-Km and a Wewmg pomt d said first reflector means has a vertical contour e4 said first reflector and beam splitter reflector generated by means of connecting all points of inmeans being relatively shaped ll&#39;l curvature to cause tersection of corresponding rav paths from said all pro ected rays in each azimuth plane to pass H [hmugh a Common poim Said pumt being also the I PI&#39;OJGCIUI&#39; lens and from said beam splitter reflector mirror image of said viewing point such that the as correspondmgto rflys between and beam line of sight paths to said beam splitter reflector l and Sald dlspkly and under sand from Said view-mg point and thc corresponding conditions of collinear lme of sight and reflected paths of projection rays reflected to said screen are P l my path? 4 collinear and represent the true vertical angles of PP P uccordmg Claim 3 a the scene and thus constitute an on-axis system to sfald P F lens Pmvldmg a 30 Vemcul P J present a real image on said display screen without and i h l di i b said vertical curvature of said first reflector means 2. Apparatus according to claim 1 wherein corresponding to a 60 vertical projection on said at said beam splitter reflector is partially silvered in 25 display screen the manner of a one-way mirror to reflect a sub-