Apparatus for producing a symbology display into a night vision system

Abstract: Apparatus for introducing superimposed symbology from a source (20) into a dimly lit scene being viewed through a viewing device (10) by utilizing a very small mirror (50) to reflect information from the source to the viewing device (10) while minimizing the interference of the reception of light from the dimly lit scene by the viewing device, reducing the light from the source to a level consistent with that from the dimly lit scene and decreasing the aperture from the source so that the symbology remains in focus over a large depth of focus.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to night vision apparatus and more particularly to a method and apparatus for producing a superimposed image of desired symbology on the view being seen in the night vision system. 2. Description of the Prior Art Night vision systems are well known in the art. For example, the Government's Aviator's Night Vision System (ANVIS) goggle comprises a binocular arrangement containing apparatus for image intensifying low intensity light which is normally available from starlight or moonlight on a scene being viewed. Apparatus for superimposing information on a scene being viewed through an optical system is also known in the art. Helmet mounted displays such as found in U.S. Patents 5,113,177 and 5,299,063 utilize a partially silvered area on the helmet visor upon which information or symbology from a CRT is projected so as to be superimposed on the scene being viewed by the wearer. Binocular night vision systems having superimposed images thereon are also known as is shown in U.S. Patents 4,915,487 and Patent 5,079,416. In all of these systems a partially silvered mirror or prism is placed in the line of vision of the system so that information from the CRT can be reflected therefrom and combined with the view being seen by the wearer. Figure 1, although not specifically showing a prior art device, nevertheless shows a way that symbology could be introduced into the scene being viewed by a night vision system using conventional thinking. In Figure 1, one of a pair of ANVIS night vision goggles, is shown by reference numeral 10. This device receives light from a dimly lit scene over a path shown by arrows 12 through a partially silvered mirror 14. The ANVIS contains image intensifiers which operate to increase the intensity of light received from the dimly lit scene. To inject desired symbology on this scene a cathode ray tube 20 is shown clamped to the ANVIS 10 by clamping member 22. Light from the CRT 20 passes generally along an axis shown by dash dot line 23 through a reflecting prism 24 and through collimating lenses 26 and 28 to the partially silvered mirror 14 where the light from the CRT 20, shown by three sets of rays 29a, 29b and 29c, are then combined with the light passing through mirror 14 from arrows 12 so that the wearer sees both images simultaneously (only a few representative ray paths have been shown for simplicity). A CRT focusing ring 30 is utilized to cause the image seen by the viewer to be in focus. Connections such as 32 and 34 may be utilized to provide power and input information to the CRT in well known fashion. Several difficulties arise with respect to the prior art and the apparatus of Figure 1. A first problem arises because the ANVIS night vision apparatus intensifies light which it receives and normally this light is very dimmed as received over paths such as shown by arrows 12. The light from the CRT, on the other hand, is much brighter than the dimly scene and accordingly the symbology which is displayed must be diminished to prevent the ANVIS from blowing out Of course filters or intensity modifiers can be utilized to reduce the amount of light from the CRT but such additional apparatus increases the weight, size and complexity of the system. Another problem lies in the fact that the partially silvered mirror 14 allows only part of the light being received along paths such as arrows 12 to be received by the ANVIS. As mentioned this light is already very dim and losing part of it makes the dimness even greater in a very undesirable fashion. A third problem arises because the ANVIS night vision goggle has an adjustable focus so that it may view objects from far away and near. When the goggle changes it's focus, the image produced by the CRT may move out of focus. An additional adjustment of the CRT focus ring 30 will then be necessary. BRIEF DESCRIPTION OF THE PRESENT INVENTION The present invention provides an apparatus as defined in Claim 1, wherein the features of the preamble are known from US Patent 4,915,487 and US Patent 5, 079, 416. In this way, the apparatus inside ANVIS operates to intensify the image. The apparatus may include the features of any of dependent Claims 2 to 8. The present invention overcomes the problems encountered in the prior art by recognizing that all of the light from the CRT 20 shown in Figure 1 need not be utilized. More particularly a very small reflector may be utilized to transfer information from the CRT to the input lens of the ANVIS. This has the advantage of not only reducing the amount of light from the CRT in a desirable fashion but also greatly reducing the amount of interference with the light being received from the dimly lit scene. Also, since the small reflecting surface effectively cuts down the aperture of the optical system from the CRT and by doing so increases the depth of focus of the system which may be typically in the range of F number 17. Thus, when the operator changes the focus of the ANVIS, the CRT will not have to be refocused since it will remain focused over a large range. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a night vision system with a cathode ray tube symbol injector arranged according to conventional thinking; and Figure 2 shows the preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to Figure 2, the apparatus which is common to that of Figure 1 will have the same reference numerals. In Figure 2 the ANVIS night vision goggle 10 is again shown receiving light from a dimly lit scene over paths such as shown by arrows 12. A CRT 20 is shown clamped to the ANVIS with a removable clamp 22 for convenient mounting of the CRT. Light from the CRT passes generally along an axis shown by dash dot line 23, is reflected from a prism 24 and passes through collimating lenses 26 and 28 where it passes to a very small reflecting prism 50 along an axis generally shown by dash dot line 52. The optic axis of the ANVIS goggle as shown is a dash dot line 54 and it will be noticed that the prism 50 is located just below axis 54 although it's position may be on the axis or at any location which provides the proper curve of light shown by lines 54a and 54b as will be explained. If desired, the input of the ANVIS night vision goggle may be provided with an input hood 56 to help minimize extraneous light. Prism 50 is shown mounted in a small interior post 58 which extends into and out of the paper and is attached to the hood 56 for firmly positioning the prism 50. Light from the reflecting prism 24 passes to the small reflecting prism 50 where it is substantially totally reflected to the objective lens or input 60 of ANVIS 10 over paths such as shown by the lines 54a and 54b. The reflecting member 50 preferrably provides an input and output area of approximately 1,5 mm by 1,5 mm. The system needs to be designed in such a fashion that the angular separation between lines 54a and 54b is sufficient to provide the desired symbology to the eye of the viewer. In one example the Government has required a field of view of 40 degrees. So the angle between lines 54a and 54b is to be 40 degrees. It will be noted that the structure including prism 50 and supporting member 58 occupy only a very small portion of the light path from the scene and the light therefrom, as shown by arrows 12, is received by the ANVIS 10. It will also be noticed that since only a very small prism 50 is utilized most of the light from the CRT is not reflected into the objective lens of the ANVIS and accordingly the amount of light received thereby is far less than was the case in Figure 1. This is desirable since the apparatus inside ANVIS 10 operates to intensify the image and with less light coming from the CRT no additional filters or light diminishing devices are necessary. It will also be seen that as the objective lens 60 moves back and forth for focusing of the ANVIS 10 no additional focusing of the CRT focus ring 30 will be necessary since the depth of focus produced by the small aperture of the reflecting prism 50 will keep the CRT in focus throughout the normal range of focus of ANVIS 10. It is, therefore, seen that we have provided a significant improvement in the insertion of symbology upon a scene being viewed by a night vision system. We have provided the superimposition of the symbology in a way that minimizes the obstruction of the low intensity light of the scene being viewed and which keeps the amount of light from the CRT at a low level consistent with the scene intensity. It is also seen that the CRT does not have to be focused each time the night vision system is focused. It will be apparent to those skilled in the art that many changes falling under the scope of claim 1 may be made to the apparatus shown in connection with the preferred embodiment. For example, while we have employed prisms 24 and 50 for reflecting the light from the CRT to the night vision apparatus planar mirrors may be used or other light conducting devices. Also while the Government ANVIS night vision goggle has been used for describing the present invention, other suitable night vision apparatus may employ the teachings of the present invention.

Claims: Apparatus for providing superimposed symbology from a CRT (20) into a scene being viewed through a night vision viewer (10), said apparatus comprising a pair of night vision goggle oculars (10) for receiving radiation from a dimly scene and intensifying the radiation therefrom to produce a viewable image of the scene; a CRT (20) for producing desired symbology to be superimposed on the image; an optical CRT imaging system positioned to conduct symbology from the CRT (20) to the viewer (10) including a first reflecting surface (24) to receive radiation from the CRT and direct it toward an area in the path of radiation from the scene to one of the night vision goggle oculars; characterized in that said optical system includes a second reflecting surface (50) being substantially totally reflecting, being small in comparison to the first reflecting surface (24) and being mounted on a narrow beam member (58) extending in air across the path from the scene to the viewer to reflect a portion of the CRT radiation from the first reflecting surface to the input of one night vision goggle ocular, the size of the second reflecting surface being so as to reduce obstruction of the light from the scene to the viewer to reduce'the amount of light from the CRT (20) to a level comparable with the light from the scene and to reduce the aperture of the optical system in order to provide a large depth of focus; and said apparatus comprises means (22) mounting the CRT and the first and second reflecting surfaces to the one of the night vision goggle oculars. Apparatus according to claim 1, characterized in that the second reflecting member (50) is made to reflect light under a predetermined field of view of approximately 40 degrees. Apparatus according to claim 1, characterized in that the area of the second reflecting member (50) is approximately one and one half millimeters by one and one half millimeters. Apparatus according to claim 1, characterized in that the second reflecting member (50) provides a F number of 17 to said CRT imaging system (26, 28). Apparatus according to claim 1 characterized in that the size of the second reflecting surface (50) reduces the intensity of radiation from the CRT (20) to a level comparable to the radiation from the scene. Apparatus according to claim 1 characterized in that the first and second reflecting surfaces (24,50) are sized to provide an optical path having an F number greater than 16. Apparatus according to claim 1 characterized in that the area of the second reflecting surface (50) is not greater than two millimeters by two millimeters. Apparatus according to claim 1 characterized in that the mounting means (22) allows attachment and detachment of the CRT (20) and of the first and second reflecting surfaces (24, 50) from the night vision goggle oculars (10).

Inventors: FERRIN FRANK J, TURNER PAUL N, FERRIN, FRANK J., TURNER, PAUL N.
Applicants: HONEYWELL INC, HONEYWELL INC.
Application year: 1995
Main classification: G02B23
IPC codes: G02B23