Abstract:
A system and method are provided for removing a reticle from visualization in a displayed view in a binocular wherein the reticle is visible during direct scene view. The system includes a filter positioned between a display element and an eyepiece wherein a visual characteristic of the filter matches a corresponding characteristic of the reticle. These matching characteristics thereby render the reticle substantially “invisible” to the user. Exemplary filters can include a monochromatic filter and a polarizer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to provisional patent application Ser. No. 61/073,513, filed Jun. 18, 2009. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to devices and methods for enhancing distance vision, and, more particularly, to such devices and methods for providing an adaptive reticle display in binoculars having both direct and image-processed viewing options. 
     2. Description of Related Art 
     Binoculars have long been known in the art for providing increased distance vision with depth perception ( FIG. 1 ). A typical binocular has two sides, each of which  10  has an objective lens  11  that creates an image that passes through a prism  12  for correctly orienting the image. Some binoculars include a reticle  13  that is superimposed on the image to achieve distance estimation. The image downstream of the prism  12  is focused at the reticle  13 , and an eyepiece  14  permits the user  15  to focus on the reticle  13 . 
     More complex binoculars are also known that have one side  20  through which a displayed image can be transmitted through the eyepiece  21  ( FIG. 2 ). The direct-image optics are substantially the same, but a visual display  22  and projection optics  23  are positioned upstream of the eyepiece  21  and reticle  24 . Here the prism  25  has one surface that is not completely reflective and serves as a beamsplitter  26 , permitting the user  27  to see through the prism  25 . The characteristics of the beamsplitter  26  determine the mix of the display  22  and scene viewed by the user  27 . Exemplary characteristics can include intensity splitting (e.g., 80/20), spectral (e.g., red/visible without red), and polarized (p and s). 
     Typically a user will not wish the reticle to be superimposed on a displayed image, for example, if the size, orientation, or location of the displayed image is different from that of the scene viewed through the objective and prism. 
     Therefore, it would be desirable to provide a binocular system that can eliminate visualization of the reticle when viewing a displayed image. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a system and method for removing a reticle from visualization in a displayed view in a binocular wherein the reticle is visible during direct scene view. The system comprises a filter positioned between a display element and an eyepiece wherein a visual characteristic of the filter matches a corresponding characteristic of the reticle. These matching characteristics thereby render the reticle substantially “invisible” to the user when viewing the displayed scene. 
     The features that characterize the invention, both as to organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description used in conjunction with the accompanying drawing. It is to be expressly understood that the drawing is for the purpose of illustration and description and is not intended as a definition of the limits of the invention. These and other objects attained, and advantages offered, by the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  (prior art) is a schematic diagram of an optical arrangement of a binocular. 
         FIG. 2  (prior art) is a schematic diagram of an optical arrangement of a binocular having a display added to one side thereof. 
         FIG. 3  is a schematic diagram of an optical arrangement having a filtered display. 
         FIG. 4  is a representation of a front plan view of a reticle designed for green illumination. 
         FIG. 5  is a graph of a bandpass for a matched display filter and reticle lines. 
         FIG. 6  is a graph of a bandpass for an unmatched display filter and reticle lines. 
         FIG. 7  is a schematic diagram of an optical arrangement including a polarized display having reticle lines aligned with the polarization direction. 
         FIGS. 8A-8C  are representations of photographs of a polarization strip being rotated for full transmission ( FIG. 8A ), partial transmission ( FIG. 8B ), and zero transmission ( FIG. 8C ). 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A description of the preferred embodiments of the present invention will now be presented with reference to  FIGS. 3-8C . 
     The system and method of the present invention serves to remove a reticle from visualization in a displayed view in a binocular wherein the reticle is visible during direct scene view. 
     In a first embodiment ( FIGS. 3-6 ) the system  30  comprises a narrowband, monochromatic filter  31  positioned in the display path. As illustrated in  FIG. 3 , an exemplary location of the filter  31  can be between the display  32  and projection optics  33  upstream of the filter  31 , and the reticle  34  and eyepiece  35  downstream of the filter  31 . 
     The display  32  in this embodiment can comprise, for example an LCD display illuminated with a narrowband LCD, although this is not intended to be limiting, and a single-color OLED-type display could also be used. These options are energy-efficient during display use. 
     The reticle  34  can comprise, for example, a glass substrate, which has a high transmission in the visible. The reticle lines  36  (see  FIG. 4 ) can be deposited on the substrate  37 , the lines  36  transmitting the display color and thereby made substantially invisible to the user  38 .  FIG. 4  is a representation of a photograph of a reticle  34  designed for green illumination. 
     It is important that the transmission and waveband of the filter  31  and reticle lines  36  be well controlled to ensure that the appearance of the lines  36  be minimized against the display  32 . One method includes matching the spectra of the display illumination  39  and the lines  40  as closely as possible, with a substantially step-function shape, with substantially either full or no transmission ( FIG. 5 ). 
     In another method, the spectra of the filter  41  and reticle lines  42  are not matched ( FIG. 6 ); however, the display spectrum  41  is fully within that  42  of the reticle lines  42 , and out-of-bandwidth transmission of the filter  41  is preferably low. 
     In the examples of  FIGS. 5 and 6 , the reticle lines  36 , 42  appear against a white-light background as having color when the user is using the binoculars for direct view, and the lines  36 , 42  substantially disappear when the user is using the binoculars for display view. 
     Experiments were undertaken wherein a blue filter was placed partially in the field at the reticle, appearing as a section of a circle; a similar blue filter was also placed partially in the field of the display, which also appeared as a section. The resulting photographs (reported but not included) illustrated that the images were substantially similar. It will be understood by one of skill in the art that other colors could be used, and, in fact, red may be preferable to minimize the impact on night vision. 
     In another experiment, green lines were deposited on a substrate, and a full filter with the same bandpass was placed downstream of the display. The lines appeared clearly in the white-light view, but substantially disappear on the display view. 
     Another embodiment of a system  50  for minimizing the appearance of reticle lines in a display ( FIG. 9 ) comprises a polarizer  51  positioned downstream of a display  52  and projection optics  53 . Here the reticle  54  has lines thereon that are also polarized. If the respective polarizations are aligned, the lines substantially disappear against a displayed image, but are visible against a real-world image, with an approximately 50% transmission, which provides sufficient contrast. 
     The use of this embodiment  50  is illustrated schematically to represent photographs in  FIGS. 8A-8C , wherein a thin strip of polarizing plastic was placed in the field at the reticle  54 . When oriented to transmit the reticle  54  ( FIG. 8A ), the line  55  is clearly visible; as the reticle  54  is rotated, the lines fade ( FIG. 8B ) and then become substantially transparent ( FIG. 8C ). 
     Another polarizing element for this embodiment  50  could comprise a wire grid having a transmission similar to that of glass, that is, approximately 96%. 
     If, for either a spectral or polarization embodiment, the transmission of the reticle is insufficiently proximate to the transmission of the substrate, it would be preferable to adjust the substrate transmission. For example, in the case of the wire grid embodiment  50 , which may achieve approximately a 90% transmission, an antireflection coating could be used on the back of the substrate to avoid loss of energy at this point. The front of the substrate could be masked at the reticle line locations, and then the substrate coated to achieve 90% transmission. The mask would then be removed, and polarized lines could be deposited, having 90% transmission of parallel polarization. 
     In this device, the reticle is approximately 50% effective against random polarization, and better matches the substrate for parallel polarization. Reducing substrate transmission to match the reticle will reduce overall transmission for the direct view mode, however. 
     In the foregoing description, certain terms have been used for brevity, clarity, and understanding, but no unnecessary limitations are to be implied therefrom beyond the requirements of the prior art, because such words are used for description purposes herein and are intended to be broadly construed. Moreover, the embodiments of the apparatus illustrated and described herein are by way of example, and the scope of the invention is not limited to the exact details of construction or use.