Abstract:
A weapon sight has an optical system that causes first radiation to propagate along a path of travel within the sight, and has a reticle generating portion that causes second radiation representing a reticle to propagate along the path of travel with the first radiation. The reticle generating portion includes a reticle illuminating portion that illuminates the reticle. The reticle illuminating portion includes a first light source having thereon a surface, light from the first light source passing through the surface and then illuminating the reticle. The reticle illuminating portion also includes a second light source spaced from the first light source, light from the second light source traveling toward the surface, being reflected and then illuminating the reticle.

Description:
TECHNICAL FIELD OF THE INVENTION 
     This invention relates in general to weapon sights and, more particularly, to techniques for illuminating a reticle in a weapon sight. 
     BACKGROUND OF THE INVENTION 
     Over the years, various techniques have been developed to help a person accurately aim a weapon such as a rifle. One common approach is to mount a sight or scope on the weapon. A person then uses the sight or scope to view an image of a scene that includes an intended target. Existing sights typically impose a reticle on the image of the scene. For example, the reticle may be in the form of crosshairs. 
     Under certain circumstances, it may be advantageous if the reticle is illuminated. Various techniques have previously been developed for illuminating a reticle. Although these known techniques have been generally adequate for their intended purposes, they have not been satisfactory in all respects. 
     SUMMARY OF THE INVENTION 
     One of the broader forms of the invention involves: causing first radiation to propagate along a path of travel within a weapon sight; causing second radiation representing a reticle to propagate along the path of travel with the first radiation; causing light from a first light source to pass through a surface of the first light source and to then illuminate the reticle; and causing light from a second light source spaced from the first light source to travel toward the surface, to be reflected, and to then illuminate the reticle 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A better understanding of the present invention will be realized from the detailed description that follows, taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a diagrammatic view of an apparatus that is an optical sight for a weapon, and that embodies aspects of the present invention. 
         FIG. 2  is a diagrammatic view showing a portion of the sight of  FIG. 1  in an enlarged scale. 
         FIG. 3  is a diagrammatic view showing a configuration that is an alternative embodiment of the configuration shown in  FIG. 2 . 
         FIG. 4  is a diagrammatic view of a configuration that is an alternative embodiment of the configuration shown in  FIG. 3 . 
         FIG. 5  is a diagrammatic view of a configuration that is yet another alternative embodiment. 
         FIG. 6  is a diagrammatic view of a configuration that is an alternative embodiment of the configuration of  FIG. 5 . 
         FIG. 7  is a diagrammatic view of still another configuration, which in an alternative embodiment of the configuration shown in  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a diagrammatic view of an apparatus that is an optical sight  10 , and that embodies aspects of the present invention. The sight  10  is designed to be mounted on a not-illustrated weapon, such as a rifle or pistol. A person uses the sight  10  to accurately aim the weapon. In particular, radiation from a remote scene  11  travels through the sight  10  along a path of travel  13  to the eye  12  of the person who is using the sight. 
     The sight  10  has a housing that is represented diagrammatically in  FIG. 1  by a broken line  16 . An optical system is provided within the housing  16 , and includes an objective lens  17 , a prism assembly  18 , and an eyepiece lens  21 . Radiation from the scene  11  that is traveling along the path of travel  13  passes successively through the objective lens  17 , prism assembly  18 , and eyepiece lens  21 . The prism assembly  18  is a configuration of a known type, and includes three prisms  26 ,  27 , and  28 . The prism assembly  18  includes several prism surfaces that reflect the radiation as it travels through the prism assembly  18  along the path of travel  13 . One of these surfaces is identified by reference numeral  31  in  FIG. 1 . 
     An optical coating  32  of a known type is provided on the prism surface  31 . The coating  32  is reflective to visible radiation that is traveling along the path of travel  13 . In a known manner, the coating  32  has at least one not-illustrated opening etched through it, in the shape of a reticle. For example, the reticle may have the form of crosshairs of a known type. The sight  10  further includes a reticle illuminating portion  41 , which is represented diagrammatically in  FIG. 1  by a broken line. Preexisting sights have a reticle illuminating portion that is simply a light source located behind the optical coating  32 . Light from the known light source impinges on the rear side of the optical coating  32 , and part of this radiation passes through the openings in the coating  32  that define the reticle. But in the disclosed embodiment of  FIG. 1 , the reticle illuminating portion  41  is different. 
     More specifically,  FIG. 2  is a diagrammatic view showing a portion of  FIG. 1  in an enlarged scale, including a portion of the prism  28 , a portion of the coating  32 , and the internal structure of the reticle illuminating portion  41 . As shown in  FIG. 2 , the reticle illuminating portion  41  includes a tritium light source  51 . In  FIG. 2 , the tritium light source  51  is a radioluminescent capsule of a type known in the art. More specifically, tritium is a radioactive isotope of hydrogen with atoms having three times the mass of ordinary light hydrogen atoms. The tritium material is provided within a capsule that is made from glass or some other suitable material, and that has a phosphor coating on its inner surface. As the tritium material decays, it emits soft beta rays that, when they strike the phosphor coating, are converted to visible light. The half life of tritium is approximately 12.5 years, and thus the tritium light source  51  has a usable life of more than 15 years. Consequently, the tritium light source glows continuously for a long time, thereby providing a safe and reliable source of light, without any need for a power source such as a battery. 
     The reticle illuminating portion  41  also includes two small lenses  52  and  53 . Light  56  emitted by the tritium light source  51  passes successively through the lenses  52  and  53  toward the coating  32 , and some of this radiation then passes through the not-illustrated openings in coating  32  that define the reticle. In the disclosed embodiment, the lens  52  has a relatively short focal length, so that it collects light over a large solid angle. Stated differently, the lens  52  has a high numerical aperture (NA). The radiation traveling away from the lens  52  is collimated, or in other words is projected to infinity. This collimated radiation is collected by the lens  53 . The lens  53  has a focal length selected so that it collects all the energy from the lens  52 , and converts this energy into a solid angle that matches the eyepiece optics  21  ( FIG. 1 ). Since this solid angle is smaller than the solid angle used for collection by the lens  52 , the lenses  52  and  53  collectively provide an increase in brightness of the illumination of the reticle at the coating  32 , in comparison to the brightness that would be realized if the lenses  52  and  53  were not present. 
     In  FIG. 1 , the objective lens  17 , prism assembly  18  and the eyepiece lens  21  represent a simple and exemplary optical system. The reticle illuminating portion  41  of  FIG. 2  can be used not only in the optical system of  FIG. 1 , but also in a variety of other optical systems. 
       FIG. 3  is a diagrammatic view showing a configuration for reticle illumination that is an alternative embodiment of the configuration shown in  FIG. 2 . The embodiment of  FIG. 3  includes all of the elements shown in  FIG. 2 , as well as some additional elements. The following discussion focuses primarily on the additional elements. In particular, a beam splitter of a known type is disposed optically between the lenses  52  and  53 . The beam splitter is transmissive to radiation having one wavelength or color, and is reflective to radiation at a different wavelength or color. In  FIG. 3 , the radiation  56  from the tritium light source  51  passes through the beam splitter  81  as it travels from the lens  52  to the lens  53 . 
     The embodiment of  FIG. 3  includes a fluorescent fiber  82  of a known type. As known in the art, the fiber  82  has a core that is made from a material such as polystyrene, and that is surrounded by a cladding made from a material such as a clear acrylic. The core is doped with a special fluorescent dye. Ultraviolet light can pass through the cladding and into the core, where the fluorescent dye absorbs the ultraviolet light and then emits visible light. The material of the dye determines the color of the visible light that is produced. Due to differences in the refractive indexes of the cladding and core, the visible light is trapped within the core, and is reflected to the ends of the fiber  82 . 
     The fiber  82  has a distal end that is not visible in  FIG. 3 , and that is disposed externally of the weapon sight  10 . The distal end of the fiber  82  can pick up ultraviolet light from sources such as sunlight, when the ambient light around the sight includes ultraviolet light. When this ultraviolet light enters the distal end of the fiber  82 , it generates visible light in the manner discussed above. The visible light then travels through the fiber  82  to the illustrated end, where it is emitted from the fiber. 
     A small lens  83  is provided between the beam splitter  81  and the illustrated end of the fiber  82 . Visible light emitted from the end of the fiber  82  passes through the lens  83 , travels at  86  to the beam splitter  81 , is reflected by the beam splitter  81 , travels to and passes through the lens  53 , and then propagates toward the coating  32 . The lens  83  is selected to maximize the coupling efficiency between the numerical aperture (NA) of the fiber  82  and the numerical aperture of the eyepiece optics. The lens  83  is similar to the lens  52 , in that it has a relatively high numerical aperture, or in other words a very short focal length, so that it can collect light over a large solid angle. The lens  53  converts that radiation into a solid angle that is smaller than the solid angle used for collection by the lens  83 . Thus, as seen by the coating  32 , the lenses  83  and  53  collectively provide an increase in brightness of the light emitted from the end of the fiber  82 , in comparison to the brightness that would be realized if the lenses  83  and  53  were not present. 
     When the weapon sight  10  is in an environment where the ambient light includes sunlight or some other source of ultraviolet radiation, the visible light emitted from the fiber  82  is significantly brighter than the light emitted by the tritium light source  51 . Thus, in this type of situation, the illumination of the reticle is effected primarily by the light produced by the fluorescent fiber  82 . In contrast, when the weapon sight  10  is being used in darkness or some other environment that has little or no ultraviolet light, the fiber  82  will be emitting little or no visible light, but the tritium light source  51  will still be active and will provide suitable illumination for the reticle. 
     In  FIG. 3 , the tritium light source  51  and the fiber  82  are selected so they produce light with different colors, and thus different wavelengths. The beam splitter  81  is designed to transmit substantially all light at the wavelength of the tritium light source  51 , and to reflect substantially all light at the wavelength of the fiber  82 . Alternatively, however, the tritium light source  51  and the fiber  82  could be selected so that they produce light at substantially the same wavelength and color, and the beam splitter  81  could be selected so that it transmits approximately half of the light at this wavelength and reflects approximately half of the light at this wavelength. Of course, this latter approach is less efficient than the former in terms of how much radiation from either source will ultimately reach the coating  32 . 
       FIG. 4  is a diagrammatic view of a configuration that is an alternative embodiment of the configuration shown in  FIG. 3 .  FIG. 4  is identical to  FIG. 3 , except that the fluorescent fiber  82  of  FIG. 3  has been replaced with a light emitting diode (LED)  91 . The LED  91  is powered by a not-illustrated battery within the weapon sight  10 , and a not-illustrated manual switch would typically be provided in series with the battery. The switch can be manually operated so that the LED  91  is selectively turned on and off. The operation of the embodiment of  FIG. 4  is similar to the operation of the embodiment of  FIG. 3 , and is therefore not described in detail here. 
       FIG. 5  is a diagrammatic view of configuration that is yet another alternative embodiment. In  FIG. 5 , the tritium light source  51  has a relatively flat surface  112  with an optical coating  111  thereon. An LED  114  is provided at a location spaced from the tritium light source  51 . Light from the tritium light source  51  passes through the surface  112  and the optical coating  111 , and travels at  116  toward the coating  32  on the prism surface  31 . Light from the LED  114  travels at  117  to the coating  111 , where it is reflected and then travels at  116  toward the coating  32 . The tritium light source  51  is oriented so as to place the surface  112  and the coating  111  at an angle that will cause light from the LED  114  to be reflected in a direction toward the coating  32 . A not-illustrated battery and a not-illustrated manual switch are coupled in series with the LED  114 . 
     In  FIG. 5 , the tritium light source  51  and the LED  114  produce light at different wavelengths, and the coating  111  is configured to transmit light at the wavelength of the tritium light source  51 , and to reflect, light at the wavelength of the LED  114 . Alternatively, however, the tritium source light  51  and the LED  114  could produce light at approximately the same wavelength, and the optical coating  111  could be configured so that approximately half of the light at this wavelength is transmitted and the other half is reflected. In another alternative configuration, the optical coating  111  could be omitted, such that light from the LED  114  is reflected directly by the surface  112  on the tritium light source  51 . However, the provision of the optical coating  111  provides a higher degree of efficiency in reflecting light emitted by the LED  114 . 
       FIG. 6  is a diagrammatic view of a configuration that is an alternative embodiment of the configuration of  FIG. 5 . The only difference between  FIGS. 5 and 6  is that, in  FIG. 6 , a lens  151  has been added between the LED  114  and the optical coating  111 . The lens  114  has a numerical aperture (NA) that is selected to match the numerical aperture of the eyepiece optics, and serves to increase the efficiency with which radiation from the LED  114  is utilized in illuminating the reticle. 
       FIG. 7  is a diagrammatic view of still another configuration, which in an alternative embodiment of the configuration shown in  FIG. 6 . The only difference between  FIGS. 6 and 7  is that the LED  114  of  FIG. 6  has been replaced with an optical fiber  181 . The optical fiber  181  is equivalent to the optical fiber  82  that was discussed above in association with  FIG. 3 . Visible radiation emitted  117  by optical fiber  181  passes through the lens  181  on its way to the optical coating  111 . 
     Although several selected embodiments have been illustrated and described in detail, it will be understood that they are exemplary, and that a variety of substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the following claims.