Abstract:
An optical sight for a photocamera viewfinder or for an aiming device of a firearm comprises a combination of a light emitting diode (LED) with a plurality of reticle patterns applied onto the surface of the LED and selectively illuminated by connecting various portions of the reticle patterns to the source of electric power supply. The switching from one reticle pattern to another is carried out electrically without the use of moving parts of the reticles or reticle images. This ensures high accuracy in positioning of reticle elements with regard to each other, e.g., with regard to the front sight center of the partially transparent mirror, and hence, with regard to the ballistic trajectory of the bullet.

Description:
FIELD OF THE INVENTION 
     The present invention relates to optical sights, in particular to an optical gun sight with reticle patterns switchable for adaptation to various shooting conditions. More specifically, the invention relates to an optical sight, such as, e.g., a gunsight or a camera viewfinder, in which reticle patterns are switched electronically without mechanical movements. 
     BACKGROUND OF THE INVENTION 
     Optical sights are used in viewfinders for aiming photocameras or in firearms for accurate aiming of rifles, pistols, shotguns and the like. In firearms, these optical sights are typically mounted in an elongated tubular barrel or housing carrying conventional ocular and objective lens systems. An erector-lens system is provided between the ocular and objective systems to provide an erect target image for viewing by the shooter. Windage and elevation adjustments permit the sight to be compensated for targets at varying ranges. 
     For example, a conventional optical sight includes a reticle, typically of cross hair or post form, which is seen by the shooter in silhouette and superimposed over the target image. The position of the firearm is adjusted until the reticle is positioned on a target-image aiming point. The primary advantage of an optical sight is that the target image and reticle are in the same focal plane, eliminating any need for the shooter to shift eye focus between sight and target as must be done with conventional open sights on a rifle. The optical sight may provide fixed or variable magnification of the target image, but such magnification is not an essential feature and is subsidiary to the primary goal of providing a target image and aiming reticle in a single focal plane. 
     Conventional reticles are highly satisfactory during conditions of full daylight, but most hunting for game animals is done under restricted lighting conditions before sunrise or just before dark. This is because most game animals are nocturnal feeders, and their search for food is made in darkness or in the relatively short periods just before or after full darkness. A conventional optical sight is difficult to use in these conditions of subdued lighting because the reticle is seen in silhouette against a low-contrast dimly lit image of the target and target background. It is not uncommon for a hunter to lose sight of the reticle entirely while attempting to aim at a game animal standing or moving against a dark background of brush or trees. In such conditions, the firearm cannot be accurately sighted, and the animal will probably escape. 
     The “fading reticle” problem is solved by illuminating the reticle itself (e.g., electrically heated incandescent reticles have been proposed), or preferably by providing a luminous dot or other mark at the aiming point of the sight. Details of the latter solution are shown in U.S. Pat. No. 3,672,782 issued in 1972 to A. Akin. This patent shows a an optical sight with a battery-operated internal lamp, which projects a luminous reticle pattern (dot, cross hair, circle, etc.) on the sight field of view and centered on the sight aiming point. The optical sight of this patent is provided with multiple reticles, which can be selectively switched to a working position in compliance with the shooting conditions. This is achieved with the use of a flexible strip of a plastic material wound on extends between a pairs of shafts. The strip is generally opaque but defines specific transparent zones forming a plurality of reticles. Rotation of the shafts moves strips in certain fashion within a chamber in the mounting leg, and rotation is continued until a selected reticle is positioned for projection onto an ocular focal plane of the sight. Positions of the reticles are fixed with the use of spring-loaded knobs. 
     A disadvantage of the device of U.S. Pat. No. 3,672,782 consists in that the sight contains moveable parts and that the strip moves back and forth. Such a system, normally, has significant plays, which impair positioning of the reticles in the focal plane, and thus impairs accuracy of shooting. 
     U.S. Pat. No. 4,554,744 issued in 1985 to C. Huckenbeck is directed to an improved illuminated-reticle optical sight having a very compact battery-housing and actuating-switch assembly, which enhances the styling of the instrument, and is simple and convenient for the shooter to use. Though the optical sight of this device does not have moveable parts, it also does not have selectivity of reticles. 
     U.S. Pat. No. 4,618,221 issued in 1986 to R. Thomas describes an adjustable telescopic sight having objective lenses, intermediate lenses, and an eyepiece. The sight is provided with an adjustable reticle device, which is disposed in the second focal plane intermediate, the eyepiece and the intermediate lenses. The adjustable reticle device is provided with a fixed centerline reticle and two identical moveable reticles located on opposite sides of the centerline reticle. The moveable reticles are each supported by a carrier, which is moveable in two orthogonal directions by means of two threaded stems carried by the body of the adjustable reticle device. The stems are each provided with knurled knobs, each of which has two arrows thereon disposed at right angles to each other on the side of the knob facing the shooter so that the shooter can readily determine the direction of movement of bullet impact upon rotation of a knob in any specific direction. 
     Although this device is capable of adjusting position of a reticle with relatively high accuracy due to micrometric movements and of selecting reticles of a few types, the choice of reticles is very limited and the adjustment is carried out due to movement of reticle parts. 
     International Patent Publication WO 00/50836 of Aug. 31, 2000 issued to K. Gunnarsson, et al. describes an optical sight with a reticle produced by projecting a reticle image from a transparent media onto a concave semitransparent mirror. The source of light is a light emitting diode (LED), which is located on a sidewall within a tubular casing of the optical sight. The LED, the transparent media with the reticle image, the semitransparent concave mirror, and the eye of the viewer form an optical system, in which the reticle image is reproduced on the eye retina, while the image of the reticle is located on the optical axis of the optical system and is seen by the eye as if it is located in the infinity or in a very remote zone. During shooting, the reticle is aligned with the image of the target, which is also seen by the viewer&#39;s eye. Such a system ensures accurate aiming and is free of moveable parts. Furthermore, the sight of the type disclosed in WO 00/50836 is a sight of a collimating type, which does not have an optical eyepiece on the viewer&#39;s side and therefore has a not limited eye relief. An eye relief is a distance from the viewer eye to the sight. However, this system has only one reticle and cannot be adjusted for different shooting conditions. 
     In order to solve the above problem, American Technologies Network Corporation, South San Francisco, Calif., has developed an optical sight of the type described in WO 00/50836, but with a turret head that contains a plurality of reticle images, which can be selectively switched to a position aligned with the optical axis by rotating the turret head. Such a system makes it possible to select reticles in compliance with the shooting conditions, shooter&#39;s vision conditions, shooter&#39;s hunting habits, type of the target, etc. Nevertheless, the turret-type reticle switching mechanism has moveable parts and therefore has inevitable plays in the rotary mechanism. Since the image of the reticle is projected to the infinity and is seen as a virtual image, even slightest deviations of the reticle image projection from the optical axis will impair accuracy of shooting. 
     Thus, all known switchable optical sights of the types described above cannot ensure stability in positioning of the reticle with respect to the center of the partially transparent mirror or pellicle, and hence, with respect to the ballistic trajectory of the bullet. This is because the plays existing in the switching mechanisms with the moveable reticles or reticle elements cannot provide aforementioned positioning accuracy. 
     OBJECTS OF THE INVENTION 
     It is an object of the invention is to provide an optical sight for use in viewfinders of photocameras, or in aiming devices of fire arms, which is simple in construction, inexpensive to manufacture, has no moving parts, and ensures selection of reticle types and images in a wide range in compliance with the shooting conditions. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a general schematic side view of the optical sight of the invention. 
     FIG. 2A is a view of the LED in the direction of arrow A of FIG.  1 . 
     FIG. 2B is a sectional view along the line IIB—IIB of FIG.  2 A. 
     FIG. 3 is a more detailed image of the pattern of reticle elements with an electrical circuit. 
     FIGS. 4 and 5 illustrate examples of other patterns of reticle elements. 
    
    
     SUMMARY OF THE INVENTION 
     An optical sight for a photocamera viewfinder or for an aiming device of a firearm comprises a combination of a light emitting diode (LED) with a plurality of reticle patterns applied onto the surface of the LED and selectively illuminated by connecting various portions of the reticle patterns to the source of electric power supply. The switching from one reticle pattern to another is carried out electrically without the use of moving parts of the reticles or reticle images. This ensures high accuracy in positioning of reticle elements with regard to each other, e.g., with regard to the front sight center of the partially transparent mirror, and hence, with regard to the ballistic trajectory of the bullet. 
     DETAILED DESCRIPTION OF THE INVENTION 
     A general schematic side view of the optical sight of the invention is shown in FIG.  1 . In the embodiment shown in FIG. 1, the optical sight  20  of the invention is implemented as a firearm sight or a firearm-aiming device. The device consists of a mounting plate  22 , which is attachable to a firearm, e.g., with the use of a dovetail connection and locking screw (not shown). The mounting plate  22  has on its distal end  24  (which is the end nearest to the target) a vertically arranged partially transparent pellicle or mirror  26  with a red-light reflection coating  28  applied onto a slightly concave surface of the mirror  26  formed on the side of the mirror facing a viewer. In FIG. 1 the viewer is represented by an image of a human eye  30 . The aforementioned coating  28  may have properties of a narrow-band mirror which passes all wavelengths except for the wavelength of 650±10 nm, which is seen as a red light. 
     On the proximal side  32 , the mounting plate  22  supports a vertical bracket  34  with an opening  36  through which the viewer&#39;s eye  30  can see the target (not shown) through the partially reflecting mirror  26 . An eyepiece  38  can be attached to the rear side of the bracket  34  for convenience of the viewer. 
     A light-emitting diode (LED)  40  is installed on the mounting plate  22  in the proximal part of the optical sight  20  and in a position offset from the optical axis X—X. The LED  40  is spaced from the coating  28  at a distance equal to half the radius of the curvature on the concave surface of the mirror so that the light beam B 1  emitted from the LED  40  is reflected from the mirror coating  28  as a collimated beam B 2 . It is understood that the mirror coating  28  is perpendicular to beam B 2 . If beam B 2  carries an image (reticle), this image will be localized on the retina of the viewer&#39;ss eye and will be seen as if it is located in the infinity. When the target appears in the vision field of the viewer, the latter moves the reticle image, and hence the rifle, to which the sight  20  is attached, and aims the weapon to the target by superposing the reticle image onto the target image. Reference numeral  42  designates a power source, e.g., a lithium battery, which supplies electric current to the LED  40 . To this point of the explanation, the optical sight is generally the same as the conventional optical sight with a reticle illuminated by a LED. 
     A distinguishing feature of the optical sight of the invention is a set of reticle elements and a method of generation of selected reticles, which can be aligned with the optical axis of the sight by using electric means, i.e., without moving any parts of reticles or reticle combinations. 
     More specifically, as shown in FIG. 2A, which is a view of the LED  40  in the direction of arrow A of FIG. 1, the reticle is formed on the outer surface of the LED  40 . FIG. 2B is a sectional view along the line IIB—IIB of FIG.  2 A. The arrangement of the LED shown in FIG. 2B is known as TO-CAN. This term is used for opto-electronic components mounted in closed containers with a transparent window. The LED unit consists of a metallic LED holder  41  which supports the LED  40 . The LED  40  is covered with a cup-shaped cover  43 . The upper electrodes (which will be described later) of the LED  40  are connected to output terminals  45   a ,  45   b ,  45   c  which protrude outside the LED assembly through insulators  47   a ,  47   b ,  47   c  (FIG.  2 A). 
     A more detailed image of the reticle and of the pattern of reticle elements is shown in FIG.  3 . As can be seen from FIG. 3, the reticle consists of a central light spot  46  and a plurality of luminous bars, in this case of four luminous bars  48 ,  50 ,  52 , and  54 . These luminous bars constitute the aforementioned upper electrodes of the LED  40 . The bars  50  and  54  are arranged symmetrically on both sides of the light spot  46  on a horizontal line X 1 —X 1 , while the bars  48  and  52  are arranged symmetrically on both sides of the light spot  46  on a vertical line Y 1 —Y 1 . Thus, the light spot  46  is located in the center of a cross formed by the luminous bars  48 ,  50 ,  52 , and  54 . 
     The luminous bars  48 ,  50 ,  52 , and  54  can be formed on the surface of the LED  40 , e.g., by a method of photolithography from a conductive material, e.g., from aluminum or chromium. In one model of the sight of the invention tested by the applicant, the LED  40  was a custom-made homo-transition type LED based on epitaxial structures of gallium arsenide phosphide alloy/gallium arsenide alloy (GaAsP/GaAs). The LED  40  was made with a large surface (with a diameter of about 2 to 3 mm) on which the radiation elements are formed so that it would be possible to perform the aforementioned photolithography. Each element of the reticle, i.e., a bar or a light point, is a closed-loop contour in the form of an elongated rectangle or a circle, so that the perimeter of the closed-loop contour determines the shape of the reticle element, i.e., rectangles, lines, circles, parts of the circle, dots, etc. As shown in FIG. 3, the upper electrodes or luminous bars  48 ,  50 ,  52 , and  54  and the light spot  46  are connected to a positive terminal  56   a  of a source of power supply  56 , e.g., a lithium battery via an electric circuit with an electric switch  58 . A negative terminal  56   b  of the power source  56  is connected to the metallic LED holder  41  (FIG.  2 B). Thus, a negative potential of the power source  56  is applied to the metallic holder  41 , which is in contact with the bottom of the LED  40 , while a positive potential is applied to the selected upper electrode which is represented by the selected elements of the reticle. The switch  58  can be a rotary type switch, a button-type switch, or an electronic switch. In the general view of the sight shown in FIG. 1, the control element of the switch  58  is shown as a rotary knob  59  which can be switched between four positions, i.e., a position “1”, a position “2”, a position “3”, and a position “OFF”. As shown in FIG. 3, the switch  58  has three switchable contacts SW 1 , SW 2 , and SW 3 , which can be closed or opened in various combinations determined by the aforementioned positions of the knob  59 . The light point  46  is connected to the switch  58  via a conductor  60 , a contact point  62  on the surface of the LED  40 , and a conductor  64 . The luminous bar  48  is connected to the switch  58  via a conductor  66 , a contact  68  on the surface of the LED  40 , and a conductor  70 . The luminous bars  50 ,  52 , and  54 , which are connected parallel to each other via conductors  72 ,  74 , and  76 , are connected to the switch  58  via a conductor  78 , a contact  80  on the surface of the LED  40 , and a conductor  82 . 
     At the maximum of its radiation, this LED generated red light of 65±10 nm. With the d.c. current of 20 μA, the LED  40  produced light with the brightness of not less than 150 μcd. 
     Operation temperature ranged from minus 60° C. to plus 70° C. 
     The reticle pattern shown in FIG. 3 makes it possible to select the following reticle shapes: a light point  46 , a light point  46  in the center of a cross formed by the luminous bars  48 ,  50 ,  52 , and  54 , a combination of the light point  46  with the luminous bars  50 ,  52 , and  54 . It is understood that this simplified pattern was shown only as an example that illustrates the principle of the invention. It is understood that many other patterns and combinations of luminous elements are possible. Examples of other patterns are shown in FIGS. 4 and 5. The pattern of FIG. 4 consists of a central light spot  84 , two horizontal luminous bars  86  and  88  arranged symmetrically on both sides of the light spot  84 , and two arched elements  90  and  92  with outward radial projections. The elements  90  and  92  are also arranged symmetrically in a vertical direction with respect to the light point  84 . In the example of FIG. 5, the reticle is formed by a central light point  94  with two concentric luminous elements  96  and  98 , each consisting of arched portions separately connected to the power source via respective conductors (not shown). In this embodiment, the light point  94  can be combined with either of the circular reticles  96  and  98 , or can be combined with both of the at the same time. 
     OPERATION OF THE OPTICAL SIGHT OF THE INVENTION 
     In operation, when a hunter needs to select a specific reticle combination which to the most extent satisfies his/her needs with regard to the shooting conditions, shooting habits, type of a target, etc., he/she selects one position of the switch  58 . For example, when only a light spot  46  is needed in the reticle of FIG. 3, the switch  58  is installed to a position, in which the light point  46  is electrically connected to the switch  58  via a conductor  60 , a contact point  62  on the surface of the LED  40 , and a conductor  64 . In this selection, which corresponds, e.g., to the position “1” of the knob  59 , the switchable contact SW 1  is closed and the switchable contacts SW 2  and SW 3  are open. When it is necessary to illuminate a light point  46  and the cross formed by the luminous bars  48 ,  50 ,  52 , and  54 , all three switchable contacts SW 1 , SW 2 , and SW 3  are closed (position “2” of the knob  59 ), and when it is necessary to select a combination of the light point  46  with the luminous bars  50 ,  52 , and  54 , the switchable contacts SW 1  and SW 3  are closed, while the switchable contact SW 2  is opened (position “3” of the knob  59 ). Position “OFF” of the knob  59  corresponds to the condition when all elements of the reticle are disconnected from the source of power supply  56 . It is understood that the switchable contacts are interlocked in such a manner that switching of contacts from one position to another automatically selects right position for the switchable contacts of the selected pattern and eliminates combination of the switchable contacts corresponding to the previous pattern. 
     Once the reticle pattern is selected, the shooter tries to find the target in the vision field of the optical sight  20  while constantly observing the reticle  44  as seen as if it is located in the infinity or in a very remote zone. The reticle  44  is aligned with the image of the target, which is also seen by the shooter&#39;s eye. 
     Thus, it has been shown that the invention provides an optical sight for use in viewfinders of photocameras, or in aiming devices of fire arms, which is simple in construction, inexpensive to manufacture, has no moving reticles or reticle elements, and ensures selection of reticle types and images in a wide range in compliance with the shooting conditions. Although the invention has been shown and described with reference to specific embodiments, it is understood that these embodiments should not be construed as limiting the areas of application of the invention and that any changes and modifications are possible, provided these changes and modifications do not depart from the scope of the attached patent claims. For example, the optical sight of the invention can be used in riflescopes, camcoders, telescopes, telescopic tubes, binoculars, surveying tools, navigation instruments, microscopes, optical micropositioning devices, etc. An unlimited variety of reticle patterns are possible, such as squares, triangles, ovals, hair lines, semi circles, or their combinations. The sight itself can be an open type or enclosed in a tubular housing. The brightness of the reticle image can be adjusted by changing the current supplied to the LED. The current adjustment control can be connected via a feedback line to an automatic exposure meter for automatically adjusting the reticle brightness in compliance with the environmental lighting conditions. The LED may emit light other than red.