Abstract:
An improved reticle for optical instruments such as telescopic sights, riflescopes and surveying telescopes, provides a primary indicator at the focal plane of the instrument and a secondary indicator spaced, axially, apart from, and viewable with, the primary indicator. When an operator&#39;s eye is properly centered on the optical axis of the instrument, the indicators provide visual feedback to the operator of such proper alignment. When an operator&#39;s eye is laterally displaced from the optical axis, the indicators provide visual feedback indicative of improper positioning of the eye. Thus, an operator may readily, and intuitively, make the necessary adjustments to the relationship of the eye to the optical axis to correct for misalignment without the need for cumbersome mechanical adjustments and special mechanisms.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to optical instruments such as telescopic sights, riflescopes, surveying telescopes, and the like, for the accurate alignment thereof with objects of interest. More particularly, the present invention relates to the reticles employed by these classes of instruments.  
           [0002]    It is well-known in the art of telescopic sights, such as riflescopes and surveying telescopes, which comprise an objective lens, or lenses, and an ocular lens, or lenses, that images of objects at different distances from an operator, being viewed by means of the optical instrument, focus at different points along the internal optical axis of the instrument. For instance, the image of a near object being viewed by an operator through the optics of such an instrument is focused at a point somewhat more rearward (closer to the ocular end) on the optical axis than is the image of a more distant object which will focus farther away from the ocular end of the optical instrument. When the optical instrument is equipped with a fixed alignment reticle, as in the case of a riflescope, this shift in focus introduces parallax error between the image of the object and that of the reticle. This means that the axially- fixed alignment reticle will not be on the same plane as the image of the object formed by the objective lens system. In this case, if the operator&#39;s eye is not perfectly aligned with the optical axis of the instrument, the images of the object and the reticle will not coincide. The result is misalignment of the object image with the image of the reticle which degrades the accuracy of optical instruments that are required to provide precise alignment of the object image with that of the reticle image.  
           [0003]    In riflescopes, parallax error is generated by the instrument being focused at a distance different from that of the target being viewed thereby in combination with the lateral displacement of the operator&#39;s eye from the optical axis. The importance of centering the eye on the optical axis of the riflescope is extremely important and is easily demonstrated. Typically, riflescopes have an eye relief of three inches to allow adequate space between the rear of the scope and the shooter&#39;s eye so that, when the rifle is discharged, the apparatus does not travel far enough back under recoil to strike the shooter&#39;s face. Considering a reasonably close target distance of one hundred yards, a one-degree deviation of the shooter&#39;s eye off-axis (a mere 0.087″ [2.2 mm] to one side) will result in a parallax error at the target of sixty-three inches. In other words, the aim is off by a distance of over five feet even though the shooter may have, otherwise, perfectly aligned the image of the crosshairs with the image of the target. Targets at greater distances will generate increasingly greater parallax error. Thus, in the example given, if the distance is increased to 200 yards, the error would double to over ten feet.  
           [0004]    Thus, when these two negative factors, parallax and displacement of the operator&#39;s eye from the optical axis, are combined, as they often are, the resulting error can be overwhelmingly great. The prior art has failed to provide visual feedback to the operator of the presence of these deleterious conditions. Until the present invention, there has been absolutely no way for the operator of instruments of these classes to be alerted to these negative conditions. The present invention remedies these defects of the prior art by providing visual indicators that serve to neutralize these negative factors that work against the accuracy of these instruments.  
           [0005]    Because of the potentially significant shift in the point of focus of images due to variations in the distance from the operator of objects of interest, some means must be provided to compensate for the discrepancies of axial alignment to eliminate the deleterious effects of parallax error which render optical alignment inaccurate for purposes where precise alignment is critical, such as the aiming of handheld hunting rifles, tactical weapons, and surveying telescopes.  
           [0006]    The prior art, such as U.S. Pat. No. 4,072,396, issued Feb. 7, 1978, to Cecil Jack Ross, has addressed this problem by providing mechanical means for the adjustment of the position of the objective lens system along the optical axis so as to move the image formed thereby to coincide with that of the alignment reticle. A severe limitation of the Ross device is that it requires coordination of the operator&#39;s hand (to turn the objective lens barrel) and eye (to observe the ‘approximate’ range-focus setting). Another major limitation of this device is it requires the user to estimate the distance to the target.  
           [0007]    A similar approach is taught by U.S. Pat. No. 3,516,736, issued Jun. 23, 1970, to William R. Weaver. The Weaver structure teaches a focusing objective for telescope sights for firearms employing a slidable lens cell and a threaded drive collar for urging the lens cell in one direction in opposition to a biasing means urging the lens cell in the opposite direction for the purpose of focusing a target image on the same plane occupied by a reticle within the telescopic sight.  
           [0008]    Another example of the prior art that seeks to overcome the problem of parallax in the alignment of optical images is taught by U.S. Pat. No. 3,336,831, issued Aug. 22, 1967, to J. Unertl, Jr. As with Ross and Weaver, Unertl utilizes a moving objective lens assembly. But, in the case of Unertl, the objective lens components are moved by a cam and pin arrangement which, according to the patent, provides greater control of the movement of the objective components. But, as in the structures of Ross and Weaver, Unertl&#39;s device requires the coordination of hand, to perform a physical act (adjustment of the objective lens barrel) and eye of the operator (to observe the ‘approximate’ range-focus setting). And, as with Ross, a limitation of the Unertl device is it depends upon the user to provide an accurate estimate of target distance.  
           [0009]    Another, and severe, drawback to the devices of the prior art such as those taught by Ross, Weaver and Unertl is that the excessive time required to estimate the target&#39;s distance and manually set the range focus before acquiring a sight picture of the target can easily mean that the target of interest may move out of sight or become aware of the user&#39;s presence due to the additional time and movements required by the act of range focusing.  
           [0010]    Perhaps the greatest drawback to the prior art as exemplified by the above references is their potential for leakage at the interface between the adjustable objective lens and the housing of the instrument. Even the smallest amount of moisture is disastrous to optical telescopes because, once inside, it vaporizes, fogging the inside lens surfaces, totally obscuring visibility through the instrument. For this reason, modern manufacturing practice in these classes of products include a final step of vacuum purging to remove all ambient air, replacing it with pure nitrogen gas which is totally inert, and, then, hermetically sealing the instrument. Such sealing is difficult to maintain in devices that utilize range-focusing objectives.  
           [0011]    A different approach to the aiming of a firearm is taught in U.S. Pat. No. 5,208,989, issued May 11, 1993, to Ronald J. Sanders. The Sanders device is directed to the aiming of a slug barrel shotgun which is a short range firearm requiring no compensation for parallax due to long range firing requirements of hunting and tactical rifled firearms and surveying instruments as contemplated by the present invention. Sanders teaches a sighting device with two plano-plano reticles, each bearing an illuminated aiming reference. There is no magnification in the optics of the Sanders device which is intended for use with firearms of the pistol class and non-firearms that require extended eye relief mounting. The Sanders structures are more akin to ‘notch and bead’ aiming arrangements than to optical instruments such as riflescopes. Thus, in applications addressed by Sanders, there is no parallax problem as in riflescopes of the magnified variety as addressed by the teachings of the present invention.  
           [0012]    U.S. Pat. No. 6,453,595, issued Sep. 24, 2002, to Dennis J. Sammut, which is a continuation-in-part of application Ser. No. 09/129,729, filed on Aug. 5, 1998, now U.S. Pat. No. 6,032,374, which is a continuation-in-part of application Ser. No. 08/986,458, filed on Dec. 8, 1997, now U.S. Pat. No. 5,920,995, discloses a reticle for riflescopes having a single so-called “ghost ring” axially centered and encircling a variety of aiming indicia, including crosshairs. The purpose of the “ghost ring” is to aid in the centering of the user&#39;s eye on the optical axis. However, how this single “ghost ring” aides the user is not entirely clear. At column 12, lines 51-53, it is stated that “By insuring that the ghost ring  41  is centered within the field of view of the scope, the reticle will likewise be centered.” However, because the overall field of view through a scope is not readily discernible by an operator it is a very unreliable reference with which to judge centering of the “ghost ring”. The reason for this is the fact that riflescopes are, as previously mentioned, designed to provide approximately three inches of eye relief (the distance from the end of the scope to the user&#39;s eye) to prevent injury from kick-back when the firearm is discharged. This distance presents the user with a sight picture that is slightly less than the overall field of view of the scope. Thus, the only thing visible to the user, other than the sight picture, is the outer ring of the ocular housing which, at three inches, appears extremely blurry and indistinct.  
         BRIEF SUMMARY OF THE INVENTION  
         [0013]    By extreme contrast, the present invention eliminates all the limitations of the prior art and permits instantaneous and intuitive, parallax-free, target acquisition with no adjustments whatsoever, no matter how varied is the distance of the target from the user. In addition, the present invention accomplishes these improvements simply and inexpensively with an easily implemented change in the configuration of the reticle utilizing fabrication means that are old and proven by years of use in the art. Furthermore, implementation of the present invention results in absolutely no increase in the cost of production for manufacturers of optical instruments. In addition, the present invention does not compromise the integrity of the hermetic sealing of the instrument.  
           [0014]    Thus, it is an object of the present invention to provide, in optical instruments such as riflescopes and surveying telescopes, and without cumbersome range-focusing mechanisms, intuitive and instantaneous axial alignment of images formed thereby to eliminate parallax error.  
           [0015]    It is another object of the present invention to eliminate the need for manual focusing of the objective lenses of optical instruments, such as riflescopes and surveying telescopes, to eliminate parallax error when aiming the instruments at objects of interest at different distances from the operator.  
           [0016]    Another advantage of the present invention is the cancellation of the deleterious effects of parallax error in the accurate aiming of optical instruments of the classes addressed by the present invention.  
           [0017]    It is yet another advantage of the present invention to provide intuitive means by which an operator may align his/her eye precisely upon the optical axis of optical instruments of these classes.  
           [0018]    Another advantage of the present invention is the elimination of the need for an operator to make any adjustments, such as for turning rings for focusing to eliminate parallax error in the aiming of optical instruments such as riflescopes.  
           [0019]    Another advantage of the present invention is the elimination of the need for an operator to estimate the distance to a target of interest in order to provide accurate aim of devices of the present invention at targets of interest at various ranges.  
           [0020]    An additional advantage of the present invention is the elimination of the need for a movable objective lens assembly in order to provide accurate aim of instruments of the classes of art addressed by the present invention.  
           [0021]    Another advantage of the present invention is the elimination of the additional time required for estimation of distance to a target of interest and the subsequent manual focusing of the objective lens to compensate for range variations.  
           [0022]    Yet another advantage of the present invention is the elimination of moving components that provide the potential for undesirable leakage between the housing and the movable components.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    [0023]FIG. 1 is a side view of an embodiment of the invention as a riflescope.  
         [0024]    [0024]FIG. 2 is a diagram of the optical components of the riflescope shown in FIG. 1.  
         [0025]    [0025]FIG. 3 is an enlarged diagrammatic side view of the reticle depicted in FIG. 2.  
         [0026]    [0026]FIG. 4 is a perspective view of the reticle shown in FIG. 2 and  3 .  
         [0027]    [0027]FIG. 5 depicts the appearance of the reticle as viewed through the ocular lens when the eye of an operator is centered on the optical axis of the riflescope.  
         [0028]    [0028]FIG. 6 is a view similar to that depicted in FIG. 4 but wherein the eye of an operator is shifted laterally off-axis by a distance of one degree (0.087″).  
         [0029]    [0029]FIG. 7 is a perspective view of the reticle of a second embodiment of the present invention.  
         [0030]    [0030]FIG. 8 depicts the appearance of the reticle of FIG. 7 as viewed through the ocular lens when the eye of an operator is centered on the optical axis of the riflescope.  
         [0031]    [0031]FIG. 9 is a view similar to that depicted in FIG. 7 but wherein the eye of an operator is shifted laterally off-axis by a distance of one degree (0.087″). 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]    For purposes of clarity and general simplicity, the present invention shall be described with regard to its embodiment as a riflescope for attachment to a firearm for the accurate aiming thereof at targets of interest to the operator, or, shooter. This is no way is to be construed as restrictive, or otherwise limiting, of the present invention&#39;s range of application in other arts, such as the art of surveying telescopes and other optical alignment instruments.  
         [0033]    An embodiment of the present invention in the form of a riflescope is shown in FIG. 1. Among numerous other components, riflescope  10  comprises a housing  12  with objective barrel  14  disposed at one end thereof and ocular barrel  16  disposed at the opposite end. Also shown are windage and elevation adjustment saddle  18  and power change ring  20 . Adjustment saddle  18  and power change ring  20  are shown only for the purpose of clarity since these components are common in modem, variable power, riflescopes, but, do not bear a direct relationship with the scope of the present invention. Contained within housing  12  are numerous optical components that are best described and understood with regard to FIG. 2.  
         [0034]    With reference to FIG. 2, objective lens  22  is carried within objective barrel  14  (FIG. 1) and ocular lens  24  is carried within ocular barrel  16  (FIG. 1). Objective lens  22  is the primary target image-forming optical element and ocular lens  24  is provided for forming a magnified image of the target and aiming reticle  36  for viewing by an operator looking into ocular lens  24 .  
         [0035]    Because a lens such as objective lens  22  forms an inverted image, riflescopes require additional optical elements intermediate of the objective and ocular lenses for the purpose of erecting the image for life-like viewing by the operator when observing the image through the ocular lens. Serving this function is erector optics tube  26  which comprises erecting lenses  28  and  30 . Together with objective lens  22 , erecting lenses  28  and  30  form a final, erect, image on image plane  32 . Ocular lens  24  is provided with means by which it can be focused upon image plane  32  so as to provide a sharp image of the target and reticle  36  for viewing by an operator. Objective lens  22 , erecting lenses  28  and  32 , and ocular lens  24  and reticle  36 , all share a common central optical axis  32 .  
         [0036]    Also, shown as a dotted line in FIG. 2, is target image focal plane  34 . Target image focal plane  34  is the plane upon which ocular lens  24  is focused for viewing by an operator.  
         [0037]    Fixedly mounted in housing  12  (FIG. 1), is reticle  36 . The elements of reticle  36  are better described and understood with reference to FIGS. 3 and 4.  
         [0038]    With reference to FIG. 3, reticle  36  is shown in a diagrammatic view from the side. Reticle  36  comprises opposing planar faces  38  and  40 . Reticle  36  may be fabricated from optically flat glass, or the like. In a prototype of the present invention, a glass reticle has a thickness of 0.100″. The significance of the thickness of the reticle will become clear as the description of the present invention proceeds.  
         [0039]    Also shown in FIG. 3 are the relationships of target image focal plane  34 , crosshairs  42 , primary indicator  44 , and secondary indicator  46 .  
         [0040]    Referring now to FIG. 4, reticle  36  is mounted within housing  12  (FIG. 2) so that planar face  38  coincides with target image focal plane  34  (FIG. 2). Carried on planar face  38  are crosshairs  42  which comprise a single vertical and horizontal line with their crossing point being precisely aligned with commonly shared optical axis  32 . Also carried on planar face  38  of reticle  36  is primary indicator  44 . Carried on opposing face  40  of reticle  36  is secondary indicator  46  which is optically identical in diameter to indicator  44 . Indicators  44  and  46  are concentric to one another and are axially centered on common optical axis  32 . It is the novelty of the relative axial displacement of indicators  44  and  46  that constitutes the subject matter of the present invention as will be explained in detail below.  
         [0041]    With reference now to FIG. 5, reticle  36  is depicted in partial view to better show the relationships of key elements of the invention. These key elements of reticle  36  are depicted as seen by an operator looking into ocular lens  24  (FIG. 2) with the viewing eye precisely aligned with common optical axis  32  (FIGS. 2, 3 and  4 ). For purposes of clarity, the target image is not depicted in the following figures of drawing. When perfectly aligned as depicted in FIG. 5, primary and secondary indicators  44  and  46  are seen to be perfectly concentric relative to one another. Therefore, the operator effectively sees only indicator  44  since its image fully covers the image of indicator  46  which is disposed on opposing face  40  of reticle  36  (FIGS. 2, 3 and  4 ). Thus, primary and secondary indicators  44  and  46  form a composite image that readily signals alignment conditions to an operator. Perfect alignment of the eye of the operator is indicated when the eye perceives an image of a single indicator (indicator  44 ) since, as mentioned, indicator  44  fully covers the view of indicator  46  when such alignment is attained. Depending upon possible variables in magnification and axial displacement, the actual diameter of indicator  46  may be slightly larger than that of indicator  44  to assure images of optically equal diameter when the composite image is viewed by an operator. The significance of these relative alignments and sizing of the indicators will be better understood and appreciated with respect to the following description of their relationships when axial alignment is not maintained as will be demonstrated in FIG. 6.  
         [0042]    With reference to FIG. 6, the eye of the operator has been shifted laterally to the left by a distance of one degree (less than one-tenth-of-an-inch) from common optical axis  32  (FIGS. 2, 3 and  4 ). A one degree shift of an operator&#39;s eye translates to an aiming error, at one hundred yards, of over five feet. This deviation from the optical axis is signaled to the operator by the obvious visible shift of the image of primary indicator  46  relative to that of secondary indicator  44 . As illustrated in FIG. 5, the slightest shift from the axial center by the eye of the operator is visually conveyed to the operator without his/her having to actually look directly at the images of indicators  44  and  46 . This is a significant feature of the present invention since the main objective of a riflescope or surveying telescope is to precisely align the image of crosshairs  42  with that of a target of interest. Thus, the operator may concentrate upon the crosshairs and target image while his/her peripheral vision checks, and, if necessary, corrects, the alignment of indicators  44  and  46 . This action very quickly becomes intuitive and automatic, thus assuring accurate aim without the deleterious effects of parallax error.  
         [0043]    As described and illustrated thus far, indicators, 44  and  46  are assumed to be of the same opaque material as crosshairs  42 . An interesting variation of the present invention is to fabricate the indicators in transparent primary complementary colors, such as red and green. When transparent complementary colors are superimposed, they produce black. Thus, when the eye of an operator is properly centered on the optical axis of the riflescope, an apparent image of a single black indicator is perceived. Even the slightest deviation of the eye from the optical axis will produce a tinge of both bright red and bright green along the edges of the image. Such color changes are readily perceived by the peripherical vision of the operator without the operator having to take his or her eye off the target of interest.  
         [0044]    Another variation would be to fabricate primary indicator  44  of the same opaque material as crosshairs  42  and fabricate secondary indicator  46  of a bright transparent color, such as red or green. When properly aligned the bright red image of secondary indicator  46  will be totally covered by that of primary indicator  44  and an operator will see no color, at all, only the black appearing image of the primary indicator.  
         [0045]    Another variation of the present invention as described thus far is shown in FIGS. 7-9.  
         [0046]    With reference now to FIG. 7, reticle  36  comprises opposing planar faces  38  and  40 . As previously described, reticle  36  may be fabricated from optically flat glass, or the like. As stated earlier, a prototype of the present invention has a thickness of 0.100″. Thus, in the prototype, faces  38  and  40  are spaced apart by the thickness of the reticle material (0.100″). Carried on planar face  38  are horizontal and vertical crosshairs  42  and primary indicator  54 . Opposing planar face  40  carries secondary indicator  56 .  
         [0047]    Indicators  54  and  56  are concentric circles of unequal diameter. Primary indicator  54  is of a larger diameter than secondary indicator  56 . The centers of indicators  54  and  56  and the crossing point of crosshairs  42  are designed so as to be centered on the optical axis of the riflescope as previously described.  
         [0048]    With reference to FIG. 8, a view of reticle  36  is shown as seen by the eye of an operator looking into the ocular lens with the eye properly centered directly on the optical axis of the riflescope. When properly aligned in this manner, the image of secondary indicator  56  appears perfectly centered inside the image of primary indicator  54  as shown in FIG. 8.  
         [0049]    [0049]FIG. 9 illustrates the effect produced by the eye of an operator being laterally displaced from the optical axis of the riflescope by an angle of one degree to the left (a lateral displacement of a mere 0.087″ [2.2 mm]). The image of secondary indicator  56  now appears eccentrically displaced to the left with regard to the image of primary indicator  54 . This shift in the relationship of the two indicators is intuitively sensed by an operator for instantaneous correction of eye positioning to restore the concentricity of the images of the indicators as shown in FIG. 8. As stated previously, a one degree deviance in the centering of the eye of the operator, as shown in FIG. 9, translates to a significant error of aim of over five feet at a distance of only one hundred yard. At a range of two hundred yards, the error would be over ten feet.  
         [0050]    In the embodiment shown in FIGS. 7-9, secondary indicator  56  is of a smaller diameter than primary indicator  54 , rather than the other way around, for a very important reason. In looking through tubular devices, the ends of the tube appear as circles, the circle at the end opposite the viewer&#39;s eye appears smaller than does the circle at the end nearer the eye. Thus, when such a tubular device is moved laterally off axis relative to the eye, the smaller, more distant circle appears to move in the same direction as the lateral displacement. In the present invention, this is also true. Therefore, it is intuitive for an operator to know in what direction the eye must be moved to regain axial alignment.  
         [0051]    While the above descriptions of the present invention contain numerous specificities, they should not be construed as limiting the scope of the invention but as mere illustrations of some of the preferred embodiments thereof. For example, the aiming indicators may be of shapes other than circles as illustrated in the embodiments presented. For example, the primary indicator may be the crosshairs, themselves, while the secondary indicator may be a second set of crosshairs spaced apart on the optical axis from the first indicator. And, in certain applications the indicators may be located in the reticle somewhere other than centered on the optical axis of the instrument. Furthermore, one, or both, of the indicators may be illuminated, or made of a self-luminous material such as tritium, so as to further emphasize the relationship between the two indicators for perfecting alignment of the instrument.  
         [0052]    Thus, the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.