Abstract:
The invention comprises a protective window for an optical sight. In accordance with one embodiment of the invention, an optical sight ( 20 ) may comprise an optical component ( 182, 300 ) transmitting an image of a scene. A protective window ( 180, 430 ) may be disposed approximate to an internal side of the optical component ( 180, 300 ) to obstruct dirt from contacting the internal side of the optical component.

Description:
RELATED APPLICATIONS 
     This application is related to copending U.S. patent. application Ser. No. 08/741,289, entitled “ALIGNMENT ELEMENT FOR MULTIPLE CHANNEL SIGHT AND METHOD”; copending U.S. patent application Ser. No. 08,741,614, entitled “RETICLE ASSEMBLY FOR OPTICAL SIGHT”; copending U.S. Patent application Ser. No. 08/741,883, entitled “CHANNEL SELECTOR FOR MULTIPLE CHANNEL SIGHT”; copending U.S. patent application Ser. No. 08/741,481, entitled “MOUNTING ASSEMBLY FOR OPTICAL SIGHT”; copending U.S. patent application Ser. No. 08/741,920, entitled MOUNTING ASSEMBLY FOR IMAGE INTENSIFIER TUBE IN OPTICAL SIGHT”. 
     TECHNICAL FIELD OF THE INVENTION 
     The present invention relates generally to optical sights, and more particularly to a protective window for an optical sight. 
     BACKGROUND OF THE INVENTION 
     Day/night sights would typically be used by military and law enforcement personnel to aim weapons used in both day time and night time conditions. Typically, a day/night sight includes an objective lens, a reticle and an eyepiece in series with parallel day and night channels. A channel selector may be used to alternatively direct an image of a target into the day or night channel. 
     In a day/night sight, the objective lens and the eyepiece may be telescopic to provide a magnified image of the target. The day channel generally uses ambient light to generate an image of the target. The image may be projected to the reticle during day time use to be viewed by the user. The night channel generally includes an image intensifier to generate an illuminated image of the target. The illuminated image may be transmitted to the reticle during night time use to be viewed by the user. The reticle may include markings for aiming the weapon. 
     A problem with day/night and other types of sights is dust enclosed within the sight. The dust may interfere with the user&#39;s view of a scene. This is especially true of telescopic sights that may magnify the dust. 
     SUMMARY OF THE INVENTION 
     Accordingly, a need has arisen in the art for an improved optical sight. The present invention provides a protective window that substantially eliminates or reduces the disadvantages and problems associated with prior optical sights. 
     In accordance with the present invention, a sight may comprise an optical component to transmit an image of a scene. A protective window may be disposed proximate to an internal side of the optical component. The protective window may be sealed to the internal side of the optical component to obstruct dirt from contacting the internal side of the optical component. 
     In one embodiment of the invention, an image intensifier tube may comprise a projecting end to project an intensified image of a scene. A protective window may be disposed between the projecting end of the image intensifier tube and an image plane. The protective window may be sealed to the projecting end to obstruct dirt from contacting the projecting end. 
     In another embodiment of the invention, a reticle assembly may include a protective window for a reticle. The protective window may be disposed between the reticle and a scene. The protective window may be sealed to the reticle to obstruct dirt from contacting the reticle. 
     Important technical advantages of the present invention include providing an improved sight. In particular, dirt enclosed within the sight is collected at a plane that is out of focus with a viewing or an image plane. Accordingly, the image of the scene may be viewed and magnified with little or no interference from dirt in the sight. 
     Still another important technical advantage of the present invention includes providing an improved image intensifier tube. In particular, a protective window may be sealed to a projecting end of the image intensifier tube. The protective window may collect dirt at a plane that is out of focus with the projecting end. Accordingly, the projecting end may be viewed and magnified with little or no interference from dirt that has settled within the sight. 
     Yet another important technical advantage of the present invention includes providing an improved reticle assembly. In particular, a protective window may be sealed to a reticle. The protective window may collect dirt at a plane that is out of focus with the reticle. Accordingly, the reticle may be viewed and magnified with little or no interference from dirt in the sight. 
     Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions, and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a side view of a telescopic day/night sight mounted to A weapon in accordance with one embodiment of the present invention; 
     FIG. 2 is a schematic drawing of the optical components of the sight of the FIG. 1; 
     FIG. 3 is a perspective view of a mirror assembly for selectively directing light into the day or night channel of the sight of FIG. 1; 
     FIG. 4 is a cross sectional view of the mirror pivot assembly of FIG. 3; 
     FIG. 5 is a exploded view of a mounting system for an image intensifier tube of the night channel of the sight of FIG. 1; 
     FIG. 6 is a cross sectional view of the mounting system for the image intensifier tube of FIG.  5 . 
     FIG. 7 is a perspective view with portions broken away of a housing for securing lenses of the sight of FIG. 1; 
     FIG. 8 is a cross sectional view of a clamping assembly for securing lenses housing of FIG. 7; 
     FIG. 9 is a perspective view of a mirror assembly for selectively directing the image of the day or night channel to a reticle assembly of the sight of FIG. 1; 
     FIG. 10 is a cross sectional view of the mirror assembly of FIG. 9; 
     FIG. 11 is an exploded view of the reticle assembly of the sight of FIG. 1; 
     FIG. 12 is a top plan view with portions broken away of the reticle assembly of FIG. 11; 
     FIG. 13 is a top plan view of an alignment element of the sight of FIG. 1; 
     FIG. 14 is a perspective view of a pair of prisms of the alignment element of FIG. 13; 
     FIG. 15 is a cross sectional view of the alignment element of FIG. 13; and 
     FIG. 16 is an exploded view of a mounting assembly of the sight of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The preferred embodiments of the present invention and its advantages are best understood by referring now in more detail to FIGS.  1 - 16  of the drawings, in which like numerals refer to like parts throughout the several views. FIG. 1 shows a perspective view of a multiple channel sight  20  for aiming a weapon  22 . The multiple channel sight  20  may be used by persons such as law enforcement and military personnel to aim the weapon  22  in disparate conditions. The weapon  22  may be a rifle or any other type of weapon system that fires an aimed projectile or aimed beam such as a laser. The multiple channel sight  20  may also be used for surveillance when not mounted on the weapon  22 . 
     In one embodiment, the multiple channel sight  20  may be a day/night sight that can be operated in day and night conditions. As shown by FIG. 1, the day/night sight  20  may include an objective lens assembly  24  at a forward end  26 , a body section  28  covered by a housing  30  and an eye piece  32  at a rearward end  34 . As used herein, the term “forward” designates a direction toward an object to be observed and the term “rearward” designates a direction toward a user of the day/night sight  20 . 
     Controls  36  for operating the day/night sight  20  may be disposed on an exterior  38  of the housing  30 . Preferably, the controls  36  are located at the top of the housing  30  so that they may be reached and manipulated with either hand of the user. Individual controls may have unique identifying embossments that allow the user to readily distinguish between the controls  36  in the dark by feel. 
     A channel selector switch  39  may also be disposed on the exterior  38  of the housing  30 . As described in detail below, the channel selector switch  39  may operate a channel selector to direct an image of a scene through one of the channels of the sight  20 . 
     An azimuth adjusting screw  40  and an elevation adjusting screw  42  for bore sighting corrections may also be provided on the exterior  38  of the housing  30 . The azimuth adjusting screw  40  allows bore sighting to be adjusted for wind speed and direction. The elevation adjusting screw  42  allows bore sighting to be adjusted for gravitational effects. 
     A protective eye guard  44  may be provided at the rearward end  34  of the sight  20 . The protective eye guard  44  may be shaped to fit around the user&#39;s eye to prevent ambient light from interfering with the user&#39;s view of the image generated by the sight. The protective eye guard  44  also prevents light generated by the sight  20  from being visible outside the sight  20 . 
     FIG. 2 illustrates optical components for one embodiment of the day/night sight  20 . The objective lens assembly  24  may collect an image of a scene. The image collected by the objective lens assembly  24  may be directed into a night channel  54  or a day channel  56 . As described in detail below, the night channel  54  may electronically intensify the image of the scene. The intensified image may be projected onto a common reticle assembly  58 . There, the image may be viewed by the user through an eyepiece  60 . As also described in detail below, the day channel  56  may relay the image of the scene onto the reticle assembly  58 . There, the user may view the image through the eyepiece  60 . 
     The day/night sight  20  may include a channel selector to alternatively direct the image of the scene into the night channel  54  or the day channel  56 . In one embodiment, the channel selector may include a first mirror assembly  64  and a second mirror assembly  66 . In this example, the first mirror assembly  64  may be disposed between the objective lens assembly  24  and entrances of the night and day channels. The second mirror assembly  66  may be disposed between exits of the night and day channels and the reticle assembly  58 . 
     An optical bench (not shown in FIG. 2) may be provided for mounting the optical components in the sight  20 . The optical bench may be one or more frames or other internal structures to which components may by mounted. The optical bench may include predefined pathways, recesses, and openings for securing the optical components in a proper spatial relation. It will be understood that the design of the optical bench will vary with the configuration and the optical components of the sight  20 . 
     In FIG. 2, the night channel  54  is located above the day channel  56  when the sight  20  is in an upright position. It should be understood that the sight  20  may be configured with the day channel  56  positioned above the night channel  54 . Additionally, the day channel  56  may be positioned along side the night channel  54 . 
     The objective lens assembly  24  of the sight  20  may be a variable zoom assembly or a single field of view assembly. For a variable zoom embodiment, the objective lens assembly  24  may include a plurality of lenses positioned along an optical axis  75 . In accordance with conventional practice, the radius of curvature of a lens will be defined as positive if the center of curvature lies rearward of the lens and will be defined as negative if the center of curvature lies forward of the lens along the optical axis. A lens will be defined as converging if the lens focusing power causes parallel light rays to converge and will be defined as diverging if the lens focusing power causes parallel light rays to appear to originate from a virtual focus. 
     For the embodiment of FIG. 2, the objective lens assembly  24  may include an objective lens  80  followed by a positive converging lens  82 , a pair of negative diverging lenses  84 , a positive diverging lens  86  and a focusing lens  88 . It should be understood that additional or disparate lenses may be used within the sight  20  in accordance with the present invention. 
     From the objective lens assembly  24 , the image of the scene passes along the optical axis  75  to the first mirror assembly  64 . As described in more detail below, the first mirror assembly  64  may include a swingable or flip-flop mirror  100  rotatable between a night position  102  and a day position  104 . In the night position  102 , the mirror  100  does not intercept the optical axis  75 . Accordingly, the image of the scene passes through the first mirror assembly  64  into the night channel  54 . 
     In the day position  104 , the mirror  100  intercepts the optical axis  75  to deflect the image of the scene into the day channel  56 . In one embodiment, the entrance of the day channel  56  is normal to the optical axis  75 . In this embodiment, the mirror  100  may intercept the optical axis  75  at a forty-five (45) degree angle to direct the image into the entrance of the day channel  56 . 
     FIGS.  3 - 4  illustrate one embodiment of the first mirror assembly  64 . As shown by FIG. 3, the first mirror assembly  64  may comprise an annular frame  110  having a central aperture  112 . The frame  110  may be secured to the optical bench (not shown in FIG. 3) with the central aperture  112  disposed along the optical axis  75 . The central aperture  112  allows the image of the scene to pass through the frame  110  when the mirror  100  is in the night position  102  (FIG.  2 ). 
     A support  114  for mounting the mirror  100  may be rotatably coupled to the frame  110  in the central aperture  112 . The support  114  may rotate about an axis  116  normal to the optical axis  75 . The mirror  100  may be mounted to the support  114  for rotation about the axis  116 . Accordingly, the mirror  100  may swing or flip-flop between the night position  102  (FIG. 2) and the day position  104  (FIG.  2 ). 
     An arm  117  may be coupled to the support  114  for rotating the first mirror assembly  64  between the night position  102  and the day position  104 . The arm  117  may be mechanically or electrically coupled to the channel selector switch  39 . The channel selector switch  39  may rotate the first and second mirror assemblies  64  and  66  together to their respective night and day positions. 
     A pivot shaft  118  may be fixably coupled to the support  114  to provide the axis  116  of rotation. The pivot shaft  118  may be a thin metal rod. The pivot shaft  118  may include opposed ends  120  extending from the support  114  for connection with the frame  110 . 
     As show by FIG. 4, the frame  110  may include a trough  122  to receive each of the opposed ends  120 . The troughs  122  may extend in alignment with one another on opposite sides of the aperture  112 . In one embodiment, the troughs  122  may be formed in the frame  110 . In this embodiment, the troughs  122  may be formed by a router or similar tool capable of forming the troughs  122  along a straight line. The troughs  122  may have substantially parallel sidewalls  124  and a furrowed bottom  126 . It will be understood that the troughs  122  may be of other shapes and configurations capable of receiving the opposed ends  120 . 
     Each end  120  of the pivot shaft  118  may be disposed in one of the troughs  122 . A plate  128  may be coupled to the frame  110  across each trough  122  to secure the ends  120  of the pivot shaft  118  in the troughs  122 . The frame  110  may include a cavity  130  across each trough  122  to receive the plates  128 . The cavities  130  may be sized to receive the plates  128  such that a top  132  of the plates  128  is flush with a surface  134  of the frame  110 . 
     In accordance with one aspect of the present invention, the plates  128  may contact the ends  120  of the pivot shaft  118  to control a shifting torque of the mirror  100  relative to the frame  110 . The shifting torque is the torque necessary to shift the mirror  100  between the night position  102  and the day position  104 . The desired shifting torque may be a balance between allowing the mirror  100  to smoothly move between the night and day positions and preventing the mirror  100  from accidentally moving between the night and day positions. 
     In one embodiment, the ends  120  of the pivot shaft  118  may extend above the troughs  122  for contact with the plates  128 . It will be understood that the ends  120  of the pivot shaft  118  and the plates  128  may otherwise contact one another within the scope of the present invention. For example, a portion of the plates  128  may extend into the troughs  122  for contact with the ends  120  of the pivot shaft  118 . In such an embodiment, the portion of the plates  128  extending into the troughs  122  may be a non integral insert (not shown). 
     The shifting torque of the mirror  100  may be controlled by regulating the friction caused by the contact between the plates  128  and the ends  120  of the pivot shaft  118 . In one embodiment, the plates  128  may each be adjustably coupled to the frame  110  by a pair of screws  136 . In this embodiment, friction caused by contact between the plates  128  and the ends  120  of the pivot shaft  118  may by regulated by tightening or loosing the screws  136 . It will be understood that the plates  128  may be otherwise adjustably coupled to the frame  110  within the scope of the present invention. 
     Returning to FIG. 2, with the mirror  100  in the night position  102 , the image of the scene passes from the objective lens assembly  24  through the first mirror assembly  64  into the night channel  54 . In the night channel  54 , the image may be received by an image intensifier tube  150  disposed along the optical axis  75 . The image intensifier tube  150  may convert the image of the scene into an electron pattern. The image intensifier tube  150  may be inverting or non-inverting. The electrons may be multiplied and transmitted onto a phosphor screen. The phosphor screen may generate an intensified image corresponding to the image of the scene. The intensified image may be projected to the reticle assembly  58  where it can be viewed by the user through the eye piece  60 . 
     In accordance with one aspect of the present invention, the image intensifier tube  150  may be mounted to the optical bench for selective rotation. Rotation of the image intensifier tube  150  rotates any offset of the intensified image generated by the image intensifier tube  150 . An offset of the intensified image may be caused by an offset between the mechanical and optical axis of the image intensifier tube  150 . Accordingly, the image intensifier tube  150  may be rotated until any offset of the intensified image at the reticle assembly  58  lies along a direction from which the intensified image can be adjusted to center. As described in more detail below, the offset of the intensified image may be centered along a direction of the reticle assembly  58  by adjusting the second mirror assembly  66 . In one embodiment, the second mirror assembly  66  may center the offset of the intensified image along a vertical direction of the reticle assembly  58 . It will be understood that the second mirror assembly  66  may be configured to instead center the intensified image along another direction of the reticle assembly  58 . 
     FIGS.  5 - 6  illustrate one embodiment of a mounting assembly  152  for rotatably mounting the image intensifier tube  150  to the optical bench (not shown in FIG.  5 ). As shown by FIG. 5, the mounting assembly  152  may comprise an annular housing  154  having a central aperture  156  to receive the image intensifier tube  150 . In one embodiment, the housing  154  may be fixably secured at a forward end  155  to the optical bench with the central aperture  156  disposed along the optical axis  75 . In this embodiment, the housing  154  may be secured to the optical bench by a pair of screws (not shown) each threaded through a tab  157  of the housing  154  into the optical bench. 
     A retainer  158  for engaging the image intensifier tube  150  may be rotatably coupled to the housing  154 . It will be understood that the housing  154  and retainer  158  may be otherwise coupled to one another and to the optical bench so long as the image intensifier tube  150  is selectably rotatable relative to the optical bench. For example, the housing  154  may be rotatably coupled to the optical bench and the retainer  158  fixably coupled to the housing  154 . 
     In one embodiment, the retainer  158  may be rotatably coupled proximate to a rearward end  159  of the housing  154 . In this embodiment, the retainer  158  may comprise a rounded slide  160 . The rounded slide  160  may have a circumference slightly smaller than that of the central aperture  156  in order to fit easily, but not loosely, and to be rotatable within the central aperture  156 . It will be understood that the retainer  158  may be otherwise coupled to the housing  154  within the scope of the invention. 
     As shown by FIG. 6, the slide  160  may include a socket  166  sized to frictionally receive the image intensifier tube  150 . The socket  166  may have an aperture  167  through which the intensified image may be projected. An alignment pin  168  may extend from the socket  166  for engagement with a mating hole (not shown) of the image intensifier tube  150 . The alignment pin  168  may index an opening  170  of the slide  160  with electrical contacts  172  of the image intensifier tube  150 . Accordingly, the slide  160  will only engage the image intensifier tube  150  when the opening  170  is aligned with the electrical contacts  172 . The alignment pin  168  may also insure that the image intensifier tube  150  rotates with the slide  160 . 
     An insert  174  may be fitted into the opening  170  to secure the electrical contacts  172  in proper relation to one another for engagement with a plug (not shown). The plug may provide power and control for the image intensifier tube  150 . The plug may be secured along a rearward side of the slide  160  by a strain relief member  176 . The strain relief member  176  prevents the plug from interfering with projection of the intensified image. It will be understood that the plug may be otherwise secured within the scope of the invention. 
     A locking device  177  may selectively secure the image intensifier tube  150  relative to the optical bench. In one embodiment, the locking device  177  may be a locking ring  178 . The locking ring  178  may have a threaded exterior adapted to engage a threaded section  179  of the housing  154 . The locking ring  178  may be tightened against the slide  160  to fixably secure the image intensifier tube  150  between the slide  160  and the optical bench. Conversely, the locking ring  178  may be loosened against the slide  160  to allow the image intensifier tube  150  to be rotated between the slide  160  and the optical bench. 
     Accordingly, the slide  160  may be rotated about the optical axis  75  to rotate the image intensifier tube  150  until any offset of the intensified image is vertically in line with the center of the reticle assembly. The locking ring  178  may then be tightened against the slide  160  to secure the image intensifier tube  150  relative to the optical bench. As previously described, the second mirror assembly  66  may then be adjusted to vertically center the intensified image at the reticle assembly  58 . 
     In accordance with one aspect of the present invention, a protective window  180  may be sealed to a projection end  182  of the image intensifier tube  150 . The projection end  182  projects the intensified image to the reticle assembly  58 . The protective window  180  may shield the projection end  182  from dirt that has settled within the sight  20 . As used herein, the term “dirt” means soiling substances such as dust, oils, and the like that are capable of interfering with the user&#39;s view of the image. 
     As shown in FIG. 6, the protective window  180  may be sealed directly to the projecting end  182  of the image intensifier tube  150 . The projecting end  182  may be a phosphorous screen. The protective window  180  may be sealed to the projecting end  182 , a shoulder spaced apart from the projecting end  182 , a spacer ring, or the like. The protective window  180  may be sealed with a known adhesive for optical surfaces or the like. 
     The protective window  180  shields the projection end  182  of the image intensifier tube  150  by collecting dirt at a plane  184  that is out of focus with the projection end  182 . Accordingly, the intensified image may be viewed and magnified with little or no interference from dirt that has settled within the sight  20 . The distance between the projection end  182  and the collecting plane  184  may be varied by adjusting the thickness of the protective window  180  or of a spacer ring. 
     From the image intensifier tube  150 , the intensified image may be propagated through the night channel  54  by one or more optical components. For the embodiment shown by FIG. 2, the night channel may include a first lens set  200  disposed along the optical axis  75  and a second lens set  202  disposed along a second optical axis  205  normal to the optical axis  75 . A ninety degree prism  206  may direct an image beam from the optical axis  75  to the second optical axis  205 . 
     The first lens set  200  may include a negative converging lens  210 , a positive diverging lens  212  and a positive converging lens  214 . The second lens set  202  may include a positive diverging lens  216  and a positive converging lens  218 . It should be understood that additional or disparate lenses may be used with the first and second lens sets  200  and  202 . 
     In accordance with one aspect of the present invention, the lenses may be clamped in a direction perpendicular to their optical axis. Perpendicular clamping prevents the lenses from moving along the optical axis during the clamping process. Such movement along the optical axis may distort the image of the scene at the reticle assembly  58 . 
     FIG. 7 illustrates one embodiment of a lens assembly  220  for housing lenses of the first lens set  200 . As shown by FIG. 7, the lens assembly  220  may include an annular housing  222  having a central aperture  224 . The central aperture  224  allows the image of the scene to pass through the housing  222  and be acted upon by the lenses. The housing  222  may be secured to the optical bench with the central aperture  224  disposed along the optical axis  75 . 
     For the first lens set  200 , a spacer  226  may be placed between the lens  210  and the lens  212  to position the lenses  210  and  212  at a desired distance from one another. Lens  214  may be positioned directly next to lens  212 . The lenses  210 ,  212  and  214  and the spacer  226  may be secured in the housing  222  with a known adhesive or the like. It will be understood that other methods may be used to secure the lenses and spacer in the housing  220 . For example, the lenses and spacer may be secured in the housing  222  by retainers, locking rings, detents and the like capable of clamping the lenses and spacer together between ends of the housing  222 . 
     FIG. 8 illustrates one embodiment of a clamping assembly  230  for clamping the lens assembly  220  in a direction perpendicular to the optical axis  75 . As shown by FIG. 8, the clamping assembly  230  may include a clamp  232  having a surface  234  adapted to engage a periphery  236  of the lens assembly  220 . The clamp  232  may be tightened to secure the lens assembly  220  between the clamp  232  and a stop  238 . 
     In one embodiment, the clamp  232  may comprise a brace  240  and a screw  242 . The brace  240  may include the surface  234  adapted to engage the periphery  236  of the lens assembly  220 . The periphery  236  of the lens assembly  220  may be the annular housing  222 . In this case, the surface  234  may have a concave shape adapted to engage the annular housing  222 . 
     The screw  242  may engage a threaded section  244  of the optical bench and contact the brace  240  opposite the surface  234 . The stop  238  may be a section of the optical bench opposite the screw  242 . The screw  240  may be adjustable in the direction of the stop  238  to secure the lens assembly  220  within the optical bench. 
     It will be understood that lenses  216  and  218  of the second lens set  202  may be secured in a lens assembly as described above in connection with FIG.  7 . It will be further understood that the lens assembly of the second lens set  202  may be clamped in the direction perpendicular to the second optical axis  205  as described above in connection with FIG.  8 . 
     Referring back to FIG. 2, the intensified image may pass from the night channel  54  to the second mirror assembly  66 . As described in more detail below, the second mirror assembly  66  may include a swingable or flip-flop mirror  250  rotatable between a night position  252  and a day position  254 . In the night position  252 , the mirror  250  may intercept the second optical axis  205  of the night channel  54  to direct the intensified image to the reticle assembly  58 . The reticle assembly  58  may be disposed along a third optical axis  255 . In one embodiment, the third optical axis  255  may be normal to the second optical axis  205 . In this embodiment, the mirror  250  may intercept the second optical axis  205  at a forty-five (45) degree angle to direct the intensified image to the third optical axis  255 . In the day position  254 , the mirror  250  does not intercept a third optical axis  255 . Accordingly, an image of the day channel  56  may pass through the second mirror assembly  66  to the reticle assembly  58 . 
     FIGS.  9 - 10  illustrate one embodiment of the second mirror assembly  66 . As shown by FIG. 9, the second mirror assembly  66  may include a support  260  rotatably coupled to the optical bench. The support  260  may rotate about an axis  262  normal to the third optical axis  255 . The mirror  250  may be mounted to the support  260  for rotation about the axis  262 . Accordingly, the mirror  250  may swing or flip-flop between the night position  252  (FIG. 2) and the day position  254  (FIG.  2 ). 
     An arm  263  may be coupled to the support  260  for rotating the second mirror assembly  66  between the night position  252  and the day position  254 . The arm  263  may be mechanically or electrically coupled to the channel selector switch  39 . As previously described, the channel selector switch  39  may rotate the first and second mirror assemblies  64  and  66  together to their respective night and day positions. 
     As best shown by FIG. 10, a pivot assembly  264  may be fixably coupled to the support  260  to provide the axis of rotation  262 . In one embodiment, the pivot assembly  264  may comprise a first insert  266  and a second insert  268 . The first and second inserts  266  and  268  may be press fit into opposite edges  270  of the support  260 . The first and second inserts  266  and  268  may have opposed recess ends  272  in alignment with one another. The outer edge of the recess ends  272  may be substantially flush with the edges  270  of the support  260 . 
     A ball  274  may engage each of the recessed ends  272 . In one embodiment, the balls  274  may be sized to sit in the recessed ends  272 . In this embodiment, the recessed ends  272  may be cone-shaped. It will be understood that the recessed ends  272  may have a different shape or configuration so long as the ends are capable of engaging the balls  274 . 
     A holder assembly  276  may engage each of the balls  274 . In one embodiment, each holder assembly  276  may include a recessed end  278  to engage one of the balls  274 . As with the recessed ends  272  of the inserts  266  and  268 , the recessed ends  278  of the holder assemblies  276  may be cone-shaped. It will be understood that the recessed ends  278  of the holder assemblies  276  may have a different shape or configuration so long as the ends are capable of engaging the balls  274 . 
     In accordance with one aspect of the present invention, the holder assemblies  276  may be adjustable along the axis  262  of rotation of the support to control a shifting torque of the mirror  250  relative to the optical bench. A shifting torque is a torque necessary to shift the mirror  250  between the night position  252  and the day position  254 . The desired shifting torque may be a balance between allowing the mirror  250  to smoothly move between the day and night positions and preventing the mirror  250  from accidentally moving between the day and night positions. 
     In one embodiment, the holder assemblies  276  may each comprise a bushing  280  and an adjustment screw  282 . The recessed end  278  for engaging the ball  274  may be disposed at an end of the adjustment screw  282 . The bushing  280  may be mounted in the optical bench along the axis of rotation  262  of the support  260 . The adjustment screw  282  may engage the bushing  280  along the axis of rotation  262 . 
     Each of the adjustment screws  282  may be threaded to adjustably engage the bushing  280 . Accordingly, the adjustment screws  282  may be tightened or loosened against the balls  274 . The shifting torque of the mirror  250  may be controlled by regulating the tension on the balls  274  caused by the adjustment screws  282 . 
     The adjustment screws  282  may each include a smooth bore section  284  press fit into smooth bore cavity  286  of the bushing  280 . The press fit prevents the support  260  from shifting from the axis of rotation  262  due to play in the threads of the bushings  280  and the adjustment screws  282 . 
     Referring back to FIG. 9, the second mirror assembly  66  may include an alignment screw  288  to control the angle at which the mirror  250  intercepts the second optical axis  205 . The alignment screw  288  may contact the back of the support  260 . The alignment screw  288  may raise the mirror  250  to reduce the angle at which the mirror  250  intercepts the second optical axis  205 . This adjustment will vertically raise the intensified image at the reticle assembly  58 . Conversely, the alignment screw  288  may lower the mirror  250  to increase the angle at which the mirror  250  intercepts the second optical axis  205 . This adjustment will vertically lower the intensified image at the reticle assembly  58 . 
     With the mirror  250  in the night position  252 , the intensified image may be directed to the reticle assembly  58 . At the reticle assembly  58 , the intensified image may be projected onto a reticle  300  (FIG.  11 ). As described in more detail below, the reticle  300  may include a targeting pattern  301  for aligning the sight  20  with a target. The position of the targeting pattern  301  may be adjusted in the reticle assembly  58  to compensate for wind speed, wind direction, and gravitational effects. Typically, the necessary reticle adjustment increases with the distance to the target. 
     In accordance with one aspect of the present invention, the reticle assembly  58  may allow for increased adjustment of the reticle  300 . This increase permits the user of the sight  20  to aim the weapon  22  at more distant targets. Adjustment of the reticle  300  may be increased by disposing sliding components of the reticle assembly  58  in slots with sidewalls that form the control surfaces for the sliding components. Accordingly, additional space need not be set aside in the reticle assembly  58  for installing control surfaces of the sliding components. 
     FIGS.  11 - 12  illustrate one embodiment of the reticle assembly  58 . As shown by FIG. 11, the reticle assembly  58  may comprise a substantially annular housing  302  with a substantially round inside surface  304  and a bottom  306 . The inside surface  304  may include a first side  310  and an opposed second side  312 . The inside surface  304  may also include a third side  314  and opposed fourth side  316  between the first and seconds sides  310  and  312 . The bottom  306  of the housing  302  may have an extended aperture  308 . The extended aperture  308  may be substantially square in shape with rounded corners. 
     A pair of opposed side walls  318  may be formed at the bottom  306  of the housing  302  along the third and fourth sides  314  and  316 . The opposed side walls  318  may form a first slot  322 . A pair of ways  320  may define the opposed side walls  318 . Accordingly, the first slot  322  may extend between the first side  310  and the second side  312  of the inside surface  304 . 
     A cross slide  330  may be disposed in the first slot  322 . The cross slide  330  may be substantially rectangular in shape and have an elongated aperture  332 . The elongated aperture  332  may be substantially rectangular in shape with rounded corners. 
     The cross slide  330  may have substantially parallel edges  334  slidably engaging the ways  320  of the housing  302 . The ways  320  function as control surfaces for the cross slide  330 . Accordingly, the cross slide  330  may slide along the ways  320  between the first side  310  and the second side  312  of the housing  302 . 
     The cross slide  330  may have opposed ends  336  facing the first and second sides  310  and  312  of the housing  302 . The ends  336  may be rounded to substantially conform to the shape of the first and second sides  310  and  312 . This allows the cross slide  330  to slide toward the first side  310  until it is substantially flush with that side and to slide toward the second side  312  until it is substantially flush with that side. Accordingly, the cross slide  330  may slide a maximum distance within the housing  302 . 
     A second slot  340  may be formed in the cross slide  330 . The second slot  340  may be substantially normal to the first slot  322 . Accordingly, the second slot  342  may extend between the third side  314  and the fourth side  316  of the housing  302 . The second slot  340  may have an open end  342 , an opposite closed end  344  and opposed side walls  346 . A pair of ways  348  may define the opposed side walls  346 . 
     A reticle holder  350  may be disposed in the second slot  342  of the cross slide  330 . The reticle holder  350  may include a base  352 , a viewing aperture  354  and a projection  356  extending from the base  352  around the viewing aperture  354 . The viewing aperture  354  may be substantially round in shape. 
     The base  352  of the reticle holder  350  may have substantially parallel edges  358  slidably engaging the ways  348  of the cross slide  330 . The ways  348  function as control surfaces for the reticle holder  350 . Accordingly, the reticle holder  350  may slide along the ways  348  between the third side  314  and the fourth side  316  of the housing  302 . 
     The base  352  of the reticle holder  350  may have opposed ends  360  facing the third and fourth sides  314  and  316  of the housing  302 . The ends  360  may be rounded to substantially conform to the shape of the third and fourth sides  314  and  316 . This allows the reticle holder  350  to slide toward the third side  314  until it is substantially flush with that side and to slide toward the fourth side  316  until it is substantially flush with that side. Accordingly, the reticle holder  350  may slide a maximum distance within the cross slide  330 . 
     The projection  356  may include an intermediate section  362  and an enlarged head  364 . The enlarged head  364  may include a top recess  366  sized to receive the reticle  300 . The reticle  300  may be substantially square in shape with rounded corners. The reticle  300  may be secured in the recess  366  with an optical adhesive or the like. It will be understood that the reticle  300  may be otherwise secured in the recess  366  within the scope of the invention. 
     As previously discussed, the reticle  300  may include the targeting pattern  301 . The targeting pattern  301  may be cross-hairs. It will be understood that other targeting patterns may be used that are capable of aligning the sight  20  with the target. 
     A first notch  368  and a second notch  370  may be formed in the head  364 . The notches  368  and  370  may extend from the reticle  300  to an exterior  372  of the head  364 . A reticle light  374  may be disposed in the first notch  368 . The reticle light  374  may illuminate the targeting pattern  301  during night time use. A status indicator  376  may be disposed in the second notch  370 . In one embodiment, the status indicator  376  may activate to alert the user of a low battery status. The reticle light  374  and the status indicator  376  may be light emitting diodes (LED). Power and control for the reticle light  374  and the status indicator  376  may be provided by a flex circuit  378 . The flex circuit  378  allows the reticle light  374  and the status indicator  376  to be moved with the reticle  300 . The flex circuit  378  may extend from the reticle holder  350  down a groove  379  of the housing  302  of the reticle assembly  58 . 
     An annular cover  380  may clamp over the enlarged head  364  to secure the reticle light  374  and the status indicator  376  in the first and second notches  368  and  370 . The cover  380  may include an aperture  384  substantially matching the shape and size of the reticle  300 . The aperture  384  allows the reticle  300  to be viewed from the eye piece  60  without interference from the cover  380 . 
     A guide ring  390  may be disposed about the intermediate section  362  of the projection  356 . The guide ring  390  may sit on the ways  320  of the first slot  322 . It will be understood that the guide ring  390  may be otherwise secured in the housing  302  as long as the guide ring  390  is positioned about the intermediate section  362 . 
     The guide ring  390  may include a guide  392  to define an area in which the reticle holder  350 , and thus the reticle  300 , may be adjusted. The guide  392  may be substantially square in shape with rounded corners. The corners may be rounded in conformance with a diameter of the intermediate section  362 . Accordingly, the intermediate section  362  may fit substantially flush against the corners of the guide  392  to maximize movement of the intermediate section  362  in the guide  392 . 
     The guide ring  390  may include an alignment pin  394 . The alignment pin  394  may engage a mating hole  396  formed in one of the ways  320  of the first slot  322 . The alignment pin  394  may index the guide  392  with the extended aperture  308  of the housing  302 , the elongated aperture  332  of the cross slide  330  and the viewing aperture  354  of the reticle holder  350 . Accordingly, as the reticle holder  350  is moved within the cross slide  330  and the cross slide  330  is moved within the housing  302 , the viewing aperture  354  continually overlaps the elongated aperture  332  and the elongated aperture  332  continually overlaps the extended aperture  308 . As a result, an image may be projected onto the reticle  300  no matter the position of the reticle  300  in the reticle assembly  58 . 
     An intermediate washer  396  may be disposed between the guide ring  390  and the reticle holder  350 . The intermediate washer  396  may reduce friction between the guide ring  390  and the reticle holder  350 . In one embodiment, the intermediate washer  396  may be constructed of Teflon. It will be understood that the intermediate washer  396  may be constructed of other materials capable of reducing friction between sliding members. 
     A locking ring  398  may secure the guide ring  390 , intermediate washer  396 , reticle holder  350  and cross slide  330  in the reticle housing  302 . The locking ring  398  may be threaded to engage threads  400  of the housing  302 . The locking ring  398  may be tightened to a point where the reticle holder  350  and the cross slide  330  move smoothly but not loosely within the reticle housing  302 . 
     As best shown by FIG. 12, a first spring element  410  may be disposed between an end of the cross slide  330  and the first side wall  310  of the housing  302 . The first spring element  410  may comprise a pair of springs  412 . The springs  412  may bias cross slide  330  away from the first side  310  of the housing  302 . Similarly, a second spring element  414  may be disposed between the closed end  344  of the second slot  340  and the base  352  of the reticle holder  350 . The second spring element  414  may comprise a pair of springs  416 . The springs  416  may bias the reticle holder  350  away from the closed end  344  of the second slot  340  which is proximate to the third side  314  of the housing  302 . 
     A first push rod  420  may contact the cross slide  330  opposite the springs  412 . The first push rod  420  may contact a strike plate  422  disposed in the cross slide  330 . The strike plate  422  may prevent wear and tear on the cross slide  330  by an end of the first push rod  420 . 
     The first push rod  420  may be adjustable relative to the housing  302 . The first push rod  420  may position the cross slide  330  at a desired position in the first slot  322  by overcoming the bias of the springs  412 . The combination of the first push rod  420  and the springs  412  may allow the cross slide  330  to be easily adjusted within the first slot  322  and may also retain the cross slide  330  at its desired position in the first slot  322 . The first push rod  420  may be coupled to the azimuth adjusting screw  40  provided on the exterior  38  of the sight housing  30 . 
     A second push rod  424  may contact the reticle holder  350  opposite the springs  416 . The second push rod  424  may contact an elongated strike plate  426  disposed in the base  352  of the reticle holder  350 . The elongated strike plate  426  may prevent wear and tear on the base  352  of the reticle holder  350  by an end of the second push rod  424 . 
     The second push rod  424  may be adjustable relative to the housing  302 . The second push rod  424  may position the reticle holder  350  to a desired position in the second slot  340  by overcoming the bias of the springs  416 . The combination of the second push rod  424  and the springs  416  may allow the reticle holder  350  to be easily adjusted within the second slot  340  and may also retain the reticle holder  350  at its desired position in the second slot  340 . The second push rod  424  may be coupled to the elevation adjusting screw  42  provided on the exterior  38  of the housing  30 . 
     Returning to FIG. 11, a protective window  430  may be sealed to the reticle  300  in accordance with one aspect of the present invention. The protective window  430  may shield the reticle  300  from dirt that has settled within the sight  20 . As previously described, the term “dirt” means soiling substances such as dust, oils and the like that are capable of interfering with the user&#39;s view of the image at the reticle  300 . 
     The protective window  430  may disposed in the viewing aperture  354  of the reticle holder  350 . The protective window  430  may be sealed in the viewing aperture  354  with a known adhesive for optical surfaces or the like. 
     The protective window  430  shields a reticle  300  by collecting dirt at a plane  432  that is out of focus with the eye piece&#39;s  60  view of the reticle  300 . Accordingly, the reticle  300  may be viewed and magnified with little or no interference from dirt that has settled within the sight  20 . The distance between the reticle  300  and the collecting plane  432  may be varied by adjusting the position of the protective window  430  in the viewing aperture  354  of the reticle holder  350 . 
     As previously described, the image projected onto the reticle  300  may be viewed by the user through the eye piece  60 . For the embodiment shown by FIG. 2, the eye piece  60  may magnify the image of the reticle  300 . In this embodiment, the eye piece  60  may comprise a negative diverging lens  440 , a positive diverging lens  442  and a positive converging lens  444 . The lenses may be adjusted relative to one another by a zoom ring  446  mounted on an exterior of the eye piece  60 . It will be understood that additional or disparate lenses may be used for the eye piece  60 . 
     Returning now to the first mirror assembly  64 , when the mirror  100  is in the day position  104 , the image of the scene  52  may be directed into the day channel  56 . In the embodiment shown by FIG. 2, the day channel  56  may include a 90 degree prism  450  to direct the image beam to the third optical axis  255 . A first lens set  452  and a second lens set  454  may be disposed in the day channel  56  along the third optical axis  255 . An alignment element  456  may be disposed along the third optical axis  255  between the first lens set  452  and the second lens set  454 . 
     The first lens set  452  may include a negative converging lens  460 , a positive diverging lens  462  and a collimating lens  464 . The second lens set  454  may include a collimating lens  466 . The collimating lenses  462  and  466  may collimate the image beam as it travels through the alignment element  456 . 
     The lenses of the first and second lens sets  452  and  454  may be secured in a lens assembly as described above in connection with FIG.  7 . The lens assemblies for the first and second lens sets  452  and  454  may be clamped in a direction perpendicular to the third optical axis  255  as described above in connection with FIG.  8 . 
     In accordance with one aspect of the present invention, the alignment element  456  may deviate the image of the day channel  56  into alignment with the intensified image of the night channel  54  at the reticle  300 . The alignment element  456  may be a Risley prism. Accordingly, the user may switch the sight  20  between the night channel  54  and the day channel  56  without need of realigning the reticle  300 . It will be understood that the alignment element  456  may be used instead in the night channel  54  to deviate the intensified image into alignment with the image of the day channel  56  at the reticle  300 . 
     As shown by FIG. 13, the alignment element  456  may comprise a housing  470  having a central aperture  472 . A first annular frame  474  and a second annular frame  476  may be disposed in the central aperture  472  of the alignment element  456 . The first annular frame  474  and the second annular frame  476  may rotate independently of one another and of the housing  470 . 
     In one embodiment, the first annular frame  474  may include a circular recess  478  along an outside surface for receiving a circular lip  480  of the housing  470 . The first annular frame  474  may rotate about the circular lip  480  of the housing  470 . An inside surface  482  of the first annular frame  474  may abut an inside surface  484  of the second annular frame  476 . The second annular frame  476  may be secured in the housing  470  by a retainer  486 . The outside surface of the second annular frame  476  may include a circular recess  488  for receiving a lip  490  of the retainer  486 . The second annular frame  476  may rotate about the circular lip  490  of the retainer  486 . The retainer  486  may be threaded to engage a threaded section  491  of the housing  470 . 
     The first annular frame  474  may include a first prism  492 . The second annular frame  476  may include the second prism  494 . In one embodiment, the first prism  492  may have a flat back  496  and an angled face  498 . The second prism  494  may have a flat back  500  and an angled face  502 . Preferably, the flat backs  496  and  500  of the first and second prisms  492  and  494  face one another. Accordingly, the prisms  492  and  494  may rotate in substantially parallel planes. This may allow the first and second prisms  492  and  494  to be placed in closely together without interfering with one another during rotation. 
     As shown best by FIG. 14, the first prism  492  and the second prism  494  may be of the same power. In this embodiment, the first and second prisms  492  and  494  may have a combined power of zero when rotated opposite one another and a power of twice that of either one when rotated parallel with one another. Rotation of one prism relative to the other will deviate the image along a straight line at the reticle  300 . Rotation of the prisms together will rotate the image at the reticle  300 . Accordingly, the image of the day channel  56  may be deviated to any point on the reticle by rotating the prisms  492  and  494  in concert, individually, or in some combination. 
     The power of the prisms  492  and  494  may be varied depending on the design and configuration of the sight  20 . Prisms  492  and  494  of a greater power will allow greater deflection of the image beam at the reticle  300 . Prisms  492  and  494  of a lesser power will allow greater accuracy in deflecting the image beam at the reticle  300 . 
     As shown best by FIG. 15, an adjustment device  506  for rotating the first annular frame  474  may comprise a threaded screw  508  for engaging a plurality of teeth  510  formed on a periphery  512  of the first annular frame  474 . The threaded screw  508  may include an enlarged head  514  at a top end and an fixed nut  516  at an opposed end. The threaded screw  508  may be positioned in operative relation with the teeth  510  of the first annular frame  474  by recesses  518  and  520  formed in the housing  470 . Accordingly, rotation of the threaded screw  508  may rotate the first annular frame  474 , and thus the first prism  492 . 
     A clamping assembly  530  may be provided for fixably securing the first annular frame  474  after the image has been aligned at the reticle  300 . In one embodiment, the clamping assembly  530  may comprise a brace  532  and a screw  534 . The brace  532  may include a surface  536  adapted to engage the periphery  512  of the first annular frame  474 . For the embodiment of FIG. 15, the surface  536  may have a concave shape adapted to fit substantially flush against the teeth  510  of the periphery  512 . 
     The screw  534  may engage a threaded section of the frame  470  and contact the brace  532  opposite the surface  536 . The screw  534  may be adjustable in the direction of the first annular frame  474  to secure the brace  532  against the first annular frame  474 . 
     Although not shown by FIG. 15, it will be understood that the second annular frame  476  may include an adjustment device for rotating the second annular frame  476  as described above in connection with the first annular frame  474 . Additionally, a clamping assembly may be provided for securing the second annular frame  476  as described above in connection with the first annular frame  474 . 
     In accordance with one aspect of the present invention, the sight  20  may be mounted to the weapon  22  with non-integral members. The non-integral members allow the sight  20  to be designed independently of the weapon  22 . Accordingly, the sight  20  may be of a modular design that can be mounted to a weapon  22  with non-integral members configured for that weapon. 
     FIG. 16 illustrates one embodiment of a mounting assembly  550  for mounting the sight  20  to the weapon  22 . As shown by FIG. 16, the mounting assembly  550  may comprise a first foot  552  operatively associated with a first clamp  554  and a second foot  556  operatively associated with a second clamp  558 . As described in more detail below, the feet  552  and  556  may be permanently secured to a bottom  560  of the sight  20  and may engage a rail  562  of the weapon  22  with the aid of the clamps  554  and  558 . It will be understood that the clamps may be reversed within the scope of the invention. 
     The first foot  552  may include a top  563  adapted to engage a first mounting section  564  of the bottom  560  of the sight  20 . A tab  566  may extend across the top  563  of the first foot  552  in a direction substantially parallel to the rail  562 . A recess  568  may be formed in the first mounting section  564  to receive the tab  566 . 
     A side  570  of the first foot  552  may be adapted to engage a first edge  572  of the rail  562 . An opposite side  574  of the first foot  552  may be adapted to engage a second edge  576  of the rail  562  in combination with the first clamp  554 . The first clamp  554  may be coupled to the opposite side  574  of the first foot  552  by a locking screw  580  and a nut  582 . The locking screw  580  may be press fit into an aperture  584  formed in the side  570  the first foot  552  and extend from the opposite side  574  of the first foot  552 . The projecting portion of the locking screw  580  may be threaded to receive the nut  582 . 
     The second foot  556  may include a top  586  adapted to engage a second mounting section  588  of the bottom  560  of the sight  20 . A tab  590  may extend across the top  586  of the second foot  556  in a direction substantially normal to the rail  562 . A recess  592  may be formed in the second mounting section  588  to receive the tab  590 . 
     A side  594  of the second foot  556  may be adapted to engage the first edge  572  of the rail  562 . An opposite side  596  of the second foot  556  may be adapted to engage the second edge  576  of the rail  562  in combination with the second clamp  558 . The second clamp  558  may be coupled to the opposite side  596  of the second foot  556  by a locking screw  598  and a nut  600 . The locking screw  598  may be press fit into an aperture  602  formed in the side  594  the second foot  556  and extend from the opposite side  596  of the second foot  556 . The projecting portion of the locking screw  598  may be threaded to receive the nut  600 . 
     The locking screw  598  may include a brace  604  for engagement with a recoil groove  606  of the rail  562 . The brace  604  may prevent the sight  20  from sliding along the rail  562  in response to the recoil of the weapon  22 . In one embodiment, the brace  604  may be formed from a portion of the locking screw  598 . 
     The rail  562  may be a Weaver rail as shown by FIG.  16 . It will be understood that feet  552  and  556  and the clamps  554  and  558  may be configured to engage other types of rails  562  in accordance with the invention. 
     The first foot  552  may be initially coupled to the first mounting section  564  of the sight by a screw  608 . Similarly, the second foot  556  may be initially coupled to the second mounting section  588  of the sight  20  by screws  610 . It will be understood that pins and coupling devices may be used in the place of the screws  608  and  610 . 
     Preferably, the screws  608  and  610  are slightly loose when the feet  552  and  556  are initially coupled to the sight  20 . This allows the sight  20  to move slightly when engaged to the rail  562 . The engagement of the tab  566  with the recess  568  allows the forward portion of the sight  20  to move parallel to the rail  562 . The engagement of the tab  590  with the recess  592  allows the rearward portion of the sight  20  to move normal to the rail  562 . This movement prevents the sight  20  from twisting or binding when the feet and clamps are secured to the rail  562 , which may cause the night and day channels  54  and  56  to become unaligned. 
     After the feet and clamps feet are secured to the rail  562 , the feet may be permanently secured to the bottom  560  of the sight  20 . In one embodiment, the feet may be permanently secured with an adhesive and by tightening the screws  608  and  610 . It will be understood that the feet may be otherwise permanently secured to the sight  20 . 
     The optical bench, housings, and frames of the sight  20  may be made of aluminum. Aluminum may be preferred because it is lightweight and relatively inexpensive. Additionally, aluminum is easy to machine and finish. It will be understood that the optical bench, housings, and frames may be made from other types of materials that are strong and lightweight. 
     The lenses, windows, prisms and other optical components of the sight  20  may be made of BK7 glass which is relatively inexpensive and well known in the art. It will be understood that the optical components may be made from other types of glass or polymers operable to transmit the image of the scene  52 . Preferably, the individual components include an anti-reflection coating to prevent reflections from interfering with the image displayed on the reticle assembly  58 . 
     Although the present invention has been described with several embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present invention encompass such changes and modifications as fall within the scope of the appended claims.