FIELD OF THE INVENTION  
         [0001]    The present invention relates generally to optical instruments, and more particularly to magnification viewers, such as those worn by surgeons and dentists.  
         BACKGROUND OF THE INVENTION  
         [0002]    Magnification viewers are well known in the art and generally comprise one or more optical loupes coupled to eyeglass frames. These magnification viewers are often worn by dentists and surgeons for extended periods of time during clinical procedures so as to provide clarity of view while avoiding a “hunched over” position that can result in debilitating neck and back strain, and which can, in turn, have an adverse effect on the success of the operation. By permitting the clinician to operate at a greater working distance from the patient, higher magnification viewers also reduce the clinician&#39;s exposure to potential contamination from aerosols.  
           [0003]    Because clinicians use magnification viewers during surgery and other procedures requiring manual precision, it is important that they be light-weight, comfortable, and provide good clarity and a wide field of vision while providing high resolution.  
           [0004]    The optical loupes of clinical magnification viewers are generally made according to the Galilean telescope design, having a single objective lens and a single eyepiece lens. Galilean telescopes are characterized by relatively narrow fields of view that are mainly limited by the diameter of the objective lens. The basic Galilean design, however, produces substantial chromatic aberration (“coloring”) and, hence, poor image quality.  
           [0005]    Since the optical loupes should be kept as short as possible to reduce torque on the nose and general wearer discomfort, an eyepiece with a shorter focal length is usually employed when an increase in magnification is desired. However, to retain a good field of view without vignetting, the diameter of the objective must also be increased. If this is done while keeping the focal length of the objective the same, the “speed” of the lens increases, resulting in a lower resolution quality. It also mandates an excessively large package. One method of overcoming the “speed” problem is to use a more complicated objective lens, though at a cost of greatly increased weight and, therefore increased strain and discomfort to the wearer.  
           [0006]    The so-called “Kellner design” (from Kellner, U.S. Pat. No. 1,197,742) in general use today contains a heavy doublet objective and a singlet eyepiece lens. While image quality is adequate at lower magnifications, excessive coloring results in poor image quality at higher magnifications. Moreover, the field of view is relatively limited in Kellner lens systems.  
           [0007]    It is known that image quality of prior art magnification viewers can be enhanced by the use of “very high index flint glass.” However, this method has not been in general use, since “very high index flint glass” generally makes the viewer too heavy for practical use. Prior art magnification viewers also require lens mounting barrels of differing sizes in order to provide a wide range of focusing or working distances. As such, the manufacturing costs for these types of prior art viewers are relatively high.  
           [0008]    There is thus a need for an improved magnification viewer capable of providing increased magnification while overcoming drawbacks of prior art viewers, such as those described above.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention provides a magnification viewer having a lightweight magnification loupe providing increased magnification with an improved image quality. In an exemplary embodiment, the loupe includes a Galilean lens system, having a single-element eyepiece lens and a two-element objective lens. The loupe can be carried on a pair of eyeglasses, or other user wearable device, either by mounting to a flip-up mounting member secured to the bridge of the eyeglass frames, or by mounting through the eyeglass lenses.  
           [0010]    In one aspect of the invention, the objective lens of the loupe has a non-circular shape, wherein adjacent pairs of oppositely disposed peripheral edges of the lens are defined by arcs having different length radii. The non-circular shape helps to minimize the weight of the loupe by reducing the overall size of the lenses while not adversely affecting the field of view. In one embodiment, a first pair of peripheral edges are defined by a first radius extending from the center of the lens, and a second pair of peripheral edges are defined by at least one second radius that extends from a point that is not coincident with the lens center. In another exemplary embodiment, the peripheral edges have a semi-elliptical shape, wherein the second pair of peripheral edges correspond to the periphery of an ellipse.  
           [0011]    In another aspect of the invention, the loupe includes a correction lens that is removably mounted in the loupe housing. The correction lens can be removed from the housing and interchangeably replaced with a different correction lens to thereby vary the working distance of the loupe. Advantageously, the interchangeable correction lens allows the loupe to accommodate a range of working distances by selective replacement of a single element that is relatively inexpensive to manufacture. When the loupes are provided in a through-the-lens arrangement, the correction lens may be provided as a prescription lens to permit the loupes to be customized to a user&#39;s optical prescription.  
           [0012]    The features and objectives of the present invention will become more readily apparent from the following Detailed Description taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the invention.  
         [0014]    [0014]FIG. 1 is a perspective view of a magnification viewer including exemplary optical loupes according to the present invention;  
         [0015]    [0015]FIG. 2 is a perspective view of another magnification viewer wherein the exemplary optical loupes are mounted through the lenses of a pair of eyeglasses;  
         [0016]    [0016]FIG. 3A is a perspective view of an exemplary optical loupe of the present invention configured for mounting to a flip-up mounting member;  
         [0017]    [0017]FIG. 3B is a perspective view of another exemplary loupe of the present invention configured for mounting through an eyeglass lens;  
         [0018]    [0018]FIG. 4A is a perspective view of another exemplary loupe configured for mounting to a flip-up mounting member;  
         [0019]    [0019]FIG. 4B is yet another exemplary loupe configured for mounting through an eyeglass lens;  
         [0020]    [0020]FIG. 5 is a cross-sectional view depicting an exemplary flip-up loupe of the present invention;  
         [0021]    [0021]FIG. 6 is a cross-sectional view depicting an exemplary through-the-lens loupe according to the present invention;  
         [0022]    [0022]FIG. 7 is a schematic diagram illustrating the lens parameters for a flip-up optical loupe of the present invention;  
         [0023]    [0023]FIG. 8 is a schematic diagram illustrating the lens parameters for an exemplary through-the-lens optical loupe of the present invention;  
         [0024]    [0024]FIG. 9 is a schematic illustration depicting the shape of an objective lens according to the present invention; and  
         [0025]    [0025]FIG. 10 is a schematic diagram depicting the shape of yet another exemplary objective lens of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0026]    Referring to FIG. 1, there is shown a magnification viewer  10  having an exemplary magnification loupe  12  according to the present invention. The magnification viewer  10  comprises a pair of spectacles  14  having eyeglass frames  16  for supporting a pair of eyeglass lenses  18  as known in the art. The magnification viewer  10  further includes first and second magnification loupes  12  secured to the eyeglass frames  16  such as by a flip-up mounting member  20  coupled to a bridge  22  of the eyeglass frames  16 . Advantageously, the loupes  12  may be pivoted by the mounting member  20  to be positioned in front of the respective eyeglass lenses  18  whereby a user may view a highly magnified image of an object positioned in front of the magnification viewers  10 . Advantageously, the magnification loupes  12  are also pivotally secured to the flip-up mounting member  20  to permit adjustment of the convergence angle of the magnification viewer.  
         [0027]    Referring now to FIGS. 3A and 5, the exemplary magnification loupe  12  of FIG. 1 is shown in greater detail. The magnification loupe  12  comprises a housing  30  for supporting the lens elements  32 ,  34  of the loupe. A first end  36  of the housing  30  has a first aperture  38  for receiving and supporting an eyepiece lens  32 . The second end  40  of the housing  30  includes a second aperture  42  sized to receive and support an objective lens  34  of the loupe  12 . In the exemplary embodiment shown, the eyepiece lens  32  comprises a single lens element and the objective lens  34  comprises a two-piece lens element. A mounting pylon  44  extends from an outer surface of the housing  30  and supports a threaded stud  46  which may be coupled to the flip-up mounting member  20  to permit pivotal adjustment of the magnification loupes  12  to vary the convergence angle of the magnification viewer  10 . Advantageously, the objective lens  34  and eyepiece lens  32  of the magnification loupe  12  cooperate to focus light entering through the objective lens  34  and passing through the eyepiece lens  32  and eyeglass lens  18  to provide a magnified image of an object disposed in front of the loupes  12 .  
         [0028]    [0028]FIG. 7 is a schematic illustration of the flip-up optical loupe lens system, together with an eyeglass lens  18 . Exemplary construction data for a magnification viewer built according to a preferred embodiment of the invention is provided in Table 1 below, with respect to the nomenclature of FIG. 7.  
                                                 TABLE 1                           Flip-up            Element   Glass   η d     ν d     Radius   Thickness   Diameter   Sep.               I   Schott   1.589   61.3   R 1  = 98.19   3.0   25.4               NSK5           R 2  = 98.19       II   Schott   1.580   53.9   R 3  = 52.10   1.5   D 1  = 13.00   S 1  = 4.1            NBALF4           R 4  = 20.16       D 2  = 13.25       III   O&#39;Hara   1.785   26.3   R 5  = 85.68   1.8   26.15   S 2  = 13.59           STIH23           R 6  = 43.17       IV   Schott   1.517   64.2   R 7  = 43.17   7.6   26.15           NBK7           R 8  = 22.39                  
 
         [0029]    In Table 1, the radius, thickness, diameter, and separation dimensions are given in millimeters. Roman numerals identify the lens elements in their respective order from the eyepoint side to the object side. η d  represents the refractive index of each element; ν d  is the abbe dispersion number; R 1 , R 2 , etc. represent the radii of the respective refractive surfaces in order, from the eyepoint side to the object side; D 1 , D 2 , etc. represent the diameter of the lens elements; and S 1 , S 2  represent the air space between the elements, measured along the optical centerline. In this example, lens element I represents a zero-power eyeglass lens having a base curve of six diopters. It will be recognized by those skilled in the art that other eyeglass lenses may be substituted for the selected eyeglass lens, with minimal affect on the performance of the magnification loupe.  
         [0030]    Referring now to FIG. 2, there is shown another magnification viewer  10   a  having an exemplary magnification loupe  50  of the present invention configured for mounting through the eyeglass lens elements  18  of a pair of eyeglasses  14 . Referring further to FIGS. 3B and 6, the exemplary magnification loupe  50  depicted in FIG. 2 comprises a housing  52  having a first aperture  54  at a first end  56  for supporting an eyepiece lens element  58  and a second aperture  60  at a second end  62  for supporting a two-piece objective lens element  64 , similar to the magnification loupe  12  depicted in FIGS. 1, 3A and  5 . However, because this magnification loupe  50  is mounted through the eyeglass lens  18 , the loupe  50  further includes a correction lens  66  mounted in the first aperture  54  of the housing  52 , adjacent the eyepiece lens  58 . The correction lens  66  may be selected to correspond to a prescription required by an individual user.  
         [0031]    Advantageously, the correction lens  66  is removably coupled to the housing  52 , whereby the correction lens  66  may be selectively removed from the housing  52  and replaced with a different correction lens having a different spherical curve to thereby vary the working distance of the loupe  50 . The correction lens  66  may be manufactured from relatively inexpensive prescription lens elements that have been cut down to the necessary diameter to be received in the loupe housing  52 . The interchangeability of correction lens  66  thus permits ready adjustment of the magnification loupe  50  to accommodate various working distances without the need to maintain and replace expensive, precision ground eyepiece or objective lens elements. Accordingly, multiple correction lens elements  66  may be used with a single set of eyepiece lenses  58  and objective lenses  64  supported in a housing  52  to provide magnification loupes  50  which may be easily converted for use at various working distances.  
         [0032]    Alternatively, the correction lens  66  may be provided according to a user&#39;s optical prescription to serve as a corrective lens. This permits the loupes to be customized for the vision correction of the user.  
         [0033]    In the exemplary embodiment shown, correction lens  66  is secured within the loupe housing  52  by a retaining ring  68  that is threadably engageable with the first end  56  of the housing  52 . The correction lens may thereby be easily removed and replaced by unthreading the retaining ring  68  using, for example, a tool (not shown) configured to engage the retaining ring  68 . While the magnification loupe  50  has been shown and described herein as having a retaining ring  68  to permit selective replacement of the correction lens  66 , it will be understood that the correction lens  66  may be retained within loupe housing  52  in various other ways, including use of a snap fit arrangement, press fitting the correction lens within the housing  52 , or other configurations and structure that would permit removal and replacement of the correction lens  66 .  
         [0034]    Referring now to FIG. 8, there is shown a schematic diagram of the lens elements for the magnification loupe  50  shown in FIGS. 2, 3B and  6 . Exemplary construction data for a magnification loupe  50  built according to a preferred embodiment are given in Table 2.  
                                                 TABLE 2                           Through-the-lens            Element   Glass   η d     ν d     Radius   Thickness   Diameter   Sep.               I   Schott   1.589   61.3   R 1  = 00     2.2   12.0               NSK5           R 2  = 00         II   Schott   1.517   64.2   R 3  = 36.49   1.5   12.0   S 1  = 0.6            NBK7           R 4  = 18.48       III   Schott   1.805   25.4   R 5  = 85.68   1.6   D 1  = 22.24   S 2  = 14.46           NSF56           R 6  = 39.71       D 2  = 23.60       IV   Schott   1.517   64.2   R 7  = 39.71    6.65   D 3  = 23.60           NBK7           R 8  = 21.55       D 4  = 23.60                  
 
         [0035]    In Table 2, the radius, thickness, diameter, and separation dimensions are given in millimeters. Roman numerals identify the lens elements in their respective order from the eyepoint side to the object side. θ d  represents the refractive index of each element; ν d  is the abbe dispersion number; R 1 , R 2 , etc. represent the radii of the respective refractive surfaces in order, from the eyepoint side to the object side; D 1 , D 2 , etc. represent the diameter of the lens elements; and S 1 , S 2  represent the air space between the elements, measured along the optical centerline.  
         [0036]    The magnification loupes  12  shown in FIGS. 1, 2 and  3 A- 3 B include objective lenses  34 ,  64  having a non-circular shape, as depicted schematically in FIG. 9. In particular, first oppositely disposed peripheral edges  70   a ,  70   b  of the objective lens  34 ,  64  are circular in shape and are defined by a common radius Ra extending from a center C 1  of the lens. Second oppositely disposed peripheral edges  72   a ,  72   b  of the objective lens  34 ,  64 , adjacent the first peripheral edges  70   a ,  70   b , comprise arcs which are not defined by the radius Ra of the first peripheral edges  70   a ,  70   b . Rather, the second peripheral edges  72   a ,  72   b  are defined by at least one second radius Rb, Rc extending from at least one center point C 2 , C 3  that is not coincident with the center C 1  of the objective lens.  
         [0037]    [0037]FIG. 10 is a schematic depiction of anther construction of non-circular objective lens  34 ,  64 . In this exemplary embodiment, the first oppositely disposed peripheral edges  70   a ,  70   b  of the objective lens  34 ,  64  are defined by circular arcs subscribed by a common radius Ra extending from a center C 1  of the lens, as described above, and second, oppositely disposed peripheral edges  72   a ,  72   b  of the lens are defined by arcs coinciding with an elliptical shape  74  having first and second foci F 1 , F 2 , wherein the sum of the distances L 1 , L 2  between the respective foci F 1 , F 2  to any point on the second peripheral edges  72   a ,  72   b  is constant. Advantageously, the non-circular shape of the exemplary objective lens  34 ,  64  allows the weight of the optical loupes  12 ,  50  to be reduced, while maintaining a field of view having a width comparable to a magnification loupe with a circular objective lens. Furthermore, the arcuate shape of the second oppositely disposed peripheral edges  72   a ,  72   b  provides a reduction in objective lens size without degrading the optical quality of the magnification loupes  12 ,  50 . The resulting loupe  12 ,  50  is light in weight and may be mounted in designer frames, which are generally smaller and lighter in weight than conventional frames for supporting magnification loupes. The non-circular shape also permits users to more easily view the true object by looking over the loupe housing  30 ,  52  as may be desired.  
         [0038]    While the magnification loupes  12 ,  50  of the present invention have been shown and described having non-circular objective lenses  34 ,  64 , it will be recognized that the loupes may be alternatively manufactured with circular lenses as shown in FIGS. 4A-4B. In particular, the optical loupe depicted in FIG. 4A is configured to be used with a flip-up mounting member  20 , as described above for the magnification viewer of FIG. 1. The magnification loupe shown in FIG. 4B is configured to be mounted through the eyeglass lenses  18  of a magnification viewer  10   b  as described above with respect to FIG. 2. In FIGS. 4A-4B, features similar to the features of magnification loupes  12 ,  50  of FIGS. 3A-3B are similarly numbered.  
         [0039]    The magnification loupes  12 ,  50  have been shown and described herein as being supported on a pair of spectacles. It will be recognized, however, that the loupes  12 ,  50  may alternatively be supported on other user wearable devices, such as headbands, facemasks, goggles, or other devices capable of supporting the loupes  12 ,  50  in close proximity to a users eyes.  
         [0040]    While the present invention has been illustrated by the description of the various embodiments thereof, and while the embodiments have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of the general inventive concept.
A magnification loupe carried by spectacles has a Galilean lens system comprising a single-element eyepiece lens and a two-element objective lens. The loupes may be mounted to eyeglass frames by a flip-up mounting member, or they may be mounted through the eyeglass lenses of the spectacles. The loupes provide high magnification while minimizing weight to thereby reduce strain and discomfort to users. In an exemplary embodiment, the objective lens has a non-circular shape that provides a wide field of view while further minimizing the weight of the loupe. A correction lens may be interchangeably coupled to the loupe housing to permit selective replacement with another correction lens to vary the working distance of the loupe.