Abstract:
An adapter for optically coupling a conventional 2D endoscope to a stereoscopic 3D camera so as to provide stereoscopic 3D visualization of an object imaged by the conventional 2D endoscope, the adapter comprising:
       a body;   a mechanical mount disposed on the body for mechanically mounting the adapter to a conventional 2D endoscope;   means for mounting the body to a stereoscopic 3D camera; and   an optical pathway disposed within the body for receiving an image from the exit pupil of the conventional 2D endoscope and projecting the received image on an appropriate portion of the stereoscopic 3D camera, wherein the optical pathway is adjustable so as to accommodate a range of different conventional 2D endoscopes.

Description:
REFERENCE TO PENDING PRIOR PATENT APPLICATION  
       [0001]    This patent application claims benefit of pending prior U.S. Provisional Patent Application Ser. No. 61/507,317, filed Jul. 13, 2011 by Yuri Kazakevich for METHOD AND APPARATUS FOR OBTAINING STEREO 3D VISUALIZATION USING COMMERCIALLY AVAILABLE 2D ENDOSCOPES (Attorney&#39;s Docket No. VIKING-6 PROV), which patent application is hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]    This invention relates to visualization devices in general, and more particularly to endoscopes. 
       BACKGROUND OF THE INVENTION 
       [0003]    U.S. Pat. No. 5,702,350 to Vry et al. describes a system in which an adapter is used to connect a stereoscopic endoscope to stereoscopic electronic documentation devices (e.g., stereoscopic CCD cameras). This system utilizes a stereoscopic endoscope (or line of stereoscopic endoscopes) specifically designed as a part of the overall stereoscopic system described in the patent. As shown in the patent, the stereoscopic endoscopes have specially designed optics and specially designed mechanical connectors to match with the set of stereoscopic documentation devices (e.g., stereoscopic CCD cameras). 
         [0004]    As opposed to the cited prior art, and as will hereinafter be discussed in detail, the present invention teaches a method and apparatus for adapting virtually any conventional, commercially-available non-stereoscopic endoscope (i.e., a 2D endoscope) to a fixed stereo camera so as to obtain stereoscopic 3D visualization. 
         [0005]    More particularly, the configuration of a typical conventional rigid non-stereoscopic endoscope is well known in the art.  FIG. 1  shows the structure of the endoscope. The non-stereoscopic (i.e., 2D) endoscope  10  comprises an elongated shaft  11 , a proximal housing  12 , a light post  13  and an eyepiece  14 . The shaft  11  typically includes at least one thin-wall inner tube  15  in addition to the outer tube  16 . Illumination fiber bundle  17  extends from the light post  13  to the distal end of the endoscope and typically is sandwiched between the inner tube  15  and the outer tube  16 . The inner tube  15  carries the optical train that typically comprises an objective lens  18 , and a number of rod-lens optical relay systems  19   a ,  19   b , . . . ,  19   n . Some endoscopes feature an oblique direction of view (e.g., 30° with respect to the longitudinal axis of the shaft  11 ), typically achieved by a prism  20 . A negative lens  21  is disposed at the distal tip of the endoscope for expansion of the optical field of view and is hermetically sealed to the shaft  11 . Sometimes an additional plane window is used at the distal tip of the endoscope for sealing the assembly, instead of using the negative lens  21  for both optical and sealing purposes. The objective lens  18  creates the first intermediate image  22  of an object under observation. Each relay system  19  creates a next intermediate image, thereby carrying the image of the object through the narrow shaft from the distal end of the endoscope  10  to the proximal end of the endoscope  10 . The last intermediate image is created at the proximal end of the endoscope  10 . 
         [0006]      FIG. 2  shows the detail of a typical proximal end construction of the 2D endoscope  10 . The last optical intermediate image  22   n  is created behind the last optical relay system  19   n . At the location of the image  22   n,  a field stop  23  is disposed that delineates the designed optical field of view and removes stray light. Typically, the field stop  23  is constructed as a thin diaphragm with a round opening in its center. An ocular lens  24  is disposed proximal to the field stop  23  at such a distance that the field stop  23  locates in the vicinity of the first focal plane of the ocular lens  24 . On account of this construction, the ocular lens  24  creates a virtual magnified image of the field stop  23  and of the intermediate image  22   n  at a long distance (typically from 250 mm to infinity) from the ocular lens  24 . This image may be observed by direct viewing through the eyepiece  14 . The optical beam emerging from the ocular lens  24  may be considered collimated. A window  25  is disposed proximal to the ocular lens  24  and is hermetically sealed to the proximal housing  12 . Thus, the 2D endoscope  10  represents a single hermetically sealed sterilizable assembly that may not be disassembled by the user. The eyepiece  14  is affixed to the proximal housing  12  and is typically made out of chemically resistant plastic, e.g., PEEK. Typically the shape and dimensions of the eyepiece are in compliance with the German standard DIN 58105.  FIG. 3  shows the DIN 58105 specifications. 
         [0007]    It is well known in the art that eyepieces formed in compliance with DIN 58105 have become the industry standard, and all major manufacturers of endoscopes produce products compatible with this eyepiece standard. When the endoscopes are used in conjunction with endoscopic cameras, the common shape of the eyepieces from different manufacturers (i.e., all complying with the DIN 58105 standard) allows for connection of different endoscopes to different cameras all across the industry. In other words, eyepieces complying with the DIN 58105 standard have become an industry standard interface for commercially available 2D endoscopes. The eyepiece is typically releasably attached to the endoscopic camera head with a locking mechanism that allows for rotation of the endoscope around its mechanical axis. Conventional endoscopes per the above description constitute the majority of commercially available endoscopes and may be found in various catalogs of endoscope manufacturers. Just a few examples are given below: 
         [0008]    (1) Laparoscope 5 mm×30°, Part Number 26046BA by Karl Storz; 
         [0009]    (2) Laparoscope 10 mm×0°, Part Number A4801A by Olympus; 
         [0010]    (3) Bariatric Laparoscope 10 mm×30°, Part Number 502-657-030 by Stryker; 
         [0011]    (4) ENT Scope, 4 mm×30°, Part Number T4302 by Linvatec; and 
         [0012]    (5) Laparoscope 10 mm×30°, Part Number 7207945 by Smith &amp; Nephew. 
         [0013]    Typically the endoscope is coupled to the camera via an optical device, i.e., an adapter, also known as an endocoupler or a camera coupler. The function of this optical device (i.e., adapter) is to focus the collimated light beam coming out of the ocular lens  24  onto the image sensor of the camera. Endocouplers include focusing optics and means for focus adjustment (most often via a manually rotatable focus ring). Typically manufacturers offer a range of endocouplers having different focal lengths. The image size obtained for a given endoscope on a given image sensor will be proportional to the focal length of the endocoupler. Some manufacturers produce endocouplers with optical zoom capability. The endocoupler may represent a stand-alone, hermetically-sealed, sterilizable device whose proximal end is releasably attached to the camera head and whose distal end releasably couples to the DIN 58105 eyepiece of the endoscope, thereby allowing the endoscope to rotate. Alternatively, the endocoupler may be permanently attached to the camera head (becoming an integral part of the camera head), in which case the distal portion of the integrated camera head (i.e., the camera head plus the endocoupler) will have a releasable locking mechanism for the DIN 58105 eyepiece. 
         [0014]    Examples of just a few of the commercial stand-alone endocouplers are given below: 
         [0015]    (1) Endocoupler, 30 mm focal length, Part Number 7204823 by Smith &amp; Nephew; 
         [0016]    (2) Endocoupler, Part Number PV127S by Aesculap; 
         [0017]    (3) Zoom endocoupler, Part Number PV126S by Aesculap; and 
         [0018]    (4) Parfocal Zoom Coupler, (20-37 mm) by Solos Endoscopy. 
         [0019]    Examples of a few of the commercial endocouplers which are integrated with camera heads include: 
         [0020]    (1) Camera head with coupler, Part Number OTV-SP1H-NA-12E by Olympus; and 
         [0021]    (2) TRICAM® Parfocal Zoom 3-Chip Camera Head, Part Number 20221030 by Karl Storz. 
       OBJECTS OF THE INVENTION  
       [0022]    A primary object of the present invention is to realize an endoscopic stereoscopic 3D visualization system using conventional, commercially-available 2D endoscopes. 
         [0023]    Another object of the present invention is to realize such a system while retaining the modular, compartmentalized structure of a conventional endoscope system (i.e., endoscope/endocoupler/camera head) already familiar to, and accepted by, users. 
       SUMMARY OF THE INVENTION 
       [0024]    The present invention provides an endoscopic stereoscopic 3D visualization system using conventional, commercially-available 2D endoscopes. 
         [0025]    And the present invention provides such a system while retaining the modular, compartmentalized structure of a conventional endoscope system (i.e., endoscope/endocoupler/camera head) already familiar to, and accepted by, users. 
         [0026]    In one preferred form of the invention, there is provided an adapter for optically coupling a conventional 2D endoscope to a stereoscopic 3D camera so as to provide stereoscopic 3D visualization of an object imaged by the conventional 2D endoscope, the adapter comprising: 
         [0027]    a body; 
         [0028]    a mechanical mount disposed on the body for mechanically mounting the adapter to a conventional 2D endoscope; 
         [0029]    means for mounting the body to a stereoscopic 3D camera; and 
         [0030]    an optical pathway disposed within the body for receiving an image from the exit pupil of the conventional 2D endoscope and projecting the received image on an appropriate portion of the stereoscopic 3D camera, wherein the optical pathway is adjustable so as to accommodate a range of different conventional 2D endoscopes. 
         [0031]    In another preferred form of the invention, there is provided a method for providing stereoscopic 3D visualization of an object imaged by a conventional 2D endoscope, the method comprising: 
         [0032]    providing an adapter for optically coupling a conventional 2D endoscope to a stereoscopic 3D camera, the adapter comprising:
       a body;   a mechanical mount disposed on the body for mechanically mounting the adapter to a conventional 2D endoscope;   means for mounting the body to a stereoscopic 3D camera; and   an optical pathway disposed within the body for receiving an image from the exit pupil of the conventional 2D endoscope and projecting the received image on an appropriate portion of the stereoscopic 3D camera, wherein the optical pathway is adjustable so as to accommodate a range of different conventional 2D endoscopes;       
 
         [0037]    positioning the adapter between the conventional 2D endoscope and the stereoscopic 3D camera so that the adapter receives an image from the conventional 2D endoscope and projects the received image on an appropriate portion of the stereoscopic 3D camera; and 
         [0038]    adjusting the optical pathway of the adapter so that the image received from the conventional 2D endoscope is properly projected on an appropriate portion of the stereoscopic 3D camera. 
         [0039]    In another preferred form of the invention, there is provided apparatus for optically coupling a conventional 2D endoscope to a stereoscopic 3D camera so as to provide stereoscopic 3D visualization of an object imaged by the conventional 2D endoscope, the apparatus comprising: 
         [0040]    a kit of adapters for disposition between a conventional 2D endoscope and a stereoscopic 3D camera, wherein each of the adapters in the kit comprises:
       a body;   a mechanical mount disposed on the body for mechanically mounting the adapter to a conventional 2D endoscope;   means for mounting the body to a stereoscopic 3D camera; and   an optical pathway disposed within the body for receiving an image from the conventional 2D endoscope and projecting the received image on an appropriate portion of the stereoscopic 3D camera;       
 
         [0045]    wherein each of the adapters in the kit comprises a different optical pathway so as to accommodate a different conventional 2D endoscope. 
         [0046]    In another preferred form of the invention, there is provided a method for providing stereoscopic 3D visualization of an object imaged by a conventional 2D endoscope, the method comprising: 
         [0047]    providing a kit of adapters for disposition between a conventional 2D endoscope and a stereoscopic 3D camera, wherein each of the adapters in the kit comprises:
       a body;   a mechanical mount disposed on the body for mechanically mounting the adapter to a conventional 2D endoscope;   means for mounting the body to a stereoscopic 3D camera; and   an optical pathway disposed within the body for receiving an image from the conventional 2D endoscope and projecting the received image on an appropriate portion of the stereoscopic 3D camera;   wherein each of the adapters in the kit comprises a different optical pathway so as to accommodate a different conventional 2D endoscope;       
 
         [0053]    selecting an appropriate adapter from the kit and positioning that adapter between the conventional 2D endoscope and the stereoscopic 3D camera so that the adapter receives an image from the conventional 2D endoscope and properly projects that image on a portion of the stereoscopic 3D camera. 
         [0054]    In another preferred form of the invention, there is provided apparatus for providing stereoscopic 3D visualization of an object, the apparatus comprising: 
         [0055]    a 2D endoscope; 
         [0056]    a stereoscopic 3D camera; and 
         [0057]    an adapter for optically coupling the conventional 2D endoscope to the stereoscopic 3D camera, the adapter comprising:
       a body;   a mechanical mount disposed on the body for mechanically mounting the adapter to the conventional 2D endoscope;       
 
         [0060]    means for mounting the body to the stereoscopic 3D camera; and
       an optical pathway disposed within the body for receiving an image from the exit pupil of the conventional 2D endoscope and projecting the received image on an appropriate portion of the stereoscopic 3D camera, wherein the optical pathway is adjustable so as to accommodate a range of different conventional 2D endoscopes.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0062]    These and other objects, features and advantages of the present invention will be more fully disclosed or rendered obvious by the following detailed description of the preferred embodiments of the invention, which is to be considered together with the accompanying drawings wherein like numbers refer to like parts and further wherein: 
           [0063]      FIG. 1  is a schematic view showing a typical conventional rigid 2D endoscope; 
           [0064]      FIG. 2  is a schematic view showing the typical proximal end construction for a conventional rigid 2D endoscope; 
           [0065]      FIG. 3  is a schematic view showing the DIN 58105 specifications for an endoscope eyepiece; 
           [0066]      FIG. 4  is a schematic view showing an adapter for connecting a wide range of different 2D endoscopes to a stereoscopic 3D camera so as to provide stereoscopic 3D visualization; 
           [0067]      FIG. 5  is a schematic view showing a dual aperture plate of a stereoscopic 3D camera; 
           [0068]      FIG. 6  is a schematic view showing a three-lens group variable focus system which may be used in connection with a relatively large exit pupil of 3 mm (typical for a laparoscope); 
           [0069]      FIG. 7  is a schematic view like that of  FIG. 6 , except showing a system which may be used in connection with a smaller exit pupil of 1.5 mm (typical for an arthroscope); 
           [0070]      FIG. 8  is a schematic view illustrating positions of the lenses and resulting magnification; 
           [0071]      FIG. 9  is a schematic view like that of  FIGS. 6 and 7 , except showing a two-lens group system instead of a three-lens group system, with the lens group positions being fixed; 
           [0072]      FIG. 10  is a schematic view showing various ways in which an image may be projected onto the image sensors of the stereoscopic 3D camera; and 
           [0073]      FIG. 11  is a schematic view showing another form of the present invention, wherein focusing means are included in the 3D adapter assembly, rather than in the stereoscopic 3D camera. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0074]    Looking first at  FIG. 4 , there is shown a first embodiment of the present invention. More particularly, in this form of the invention, the system for rendering stereoscopic 3D visualization preferably includes three self-contained, hermetically-sealed components: a conventional 2D endoscope  10 , a 3D adapter  36  and a 3D camera head  28 . It should be appreciated that the specific optical characteristics of 2D endoscopes vary from scope to scope, based on a variety of factors, including field stop  23 , ocular lens  24  and exit pupil  26 . As will hereinafter be discussed, the 3D adapter must take these factors into account in order to properly provide stereoscopic visualization using a conventional 2D endoscope. 
         [0075]      FIG. 4  shows the proximal portion of the conventional 2D endoscope  10  having the DIN 58105 eyepiece  14 , the ocular lens  24  and the field stop  23 . The exit pupil  26  of the endoscope is located near the second focal plane of the ocular lens  24 . 
         [0076]    The 3D camera head  28  comprises two image sensors  29   a  and  29   b  corresponding to the “Right” and “Left” images, respectively, of the 3D camera. The image sensors are typically placed on printed circuit boards  30   a,    30   b  that contain the driver circuitry and other communication/service electronics that need to be located in physical proximity to the image sensors. The rest of the signal processing chain, as well as power supplies, etc., reside in the camera controller unit (not shown) connected to the camera head via a cable  31 , as is well known in the art. The camera head  28  also includes the channel separation means  32 , schematically shown in  FIG. 4  by a pair of mirror surfaces. Other beam separation means are also possible, as is well known in the art. The camera head  28  receives the input optical beam from 2D endoscope  10  (and 3D adapter  36 ) through the entrance window  33  which is hermetically sealed to the camera head housing. 
         [0077]    Proximal to the window  33  is disposed a dual aperture plate  34 , which shown in more detail in  FIG. 5 . Dual aperture plate  34  divides the single image channel emerging from the conventional 2D endoscope  10  (and 3D adapter  36 ) into the two image channels forwarded to left and right image sensors  29   a ,  29   b , respectively, of the 3D camera head  28 , whereby to produce stereoscopic 3D visualization from a conventional 2D endoscope. Focusing optics  35  are schematically shown in  FIG. 4  as a single lens disposed proximal to the dual aperture plate  34 . 
         [0078]    Typically the camera head is the most expensive component of the system, so the main idea behind the present invention is to create a modular system where the user would have to buy one 3D camera head and adapt most (or all) of the conventional, commercially-available 2D endoscopes (that are in a healthcare facility&#39;s inventory) to 3D visualization. This purpose is attained by providing the 3D adapter  36  which is described in more detail below. Significantly, in this form of the invention, a single 3D adapter is capable of working with a wide range of different 2D endoscopes, each having different optical characteristics, and still provide proper stereoscopic 3D visualization with a single 3D camera head  28 . 
         [0079]    In this form of the invention, the 3D adapter  36  represents a telescopic system that projects the exit pupil  26  of the endoscope  10  onto the dual aperture plate  34  of camera head  28  with appropriate magnification so that both apertures of dual aperture plate  34  are within the diameter of the projected pupil (see  FIG. 5 ). It is well known in the art that the exit pupil sizes of conventional, commercially-available 2D endoscopes vary depending on specific designs/manufacturers, as well as based on the physical size of the endoscopes and their clinical applications. Typically smaller diameter endoscopes (e.g., arthroscopes, ENT scopes, etc.) have smaller exit pupils compared to larger diameter endoscopes (e.g., laparoscopes, thoracoscopes, etc.). In order to be able to use a single 3D camera head with various endoscopes, there should be an optical means that performs at least two functions: (1) projects the image of the exit pupil of the endoscope onto the aperture plate  34 , maintaining approximately the same size of this image for different types of endoscopes; and (2) projects the image of the field stop  23  onto the image sensors  29   a ,  29   b.  The 3D adapter  36  of the present invention performs both of these functions. 
         [0080]    Mechanically, the distal end of the adapter should be able to couple to the DIN 58105 eyepiece of the conventional 2D endoscope  10 , whereas the proximal end of the adapter should couple to the 3D camera head  28 .  FIG. 4  shows one version of such a 3D adapter.  FIG. 6  shows an example of the first order optical lay-out of the system. The system in  FIG. 6  represents a three-lens group variable focus system. In the lay-out, each lens group is schematically shown as a single lens. It should be appreciated that the optical system shown in  FIG. 6  is not a “true zoom” system, in the sense that the total distance between the locations of the object (i.e., the exit pupil  26  of the endoscope) and the image (i.e., the aperture plate  34 ) does not remain the same during magnification change, as it would in a “true zoom” system. A true zoom optical system is also possible for realization of this invention if desired. Typically the true zoom system would require more lens groups and at least one group with the negative optical power. However the system shown in  FIGS. 4 and 6  is simpler and uses only three lens groups, all of them having positive power. The main reason why the true zoom system is not required for the present invention is due to the fact that the exit pupil of the endoscope has to be magnified to the certain image size only once for the particular scope being used, and thereafter the position of the system can be fixed for this particular type of endoscope and not changed any more during the procedure. In other words, the physical distance between the endoscope  10  and the camera head  28  needs to be fixed during the procedure, although it does not need to be the same for different endoscopes. This principle of operation of the 3D adapter will be explained in more detail below. 
         [0081]    The optical system of the 3D adapter is shown in  FIG. 6 . The three lens groups are designated as L 1 , L 2  and L 3  and also by the numerals  37 ,  38 ,  39 . The optical system operates as follows. 
         [0082]    Let&#39;s assume that the 2D endoscope  10  which is to be mounted to the 3D camera has an exit pupil  26  that requires that it be magnified by a magnification factor M 1  for proper use with the 3D camera. For this particular endoscope, the lenses L 1 , L 2 , and L 3  shall assume specific axial positions relative to each other, and to the aperture plate  34 , in order to provide the desired image magnification. These positions can be recorded as a set of distances d 1 , d 2 , d 3  of each lens from the aperture plate  34 . Let&#39;s now assume that a different type of endoscope  10  is used with a different exit pupil size that requires a different magnification M 2  for the image of the exit pupil on dual aperture plate  34  to stay unchanged. To achieve this new magnification, the lenses L 1 , L 2  and L 3  shall be disposed at different distances from the aperture plate  34 . A numerical example of first-order optics design of the variable focus system is given below in Table I. 
         [0083]      FIG. 6  shows a first-order optical lay-out corresponding to an endoscope with a relatively large exit pupil of 3 mm, which is typical for a laparoscope. The lens data for this example are assumed to be as follows: 
         [0084]    Field stop diameter: 3 mm 
         [0085]    Ocular focal length: 15 mm 
         [0086]    Exit Pupil diameter: 3 mm 
         [0087]    Distance from exit pupil to lens L 1 : 4 mm 
         [0088]    Focal length of L 1 : 6 mm 
         [0089]    Focal length of L 2 : 8 mm 
         [0090]    Focal length of L 3 : 10 mm 
         [0000]    In this case, the required magnification between the exit pupil  26  and the image of the exit pupil on the dual aperture plate  34  is set to −1 for this particular example. The minus sign indicates the inverted image. 
         [0091]      FIG. 7  shows the lay-out corresponding to a smaller exit pupil of 1.5 mm, typical for smaller endoscopes, e.g., arthroscopes. In order to maintain the same diameter of the image of the exit pupil  26  on the dual aperture plate  34 , the magnification should double to −2. As can be seen in  FIG. 7 , this is accomplished by different positions of lenses L 1 , L 2  and L 3 . Note that in  FIG. 7 , the field stop diameter of the endoscope is changed to 2 mm, as would be typical of a smaller endoscope, and the ocular focal length is changed to 12 mm, again typical for smaller endoscopes. The other initial parameters remain the same as in  FIG. 6 . 
         [0092]    Thus the example shows a system with magnification variability of 2 times. 
         [0093]    All magnification values between −1 and −2 can also be attained: the positions of the lenses for the entire range, with 0.1 magnification step, is given in Table 1. 
         [0000]    
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Pupil Magnification vs. L1, L2 and L3 axial positions 
               
             
          
           
               
                   
                 d1 
                 d2 
                 d3 
                 M 
               
               
                   
                   
               
             
          
           
               
                   
                 18.367 
                 9.167 
                 4.5 
                 −1 
               
               
                   
                 18.769 
                 10.049 
                 4.17 
                 −1.1 
               
               
                   
                 19.009 
                 10.769 
                 3.88 
                 −1.2 
               
               
                   
                 19.134 
                 11.374 
                 3.63 
                 −1.3 
               
               
                   
                 19.176 
                 11.896 
                 3.42 
                 −1.4 
               
               
                   
                 19.161 
                 12.361 
                 3.25 
                 −1.5 
               
               
                   
                 19.107 
                 12.787 
                 3.12 
                 −1.6 
               
               
                   
                 19.027 
                 13.187 
                 3.03 
                 −1.7 
               
               
                   
                 18.933 
                 13.573 
                 2.98 
                 −1.8 
               
               
                   
                 18.832 
                 13.952 
                 2.97 
                 −1.9 
               
               
                   
                 18.733 
                 14.333 
                 3 
                 −2 
               
               
                   
                   
               
             
          
         
       
     
         [0094]    The diagram illustrating positions of the lenses and resulting magnification (negative sign omitted) is shown in  FIG. 8 . 
         [0095]    As follows from the above discussion and the given example, the system is not a “true zoom” since the distance between the endoscope  10  (or its field stop  23  as a reference) is not preserved during magnification change. Rather, the distance between the exit pupil and lens L 1  remains constant. Mechanically this means that each endoscope  10  is mounted into the 3D adapter  36  in such a way that its exit pupil is disposed at a pre-determined distance from the lens L 1  (4 mm in the numerical example above). Then, when magnification changes, the endoscope  10  is allowed to travel together with the lens L 1  without changing the distance between L 1  and the exit pupil  26 . 
         [0096]    Referring back to  FIG. 4 , such a mechanical arrangement is shown. Such an arrangement may be achieved by having the lens L 1  mounted in a telescopic sleeve  40  that is dynamically sealed to the main housing  41  of the 3D adapter  36 . The 3D adapter  36  further comprises a locking mechanism  42  that receives the DIN 58105 eyecup  14  of the conventional endoscope. Such locking mechanisms are well known in the art and are present in all of the endocoupler product examples given above. Different types and makes of endoscopes have different locations of exit pupils with respect to the proximal end  43  of the eyecup  14 . However, for the proper operation of the optical system, the distance between the exit pupil  26  and the lens  37  (L 1 ) shall be maintained constant for all the endoscopes (e.g., 4 mm as in the numerical example above). This can be easily achieved by making the locking mechanism  42  axially pre-adjustable with respect to the sleeve  40 . Various known means may be used, such as a threaded connection between the housing of the locking mechanism  42  and the sleeve  40 . 
         [0097]    After the distance between the exit pupil  26  and the lens  37  has been adjusted to the designed value, the axial position of the mechanism  42  to the lens  37  is fixed, for example by means of locking screws (not shown). The axial position of the mechanism  42  to lens  37  remains fixed for the remainder of the time that the 3D adapter is used to connect that particular 2D endoscope (or that particular type of 2D endoscope) to the 3D camera. The means for axial movements of the lenses according to pre-determined relations are well known in the art and are widely used in commercially-available zoom and variable focus systems. These means are not themselves a subject of the present invention, except to the extent that they provide a means to achieve the goals of the invention, i.e., to provide stereoscopic 3D visualization using commercially available 2D endoscopes. What is shown in  FIG. 4  is a simplified example of one such mechanical arrangement. 
         [0098]    The main housing 41 of the 3D adapter  36  includes axial slots  44 ,  45  and  46  that maintain axial movement of the lenses  37 ,  38  and  39  and also limit the ranges of their axial displacements. The 3D adapter  36  also comprises a zoom sleeve  47  that includes three helical slots (not shown) designed in correspondence with the optical prescription of the zoom positions of the lenses  37 ,  38 ,  39  (such as, for example, per Table 1). The zoom sleeve  47  is permanently affixed to the adjustment ring  48 . Pins  49 ,  50  and  51  are disposed in corresponding helical slots of the zoom sleeve  47  with the slide mechanical fit to the edges of the slots. These pins also extend through the axial slots  44 ,  45  and  46  where they also have a slide fit with the edges. The pins  49 ,  50  and  51  are affixed to the lens sleeves  40 ,  52  and  53 , respectively. When the adjustment ring  48  is rotated by the user, the zoom sleeve  47  rotates with it, then the pins  49 ,  50  and  51  ride along the helical slots of the zoom sleeve  47  and simultaneously along the axial slots  44 ,  45 ,  46 . The lenses  37 ,  38  and  39  will perform the designed axial movements, since they are being driven by the pins  49 ,  50  and  51  affixed to the lens sleeves  40 ,  52  and  53 . 
         [0099]    It should be appreciated that, for each type of commercially available 2D endoscope, the adjustment of the 3D adapter  36  is pre-set and is not intended to be changed during its actual use (e.g., during a surgical procedure). 
         [0100]    Therefore, when the 3D adapter is adjusted for a certain type of endoscope, the adjustment ring  48  may be locked by any known means, such as locking screws (not shown) so that it thereafter remains locked in that position during the use of that type of endoscope (of course, when the type of endoscope is changed, adjustment ring  48  must be unlocked and manipulated so as to adjust for the use of a different type of endoscope). In the preferred embodiment, the 3D adapter  36  represents a stand-alone, hermetically sealed, sterilizable device similar to the commercially-available 2D endocouplers used in conventional 2D endoscopic systems and the commercially-available 3D endocouplers used in conventional 3D endoscopic systems. In  FIG. 4 , the seals are schematically shown as O-ring cross-sections for illustration purposes only. 
         [0101]    The proximal end of the 3D adapter  36  includes a proximal window  54  that is hermetically sealed to the housing  41 . In the preferred embodiment, the 3D adapter  36  releaseably attaches to the camera head  28 , e.g., by a proximally-threaded housing  41  (male thread) connecting to the female thread at the distal end of the camera head  28 . Again, this connection is typical for endocouplers where a C-mount thread connection is commonly used. 
         [0102]    It should be appreciated that  FIGS. 4-8  show the general principles of one preferred construction for the present invention. Optical components schematically shown as single lenses may be compound lenses or lens groups; the details of the mechanical design may vary; the 3D adapter  36  may be permanently integrated to the camera head  28 ; the configuration of the apertures in the aperture plate  34  may also vary depending on the desired balance between 3D effect, light efficiency and image quality. 
         [0103]    It should also be noted that the 3D adapter in fact constitutes an additional relay system so that the images on the image sensors  29   a  and  29   b  become inverted. The simplest way to restore the “upright” orientation of the images is by electronic means, i.e., by applying a simultaneous “mirror” and “top-to-bottom” flip to the image processing chain. These electronic means are well known in the art. Alternatively, although more cumbersome, an image-inverting prism may be included in the 3D coupler optical train. 
         [0104]    The focusing lens  35  in the camera head  28  is schematically shown as a single lens. In practice, it may be a compound lens or a group of lenses. It can also carry a re-focusing function if combined with known means of axial movement for focusing. Moreover the lens  35  could be a zoom system that would then also adjust magnification of the image on the image sensors  29   a  and  29   b.    
         [0105]    The channel separation means  32  is schematically shown as two mirrors. In practice, various means are possible, such as arrangements using prisms where the image sensors  29   a  and  29   b  may be positioned in one plane perpendicular to the optical axis of the endoscope. 
         [0106]    Thus it will be seen that, in one form of the invention, a single, adjustable 3D adapter may be interposed between any one of the many commercially available 2D endoscopes and the 3D camera, and the adjustable 3D adapter may be adjusted so as to accommodate the specific optics of the endoscope being used. In other words, in this form of he invention, a single, adjustable adapter can accommodate a wide range of different commercially available 2D endoscopes. This form of the invention can be very useful where a 3D camera must be used with a wide range of different 2D endoscopes. 
         [0107]    There may be situations where a simplified version of the 3D adapter is advantageous. For example, if the medical facility chooses to have just one type of conventional 2D endoscope to be used for 3D visualization, a simplified 3D adapter may be used. In that case, the variable magnification feature of the 3D adapter shown in  FIG. 4  is no longer necessary, and a simplified 3D adapter (having fixed magnification) may be used. Thus, in a second form of the invention, a fixed magnification 3D adapter may be provided. 
         [0108]    A simplified two-lens group optical design of the 3D adapter with fixed magnification is shown in  FIG. 9  (the first-order optical design scheme is shown). In  FIG. 9 , the distance between the exit pupil  26  of the endoscope and the first lens L 1  is equal to the focal length of L 1 . The intermediate image of the field stop  23  (and of the object under observation) is then formed in the vicinity of the second focal plane of the lens L 1 . The lens L 3  is disposed at the distance from L 1  that is equal to the sum of focal lengths of L 1  and L 3 , so that the intermediate image is in the first focal plane of the lens L 3 . Therefore the collimated beam is obtained proximally to the lens L 3 . The magnification of the image of the exit pupil formed on the dual aperture plate  34  calculates as the ratio of the focal lengths of L 3  and L 1 . The opto-mechanical implementation of this embodiment will be a significantly simplified version of the design shown in  FIG. 4 . There are only two lens groups instead of three lens groups. The lens group positions are fixed, so no zoom sleeves with helical slots, nor telescopic sleeves, are required. 
         [0109]    In this form of the invention, it is possible to provide a kit of different 3D adapters, each with a different fixed magnification, with the appropriate 3D adapter being selected from the kit according to the specific optical properties of the particular 2D endoscope which is to be mounted to the 3D camera. 
         [0110]    Sometimes it is desirable to be able to attain a certain optical magnification of the image formed on the image sensors  29   a  and  29   b  relative to the intermediate image at the field stop  23 . By way of example, in some instances the users may prefer to observe the entire field of view obtained by the endoscope. In that case the image of the field stop  23  will be projected on the image sensors in such a way that the image is inscribed inside the sensing area (see  FIG. 10 , left picture). The hatched area will appear black on the monitor. By way of further example, in other instances the users may prefer to fill the entire monitor with the image, which is illustrated in  FIG. 10  on the right. All scenarios in between are also possible. 
         [0111]    In conventional 2D endoscopic visualization, obtaining different magnification is achieved by either utilizing a zoom endocoupler (or a camera head with integrated zoom optics) or by using a set of fixed focal length endocouplers per user preference. In other words, the user who prefers filling the entire screen will be selecting an endocoupler with longer focus and vice versa. One drawback of the embodiment shown in  FIG. 4  is that the focusing lens  35  is included in the camera head  28  assembly, which is the most expensive part of the system. In order to change magnification, a different camera head would need to be used.  FIG. 11  schematically shows another embodiment of the invention overcoming this drawback. In this embodiment, the dual aperture plate  34  is included in the 3D adapter  36 . Focusing lenses  55   a  and  55   b  (schematically shown as single lens elements) are disposed in 3D adapter  36  in proximity to the openings in the dual aperture plate  34 . A different arrangement for channel separation is illustrated in  FIG. 11  compared to  FIG. 4 . The channel separation elements  32  represent two sets of parallel mirror surfaces easily achieved by actual mirrors or rhomboid type prisms.  FIG. 11  shows only the proximal part of the 3D adapter  36 , the distal portion may be similar to the design shown in  FIGS. 4 ,  6 ,  7 , or to the simplified version of  FIG. 9 . Since the focusing lenses  55   a  and  55   b  reside within the 3D adapter  36 , the image magnification is determined by a combination of the 2D endoscope  10  and the 3D adapter  36 . A set of adapters with different magnifications may be used, similarly to the conventional 2D visualization using a set of 2D endocouplers. 
         [0112]    Alternatively, lenses  55   a,    56   a  (shown as a single lenses for illustration purpose only) may incorporate a zoom feature providing variable magnification as desired. 
         [0113]    Thus it will be appreciated that, in order to couple a conventional 2D endoscope to a 3D camera so as to provide stereoscopic 3D visualization of a scene, an adapter must be interposed between the 2D endoscope and the 3D camera. Inasmuch as optical characteristics vary from endoscope to endoscope (depending on field stop  23 , ocular focal length  24  and exit pupil diameter  26 , among other things), the adapter must provide optics which are appropriate for the particular 2D endoscope being used. In one form of the invention, this is achieved by providing an adjustable 3D adapter. In another form of the invention, this is achieved by providing a kit of different 3D adapters, with an appropriate adapter being selected according to the particular 2D endoscope being used. 
       Further Modifications 
       [0114]    It should be understood that many additional changes in the details, materials, steps and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the present invention, may be made by those skilled in the art while still remaining within the principles and scope of the invention.