Abstract:
A stereoscopic lens system for a stereo endoscope is disclosed, the stereoscopic lens system converting light propagated from an object and received at an objective end of the stereoscopic lens system to left and right optical images at an image plane end of the stereoscopic lens system. The system includes at least one linearly movable left optical element configured to selectably adjust the magnification and field of view of the left image in response to linear movement and at least one linearly movable right optical element configured to selectably adjust the magnification and field of view of the right image in response to linear movement. The at least one linearly movable left optical element and the at least one linearly movable right optical element are selectably movable in fixed relation to each other.

Description:
BACKGROUND 
       [0001]    The present disclosure relates generally to optical lens systems, and, more particularly, relates to stereoscopic objective lens designs with a zoom function adapted for use in stereo video endoscopes. 
         [0002]    Medical endoscopes are widely utilized to view internal regions of the human body during diagnostic, surgical, and other medical procedures. Endoscopes typically include a long, thin, rigid or semi-rigid optical cylinder affixed to a viewing mechanism. The cylinder is sufficiently narrow to be inserted through a small opening in the body, which may be natural or surgical. When the endoscope is inserted and positioned for use, an image of the object being viewed is formed at an inserted end of the endoscope by an objective lens. The image passes through a series of relay lenses down the cylinder to an eye lens or video camera at a viewing end of the endoscope. 
         [0003]    In recent years, researchers have attempted to improve the imaging available through endoscopic devices by developing stereoscopic video endoscopes. These endoscopes present an apparently three-dimensional image on a video monitor. The stereoscopic effect is created by producing two optical images—a left image and a right image—through the endoscope. The left and right optical images are presented by the endoscope to left and right image sensors, which may be charge-coupled device (CCD) cameras or other image sensing devices. The sensing devices convert the left and right optical images into left and right video images which are then presented as alternating left-right images on a monitor, at a switching rate higher than the flicker-sensing limit of the human eye, so that observed images appear flicker-free. 
         [0004]    In existing stereoscopic video endoscopes, the object position, which corresponds to the distance from the end of the endoscope to the area of interest, is fixed at the location corresponding to the stereo plane designed into the endoscope. Any departure from this plane causes differential results in the stereoscopic effect. Nevertheless, surgeons commonly change the distance to the object of interest when using a stereoscopic video endoscope. For example, to see more area, the surgeon may pull the endoscope away from the object of interest, and conversely to increase the magnification, the surgeon may move the endoscope closer to the object of interest. It would be desirable to have a stereoscopic video endoscope that provides the ability to change the magnification without moving the endoscope. 
       SUMMARY 
       [0005]    The inventors have realized that by including an objective lens system with a linear zoom mechanism in a stereo endoscope, the user is provided with the ability to change the magnification and/or field of view without moving the endoscope, and thus without degrading the 3D effect. The inventors have also realized that further including an angle reduction telescope in the endoscope provides the user with an angled line of sight. The angle reduction telescope may be incorporated in a rotatable end of the endoscope, thereby allowing the user to view additional areas of interest without changing the position of the endoscope. 
         [0006]    In one aspect, a stereoscopic lens system for a stereo endoscope is disclosed, the stereoscopic lens system converting light propagated from an object and received at an objective end of the stereoscopic lens system to left and right optical images at an image plane end of the stereoscopic lens system. The system includes at least one linearly movable left optical element configured to selectably adjust the magnification and field of view of the left image in response to linear movement and at least one linearly movable right optical element configured to selectably adjust the magnification and field of view of the right image in response to linear movement. The at least one linearly movable left optical element and the at least one linearly movable right optical element are selectably movable in fixed relation to each other. 
         [0007]    In some embodiments, the system includes one or more optical elements adapted to collect light from an object and direct first and second portions of the light along a left optical path and a right optical path respectively; a left group of optical elements having an optical axis disposed along the left optical path and configured to provide a selectably magnified left image of the object at the image plane; and a right group of optical elements having an optical axis disposed along the right optical path and configured to provide a selectably magnified left image of the object at the image plane. The left and right groups of optical elements each include at least one fixed zoom lens, at least one object side movable zoom lens proximate the object end, and linearly movable along the optical axis, at least one image side movable zoom lens proximate the image plane, and linearly movable along the optical axis, the at least one object side movable zoom lens and the at least one image side movable zoom lens being selectably movable in fixed relation to each other. The magnification and field of view of the left image and the magnification and field of view of the right image depend on the position of the movable zoom lenses of said left group of optical elements and right group of optical elements, respectively. 
         [0008]    In some embodiments, the at least one object side movable zoom lens and the at least one image side movable zoom lens of the left group of optical elements are movable in fixed relationship to the at least one object side movable zoom lens and the at least one image side movable zoom lens of the right group of optical elements. 
         [0009]    In some embodiments, the at least one object side movable zoom lens and the at least one image side movable zoom lens of the left group of optical elements and the at least one object side movable zoom lens and at least one image side movable zoom lens of the right group of optical elements are affixed to a selectably movable platform. 
         [0010]    In some embodiments, for each of the left group of optical elements and the right group of optical elements, the at least one fixed zoom lens includes a positive lens, the at least one object side lens includes a negative lens, and the at least one image side lens includes a negative lens. 
         [0011]    In some embodiments, corresponding portions of the left and right images are mapped to within a selected distance of each other at the image plane. 
         [0012]    In some embodiments, the one or more optical elements adapted to collect light from an object and direct first and second portions of the light along a left optical path and a right optical path includes at least one collimator lens proximate the objective end for collecting and substantially collimating light from points on the object, at least one right stereo lens and at least one left stereo lens adjacent to the collimator lens for collecting light from the collimator lens. The optical axis of the right and left stereo lenses are substantially parallel to the optical axis of the collimator lens. The collimator lens and the right and left stereo lenses are arranged so that the collimator lens provides equal-angle light ray pairs from symmetrically disposed object points to the right and left stereo lenses. 
         [0013]    In some embodiments, the system also includes a cover glass adjacent the at least one collimator lens and proximate the objective end. In some embodiments, the cover glass includes fused silica. The cover glass may be scratch resistant. 
         [0014]    In some embodiments, the system also includes at least one left relay lens positioned along the left optical path; and at least one right relay lens positioned along the right optical path. 
         [0015]    In some embodiments, the at least one right relay optical lens is positioned between the at least one right stereo lens and the right group of optical elements, and the at least one left relay optical lens is positioned between the at least one left stereo lens and the left group of optical elements. 
         [0016]    In some embodiments, the at least one right relay optical lens is configured to relay a pupil from a position adjacent to the at least one right stereo lens into the right group of optical elements, and the at least one left relay optical lens is configured to relay a pupil from a position adjacent to the at least one left stereo lens into the left group of optical elements. 
         [0017]    In some embodiments the system also includes at least one right imaging lens configured to receive light from the right group of optical elements and to provide the right image at the image plane, and at least one left imaging lens configured to receive light from the left group of optical elements and to provide the left image at the image plane. 
         [0018]    In some embodiments, the left group of optical elements and the right group of optical elements each comprise first and second linearly movable zoom lenses positioned on opposing sides of a fixed zoom lens and movable in fixed relation to each other. 
         [0019]    In some embodiments the system also includes a reduction telescope configured to provide an angled line of sight. For example, in some embodiments the system also includes a pupil-imaging lens aligned along the optical axis of the least one collimator lens and positioned closer to the objective end than the at least one collimator lens, and an angle reduction telescope aligned along the optical axis with the at least one collimator lens and positioned closer to the objective end than the pupil-imaging lens, the angle reduction telescope configured to provide an angled line of sight. In some embodiments, the angle reduction telescope is configured to be rotatable in a rotation plane positioned between the angle reduction telescope and the pupil-imaging lens. 
         [0020]    In some embodiments, the at least one linearly movable left optical element and the at least one linearly movable right optical are configured to provide at least three times magnification of the object at the left image and the right image respectively. 
         [0021]    In some embodiments, the lens system is configured to provide the left and right optical images with substantially diffraction limited resolution across the field of view of the endoscope. 
         [0022]    A number of documents are incorporated herein by reference. In case of conflict, the current specification will control. The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  is a schematic diagram depicting a stereo video endoscope utilizing an objective lens system. 
           [0024]      FIG. 2  is an optical schematic diagram depicting an objective lens system, showing light rays transmitted through the system. 
           [0025]      FIG. 3  is an optical schematic diagram depicting the objective lens system of  FIG. 2  in combination with relay lenses for transmitting the optical images. 
           [0026]      FIG. 4  is an optical schematic diagram of the objective lens system of  FIG. 2  illustrating the location of the surfaces specified in Table A. 
           [0027]      FIG. 5  is an optical diagram of the objective lens system of  FIG. 2  incorporating gradient index lenses in place of the doublet lenses. 
           [0028]      FIGS. 6 and 7  are optical schematic diagrams depicting an objective lens system wherein the collimating lens system is formed of a combination of singlet and doublet lenses. 
           [0029]      FIGS. 8A and 8B  show an optical schematic diagram depicting an objective lens system with a zoom set for a wide field of view, showing light rays transmitted through the system. 
           [0030]      FIGS. 9A and 9B  show an optical schematic diagram depicting an objective lens system with a zoom set for a narrow field of view, showing light rays transmitted through the system. 
           [0031]      FIG. 10  is a summary of optical data related to the working example of Table D. 
           [0032]      FIG. 11  is an optical schematic diagram depicting an objective lens system with a rotational front, showing light rays transmitted through the system. 
           [0033]      FIG. 12  is an expanded view of the rotational front shown in  FIG. 11 , showing light rats translated through system. 
           [0034]      FIG. 12   a  illustrates the operation of stereo endoscope with a rotatable front end. 
           [0035]      FIG. 13  is an optical schematic diagram illustrating the zoom operation of the objective lens system shown in  FIG. 1I . 
           [0036]      FIG. 14  is a summary of optical data related to the working example of Table E. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0037]      FIG. 1  depicts an endoscope objective system  100 , utilized in a stereo video endoscopy system  1  for generating stereoscopic images of an object  12 . The system  1  includes a stereoscopic endoscope  10  containing objective system  100 , sensing modules  152 ,  154 , switching module  156 , and a monitor  158 . In addition to objective lens system  100 , the endoscope  10  includes conventional relay lenses or optical fibers  150  for transmitting light collected by the endoscope objective system  100  to light sensing modules  152 ,  154 . 
         [0038]    The endoscope objective system  100  generates left and right optical images of the object  12  that are processed by sensing elements  152 ,  154  and video switching module  156  in a known manner to display an apparently three-dimensional image of the object  12  on video monitor  158 . 
         [0039]    The stereoscopic effect is created by producing two optical images—a left image and a right image—through the endoscope objective system  100 . The left and right optical images generated by the objective system  100  are presented by the relay lens or optical fiber system  150  to left and right image sensors  152 ,  154 , which can be conventional charge-coupled device (CCD) cameras or other image sensing devices. The CCD elements operate in a known manner to convert the light collected by the objective system  100 , and transmitted by the relay lenses or optical fibers  150 , into electrical signals representative of the left and right optical images of the object  12 . 
         [0040]    Conventional video switching circuitry  156  transmits the electronic signals representative of left and right video images as alternating left-right images on the monitor  158 . In accord with known video practice, these alternating images are presented at a switching rate higher than the flicker-sensing limit of the human eye, so that observed images appear flicker-free. 
         [0041]    Moreover, the images can be alternately switched from a left-hand polarization mode to a right-hand polarization mode, such that, for example, the left image has a left-hand polarization and the right image has a right-hand polarization. The observer wears polarized glasses in which the left lens has the left-hand polarization and the right lens has the right-hand polarization. Thus, when the observer views the monitor  158 , the left eye sees only images from the left channel of the endoscope system and the right eye sees only images from the right channel, resulting in stereoscopic viewing. Video switching and display equipment of this commercially available from Stereographic, Inc. of San Rafael, Calif.; and from Tektronix Corp, of Beaverton, Oreg. 
         [0042]    The accuracy and quality of the image displayed on monitor  158  is controlled by the performance of the endoscope objective system  100 .  FIGS. 2 and 3  depict an objective lens system  100 , showing light rays transmitted through the system.  FIGS. 2 and 3  depict the same system, with two elements being omitted from  FIG. 3  for purposes of clarity. 
         [0043]    As indicated in  FIG. 2 , one embodiment of the objective system  100  includes two full-diameter doublets  110 ,  112  and a double set of two half-diameter identical doublets  114 ,  116 ,  118 ,  120 . The full-diameter doublets collimate object points, i.e., image them to infinity. Most of the optical power required to accomplish this collimation is provided by the first collimator doublet  110  closest to the object  12 , while the second collimator doublet  112  can have a very low optical power. 
         [0044]    Those skilled in the art will appreciate that the lenses of the objective system  100  depicted in  FIG. 2  define a sequence of sixteen optical surfaces. A working example of a set of lenses objective system  100  is set forth below in Table A. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE A 
               
               
                   
               
               
                 SURFACE 
                 RADIUS 
                 THICKNESS 
                 APERTURE 
                 GLASS 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1 
                 — 
                 4.002608 
                 0.225000 
                 AIR 
               
               
                 2 
                 6.211875 
                 2.500000 
                 3.000000 
                 SK5 
               
               
                 3 
                 4.462623 
                 1.500000 
                 3.000000 
                 SF8 
               
               
                 4 
                 53.596342 
                 0.400000 
                 3.000000 
                 AIR 
               
               
                 5 
                 −11.075366 
                 1.600000 
                 2.500000 
                 SK5 
               
               
                 6 
                 −3.318618 
                 1.500000 
                 3.000000 
                 SF8 
               
               
                 7 
                 −31.896589 
                 −1.200000 
                 2.500000 
                 AIR 
               
               
                 8 
                 — 
                 1.900000 
                 0.464074 
                 AIR 
               
               
                 9 
                 2.747539 
                 1.600000 
                 1.500000 
                 SSKN8 
               
               
                 10 
                 −3.153676 
                 0.700000 
                 1.500000 
                 SF1 
               
               
                 11 
                 4.815753 
                 0.250000 
                 1.500000 
                 AIR 
               
               
                 12 
                 2.747539 
                 1.600000 
                 1.500000 
                 SF1 
               
               
                 13 
                 −3.153676 
                 0.700000 
                 1.500000 
                 SSKN8 
               
               
                 14 
                 4.815753 
                 0.400000 
                 1.500000 
                 AIR 
               
               
                 15 
                 — 
                 0.001000 
                 1.400000 
                 BK7 
               
               
                 16 
                 — 
                 — 
                 1.400000 
                 AIR 
               
               
                   
               
             
          
         
       
     
         [0045]    In Table A, the numerical value in the “RADIUS” and “THICKNESS” columns are set forth in millimeters. The “GLASS” descriptions are standard optical glass characterizations as found in the product catalog of the Schott Glass Company of the Federal Republic of Germany. The “THICKNESS” column refers to the distance to the next optical surface. For example, in connection with surface  3 , the number 1.5000 signifies 1.5 millimeters to surface  4 . The column “RADIUS” refers to the radii of curvature of the respective curved surfaces. In this working example, the lens diameters are 6 millimeters for the large doublets and 3 millimeters for the small doublets. The overall object-to-image distance is 28.3 millimeters. The image diameter is 2.5 millimeters. 
         [0046]    In Table A, the surfaces correspond to the labeled surfaces in  FIG. 4 . The surfaces in the table identified as 1, 8, 15 and 16 do not correspond to actual surfaces, but are artifacts introduced by the specific program employed to generate this table. For clarity the numbered surfaces from table A are designated with an S following the numeral, for example, the surface designated  2 S in  FIG. 4  corresponds to the surface  2  in table A. 
         [0047]    The system  100  is designed so that all parts of each left/right image are mapped to within a selected distance of each other such that stereoscopic image quality is maintained. For video applications, this selected distance is typically a fraction of a video pixel. This is a difficult condition to satisfy, because the object-to-image ray paths through the lens system are quite different for the left and right image points of a common object point.  FIG. 2  clearly illustrates this path difference. The ray paths shown in  FIG. 2  demonstrate how differently an object point is imaged through the lens elements for the left and right images. 
         [0048]    The objective system  100  depicted in  FIG. 2  is able to map all parts of each left/right image to within a fraction of a video pixel to each other, because the large collimator doublets present equal-angle pairs from symmetrically disposed object points to the small stereo doublet pairs. 
         [0049]    This exact equal-angle solution results in an accurate object/image mapping onto the final stereo image pair. Accuracy is also enhanced by the combination of a first high power collimator doublet  110  and a second, lower power collimator doublet  112 . This second doublet  112  strongly influences the optical solution to the image-mapping problem. 
         [0050]    A further advantage is provided in that the smaller doublets  114 ,  116 ,  118 , and  120  are identical, so that they can be most economically fabricated in production quantities. This characteristic tends to offset the inherent difficulty of manufacturing small lenses. The larger, and hence easier to fabricate, doublets carry the corrective burden, so that the smaller, more difficult to manufacture lenses can be as simple as possible. 
         [0051]      FIG. 5  illustrates an objective system  100  where the lens systems are formed of gradient index lenses (GRINS) in place of the doublet lenses. These lenses can be manufactured to duplicate the optical performance of the doublet lenses. In  FIG. 5  a full diameter GRIN collimator lens  210  performs the collimator function and a matched pair of GRIN one half diameter stereo lenses  214  an  216  complete the objective lens assembly. The pair of stereo lenses produces left and right images  226  and  228  on the image plane. (A pair of aperture stops  220  and  222  may be employed to define the pupils.) 
         [0052]    Of course aperture stops may be placed at other locations in the objective lens system according to the purposes of the designer. 
         [0053]      FIGS. 6 and 7  illustrate objective lens systems in which the collimator lens system is formed of a combination of singlet and doublet lenses. The embodiment of the objective system  100  illustrated in  FIG. 6  includes in the collimator lens system  306  a singlet lens  310  coupled to a doublet lens  312 , coupled to another singlet lens  313 . The stereo lens pair system  308  is formed as in  FIG. 2  by a pair of doublet lenses  314  ad  316  coupled to a second pair of doublet lenses  316  and  320 . The full diameter lens system collimates object points. The critical requirement is that the collimator system present equal angle pairs from symmetrically disposed object points to the small stereo lens pairs. This can be accomplished with a doublet lens system as illustrated in  FIG. 2 , a GRIN lens system as illustrated in  FIG. 5 , combinations of singlets and doublets as illustrated in  FIG. 6  or  7 , triplet lenses or combinations of the above. Of course, the stereo lens system can be formed of GRIN lenses also, as well as combinations of singlets, doublets, and triplets as above. 
         [0054]    A working example of a set of lenses for implementation of the objective lens system  100  illustrated in  FIG. 6  is set forth in Table B. As in Table A, the numerical value in the radius and thickness columns are in millimeters. The “GLASS” descriptions are standard optical glass characterizations as found in the product catalog of the Schott Glass Company of the Federal Republic of Germany. The “THICKNESS” column refers to the distance to the next optical surface. For example, in connection with surface  3 , the number 1.5000 signifies 1.5 millimeters to surface  4 . The column “RADIUS” refers to the radii of curvature of the respective curved surfaces. 
         [0055]    In Table B lens surfaces  1 ,  2 ,  9 ,  16  and  17  do not correspond to actual lens surfaces. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE B 
               
             
             
               
                   
               
               
                 STEREO OBJECTIVE, TYPE 3 
               
             
          
           
               
                 SUR- 
                   
                   
                   
                   
                   
               
               
                 FACE 
                 RADIUS 
                 THICKNESS 
                 APERTURE 
                 GLASS 
                 SPE 
               
               
                   
               
             
          
           
               
                 1 
                 — 
                 −3.222728 
                 0.180000A 
                 AIR 
                   
               
               
                 2 
                 — 
                 2.000000 
                 3.000000 
                 SIO2 
                 C 
               
               
                 3 
                 3.000000 
                 1.130000 
                 2.000000 
                 AIR 
               
               
                 4 
                 −6.917339 
                 1.500000 
                 2.000000 
                 SF1 
               
               
                 5 
                 9.000000 
                 2.200000 
                 3.000000 
                 LAKN12 
               
               
                 6 
                 −8.000000 
                 0.505000 
                 3.000000 
                 AIR 
               
               
                 7 
                 −3.200000 
                 2.500000 
                 2.100000 
                 F4 
               
               
                 8 
                 −3.422239 
                 −1.400000 
                 3.000000 
                 AIR 
               
               
                 9 
                 — 
                 2.200000 
                 1.000000 
                 AIR 
               
               
                 10 
                 44.701000 
                 2.500000 
                 1.500000 
                 LAK8 
               
               
                 11 
                 −2.100000 
                 2.000000 
                 1.500000 
                 SF1 
               
               
                 12 
                 −8.920000 
                 0.500000 
                 1.500000 
                 AIR 
               
               
                 13 
                 8.920000 
                 2.000000 
                 1.500000 
                 SF1 
               
               
                 14 
                 2.100000 
                 2.500000 
                 1.500000 
                 LAK8 
               
               
                 15 
                 −44.701000 
                 2.395144 
                 1.500000 
                 AIR 
               
               
                 16 
                 — 
                 0.001000 
                 1.250000 
                 BK7 
               
               
                 17 
                 — 
                 — 
                 1.250000 
                 AIR 
               
               
                   
               
             
          
         
       
     
         [0056]      FIG. 7  illustrates another collimator lens combination  306 , employing a sequence of let lenses  320  and  322  followed by doublet lenses  323 . The physical characteristics sequence are set forth in Table C (the units of numerical values and meaning of the headings are the same as in the tables above). 
         [0057]    Table C is a working example of the objective lens system illustrated in  FIG. 7 . 
         [0058]    In Table C lens surfaces  1 ,  2 ,  9 ,  16  and  17  do not correspond to physical lens surfaces. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE C 
               
             
             
               
                   
               
               
                 STEREO VIDEO SYSTEM 
               
             
          
           
               
                 SUR- 
                   
                   
                   
                   
                   
               
               
                 FACE 
                 RADIUS 
                 THICKNESS 
                 APERTURE 
                 GLASS 
                 SPE 
               
               
                   
               
             
          
           
               
                 1 
                 — 
                 −3.095070 
                 0.160000A 
                 AIR 
                   
               
               
                 2 
                 — 
                 2.000000 
                 3.000000 
                 SIO2 
                 C 
               
               
                 3 
                 3.000000 
                 1.245000 
                 2.000000 
                 AIR 
               
               
                 4 
                 −4.400000 
                 2.200000 
                 2.000000 
                 F4 
               
               
                 5 
                 −3.522702 
                 0.244000 
                 3.000000 
                 AIR 
               
               
                 6 
                 −2.856443 
                 2.000000 
                 2.100000 
                 LAKN12 
               
               
                 7 
                 −9.000000 
                 2.000000 
                 3.000000 
                 SF1 
               
               
                 8 
                 −4.387343 
                 −1.400000 
                 3.000000 
                 AIR 
               
               
                 9 
                 — 
                 2.200000 
                 1.000000 
                 AIR 
               
               
                 10 
                 44.701000 
                 2.500000 
                 1.500000 
                 LAK8 
               
               
                 11 
                 −2.100000 
                 2.000000 
                 1.500000 
                 SF1 
               
               
                 12 
                 −8.920000 
                 0.500000 
                 1.500000 
                 AIR 
               
               
                 13 
                 8.920000 
                 2.000000 
                 1.500000 
                 SF1 
               
               
                 14 
                 2.100000 
                 2.500000 
                 1.500000 
                 LAK8 
               
               
                 15 
                 −44.701000 
                 2.669074 
                 1.500000 
                 AIR 
               
               
                 16 
                 — 
                 0.001000 
                 1.250000 
                 BK7 
               
               
                 17 
                 — 
                 — 
                 1.250000 
                 AIR 
               
               
                   
               
             
          
         
       
     
         [0059]    As indicated in  FIG. 1 , the endoscope objective system  100  can be utilized in connection with optical fiber elements or a set of relay lenses  150  to conduct light from the objective system to the sensing element  152 ,  154 . An example of the relay lens system  150  that can be employed with the objective system  100  is depicted in  FIG. 3 . 
         [0060]    The relay lens system of  FIG. 3  includes a plurality of rod relays  160 ,  162 ,  164  utilized in combination with objective system  100 . Those skilled in the art will recognize that a wide range of relay lens systems can be employed with an objective system of the type described herein. 
         [0061]    Alternatively, an endoscope of the type described herein can employ a conventional CCD array mounted within the same housing as the objective system. As indicated in  FIG. 2 , the CCD array can include left and right sensing elements  152 ,  154 , disposed to receive the optical images generated at the output of doublets  118  and  120 . The design and construction of CCD elements having more than one photosensitive region in a monolithic package is well known in the art. The electrical signals generated by the CCD array can be conducted from the housing by a conventional conduit. This configuration eliminates the requirement for a relay lens system or optical fibers. 
         [0062]    The system  100  depicted in  FIGS. 2 and 3  offers advantages for use in medical endoscopes and industrial borescopes. The configuration offers the advantage of being adaptable to fit into a small tube diameter, as small as 3 millimeters. The design also affords high resolution and low distortion for diagnostic and surgical use, and for high-accuracy industrial measurement applications. 
         [0063]    The systems as described above can be modified to provide additional capabilities including the ability to provide zoom and rotation. By providing a zoom capability, an operator of the system can alter a field of view between a narrow field of view and a wide field of view without adjusting the position of the system. By providing a rotational capability, an operator of the system can change the line of sight and thus effectively view different areas of an object without adjusting the position of the system. In is to be understood that systems incorporating these additional capabilities may also include any of the various features presented in relation to the systems described above. 
         [0064]      FIGS. 8A and 8B  show an optical schematic diagram depicting an objective lens system with a zoom set for a wide field of view, showing light rays transmitted through the system.  FIG. 8A  shows the part of the objective lens system closer to the objective end, and  FIG. 8B  shows the part of the objective lens system closer to the image end. As shown in  FIG. 8A , the system includes a cover glass  402 , full diameter objective lenses  404  and  406 , and half-diameter stereo lens pair  408 . The cover glass  402  is preferably formed of a fused silica or other material capable of forming a hard surface to resist scratching and damage to the system, but is not necessary for the system. The full diameter objective lenses  404  and  406  can be implemented in the same manner as the lenses described above for collimating the object points. Although shown as doublets in a manner similar to those in  FIG. 2 , the full diameter objective lenses  404  and  406  can also be implemented as singlet lenses, some combination of singlet and doublet lenses, or gradient index lenses. 
         [0065]    The half-diameter stereo lens pair  408  produces left and right images from the light collimated by the full diameter objective lenses  404  and  406 . The half-diameter stereo lens pair  408  can be implemented in the same manner as the lenses described above for producing left and right images from the collimated object points. Although shown as doublets in a manner similar to those in  FIG. 2 , the half-diameter objective lens pair  408  can also be singlet lenses, some combination of singlet and doublet lenses, or gradient index lenses. 
         [0066]    As shown in  FIG. 8B , the objective lens system also includes relay lenses  412  and  414 , movable zoom lenses  416  and  418 , fixed zoom lens  420 , and final imaging lenses  422  and  424 . All of these lenses are half-diameter lenses like the half-diameter objective lens pair  408  and are aligned along an optical axis with the half-diameter objective lens pair  408 . The relay lenses  412  and  414  may be identical pairs of right and left lenses and are configured to form a unit magnification telescope to relay a pupil from a position between the half-diameter objective lens pair and the relay lenses  412  into the movable zoom lens  416 . 
         [0067]    The movable zoom lenses  416  and  418  are preferably implemented as right and left pairs of negative lenses (i.e., causing incident light to diverge) and are configured to be movable in a straight line in fixed relation to each other along the optical axis. The mechanism for moving the movable zoom lenses  416  and  418  can be any mechanical and/or electronic device capable of moving the movable zoom lenses  416  and  418  in a straight line. The moving mechanism can be relatively simple and need not include any cam arrangement. For example, the moving mechanism can be implemented as a single simple platform upon which the movable zoom lenses  416  and  418  are mounted. The movable zoom lenses  416  and  418  may be actuated to provide the zoom effect using any suitable system. For example, in some embodiments, the movable lenses may be actuated using a hand-actuated, spring loaded push-pull wire guide system (not shown). In some embodiments, the movable lenses my be actuated by a driving motor controlled by a switch (not shown). In various embodiments, the switch could be, for example, a hand, foot, or even voice controlled device operated by the user of the zoom endoscope, or an assistant. 
         [0068]    The fixed zoom lens  420  is preferably implemented as a right and left pair of positive lenses (i.e., causing incident light to converge to a focal point). The fixed zoom lens  420  is positioned in between the movable zoom lenses  416  and  418 . 
         [0069]    The final imaging lenses  422  and  424  are preferable implemented as right and left pairs of lenses for producing right and left images on an image plane. The CCD  152  (and CCD  154 , not shown in  FIG. 8B ) can detect the right and left images at the image plane and convert the collected light into electrical signals representative of the left and right optical images of the object. 
         [0070]    In the position shown in  FIG. 8B , the movable zoom lens  416  is adjacent to the relay lens  414 , and the movable zoom lens  418  is adjacent to the fixed zoom lens  420 . In this position, the movable zoom lenses  416  and  418  and the fixed zoom lens  420  provide a wide field of view as shown in  FIG. 8A . 
         [0071]      FIGS. 9A and 9B  show an optical schematic diagram depicting an objective lens system with a zoom set for a narrow field of view, showing light rays transmitted through the system. The component lenses of the system of  FIGS. 9A and 9B  are the same as those shown in  FIGS. 8A and 8B . Accordingly, a repeated description of them has been omitted. 
         [0072]    In the position shown in  FIG. 9B , the movable zoom lens  416  is adjacent to the fixed zoom lens  420 , and the movable zoom lens  418  is adjacent to the final imaging lens  422 . In this position, the movable zoom lenses  416  and  418  and the fixed zoom lens  420  provide a narrow field of view as shown in  FIG. 9A . 
         [0073]    Table D is a working example of the objective lens system illustrated in  FIGS. 8A-9B . Those skilled in the art will appreciate that the lenses of the system define a sequence of optical surfaces, as listed in the table. The units of numerical values and meaning of the column headings are the same as in the tables above. “Diameter” refers to the diameter of the surface in millimeters.  FIG. 10 , as will be understood by those in the art, shows the optical system characteristics (e.g. effective focal length, f/# at the image plane, etc.) corresponding to the working example shown in Table D. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE D 
               
               
                   
               
               
                 Surface 
                 Radius 
                 Thickness 
                 Glass 
                 Diameter 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 OBJ 
                 Infinity 
                 25 
                 AIR 
                 20 
               
               
                  1 
                 Infinity 
                 0.8 
                 SILICA 
                 3 
               
               
                  2 
                 Infinity 
                 0.21 
                 AIR 
                 3 
               
               
                  3 
                 −3.864 
                 0.8 
                 SFL6 
                 2.5 
               
               
                  4 
                 −3.965 
                 0.8 
                 LAK8 
                 3 
               
               
                  5 
                 6.82 
                 1 
                 AIR 
                 3 
               
               
                  6 
                 — 
                 0 
                   
                 — 
               
               
                 STOP 
                 Infinity 
                 0.3 
                 AIR 
                 0.2 
               
               
                  8 
                 — 
                 0 
                   
                 — 
               
               
                  9 
                 50.1 
                 1 
                 LAK8 
                 3 
               
               
                 10 
                 −2.687 
                 0.8 
                 SFL6 
                 3 
               
               
                 11 
                 −4.216 
                 0.4 
                 AIR 
                 3 
               
               
                 12 
                 — 
                 0 
                   
                 — 
               
               
                 13 
                 Infinity 
                 0.16 
                 AIR 
                 0 
               
               
                 14 
                 3.248 
                 0.7 
                 SFL6 
                 1.5 
               
               
                 15 
                 1.112 
                 1 
                 LAK8 
                 1.5 
               
               
                 16 
                 −3.200443 
                 2.266537 
                 AIR 
                 1.5 
               
               
                 17 
                 Infinity 
                 7.5 
                 AIR 
                 1.000848 
               
               
                 18 
                 10.18 
                 0.5 
                 SF5 
                 1.5 
               
               
                 19 
                 3.59 
                 1.17 
                 BK7 
                 1.5 
               
               
                 20 
                 −5.15 
                 0.5 
                 AIR 
                 1.5 
               
               
                 21 
                 6.83 
                 0.6 
                 BK7 
                 1.5 
               
               
                 22 
                 −5.83 
                 0.7 
                 SF5 
                 1.5 
               
               
                 23 
                 Infinity 
                 0.7 
                 AIR 
                 1.5 
               
               
                 24 
                 −6.59 
                 0.8 
                 BK7 
                 1.5 
               
               
                 25 
                 6.59 
                 3.6 
                 AIR 
                 1.5 
               
               
                 26 
                 Infinity 
                 0.7 
                 SF5 
                 1.5 
               
               
                 27 
                 −4.333 
                 0.7 
                 AIR 
                 1.5 
               
               
                 28 
                 −6.59 
                 0.8 
                 BK7 
                 1.5 
               
               
                 29 
                 6.59 
                 3.6 
                 AIR 
                 1.5 
               
               
                 30 
                 2.88 
                 0.6 
                 BK7 
                 1.5 
               
               
                 31 
                 2.65 
                 0.6 
                 SF4 
                 1.5 
               
               
                 32 
                 9.665 
                 0.7 
                 AIR 
                 1.5 
               
               
                 33 
                 Infinity 
                 1.1 
                 BK7 
                 1.5 
               
               
                 34 
                 −1.515 
                 0.7 
                 SF4 
                 1.5 
               
               
                 35 
                 2.88 
                 1.1 
                 BK7 
                 1.5 
               
               
                 36 
                 −2.88 
                 6.672692 
                 AIR 
                 1.5 
               
               
                 IMAGE 
                 6.18 
                   
                   
                 0.7860716 
               
               
                   
               
             
          
         
       
     
         [0074]      FIG. 11  is an optical schematic diagram depicting a lens system  500  of the type shown in  FIGS. 8A-9B  with the addition of a rotational front, showing light rays transmitted through the system. As shown in  FIG. 11 , the system includes full diameter objective lenses  404  and  406  and a half-diameter stereo lens pair  408  as shown in  FIGS. 8A and 9A  (although other collimating and stereo lens combinations as described above can also be used). The system also includes the relay lenses  412  and  414 , movable zoom lenses  416  and  418 , fixed zoom lens  420 , and final imaging lenses  422  and  424  shown in  FIGS. 8B and 9B . Note that, for simplicity, only the half diameter optical elements along the right-image optical path are shown. 
         [0075]    The system of  FIG. 11  also includes a pupil-imaging lens  502  and an angle-reduction telescope  504 . The pupil-imaging lens  502  is aligned along the optical axis with objective lenses  404  and  406 . The pupil-imaging lens  502  can be configured as a doublet lens and is preferably configured to generate a focal point between itself and the objective lens  404 . The angle reduction telescope  504  is also aligned along the optical axis with the objective lenses  404  and  406 . 
         [0076]      FIG. 12  shows an expanded view of pupil imaging lens  502  and angle reduction telescope  504 . The angle reduction telescope  504  includes a prism  506  in which left three-dimensional pupil  508  and right three-dimensional pupil  510  are formed. The angle reduction telescope  504  is configured to adjust the line of sight through which an object is observed. For example, the line of sight may be angled at 30 degrees from the plane of the system. 
         [0077]    The angle reduction telescope  504  is also rotatable in a rotation plane  512  positioned between the angle reduction telescope  504  and the pupil-imaging lens  502 . The rotation of the angle reduction telescope  504  enables a user of the system to view different portions of the object of interest. 
         [0078]      FIG. 12   a  illustrates the operation of a stereo endoscope with a rotatable front end  602  as described above. Initially, the endoscope views field of view  604  along a 30 degree line of sight  606 . The front end  602  is then rotated, allowing the user to view, for example, fields of view fields of view  606 ,  608 , and  610 . Note that this configuration allows the angle rotation telescope  504  to be rotated without rotating the entire endoscope. This allows the 3D plan of the endoscope to remain fixed, for example, in the horizontal position as is normal and comfortable to human vision Note also that, in the embodiment shown, the rotation plane  512  is located at a position where the light rays from the angle reduction telescope are well collimated, thereby reducing sensitivity to wobble (i.e. deviations from ideal rotation in rotation plane  512 ). 
         [0079]      FIG. 13  shows lens system  500  at three different zoom settings. Note that, for simplicity, only the half diameter optical elements along the right-image optical path are shown. In the topmost schematic, the movable zoom lens  418  is located adjacent to the fixed zoom lens  420 . This configuration provides a wide field of view (as shown, 44 mm in diameter). In the middle schematic, the movable zoom lenses  416  and  418  have been moved in fixed relation to one another toward the image end of the lens system  500 , providing an intermediately sized field of view (as shown, 32 mm in radius). In the bottom schematic, the movable zoom lenses  416  and  418  have been moved in fixed relation to each other further towards the image end of lens system  500 , so that the movable lens  416  is adjacent to the fixed lens  420 . This configuration provides a small field of view (as shown 14 mm), and correspondingly high magnification. 
         [0080]    Table E is a working example of lens system  500  illustrated in  FIG. 11 . Those skilled in the art will appreciate that the lenses of the system define a sequence of optical surfaces, as listed in the table. The units of numerical values found in the table and meaning of the column headings are the same as in the tables above. “Diameter” refers to the diameter of the surface in millimeters.  FIG. 14 , as will be understood by those in the art, shows the optical characteristics corresponding to the working example shown in Table E. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE E 
               
               
                   
               
               
                 Surface 
                 Radius 
                 Thickness 
                 Glass 
                 Diameter 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 OBJECT 
                 Infinity 
                 15 
                   
                 22 
               
               
                  1 
                 Infinity 
                 1 
                 SILICA 
                 4.05 
               
               
                  2 
                 2.165 
                 0.51 
                 AIR 
                 2.8 
               
               
                  3 
                 Infinity 
                 2.2 
                 LAH58 
                 4.05 
               
               
                  4 
                 — 
                 0 
                   
                 — 
               
               
                  5 
                 Infinity 
                 0 
                 MIRROR 
                 8 
               
               
                  6 
                 — 
                 −2.3 
                   
                 — 
               
               
                  7 
                 — 
                 0 
                   
                 — 
               
               
                  8 
                 Infinity 
                 0 
                 MIRROR 
                 4.4 
               
               
                  9 
                 Infinity 
                 0 
                 LAH58 
                 10 
               
               
                 10 
                 — 
                 2 
                   
                 — 
               
               
                 11 
                 Infinity 
                 1.2 
                 S-BSM36 
                 3 
               
               
                 12 
                 −2.86 
                 0.6 
                 AIR 
                 3 
               
               
                 13 
                 6.68 
                 1.8 
                 BASF13 
                 4 
               
               
                 14 
                 −2.86 
                 0.8 
                 PBH11 
                 4 
               
               
                 15 
                 −22.162 
                 0.25 
                 AIR 
                 4 
               
               
                 16 
                 2.164524 
                 1.6 
                 BASF13 
                 4 
               
               
                 17 
                 2.687 
                 8 
                 AIR 
                 3.2 
               
               
                 18 
                 Infinity 
                 2.5 
                 SK5 
                 6 
               
               
                 19 
                 −7.58 
                 1 
                 AIR 
                 6 
               
               
                 20 
                 57.357 
                 1.2 
                 SF5 
                 6 
               
               
                 21 
                 5.203 
                 2.8 
                 SK5 
                 6 
               
               
                 22 
                 −16.778 
                 1 
                 AIR 
                 6 
               
               
                 23 
                 — 
                 1 
                 AIR 
                 — 
               
               
                 STOP 
                 Infinity 
                 10 
                 AIR 
                 2 
               
               
                 25 
                 7.39 
                 1.68 
                 BK7 
                 3 
               
               
                 26 
                 −5.15 
                 1 
                 SF5 
                 3 
               
               
                 27 
                 −14.62 
                 21.53417 
                 AIR 
                 3 
               
               
                 28 
                 14.62 
                 1 
                 SF5 
                 3 
               
               
                 29 
                 5.15 
                 1.68 
                 BK7 
                 3 
               
               
                 30 
                 −7.39 
                 1 
                 AIR 
                 3 
               
               
                 31 
                 9.81 
                 1.2 
                 BK7 
                 3 
               
               
                 32 
                 −8.367 
                 1 
                 SF5 
                 3 
               
               
                 33 
                 Infinity 
                 1 
                 AIR 
                 3 
               
               
                 34 
                 −9.46 
                 0.8 
                 BK7 
                 3 
               
               
                 35 
                 9.46 
                 5.2 
                 AIR 
                 3 
               
               
                 36 
                 Infinity 
                 1 
                 SF5 
                 2.8 
               
               
                 37 
                 −6.221 
                 1 
                 AIR 
                 2.8 
               
               
                 38 
                 −9.46 
                 0.8 
                 BK7 
                 3 
               
               
                 39 
                 9.46 
                 5.2 
                 AIR 
                 3 
               
               
                 40 
                 4.089938 
                 1.2 
                 BK7 
                 2.7 
               
               
                 41 
                 3.795909 
                 1.2 
                 SF4 
                 2.7 
               
               
                 42 
                 13.63035 
                 0.7 
                 AIR 
                 2.7 
               
               
                 43 
                 Infinity 
                 1.6 
                 BK7 
                 2.7 
               
               
                 44 
                 −2.161934 
                 1 
                 SF4 
                 2.7 
               
               
                 45 
                 4.086527 
                 1.6 
                 BK7 
                 2.7 
               
               
                 46 
                 −4.086527 
                 8.642132 
                 AIR 
                 2.7 
               
               
                 IMAGE 
                 Infinity 
                   
                   
                 1.4 
               
               
                   
               
             
          
         
       
     
         [0081]    In various embodiments, the stereo zoom endoscope objective lens systems described above can be constructed so as to provide magnification of three times (3×) or more. In some embodiments, the resolution of the lens system may be substantially diffraction limited over the entire field of view. In some embodiments, the system can also provide constant optical speed (i.e. f/#) at the left and right images. In various embodiments, optical speed of the system at the images can correspond to an f/# of about 8 or greater. 
         [0082]    It is to be understood that, in any of the examples presented, any lens or group of lens may be replaces by an equivalent optical element or elements such as, for example, a GRIN lens, a reflective element (e.g., a curved mirror), or diffractive element (e.g., a hologram). 
         [0083]    As used herein, the term “optical” is intended to refer not only to the visible spectrum, but also, for example, ultraviolet and infrared light. 
         [0084]    A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are in the following claims.