Patent Publication Number: US-2015073219-A1

Title: Stereoscopic endoscope

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Japanese Priority Patent Application JP 2013-186481 filed Sep. 9, 2013, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     The present technology relates to a stereoscopic endoscope provided with a pupil splitting polarizing element that includes a pair of polarizers, in which light is polarized by a pair of polarizers in order to generate a right eye image and a left eye image, respectively, and the polarized light is incident on an imaging device. 
     A stereoscopic endoscope which uses an imaging optical system that acquires a stereoscopic image has been proposed in the related art (refer to Japanese Patent No. 3285217 and Japanese Unexamined Patent Application Publication No. 8-292379, for example). 
     The stereoscopic endoscope disclosed in Japanese Patent No. 3285217 is configured such that two lens barrels for a left eye and for a right eye, respectively, are disposed at an interval corresponding to a desired parallax amount, and that a stereoscopic image is obtained using the parallax between the left eye and the right eye. 
     The stereoscopic endoscope disclosed in Japanese Unexamined Patent Application Publication No. 8-292379 is configured such that a pupil splitting mirror which separates an optical path into two, for the left eye and for the right eye, is disposed at a pupil position of a single objective optical system, and that two sets of image forming optical systems which form two split images and corresponding two sets of imaging devices are disposed to acquire a stereoscopic image. 
     However, in the stereoscopic endoscope disclosed in Japanese Patent No. 3285217, since two lens barrels are necessary, the diameter is increased and the weight becomes heavy. In particular, in recent years, the frequency of performing surgical operations using a minimally invasive endoscope has increased; and, in such operations, an increase in the diameter of the portion that is inserted into the body entails an increase in the load on the patient. 
     In the stereoscopic endoscope disclosed in Japanese Unexamined Patent Application Publication No. 8-292379, a pupil splitting mirror, two sets of image forming optical systems, and two sets of imaging devices are necessary; as such, the number of components is great and the diameter and weight are increased. 
     Therefore, a type of stereoscopic endoscope in which a single imaging optical system and a single imaging device are disposed has been proposed as a stereoscopic endoscope in which an increase in the diameter and the weight is avoided and miniaturization and weight reduction are achieved (refer to Japanese Unexamined Patent Application Publication No. 2013-106189, for example). 
     The stereoscopic endoscope disclosed in Japanese Unexamined Patent Application Publication No. 2013-106189 is provided with a polarization filter that includes a first filter portion (a first region) and a second filter portion (a second region) for generating the right eye image and the left eye image, respectively. In the first filter portion, a first polarized light component which oscillates in a first direction is transmitted, and a second polarized light component which oscillates in a second direction, which is perpendicular to the first direction, is blocked. In the second filter portion, the first polarized light component is blocked, and the second polarized light component is transmitted. The first polarized light component, which is transmitted through the first filter portion, and the second polarized light component, which is transmitted through the second filter portion, are incident on an imaging device. 
     SUMMARY 
     Incidentally, in the stereoscopic endoscope which is configured such that each polarization takes place at a different region, as disclosed in Japanese Unexamined Patent Application Publication No. 2013-106189, it is important for the acquisition of a favorable stereoscopic image that light of a predetermined intensity is incident on each region in which the polarization of the polarizer is performed, and it is necessary to secure high positional precision for each region. 
     It is desirable to acquire a favorable stereoscopic image by achieving an improvement in the positional precision of the pair of polarizers of the pupil splitting polarizing element. 
     According to an embodiment of the present technology, there is provided a stereoscopic endoscope, which includes an imaging optical system including a diaphragm which adjusts light intensity and a pupil splitting polarizing element that has a pair of polarizers which are disposed to line up along a splitting line as a boundary; a scope holder in which at least the pupil splitting polarizing element is disposed in an inner portion thereof; and an imaging device on which light is incident via the imaging optical system. Light which is incident on the pupil splitting polarizing element is polarized by the pair of polarizers in order to generate a right eye image and a left eye image, respectively. A direction that is perpendicular to both the splitting line and an optical axis is a positioning direction. Positioning portions are provided to position the pupil splitting polarizing element in relation to a conjugate position of the diaphragm, or a proximity thereof, in the positioning direction. 
     Accordingly, the pupil splitting polarizing element is positioned, by the positioning portion, in relation to the conjugate position of the diaphragm, or the proximity thereof, in the positioning direction. 
     It is desirable that the stereoscopic endoscope described above further include an element holder which holds the pupil splitting polarizing element. 
     Accordingly, the pupil splitting polarizing element is attached to the scope holder in a state of being held in the element holder. 
     In the stereoscopic endoscope described above, it is desirable that positioning grooves which extend in the positioning direction be formed in one of the scope holder and the element holder, that positioning pins which extend in an optical axis direction and are supported in the positioning grooves to slide freely be provided on the other of the scope holder or the element holder, that the positioning portions be configured of the positioning pins and the positioning grooves, and that the pupil splitting polarizing element be positioned by changes in relative position of the positioning pins and the positioning grooves. 
     Accordingly, the pupil splitting polarizing element is positioned due to the relative position between the positioning pin and the positioning groove changing when the positioning pin is guided by the positioning groove. 
     It is desirable that the stereoscopic endoscope described above further include adjusting screws of which a position thereof in the positioning direction is changed when distal ends thereof are pressed against the element holder and the adjusting screws are rotated, and that the positioning be performed when the adjusting screws are rotated, with positions of the element holder and the pupil splitting polarizing element being changed. 
     Accordingly, the position of the pupil splitting polarizing element changes according to the rotation amount of the adjusting screws. 
     In the stereoscopic endoscope described above, it is desirable that the adjusting screw be rotated by an adjusting jig, and that a jig insertion hole into which the adjusting jig is inserted be formed in the scope holder. 
     Accordingly, the positioning is performed when the adjusting screw is rotated by the adjusting jig from the outside of the scope holder. 
     In the stereoscopic endoscope described above, it is desirable that positioning marks for positioning the splitting line during attachment of the pupil splitting polarizing element to the element holder be formed in the element holder. 
     Accordingly, the pupil splitting polarizing element is positioned when the splitting line is matched to the positioning marks. 
     In the stereoscopic endoscope described above, it is desirable that a retaining surface be formed on the scope holder, and that biasing springs which bias the element holder in an optical axis direction, press the element holder against the retaining surface, and position the pupil splitting polarizing element in the optical axis direction. 
     Accordingly, the attachment of the pupil splitting polarizing element to the scope holder and the positioning of the pupil splitting polarizing element in the optical axis direction are performed at the same time. 
     In the stereoscopic endoscope described above, it is desirable that cut-out surfaces be formed on an outer circumference of the element holder, and that member disposition spaces, in which predetermined members are disposed, be formed between the element holder and the scope holder by the cut-out surfaces. 
     Accordingly, the space in the inner portion of the scope holder is used as a space for disposing predetermined members. 
     In the stereoscopic endoscope described above, it is desirable that the pupil splitting polarizing element be disposed in the conjugate position of the diaphragm. 
     Accordingly, the pupil splitting polarizing element is disposed in an optimal position without influencing the optical performance of the imaging optical system. 
     In the stereoscopic endoscope described above, it is desirable that the pupil splitting polarizing element be disposed in a proximity of the conjugate position of the diaphragm. 
     Accordingly, the pupil splitting polarizing element is disposed in an optimal position taking aberration which occurs in the imaging optical system into consideration. 
     In the stereoscopic endoscope of the embodiment of the present technology, the pupil splitting polarizing element is positioned, by the positioning portion, in relation to the conjugate position of the diaphragm, or the proximity thereof, in the positioning direction; thus it is possible to acquire a favorable stereoscopic image with an improvement in the positional precision of the pair of polarizers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1 , together with  FIGS. 2 to 22 , shows a stereoscopic endoscope of an embodiment of the present technology, and is a perspective view of the stereoscopic endoscope; 
         FIG. 2  is a perspective view showing the stereoscopic endoscope in a state in which a monocular endoscope and an imaging head unit are separated; 
         FIG. 3  is an enlarged plan view of a scope holder; 
         FIG. 4  is a schematic view showing an imaging device; 
         FIG. 5  is an enlarged front view of the scope holder; 
         FIG. 6  is an enlarged vertical cross sectional view of the scope holder; 
         FIG. 7  is an enlarged horizontal cross sectional view of the scope holder; 
         FIG. 8  is a schematic enlarged exploded perspective view of a polarizing element block; 
         FIG. 9  is a schematic enlarged side view of the polarizing element block; 
         FIG. 10  is an enlarged perspective view of an element holder; 
         FIG. 11  is an enlarged front view of the element holder; 
         FIG. 12  is an enlarged horizontal cross sectional view of the element holder; 
         FIG. 13  is an enlarged perspective view of the polarizing element block; 
         FIG. 14  is a cross-sectional view along the XIV-XIV line of  FIG. 13 ; 
         FIG. 15  is an enlarged exploded perspective view showing the scope holder, the polarizing element block, biasing springs and the like; 
         FIG. 16  is an enlarged perspective view showing a state in which the polarizing element block is disposed in an inner portion of the scope holder; 
         FIG. 17  is an enlarged perspective view showing the state in which the polarizing element block is disposed in the inner portion of the scope holder when viewed from a different direction from that in  FIG. 16 ; 
         FIG. 18  is an enlarged horizontal cross sectional view showing a state in which the polarizing element block is disposed in the inner portion of the scope holder; 
         FIG. 19  is an enlarged vertical cross sectional view showing a state in which the polarizing element block is disposed in the inner portion of the scope holder; 
         FIG. 20  is an enlarged partial cross sectional front view showing a state in which the polarizing element block is disposed in the inner portion of the scope holder; 
         FIG. 21  is an enlarged partial cross sectional front view showing a state before positioning work of the polarizing element block in relation to the scope holder is performed; and 
         FIG. 22  is an enlarged partial cross sectional front view showing a state in which the positioning work of the polarizing element block in relation to the scope holder is performed. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, description will be given of an embodiment of the stereoscopic endoscope of the present technology according to the attached drawings. 
     In the description hereinafter, the directions front, rear, up, down, left and right are indicated as seen from the perspective of a photographer when photographing with the stereoscopic endoscope. Therefore, an object side is the front, and the side of the photographer (the image side) is the rear. 
     Note that, the directions front, rear, up, down, left and right indicated hereinafter are intended to facilitate explanation, and embodiments of the present technology are not limited to these directions. 
     Schematic Configuration of Stereoscopic Endoscope 
     A stereoscopic endoscope  1  is configured of a removable monocular endoscope  2  and an imaging head unit  3  (refer to  FIGS. 1 and 2 ). An imaging optical system that includes various optical components such as a lens, a diaphragm, and a polarizing element for imaging an object is provided in the inner portions of the monocular endoscope  2  and the imaging head unit  3 . 
     The monocular endoscope  2  is a so-called hard mirror in which the portion that is inserted into the body is formed hard, and includes an insertion portion  4 , which is long, thin and extends in the front-rear direction in which the insertion portion  4  is inserted into the body, and an observation portion  5  which is provided to continue from the rear end of the insertion portion  4 . The diameter of the observation portion  5  is larger than that of the insertion portion  4 . 
     The rear end portion of the observation portion  5  is provided as a joining portion  5   a , which is formed in a shape in which the diameter thereof increases away from the insertion portion  4 . The surface of the front side of the joining portion  5   a  is an inclined surface  5   b.    
     An objective optical system (not shown) that includes a plurality of lenses and the like, generally one or more relay optical systems, and an ocular optical system are disposed in the inner portion of the monocular endoscope  2  in order from the front side of the insertion portion  4  to the rear side. A brightness diaphragm (hereinafter referred to as a “diaphragm”) is provided in the hard mirror optical system. An image of the object is formed by the objective optical system, and the formed image is transmitted to the ocular optical system by the relay optical system. During photography, the light that is incident on the monocular endoscope  2  from the object side forms a primary image between the objective optical system and the relay optical system, forms a secondary (or higher order) image between the relay optical system and the ocular optical system, and afocal light is emitted from the observation portion  5  toward the imaging head unit  3 . 
     Note that, using the monocular endoscope  2 , it is possible to perform monocular observation using a video system corresponding to the monocular endoscope  2 , for example. 
     The imaging head unit  3  includes an imaging unit  6  and a connecting portion  7 . The monocular endoscope  2  is joined to the front end portion of the imaging unit  6 , and the connecting portion  7  is attached to the rear end portion of the imaging unit  6 . A connector (not shown) is connected to the connecting portion  7 , and the imaging head unit  3  is connected to a power source circuit or the like via the connector. 
     The imaging unit  6  is formed of a scope holder  8  that functions as an outer barrel, and the necessary components that are disposed in the inner portion of the scope holder  8 . 
     The scope holder  8  is formed in a shape that extends in the front-rear direction, and cutout portions  8   a ,  8   a  that are open to both sides are formed in a portion of the scope holder  8  excluding both the front and the rear end portions. In the scope holder  8 , the front end portion and the rear end portion are each formed in a cylindrical shape, and as shown in  FIG. 3 , the front end portion is provided as an attaching portion  9 , the rear end portion is provided as an element displacement portion  10 , and the portion between both the front and the rear end portions is provided as a lens displacement portion  11 . 
     An imaging device  12  is displaced on the element displacement portion  10  of the scope holder  8 . As shown in  FIG. 4 , the imaging device  12  is a layered imaging device, and is configured such that wire-grid polarizers  12   a ,  12   a ,  12   b ,  12   b , . . . of +45° and −45°, using a vertical line as a reference, are provided at predetermined corresponding positions on a detection surface. 
     An attachment lens  13  is disposed on the lens displacement portion  11  of the scope holder  8 . 
     A joining space  9   a , a disposition space  9   b , and a communicating space  9   c  are formed in order from the front side on the inside of the attaching portion  9  of the scope holder  8  (refer to  FIGS. 5 to 7 ). The outer diameters of the joining space  9   a , the disposition space  9   b , and the communicating space  9   c  become smaller in this order; and, in the inner circumferential portion of the attaching portion  9 , a step-shaped bearing surface  14  facing forward is formed between the joining space  9   a  and the disposition space  9   b , and a step-shaped retaining surface  15  facing forward is formed between the disposition space  9   b  and the communicating space  9   c.    
     In the attaching portion  9 , attaching holes  9   d ,  9   d ,  9   d  are formed on the portion on which the joining space  9   a  is formed to be spaced equidistantly from one another in the circumferential direction. 
     In the attaching portion  9 , jig insertion holes  9   e ,  9   e  are formed on both left and right end portions, respectively, of the outside of the disposition space  9   b , the jig insertion holes  9   e ,  9   e  are formed by penetrating to communicate the outside of the attaching portion  9  with the disposition space  9   b . Screw grooves are formed in the jig insertion holes  9   e ,  9   e.    
     In the attaching portion  9 , screw holes  9   f ,  9   f  are formed on both top and bottom end portions, respectively, on the outside of the communicating space  9   c , and the screw holes  9   f ,  9   f  are penetrated in the front-back direction. In the attaching portion  9 , positioning grooves  9   g ,  9   g  which extend to the left and the right and are penetrated through the front and back are formed on both left and right end portions, respectively, on the outside of the communicating space  9   c , and each of the positioning grooves  9   g ,  9   g  are open to the inside. 
     A polarizing element block  16  is displaced in the disposition space  9   b  of the attaching portion  9 . The polarizing element block  16  is formed of a pupil splitting polarizing element  17 , and an element holder  18  that holds the pupil splitting polarizing element  17 . 
     The pupil splitting polarizing element  17  includes a pair of polarizers  17   a ,  17   b , each of which is formed in a crescent-shape, and the polarizers  17   a ,  17   b  are disposed to line up to the left and right with the linear side edge of each as the boundary (refer to  FIG. 8 ). The boundary of the polarizers  17   a ,  17   b  is a splitting line P. Circular plate shaped glass plates  19 ,  19  are joined from the front and the rear to the polarizers  17   a ,  17   b  that are lined up on the left and the right (refer to  FIGS. 8 and 9 ). The polarizers  17   a ,  17   b  have axes that easily transmit light polarized at +45° and at −45°, respectively, using the splitting line P as a reference. Note that, the transmission axes are not limited to those described above, and may also be 0° and 90°. In this case, the imaging device  12  is provided with wire-grid polarizers of 0° and 90°, using a vertical line as a reference. 
     The element holder  18  is formed in an annular shape, and as shown in  FIGS. 10 to 12 , includes cutout surfaces  18   a ,  18   a , side surfaces  18   b ,  18   b , and four arc surfaces  18   c ,  18   c , . . . . The cutout surfaces  18   a ,  18   a  are positioned on the top and bottom of the element holder  18  and the outer circumferential surfaces face upward or downward, the side surfaces  18   b ,  18   b  are positioned on the left and the right to face leftward or rightward, and the arc surfaces  18   c ,  18   c , . . . extend in the circumferential direction. The four arc surfaces  18   c ,  18   c , . . . are positioned between the cutout surfaces  18   a ,  18   a  and the side surfaces  18   b ,  18   b , respectively. Positioning marks M, M that extend vertically are formed in the central portion in the horizontal direction of both top and bottom end portions on the front surface of the element holder  18 . 
     Positioning pins  20 ,  20  are attached to both left and right end portions, respectively, of the element holder  18 , and each of the positioning pins  20 ,  20  protrude to the rear. The diameter of the positioning pin  20  is formed at approximately the same size as the width in the vertical direction of the positioning groove  9   g  which is formed on the attaching portion  9  of the scope holder  8 . 
     An attaching concave portion  21  which is open to the front is formed in the inner circumferential portion of the element holder  18 . The outer diameter of the attaching concave portion  21  is approximately the same size as the outer diameter of the pupil splitting polarizing element  17 . Adhesion concave portions  22 ,  22 , . . . which are open to the front are formed in the outer circumferential side of the attaching concave portion  21  on the element holder  18  to be spaced from one another in the circumferential direction, and the adhesion concave portions  22 ,  22 , continue from the attaching concave portion  21 . The space of the rear side of the attaching concave portion  21  in the element holder  18  is formed as a light transmitting hole  23 , and the diameter of the light transmitting hole  23  is smaller than the diameter of the attaching concave portion  21 . The front surface that forms the attaching concave portion  21  of the element holder  18  is formed as a seating surface  21   a.    
     The pupil splitting polarizing element  17  is inserted into the attaching concave portion  21  from the front side, the outer circumferential portion in the rear surface thereof is pressed against the seating surface  21   a , and is positioned such that the splitting line P matches the positioning marks M, M which are formed in the element holder  18  (refer to  FIG. 13 ). The pupil splitting polarizing element  17  that is positioned in this manner is fixed to the element holder  18  using adhesive  24 ,  24 , . . . , which the adhesion concave portions  22 ,  22 , . . . are filled with, respectively, and the polarizing element block  16  is configured by the pupil splitting polarizing element  17  being fixed to the element holder  18  (refer to  FIGS. 13 and 14 ). 
     As described above, since the positioning marks M, M for performing positioning of the splitting line P are formed in the element holder  18 , it is possible to easily and reliably position the polarizers  17   a ,  17   b  in relation to the element holder  18 . 
     Attachment of Polarizing Element Block to Scope Holder 
     The polarizing element block  16  is attached to the scope holder  8  in a state of being retained by biasing springs  25 ,  25  (refer to  FIGS. 15 to 20 ). The biasing spring  25  is a plate spring that faces the front and rear directions, for example, and is formed of an attachment target surface portion  26  and retaining arm portions  27 ,  27  which protrude from approximately the sides of the target surface portion  26 , and are formed in an arc shape. An insertion through hole  26   a  is formed in the attachment target surface portion  26 . 
     The polarizing element block  16  is disposed in the disposition space  9   b  which is formed in the attaching portion  9  of the scope holder  8 , and the positioning pins  20 ,  20  are inserted into the positioning grooves  9   g ,  9   g , respectively. At this time, since the cutout surfaces  18   a ,  18   a  are formed in the element holder  18 , voids are formed in both top and bottom end portions of the disposition space  9   b . The voids are formed as member disposition spaces  28 ,  28 . 
     Screw insertion members  29 ,  29  are disposed in the member disposition spaces  28 ,  28 , respectively. A screw insertion through hole  29   a  is formed in the screw insertion member  29 . 
     The attachment target surface portions  26 ,  26  of the biasing springs  25 ,  25  are pressed against the screw insertion members  29 ,  29 , from the front side, respectively, attaching screws  30 ,  30  are inserted through the insertion through holes  26   a ,  26   a  and the screw insertion members  29 ,  29 , respectively, in order, and the attaching screws  30 ,  30  are screwed into the screw holes  9   f ,  9   f  which are formed in the attaching portion  9  of the scope holder  8 . Therefore, the biasing springs  25 ,  25  are fixed to the attaching portion  9  by the attaching screws  30 ,  30  via the screw insertion members  29 ,  29 , respectively. 
     In regard to the polarizing element block  16 , in a state in which the biasing springs  25 ,  25  are each fixed to the attaching portion  9 , the top portion and the bottom portion of the element holder  18  are retained from the front by the retaining arm portions  27 ,  27 , . . . of the biasing springs  25 ,  25 , respectively, and the element holder  18  is disposed in the disposition space  9   b  with the outer circumferential portion thereof being pressed against the retaining surface  15  of the attaching portion  9 . 
     The polarizing element block  16  is pressed against the retaining surface  15  by being retained from the front by the retaining arm portions  27 ,  27 , . . . of the biasing springs  25 ,  25 , and the positioning pins  20 ,  20  are inserted into the positioning grooves  9   g ,  9   g , respectively; thus, the polarizing element block  16  is capable of moving in the horizontal direction in relation to the scope holder  8 . The positioning pins  20 ,  20  and the positioning grooves  9   g ,  9   g  allow the polarizing element block  16  to move in the horizontal direction in relation to the scope holder  8 , and function as positioning portions which position the polarizing element block  16  in the horizontal direction in relation to the scope holder  8 . Therefore, the horizontal direction, that is, the direction that is perpendicular to both the splitting line P of the pupil splitting polarizing element  17  and the optical axis is set to be the positioning direction. 
     The pupil splitting polarizing element  17  is positioned in the optical axis direction (the front-rear direction) in relation to the scope holder  8  by the polarizing element block  16  being pressed against the retaining surface  15 . 
     The pupil splitting polarizing element  17  is positioned in the vertical direction and the direction around the optical axis in relation to the scope holder  8  by the positioning pins  20 ,  20  being inserted into the positioning grooves  9   g ,  9   g , respectively. 
     In a state in which the element holder  18  is disposed in the disposition space  9   b  by being pressed against the retaining surface  15 , the pupil splitting polarizing element  17  is disposed at the conjugate position of the diaphragm. 
     In the stereoscopic endoscope  1  that is configured as described above, when substantially afocal light which is emitted from the observation portion  5  of the monocular endoscope  2  is incident on the pupil splitting polarizing element  17 , the incident light is polarized by the polarizers  17   a ,  17   b  of the element holder  18  in order to generate a right eye image and a left eye image, respectively. The polarized light is polarized by the wire-grid polarizers  12   a ,  12   a ,  12   b ,  12   b , . . . of +45° and −45°, respectively, is subjected to photoelectric conversion in the imaging device  12 , the right eye image and the left eye image are each generated, and the stereoscopic image is acquired. 
     As described above, the pupil splitting polarizing element  17  is attached to the attaching portion  9  of the scope holder  8  in a state of being held in the element holder  18 . Therefore, it is easy to dispose the pupil splitting polarizing element  17  in the inner portion of the scope holder  8 , it is not necessary to grip the pupil splitting polarizing element  17  to dispose the pupil splitting polarizing element  17  on the inner portion of the scope holder  8 , the pupil splitting polarizing element  17  is not dirtied or broken, and it is easy to handle the pupil splitting polarizing element  17 . 
     As described above, by disposing the pupil splitting polarizing element  17  in the conjugate position of the diaphragm, the pupil splitting polarizing element  17  is disposed in an optimal position without influencing the optical performance of the imaging optical system, and it is possible to achieve miniaturization in the optical axis direction in addition to securing favorable optical performance of the stereoscopic endoscope  1 . 
     Note that, in the above description an example is given in which the pupil splitting polarizing element  17  is disposed in the conjugate position of the diaphragm; however, the pupil splitting polarizing element  17  may be disposed in the proximity of the conjugate position of the diaphragm. 
     Disposing the pupil splitting polarizing element  17  in the proximity of the conjugate position of the diaphragm allows the pupil splitting polarizing element  17  to be disposed in an optimal position taking aberration that occurs in the imaging optical system into consideration, and it is possible to achieve miniaturization in the optical axis direction in addition to securing more favorable optical performance of the stereoscopic endoscope  1 . 
     Positioning Work of Polarizing Element Block 
     Next, description will be given of the positioning work of the polarizing element block  16  in the horizontal direction in relation to the conjugate position of the diaphragm, or the proximity thereof (refer to  FIGS. 21 and 22 ). 
     The pupil splitting polarizing element  17  is positioned in the horizontal direction by positioning the polarizing element block  16  in the horizontal direction. The positioning work of the polarizing element block  16  in the horizontal direction in relation to the conjugate position of the diaphragm, or the proximity thereof, is performed in a state in which the polarizing element block  16  is pressed against the retaining surface  15  by being retained from the front by the biasing springs  25 ,  25 . 
     In the positioning work of the polarizing element block  16  in the horizontal direction, adjusting screws  31 ,  31  are respectively screwed into the jig insertion holes  9   e ,  9   e  that are formed in the attaching portion  9 , adjusting jigs  100 ,  100  such as screwdrivers are inserted into the jig insertion holes  9   e ,  9   e , and the positioning work is performed by causing the adjusting screws  31 ,  31  to rotate using the adjusting jigs  100 ,  100 . 
     The distal ends of the adjusting screws  31 ,  31  respectively make contact with the side surfaces  18   b ,  18   b  of the element holder  18 . Therefore, due to the adjusting screws  31 ,  31  being rotated and the position in the horizontal direction changing, the contact positions of the adjusting screws  31 ,  31  in relation to the side surfaces  18   b ,  18   b  change and the polarizing element block  16  is displaced in relation to the scope holder  8 ; thus the pupil splitting polarizing element  17  is positioned in the horizontal direction in relation to the conjugate position of the diaphragm, or the proximity thereof. 
     Specifically, in a state in which the polarizing element block  16  is disposed in the disposition space  9   b  (refer to  FIG. 21 ), one of the adjusting screws  31  is positioned distanced from one of the side surfaces  18   b  of the element holder  18  in one of the left and right directions; and, in this state, the other adjusting screw  31  is rotated by the adjusting jig  100  approaching the element holder  18 . When the other adjusting screw  31  is rotated by the adjusting jig  100 , due to the other side surface  18   b  of the element holder  18  being pressed by the other adjusting screw  31 , the positioning pins  20 ,  20  slide in the positioning grooves  9   g ,  9   g , and the polarizing element block  16  is displaced in one of the left and right directions (refer to  FIG. 22 ). The position of the element holder  18  in the horizontal direction in relation to the scope holder  8  changes due to the polarizing element block  16  being moved in the horizontal direction in this manner, and the element holder  18  is positioned in relation to the conjugate position of the diaphragm, or the proximity thereof. 
     Note that, as described above, the positioning work of the polarizing element block  16  in relation to the conjugate position of the diaphragm, or the proximity thereof, is performed in a state in which the polarizing element block  16  is retained from the front by the biasing springs  25 ,  25 . Therefore, when the polarizing element block  16  is displaced in the horizontal direction in relation to the scope holder  8 , the front surface of the polarizing element block  16  slides in relation to the retaining arm portions  27 ,  27 , . . . of the biasing springs  25 ,  25 . 
     The positioning work as described above is performed in a state in which the monocular endoscope  2  is joined to the imaging head unit  3 . The monocular endoscope  2  is joined to the imaging head unit  3  by the joining portion  5   a  of the observation portion  5  in the monocular endoscope  2  being inserted, from the front side, into the joining space  9   a  which is formed in the attaching portion  9  of the scope holder  8 , screw members  32 ,  32 ,  32  being screwed into the attaching holes  9   d ,  9   d ,  9   d  which are formed in the attaching portion  9 , and one end portion of each of the screw members  32 ,  32 ,  32  being engaged with the inclined surface  5   b  of the joining portion  5   a.    
     When the positioning work is performed, in a state in which the monocular endoscope  2  is joined to the imaging head unit  3 , a light emitting plate which has a white surface (a diffusing surface) with a uniform luminance is photographed by the stereoscopic endoscope  1 , and a video signal of left and right images (a left eye image and a right eye image) is acquired. 
     When acquiring the video signal, an evaluation value such as that described hereinafter is set in advance for the light intensity distribution difference between the left and right images, and positional adjustment is performed using the positioning work described above such that the evaluation value reaches a minimum based on the acquired video signal. The three points of the screen center, the screen left periphery, and the screen right periphery are selected, for example, as the evaluation points for setting the evaluation value. 
     The luminance value of the left eye image is set to PLi (where i=1, 2, 3, which indicate the screen center, the screen left periphery, and the screen right periphery, respectively, and this also applies hereinafter), and the luminance value of the right eye image is set to PRi. The luminance value of the left eye image is set to PL′i and the luminance value of the right eye image is set to PR′i in relation to the optimal position in the horizontal direction of the polarizing element block  16 , which is determined on the basis of a design value of the imaging optical system which is provided in the stereoscopic endoscope  1 . 
     A center region ΦCoffs=PL1−PR1, a left region ΦLoffs=PL2−PR2, and a right region ΦRoffs=PL3−PR3 are considered as the evaluation value, which is defined from the luminance value between the left and right images. At this time, since it can be considered that ΦCoffs=ΦLoffs=ΦRoffs, it is sufficient to consider only one, ΦCoffs for example, of ΦCoffs, ΦLoffs, or ΦRoffs as the evaluation value. In reality, adjustment balance may be obtained by using an evaluation value obtained by weighting ΦCoffs, ΦLoffs, and ΦRoffs in consideration of aberration of the optical system or the like. 
     At this time, it is possible to calculate, for the system, an error sensitivity ψCoffs=dΦCoffs/dx of the evaluation value in relation to the displacement in the horizontal direction of the pupil splitting polarizing element  17 , and the value thereof is stored in the memory of the system. Note that, dx is the adjustment amount by which the pupil splitting polarizing element  17  is displaced in the horizontal direction during the positioning work. 
     An evaluation value ΦCoffs in relation to the present position of the pupil splitting polarizing element  17  is calculated from the PLi and the PRi that are acquired from the video signal. If the difference from the design value ΦC′offs (PL′ 1 −PR′1) is used, then dx=(ΦCoffs−ΦC′offs)/ψCoffs is calculated. 
     When the adjustment amount dx is calculated as described above, the position of the pupil splitting polarizing element  17  is adjusted by rotating the adjusting screws  31 ,  31  such that the pupil splitting polarizing element  17  moves to the left or the right by dx amount. After adjusting the position of the pupil splitting polarizing element  17  in this manner, the light emitting plate is photographed by the stereoscopic endoscope  1  again and the video signal of the left and right images is acquired. The adjustment amount dx is calculated again in the same manner as described above, based on the acquired value of the video signal, and the position of the pupil splitting polarizing element  17  is adjusted by rotating the adjusting screws  31 ,  31  according to the calculated dx amount. 
     Such acquisition of the video signal and position adjustment of the pupil splitting polarizing element  17  based on the calculated adjustment amount dx are performed repeatedly, as necessary, the positional adjustment of the pupil splitting polarizing element  17  is ended when the evaluation value ΦCoffs falls in an acceptable range, and the positioning work in the horizontal direction of the polarizing element block  16  is completed. When the positioning work is completed, the polarizing element block  16  is fixed to the scope holder  8  using an adhesive or the like. 
     As described above, the positioning work of the pupil splitting polarizing element  17  in relation to the conjugate position of the diaphragm, or the proximity thereof, is performed by the adjusting screws  31 ,  31 , the positions of which in the horizontal direction are changed in relation to the scope holder  8 , being rotated. Therefore, the position of the polarizing element block  16  is changed according to the rotation amount of the adjusting screws  31 ,  31 , it is easy to adjust the position of the polarizing element block  16 , and it is possible to achieve an improvement in workability in the positioning work of the pupil splitting polarizing element  17 . 
     The adjusting screws  31 ,  31  are rotated by the adjusting jigs  100 ,  100 , and the jig insertion holes  9   e ,  9   e  into which the adjusting jigs  100 ,  100  are inserted are formed in the scope holder  8 ; thus, it is possible to perform the positioning work from the outside of the scope holder  8 , and it is possible to achieve an improvement in the workability of in the positioning work. 
     Note that, in the above description an example is given in which the positional adjustment of the pupil splitting polarizing element  17  is performed by the adjusting screws  31 ,  31 ; however, the positional adjustment of the pupil splitting polarizing element  17  is not limited to being performed by the adjusting screws  31 ,  31 , and may be performed using an actuator mechanism such as a micro motor or a stepping motor. 
     CONCLUSION 
     As described above, the stereoscopic endoscope  1  is provided with the pupil splitting polarizing element  17  which includes the pair of polarizers  17   a ,  17   b  which are disposed to line up along the splitting line P as a boundary, and it is possible to position the pupil splitting polarizing element  17  in relation to the conjugate position of the diaphragm, or the proximity thereof, in the horizontal direction, which is a direction perpendicular to both the splitting line P and the optical axis. 
     Therefore, since the pupil splitting polarizing element  17  is positioned in the direction in which the polarizers  17   a ,  17   b  are lined up, an improvement in the positioning precision of the pair of polarizers  17   a ,  17   b  is achieved, and it is possible to acquire a favorable stereoscopic image. 
     Since the positioning portion for positioning the pupil splitting polarizing element  17  is configured of the positioning pins  20 ,  20  and the positioning grooves  9   g ,  9   g , it is possible to position the pupil splitting polarizing element  17  reliably using a simple configuration. 
     The retaining surface  15  is provided on the scope holder  8 , and the biasing springs  25 ,  25  which bias the element holder  18  in the optical axis direction, press the element holder  18  against the retaining surface  15 , and position the pupil splitting polarizing element  17  in the optical axis direction are provided. 
     Therefore, it is easy to position the pupil splitting polarizing element  17  in the optical axis direction, the pupil splitting polarizing element  17  is attached to the scope holder  8  and positioned in the optical axis direction at the same time, and it is possible to achieve an improvement in the workability of the pupil splitting polarizing element  17  in the attachment work in relation to the scope holder  8  and in the positioning work in the optical axis direction. 
     The cutout surfaces  18   a ,  18   a  are formed in the element holder  18 , and the member disposition spaces  28 ,  28 , in which the screw insertion members  29 ,  29  are disposed are formed between the element holder  18  and the scope holder  8 , by the cutout surfaces  18   a ,  18   a.    
     Therefore, the space in the inner portion of the scope holder  8  is used effectively, and it is possible to achieve miniaturization of the stereoscopic endoscope  1 . 
     Present Technology 
     The present technology may adopt the following configurations. 
     (1) A stereoscopic endoscope includes an imaging optical system including a diaphragm which adjusts light intensity and a pupil splitting polarizing element that has a pair of polarizers which are disposed to line up along a splitting line as a boundary; a scope holder in which at least the pupil splitting polarizing element is disposed in an inner portion thereof; and an imaging device on which light is incident via the imaging optical system. Light which is incident on the pupil splitting polarizing element is polarized by the pair of polarizers in order to generate a right eye image and a left eye image, respectively. A direction that is perpendicular to both the splitting line and an optical axis is a positioning direction. Positioning portions are provided to position the pupil splitting polarizing element in relation to a conjugate position of the diaphragm, or a proximity thereof, in the positioning direction. 
     (2) The stereoscopic endoscope according to (1) further includes an element holder which holds the pupil splitting polarizing element. 
     (3) In the stereoscopic endoscope according to (2), positioning grooves which extend in the positioning direction are formed in one of the scope holder and the element holder. Positioning pins which extend in an optical axis direction and are supported in the positioning grooves to slide freely are provided on the other of the scope holder or the element holder. The positioning portions are configured of the positioning pins and the positioning grooves. The pupil splitting polarizing element is positioned by changes in relative position of the positioning pins and the positioning grooves. 
     (4) The stereoscopic endoscope according to (2) or (3) further includes adjusting screws of which a position thereof in the positioning direction is changed when distal ends thereof are pressed against the element holder and the adjusting screws are rotated. The positioning is performed when the adjusting screws are rotated, with positions of the element holder and the pupil splitting polarizing element being changed. 
     (5) In the stereoscopic endoscope according to (4), the adjusting screw is rotated by an adjusting jig. A jig insertion hole into which the adjusting jig is inserted is formed in the scope holder. 
     (6) In the stereoscopic endoscope according to any one of (2) to (5), positioning marks for positioning the splitting line during attachment of the pupil splitting polarizing element to the element holder are formed in the element holder. 
     (7) In the stereoscopic endoscope according to any one of (2) to (6), a retaining surface is formed on the scope holder. Biasing springs which bias the element holder in an optical axis direction, press the element holder against the retaining surface, and position the pupil splitting polarizing element in the optical axis direction. 
     (8) In the stereoscopic endoscope according to any one of (2) to (7), cutout surfaces are formed on an outer circumference of the element holder. Member disposition spaces, in which predetermined members are disposed, are formed between the element holder and the scope holder by the cutout surfaces. 
     (9) In the stereoscopic endoscope according to any one of (1) to (8), the pupil splitting polarizing element is disposed in the conjugate position of the diaphragm. 
     (10) In the stereoscopic endoscope according to any one of (1) to (8), the pupil splitting polarizing element is disposed in a proximity of the conjugate position of the diaphragm. 
     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.