Patent Publication Number: US-2018045869-A1

Title: Optical observation device and method of controlling optical observation device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of PCT International Application No. PCT/JP2016/057218 filed on Mar. 8, 2016, which claims priority under 35 U.S.C §119(a) to Japanese Patent Application No. 2015-083157 filed on Apr. 15, 2015. The above application is hereby expressly incorporated by reference, in its entirety, into the present application. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an optical observation device including a polarizing element and a method of controlling an optical observation device. 
     2. Description of the Related Art 
     When a scene including the surface of the water, window glass or the like is observed in an optical observation device such as binoculars, a situation may occur in which reflected light from the surface of the water, window glass or the like is strong, and an original observation object is not likely to be visually recognized. Consequently, an optical observation device such as binoculars having a polarizing element incorporated into an optical system is known in order to cut unnecessary light such as reflected light (see JP2010-2574A). This polarizing element guides an observation image in which the unnecessary light is cut to an ocular portion by transmitting only a linear polarized component in a direction along a polarization axis from the optical image. 
     However, optimum orientations of the polarizing element for cutting the unnecessary light are different from each other depending on an observation object. Therefore, in order to obtain a satisfactory observation image, it is necessary to rotate the polarizing element and to be directed toward an optimum direction in which the visibility of the observation image is most improved. Binoculars disclosed in JP2010-2574A include a half mirror and a sensor portion in order to automatically set the orientation of the polarizing element in an optimum direction. The half mirror guides a linear polarized component transmitted through the polarizing element to the ocular portion and the sensor portion. 
     In the binoculars disclosed in JP2010-2574A, an optimum direction is detected on the basis of an imaging signal obtained in the sensor portion while the polarizing element is rotated, and the angle of the polarizing element is set in the detected optimum direction. Thereby, the orientation of the polarizing element is automatically set in the optimum direction. 
     However, the binoculars disclosed in JP2010-2574A are configured such that light transmitted through the polarizing element is branched by the half mirror and is guided to the ocular portion and the sensor portion. Therefore, even in a situation in which a user observes an observation image from the ocular portion, the polarizing element is rotated in order to detect an optimum direction, and thus there is a problem in that the brightness of the observation image changes with the rotation of the polarizing element. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an optical observation device that makes it possible to set a polarizing element at an optimum angle without changing the brightness of an observation image, and a method of controlling an optical observation device. 
     According to the present invention, there is provided an optical observation device comprising an objective lens, an observation unit, a first polarizing element, a first rotation drive unit, a linear polarized component extraction unit, an imaging element, a polarization direction detection unit, and a rotation control unit. The objective lens allows light to be incident thereon from an observation object. An observation unit has an incidence ray incident on the objective lens guided thereto through a first optical path. A first polarizing element is a polarizing element that transmits a specific linear polarized component, and is rotatably disposed on a surface orthogonal to an optical axis of the first optical path. A first rotation drive unit rotates and drives the first polarizing element. A linear polarized component extraction unit is disposed on a second optical path having the same angle of view as that of the first optical path or having a larger angle of view than that of the first optical path, and extracts linear polarized components from the incidence ray, respectively, with respect to a plurality of polarization directions. An imaging element individually captures images of the respective linear polarized components extracted by the linear polarized component extraction unit and outputs imaging signals. A polarization direction detection unit detects an optimum polarization direction based on an image of the observation object, on the basis of the imaging signals. A rotation control unit controls the first rotation drive unit, to set the first polarizing element at an angle that allows transmission of a linear polarized component in the optimum polarization direction. 
     It is preferable that the polarization direction detection unit detects a polarization direction in which luminance of the image of the observation object becomes lowest. 
     It is preferable that the linear polarized component extraction unit includes a second polarizing element which is a polarizing element that transmits the specific linear polarized component, and is disposed on a surface orthogonal to an optical axis of the second optical path, and a second rotation drive unit that rotates and drives the second polarizing element, and sequentially extracts linear polarized components, respectively, with respect to the plurality of polarization directions by causing the imaging element to perform multiple times of imaging operations within a constant angular range in which the second polarizing element is rotated. 
     It is preferable that the angular range is 180°. 
     It is preferable that the linear polarized component extraction unit is a third polarizing element, having a plurality of polarization regions divided and fixedly disposed on the second optical path, which simultaneously extracts linear polarized components with respect to the plurality of polarization directions, polarization directions of linear polarized components transmitted by the respective polarization regions being different from each other. 
     It is preferable that the third polarizing element is provided on an imaging surface of the imaging element. 
     It is preferable that the imaging element is a color sensor having multi-color pixels, and is configured such that at least one or more pixels of each color are disposed in one polarization region. 
     It is preferable to further comprise: a dimming element, having a plurality of segments of which light transmittance is variable, which is disposed on the first optical path; and a dimming element control unit that controls light transmittances of the respective segments on the basis of the imaging signals in which the optimum polarization direction is detected. 
     It is preferable to further comprise an ocular lens provided on the first optical path between the first polarizing element and the observation unit, wherein the dimming element is disposed between the ocular lens and the observation unit. 
     It is preferable that a half mirror is disposed on the first optical path, and that the second optical path is branched from the first optical path by the half mirror. 
     It is preferable to further comprise: a rotation stop operating unit that makes it possible for a user to stop a rotation of the first polarizing element which is rotated during execution of a calibration operation for calibrating a set position of the first polarizing element by the rotation control unit; and a calibration control unit that drives the first rotation drive unit to rotate the first polarizing element, and calibrates the set position on the basis of a difference between a rotation stop position of the first polarizing element stopped by the rotation stop operating unit being operated at a position where an amount of light of an optical image of the observation object guided to the observation unit becomes smallest and the optimum polarization direction detected by the polarization direction detection unit. 
     It is preferable to further comprise a display unit that displays an image based on the imaging signals in which the optimum polarization direction is detected. 
     It is preferable that the image displayed on the display unit is guided to the observation unit through the first optical path. 
     It is preferable to further comprise a calibration operation start operating unit for starting the calibration operation, wherein the calibration control unit rotates the first polarizing element while the calibration operation start operating unit is operated, and the rotation stop operating unit is operated. 
     According to the present invention, there is provided a method of controlling an optical observation device, the device including an objective lens on which light is incident from an observation object, an observation unit to which an incidence ray incident on the objective lens is guided through a first optical path, a first polarizing element which is a polarizing element that transmits a specific linear polarized component, and is rotatably disposed on a surface orthogonal to an optical axis of the first optical path, a first rotation drive unit that rotates and drives the first polarizing element, a linear polarized component extraction unit, disposed on a second optical path having the same angle of view as that of the first optical path or having a larger angle of view than that of the first optical path, which extracts linear polarized components from the incidence ray, respectively, with respect to a plurality of polarization directions, an imaging element that individually captures images of the respective linear polarized components extracted by the linear polarized component extraction unit and outputs imaging signals, and a polarization direction detection unit that detects an optimum polarization direction based on an image of the observation object, on the basis of the imaging signals, the method comprising controlling the first rotation drive unit, to set the first polarizing element at an angle that allows transmission of a linear polarized component in the optimum polarization direction. 
     According to the present invention, the optimum polarization direction is detected on the basis of the imaging signal obtained by individually capturing images of a plurality of linear polarized components extracted by the linear polarized component extraction unit disposed on the second optical path, and the first polarizing element disposed on the first optical path is set at an angle that allows the transmission of a linear polarized component in the optimum polarization direction. Therefore, it is possible to provide an optical observation device that makes it possible to set a polarizing element at an optimum angle without changing the brightness of an observation image, and a method of controlling an optical observation device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of the outward appearance of binoculars. 
         FIG. 2  is a block diagram illustrating a configuration of the binoculars. 
         FIG. 3  is a diagram illustrating rotation control of a first polarizing element. 
         FIG. 4  is a diagram illustrating rotation control of a second polarizing element. 
         FIG. 5  is a diagram illustrating a relationship between the rotation angle and the imaging timing of the second polarizing element. 
         FIG. 6  is a diagram illustrating a region of detection of luminance. 
         FIG. 7  is a flow diagram illustrating an operation of an automatic mode. 
         FIG. 8  is a diagram illustrating detection of an optimum polarization direction based on the frequency distribution of pixel values. 
         FIG. 9  is a block diagram illustrating a polarization control unit of a second embodiment. 
         FIG. 10  is a diagram illustrating a third polarizing element. 
         FIG. 11  is a block diagram illustrating a configuration of binoculars of a third embodiment. 
         FIG. 12  is a diagram illustrating a color filter. 
         FIG. 13  is a diagram illustrating a relationship between first to sixth polarization regions and the color filter. 
         FIG. 14  is a block diagram illustrating a configuration of binoculars of a fourth embodiment. 
         FIG. 15  is a diagram illustrating segments of a dimming element. 
         FIG. 16  is a block diagram illustrating a configuration of binoculars of a fifth embodiment. 
         FIG. 17  is a diagram illustrating a configuration in which a second optical path is branched using an erecting prism. 
         FIG. 18  is a block diagram illustrating a configuration of binoculars of a sixth embodiment. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     In  FIG. 1 , binoculars  10  include a first optical system  10 R, a second optical system  10 L, and an imaging optical system  101 . The first optical system  10 R erects an optical image of an observation object which is incident along an optical axis AR, and guides the optical image to a first ocular portion ER with which an observer&#39;s right eye comes into contact. The second optical system  10 L erects an optical image of the observation object which is incident along an optical axis AL from the observation object, and guides the optical image to a second ocular portion EL with which the observer&#39;s left eye comes into contact. The first ocular portion ER and the second ocular portion EL corresponds to an “observation unit” in the claims. 
     The imaging optical system  101  guides an optical image of the observation object which is incident along an optical axis AI to an imaging element  28  (see  FIG. 2 ) provided inside the binoculars  10 . The optical axis AR, the optical axis AL, and the optical axis AI are parallel to each other. The optical axis AR and the optical axis AL correspond to a “first optical path” in the claims. The optical axis AI corresponds to a “second optical path” in the claims. 
     The binoculars  10  are provided with an operating unit  11 . The operating unit  11  includes a mode switching button  11   a  and a zoom operating unit  11   b.  The mode switching button  11  a is operated when an observation mode is switched. The observation mode includes a fixed mode and an automatic mode. In the fixed mode, the polarization axis of a first polarizing element  16  (see  FIG. 2 ) described later is fixed in a constant direction. In the automatic mode, the polarization axis of the first polarizing element  16  is automatically controlled so as to be directed toward an optimum polarization direction at all times. The zoom operating unit  11  b is operated when zoom magnification is changed. 
     In  FIG. 2 , the first optical system  10 R includes an objective lens  12 , an erecting prism  14 , a first polarizing element  16 , and an ocular lens  18 . The objective lens  12 , the erecting prism  14 , the first polarizing element  16 , and the ocular lens  18  are disposed on the optical axis AR of the first optical system I OR in this order from the observation object side. 
     Light is incident on the objective lens  12  from the observation object. The objective lens  12  is constituted by a plurality of optical lenses. The objective lens  12  is configured such that the optical images can be focused by moving all or some of the plurality of optical lenses using a mechanism which is not shown. 
     The erecting prism  14  is a Schmidt-Pechan type prism, and erects and emits an optical image of the observation object incident from the objective lens  12 . The erecting prism  14  is constituted by an auxiliary prism  14 A and a roof prism  14 B. The optical image is incident on the auxiliary prism  14 A from the objective lens  12 . The optical image is incident on the roof prism  14 B from the auxiliary prism  14 A. The roof prism  14 B emits the erected optical image. 
     The first polarizing element  16  is a polarization filter that transmits a linear polarized component in a direction along a polarization axis r 1  (see  FIG. 3 ) from the optical image. The linear polarized component transmitted through the first polarizing element  16  is incident on the ocular lens  18 . 
     The first polarizing element  16  of the first optical system  10 R is configured such that the polarization axis r 1  is orthogonal to the optical axis AR and is rotatably disposed using the optical axis AR as the axis of rotation. In addition, the first polarizing element  16  of the second optical system  10 L is configured such that the polarization axis r 1  is orthogonal to the optical axis AL and is rotatably disposed using the optical axis AL as the axis of rotation. The first polarizing element  16  is rotated and driven by a first rotation drive unit  20 . 
     As shown in  FIG. 3 , the first rotation drive unit  20  recognizes an angle α between the polarization axis r 1  of the first polarizing element  16  and a reference direction r 0 . The first rotation drive unit  20  changes the angle α by rotating the first polarizing element  16 . The reference direction r 0  is a direction perpendicular to a plane including the optical axis AR and the optical axis AL. 
     The first rotation drive unit  20  rotates the first polarizing element  16  of the second optical system  10 L together with the first polarizing element  16  of the first optical system  10 R. The first rotation drive unit  20  is controlled by a rotation control unit  32 . 
     The ocular lens  18  is disposed on a first optical path. Incidence ray having passed through the objective lens  12 , the erecting prism  14 , and the first polarizing element  16  is guided to the ocular lens  18 . The ocular lens  18  is constituted by a plurality of optical lenses including a zoom lens  18   a.  The angle of view of the first optical path can be changed by moving the zoom lens  18   a  on the basis of the operation of the zoom operating unit  11   b . The angle of view becomes smaller as zoom magnification increases by the operation of the zoom operating unit  11   b.    
     Similarly to the first optical system  10 R, the second optical system  10 L includes an objective lens  12 , an erecting prism  14 , a first polarizing element  16 , and an ocular lens  18 . The objective lens  12 , the erecting prism  14 , the first polarizing element  16 , and the ocular lens  18  are disposed on the optical axis AL of the second optical system  10 L in this order from the observation object side. 
     In addition, a polarization control unit  22  is provided inside the binoculars  10 . The polarization control unit  22  is disposed on the optical axis AI of the imaging optical system  101 . The polarization control unit  22  operates in a case where the observation mode is set to the automatic mode by the mode switching button  11  a being operated. 
     The polarization control unit  22  includes an objective lens  24 , a linear polarized component extraction unit  26 , the imaging element  28 , a polarization direction detection unit  30 , and the rotation control unit  32 . Light is incident on the objective lens  24  from the observation object. Similarly to the objective lens  12 , the objective lens  24  is configured such that the optical images can be focused. 
     The angle of view of the imaging optical system  101  is coincident with the angle of view in a case where zoom magnification is smallest in the first optical system  10 R and the second optical system  10 L. That is, in a case where the zoom magnification is smallest, an observation range observed the first ocular portion ER and the second ocular portion EL and an imaging range based on the imaging element  28  are coincident with each other. 
     In the linear polarized component extraction unit  26 , an incidence ray is incident from the objective lens  24 , and linear polarized components are respectively extracted from the incidence ray with respect to a plurality of polarization directions. The linear polarized component extraction unit  26  is constituted by a second polarizing element  34  and a second rotation drive unit  36 . 
     The second polarizing element  34  is a polarization filter that transmits a linear polarized component in a direction along a polarization axis r 2  (see  FIG. 4 ) from the optical image. Light transmitted through the second polarizing element  34  is incident on the imaging element  28 . 
     The second polarizing element  34  is configured such that the polarization axis r 2  is orthogonal to the optical axis AI and is rotatably disposed using the optical axis AI as the axis of rotation. The second polarizing element  34  is rotated and driven by the second rotation drive unit  36 . 
     As shown in  FIG. 4 , the second rotation drive unit  36  recognizes an angle θ between the polarization axis r 2  of the second polarizing element  34  and the reference direction r 0 . The second rotation drive unit  36  changes the angle θ by rotating the second polarizing element  34 . The second rotation drive unit  36  is controlled by the polarization direction detection unit  30 . The second rotation drive unit  36  corresponds to a “second drive unit” in the claims. 
     The imaging element  28  outputs imaging signals by individually capturing images of the respective linear polarized components extracted by the linear polarized component extraction unit  26 . An example of the imaging element  28  to be used includes a complementary metal oxide semiconductor (CMOS) type image sensor or a charge coupled device (CCD) type image sensor. Meanwhile, in the present embodiment, a monochrome image sensor which does not have a color filter is used as the imaging element  28 . 
     The polarization direction detection unit  30  causes the imaging element  28  to perform imaging while changing the angle θ of the second polarizing element  34 , acquires a plurality of imaging signals, and obtains the luminance of an observation image from each of the imaging signals, to thereby detect an optimum polarization direction which is a polarization direction optimum for observation. In the present embodiment, the polarization direction detection unit  30  specifies a polarization direction in which the luminance of the observation image becomes lowest as the optimum polarization direction. 
     Specifically, the polarization direction detection unit  30  controls the second rotation drive unit  36  and the imaging element  28 , synchronizes a change timing of the angle θ of the second polarizing element  34  with an imaging timing t based on the imaging element  28 , as shown in  FIG. 5 , and causes the imaging element  28  to perform an imaging operation every time the angle θ is changed by a predetermined angle. 
     Since the polarization direction detection unit  30  detects a polarization direction (optimum polarization direction) in which the luminance of the observation image becomes lowest, the amount of change in the angle θ changing between imaging timings is preferably as small as possible, but is set to 30° in the present embodiment. Meanwhile, the polarization direction detection unit  30  stops the second polarizing element  34  for a predetermined period every time the angle θ of the second polarizing element  34  is changed by 30° by the second rotation drive unit  36 , and causes the imaging element  28  to perform an imaging operation during this stop. 
     In addition, in order to detect an optimum polarization direction, it is not necessary to detect the optimum polarization direction on the basis of a plurality of imaging signals obtained in a range in which the angle of the second polarizing element  34  is 360°, and it is sufficient to just detect the optimum polarization direction on the basis of a plurality of imaging signals obtained in a range in which the angle of the second polarizing element  34  is 180°. This is because linear polarized components obtained in a case where the directions of the polarization axis r 2  of the second polarizing element  34  are different from each other by 180° are the same as each other. 
     Therefore, the polarization direction detection unit  30  detects an optimum polarization direction on the basis of a plurality of imaging signals obtained within a range in which the angle of the second polarizing element  34  is 180°. In the present embodiment, since the amount of change in the angle θ changing between the respective imaging timings is set to 30°, the optimum polarization direction is detected on the basis of 6 frames&#39; worth of imaging signals (signal group) obtained by six imaging timings. 
     Specifically, the polarization direction detection unit  30  first detects an optimum polarization direction on the basis of 6 frames&#39; worth of signal group G 1  at imaging timings t 1  to t 6 . In a case where an imaging signal is obtained at an imaging timing t 7 , the polarization direction detection unit  30  detects an optimum polarization direction on the basis of 6 frames&#39; worth of signal group G 2  at imaging timings t 2  to t 7 . Thereafter, similarly, every time a new imaging signal is obtained, an optimum polarization direction is detected on the basis of 6 frames&#39; worth of signal group constituted by this new 1 frame&#39;s worth of imaging signal and the previous 5 frames&#39; worth of imaging signals. In this manner, the frequency of detection of an optimum polarization direction increases by forming a signal group and detecting an optimum polarization direction. 
     In addition, when the luminance of the observation image is obtained from each imaging signal, the polarization direction detection unit  30  obtains the luminance from the imaging signal on the basis of a pixel signal within a region corresponding to the angle of view of the first optical path. Specifically, since the angle of view of the first optical path changes depending on zoom magnification based on the operation of the zoom operating unit  11   b,  the polarization direction detection unit  30  receives a signal relating to the zoom magnification from the zoom operating unit  11   b , and sets a detection region  39  corresponding to the angle of view of the first optical path, within an imaging range  38  based on the imaging element  28 , in accordance with the zoom magnification, as shown in  FIG. 6 . The polarization direction detection unit  30  calculates the luminance by obtaining an average value of pixel signals within the detection region  39 . 
     The polarization direction detection unit  30  obtains the luminance of each imaging signal within a signal group, and sets the angle θ P  of the second polarizing element  34  in which an imaging signal having minimum luminance is obtained to an optimum polarization direction. Meanwhile, in a case where the angle θ P  obtained as the optimum polarization direction is equal to or greater than 180°, a value subtracted by 180° from this angle θ P  is set to the optimum polarization direction. This is because linear polarized components obtained in a case where the directions of the polarization axis r 2  of the second polarizing element  34  are different from each other by 180° are the same as each other. 
     The rotation control unit  32  controls the first rotation drive unit  20 , and rotates the first polarizing element  16  at an angle that allows the transmission of a linear polarized component in the optimum polarization direction detected by the polarization direction detection unit  30 . Specifically, the rotation control unit  32  rotates the first polarizing element  16  so that the angle a of the first polarizing element  16  is set to the angle θ P  obtained as the optimum polarization direction. As described above, in a case where the angle θ P  is equal to or greater than 180°, a value subtracted by 180° from this angle θ P  is set to the optimum polarization direction, and thus the angle α of the first polarizing element  16  is changed within a range of 0°≦α&lt;180°. 
     The action of the binoculars  10  configured in this manner will be described with reference to a flow diagram shown in  FIG. 7 . The binoculars  10  bring the polarization control unit  22  into operation in a case where the mode switching button  11   a  is operated, and the automatic mode is started (YES in step S 11 ). 
     The polarization direction detection unit  30  acquires imaging signals by the imaging element  28  (step S 13 ) while changing the angle θ of the second polarizing element  34  by every 30° (step S 12 ). The polarization direction detection unit  30  calculates luminance on the basis of each of the acquired imaging signals, and detects the angle θ P  at which the luminance becomes lowest as the optimum polarization direction (step S 14 ). Specifically, every time the angle θ is changed and a new imaging signal is obtained, the polarization direction detection unit  30  detects an optimum polarization direction on the basis of 6 frames&#39; worth of signal group constituted by this new 1 frame&#39;s worth of imaging signal and the previous 5 frames&#39; worth of imaging signals. 
     The rotation control unit  32  controls the first rotation drive unit  20 , and rotates the first polarizing element  16  at an angle that allows the transmission of a linear polarized component in the detected optimum polarization direction (step S 15 ). Step S 12  to step S 15  are repeatedly performed while the observation mode is set to the automatic mode (NO in step S 16 ). In a case where the mode switching button  11   a  is operated again, the automatic mode is terminated (YES in step S 16 ). 
     In this manner, in the automatic mode, since the optimum polarization direction is sequentially detected while the second polarizing element  34  is rotated, and the first polarizing element  16  is set in the optimum polarization direction every time the optimum polarization direction is detected, the first polarizing element  16  can be maintained in the optimum polarization direction at all times. Therefore, a case does not occur in which the brightness of the observation image changes with the detection of the optimum polarization direction, as in the related art. When a user observes a scene including the surface of the water, window glass or the like, the user can observe an observation image in which unnecessary light such as reflected light is cut. This automatic mode is suitable for a scene in which an observation object changes, and a great fluctuation occurs in unnecessary light such as reflected light. 
     In addition, in the fixed mode, the rotation control unit  32  controls the first rotation drive unit  20 , and sets the angle α of the first polarizing element  16  to 0°. In this fixed mode, since the polarization control unit  22  does not operate, electric power saving is achieved. This fixed mode is suitable for a scene in which there is a small change in the observation object, and a great fluctuation does not occur in unnecessary light such as reflected light. 
     Meanwhile, in the embodiment, the optimum polarization direction is detected on the basis of the luminance of the imaging signal, but the optimum polarization direction may be detected on the basis of the frequency distribution of the pixel value of the imaging signal.  FIG. 8  shows the frequency distribution of pixel values based on the imaging signal obtained by capturing an image of an observation object. The pixel values for generating this frequency distribution are acquired from the inside of the aforementioned detection region  39 . 
     In a scene including the surface of the water, window glass or the like, the luminance of unnecessary light such as reflected light tends to be high. For this reason, in a situation where the angle θ of the second polarizing element  34  is not in an optimum polarization direction, and the unnecessary light is not sufficiently cut, the frequency distribution shows a great frequency in a region (high-luminance region) having a large pixel value, as shown in (A) of  FIG. 8 . Therefore, the optimum polarization direction can be detected by obtaining an angle θ P  at which a cumulative frequency in a high-luminance region is minimized. 
     Specifically, a threshold value TH is set, a cumulative frequency equal to or greater than the threshold value TH is obtained from an imaging signal obtained every time the angle θ of the second polarizing element  34  is changed, an angle θ P  at which this cumulative frequency is minimized is obtained, and this direction is set to an optimum polarization direction. In this optimum polarization direction, since the entirety of unnecessary light such as reflected light is substantially cut by the second polarizing element  34 , the cumulative frequency equal to or greater than the threshold value TH is set to substantially zero, as shown in (B) of  FIG. 8 . 
     In this manner, the optimum polarization direction can be detected on the basis of the cumulative frequency equal to or greater than the threshold value TH. The threshold value TH may be appropriately changed. 
     Meanwhile, in the embodiment, the rotation of the second polarizing element  34  is stopped every time the angle θ of the second polarizing element  34  is changed by a predetermined angle, and the imaging element  28  is caused to perform imaging during this stop, but the imaging element  28  may be caused to perform imaging at a timing when the angle θ takes a predetermined angle in a state where the second polarizing element  34  is rotated at a constant speed. 
     Second Embodiment 
     In the first embodiment, a plurality of linear polarized components are sequentially extracted from an optical image by rotating the second polarizing element  34 , but in a second embodiment, the plurality of linear polarized components are simultaneously extracted. 
     As shown in  FIG. 9 , a polarization control unit  40  of the second embodiment is configured such that a third polarizing element  42  is fixedly disposed between the objective lens  24  and the imaging element  28 , instead of the second polarizing element  34  and the second rotation drive unit  36  of the polarization control unit  22 . The third polarizing element  42  corresponds to a “linear polarized component extraction unit” in the claims. 
     As shown in  FIG. 10 , the third polarizing element  42  has first to sixth polarization regions A 1  to A 6  of which the polarization axes are different in direction from each other. The first to sixth polarization regions A 1  to A 6  have repetitive patterns arrayed in longitudinal and transverse directions. The angles of the polarization axes of the first to sixth polarization regions A 1  to A 6  with respect to the reference direction r 0  are set to 0°, 30°, 60°, 90°, 120°, and 150° in order. 
     Therefore, the same linear polarized components in 6 directions as those in the first embodiment are simultaneously extracted by causing the optical image to be incident on the first to sixth polarization regions A 1  to A 6 . Meanwhile, the first to sixth polarization regions A 1  to A 6  have repetitive patterns arrayed in longitudinal and transverse directions. Therefore, even in a case where the size of the detection region  39  changes due to a change in the angle of view associated with a zoom operation, at least a set of first to sixth polarization regions A 1  to A 6  are included within the detection region  39 . 
     In the second embodiment, the luminance of each linear polarized component is obtained on the basis of the pixel value of the detection region  39 , and an optimum polarization direction in which this luminance is minimized is detected. Other configurations of the second embodiment are the same as those of the first embodiment. 
     In the second embodiment, since the linear polarized components are simultaneously extracted with respect to a plurality of polarization directions, a detection time in an optimum polarization direction is further shortened than in a case where the linear polarized components are sequentially extracted as in the first embodiment. In addition, in the second embodiment, since it is not necessary to provide the second rotation drive unit  36  for rotating the second polarizing element  34  as in the first embodiment, space saving and electric power saving is achieved. 
     Meanwhile, the third polarizing element  42  may be directly formed on the imaging surface of the imaging element  28  by a semiconductor manufacturing process or the like. In addition, in the second embodiment, it is also possible to detect an optimum polarization direction on the basis of the frequency distribution of the pixel values of the imaging signal. 
     Third Embodiment 
     In a third embodiment, it is possible to perform recording of an image obtained by the imaging element  28 , and to guide this image to the first ocular portion ER and the second ocular portion EL. As shown in  FIG. 11 , binoculars  50  of the third embodiment include a shooting button  52 , a memory  54 , a display unit  56 , and a half mirror  58 , in addition to the configuration of the binoculars  10  of the first embodiment. 
     In addition, in the first embodiment, a monochrome image sensor is used as the imaging element  28 , but in the third embodiment, a color image sensor having multi-color pixels is used as the imaging element in order to display a color image on the display unit  56 . 
     As shown in  FIG. 12 , each pixel of the imaging element  28  is provided with any of a B(blue) filter, a G(green) filter, and a R(red) filter. In the present embodiment, the color array of a color filter is set to a Bayer array. The B pixel provided with a B filter outputs a B imaging signal. The G pixel provided with a G filter outputs a G imaging signal. The R pixel provided with a R filter outputs a R imaging signal. 
     In the present embodiment, the polarization direction detection unit  30  generates a luminance signal by performing Y/C conversion on the imaging signal of BGR which is output from the imaging element  28 . The polarization direction detection unit  30  detects an optimum polarization direction on the basis of the luminance of the observation image obtained from the luminance signal. 
     The shooting button  52  is operated when the still image of the observation object is captured. The operation of the shooting button  52  is effective at the time of the automatic mode. An image based on the imaging signal in which the optimum polarization direction is detected by the polarization direction detection unit  30 , when the shooting button  52  is operated, is stored as an optimum image in the memory  54 . In addition, the display unit  56  displays the optimum image. 
     The half mirror  58  is disposed on the optical axis AR between the ocular lens  18  and the first ocular portion ER in the first optical system  10 R, and is disposed on the optical axis AL between the ocular lens  18  and the second ocular portion EL in the second optical system  10 L. The image displayed on the display unit  56  is guided to the first ocular portion ER and the second ocular portion EL through the half mirror  58 . The image displayed on display unit  56  is superimposed on the optical image. 
     In this manner, in the third embodiment, in a case where a still image is captured, an optimum still image in which unnecessary light such as reflected light is cut is automatically acquired. In addition, this optimum still image can be confirmed through the first ocular portion ER and the second ocular portion EL. 
     Meanwhile, in the third embodiment, similarly to the second embodiment, the third polarizing element  42  is used instead of the second polarizing element  34 , and thus it is possible to simultaneously extract a plurality of linear polarized components from the optical image. In this case, as shown in  FIG. 13 , in order to generate a luminance signal from each of the first to sixth polarization regions A 1  to A 6 , at least or more of each of the B pixel, the G pixel, and the R pixel are disposed in each of the first to sixth polarization regions A 1  to A 6 . 
     In addition, in the third embodiment, a primary color sensor of BGR is used as the imaging element  28 , but a complementary color sensor may be used instead thereof. 
     In addition, in the third embodiment, a configuration is used in which the image displayed on the display unit  56  is superimposed on the optical image, but a configuration may be used in which the first optical system  10 R and the second optical system  10 L are provided with a shutter mechanism to thereby light-shield the first optical system  10 R and the second optical system  10 L while an image is displayed on the display unit  56 , and only a display image of the display unit  56  is guided to the first ocular portion ER and the second ocular portion EL. In addition, the half mirror  58  may be provided on any one of the optical axis AR and the optical axis AL, without being provided on both the optical axes. 
     In addition, in the third embodiment, a configuration is used in which the display image of the display unit  56  is guided to the first ocular portion ER and the second ocular portion EL, but a configuration may be used in which the display unit  56  may be provided in the housing (not shown) of the binoculars  50 , and the display image of the display unit  56  may be displayed directly to a user without being guided to the first ocular portion ER and the second ocular portion EL. The display unit  56  in this case corresponds to an “observation unit” in the claims. 
     Fourth Embodiment 
     In a first embodiment, the visibility of the observation image is increased by cutting unnecessary light such as reflected light in the first polarizing element  16  when a scene including the surface of the water, window glass or the like is observed. However, not only unnecessary light such as reflected light, but also direct light from a high-luminance subject such as the sun, and the like are included in a scene to be observed, and such light lowers the visibility of the observation image without being sufficiently cut in the first polarizing element  16 . 
     Therefore, as shown in  FIG. 14 , binoculars  60  of the fourth embodiment are provided with a dimming element  62  and a dimming element control unit  64 , in addition to the configuration of the binoculars  10  of the first embodiment. 
     As shown in  FIG. 15 , the dimming element  62  has a plurality of segments S of which the light transmittance is variable. The dimming element  62  is disposed between the ocular lens  18  and the first ocular portion ER of the first optical system  10 R, and the ocular lens  18  and the second ocular portion EL of the second optical system  10 L. 
     The dimming element  62  is constituted by, for example, a polymer network liquid crystal (PNLC) filter. The segments S of the dimming element  62  are arrayed in a two-dimensional matrix. The dimming element  62  adjusts (dims) the amount of light of the optical image from the ocular lens  18  for each of the segments S. 
     The dimming element control unit  64  individually controls the light transmittances of the respective segments S of the dimming element  62 , on the basis of the imaging signal in which the optimum polarization direction is detected by the polarization direction detection unit  30 . The dimming element control unit  64  ascertains a correspondence relation between the pixel of the imaging element  28  and the segment S. 
     The dimming element control unit  64  acquires the imaging signal in which the optimum polarization direction is detected by the polarization direction detection unit  30 , from the imaging element  28 . The dimming element control unit  64  obtains the luminance of a pixel corresponding to the segment S of the dimming element  62 , on the basis of the acquired imaging signal. The dimming element control unit  64  obtains luminance for each segment S by obtaining the average value of luminance with respect to the pixel corresponding to the segment S. The dimming element control unit  64  specifies a segment S including a high-luminance region of which the luminance is equal to or greater than a specific threshold value, among the respective segments S. The dimming element control unit  64  lowers the light transmittance of the specified segment S, to thereby reduce the amount of light transmitted through this segment S. 
     In this manner, in the present embodiment, the light transmittance of a segment S corresponding to a high-luminance subject such as the sun is lowered, and thus the visibility of the observation image further improves. 
     Meanwhile, the dimming element  62  is disposed between the ocular lens  18  and the first ocular portion ER, and the ocular lens  18  and the second ocular portion EL, but the dimming element  62  may be disposed on the optical axis AR and the optical axis AL, and the disposition position is particularly limited. However, it is preferable that the dimming element  62  is disposed at a position close to the first ocular portion ER and the second ocular portion EL. 
     Fifth Embodiment 
     In the first embodiment, the second optical path for incorporating the optical image into the polarization control unit  22  is provided independently from the first optical path of the first optical system  10 R and the second optical system  10 L, but the second optical path may be formed by branching the first optical path through an optical member. 
     In the binoculars  70  of the fifth embodiment, as shown in  FIG. 16 , an optical member  72  is provided between the objective lens  12  and the erecting prism  14  of the first optical system  10 R in addition to the configuration of the binoculars  10  of the first embodiment, and thus the optical axis AI is branched from the optical axis AR. 
     The optical member  72  is, for example, a transparent plate, reflects a portion of an incidence ray from the objective lens  12  using Fresnel reflection to guide the reflected light to the polarization control unit  22 , and transmits other light to guide the transmitted light to the erecting prism  14 . 
     In the present embodiment, since the optical axis AI is branched from the optical axis AR by the optical member  72 , the objective lens  12  is shared by the first optical system  10 R and the imaging optical system  101 . Therefore, the angle of view of the first optical path and the angle of view of the second optical path are the same as each other at all times. Therefore, in the present embodiment, as in the first embodiment, the detection region  39  for detecting luminance is not required to be changed in accordance with the angle of view of the first optical path, and the luminance may be calculated using all the signals within the imaging range  38  at all times, regardless of zoom magnification. 
     In addition, the optical member  72  may be disposed so that the angle of incidence of light propagating through the first optical path (optical axis AR) on the optical member  72  is set to a Brewster&#39;s angle. In this case, light reflected by the optical member  72  and guided to the second optical path (optical axis AI) is changed to a substantially S-polarized component. Since this S-polarized component is a main component included in the unnecessary light, a change in luminance associated with the rotation of the second polarizing element  34  clarifies, and the accuracy of detection of an optimum polarization direction improves. 
     Meanwhile, in the present embodiment, it goes without saying that the third polarizing element  42  can be used instead of the second polarizing element  34 . In addition, the optical member  72  may be other optical members such as a half mirror. 
     In addition, as shown in  FIG. 17 , the second optical path (optical axis AI) for incorporating the optical image into the polarization control unit  22  may be formed by providing a half mirror  74  on the non-total reflection surface of the erecting prism  14  instead of the optical member  72 , and emitting a portion of the optical image from the erecting prism  14 . Thereby, space saving is further achieved. 
     Sixth Embodiment 
     In the embodiment, the angle α of the first polarizing element  16  is set on the basis of the optimum polarization direction (angle θ P ) detected by the polarization direction detection unit  30 . However, depending on the use condition of the binoculars  10 , there is the possibility of a shift occurring in an optimum polarization direction and the set position of the first polarizing element  16  which is set in reality on the basis of this optimum polarization direction. Consequently, binoculars  80  of the sixth embodiment can execute a calibration operation for calibrating the set position of the first polarizing element  16  by the rotation control unit  32 . 
     In  FIG. 18 , the binoculars  80  of the sixth embodiment includes a calibration operation start operating unit  82 , a rotation stop operating unit  84 , and a calibration control unit  86 , in addition to the configuration of the binoculars  10  of the first embodiment. 
     The calibration operation start operating unit  82  is operated when the calibration operation is started. The rotation stop operating unit  84  is operated when a user stops the rotation of the first polarizing element  16  rotated during the execution of the calibration operation. 
     In a case where the calibration operation start operating unit  82  is operated, the calibration control unit  86  rotates the first polarizing element  16  by driving the first rotation drive unit  20 . In a case where the first polarizing element  16  is rotated, the brightness of the observation image periodically changes with the rotation of the first polarizing element  16 . A user is caused to operate the rotation stop operating unit  84  at a timing when the brightness becomes lowest. 
     In a case where the rotation stop operating unit  84  is operated, the calibration control unit  86  stops the rotation of the first polarizing element  16 , and detects the rotation stop position of the stopped first polarizing element  16 . The rotation stop operating unit  84  specifies the angle α of the first polarizing element  16  on the basis of the detected rotation stop position. 
     The calibration control unit  86  compares the specified angle α with the angle θ P  corresponding to the optimum polarization direction detected by the polarization direction detection unit  30 , and obtains an angle difference. The calibration control unit  86  controls the rotation control unit  32 , and calibrates the set position of the first polarizing element  16  based on the optimum polarization direction, on the basis of the obtained angle difference. 
     Meanwhile, in the sixth embodiment, the set position of the first polarizing element  16  is calibrated on the basis of the rotation stop position of the first polarizing element  16  stopped at a timing when the brightness of the observation image becomes lowest, but the set position of the first polarizing element  16  may be calibrated on the basis of the rotation stop position of the first polarizing element  16  stopped at a timing when the brightness of the observation image becomes highest. 
     In addition, the calibration control unit  86  may calibrate the set position of the first polarizing element  16  on the basis of both the rotation stop position of the first polarizing element  16  stopped at a timing when the brightness of the observation image becomes lowest and the rotation stop position of the first polarizing element  16  stopped at a timing when the brightness of the observation image becomes highest. 
     In addition, in the sixth embodiment, the operation of the rotation stop operating unit  84  is performed on the basis of the observation image to be observed through the first ocular portion ER and the second ocular portion EL, but the rotation stop operating unit  84  may be operated while an image displayed on the display unit  56  of the third embodiment is observed. In this case, for example, a configuration is used in which the optical image is prevented from being guided to the second optical system  10 L by a shutter mechanism or the like, and the image from the display unit  56  is guided to the second ocular portion EL. Therefore, the optical image is guided to the first ocular portion ER, and an image (optimum image) generated on the basis of the imaging signal in which the optimum polarization direction is detected is guided to the second ocular portion EL. Thereby, a user can perform the operation of the rotation stop operating unit  84  while observing the optimum image through the user&#39;s left eye, and observing a real optical image through the user&#39;s right eye. 
     In the respective embodiments, the present invention has been described by taking an example of binoculars, but the present invention can also be applied to other optical observation devices such as a monocle or a telescope. 
     EXPLANATION OF REFERENCES 
       10 ,  50 ,  60 ,  70 ,  80  binoculars 
       10 R: first optical system 
       10 L: second optical system 
       10 I: imaging optical system 
       11 : operating unit 
       11   a : mode switching button 
       11   b : zoom operating unit 
       12 : objective lens 
       14 : erecting prism 
       14 A: auxiliary prism 
       14 B: roof prism 
       16 : first polarizing element 
       18 : ocular lens 
       18   a : zoom lens 
       20 : first rotation drive unit 
       22 ,  40 : polarization control unit 
       24 : objective lens 
       26 : linear polarized component extraction unit 
       28 : imaging element 
       30 : polarization direction detection unit 
       32 : rotation control unit 
       34 : second polarizing element 
       36 : second rotation drive unit 
       38 : imaging range 
       39 : detection region 
       42 : third polarizing element 
       52 : shooting button 
       54 : memory 
       56 : display unit 
       58 ,  74 : half mirror 
       62 : dimming element 
       64 : dimming element control unit 
       72 : optical member 
       82 : calibration operation start operating unit 
       84 : rotation stop operating unit 
       86 : calibration control unit 
     AR: optical axis 
     AL: optical axis 
     AI: optical axis 
     ER: first ocular portion 
     EL: second ocular portion 
     r 1 : polarization axis 
     r 2 : polarization axis