Patent Publication Number: US-2018045940-A1

Title: Microscope and optical unit

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2016-157654, filed on Aug. 10, 2016 and Japanese Patent Application No. 2017-113811, filed on Jun. 8, 2017, the entire contents of which are incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     The disclosure relates to an upright microscope and an optical unit for irradiating a specimen on a stage with illumination light to form an observation image. 
     2. Related Art 
     Upright microscopes have been used in various fields, such as a medical field and a biological field, for the purpose of research, examination, and education (e.g., refer to JP 2011-53324 A). In JP 2011-53324 A, an optical unit is disposed between an objective lens and a lens barrel using a buildup method. More specifically, by building up the optical unit on an arm portion that holds a revolver, the optical unit is disposed between the arm portion and the lens barrel. The optical unit is thereby disposed between the objective lens and the lens barrel, and an optical element having predetermined optical characteristics can be inserted onto an observation light path. 
     SUMMARY 
     In some embodiments, a microscope includes: a main body having: a base portion; a pillar portion vertically disposed on part of an outer edge portion of the base portion; and an arm portion extending from an end of the pillar portion to face the base portion, an opposite end of the pillar portion connecting to the base portion; an objective lens support portion provided on one side of the arm portion facing the base portion, the objective lens support portion being configured to hold an objective lens that is detachable from the objective lens support portion; an observation portion provided on an opposite side of the arm portion and configured to hold an eyepiece that is detachable from the observation portion; and an optical unit configured to hold an optical element. The arm portion includes a holding portion configured to hold the optical unit and locate the optical unit at a position intersecting with an optical axis of the objective lens held by the objective lens support portion. 
     In some embodiments, an optical unit used for a microscope is provided. The microscope includes: a main body having: a base portion; a pillar portion vertically disposed on part of an outer edge portion of the base portion; and an arm portion extending from an end of the pillar portion to face the base portion, an opposite end of the pillar portion connecting to the base portion; an objective lens support portion provided on one side of the arm portion facing the base portion, the objective lens support portion being configured to hold an objective lens that is detachable from the objective lens support portion; and an observation portion provided on an opposite side of the arm portion and configured to hold an eyepiece that is detachable from the observation portion. The arm portion includes a holding portion configured to house the optical unit and locate the optical unit at a position intersecting with an optical axis of the objective lens held by the objective lens support portion. The optical unit includes an optical element configured to be inserted onto a light path passing through the optical axis of the objective lens held by the objective lens support portion. 
     The above and other features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram illustrating a schematic configuration of a microscope according to a first embodiment of the present invention; 
         FIG. 2  is a diagram schematically illustrating a configuration of a main part of the microscope according to the first embodiment of the present invention; 
         FIG. 3  is a diagram schematically illustrating a configuration of a main part of the microscope according to the first embodiment of the present invention; 
         FIG. 4  is a perspective view schematically illustrating a configuration of an optical unit of the microscope according to the first embodiment of the present invention; 
         FIG. 5  is a diagram illustrating a configuration of a region R 1  illustrated in  FIG. 1 ; 
         FIG. 6  is a diagram illustrating a configuration of a region R 2  illustrated in  FIG. 5 ; 
         FIG. 7  is a schematic diagram illustrating a schematic configuration of the microscope according to the first embodiment of the present invention; 
         FIG. 8  is a diagram illustrating a configuration of a region R 3  illustrated in  FIG. 7 ; 
         FIG. 9  is a schematic diagram illustrating a schematic configuration of a microscope according to a second embodiment of the present invention; 
         FIG. 10  is a diagram illustrating a configuration of a region R 4  illustrated in  FIG. 9 ; 
         FIG. 11  is a schematic diagram illustrating a schematic configuration of a microscope according to a third embodiment of the present invention; 
         FIG. 12  is a diagram illustrating a configuration of a region R 5  illustrated in  FIG. 11 ; 
         FIG. 13  is a schematic diagram illustrating a schematic configuration of a microscope according to a fourth embodiment of the present invention; 
         FIG. 14  is a diagram illustrating a configuration of a region R 6  illustrated in  FIG. 13 ; 
         FIG. 15  is a schematic diagram illustrating a schematic configuration of a microscope according to a modified example of the fourth embodiment of the present invention; 
         FIG. 16  is a schematic diagram illustrating a schematic configuration of a microscope according to a fifth embodiment of the present invention; 
         FIG. 17  is a diagram illustrating a configuration of a region R 7  illustrated in  FIG. 16 ; 
         FIG. 18  is a schematic diagram illustrating a configuration of a main part of a microscope according to a first modified example of the fifth embodiment of the present invention; 
         FIG. 19  is a schematic diagram illustrating a configuration of a main part of a microscope according to a second modified example of the fifth embodiment of the present invention; 
         FIG. 20  is a schematic diagram illustrating a configuration of a main part of a microscope according to a third modified example of the fifth embodiment of the present invention; 
         FIG. 21  is a schematic diagram illustrating a configuration of a main part of a microscope according to a fourth modified example of the fifth embodiment of the present invention; 
         FIG. 22  is a schematic diagram illustrating a schematic configuration of a microscope according to a sixth embodiment of the present invention; 
         FIG. 23  is a diagram illustrating a configuration of a region R 8  illustrated in  FIG. 22 ; and 
         FIG. 24  is a schematic diagram illustrating a configuration of a main part of the microscope according to the sixth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments of the present invention will be described in detail below with reference to the drawings. The present invention is not limited to the following embodiments. The drawings to be referred to in the following description only schematically illustrate shapes, sizes, and positional relationships to such a degree that the description of the present invention can be understood. In other words, the present invention is not limited to the shapes, sizes, and positional relationships that are exemplified in the drawings. 
     First Embodiment 
     A microscope according to some embodiments of the present invention will be described with reference to the drawings.  FIG. 1  is a schematic diagram illustrating a schematic configuration of a microscope according to a first embodiment of the present invention. As illustrated in  FIG. 1 , a microscope  1  is an upright microscope formed by a stage  3 , an objective lens  4 , an optical unit  8 , and the like being attached to a main body  2 . A front face of the microscope  1  faces a user in use. That is, the right side of  FIG. 1  corresponds to the front face of the microscope  1 , and the left side of  FIG. 1  corresponds to a back side of the microscope  1 . The microscope  1  illustrated in  FIG. 1  illustrates a state in which an illumination light path Na of the optical unit  8  is disposed at a first position where the illumination light path Na connects to an observation light path Nb. 
     The main body  2  includes a base portion  2   a , a pillar portion  2   b , and an arm portion  2   c . The base portion  2   a  is directly placed on a location where the microscope  1  is disposed, such as on a desk. The pillar portion  2   b  is vertically disposed on a rear side of the base portion  2   a . The arm portion  2   c  extends from an upper end of the pillar portion  2   b  toward the front face of the microscope  1 . The base portion  2   a  is provided with a control board (not illustrated) for controlling the entire microscope  1 . The control board relays power supply from the outside to each unit, or has a built-in power source in itself and relays power supply to each unit. 
     The base portion  2   a  includes a light source  9  for emitting transmission illumination light, and a collector lens  91  for collecting illumination light. The light source  9  is realized by using, for example, a light emitting diode (LED) light source (solid-state light source), and lights up and goes out under the control of the control board. The LED light source is formed by using, for example, a monochroic LED and a fluorescent member, and emits white-color illumination light. The fluorescent member has a dome shape to which fluorescent material is applied, and covers the LED. In this configuration, the fluorescent member is excited by light emitted by the LED, to emit light. 
     The stage  3  on which a specimen S as an observation target is placed is provided on the front face of the pillar portion  2   b . The stage  3  is supported on the pillar portion  2   b  via a focusing guide, and is movable along an optical axis of the objective lens  4  disposed on the observation light path Nb, by an operation of a focus handle  3   a , for example. The focus handle  3   a  is configured to be rotatable, and using the rotation of itself, moves the stage  3  by a known method such as a gear and a rack-and-pinion. The stage  3  is movable on a plane vertical to the optical axis of the objective lens  4 , by an operation handle  3   b . The specimen S is held on a holding member such as, for example, a laboratory dish and a glass slide. 
     The stage  3  is provided with a brightness diaphragm  92  and a condenser lens  93 . Illumination light emitted from the light source  9  is collected by the collector lens  91 , and a numerical aperture is adjusted by the brightness diaphragm  92 . After that, illumination light having passed through the brightness diaphragm  92  is collected by the condenser lens  93  to illuminate the specimen S. The collector lens  91 , the brightness diaphragm  92 , and the condenser lens  93  constitute an illumination optical system for performing critical illumination for the specimen S. At this time, the light source  9  and the specimen S, and an exit pupil of the objective lens  4  and the brightness diaphragm  92  are disposed at positions conjugated to each other. 
       FIG. 2  is a diagram schematically illustrating a configuration of a main part of the microscope according to the first embodiment of the present invention, and is a diagram illustrating a configuration of a main part of the main body  2  that is in a state in which the optical unit  8  is inserted.  FIG. 3  is a diagram schematically illustrating a configuration of a main part of the microscope according to the first embodiment of the present invention, and is a diagram illustrating a configuration of a main part of the main body  2  that is in a state in which the optical unit  8  is removed. 
     The arm portion  2   c  includes a revolver  5  (objective lens support portion) and an observation portion  6  (lens barrel). The revolver  5  is installed at a bottom part on a distal end side in an extending direction of the arm portion  2   c . The observation portion  6  is installed at an upper part on the distal end side in the extending direction of the arm portion  2   c . The revolver  5  and the observation portion  6  are disposed so as to face each other via the arm portion  2   c.    
     For example, a plurality of objective lenses  4  having different magnifications can be attached to the revolver  5 , and by rotating the revolver  5 , observation can be performed with the objective lens  4  having a desired magnification being inserted onto the observation light path Nb. 
     An eyepiece  7  is attached to the observation portion  6 . The observation portion  6  includes therein reflection mirrors  61  and  62  to guide observation light to the eyepiece  7  via the reflection mirrors  61  and  62 , and forms an observation image at the eyepiece  7 . The eyepiece  7  is formed by a tube lens and the like to magnify an intermediate image formed by the tube lens. 
     A holding portion  21  and a wall portion  22  are formed on the arm portion  2   c . The holding portion  21  holds the optical unit  8  so as to be insertable and removable. The wall portion  22  is provided on a side connecting to the pillar portion  2   b , and extends toward the back side to form a space connecting to an opening of the holding portion  21 . The arm portion  2   c  includes an opening for passing the observation light path Nb. A plane P passing through the opening of the holding portion  21  that is provided on the side on which the optical unit  8  is inserted, and being parallel to a direction vertical to a placement surface (for example, direction parallel to the optical axis of the objective lens  4 ) is positioned between the pillar portion  2   b  and the observation portion  6 . The opening of the holding portion  21  is thereby disposed at a position closer to the user. In this manner, by bringing the position of a grip portion  81   b  in the insertion of the optical unit  8  closer to the front face (user side), the operability of the optical unit  8  can be enhanced. 
       FIG. 4  is a perspective view schematically illustrating a configuration of an optical unit of the microscope according to the first embodiment of the present invention.  FIG. 5  is a diagram illustrating a configuration of a region R 1  illustrated in  FIG. 1 .  FIG. 6  is a diagram illustrating a configuration of a region R 2  illustrated in  FIG. 5 . The optical unit  8  includes a light source and an optical system for emitting epi-illumination light onto the specimen S. 
     The optical unit  8  includes a casing  81  having a longitudinal direction extending in a direction of inserting and removing the optical unit  8  into and from the main body  2 . The casing  81  is a hollow prismatic body, and includes an optical holding portion  81   a  and the grip portion  81   b . The optical holding portion  81   a  houses the light source and the illumination optical system. The grip portion  81   b  abuts the optical holding portion  81   a  in the longitudinal direction of the optical holding portion  81   a , and is gripped by the user when the optical unit  8  is inserted into or removed from the main body  2 . 
     Openings  810   a  and  810   b  for passing the observation light path Nb when the optical unit  8  is attached to the main body  2  are formed at an end portion on an opposite side of the grip portion  81   b  side of the optical holding portion  81 a. The grip portion  81   b  is provided with a control board for controlling on/off and the like of the light source, a switch for performing an instruction input of the on/off, and a light adjustment operating unit  82  for adjusting a light amount of the light source (a light source  83  to be described below) included in the optical unit  8 . The optical unit  8  itself may include a power source, and supply power to the light source  83 , or power may be supplied via an external power source and the main body  2 . 
     Inside the optical holding portion  81 a, provided are the light source  83 , a field diaphragm  84  for adjusting an illumination field formed by light emitted from the light source  83 , a collector lens  85  for collecting light having passed through the field diaphragm  84 , an excitation filter  86  for passing light having a specific wavelength band from the collector lens  85 , a dichroic mirror  87  for bending the light having passed through the excitation filter  86 , in a direction oriented toward the objective lens  4  on the observation light path Nb, and passing light having wavelength bands other than the wavelength band transmitted through the excitation filter  86 , among the light having passed through the objective lens  4 , and an absorption filter  88  for absorbing light having wavelength bands other than the specific wavelength band, among the light having passed through the dichroic mirror  87 , and passing light having the specific wavelength band. The field diaphragm  84 , the collector lens  85 , the excitation filter  86 , and the dichroic mirror  87  constitute an epi-illumination optical system for performing Kohler illumination for the specimen S. In the first embodiment, in a state in which the illumination light path Na of the optical unit  8  is disposed at the first position where the illumination light path Na connects to the observation light path Nb, the light source  83  and the exit pupil of the objective lens  4 , and the field diaphragm  84  and the specimen S are disposed at positions conjugated to each other. 
     The optical holding portion  81   a  preferably has the minimum size that can store the light source  83 , the epi-illumination optical system, and the excitation filter  86 . Here, in the dichroic mirror  87  having the largest occupancy in a cross-section vertical to the longitudinal direction of the optical holding portion  81   a , a length in a direction intersecting with a plane through which the illumination light path Na and the observation light path Nb pass, for example, a length of a side inclined with respect to the illumination light path Na among four sides of a rectangle is denoted by d 1  (refer to  FIG. 5 ). When the dichroic mirror  87  is inclined by 45° with respect to the illumination light path Na, a height d 2  in the observation light path Nb direction of the optical holding portion  81   a  becomes d 2 =d 1  sin 45°. For example, when the length d 1  is 38 mm, the height d 2  becomes about 26.9 mm. In this case, the optical holding portion  81   a  sets a height d 3  in the observation light path Nb direction to a height larger than 26.9 mm. At this time, it is preferable to design so as to have the minimum height that can store the illumination optical system and the like. 
     The light adjustment operating unit  82  includes a dial rotatable around a predetermined axis, and the like, and can perform a light amount change input according to an instruction position changing based on the rotation of itself. Illumination light emitted from the light source  83  is emitted with a light amount set according to the angle of rotation from a reference position in the light adjustment operating unit  82 . 
     The light source  83  emits, for example, illumination light including light having a wavelength band to excite the specimen S. In other words, in the first embodiment, the illumination light emitted by the light source  83  travels along the illumination light path Na, an illumination field is adjusted by the field diaphragm  84 , and the light is collected by the collector lens  85 . After that, the illumination light having passed through the collector lens  85  becomes light (excitation light) having a specific wavelength band, i.e., a wavelength band including an excitation wavelength that excites the specimen S, by passing through the excitation filter  86 . The excitation light is bent by the dichroic mirror  87 , and emitted onto the specimen S via the objective lens  4 . Fluorescence emitted by the specimen S being excited is taken into the objective lens  4 , and light having wavelength bands other than the wavelength band of the excitation light passes through the dichroic mirror  87 . After that, light having the wavelength band of the fluorescence of an observation target passes through the absorption filter  88 , and observation light having passed through the absorption filter  88  forms an image at the eyepiece  7 . 
     The casing  81  extends in a progressing and regressing direction of the optical unit  8 , and includes a plate spring  89  elastically-deformable in a direction approaching or being separated from the main body  2 . One end of the plate spring  89  is fixed by a screw or the like, and the plate spring  89  elastically deforms using this fixed end as a supporting point. The other end of the plate spring  89  is provided with a latch claw  89   a.    
     A contact portion  811  contacting the main body  2  is formed in the casing  81 . When the optical unit  8  is inserted into the main body  2 , the contact portion  811  comes into contact with a wall surface  201  on the illumination side of the arm portion  2   c.    
     As illustrated in  FIG. 6 , when the optical unit  8  is inserted into the holding portion  21  of the arm portion  2   c , while deviating toward the inside of the casing  81 , the latch claw  89   a  travels while sliding on an internal wall surface of the holding portion  21 . After that, the latch claw  89   a  engages with a click step portion  211   a  immediately before or simultaneously with the contact portion  811  contacting the wall surface  201  of the arm portion  2   c . The optical unit  8  is thereby latched at a position where the illumination light path Na intersects with the observation light path Nb, and connects to the observation light path Nb, and enters a state of being prevented from dropping out in a direction of retracting from the main body  2 . 
     Furthermore, the casing  81  includes a latch portion  812  that can be latched to the main body  2  at a position retracted from the observation light path Nb of the optical unit  8 , and a spring member  813  for biasing the latch portion  812  toward the outer surface of the casing  81  so as to be able to progress and regress. 
       FIG. 7  is a schematic diagram illustrating a schematic configuration of the microscope according to the first embodiment of the present invention, and illustrates a state in which the dichroic mirror  87  of the optical unit  8  is retracted from the observation light path Nb.  FIG. 8  is a diagram illustrating a configuration of a region R 3  illustrated in  FIG. 7 . When the optical unit  8  is inserted into the holding portion  21  of the arm portion  2   c , the latch portion  812  advances while deviating toward the inside of the casing  81  along an inclined surface  211   b  of a protruding portion  211  formed inside the holding portion  21 . After passing through a step portion  211   c , the latch portion  812  enters a state of protruding from the outer surface of the casing  81  by the biasing of the spring member  813 . If the optical unit  8  retracts from the main body  2  from this state, that is, if the dichroic mirror  87  of the optical unit  8  moves in a direction retracting from the observation light path Nb, the latch portion  812  comes into contact with the step portion  211   c  to be engaged therewith, and the optical unit  8  enters a state of being disposed at a second position where the illumination light path Na is retracted from the observation light path Nb (refer to  FIG. 8 ). In the state illustrated in  FIGS. 7 and 8 , because the illumination light path Na of the optical unit  8  is retracted from the observation light path Nb, epi-illumination observation is not performed, and transmitted-light illumination observation can be performed by the light source  9 . In this manner, in the first embodiment, by switching the position of the optical unit  8 , the illumination light path Na of the epi-illumination optical system can take any of the first position where the illumination light path Na intersects with the observation light path Nb passing through the objective lens  4  attached to the revolver  5 , and the second position where the illumination light path Na is retracted from the observation light path Nb. In the first embodiment, the latch portion  812 , the spring member  813 , and the step portion  211   c  constitute a regulating mechanism. 
     As illustrated in  FIG. 2 , when the optical unit  8  is inserted into the arm portion  2   c , the optical unit  8  is in a state in which the grip portion  81   b  is disposed in a space formed by the wall portion  22 , and part of the grip portion  81   b  is exposed from the arm portion  2   c , and the grip portion  81   b  does not extend from the pillar portion  2   b  toward the back side. Thus, the user can easily grip the grip portion  81   b  even from the front face side. 
     When the optical unit  8  is removed from the main body  2 , as illustrated in  FIG. 8 , by pulling out the optical unit  8  in a state in which the latch portion  812  is pressed by inserting a bar member  100  from a hole portion  211   d  formed in the arm portion  2   c , the optical unit  8  can be removed from the main body  2 . 
     In the first embodiment, the hole portion  211   d  is provided below the observation portion  6  (refer to  FIG. 7 ), and the bar member  100  can be inserted thereinto in a state in which the observation portion  6  is removed. Alternatively, the hole portion  211   d  may be formed at a position deviated from an attachment region of the observation portion  6  so that the bar member  100  can be inserted thereinto without removing the observation portion  6 . 
     According to the first embodiment, by switching an insertion position of the optical unit  8  with respect to the arm portion  2   c , the illumination optical system is made insertable onto and removable from the observation light path Nb. Thus, an observation method, for example, epi-illumination observation and transmitted-light illumination observation can be switched without changes in heights of the observation portion  6  and the eyepiece  7  that are caused by the optical unit  8 . With this configuration, the insertion and removal of an optical element, more specifically, the insertion and removal of the dichroic mirror  87  onto and from the observation light path Nb can be easily performed while suppressing a change in height of the observation portion  6  being a lens barrel. By suppressing a change in height of the lens barrel in this manner, a change in eyepoint of the user can be suppressed. 
     The conventional buildup method requires a countermeasure of, for example, making the thickness of an arm portion thinner for suppressing a change in eyepoint that is caused by the addition of an optical unit. Thus, the thinned arm portion may decrease rigidity. In contrast to this, in the first embodiment, because the height of the observation portion  6  does not change when the optical unit  8  is added to the main body  2 , the thickness of the arm portion  2   c  needs not be made thinner, and a decrease in rigidity of the arm portion  2   c  can be suppressed. 
     In the first embodiment, because an exposed portion of the optical unit  8  inserted into the arm portion  2   c  is provided with the grip portion  81   b , a good operability in the switching of an observation method can be realized. 
     In the first embodiment, because the wall portion  22  extending toward the back side is provided in the arm portion  2   c , rigidity is added to the arm portion  2   c , and the rigidity of the main body  2  can be enhanced. 
     In the first embodiment, although in the arm portion  2   c , the optical unit  8  can take the first position and the second position, the optical unit  8  is only required to be located at least at the first position. In other words, when transmitted-light illumination observation is performed, the optical unit  8  may be removed from the arm portion  2   c.    
     Second Embodiment 
     Next, a second embodiment of the present invention will be described.  FIG. 9  is a schematic diagram illustrating a schematic configuration of a microscope according to the second embodiment of the present invention.  FIG. 10  is a diagram illustrating a configuration of a region R 4  illustrated in  FIG. 9 . A microscope  1 A according to the second embodiment includes an optical unit  8 A in place of the optical unit  8 . 
     The optical unit  8 A includes a casing  81  having a longitudinal direction extending in a direction of inserting and removing the optical unit  8 A into and from a main body  2 . The casing  81  is a hollow prismatic body, and includes an optical holding portion  81   a  and a grip portion  81   b . The optical holding portion  81   a  houses a light source and an illumination optical system. The grip portion  81   b  abuts the optical holding portion  81   a  in the longitudinal direction of the optical holding portion  81   a , and is gripped by the user when the optical unit  8 A is inserted into or removed from the main body  2 . The grip portion  81   b  has a configuration similar to the aforementioned configuration. 
     In the optical unit  8 A, in addition to the aforementioned configuration, the optical holding portion  81   a  is further provided with an operating member  814  for operating the movement of the position of the optical unit  8 A with respect to an arm portion  2   c . For example, the operating member  814  has a bar shape, and protrudes in an illumination light path Na direction from a surface from which a contact portion  811  of the optical holding portion  81   a  extends. At a position where the optical unit  8  is retracted from an observation light path Nb, the operating member  814  is located away from the observation light path Nb. 
     In the second embodiment, a hole portion  24   a  into which the operating member  814  can be inserted is formed in a wall portion  24  on the front face side of the arm portion  2   c . If the optical unit  8  is inserted into a holding portion  21  from the rear surface, the operating member  814  protrudes toward the front face side from the hole portion  24   a . The user can switch the position of the optical unit  8 A with respect to the arm portion  2   c  by moving the operating member  814  back and forth in the longitudinal direction. 
     According to the second embodiment, similarly to the first embodiment, by switching an insertion position of the optical unit  8 A with respect to the arm portion  2   c , the illumination optical system is made insertable onto and removable from the observation light path Nb. Thus, an observation method, for example, epi-illumination observation and transmitted-light illumination observation can be switched without changes in positions of an observation portion  6  and an eyepiece  7  that are caused by the optical unit  8 A. An optical element can be thereby easily inserted onto and removed from an observation light path while suppressing a change in eyepoint. 
     In addition, according to the second embodiment, because the operating member  814  protruding toward the front face side of the main body  2  is provided in the optical unit  8 A, as compared with the first embodiment, the switching of an insertion position of the optical unit  8 A with respect to the arm portion  2   c  can be performed further easily. 
     Third Embodiment 
     Next, a third embodiment of the present invention will be described.  FIG. 11  is a schematic diagram illustrating a schematic configuration of a microscope according to the third embodiment of the present invention.  FIG. 12  is a diagram illustrating a configuration of a region R 5  illustrated in  FIG. 11 . A microscope  1 B according to the third embodiment includes an optical unit  8 B in place of the optical unit  8 . 
     The optical unit  8 B includes a casing  81 A having a longitudinal direction extending in a direction of inserting and removing the optical unit  8 B into and from a main body  2 . The casing  81 A is a hollow prismatic body, and houses a light source and an illumination optical system. 
     The optical unit  8 B includes an optical holding portion  81 a. The optical holding portion  81   a  includes the operating member  814  and a light adjustment operating unit  82   a  that is provided at the distal end in a direction of inserting the optical unit  8 B into a holding portion  21  and adjusts a light amount of a light source  83  of the optical unit  8 B, in addition to the elements according to the first embodiment. The light adjustment operating unit  82   a  electrically connects to a control board via a cable or the like (not illustrated), and outputs information about a rotation angle of itself. 
     In the third embodiment, a hole portion  25   a  into which the operating member  814  can be inserted, and which exposes the light adjustment operating unit  82   a  is formed in a wall portion  25  on the front face side of an arm portion  2   c . The user can switch the position of the optical unit  8 B with respect to the arm portion  2   c  by moving the operating member  814  back and forth in the longitudinal direction, and furthermore, can adjust a light amount of the light source  83  by operating the light adjustment operating unit  82   a  from the front face side. 
     According to the third embodiment, similarly to the first embodiment, by switching an insertion position of the optical unit  8 B with respect to the arm portion  2   c , the illumination optical system is made insertable onto and removable from an observation light path Nb. Thus, an observation method, for example, epi-illumination observation and transmitted-light illumination observation can be switched without changes in positions of an observation portion  6  and an eyepiece  7  that are caused by the optical unit  8 B. An optical element can be thereby easily inserted onto and removed from an observation light path while suppressing a change in eyepoint. 
     In addition, according to the third embodiment, in the optical unit  8 B, because the light adjustment operating unit  82   a  is exposed to the front face side of the main body  2 , as compared with the first embodiment, a light amount of the light source  83  can be adjusted further easily. 
     Fourth Embodiment 
     Next, a fourth embodiment of the present invention will be described.  FIG. 13  is a schematic diagram illustrating a schematic configuration of a microscope according to the fourth embodiment of the present invention.  FIG. 14  is a diagram illustrating a configuration of a region R 6  illustrated in  FIG. 13 . A microscope  10  according to the fourth embodiment includes an optical unit  8 C in place of the optical unit  8 . 
     The optical unit  8 C includes a casing  81 B having a longitudinal direction extending in a direction of inserting and removing the optical unit  8 C into and from a main body  2 . The casing  81 B is a hollow prismatic body, and includes an optical holding portion  81   c  and a grip portion  81 d. The optical holding portion  81   c  houses a light source and an illumination optical system. The grip portion  81   d  abuts the optical holding portion  81   c  in the longitudinal direction of the optical holding portion  81   c , and is gripped by the user when the optical unit  8 C is inserted into or removed from the main body  2 . 
     Openings  810   c  and  810   d  for passing an observation light path Nb when the optical unit  8 C is attached to the main body  2  are formed at an end portion on an opposite side of the grip portion  81   d  side of the optical holding portion  81   c . A variable power lens  815  for varying an enlarging magnification of an observation image is provided in the optical holding portion  81   c.    
     The casing  81 B includes the plate spring  89 . A contact portion  811  contacting the main body  2  is formed at the distal end in the insertion direction of the optical holding portion  81   c . When the optical unit  8 C is inserted into the main body  2 , the contact portion  811  comes into contact with a wall surface on an illumination side of an arm portion  2   c , and a latch claw  89   a  included in the plate spring  89  engages with a click step portion  211   a  (refer to  FIG. 6 ). The optical unit  8 C thereby enters a state of being positioned in a direction retracting from the main body  2 . 
     Furthermore, the casing  81 B includes the latch portion  812  and the spring member  813 . With this configuration, also in the fourth embodiment, the optical unit  8 C can be switched to a first position where the variable power lens  815  is disposed on the observation light path Nb, and a second position where the variable power lens  815  is retracted from the observation light path Nb (for example, refer to  FIGS. 7 and 8 ). By switching the position of the optical unit  8 C in this manner, in transmitted-light illumination observation performed using a light source  9 , observation can be performed while switching the presence and absence of the variable power lens  815 . 
     When the optical unit  8 C is removed from the main body  2 , as illustrated in  FIG. 8 , by pulling out the optical unit  8 C in a state in which the latch portion  812  is pressed by inserting a bar member  100  from a hole portion  211   d  formed in the arm portion  2   c , the optical unit  8 C can be removed from the main body  2 . 
     According to the fourth embodiment, by switching an insertion position of the optical unit  8 C with respect to the arm portion  2   c , the illumination optical system is made insertable onto and removable from the observation light path Nb. Thus, an observation method can be switched to, for example, observation with an enlarging magnification of an observation image that is varied by the variable power lens  815 , without changes in positions of an observation portion  6  and an eyepiece  7  that are caused by the optical unit  8 C. An optical element can be thereby easily inserted onto and removed from an observation light path while suppressing a change in eyepoint. As in the fourth embodiment, aside from the epi-illumination optical system in the first to third embodiments, an optical unit for changing an enlarging magnification may be employed. An optical unit including an optical element other than an illumination optical system may also be employed, such as an optical unit for performing differential interference contrast microscopy. 
     Modified Example of Fourth Embodiment 
     Next, a modified example of the fourth embodiment of the present invention will be described.  FIG. 15  is a schematic diagram illustrating a schematic configuration of a microscope according to a modified example of the fourth embodiment of the present invention. A microscope  1 C_ 1  according to this modified example includes an optical unit  8 C_ 1  in place of the optical unit  8 C. The microscope  1 C_ 1  includes an observation portion  6 A in place of the observation portion  6 . Other configurations are similar to those in the first embodiment. 
     In addition to the reflection mirrors  61  and  62 , the observation portion  6 A includes a tube lens  63 , and an eyepiece  7  is attached onto a light path of light reflected by the reflection mirror  62 . 
     The longitudinal direction of the optical unit  8 C_ 1  extends in an insertion and removal direction with respect to the main body  2 , and the optical unit  8 C_ 1  includes an optical holding portion  81   c _ 1  being a casing for housing a prism  816  and a light reflecting mirror  817 . The optical holding portion  81   c _ 1  is provided with an attachment portion  81   c _ 2  to which the observation portion  6 A is attached. The observation portion  6 A attached to the optical holding portion  81   c _ 1  functions as a grip portion to be gripped by the user when the optical unit  8 C_ 1  is inserted into and removed from the main body  2 . 
     When the optical unit  8 C_ 1  is attached to the main body  2 , the prism  816  divides light on the observation light path Nb that has been taken into the objective lens  4 , into light on an observation optical axis Nb_ 1  and light on an observation optical axis Nb_ 2 . The light on the observation optical axis Nb_ 2  enters the light reflecting mirror  817 , and is reflected by the light reflecting mirror  817 , and then, enters the tube lens  63 . 
     The light reflecting mirror  817  reflects light in a direction vertical to the observation optical axis Nb_ 2 , for example. 
     An opening through which the observation light path Nb passes and an opening through which light toward the observation portion  6 A passes when the optical unit  8 C_ 1  is attached to the main body  2  are formed in the optical holding portion  81   c _ 1 . The optical holding portion  81   c _ 1  includes elements related to the insertion and removal into and from the main body  2 , such as the plate spring  89 , the contact portion  811 , the latch portion  812 , and the spring member  813 . Also in this modified example, the optical unit  8 C_ 1  can be switched to a first position where the prism  816  is disposed on the observation light path Nb, and a second position where the prism  816  is retracted from the observation light path Nb. By switching the position of the optical unit  8 C_ 1  in this manner, in transmitted-light illumination observation performed using the light source  9 , observation can be performed while switching whether to cause observation light to enter the observation portion  6 A on the optical unit  8 C_ 1  side. 
     In this modified example, because the observation portion  6 A is included as the optical unit  8 C_ 1 , the optical unit  8 C_ 1  including the observation portion  6 A functions as a facing discussion lens barrel by being used together with the observation portion  6 A attached to the main body  2 . 
     Fifth Embodiment 
     Next, a fifth embodiment of the present invention will be described.  FIG. 16  is a schematic diagram illustrating a schematic configuration of a microscope according to the fifth embodiment of the present invention.  FIG. 17  is a diagram illustrating a configuration of a region R 7  illustrated in  FIG. 16 . A microscope  1 D according to the fifth embodiment includes an optical unit  8 D in place of the optical unit  8 . The microscope  1 D includes an observation portion  6 A in place of the observation portion  6 . As described above, the observation portion  6 A includes reflection mirrors  61  and  62  and a tube lens  63 , and an eyepiece  7  is attached onto a light path of light reflected by the reflection mirror  62 . Other configurations are similar to those in the first embodiment. 
     The optical unit  8 D includes a casing  81 C having a longitudinal direction extending in an insertion and removal direction with respect to a main body  2 . The casing  81 C includes an optical holding portion  81   e  and a grip portion  81   f . The optical holding portion  81   e  houses a prism  820 , a tube lens  830 , and an image sensor  840 . The grip portion  81   f  abuts the optical holding portion  81   e  in the longitudinal direction of the optical holding portion  81 e, and is gripped by the user when the optical unit  8 D is inserted into or removed from the main body  2 . In the fifth embodiment, the prism  820  and the tube lens  830  form an image forming optical system. 
     When the optical unit  8 D is attached to the main body  2 , the prism  820  divides light on an observation light path Nb that has been taken into an objective lens  4 , into light with an observation optical axis Nb_ 1  and light with an observation optical axis Nb_ 2 . Among the light divided by the prism  820 , the light with the observation optical axis Nb_ 2  enters the tube lens  830 , and light formed by the tube lens  830  enters the image sensor  840 . 
     The image sensor  840  is mounted on a substrate  841 . The substrate  841  is connected to a driving substrate (illustration is omitted) via an internal cable (not illustrated). The driving substrate is electrically connected with a cable  850  for connecting to an external processing apparatus. Image data acquired by the image sensor  840  is input to the external processing apparatus via the cable  850 . In the external processing apparatus, image data is generated based on an electrical signal generated through photoelectric conversion performed by the image sensor  840 . The image data is displayed on the processing apparatus, another monitor, or the like. 
     An opening  810   e  through which the observation light path Nb passes and an opening  810   f  through which light toward the observation portion  6 A passes when the optical unit  8 D is attached to the main body  2  are formed at an end portion on an opposite side of the grip portion  81   f  side of the optical holding portion  81   e.    
     The casing  81 C includes the plate spring  89 . A contact portion  811  contacting the main body  2  is formed at the distal end in the insertion direction of the optical holding portion  81   e . When the optical unit  8 D is inserted into the main body  2 , the contact portion  811  comes into contact with a wall surface on an illumination side of an arm portion  2   c , and a latch claw  89   a  included in the plate spring  89  engages with a click step portion  211   a  (refer to  FIG. 6 ). The optical unit  8 D thereby enters a state of being positioned in a direction retracting from the main body  2 . 
     Furthermore, the casing  81 C includes the latch portion  812  and the spring member  813 . With this configuration, also in the fifth embodiment, the optical unit  8 D can be switched to a first position where the prism  820  is disposed on the observation light path Nb, and a second position where the prism  820  is retracted from the observation light path Nb. By switching the position of the optical unit  8 D in this manner, in transmitted-light illumination observation performed using a light source  9 , observation can be performed while switching whether to cause observation light to enter the image sensor  840 . 
     When the optical unit  8 D is removed from the main body  2 , as described above, by pulling out the optical unit  8 D in a state in which the latch portion  812  is pressed by inserting a bar member  100  from a hole portion  211   d  formed in the arm portion  2   c , the optical unit  8 D can be removed from the main body  2 . 
     According to the fifth embodiment, similarly to the first embodiment, by switching an insertion position of the optical unit  8 D with respect to the arm portion  2   c , the image forming optical system is made insertable onto and removable from the observation light path Nb. Thus, an observation method, more specifically, observation using the observation portion  6 A and observation using an image that is based on an electrical signal generated by the image sensor  840  can be switched without changes in positions of the observation portion  6 A and the eyepiece  7  that are caused by the optical unit  8 D. An optical element can be thereby easily inserted onto and removed from an observation light path while suppressing a change in eyepoint. 
     In addition, according to the fifth embodiment, because the optical unit  8 D includes the image forming optical system, an image of a specimen S can be acquired. If a focal length of the tube lens  830  is shortened without using a focal length common to the tube lens  63  of the observation portion  6 A, the total length of the casing  81 C can be shortened by using the image sensor  840  having a small size. Thus, a compact and easily-handled optical unit can be provided. Furthermore, according to the fifth embodiment, because a gravity center can be kept low even if the optical unit  8 D is attached to the main body  2 , safety is enhanced. Furthermore, because the entire height does not become high, storage easiness is enhanced. On the other hand, in the convention technique, when a unit for capturing a specimen image is provided, a trinocular lens barrel, a tube lens straight tube, and a trinocular intermediate lens-barrel have been assembled onto a frame (e.g., arm portion) of a microscope, and a camera has been stacked thereonto. Thus, the entire height of the microscope has been high. 
     In the fifth embodiment, by using the prism  820  that divides light based on a light path division ratio for guiding observation light toward both the observation portion  6 A side and the image sensor  840  side, visual observation and observation using an image obtained by the image sensor  840  can be simultaneously performed. In the fifth embodiment, a light path is divided using the prism  820 . Alternatively, instead of a prism that divides a light path, a mirror for reflecting observation light toward the tube lens  830  may be used. In this case, as compared with a case of dividing a light path, a brighter image can be obtained. Meanwhile, if the optical unit  8 D is disposed at the second position, observation using the observation portion  6 A can be performed. 
     First Modified Example of Fifth Embodiment 
     Next, a first modified example of the fifth embodiment of the present invention will be described.  FIG. 18  is a schematic diagram illustrating a configuration of a main part of a microscope according to the first modified example of the fifth embodiment of the present invention. The microscope according to the first modified example includes an optical unit  8 D_ 1  in place of the optical unit  8 D. 
     The longitudinal direction of the optical unit  8 D_ 1  extends in an insertion and removal direction with respect to a main body  2 , and the optical unit  8 D_ 1  includes an optical holding portion  81   e _ 1  being a casing for housing a prism  820  and a tube lens  830 . A camera unit  860  is attached to the optical holding portion  81   e _ 1  via an attachment portion  81   e _ 2 . An opening  810   e  through which the observation light path Nb passes and an opening  810   f  through which light toward the observation portion  6 A passes when the optical unit  8 D_ 1  is attached to the main body  2  are formed in the optical holding portion  81   e _ 1 . The optical holding portion  81   e _ 1  includes elements related to the insertion and removal into and from the main body  2 , such as the plate spring  89 , the contact portion  811 , the latch portion  812 , and the spring member  813 . 
     The attachment portion  81   e _ 2  is provided with a parfocality adjustment unit  81   e _ 3 . The parfocality adjustment unit  81   e _ 3  is realized by a configuration that can move the camera unit  860  in an observation optical axis Nb_ 2  direction, i.e., a known driving system such as, for example, a screw driving system. The camera unit  860  includes an image sensor  861 , and functions as a grip portion to be gripped by the user when the optical unit  8 D_ 1  is inserted into and removed from the main body  2 . The camera unit  860  may include a signal processor for processing an electrical signal generated by the image sensor  861 , and a storage for storing the electrical signal and image data obtained based on the electrical signal. 
     In the first modified example, a distance between the tube lens  830  and the camera unit  860  can be adjusted by the parfocality adjustment unit  81   e _ 3  according to the characteristics of the camera unit  860  to be attached. 
     According to the first modified example, in a configuration in which the image sensor  861  is separately provided as the camera unit  860 , the camera unit  860  can be selected according to the desire of the user. Thus, system extensibility is enhanced. 
     Second Modified Example of Fifth Embodiment 
     Next, a second modified example of the fifth embodiment of the present invention will be described.  FIG. 19  is a schematic diagram illustrating a configuration of a main part of a microscope according to the second modified example of the fifth embodiment of the present invention. The microscope according to the second modified example includes an optical unit  8 D_ 2  in place of the optical unit  8 D_ 1 . 
     The longitudinal direction of the optical unit  8 D_ 2  extends in an insertion and removal direction with respect to a main body  2 , and the optical unit  8 D_ 2  includes an optical holding portion  81   e _ 4  being a casing for housing an image forming optical system formed by a prism  820 , a tube lens  831  and a light reflecting mirror  831   a . The tube lens  831  has a focal length longer than that of the tube lens  830 . The light reflecting mirror  831   a  reflects light in a direction vertical to the observation optical axis Nb_ 2 , for example. 
     A camera unit  870  is attached to the optical holding portion  81   e _ 4  via an attachment portion  81   e _ 2 . The attachment portion  81   e _ 2  is provided with a parfocality adjustment unit  81   e _ 3 . The camera unit  870  includes an image sensor  871 , and functions as a grip portion to be gripped by the user when the optical unit  8 D_ 2  is inserted into and removed from the main body  2 . The camera unit  870  may include a signal processor for processing an electrical signal generated by the image sensor  871 , and a storage for storing the electrical signal and image data obtained based on the electrical signal. 
     An opening  810   e  through which the observation light path Nb passes and an opening  810   f  through which light toward the observation portion  6 A passes when the optical unit  8 D_ 2  is attached to the main body  2  are formed in the optical holding portion  81   e _ 4 . The optical holding portion  81   e _ 4  includes elements related to the insertion and removal into and from the main body  2 , such as the plate spring  89 , the contact portion  811 , the latch portion  812 , and the spring member  813 . 
     In the second modified example, similarly to the first modified example, a distance between the tube lens  831  and the camera unit  870  can be adjusted by the parfocality adjustment unit  81   e _ 3  according to the characteristics of the camera unit  870  to be attached. 
     According to the second modified example, the camera unit  870  is disposed at an upper part of the arm portion  2   c , and light on the observation light path Nb_ 2  is bent. With this configuration, even if the large-sized camera unit  870  is provided, contact with a wall portion  22  of the arm portion  2   c  can be avoided without elongating the depth of the casing. Thus, a system can be expanded in a reduced space. 
     Third Modified Example of Fifth Embodiment 
     Next, a third modified example of the fifth embodiment of the present invention will be described.  FIG. 20  is a schematic diagram illustrating a configuration of a main part of a microscope according to the third modified example of the fifth embodiment of the present invention. The microscope according to the third modified example includes an optical unit  8 D_ 3  in place of the optical unit  8 D_ 2 . 
     The longitudinal direction of the optical unit  8 D_ 3  extends in an insertion and removal direction with respect to a main body  2 , and the optical unit  8 D_ 3  includes an optical holding portion  81   e _ 5  being a casing for housing an image forming optical system formed by a prism  820 , a tube lens  832 , a light reflecting mirror  832   a , and an eyepiece  832   b . The tube lens  832  has a focal length longer than that of the tube lens  830 . The light reflecting mirror  832   a  reflects light in a direction vertical to the observation optical axis Nb_ 2 , for example. The eyepiece  832   b  is a lens for forming an image in a portable device  880  having an imaging function that is to be installed, such as a smartphone. An end portion of the optical holding portion  81   e _ 5  on an opposite side of a side inserted into the main body  2  functions as a grip portion to be gripped by the user when the optical unit  8 D_ 3  is inserted into and removed from the main body  2 . 
     The portable device  880  is attached to the optical holding portion  81   e _ 5  via a mount portion  81   e _ 6 . A parfocality adjustment unit  81   e _ 7  is provided between the optical holding portion  81   e _ 5  and the mount portion  81   e _ 6 . The parfocality adjustment unit  81   e _ 7  is realized by using a configuration similar to those of the parfocality adjustment unit  81   e _ 3 , and adjusts a distance between the eyepiece  832   b  and a camera portion  881  including an image sensor that is included in the portable device  880 . An opening  810   e  through which the observation light path Nb passes and an opening  810   f  through which light toward the observation portion  6 A passes when the optical unit  8 D_ 3  is attached to the main body  2  are formed in the optical holding portion  81   e _ 5 . The optical holding portion  81   e _ 5  includes elements related to the insertion and removal into and from the main body  2 , such as the plate spring  89 , the contact portion  811 , the latch portion  812 , and the spring member  813 . 
     In the third modified example, similarly to the first modified example, a distance between the eyepiece  832   b  and the camera portion  881  of the portable device  880  can be adjusted by the parfocality adjustment unit  81   e _ 7  according to the characteristics of the portable device  880  to be attached. 
     As in the third modified example, since the portable device  880  having the imaging function is attached to the optical unit  8 D_ 3 , an image of a specimen S can be easily acquired by the camera portion  881 . 
     Fourth Modified Example of Fifth Embodiment 
     Next, a fourth modified example of the fifth embodiment of the present invention will be described.  FIG. 21  is a schematic diagram illustrating a configuration of a main part of a microscope according to the fourth modified example of the fifth embodiment of the present invention. The microscope according to the fourth modified example includes an optical unit  8 D_ 4  in place of the optical unit  8 D. 
     The longitudinal direction of the optical unit  8 D_ 4  extends in a direction of inserting and removing the optical unit  8 D_ 4  into and from a main body  2 , and the optical unit  8 D_ 4  includes an optical holding portion  81   e _ 8  being a casing for housing a prism  820  (first prism), a tube lens  833 , a second prism  833   a , a collector lens  833   b , an image sensor  842 , and a light source  843 . An end portion of the optical holding portion  81   e _ 8  on an opposite side of a side inserted into the main body  2  functions as a grip portion to be gripped by the user when the optical unit  8 D_ 4  is inserted into and removed from the main body  2 . In the fourth modified example, an image forming optical system is formed by the prism  820 , the tube lens  833 , and the second prism  833   a.    
     The second prism  833   a  forms a light source image by transmitting part of light transmitted through the collector lens  833   b . Illumination light using the light source image as a secondary light source passes through the tube lens  833  serving as a field lens, and is partially reflected by the prism  820 , to form again a light source image at a pupil position of the objective lens  4 . Using the light source image as a tertiary light source, the objective lens  4  itself serves as a condenser, and light based on the tertiary light source is emitted onto the specimen S as uniform epi-illumination light. In the fourth modified example, an epi-illumination optical system is formed by the prism  820 , the tube lens  833 , the second prism  833   a , and the collector lens  833   b . The second prism  833   a  bends part of light having passed through the tube lens  833  from the prism  820  side, toward the image sensor  842  side. The image sensor  842  and the light source  843  drive under the control of the main body  2  or an external processing apparatus via a cable (not illustrated). 
     An opening  810   e  through which the observation light path Nb passes and an opening  810   f  through which light toward the observation portion  6 A passes when the optical unit  8 D_ 4  is attached to the main body  2  are formed in the optical holding portion  81   e _ 8 . The optical holding portion  81   e _ 8  includes elements related to the insertion and removal into and from the main body  2 , such as the plate spring  89 , the contact portion  811 , the latch portion  812 , and the spring member  813 . 
     As in the fourth modified example, in the configuration including the image forming optical system and the epi-illumination optical system, by attaching the optical unit  8 D_ 4 , epi-illumination using uniform illumination light can be performed, and an observation image from the specimen S can be acquired. 
     Also in the first to fourth modified examples, a mirror for reflecting observation light may be used in place of the prism  820 . 
     Sixth Embodiment 
     Next, a sixth embodiment of the present invention will be described.  FIG. 22  is a schematic diagram illustrating a schematic configuration of a microscope according to the sixth embodiment of the present invention.  FIG. 23  is a diagram illustrating a configuration of a region R 8  illustrated in  FIG. 22 .  FIG. 24  is a schematic diagram illustrating a configuration of a main part of the microscope according to the sixth embodiment of the present invention, and is a diagram illustrating a configuration of an optical unit. A microscope  1 E according to the sixth embodiment includes an optical unit  8 E in place of the optical unit  8 , and further includes an observation portion  6 A in place of the observation portion  6 . Other configurations are similar to those in the first embodiment. 
     The optical unit  8 E includes a casing  81 D having a longitudinal direction extending in an insertion and removal direction with respect to a main body  2 . The casing  81 D includes an optical holding portion  81   g  and a grip portion  81 f. The optical holding portion  81   g  houses an image forming optical system formed by a prism  820 , a tube lens  830 , and an image sensor  840 . The grip portion  81   f  abuts the optical holding portion  81   g  in the longitudinal direction of the optical holding portion  81   g , and is gripped by the user when the optical unit  8 E is inserted into or removed from the main body  2 . The prism  820 , the tube lens  830 , and the image sensor  840  are similar to those in the fifth embodiment. Image data acquired by the image sensor  840  is input to the external processing apparatus via the cable  850 . 
     The optical holding portion  81   g  includes a light path division portion  900  for holding the prism  820 , and an optical main body portion  910  for holding the tube lens  830  and the image sensor  840 . The light path division portion  900  is detachably attached to the optical main body portion  910 , and corresponds to a light path changing unit. 
     In the optical main body portion  910 , on a surface connecting to the light path division portion  900 , a slide male dovetail  911  is formed. In the slide male dovetail  911 , an opening  912  for passing light bent by the prism  820  in an observation optical axis Nb_ 2  direction is formed. The slide male dovetail  911  includes a positioning wall  913  being a surface for positioning the light path division portion  900  by contacting part of the light path division portion  900  when the light path division portion  900  is attached. 
     In the light path division portion  900 , on a surface connecting to the optical main body portion  910 , a slide female dovetail  901  to be engaged with the slide male dovetail  911  is formed. In the slide female dovetail  901 , an opening  904  for emitting light bent by the prism  820  in the observation optical axis Nb_ 2  direction is formed. The light path division portion  900  includes a projection portion  902  that contacts the positioning wall  913  when the light path division portion  900  is attached to the optical main body portion  910 , and a fixing screw  903  for fixing the light path division portion  900  to the optical main body portion  910  with being in contact with the optical main body portion  910 . 
     An opening  810   e  through which the observation light path Nb passes and an opening  810   f  through which light toward the observation portion  6 A passes when the optical unit  8 E is attached to the main body  2  are formed at an end portion of the light path division portion  900  on an opposite side of a side connecting to the optical main body portion  910 . 
     The light path division portion  900  and the optical main body portion  910  are connected to each other by being slid in a state in which the slide female dovetail  901  and the slide male dovetail  911  are engaged. At this time, by the projection portion  902  contacting the positioning wall  913 , the light path division portion  900  is positioned with respect to the optical main body portion  910 . By screwing the fixing screw  903  into the optical main body portion  910  after the positioning, the light path division portion  900  is fixed onto the optical main body portion  910 . By loosening the fixing screw  903 , the light path division portion  900  can be removed from the optical main body portion  910  while being slid thereon. In this manner, the light path division portion  900  is detachably attached to the optical main body portion  910 . 
     The casing  81 D includes the plate spring  89 . A contact portion  811  contacting the main body  2  is formed at the distal end in the insertion direction of the light path division portion  900 . When the optical unit  8 E is inserted into the main body  2 , the contact portion  811  comes into contact with a wall surface on an illumination side of an arm portion  2   c , and a latch claw  89   a  included in the plate spring  89  engages with a click step portion  211   a  (refer to  FIG. 6 ). The optical unit  8 E thereby enters a state of being positioned in a direction retracting from the main body  2 . 
     Furthermore, the light path division portion  900  includes the latch portion  812  and the spring member  813 . With this configuration, also in the sixth embodiment, the optical unit  8 E can be switched to a first position where the prism  820  is disposed on the observation light path Nb, and a second position where the prism  820  is retracted from the observation light path Nb. By switching the position of the optical unit  8 E in this manner, in transmitted-light illumination observation performed using a light source  9 , observation can be performed while switching whether to cause observation light to enter the image sensor  840 . 
     When the optical unit  8 E is removed from the main body  2 , as described above, by pulling out the optical unit  8 E in a state in which the latch portion  812  is pressed by inserting a bar member  100  from a hole portion  211   d  formed in the arm portion  2   c , the optical unit  8 E can be removed from the main body  2 . 
     According to the sixth embodiment, similarly to the first embodiment, by switching an insertion position of the optical unit  8 E with respect to the arm portion  2   c , the image forming optical system is made insertable onto and removable from the observation light path Nb. Thus, an observation method, more specifically, observation using the observation portion  6 A and observation using an image that is based on an electrical signal generated by the image sensor  840  can be switched without changes in positions of the observation portion  6 A and an eyepiece  7  that are caused by the optical unit  8 E. An optical element can be thereby easily inserted onto and removed from an observation light path while suppressing a change in eyepoint. 
     In addition, according to the sixth embodiment, similarly to the fifth embodiment, because the optical unit  8 E includes the image forming optical system, an image of a specimen S can be acquired. If a focal length of the tube lens  830  is shortened without using a focal length common to the tube lens  63  of the observation portion  6 A, the total length of the casing  81 D can be shortened by using the image sensor  840  having a small size. Thus, a compact and easily-handled optical unit  8 E can be provided. Furthermore, because a gravity center can be kept low even if the optical unit  8 E is attached to the main body  2 , safety is enhanced. Furthermore, because the entire height does not become high, storage easiness is enhanced. 
     In the sixth embodiment, any of a plurality of light path division portions  900  having prisms  820  with different light path division ratios that guide observation light toward both the observation portion  6 A side and the optical main body portion  910  (image sensor  841 ) side can be attached. In other words, in the sixth embodiment, in the optical unit  8 E, the light path division portion  900  can be replaced with a light path division portion  900  having a prism  820  with a light path division ratio suitable for observation. With this configuration, in the optical unit  8 E, the replacement of a prism with a different light path division ratio can be easily performed. 
     In addition, in the sixth embodiment, the light path division portion  900  and the optical main body portion  910  are connected using the slide female dovetail  901  and the slide male dovetail  911 . Alternatively, the light path division portion  900  and the optical main body portion  910  may be connected using a known connection method. 
     According to some embodiments, it is possible to easily insert and remove an optical element onto and from an observation light path while suppressing a change in height of a lens barrel. 
     Various embodiments can be formed by appropriately combining a plurality of elements disclosed in the above-mentioned embodiments. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.