Abstract:
An optical element change-over control apparatus is provided that has an optical element change-over member capable of holding a plurality of optical elements and rotating alternatively to locate a specific optical element on an optical path. A control element drives a driving element to rotate the optical element change-over member and counts positioning signals delivered from a positioning detecting element during a time interval that elapses from the instant that a point of origin of the optical element change-over member is first detected by an origin detecting element until the point of origin of the optical element change-over member is secondly detected by the origin detecting element, thereby detecting the number of change-over stages of the optical element change-over member.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-224345, filed Jul. 25, 2000, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to an optical element change-over control apparatus for automatically changing necessary optical elements for various observations and an optical microscope using the control apparatus. 
     Various microscopic observation methods are used in the fields of medicine, biology, industries, etc. These observation methods, including the bright-field, dark-field, differential-interference contrast, and fluorescent observation methods, are changed over to one another by selecting necessary optical elements. 
     Further, a plurality of objective lens are used, and two or more types of objective lenses are required depending on the technical fields and applications. In order to meet this requirement with high efficiency, optical element change-over means, such as a revolver, cube cassette, filter turret, etc., are developed as component units that can be attached to a microscope. So-called system microscopes are prevailing microscopes that incorporate components selected according to the field of application and have the necessary number of change-over stages for the viewing method. One such system microscope may use, for example, a six-hole revolver, among other ones including 5-, 7-, and 8-hole revolvers. The cube cassette may, for example, be a 4-hole cube cassette selected among other ones including 6- and 8-hole cube cassettes. With this arrangement, the objective lens can be designed for 6-stage change-over, and the viewing method for 4-stage change-over. If the unit is replaced in the microscope of this type, the degree of freedom of microscope control changes, so that the control function must be changed in many cases. Further, the degree of freedom of the currently set unit, e.g., the number of holes of the revolver, should be learned in advance by any method. Described in Jpn. Pat. Appln. KOKAI Publication No. 8-179218, for example, is a microscopic system, which comprises motor-operated loading-unloading means for inserting into and removing various optical members from an optical path, detecting means for detecting any of the optical members in the optical path, input means for inputting control instructions from an operator, and control means. The control means receives information on the state of the optical member from the detecting means, and delivers a control command to the loading-unloading means to control the insertion of the optical member concerned in response to a control instruction inputted through the input means. The microscopic system further comprises setting means for optionally setting element data on various optical members, memory means capable of storing the element data on the optical members set by means of the setting means and holding the element data even in a power-off state, and display means for displaying the contents of the element data on the optical members. According to this microscopic system, optical members having new element data can be added to the optical member unit, and optimum control of a lighting system and an aiming system can be carried out with use of the added optical members. By retrieving the optical members, the environment of the microscope can be easily built up, and the resulting microscopic system can enjoy improved operating efficiency. 
     According to the microscopic system described in the aforesaid publication, however, the general control of the microscope is optimized in accordance with only element data on the objective lens that is attached to the revolver and element data on a filter that is attached to the cube cassette and applied to the viewing method. Thus, the control cannot cope with change of the number of change-over stages of the optical member unit, such as the number of holes of the revolver and the number of change-over stages of the cube cassette. If optical element change-over units including a revolver with a different number of holes or a cube cassette with a different number of change-over stages are attached so that the number of changeable objective lenses or the number of change-over stages of the viewing method is changed, therefore, it is necessary to change the control function and configuration. 
     The present invention has been contrived in consideration of these circumstances, and its object is to provide an optical element change-over control apparatus that is capable of carrying out smooth microscopic operation by detecting the number of change-over stages of optical element change-over units, such as a revolver, cube cassette, filter turret, etc., without changing the control function even in the case where the number of change-over stages of the change-over units is changed as the change-over units attached to the body of a microscope are replaced. And it is also an object of the invention to provide a microscope that utilizes such an optical element change-over control apparatus. 
     BRIEF SUMMARY OF THE INVENTION 
     In order to achieve the above object, an optical element change-over control apparatus according to a first aspect of the present invention comprises: an optical element change-over member capable of holding a plurality of optical elements and rotating alternatively to locate a specific optical element on an optical path; a driving element for rotating the optical element change-over member; a positioning detecting element for detecting the selected optical element being positioned so that the optical element stays in a predetermined position on the optical path and outputting positioning signals; an origin detecting element for detecting the point of origin of the optical element change-over member; and a control element for driving the driving element to rotate the optical element change-over member and counting the positioning signals delivered from the positioning detecting element during the time interval that elapses from the instant that the point of origin of the optical element change-over member is first detected by means of the origin detecting element until the point of origin of the optical element change-over member is secondly detected by means of the origin detecting element, thereby detecting the number of change-over stages of the optical element change-over member. 
     Further, a microscopic apparatus according to a second aspect of the invention uses an optical element change-over control apparatus, which comprises: an optical element change-over member capable of holding a plurality of optical elements and rotating alternatively to locate a specific optical element on an optical path; a driving element for rotating the optical element change-over member; a positioning detecting element for detecting the selected optical element being positioned so that the optical element stays in a predetermined position on the optical path and outputting positioning signals; an origin detecting element for detecting the point of origin of the optical element change-over member; and a control element for driving the driving element to rotate the optical element change-over member and counting the positioning signals delivered from the positioning detecting element during the time interval that elapses from the instant that the point of origin of the optical element change-over member is first detected by means of the origin detecting element until the point of origin of the optical element change-over member is secondly detected by means of the origin detecting element, thereby detecting the number of change-over stages of the optical element change-over member. 
     According to a third aspect of the invention, there is provided a method for detecting the number of change-over stages of an optical element change-over member capable of holding a plurality of optical elements and rotating alternatively to locate a specific optical element on an optical path, the method comprising: a member rotating step of driving a driving element to rotate the optical element change-over member; a first origin position detecting step of detecting the origin position of the optical element change-over member by means of an origin detecting element; a positioning signal detecting step of determining whether or not a positioning signal, indicative of the selected optical element being positioned so that the optical element stays in a predetermined position on the optical path, is detected after the origin position is detected and incrementing a count value indicative of the number of change-over stages of the optical element change-over member by one every time the positioning signal is detected; and a second origin position detecting step of determining whether or not the origin position of the optical element change-over member is detected again during the execution of the positioning signal detecting step and stopping the rotation of the optical element change-over member when the origin position is detected. 
     Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention. 
     FIG. 1 is a diagram showing an outline of an apparatus according to a first embodiment of the present invention; 
     FIG. 2 is a diagram showing a control section and an operating section of the apparatus according to the first embodiment; 
     FIG. 3 is a front view of a filter cassette of the apparatus according to the first embodiment; 
     FIG. 4 is a partial side view of the filter cassette of the apparatus according to the first embodiment; 
     FIG. 5 is a front view of a six-stage filter cassette of the apparatus according to the first embodiment; 
     FIG. 6 is a front view of an eight-stage filter cassette of the apparatus according to the first embodiment; 
     FIG. 7 is a flowchart for controlling the apparatus according to the first embodiment; and 
     FIG. 8 is a flowchart for controlling an apparatus according to a second embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A first embodiment of the present invention will now be described with reference to FIGS. 1 and 2. In an optical system of a microscope, light from a light source  1  for transmissive illumination, e.g., a halogen lamp, is condensed by means of a collector lens  2  and transmitted through a transmissive field stop  3 , and then lands on a filter turret  4  for transmission that can be inserted into and removed from the body of the microscope. The filter turret  4  is fitted with six different filters for six-stage change-over. These filers include, for example, an ND filter  4   a  for adjusting the brightness of the light source  1  for transmission without changing its color temperature, a compensating filter  4   b  for color correction. Desired filters can be alternatively inserted into and removed from the lighting optical system. 
     Illumination light transmitted through the filter turret  4  for transmission is guided through a transmissive aperture stop  5 , condenser optical element unit  6 , and condenser top lens unit  7  and applied to a specimen S on a specimen stage  8  from under the stage  8 . The condenser optical element unit  6  is composed of six different condensers  6   a  to  6   f  (of which  6   c  to  6   f  are not shown) that can be alternatively inserted into and removed from the optical path. The condenser top lens unit  7  is composed of a plurality of condenser top lenses  7   a  and  7   b  that can be alternatively inserted into the optical path. Further, the specimen stage  8  can two-dimensionally move the specimen S within a plane that extends at right angles to the optical axis of the microscope and vertically move for focusing along the optical axis. 
     Above the specimen stage  8 , moreover, a six-stage revolver  10  that can be loaded with six different objective lenses  9   a  to  9   f  (of which  9   b  to  9   f  are not shown) is removably held for rotation on the lower surface of an arm end portion (not shown) of the microscope. Any of the objective lenses  9   a  to  9   f  can be inserted into or removed from the optical path on the optical axis in the observational light path by rotating the revolver  10 . Further, a cube cassette  11  is located on the optical axis on the observational light path on the upper surface of the arm end portion of the microscope. The cube cassette  11  is in the form of a four-stage turret that is loaded with four different filter cubes  11   a  to  11   d  (of which  11   c  and  11   d  are not shown). Any of the filter cubes can be alternatively inserted into and removed from the optical path by various microscopic methods. 
     Light transmitted through the cube  11   a  of the cube cassette  11  is branched in two directions by means of a beam splitter  12 . One of the resulting branch light beam is guided to an eyepiece  13 , and the other to a photographic optical path (not shown). 
     Further, light from a light source  14  for incident illumination, formed of a mercury vapor lamp, is condensed by means of a collector lens  15 , and landed on an incident light filter turret  16  that is changeably attached to the microscope body (not shown). The filter turret  16 , which is changeable in six stages, is fitted with six different filters  16   a  to  16   f  (of which  16   c  to  16   f  are not shown). The filter  16   a  is an ND filter for adjusting the brightness of the light source  14  for incident illumination without changing its color temperature, while the filter  16   b  is a compensating filter for color correction. Any of the filters  16   a  to  16   f  can be alternatively inserted into and removed from the optical path. 
     Light from the light source  14  for incident illumination is guided through the ND filter  16   a , an incident aperture stop  17 , and an incident field stop  18 . The light is refracted downward by means of a filter cube  11   a  that is inserted in the optical path, and is landed on the specimen S to illuminate it through the objective lens  9   a . Fluorescent light or reflected observational light from the illuminated specimen S is transmitted again through the objective lens  9   a  and the cube cassette  11  and branched by means of the beam splitter  12 . One of the resulting branch beams is guided to the eyepiece  13 , and the other to the photographic optical path (not shown). 
     A control section  19  and an operating section  20  shown in FIG. 1 will now be described with reference to FIG.  2 . 
     The control section  19  is composed of a CPU  21 , ROM  22 , RAM  23 , and nonvolatile memory  24 , which are connected to one another by means of their respective CPU buses. The ROM  22  is stored with programs in which control contents are described, while the RAM  23  is loaded with data for control operation. The nonvolatile memory  24 , which may be an EEPROMM, NVRAM, or flash memory, stores or reads necessary information as the programs are executed. 
     The operating section  20  is formed of a display element  25  and a switch input element  26 , which are connected to the CPU  21 . The operating section  20  delivers an operation signal from the switch input element  26  to the CPU  21 , and controls position information on various driving elements  27  to  31  (mentioned later). 
     Further, the control section  19  is provided with an external I/F (not shown) such as an RS-232C, USB, or Ethernet. When it receives a command from an external controller such as a PC through the I/F, the control section  19  can carry out driving element control that is equivalent to operation through the operating section  20 . 
     The following is a description of the driving elements  27  to  31 . 
     In response to a driving signal from the control section  19 , the transmissive filter turret driving element  27  rotates the transmissive filter turret  4 , thereby alternatively inserting into or removing one of filters  4   a  to  4   f  from the optical path. 
     In response to a driving signal from the control section  19 , a condenser unit driving element  28  carries out stop adjustment for the transmissive aperture stop  5 , and rotates the condenser optical element unit  6  and the condenser top lens unit  7 , thereby alternatively inserting into or removing the desired optical element  6   a  or  6   b  and the top lens  7   a  or  7   b  from the optical path. 
     In response to a driving signal from the control section  19 , a revolver driving element  29  rotates the revolver  10 , thereby alternatively inserting into or removing one of the objective lenses  9   a  to  9   f  from the optical path. 
     In response to a driving signal from the control section  19 , a cube cassette driving element  30  rotates the cube cassette  11 , thereby alternatively inserting into or removing one of the filter cubes  11   a  to  11   d  from the optical path. 
     In response to a driving signal from the control section  19 , an incident filter turret driving element  31  rotates the incident filter turret  16 , thereby alternatively inserting into or removing one of the filters  16   a  to  16   f  from the optical path. 
     The cube cassette driving element  30  will further be described with reference to FIGS. 3 and 4. FIGS. 3 and 4 are a front view and a side view, respectively, of the cube cassette  11 . In the cube cassette  11 , the cubes  11   a  to  11   d  are arranged at equal spaces on the circumference of a circle on a disc  11 - 1 . The disc  11 - 1  is rotated by means of a pulse motor  30 - 1  of the cube cassette driving element  30 . A magnet  11 - 2  for detecting the origin position of the disc  11 - 1  is attached to the outer peripheral surface of the disc  11 - 1 . A Hall element  30 - 2  of the cube cassette driving element  30  is located in a position opposite to the magnet  11 - 2 . Corresponding in position to the cubes  11   a  to  11   d , respectively, moreover, openings  11 - 3  to  11 - 6  are provided on the outer periphery of the disc  11 - 1 . The openings  11 - 3  to  11 - 6  are used to detect positioning of the cubes  11   a  to  11   d  on an optical path OP. Held on the cube cassette driving element  30 , furthermore, is a photo-interrupter  30 - 3 , which detects the openings  11 - 3  to  11 - 6 . When the filter cube  11   c  is located on the optical path OP, correct positioning of the cube  11   c  on the optical path OP can be detected by detecting the presence of the opening  11 - 5  by means of the photo-interrupter  30 - 3 . 
     The filter turret  4 , revolver  10 , and incident filter turret  16 , like the cube cassette  11 , are provided with a magnet for origin position detection and openings for positioning detection each. Like the cube cassette driving element  30 , moreover, the transmissive filter turret driving element  27 , condenser unit driving element  28 , and revolver driving element  29  are provided with a Hall element and a photo-interrupter each. Thus, the origin position and the optical elements that are situated on the optical path can be detected. 
     The searching operation of the cube cassette  11  will now be described with reference to the flowchart of FIG.  7 . 
     First, the control section  19  is started to clear the count number in a counter (not shown) (C:  0 ; Step S 1 ). Thereafter, the disc  11 - 1  is rotated by means of the cube cassette driving element  30  (Step S 2 ). As the disc  11 - 1  rotates in this manner, the position of the magnet  11 - 2  on the disc  11 - 1  is detected by means of the Hall element  30 - 2 . If the origin position of the disc  11 - 1  is detected by doing this (Step S 3 ), counting detected positioning signals is started (Step S 4 ). As the disc  11 - 1  further rotates so that the opening  11 - 5  is detected by means of the photo-interrupter  30 - 3 , the positioning signals are detected, and the count C is upped (C:  1 ; Step S 5 ). 
     Further, counting the positioning signals for the disc  11 - 1  is continued. As the disc  11 - 1  then rotates, the opening  11 - 4  reaches the photo-interrupter  30 - 3 , whereupon the count C is upped (C:  2 ; Step S 5 ). Likewise, the detected positioning signals for the openings  11 - 3  and  11 - 6  continue to be counted in succession, and the count C is upped (C:  3 , C:  4 ; Step S 5 ) on each occasion. 
     If the disc  11 - 1  further continues to be rotated, the magnet  11 - 2  that is held on the disc  11 - 1  is detected again by means of the Hall element  30 - 2  that is held in the cube cassette driving element  30 , and therefore, the origin position of the disc  11 - 1  is detected again (Step S 6 ), whereupon the rotation of the disc  11 - 1  stops (Step S 7 ). Then, the count (C:  4 ) is loaded into the nonvolatile memory  24 , whereupon the searching operation is finished. The number of change-over stages (four stages) of the cube cassette  11  can be detected by examining the value of the count C. 
     FIG. 5 shows a six-stage cube cassette  110  that is used in place of the cube cassette  11 . Searching operation with use of the cube cassette  110  will now be described with reference to the flowchart of FIG.  7 . 
     In the cube cassette  110 , a magnet  110 - 2  for origin detection is attached to the peripheral edge of the disc  110 - 1 , six different cubes  110   a  to  10   f  are placed on the disc  110 - 1 , and openings  110 - 3  to  110 - 8  are provided corresponding to the cubes  110   a  to  110   f , respectively. 
     The control section  19  starts the searching operation for the cube cassette  110 . First, the count number in the counter (not shown) is cleared (C:  0 ; Step S 1 ). Thereafter, the disc  110 - 1  is rotated by means of the cube cassette driving element  30  (Step S 2 ). As the disc  110 - 1  rotates in this manner, the position of the magnet  110 - 2  on the disc  110 - 1  is detected by means of the Hall element  30 - 2 . If the origin position of the disc  110 - 1  is detected by doing this (Step S 3 ), the counter starts counting detected positioning signals (Step S 4 ). As the disc  110 - 1  further rotates so that the opening  110 - 6  is detected by means of the photo-interrupter  30 - 3 , the positioning signals are detected, and the count C is upped (C:  1 ; Step S 5 ). Further, counting the positioning signals for the disc  110 - 1  is continued. If the opening  110 - 5  is detected by means of the photo-interrupter  30 - 3  as the disc  110 - 1  rotates, the count C is upped (C:  2 ; Step S 5 ). Likewise, the opening  110 - 4  is detected, and the count C is upped (C:  3 ; Step S 5 ). Likewise, the openings  110 - 3 ,  110 - 8  and  110 - 7  are detected, and the count C is upped (C:  4 , C:  5 , C:  6 ; Step S 5 ). 
     If the rotation of the disc  110 - 1  is continued, moreover, the magnet  110 - 2  held on the disc  110 - 1  is detected again by means of the Hall element  30 - 2  that is held in the cube cassette driving element  30 . Thereupon, the origin position of the disc  110 - 1  is detected (Step S 6 ), and the rotation of the disc  110 - 1  stops (Step S 7 ). Then, the count (C:  6 ) is loaded into the nonvolatile memory  24 , whereupon the searching operation is finished. The number of change-over stages (six stages) of the cube cassette  11  can be detected by examining the value of the count C. 
     FIG. 6 shows an eight-stage cube cassette  120 . For searching operation in this case, the number of change-over stages (eight stages) of the cube cassette  120  can be also detected with reference to the flowchart of FIG.  7 . 
     In the cube cassette  120 , a magnet  120 - 2  for origin detection is attached to the peripheral edge of a disc  120 - 1 , eight different cubes  120   a  to  120   h  are placed on the disc  120 - 1 , and openings  120 - 3  to  120 - 10  are provided corresponding to the cubes  120   a  to  120   f , respectively. 
     According to the first embodiment described above, the control can be started when the apparatus is switched on as the so-called initializing operation. If searching operation is started by a first cycle of change-over operation for the cube cassette based on the operation of the operating section  20 , instead of switching the apparatus on, the searching operation can be carried out only when necessary. Thus, the time that is required by the searching operation with the power on can be saved. 
     In connection with the first embodiment, the cube cassettes  11 ,  110  and  120  have been described as components that constitute an optical element change-over control apparatus. However, searching operation for the number of change-over stages of the optical element can be also carried out with respect to replaceable transmissive filter turrets  4  and  40 , revolvers  10  and  100 , and incident filter turrets  16  and  160  shown in FIG.  1 . 
     A second embodiment of the invention will now be described with reference to the flowchart of FIG.  8 . 
     An optical element change-over control apparatus and an optical microscope using the same according to the second embodiment resemble the ones according to the first embodiment. According to the second embodiment, switches  100   a  and  100   b  are additionally used as setting members for previously setting the control section  19  or the operating section  20  to settle whether or not to execute operation for detecting the point of origin of the optical element change-over member. For example, dip switches are used as the switches  100   a  and  100   b.    
     The present invention will now be described in connection with the cube cassette  11  shown in FIG. 3 with reference to the flowchart of FIG.  8 . 
     First, the state of the switch  100   a  or  100   b  that is attached to the control section  19  or the operating section  20  is examined (Step S 1 ). If the switch  100   a  or  100   b  is off, searching operation is not executed. In this case, the value of the count C is read from the nonvolatile memory  24  and detected as the number of change-over stages of the cube cassette (END). If the switch  100   a  or  100   b  is on, on the other hand, searching operation for the cube cassette  11  is started. After the control section  19  is started to clear the count number in the counter (not shown) (C:  0 ; Step S 2 ), the disc  11 - 1  is rotated by means of the cube cassette driving element  30  (Step S 3 ). As the disc  11 - 1  rotates in this manner, the position of the magnet  11 - 2  on the disc  11 - 1  is detected by means of the Hall element  30 - 2 . If the origin position of the disc  11 - 1  is detected by doing this (Step S 4 ), counting the positioning signals is started (Step S 5 ). As the disc  11 - 1  further rotates so that the opening  11 - 5  is detected by means of the photo-interrupter  30 - 3 , the positioning signals are outputted, and the count C is upped (C:  1 ; Step S 6 ). Further, counting the positioning signals for the disc  11 - 1  is continued. If the opening  11 - 4  is detected by means of the photo-interrupter  30 - 3  as the disc  11 - 1  rotates, the count C is upped (C:  2 ; Step S 6 ). Likewise, the positioning signals for the openings  11 - 3  and  11 - 6  continue to be counted in succession, and the count C is upped (C:  3 , C:  4 ; Step S 6 ) on each occasion. 
     If the disc  11 - 1  further continues to be rotated, the magnet  11 - 2  that is held on the disc  11 - 1  is detected again by means of the Hall element  30 - 2  that is held in the cube cassette driving element  30 , and therefore, the origin position of the disc  11 - 1  is detected (Step S 7 ), whereupon the rotation of the disc  11 - 1  stops (Step S 8 ). Then, the value of the count C (C:  4 ) is loaded into the nonvolatile memory  24 , whereupon the searching operation is finished (END). The number of change-over stages (four stages) of the cube cassette  11  can be obtained by examining the value of the count C. 
     The following is a description of optical element searching operation with use of the six-stage cube cassette  110  of FIG. 5 in place of the cube cassette  11 . 
     First, the state of the switch  100   a  or  100   b  that is attached to the control section  19  or the operating section  20  is examined (Step S 1 ). If the switch  100   a  or  100   b  is off, searching operation is not executed. In this case, the count is read from the nonvolatile memory  24 , and its value is detected as the number of change-over stages of the cube cassette (END). If the switch  100   a  or  100   b  is on, on the other hand, searching operation for the cube cassette  110  is started. After the count number in the counter (not shown) is first cleared (C:  0 ; Step S 2 ), the disc  110 - 1  is rotated by means of the cube cassette driving element  30  (Step S 3 ). As the disc  110 - 1  rotates in this manner, the position of the magnet  110 - 2  on the disc  110 - 1  is detected by means of the Hall element  30 - 2 . If the origin position of the disc  110 - 1  is detected by doing this (Step S 4 ), the counter starts counting the positioning signals. As the disc  110 - 1  is further rotated so that the opening  110 - 6  is detected by means of the photo-interrupter  30 - 3 , the positioning signals are outputted, and the count C is upped (C:  1 ; Step S 5 ). Further, counting the positioning signals for the disc  110 - 1  is continued. If the opening  110 - 5  is detected by means of the photo-interrupter  30 - 3  as the disc  110 - 1  rotates, the count C is upped (C:  2 ; Step S 5 ). Likewise, the count C is upped (C:  3 ; Step S 5 ) as the opening  110 - 4  is detected by means of the photo-interrupter  30 - 3 . Likewise, moreover, the count C is upped (C:  4 , C:  5 , C:  6 ; Step S 6 ) as the openings  110 - 3 ,  110 - 8  and  110 - 7  are detected in succession by means of the photo-interrupter  30 - 3 . 
     If the disc  110 - 1  further continues to be rotated, the magnet  110 - 2  that is held on the disc  110 - 1  is detected again by means of the Hall element  30 - 2  that is held in the cube cassette driving element  30 , and therefore, the origin position of the disc  110 - 1  is detected (Step S 7 ), whereupon the rotation of the disc  110 - 1  stops (Step S 8 ). Then, the value of the count C (C:  6 ) is loaded into the nonvolatile memory  24 , whereupon the searching operation is finished. 
     The number of change-over stages (six stages) of the cube cassette  110  can be detected by examining the value of the count C. 
     For searching operation for the eight-stage cube cassette  120  shown in FIG. 6, the number of change-over stages (eight stages) of the cube cassette  120  can be also detected with reference to the flowchart of FIG.  8 . 
     The control according to second embodiment described above, like the control according to first embodiment, can be started when the apparatus is switched on as the so-called initializing operation. If searching operation is started by a first cycle of change-over operation for the cube cassette based on the operation of the operating section  20 , instead of switching the apparatus on, the searching operation can be carried out only when necessary. Thus, the time that is required by the searching operation with the power on can be saved. 
     In connection with the second embodiment, the cube cassettes  11 ,  110  and  120  have been described as components that constitute the optical element change-over control apparatus. However, the number of change-over stages can be also detected by means of the change-over control apparatus with respect to the transmissive filter turrets  4  and  40 , revolvers  10  and  100 , and incident filter turrets  16  and  160  shown in FIG.  1 . 
     According to the present invention, the optical element unit to be attached to the microscope body can be replaced. If the number of change-over stages is changed, therefore, the control function need not be changed at all. Thus, the microscope can be smoothly operated by detecting the number of change-over stages of the newly set optical element unit. 
     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.