Abstract:
An inverted fluorescence microscope is described which irradiates an excitation light onto a sample for observation of a fluorescent image of the sample. The fluorescence microscope includes (a) a transmissive illumination light source, which is arranged above a stage for placing the sample and the transmissive illumination light source is arranged facing a horizontal direction; (b) a tilt mirror, which reflects light from the transmissive illumination source and illuminates the sample on the stage from above; (c) a transmissive illumination optical unit including at least the tilt mirror is disposed so as to move in a direction in which the transmissive illumination optical unit is brought away from the stage from a normal position; and (d) a sample cover for shielding a light from the stage, wherein the sample cover is displaceable so as to expose the stage.

Description:
The present application claims foreign priority based on Japanese Patent Application No. 2004-351358, filed Dec. 3, 2004, the contents of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The present invention relates to a fluorescence microscope. 
   2. Related Art 
   A fluorescence microscope on which a fluorescence emitted by a sample is observed is known as one type of microscope. The fluorescence microscope includes an upright type where an objective lens is arranged above a stage and an inverted type where an objective lens is arranged below a stage. The basic structure of the fluorescence microscope comprises an epi illumination section for irradiating excitation light onto a sample and a fluorescence observation section for observing an image formed from a fluorescence emitted by the sample. The fluorescence observation section includes an eye lens optical system for human eye observation and/or an imaging portion such as a CCD camera. The excitation light from the epi illumination section is irradiated onto a sample via a filter. 
   Generally, a fluorescence microscope has been placed in a darkroom to perform fluorescence observation in the darkroom. In recent years, it is a more common practice to display an image from an imaging portion attached to a fluorescence microscope on an image display portion such as a CRT and an LCD for observation purposes or process image data on a personal computer. 
   In such a use environment, operation of a personal computer in a darkroom is rather inconvenient and light emitted from a CRT may be incident around the stage of a fluorescence microscope thus degrading the quality of a fluorescent image. In order to solve these problems, JP-A-2002-207177 proposes provision of walls that shield light from a stage for placing a sample and an objective lens. This proposal has an advantage of doing without a need to work in a darkroom for fluorescence observation. 
   An assumption that a fluorescence microscope can be used for fluorescence observation without using a darkroom will naturally lead to a request to use a fluorescence microscope on a private desk in a library where routine work is performed. This presents a need for a more compact fluorescence microscope. The external design of a fluorescence microscope is requested to be sleeker. 
   JP-A-2002-207177 that proposes provision of walls that shield light from a stage for placing a sample and an objective lens, or a sample cover, discloses a set of double doors of the sample cover enclosing the stage in  FIG. 1  and proposes a hinged door in  FIG. 4 . In case a sample door of such a form is provided, when the sample cover is opened, the sample cover significantly protrudes on the side of the fluorescence microscope, which greatly increases the substantial footprint of the fluorescence microscope. 
   JP-A-2002-207177 discloses, in  FIG. 6 , a lightproof method by suspending a curtain around a stage while supported by a curtain rail. According to this curtain method, opening the curtain for expose the stage does not increase the substantial footprint of the fluorescence microscope. However, a suspended curtain has problems with lightproofness and durability as well as the appearance is not favorable and could degrade the commerciality of the fluorescence microscope. 
   SUMMARY OF THE INVENTION 
   A main object of the invention is to provide a fluorescence microscope that avoids, as much as possible, the increase in the substantial footprint of the fluorescence microscope due to a lightproof member when the lightproof member around a stage is opened to expose the stage. 
   A further object of the invention is to provide a fluorescence microscope that is favorable in terms of its appearance as well as the above main purpose. 
   The technical challenge of the invention may be attained, in accordance with the invention, by providing: 
   a fluorescence microscope comprising: a stage for placing a sample; and 
   an objective lens arranged adjacently to the stage; the fluorescence microscope irradiating excitation light onto a sample on the stage for observation of a fluorescent image of the sample; characterized in that the fluorescence microscope comprises a sample cover for shielding light from the stage and that 
   the fluorescence microscope is capable of exposing the stage while the sample cover is displaced upward, downward or backward. 
   According to the invention, the sample cover assumed when the stage is exposed is in a position displaced upward, downward or backward from the stage. This minimizes the increase in the footprint of the fluorescence microscope. The sample cover may be typically fabricated from a plate member of a molded metal or plastic, so that the sample cover has an excellent durability. Also, it is easy to provide an external design to provide a good appearance of the sample cover. 
   According to a preferred embodiment of the invention, the fluorescence microscope further comprises a main unit enclosing the fluorescence microscope, characterized in that the sample cover is displaced upward, downward or backward along the front face of the main unit case thus exposing the stage. 
   When a fluorescence microscope is enclosed by a main unit case, it is easy to apply a design to the appearance of the main unit case so that it is possible to design a good appearance of the overall shape of the fluorescence microscope. 
   The fluorescence microscope according to the invention may be an inverted type or an upright type where an objective lens is arranged above a stage as disclosed in JP-A-2002-207177. 
   In an embodiment of the invention, the main unit case further includes a lower cover positioned below the sample cover, the lower cover having a cross section of a trapezoid substantially the same as that of the sample cover. The sample cover is displaced forward and downward in order for the sample cover to be adjacent to the lower cover to cause the sample cover to overlap the lower cover. The cross section of the sample cover may have a shape of “C” in alphabet having side faces and a front face or may have an arc shape of a convex facing forward. 
   The sample cover included in the invention may be split side by side and the right/left split sample covers may be once displaced outward in horizontal direction then moved backward so that the stage will be exposed. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an external view of an inverted fluorescence microscope according to an embodiment showing a state where the sample cover is closed; 
       FIG. 2  illustrates the use form of a fluorescence microscope according to the embodiment; 
       FIG. 3  is a perspective view illustrating the layout of each of the illumination system and the imaging system included in the inverted fluorescence microscope according to the embodiment; 
       FIG. 4  is a plan view illustrating a rotary filter cassette change mechanism included in the inverted fluorescence microscope according to the embodiment; 
       FIG. 5  illustrates the operation effect that accompanies the V-shaped arrangement of an epi illumination system and an imaging system employed by the inverted fluorescence microscope according to the embodiment; 
       FIG. 6  is an exploded perspective view of a two-segment chassis constituting the framework of the fluorescence microscope according to the embodiment; 
       FIG. 7  illustrates the arrangement of a transmissive illumination system, an epi illumination system, an imaging system, and various power supply units mounted on a chassis; 
       FIG. 8  illustrates the specific arrangement of a power supply unit mounted on a chassis; 
       FIG. 9  is a perspective view showing the specific configuration of the rotary filter cassette change mechanism illustrated in  FIG. 4 ; 
       FIG. 10  is a perspective view showing the state where the rotary filter cassette change mechanism is incorporated into a chassis; 
       FIG. 11  is a perspective view showing the transmissive illumination unit where the flip-up mechanism of a heat insulation housing and an optical unit included in the transmissive illumination system is incorporated, with the optical unit in normal position; 
       FIG. 12  is a plan view of the transmissive illumination unit shown in  FIG. 11 ; 
       FIG. 13  is a perspective view corresponding to  FIG. 11  that shows the state where the optical unit is flipped up; 
       FIG. 14  is a perspective view corresponding to  FIG. 1  of the external view of the fluorescence microscope according to the embodiment that shows the state where the optical unit is flipped up; 
       FIG. 15  illustrates a variation of the flip-up transmissive illumination optical unit disclosed in  FIG. 11 ; 
       FIG. 16  illustrates another variation of the flip-up transmissive illumination optical unit disclosed in  FIG. 11 ; 
       FIG. 17  illustrates the specific arrangement of the various power supply units incorporated into an upper chassis; 
       FIG. 18  illustrates the specific arrangement of the various power supply units and various boards incorporated into the upper chassis; 
       FIG. 19  shows a state where a controller is incorporated into a chassis; 
       FIG. 20  illustrates a structure for forcibly air-cooling the light source included in the epi illumination system and the adjacent heat absorption filter; 
       FIG. 21  illustrates an electric fan unit assembled to the rear end face of the chassis and the related vibration damping member; 
       FIG. 22  is a plan view illustrating forced air cooling of the top portion of the upper chassis; 
       FIG. 23  is a plan view illustrating forced air cooling of the bottom portion of the upper chassis; 
       FIG. 24  illustrates a sample cover included in the fluorescence microscope according to the embodiment; 
       FIG. 25  is a side view corresponding to  FIG. 24  of the fluorescence microscope according to the embodiment; 
       FIG. 26  illustrates the state where the sample cover of the fluorescence microscope according to the embodiment is displaced downward to expose a stage; 
       FIG. 27  illustrates a mechanism for displacing the sample cover downward; 
       FIG. 28  illustrates automated opening/closing of the sample cover by incorporating an electric motor into the mechanism for displacing the sample cover downward in relation to  FIG. 27 ; 
       FIG. 29  illustrates a variation of a method for displacing the sample cover downward; 
       FIG. 30  illustrates an example where the upper area of the stage is covered by a retractable lid instead of a sample cover. 
       FIG. 31  illustrates an example where the stage is exposed with the sample cover displaced forward; 
       FIG. 32  illustrates an example where the sample cover split into two cover segments sideways is once displaced transversely and then backward in order to expose the stage; 
       FIG. 33  is a perspective view illustrating an example where a tray that can be inserted/drawn in back-and-forth directions is arranged in order to prevent contamination of the area below the stage, with the tray arranged below the stage; and 
       FIG. 34  is a perspective view illustrating an example, with relation to  FIG. 33 , where the tray that can be inserted/drawn in back-and-forth directions is arranged in order to prevent contamination of the area below the stage, with the tray drawn out from below the stage. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is an external perspective view of an inverted fluorescence microscope. In  FIG. 1 , an inverted fluorescence microscope comprises a sample cover  3  in front of a main unit case  2 . The sample cover  3  can be displaced downward along a lower cover  4  substantially comprising part of the main unit case  2  below, thereby inserting/retrieving a sample. By bringing the sample cover  3  in the state of  FIG. 1 , that is, in a closed state, it is possible to perform fluorescence observation. The main unit case  2 , sample cover  3  and lower cover  4  are made of a plate member of a molded metal or plastic. 
   Referring to  FIG. 2 , the inverted fluorescence microscope  1  comprises, inside the main case  2 , a bright field transmissive illumination system, an epi illumination system, an imaging system, as well as a power supply unit, power supply board, and a controller. The inverted fluorescence microscope  1 , when connected to a monitor  6  via a personal computer (PC), allows the user to make various operations and setting by using a mouse  8  and a keyboard  7 . 
     FIG. 3  shows an overall configuration of the bright field transmissive illumination system, epi illumination system, and imaging system. In  FIG. 3 , a reference number  10  represents a bright field transmissive illumination system,  11  an epi illumination system, and  12  an imaging system. The bright field transmissive illumination system is arranged above the height position of a stage  13  while the epi illumination system and the imaging system are arranged below the height position of a stage  13 . 
   The bright field transmissive illumination system  10  for use in observation by way of transmissive light typically comprises a transmissive illumination lamp  15  consisting of a halogen lamp. As those skilled in the art will immediately notice, the halogen lamp is arranged facing the horizontal direction. Light  16  emitted from the halogen lamp  15  is directed downward in vertical direction by a tilt mirror  17 , passes through a condenser lens (not shown), and irradiates a sample S on the stage  13 . 
   The epi illumination system  11  for use in fluorescence observation typically comprises an epi illumination lamp  20  consisting of a mercury lamp. The mercury lamp  20  is arranged in horizontal direction. The light emitted from the mercury lamp  20  passes through a heat absorption filter  21  and a collector lens, then an excitation filter to be transformed into excitation light having a specific short wavelength band. The excitation light is directed upward in vertical direction to the sample S by a tilt dichroic mirror, and passes through the objective lens  28  to irradiate the sample from below. 
   The excitation filter and the dichroic mirror are incorporated into a filter cassette  22 . In the example of  FIG. 3 , four types of filter cassette  22  having different characteristics from each other are arranged linearly adjacent to each other in horizontal direction. That is, selection of the filter cassette  22  is linear. In order to select an arbitrary filter cassette  22  from a plurality of filter cassettes  22 , the user rotates an operation control  23  to cause the filter cassette  22  to be linearly displaced along a guide rail  25  by way of a rack-and-pinion gear  24 . This operation may be effected using a power motor. 
   The fluorescence microscope  1  shown in  FIG. 1  employs a rotary system shown in  FIG. 4  instead of the above linear-motion system. The rotary filter cassette system has a horizontal disc  26  to detachably mount four filter cassettes  22  of different characteristics. On the horizontal disc  26  are arranged the filter cassettes  22  equidistantly to each other (in 90-degree intervals). The horizontal disc  26  is driven by a related power motor and rotates about a vertical axis  27 . By rotating the horizontal disc  26 , it is possible to select a filter cassette  22  of a desired characteristic. As a variation, the horizontal disc  26  may be manually rotated, like the operation control  23  described referring to  FIG. 4 . 
   Returning to  FIG. 3 , the stage  13  arranged adjacent upward to the objective lens  28  individually travels in X and Y-axis directions that cross an optical axis. By moving the objective lens  28  up and down in Z-axis direction with the stage  13  stationary in vertical direction, it is possible to adjust the relative positions of the stage  13  and the objective lens  28 . Or, the stage  13  may be moved in Z-axis direction as well as X and Y-axis directions in order to adjust the relative distance to the objective lens  28 . While such relative positioning of the stage  13  and the objective lens  28  may be made manually, it is made using a power motor described below in this embodiment. 
   The imaging system  12  comprises an imaging mirror  30  arranged directly below the filter cassette  22 , an imaging barrel  31  extending horizontally toward the imaging mirror  30 , and an imaging unit  32  (for example a CCD camera) attached to an end of the imaging barrel  31 . 
   In the area below the stage  13 , when the epi illumination system  11  and the imaging system  12  both extending in horizontal direction are viewed from above, the horizontal axis L 1  of the epi illumination system  11  and the horizontal axis L 2  of the imaging system  12  are arranged in the V shape with an angle of nip θ 0 . As best understood from  FIG. 4 , the mercury lamp  20  and the CCD camera  32  are arranged offset to each other side by side as seen from above. 
   In this way, by arranging epi illumination system  11  and the imaging system  12  both extending in horizontal direction in the shape of V, the mercury lamp  20  and the CCD camera  32  are arranged offset to each other side by side. Without considering the interference between the mercury lamp  20  and the CCD camera  32  both of which are relatively large, it is possible to reduce the height dimension of the fluorescence microscope  1  by setting to minimum the vertical spacing between the epi illumination system  11  and the imaging system  12  positioned below the same. In other words, in case the mercury lamp  20  and the CCD camera  32  are arranged up and down within the same vertical plane, the spacing between the epi illumination system  11  and the imaging system  12  is limited by the interference between the mercury lamp  20  and the CCD camera  32 . 
   As in this embodiment, when the epi illumination system  11  and the imaging system  12  both extending in horizontal direction are arranged in the shape of V in order to set to minimum the vertical spacing between the epi illumination system  11  and the imaging system  12  positioned below the same, the distance between the filter cassette  22  and the imaging mirror  30  is also reduced. This allows the length dimension of the imaging barrel to be reduced. 
   This approach is detailed referring to  FIG. 5 . A reference sign A in  FIG. 5  represents the distance between the objective lens  28  and the imaging mirror  30  while a reference sign B represents the distance between the imaging mirror  30  and the CCD light-receiving surface of the CCD camera  32 . The light from the objective lens  28  to the imaging mirror is diffused while the light from the imaging mirror  30  to the CCD camera  32  is convergent. The diffusion angle θ 1  in the diffused system is equal to the light convergence angle θ 2 . Thus, the shorter the distance A is, the shorter the distant B becomes. It is thus possible to reduce the length dimension of the imaging barrel  31 . 
   The transmissive illumination system  10  and the epi illumination system  11  are used selectively. When the transmissive illumination system  10  is selected, transmissive illumination light  16  emitted by the halogen lamp  15  is reflected on the tilt mirror  17  to illuminate the sample S from above. An image of the sample S obtained by way of the transmissive illumination light  16  passes through the objective lens  28 , the dichroic mirror of the filter cassette  22 , an absorption filter, the imaging mirror  30 , and is captured by the CCD camera  32  arranged in horizontal direction. 
   When the epi illumination system  11  is selected, light emitted by the mercury lamp  20  passes through a heat absorption filter, a collector lens, and the excitation filter of the filter cassette  22  and a dichroic mirror, then the resulting excitation light irradiates the sample S from below. The fluorescent matter included in the sample S in preprocessing receives excitation light to irradiate a fluorescence. The fluorescent image passes through the objective lens  28 , the dichroic mirror and the absorption filter, and is captured by the CCD camera  32 . 
   The fluorescence microscope  1  shown in  FIG. 1  has a chassis  35  shown in  FIG. 6  as a framework. The chassis  35  has a two-segment structure of an upper chassis  36  and a lower chassis  37 . The upper chassis  36  and the lower chassis  37  are both aluminum-alloy die castings or castings which are lightweight and which have relatively low thermal expansion coefficients. Referring to  FIG. 7 , the transmissive illumination system  10  is arranged on the upper chassis  36 . The epi illumination system  11  and the imaging system  12  are arranged on the lower chassis  37 . Inside the chassis  35  are placed various boards such as a controller board and a power board, as well as one side of the transmissive illumination system  10 , and various power supply units between the transmissive illumination system  10  and the epi illumination system  11 . On the rear surface of the chassis  35  are attached a plurality of (three in the embodiment) electric fan units  38  in vertical alignment. Heat generated inside the chassis  35 , for example, heat from the halogen lamp  15 , the mercury lamp, various power supply units and the motor is forcibly exhausted to outside from behind the chassis  35 . 
   As shown in  FIG. 6 , in the side walls of the chassis  35  are formed numerous apertures  35   a . These apertures  35   a  are intended for a lightweight design and mounting of components, and introduction of external air as mentioned later. 
     FIG. 8  shows some of the components assembled into the chassis  35 . In  FIG. 8 , a reference numeral  40  represents a power supply unit for feeding power to the mercury lamp  20  of the epi illumination systems, indicated as feature  11   a  for purposes of this view,  41  a power supply unit for feeding power to control systems such as a motor system incorporated into the fluorescence microscope  1 ,  42  a power supply unit for feeding power to the halogen lamp  15  of the transmissive illumination system  10 , and  43  a motor drive circuit board for driving various motors incorporated into the fluorescence microscope  1 . The motor drive circuit board  43  controls, for example, a motor  45  for driving the stage  13  in X-axis and Y-axis directions, a motor (not shown) for driving the power zoom mechanism of the imaging system  12 , and a motor (not shown) for driving the diaphragm of the mercury lamp  20 . While a motor for positioning of the stage  13  in Z-axis direction is mounted on a common motor platform  46 , a cover  47  is attached to the motor so that it does not appear in  FIG. 8 . 
   As understood from  FIG. 8 , the stage  13 , the motor  45  for driving the same, the objective lens  28  are formed into a unit, which is assembled to the lower chassis  37 . 
     FIG. 9  shows the aforementioned rotary filter cassette system. The central vertical axis  27  of the horizontal disc  26  is assembled to the base plate  50 . On the periphery of the horizontal disc  26  are attached a circular ring gear  51 . The drive gear  52  that is engaged with the circular ring gear  51  is driven by the motor  53  fixed to the base plate  50 . The motor  53  is rotation-controlled by the motor drive circuit board  43  shown in  FIG. 8  brings a desired filter cassette  22  in position. As mentioned earlier, the light emitted from the mercury lamp  20  passes through the excitation filter  55  of the filter cassette  22  and the dichroic mirror  56  and irradiates as excitation light the sample S. The system for driving the stage  13  shown in  FIG. 8  and the rotary filter cassette system of  FIG. 9  are assembled to the front of the lower chassis  37 , as understood from  FIG. 10 . 
   On the top end of the upper chassis  36  is mounted a unit  60  of the transmissive illumination system  10 , in the widthwise center.  FIG. 11  is a perspective view of the transmissive illumination unit  60 .  FIG. 12  is a plan view of the transmissive illumination unit  60 . The transmissive illumination unit  60  comprises a transmissive illumination housing  61  extending horizontally. The transmissive illumination housing  61  accommodates a halogen lamp  15  and a heat absorption filter (not shown) arranged adjacent to the halogen lamp  15 . On the top of the front end of the transmissive illumination housing  61  is provided a pivot shaft  62  extending in a direction transverse to the housing  61 . To the pivot shaft  62  is attached a transmissive illumination optical unit  64 . The transmissive illumination optical unit  64  can rotate upward about the pivot shaft  62 . The transmissive illumination optical unit  64  includes a tilt mirror  17  and a condenser lens  66 . The transmissive illumination optical unit  64  further has a plate  67  slidable widthwise. The user may manually operate the plate  67  to select a unit for phase observation and one for bright field observation. 
   To one end of the pivot shaft  62  is attached a damper  69  via a link  68 . The base end of the damper  69  is rotatably attached to the rear end of the transmissive illumination housing  61 . When the user applies a force to lift up the transmissive illumination optical unit  64 , the transmissive illumination optical unit  64  gently rotates upward by way of the damper  69  and takes the flip-up position tilted by approximately  45  degrees ( FIGS. 13 ,  14 ). When the user applies a force to press down the transmissive illumination optical unit  64  in the flip-up position shown in  FIGS. 13 ,  14 , the transmissive illumination optical unit  64  gently rotates downward by way of the damper  69  and returns to the normal position shown in  FIG. 11  and  FIG. 1  corresponding to  FIG. 11 . 
   In this way, by arranging sideways the light source of the transmissive illumination system  10 , the height dimension of the fluorescence microscope  1  is dramatically reduced. Also, retract operation of the transmissive illumination optical unit  64  by way of flip-up operation may be employed. By flipping up the transmissive illumination optical unit  64  to retract it upward from a normal position, it is possible to bring the transmissive illumination optical unit  64  away from the stage  13  or objective lens  28  without impairing the compactness of the small-sized fluorescence microscope  1  as well as maintaining the good external appearance. 
   Returning to  FIGS. 11 ,  13 , to the front end of the transmissive illumination housing  61  extending horizontally is fixed a proximity switch  70  facing the link  68 . The proximity switch  70  works as a sensor for detecting the flip-up position and normal position of the transmissive illumination optical unit  64 . Detecting the flip-up position ( FIG. 13 ) of the transmissive illumination optical unit  64 , the output signal from the proximity switch  70  forcibly turns off the halogen lamp  15  or reduces its light quantity to minimum. 
   When the transmissive illumination optical unit  64  takes the flip-up position ( FIG. 14 ) approximately 45 degrees upward from the normal position, the transmissive illumination optical unit  64  is brought away from the stage  13  or objective lens  28 . The user displaces the transmissive illumination optical unit  64  in the flip-up position as well as displaces downward the sample cover  3  detailed later to expose the stage  13 , thereby facilitating insertion/retrieval of the sample S, or to be more specific, insertion/retrieval of a petri dish or a preparation carrying the sample S. The ring plate  13   a  equipped with a light aperture the objective lens  28  faces from below (refer to  FIG. 10 , for example) is detachable from the stage  13 . In case the ring plate  13   a  is placed on the stage  13  together with a petri dish for positioning of the Petri dish accommodating the sample S, the transmissive illumination optical unit  64  is conveniently placed in the flip-up position. 
   By displacing the transmissive illumination optical unit  64  into the flip-up position to retract the flip-up position away from the objective lens  28 , it is made easy to replace the objective lens  28  or clean the stage  13 . When the transmissive illumination optical unit  64  is displaced from the normal position to the flip-up position, the transmissive illumination light source (halogen lamp)  15  is accordingly turned off in a forcible fashion or its light quantity is reduced to minimum. This prevents dazzling of the user who directly receives light from the halogen lamp  15 . 
   While the transmissive illumination optical unit  64  is rotated upward, the transmissive illumination optical unit  64  may be retracted from the normal position by sliding the transmissive illumination optical unit  64  along the front surface of the main unit case  2 .  FIG. 15  shows an example of retracting the transmissive illumination optical unit  64  upward in a linear fashion from the normal position.  FIG. 16  shows an example of retracting the transmissive illumination optical unit  64  widthwise in a linear fashion from the normal position. 
   On the side of the transmissive illumination housing  61  accommodating the halogen lamp  15  and a related heat absorption filter, that is, on the side of the upper chassis  36 , are arranged a power supply unit for a halogen lamp  15  and a system power unit  42 . On the upper chassis  36  are arranged a power supply board  71 , a drive circuit  72  (see  FIG. 23 ) for the z-axis drive motor for the stage  13 , and a mercury lamp power supply unit  40 , below the transmissive illumination housing  61  (see  FIGS. 17 and 18 ). On the other hand, on the side of the lower chassis  37  is arranged a main control board (controller)  73  as understood from  FIG. 19 . The main control board  73  intrudes up to the upper chassis  36 . 
     FIG. 20  is a schematic view of the air-cooling structure of the epi illumination system  11 . It is to be understood that the air-cooling structure is substantially the same in the transmissive illumination system  10 . 
   The mercury lamp  20  as a light source of the epi illumination system  11  and a plurality of heat absorption filters  75  are accommodated in an epi illumination housing  76  made of a plastic material as a thermal insulation. The epi illumination housing  76  has an air cooling passage  77  extending backward from the heat absorption filter  75 . The rear end of the air cooling passage  77  is open toward an electric fan unit  38  that is in the lowermost position. 
   Around the mercury lamp  20  are preferably provided a partition wall  78  having a cross section of a rectangle. The partition wall  78  forms a second air cooling passage  79  around the mercury lamp  20 . The epi illumination housing  76  comprises an air inlet  80  in the area below the heat absorption filter  75 . Air is introduced into the epi illumination housing  76  via the air inlet  80 . The air that has flowed into the epi illumination housing  76  cools the heat absorption filter  75 , passes through the main air cooling passage  77  and is exhausted to outside by the electric fan unit  38 . The air introduced into the epi illumination housing  76  also passes through a second air cooling passage  79 , cools the mercury lamp  20 , passes through the main air cooling passage  77 , and is exhausted to outside by the electric fan unit  38 . 
   The heat absorption filter  75  whose heat absorption capability dissipates due to heat saturation and the mercury lamp  20  that becomes extremely hot are enclosed by the thermal insulation housing  76  so as to prevent the heat of the heat absorption filter  75  and the mercury lamp  20  from flowing into the chassis  35 . While doing so, the heat in the thermal insulation housing  76  is forcibly exhausted outside together with the air introduced into the thermal insulation housing  76  by way of the electric fan unit n 38 . This prevents heat from the mercury lamp  20  from being carried to the sample S via the heat-saturated heat absorption filter  75 , together with the light emitted by the mercury lamp  20 , as well as from flowing into the chassis  35 . 
   Concerning the cooling of the transmissive illumination system  10 , the epi illumination system  11  or the heat absorption filter, a heat sink may be used. For example, a heat sink may be added to the heat absorption filter of the transmissive illumination system  10  or epi illumination system  11  in order to prevent heat saturation of the heat absorption filter  75 . 
   The fluorescence microscope  1  of this embodiment has the mercury lamp  20  and various power supply units as heat sources enclosed by the main unit case  2 . Thermal inflation of a chassis  35 , for example, due to heat from internal components, could slightly change the focus or cause the living organisms of the sample S to fail or die. In order to cope with this, the fluorescence microscope  1  of this embodiment provides an electric fan unit  38  at the rear end of the chassis  35  and a vent  81  in the side face of the main unit case  2 , as understood from  FIG. 1 . Hot air inside the main unit case  2  is thus exchanged with the external air flowing from the vent  81 . The mercury lamp  20 , the halogen lamp  15  and the related heat absorption filter  75  are enclosed by the thermal insulation housing  76 ,  61  so as to prevent heat from the mercury lamp and the like from flowing into the chassis  35  and purge the heat by using the electric fan unit  38 . This provides air cooling of the mercury lamp  20  and the halogen lamp  15 . 
   For a light source that becomes extremely hot, such as the mercury lamp  20 , a second air cooling passage  79  is formed whose cross section area of the passage is relatively small is formed around the mercury lamp  20  by way of the surrounding partition wall  70 . This lets air pass around the mercury lamp  20  at a relatively high speed, which exhausts to outside a huge amount of heat emitted by the mercury lamp  20 . 
   The heat absorption filter  75  related to the mercury lamp  20  is similarly air-cooled. This prevents the heat absorption capability of the heat absorption filter  75  from being dissipated or lowered by heat, and also prevents the heat generated by the heat saturation of the heat absorption filter  75  from being delivered to the sample S together with the light emitted by the mercury lamp  20 . 
   While three electric fan units  38  are attached to the rear end face of the main unit case  2  in the embodiment, the three electric fan units  38  are mounted on the main unit case  2  via a plurality of gel or rubber vibration damping members  85  (i.e.,  85   a ,  85   b ,  85   c ). In the related art, it was a common practice not to provide an electric fan unit as a vibration source in equipment where vibration is extremely avoided. By interposing the vibration damping member  85 , it is possible to prevent the vibration caused by the electric fan unit  38  from being transmitted to the chassis  35 . The electric fan unit  38  is preferably a unit of a relatively low rpm, such as 3000 rpm. 
   Concerning the vibration damping member  85 , in order to absorb the vibration of each component in vertical, horizontal and back-and-forth directions of the electric fan unit  38 , it is preferable to provide first vibration damping members  85   a  ( FIG. 17 ) on the top face and bottom face of the electric fan unit  38 , second vibration damping members  85   b  ( FIG. 17 ) on the side faces of the electric fan unit  38 , and third damping members  85   c  ( FIG. 21 ) on the front and/or rear faces of the electric fan unit  38 . That is, the vibration damping members  85  are provided between the electric fan unit  38  and the associated fan cover  38   a  and between the electric fan unit  38  and the chassis  37 . 
   Three electric fan units mounted in vertical alignment on the rear face of the fluorescence microscope  1  in this embodiment will be called a top fan  38 T, a middle fan  38 M and a bottom fan  38 B. As understood from the air flow indicated by an arrow in  FIG. 22 , the top fan  38 T contributes to air cooling of the top portion of the upper chassis  36 , such as air cooling of the halogen lamp  15  for transmissive illumination and its related heat absorption filter as well as the halogen power supply unit  42 . 
   As understood from the air flow indicated by an arrow in  FIG. 23  as a bottom view of the upper chassis  36  seen from below, the middle fan  38 M contributes to air cooling of the bottom portion of the upper chassis  36  where a mercury lamp power unit  40  and a system power supply unit  41  are arranged. 
   As understood from the air flow indicated by an arrow in  FIG. 20 , the top fan  38 T contributes to air cooling of the mercury lamp  20  and its related heat absorption filter  75  arranged on the lower chassis  37 . 
   As a variation, it is possible to configure the top fan  38 T and the middle fan  38 M into a common fan and use the common fan to perform forced air cooling of the top and bottom portions of the upper chassis  36 . 
   The main control board (controller)  73  is enclosed by the chassis  35 , which ensures noise resistance. 
   The aforementioned sample cover  3  can be displaced downward along the outer surface of the lower cover below. The sample cover  3  may have a width W 1  ( FIG. 24 ) slightly greater than the width W 2  of the lower cover  4 . The sample cover may have a cross section whose shape is “C” in alphabet enclosing the sides and front of the stage  13 . The sample cover may have a shape similar to that of the lower cover  4  and may have a cross section slightly greater than that of the lower cover  4 . As a variation, as long as the lower cover  4  has a cross section in an arc as a convex facing forward, the sample cover  3  may have a cross section similar to and slightly greater than that of the lower cover  4 . 
   The sample cover  3  can be displaced along the front face and side faces of the lower cover  4  ( FIG. 26 ). With the sample cover  3  displaced downward, the front face and side faces of the stage  13  are exposed. This allows a sample S to be set to the stage  13  or retrieve the sample S placed on the stage  13 . In this practice, the transmissive illumination optical unit  64  may be rotated to the flip-up position shown in  FIG. 14  as required. 
   The sample cover  3  and the lower cover  4  each preferably comprises across section of a trapezoid, the front width being smaller than the rear width as seen from above, as understood from  FIG. 24 . In the illustrated example, the sample cover  3  and the lower cover  4  each has a cross section of a trapezoid, the front width being approximately 220 mm and the rear width being approximately 280 mm as seen from above. That is, the sample cover  3  and the lower cover  4  each comprises tapered sides that are tapering toward the front. Thus, by once moving the sample cover  3  forward and downward and moving downward along the outer surface of the lower cover  4  in front of the lower cover  4 , by way of the parallel link structure described below, it is possible to descend the sample cover  3  along the front surface of the lower cover  4  without the sample cover  3  interfering with the lower cover  4 . The sample cover  3  has the same external shape as the lower cover  4 , which improves external appearance of these covers. 
   As shown in  FIG. 27 , the sample cover  3  is linked to the main unit case  2  by upper and lower links  92 ,  93  parallel to each other, provided between a first bracket  90  provided at the rear end of its both sides and a second bracket  91  provided at the front end of the main unit case  2 . By using the parallel links  92 ,  93 , the sample cover  3  can move up and down along the front surface and both sides of the lower cover  4  while being translated. 
   Referring to  FIGS. 27 and 28 , the first bracket  90  comprises a metal piece  95  extending along the rear end edge. The second bracket  91  is provided with a permanent magnet  96  at a position that faces the metal piece  95  when the sample cover  3  is closed. Thus, when the sample cover  3  is displaced upward and the stage  13  is shielded, the metal piece  95  is stuck to by the permanent magnet  96  and the closure position of the sample cover  3  is maintained by the magnetic force of the permanent magnet  96 . 
   While the sample cover  3  described referring to  FIG. 27  above is manually opened/closed, the sample cover  3  may be opened/closed with a motor-driven mechanism by providing an electric motor  98  (see  FIG. 28 ) at the second bracket  91  on the main unit case  2 , linking the electric motor  98  for example with the upper link  92  by using a gear  99 , and rotating the motor in forward or backward directions. 
   When the sample cover  3  takes the upper position, the upper area of the sample cover  3  is covered by a canopy plate  100 , which places the stage  13  and its surroundings into the darkroom state. While the canopy plate  100  extending horizontally is fixed at the bottom end of the transmissive illumination optical unit  64  in the embodiment, it may be detachably mounted on the main unit case  2  in the variation. 
   Detachably mounting the canopy plate  100  advantageously applies to a case where strict lightproof environment is not required depending on the type of a sample S and the sample cover  3  alone is positioned in the upper position or closed in the absence of the canopy plate  100  so that an image of the sample S is captured in the semi-darkroom state. 
   As mentioned above, the sample cover  3  is moved vertically along the surface of the lower cover  4 . Thus, even when the sample cover  3  is opened and the stage  13  is exposed, the sample cover  3  overlaps with the lower cover  4  in back-and-forth directions, so that the open sample cover  3  does not narrow the work space of the user. 
   As a variation of the embodiment shown in  FIG. 26 , the sample cover  3  may be displaced upward to expose the stage  13 . As shown in  FIG. 29 , the stage  13  may be exposed by causing the sample cover  410  to perform arc operation downward, where transmissive illumination optical unit  400 , lower cover  420 , and main unit case  310  are also shown in this figure. 
   As shown in  FIG. 30 , a configuration is possible where a lid  102  is provided to cover the entirety of top area of the lower cover  4  and the rear end edge of the top  102   a  of the lid  102  is hinged to the main unit case  2  in order to open/close the lid  102 . 
   As shown in  FIG. 31 , the sample cover  3  with the top  102   a  integrated may be inserted/removed at the front of the stage  13 . That is, a configuration is possible where the sample cover  3  with the top  102   a  is detachably provided on the main unit case  2  from the front and the sample cover  3  is pulled out of the main unit case  2  when the sample S is extracted/inserted thereby exposing the stage  13 . 
   As shown in  FIG. 32 , a configuration is possible where the sample cover  3  is split into a left split cover  3 L and a right split cove  3 R and, when the stage  13  is exposed, the left split cover  3 L is once displaced leftward and the right split cover  3 R is once displaced rightward, then the covers are displaced backward along the side faces of the main unit case  2 . 
   As shown in  FIGS. 33 ,  34 , an optional configuration is possible where a rectangular horizontal tray  105  larger than the stage  13  is provided below and adjacent to the stage  13  and the both edges of the side faces of the horizontal tray  105  are slidably engaged with a horizontal guide rail  106  extending in back-and-forth directions so as to allow the horizontal tray  105  to be removed forward. On the horizontal tray  105 , a slit  105   a  (having a width substantially the same as the diameter of the objective lens  28 ) extending in back-and-forth directions on the side where interference with the objective lens  28  may take place, in order to avoid interference with the objective lens  28 , as understood from  FIGS. 33 ,  34 . This allows the horizontal tray  105  to be placed in a more inner position than the objective lens  28 . 
   By providing a detachable horizontal tray  105  below the stage  13 , it is possible to prevent, for example, a sample culture solution or sample S from dropping via the light aperture in the stage  13  directly below the stage  13  and contaminating a member in the area below the stage  13 , for example the objective lens  28 . By providing a horizontal tray  105 , the horizontal tray catches any dropping culture solution. It is thus possible to remove the sample S by simply drawing the horizontal tray  105 . This prevents contamination of the objective lens  28  thereby improving the ease of maintenance of the fluorescence microscope  1 . 
   As understood from the above description, the fluorescence microscope  1  of the embodiment arranges sideways the light source  15  of the transmissive illumination system  10  and provide the transmissive illumination system  10  with a tilt mirror  17  to refract the transmissive illumination light thus dramatically reducing the height dimension of the fluorescence microscope  1 . Inside the main unit case  2  are densely mounted the imaging system  12 , transmissive and epi illumination systems  10 ,  11  as well as all the associated power supply units  40 ,  41 ,  42 , the power supply board  71 , and the controller board  73 . Such a layout of the fluorescence microscope has not been encountered. The fluorescence microscope  1  of the embodiment features the V-shaped arrangement of the epi illumination system  11  and the imaging system  12 , the power supply units  40  through  42  arranged in the clearance between the transmissive illumination system  10  and the epi illumination system  11  whose power supplies  15 ,  20  are arranged sideways. Such an innovative arrangement has contributed to reduction in the overall dimensions, in particular the height dimension. 
   For example, in case the power supply units  40  through  42  are arranged below the imaging system  12 , the height dimension of the fluorescence microscope  1  increases and the problem of heat rising from the power supply units  40  through  42  occurs. In case the power supply units  40  through  42  are arranged on the sides of the transmissive illumination system  10  and the epi illumination system  11 , the width dimension of the fluorescence microscope increases. 
   According to the fluorescence microscope  1  where the power supply units  40  through  42  are arranged in the clearance between the transmissive illumination system  10  and the epi illumination system  11 , the width dimension and the height dimension can be reduced as mentioned above. The heat from the power supply units  40  through  42  rises. This minimizes the influence of heat from the power supply units  40  through  42  on the epi illumination system placed below the power supply units for which heat countermeasures are required most. 
   The chassis  35  is split into an upper part and a lower part. The power supply units  40  through  42  are mounted on the upper chassis  36  while the epi illumination system  11  enclosed by the heat insulation housing  76  with air-cooling measures are mounted on the lower chassis  37 . This minimizes the thermal expansion of the lower chassis  37 . Moreover, a unit including the objective lens  28  and the stage  13  is assembled to the lower chassis  37 . This prevents the objective lens  28  from going out of focus in prolonged fluorescence observation. 
   The fluorescence microscope  1  according to the embodiment employs, as mentioned above, the transmissive illumination system  10  equipped with the light source  15  provided sideways and arranges the epi illumination system  11  and the imaging system  12  in the shape of V as seen from above. The main unit case  2  having a minimum volume required to enclose the three fundamental components features an unprecedented compactness, as those skilled in the art will readily appreciate. Further, those skilled in the art will be surprised at the configuration where the imaging system  12 , the transmissive and epi illumination systems  10 ,  11  as well as the power supply units  40  through  42  as a heat source and the power supply board  71  are arranged inside the main unit case  2  that is in particular small in the height dimension. This is virtually impossible unless sophisticated heat countermeasures are taken. For the heat countermeasures, the related art fluorescence microscopes have avoided use of an electric fan although the invention intentionally employs the electric fan  38  to perform forced ventilation. The halogen lamp  15  and the mercury lamp  20  that generates a huge amount of heat are enclosed by the heat insulation housings  61 ,  76  in order to confine the heat emitted from the lamps  15 ,  20  and exhaust to outside the huge amount of heat in the heat insulation housings  61 ,  76  by using the electric fan  38 . Similarly, the heat absorption filter  75  related to the lamps  15 ,  20  is enclosed by the heat insulation housings  61 ,  76  in order to perform air-cooling of the filter by way of the flow of air generated by the electric fan  38  related to the heat insulation housings  61 ,  76 , thereby preventing heat saturation of the heat absorption filter  75 . 
   The inside of the main unit case  2  is designed in three vertical layers. The bottom electric fan  38 B is provided for the epi illumination system  11  and the imaging system  12  positioned in the bottom layer. The middle electric fan  38 M is provided for the power supply units  40  through  42  positioned in the middle layer. The top electric fan  39 T is provided for the transmissive illumination system  10  positioned in the top layer. Forced ventilation is performed in each layer so that the influence of heat between layers is minimized.