Abstract:
A microscope includes a member supported for movement relative to a base along a path of travel, and optics on the member for imaging a region that includes a location for a specimen. The method and apparatus involve: effecting relative movement of a cam operatively coupled to one of the member and the base with respect to a cam follower operatively coupled to the other of the member and the base in a manner so that the cam follower slides along a cam surface on the cam; and responding to the sliding movement of the cam follower along the cam surface by effecting relative movement of the cam and cam follower in a manner that in turn effects movement of the member along the path of travel relative to the base.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates in general to microscopes and, more particularly, to techniques for focusing a microscope. 
       BACKGROUND 
       [0002]    In a microscope used for fluorescence microscopy, the focusing optics do not need to be moved a large distance in order to achieve the necessary degree of focus. Instead, only a small amount of movement is needed, but it is desirable that this movement be carried with a very high degree of accuracy, for example in small increments on the order of about 10 microns. Although existing microscopes have provided an adequate degree of accuracy in focus, this accuracy has not been entirely satisfactory. This is due in part to the fact that existing focus drives tend to have a degree of backlash that reduces the accuracy of the focus. 
         [0003]    A further consideration is that, in fluorescence microscopy, light emitting diode (LED) devices are used as light sources. Sometimes it is necessary to change a light source, for example to replace an LED that has failed, or to change the color (wavelength) of the illumination. In order to change a light source, it is typically necessary to carry out a significant degree of disassembly of the microscope in order to reach the light source. Moreover, where the replacement is being carried out in order to adjust the wavelength of the illumination, it may also be necessary to adjust the focal length, and/or change some optical components such as lenses and/or filters. This can involve replacing several independent components. As a result, the overall procedure, while adequate for its intended purposes, tends to be time consuming, and can involve replacement of multiple components on an item-by-item basis. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    A better understanding of the present invention will be realized from the detailed description that follows, taken in conjunction with the accompanying drawings, in which: 
           [0005]      FIG. 1  is a diagrammatic perspective view of a microscope that embodies aspects of the invention. 
           [0006]      FIG. 2  is a diagrammatic sectional side view, taken along the section line  2 - 2  in  FIG. 1 . 
           [0007]      FIG. 3  is a diagrammatic perspective exploded view showing selected components from the microscope of  FIGS. 1 and 2 . 
           [0008]      FIG. 4  is a diagrammatic fragmentary sectional side view that shows, in an enlarged scale, a portion of the structure of  FIG. 2 . 
           [0009]      FIGS. 5 and 6  are respectively a diagrammatic perspective view and a diagrammatic top view that show, in an enlarged scale, a gear that is a component of the microscope of  FIG. 1 . 
           [0010]      FIG. 7  is a diagrammatic fragmentary side view of the gear of  FIGS. 5 and 6 , and adjacent portions of other components of the microscope of  FIG. 1 . 
           [0011]      FIG. 8  is a diagrammatic perspective view of one of two identical cam follower parts that are components of the microscope of  FIG. 1 . 
           [0012]      FIG. 9  is a diagrammatic central sectional side view of an illumination module that is a component of the microscope of  FIG. 1 . 
           [0013]      FIG. 10  is a diagrammatic perspective exploded view of the illumination module of  FIG. 9 . 
           [0014]      FIG. 11  is a diagrammatic central sectional side view similar to  FIG. 9 , but showing a different illumination module that is a component of the microscope of  FIG. 1 . 
           [0015]      FIG. 12  is a diagrammatic central sectional side view similar to  FIGS. 9 and 11 , but showing yet another illumination module that is a component of the microscope of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0016]      FIG. 1  is a diagrammatic perspective view of a microscope  10  that embodies aspects of the invention. For simplicity and clarity, an outer housing of the microscope  10  has been omitted in the drawings. The microscope  10  is used for fluorescence analysis, but could alternatively be used for some other purpose.  FIG. 2  is a diagrammatic sectional side view of the microscope  10 , taken along the section line  2 - 2  in  FIG. 1 . 
         [0017]    The microscope  10  has an aluminum base  12  that includes a lower part  16  in a form of a base plate, and an upper part  17  in the form of a shell. The shell  17  is fixedly secured to the base plate  16  by a plurality of screws  18 . As best seen in  FIG. 2 , the base  12  has a chamber  21  therein, defined by a downwardly open recess in the shell  17 . The upper portion of the shell  17  includes a vertically upwardly extending projection  23  having a cylindrical outer surface that is concentric to a vertical axis  25 . A cylindrical opening  24  extends vertically through the projection  23 . The cylindrical opening  24  is concentric to the vertical axis  25 , has a lower end that opens into the chamber  21 , and has an upper end that opens through a top surface  27  of the shell  17 . The top surface  27  is an axially upwardly facing annular bearing surface. A radially outwardly facing annular bearing surface  28  is provided adjacent the upper end of the projection  23 . The bearing surfaces  27  and  28  are each concentric to the vertical axis  25 . 
         [0018]    The shell  17  has eight uniformly circumferentially spaced cylindrical openings that extend therethrough from the chamber  21  to the outer surface of the shell at an angle of approximately 45° with respect to the vertical axis  25 . Two of the these openings are visible in  FIG. 2 , and are respectively designated by reference numerals  31  and  32 . 
         [0019]    The base plate  16  has a downwardly converging frustoconical opening  36  therethrough. The opening  36  is concentric to the vertical axis  25 . At its upper end, the opening  36  communicates with the chamber  21 . A conventional and not-illustrated specimen support can be removably secured against an underside of the base plate  16 , in order to support a specimen at a location  37  that is identified in  FIG. 2  by a small rectangle. 
         [0020]      FIG. 3  is a diagrammatic perspective exploded view showing selected components from the microscope  10  of  FIGS. 1 and 2 . With reference to  FIGS. 1 through 3 , an aluminum support column  41  has its lower end fixedly secured to the base plate  16  by several screws  42 , and extends vertically upwardly from the base plate. As shown in  FIGS. 2 and 3 , an electric motor  46  is fixedly secured to an upper portion of the support column  41 , with an orientation so that a rotatable shaft  47  of the motor protects vertically downwardly from the motor. In the disclosed embodiment, the motor  46  is a stepper motor, but it could alternatively be any other suitable type of motor. A pinion gear  48  is fixedly secured to the lower end of the shaft  47 , for a purpose discussed later. An anti-rotation section  51  is also fixedly secured to the upper portion of the support column  41 , and has a vertically extending slot  52  therein for a purpose discussed later. 
         [0021]    With reference to  FIGS. 1 and 2 , the microscope  10  has eight illumination modules, three of which are designated by respective reference numerals  61 ,  62  and  63 . AS discussed above, the shell has eight circumferentially-spaced openings therethrough, two of which are identified by reference numerals  31  and  32 . Each of these eight openings has fixedly but removably installed therein a respective one of the eight illumination modules, including the three illumination modules identified by reference numerals  61 ,  62  and  63 . The eight illumination modules are each held in place by a single removable screw, for example as shown in  67  and  68  in  FIG. 2  for the illumination modules  61  and  62 . Each of the eight illumination modules can emit radiation that illuminates a not-illustrated specimen disposed at the location  37 . In the microscope  10 , the eight illumination modules are all different from each other. For example, the illumination modules each emit radiation having respective distinct characteristics, and typically no more than one of the eight illumination modules is energized at any given point in time. The structure and operation of the illumination modules is discussed in more detail later. 
         [0022]    As shown in  FIGS. 2 and 3 , the microscope  10  includes a tubular barrel member  81  that is made of aluminum and that extends vertically through the cylindrical opening  24  in the projection  23  of the shell  17 . The barrel member  81  has a cylindrical outer surface  82  that is concentric to the vertical axis  25 , and that has a diameter slightly less than the inside diameter of the cylindrical opening  24 . The cylindrical surface  82  slidably engages the cylindrical inner surface of the opening  24 , so that the barrel member  81  is capable of reciprocal vertical sliding movement relative to the shell  17 . 
         [0023]      FIG. 4  is a diagrammatic fragmentary sectional side view that shows, in an enlarged scale, a portion of the structure of  FIG. 2 , including a lower portion of the barrel member  81 , and some surrounding structure. As shown in  FIG. 4 , the barrel member  81  has an annular recess  86  near a lower end thereof. A retaining ring  87  is fixedly engaged in the annular recess  86  with a snap fit. A flat washer  91  encircles the barrel member  81  above the retaining ring  87 , and has an upper surface that is disposed against a top surface of the chamber  21  in the shell  17 . A resilient helical compression spring  92  encircles the barrel member  81  between the retaining ring  87  and the washer  91 , and yieldably urges the retaining ring  87  away from the washer  91 . This in turn causes the barrel member  81  to be urged downwardly in relation to the shell  17 . 
         [0024]    As best seen in  FIGS. 2 ,  3  and  4 , an annular gear  101  encircles the barrel member  81 . In the disclosed embodiment, the gear  101  is made of aluminum, but it could alternatively be made of any other suitable material. The gear  101  has a radially inwardly facing cylindrical bearing surface  102  that slidably engages the cylindrical surface  82  on the barrel member  81 , an annular axially-facing bearing surface  103  that slidably engages the bearing surface  27  on the shell  17 , and a radially-inwardly facing annular bearing surface  104  that slidably engages the bearing surface  28  on the shell. As a result of the sliding engagement of these pairs of bearing surfaces, the annular gear  101  can rotate relative to the shell  17  and the barrel member  81 . A lubricant is provided between these pairs of bearing surfaces. The lubricant used in the disclosed embodiment is available commercially as BRAYCOTE® 601 EF from Castrol Industrial North America, Inc. of Naperville, Ill. Alternatively, however, any other suitable lubricant could be used, or for some applications the lubricant could be omitted. 
         [0025]    The annular gear  101  has a plurality of gear teeth  107  extending around the periphery thereof. As shown in  FIG. 2 , the gear teeth  107  on the gear  101  engage the gear teeth on the pinion gear  48 . Thus, when the motor  46  rotates the gear  48 , the gear  48  in turn rotates the gear  101 . 
         [0026]      FIGS. 5 and 6  are respectively a diagrammatic perspective view and a diagrammatic top view of the gear  101 , showing the gear in an enlarged scale. With reference to  FIGS. 4 ,  5 , and  6 , the upper portion of the gear  101  serves as an annular cam  111  that extends completely around the barrel member  81 . The cam  111  has thereon an upwardly-facing annular cam surface  112  that extends completely around the barrel member  81 . As best seen in  FIGS. 5 and 6 , the cam surface  112  has two short transition surface portions  116  and  117  at diametrically opposed locations, and has longer cam surface portions  118  and  119  disposed between the transition surface portions  116  and  117 . In a counterclockwise direction  123 , as viewed in  FIG. 5 , the cam surface portion  118  progressively rises with a gradual slope from the transition surface portion  117  to the transition surface portion  116 , the transition surface portion  116  then progressively drops with a significantly greater slope, the cam surface portion  119  then progressively rises with a gradual slope from the transition surface portion  116  to the transition surface portion  117 , and then the transition surface portion  117  progressively drops with a significantly greater slope. 
         [0027]      FIG. 7  is a diagrammatic fragmentary side view of the gear  101 , and adjacent portions of the barrel member  81  and shell  17 . With reference to  FIGS. 3 and 7 , two screws  131  are disposed on diametrically opposite sides of the barrel member  81 . The screws  131  each extend radially with respect to the vertical axis  25 , and each engage a respect threaded radial opening provided in the barrel member  81 . Two identical cam follower parts  132  are provided, and each is pivotally supported on a respective one of the two screws  131 . The cam follower parts  132  each slidably engage the cam surface  112  on the gear  101 . In the disclosed embodiment, the cam follower parts  132  are each made of nylon. However, they could alternatively be made of any other suitable material. 
         [0028]      FIG. 8  is a diagrammatic perspective view of one of the cam follower parts  132 . As shown in  FIG. 8 , the cam follower part  132  has a cylindrical opening  136  which extends therethrough, and which rotatably receives a shank of the associated screw  131 . The cylindrical opening  136  is concentric to a pivot axis  137  of the cam follower part  132 . The cam follower part has, on one side thereof, two spaced planar surfaces  141  and  142  that are substantially co-planar, and are separated by a shallow recess  143 . The surfaces  141  and  142  are slider surfaces that each slidably engage the cam  112  on the gear  101 . 
         [0029]    As discussed above in association with  FIG. 4 , the compression spring  92  urges the barrel member  81  downwardly in relation to the shell  17  and the gear  101 . As a result, the cam follower parts  132  on the barrel member  81  are urged downwardly against the upwardly-facing cam surface  112  on the gear  101 , and this in turn urges the bearing surface  103  on the gear against the bearing surface  27  on the shell  17 . 
         [0030]      FIG. 1  shows an annular protective cover  146  that is provided around the barrel member  81  just above the gear  101 , in order to cover and protect the cam surface  112  and the cam follower parts  132 . The lower end of the cover  146  rests on top of the gear  101 , at a location just radially outwardly of the cam  111  with the cam surface  112 . Although the protective cover  146  is shown in  FIG. 1 , for clarity it is omitted from the other drawing figures. 
         [0031]    With reference to  FIGS. 1 ,  2  and  3 , a horizontal plate is fixedly mounted to an upper end of the barrel member  81 . An anti-rotation flange  157  is fixedly secured to and extends vertically downwardly from the underside of the plate  156 , at a location spaced radially outwardly from the barrel member  81 . The anti-rotation flange  157  has at its lower end a horizontally outwardly projecting tab  158  that is vertically slidably received within the vertical slot  52  of the anti-rotation section  51 . The cooperation of the tab  158  and slot  52  prevents rotation of the barrel member  81  relative to the shell  17 . 
         [0032]    A circuit board  161  is disposed above and supported by the plate  156 . An image sensor  162  of a known type is mounted on the circuit board  161 , at a location so that the vertical axis  25  extends through a central portion of the image sensor. The plate  156  has an opening  164  ( FIG. 2 ) that is disposed just below the image sensor  162 . 
         [0033]    With reference to  FIGS. 2 and 4 , an optics assembly  166  is installed within the barrel member  81 , near the lower end of the barrel member. The optics assembly  166  includes several optical components, such as lenses. A detailed understanding of the optics  166  is not necessary to an understanding of the present invention, and the optics  166  are therefore not described here in detail. With reference to  FIG. 2 , the optics  166  form on the image sensor  162  an image of a region that is disposed at the lower end of the frustoconical opening  36 , and that includes the location  37  at which a specimen can be supported. 
         [0034]    As discussed above, the microscope  10  includes eight illumination modules, three of which are identified by reference numerals  61 ,  62 , and  63 . As also discussed above, these eight illumination modules are not all identical. For example, each emits radiation with a respective different color (wavelength). 
         [0035]      FIG. 9  is a diagrammatic central sectional side view of the illumination module  62 .  FIG. 10  is a diagrammatic perspective exploded view of the illumination module  62 . With reference to  FIGS. 9 and 10 , the illumination module  62  includes a member or cap  201  having a circular planar wall  202 , and having a flange  203  that projects axially from a peripheral edge of the wall  201 . A recess or gap  204  is provided through the flange  203 . The member  201  is thermally conductive. In the disclosed embodiment, the member  201  is made from aluminum, but it could alternatively be made from any other suitable material. 
         [0036]    A heat sink  207  has a base plate  208 , and a plurality of spaced parallel projections  209  that extend outwardly from the base plate  208  on one side thereof. The heat sink  207  is thermally conductive. In the disclosed embodiment, the heat sink  207  is made from aluminum, but it could alternatively be made of any other suitable material. The base plate  208  of the heat sink  207  is fixedly secured to the circular wall  202  of the member  201  by a thermally-conductive adhesive that is not separately shown in the drawings. In the disclosed embodiment, the thermally-conductive adhesive is obtained commercially under the tradename TRA-BOND 2151 from TRA-CON, Inc. of Bedford, Mass. However, the heat sink  207  and member  201  could alternatively be physically and thermally coupled in any other suitable manner. 
         [0037]    The illumination module  62  includes a small and elongate circuit board  212  with a radiation source  213  mounted on one end portion thereof, and an electrical connector  214  mounted on an opposite end portion thereof. The connector  214  and radiation source  213  are on opposite sides of the circuit board. The electrical connector  214  has two electrically conductive pins  216 , and one end of each pin is soldered to a respective electrically-conductive run on the circuit board. The circuit board electrically couples the pins  216  of the connector  214  to respective terminals of the radiation source  213 . In the disclosed embodiment, the radiation source  213  is a commercially-available light emitting diode (LED), and is therefore not described here in detail. The radiation source  213  in the illumination module  62  emits radiation having a center wavelength corresponding to a color commonly known as cyan. A not-illustrated cable has one end detachably coupled to the connector  214 , and another end detachably coupled to a connector on another circuit board, in order to supply electrical power through the connector  214  and the circuit board  212  to the radiation source  213 . 
         [0038]    The end portion of the circuit board  212  having the radiation source  213  thereon is disposed against and fixedly secured to the circular wall  202  of the member  201 . In the disclosed embodiment, this portion of the circuit board is adhesively secured to the wall  202  with the same thermally-conductive epoxy used to secure the heat sink  207  to the member  201 . However, the heat sink  207 , circuit board  212  and member  201  could alternatively be physically and thermally coupled in any other suitable manner. The opposite end portion of the circuit board  212  projects outwardly beyond the member  201 , through the gap  204  in the flange  203 . This end portion of the circuit board has a circular opening  217  therethrough adjacent the electrical connector  214 . The screw  68  ( FIG. 1 ) extends through the opening  217 , in order to releasably secure the illumination module  62  to the shell  17  of the microscope  10 . 
         [0039]    With reference to  FIGS. 9 and 10 , the illumination module  62  includes a cylindrical tubular support  221  that has three notches  222  (FIG.  9 ) and  223 - 224  ( FIG. 10 ) in one end thereof. In the disclosed embodiment, the support  221  is made from aluminum, but it could alternatively be made from any other suitable material. The notched end of the tubular support  221  is received within the flange  203  on the member  201 , with the notch  222  aligned with the gap  204  in the flange  203 . The notched end of the tubular support  221  has an outside diameter that is only slightly less than the inside diameter of the flange  203 . An adhesive is provided between these two surfaces in order to fixedly secure the tubular support  221  to the member  201 . In the disclosed embodiment, this adhesive is obtained commercially as LOCTITE® 380 from Henkel Corporation of Rocky Hill, Conn. However, it would alternatively be possible to couple the tubular support  221  to the member  201  in any other suitable manner. 
         [0040]    The circuit board  212  extends outwardly through the notch  222  in the support  221 . The notches  223  and  224  in the support  221  receive respective corners of the rectangular circuit board. At its outer end, the tubular support  221  has in its outer surface a circumferentially-extending annular groove  227 . 
         [0041]    An optical filter  231  of a known type is supported within the tubular support  221 , near the outer end thereof. The filter  231  is held in place by a ring  232  of adhesive. In the disclosed embodiment, the adhesive includes a bond material obtained commercially under the trademark URALANE® 5753 from Huntsman Corporation of The Woodlands, Tex., with the addition of 0.4% by weight carbon lampblack to blacken and avoid fluorescence of the URALANE® bond material. Alternatively, however, the filter  231  could be held in place in any other suitable manner. The filter  231  is a bandpass filter having a center wavelength that is substantially the same as the center wavelength of the radiation emitted by the radiation source  213  (cyan). 
         [0042]    A collimating lens  236  of a known type is provided within the tubular support  221 , at a location between the filter  231  and the radiation source  213 . The lens  236  is fixedly held in place by a ring  237  of the URALANE® adhesive mentioned above. However, the lens  236  could alternatively be held in place in any other suitable manner. 
         [0043]    The illumination module  62  includes a cylindrical tubular extension  241  that is made of aluminum, but that could alternatively be made of any other suitable material. The tubular extension  241  has at one end an annular axial projection  242 . The annular projection  242  is received within the annular recess  227  in the tubular support  221 . The diameter of the radially-outwardly facing cylindrical surface in the recess  227  is slightly less than the diameter of the radially inwardly facing cylindrical surface on the annular projection  242 . A quantity of the above-mentioned LOCTITE® 380 adhesive is provided between these two cylindrical surfaces, in order to fixedly secure the tubular extension  241  to the tubular support  221 . 
         [0044]    A focusing or condenser lens  246  of a known type is provided within the tubular extension  241 , near the outer end thereof. The lens  246  is fixedly held in place by a ring  247  of the above-mentioned URALANE® 5753 adhesive. Alternatively, however, the lens  246  could be secured in place in any other suitable manner. 
         [0045]    A cylindrical thermal barrier sleeve  251  encircles the tubular support  221 , and has an inside diameter that is only slightly larger than the outside diameter of the tubular support  221 . The thermal barrier sleeve  251  is fixedly secured to the tubular support  221  by a quantity of the above-mentioned LOCTITE® 380 adhesive. Alternatively, however, the sleeve  251  could be secured to the tubular support  221  in any other suitable manner. In the disclosed embodiment, the thermal barrier sleeve  251  is made of nylon. However, it could alternatively be made of any other suitable material that is thermally non-conductive, including but not limited to a plastic material. 
         [0046]    Radiation emitted by the radiation source  213  travels downwardly in  FIG. 9 , and passes successively through the lens  236 , the bandpass filter  231 , and the lens  246 . The lens  236  collimates the radiation from the source  213 , the bandpass filter  231  removes wavelengths above and below the center wavelength of interest (which for the illumination module  62  is cyan), and the lens  246  takes the collimated and filtered radiation and focuses it to the specimen location  37  ( FIG. 2 ). The filter  231  is positioned so that it is disposed in collimated radiation, with a reduced aperture. The filter  231  and the lenses  236  and  246  constitute all of the optics needed to deliver radiation from the radiation source  213  to the specimen location  37 , and are all present within the removable illumination module  62 . When the illumination module  62  is installed in the microscope  10 , the thermal barrier sleeve  251  is disposed between the tubular support  221  and the shell  17 , and resists heat flow from the illumination module to the shell. The majority of the heat emitted by the radiation source  213  flows through the member  202  to the heat sink  207 , and is discharged to the ambient air disposed externally of the base  12  of the microscope. 
         [0047]    The illumination module  62  is intentionally configured to be a very low-cost component. In this regard, the illumination module  62  uses a minimal number of optical components. Further, the filter  231  and the lenses  236  and  246  are each an inexpensive, mass-produced component that can be readily commercially obtained. For example, the lenses  236  and  246  can each be a molded plastic part. The heat sink  207  is also an inexpensive, mass-produced component that is readily commercially available. The illumination module  62  does not contain any threaded parts that screw together, and that would be relatively expensive to fabricate. Instead, the radiation source  213  and the connector  214  are each soldered to the circuit board  212 , and the circuit board  212  and other components are coupled to each other through the use of appropriate low-cost adhesives, including a thermally-conductive adhesive where appropriate. 
         [0048]      FIG. 11  is a diagrammatic central sectional side view similar to  FIG. 9 , but showing the illumination module  61  rather than the illumination module  62 . The illumination module  61  is identical to the illumination module  62 , except for certain differences that are discussed below. Parts in  FIG. 11  that are similar or identical to parts in  FIG. 9  are identified in  FIG. 11  with the same reference numerals used for those parts in  FIG. 9 . 
         [0049]    The illumination module  61  has on the circuit board  212  a radiation source  301 . The radiation source  301  is an LED that produces radiation at a center wavelength different from the center wavelength of radiation emitted by the radiation source  213  of  FIG. 9 . In particular, the radiation source  301  emits radiation with a wavelength corresponding to the color red. The illumination module  61  has a bandpass filter  303  that is different from the bandpass filter  231  of  FIG. 9 , in that the bandpass filter  303  has a center wavelength that is the same as the center wavelength of the radiation emitted by the radiation source  301 . In particular, the filter  303  has a passband with a center wavelength corresponding to the color red. 
         [0050]    The illumination module  61  has a cylindrical tubular extension  311  that is similar to the tubular extension  241  in the embodiment of  FIG. 9 , except that the tubular extension  311  is axially shorter than the tubular extension  241 . The tubular extension  311  has an annular axial projection  312  that engages and is adhesively secured in the annular recess  227  of the tubular support  221 . The illumination module  61  has a focusing lens  316  that is fixedly mounted in the lower end of the tubular extension  311 , in place of the focusing lens  246  in the embodiment of  FIG. 9 . The focusing lens  316  is selected to properly focus the radiation with a red wavelength that is emitted by the radiation source  301 . The shorter axial length of the tubular extension  311 , in comparison to the axial length of the tubular extension  241  in  FIG. 9 , reflects the fact that the focal length of the lens  316  is different from the focal length of the lens  246 . 
         [0051]      FIG. 12  is a diagrammatic central sectional side view similar to  FIGS. 9 and 11 , but showing the illumination module  63 . The illumination module  63  is identical to the illumination  62  of  FIG. 9 , except for certain differences that are discussed below. The illumination module  63  does not include the filter  231 , tubular extension  241 , lens  246 , or retaining rings  232  and  247  that are present in the illumination module  62  of  FIG. 9 . In addition, a radiation source  341  provided on the circuit board  212  is different from the radiation source  213  shown in  FIG. 9 . In particular, the radiation source  341  of  FIG. 12  is an LED that emits radiation with a plurality of different wavelengths, or in other words radiation that is commonly referred to as “white light”. The lens  236  collimates this white light. Since this radiation contains a variety of wavelengths, there is no need for a bandpass filter such as that shown at  231  in  FIG. 9 , or a focusing lens such as that shown at  246  in  FIG. 9 . 
         [0052]    Although selected embodiments have been illustrated and described in detail, it should be understood that a variety of substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the claims that follow.