Patent Publication Number: US-2023161144-A1

Title: Unique oblique lighting technique using a brightfield darkfield objective and imaging method relating thereto

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application No. 62/063,564, filed Oct. 14, 2014, and incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to imaging techniques and apparatus. In particular embodiments, it relates to topographical imaging techniques. In particular embodiments, it relates to imaging apparatus employing brightfield/darkfield objective, and improvements to such apparatus by employing a light barrier in the darkfield channel. 
     BACKGROUND OF THE INVENTION 
     Standard techniques for creating 3D topographies include stylus instruments, profilometers, ultrasonic transducers, and laser triangulation among others. Shape-from-shading (SFS) and photometric stereo (PMS) have been used to create topographies by illuminating a specimen  1  with one or more a light sources  2 ,  3  directing oblique light  4 ,  5  toward the specimen  1  at an angle from 5 to 85 degrees and more typically from 25 to 75 degrees, as generally represented in  FIG.  1   . The oblique illumination is reflected from the surface S of the object as reflected light  6 , and is captured by an image sensor (not shown) such as a CCD or CMOS sensor of a digital camera  7 . The light sources are moved to different positions located circumferentially around the object, with images taken at these different positions. These images are used to calculate the topography of the specimen  1  by known means, employing appropriate processor(s)  8 . 
     A standard reflected light microscope employing brightfield and darkfield functionality is shown in  FIGS.  2  and  3   . In this example the microscope  10  is equipped with a camera  12 . Oculars may also be present, such that the numeral  12  is to broadly represent oculars and/or a camera. Although the following description will refer to a reflected light microscope, similar techniques apply to transmitted light microscopes or instruments using brightfield/darkfield microscope objectives. A reflected light microscope  10  will be referenced in the following descriptions but the technology may apply to any imaging system using a brightfield/darkfield objective. The systems generally consist of a light source  14  providing light  24 , a vertical illuminator  16 , a brightfield/darkfield (BD) switch  18  and a BD objective  20 . U.S. Pat. Nos. 3,930,713 and 4,687,304 describe a BD objective. In a standard BD objective  20 , two channels are provided to guide the light to the specimen  1 . The light  24  is directed to a mirror  25  that reflects the light  24  toward the specimen  1  downwardly through the vertical illuminator  16 , the nosepiece  28 , and BD objective  20 . The BD switch  18 , as schematically shown, serves to limit the light  24  to pass either into a brightfield channel  22  or darkfield channel  26  separated by a shield wall  21 . With the BD switch  18  in a bright field position as in  FIG.  2   , the light  24  is limited to a beam that is reflected off of the mirror  25  to enter the brightfield channel  22 , which directs the illuminating light  24 ′ through the BD objective  20  toward the surface S of the specimen  1  at an angle perpendicular (90 degrees) to the plane of the specimen  1  and allows the reflected light  30  to pass to the oculars or camera  12 . As seen in  FIG.  3   , when the BD switch  18  is in a darkfield position the light  24  is limited to an annular beam that is reflected off of the mirror  25  to enter the darkfield channel  26 , which is an annular channel directing illuminating light  24 ″ toward the specimen at an angle less than 90 degrees and typically 25 to 75 degrees. 
     It can be seen in  FIG.  2    that the light path in brightfield (illuminating light  24 ′) is projected through the center of the nosepiece  28  and through the brightfield channel  22  of the BD objective  20 . The reflected light  30  is reflected back through the brightfield channel  22 , through the nosepiece  28  and tube lens  32  and is affected by any oculars and/or captured by a camera  12 . It is seen here that the illumination light  24 ′ in brightfield is at 90 degrees to the surface S of the specimen  1  and the reflected light  30  that is measured travels parallel to the illumination light  24 ′ but in an opposite direction. The projected illuminating light  24 ′ illuminates the entire field of view. 
       FIG.  3    shows the microscope  10  in darkfield mode. Here the light  24  is blocked by the darkfield switch  18  so that no light passes through the brightfield channel  22  and is instead directed to pass through the darkfield channel  26  as illuminating light  24 ″. This produces an annular beam (or, in other terms, a hollow cylinder or annular cylinder) of light that is projected toward the specimen  1  at an oblique angle determined by the design of the objective  20  and wall of the darkfield channel  26 . As known, the BD objective will have mirrors and/or prisms and/or light diffusers built into the objective to direct the oblique light. The illuminating light  24 ″ reflects off the surface S of the specimen  1  and the reflected light  30  travels up the brightfield channel to the ocular or camera  12 . The projected darkfield illuminating light  24 ″ illuminates the entire field of view from about the entire periphery (360 degrees) of the objective. 
     In brightfield imaging it can be seen that the field of view F, which takes in at least a portion of the specimen  1 , is filled by direct 90 degrees illumination (the incoming illuminating light  24 ′ is orthogonal to the general resting plane of the specimen  1 ) whereas in darkfield imaging, the field of view F is filled by oblique illumination (the incoming illuminating light  24 ″ is at an oblique angle to the general resting plane of the specimen  1 ). The darkfield illumination is evenly distributed through the 360 degree circumference of the BD objective  20 . 
     SUMMARY OF THE INVENTION 
     In a first embodiment, the present invention provides a process for imaging a surface of a specimen with an imaging system that employs a BD objective having a darkfield channel and a bright field channel, the BD objective having a circumference, the process including the steps of: obliquely illuminating the specimen through the darkfield channel with a first arced illuminating light that obliquely illuminates the specimen through a first arc of the circumference, said first arced illuminating light reflecting off of the surface of the specimen; recording a first image of the specimen from the first arced illuminating light reflecting off the surface of the specimen; and generating a 3D topography of the specimen by processing the first image through a topographical imaging technique. 
     In a second embodiment, the present invention provides an imaging system as in any of the forgoing embodiments, wherein the first arc is from 1 degree or more to 180 degrees or less. 
     In a third embodiment the present invention provides an imaging system as in any of the forgoing embodiments, wherein the first arc is from 2 degrees or more to 5 degrees or less. 
     In a fourth embodiment, the present invention provides an imaging system as in any of the forgoing embodiments, further including the step of: obliquely illuminating the specimen through the darkfield channel with a second arced illuminating light that obliquely illuminates the specimen through a second arc of the circumference different from said first arc, said second arced illuminating light reflecting off of the surface of the specimen; and recording a second image of the specimen from the second arced illuminating light reflecting off the surface of the specimen, wherein said step of generating a 3D topography includes processing the second image through a topographical imaging technique. 
     In a fifth embodiment, the present invention provides an imaging system as in any of the forgoing embodiments, wherein all said obliquely illuminating steps include: providing a light barrier in the darkfield channel, the light barrier having a body that does not permit the passage of light therethrough, and a darkfield opening in the body that does permit the passage of light therethrough, and delivering illuminating light into the darkfield channel to the light barrier and through the darkfield opening to provide the arced illuminating light that obliquely illuminates the specimen. 
     In a sixth embodiment, the present invention provides an imaging system as in any of the forgoing embodiments, including a processor controls the oblique illumination of any said oblique illumination step and controlling any said image recording step. 
     In a seventh embodiment, the present invention provides an imaging system as in any of the forgoing embodiments, wherein the processor controls said step of generating a 3D topography. 
     In an eighth embodiment, the present invention provides an imaging system as in any of the forgoing embodiments, including the step of: orthogonally illuminating the specimen through the brightfield channel with brightfield illuminating light, said brightfield illuminating light reflecting off of the surface of the specimen; and recording a third image of the specimen from the brightfield illuminating light reflected off the surface of the specimen, wherein said step of generating a 3D topography includes processing the third image through a topographical imaging technique. 
     In a ninth embodiment, the present invention provides an imaging system as in any of the forgoing embodiments, wherein the topographical imaging technique is selected from shape from shading techniques, photometric stereo techniques, and Fourier ptychography modulation techniques. 
     In a tenth embodiment, the present invention provides an improvement to an imaging apparatus for imaging a surface of a specimen, the imaging apparatus employing a BD objective having a darkfield channel and a bright field channel, the BD objective having a circumference. The improvement includes placing a light barrier in the darkfield channel, the light barrier having a body that does not permit the passage of light therethrough, and a darkfield opening in the body that does permit the passage of light therethrough, such that the body blocks illuminating light traveling through the darkfield channel toward the specimen. The opening defines a passage for the illuminating light traveling through the darkfield channel toward the specimen, and thus defines arced illuminating light that obliquely illuminates the specimen through the darkfield channel from a discrete direction through only an arc of the circumference. 
     In an eleventh embodiment, the present invention provides an imaging apparatus as in any of the forgoing embodiments, wherein said arc is from 1 degree or more to 180 degrees or less. 
     In a twelfth embodiment, the present invention provides an imaging apparatus as in any of the forgoing embodiments, wherein said arc is from 2 degrees or more to 5 degrees or less. 
     In a thirteenth embodiment, the present invention provides an imaging apparatus as in any of the forgoing embodiments, further comprising a processor employing topographical imaging techniques on images taken by said imaging apparatus. 
     In a fourteenth embodiment, the present invention provides an imaging apparatus as in any of the forgoing embodiments, wherein the light barrier rotates so as to permit the placement of said opening at variable positions about said circumference. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic representation of a prior art process and apparatus for oblique illumination of a specimen for recording by a camera; 
         FIG.  2    is a schematic representation of a prior art brightfield/darkfield microscope, shown in brightfield imaging mode; 
         FIG.  3    is a schematic representation of a prior art brightfield/darkfield microscope, shown in darkfiled imaging mode; 
         FIG.  4    is a schematic representation of a brightfield/darkfield microscope in accordance with this invention, shown in brightfield imaging mode; 
         FIG.  5    is a schematic representation of a brightfield/darkfield microscope in accordance with this invention, shown in darkfield imaging mode; 
         FIG.  6    is a top plan view of an embodiment of a light barrier of this invention; 
         FIG.  7    is a side view of an embodiment of a light barrier of this invention; 
         FIG.  8 A  is a schematic representation of another embodiment of a light barrier of this invention, showing a plug unit providing multiple plugs to selectively cover and uncover two openings therein, with the plug moved to uncover the opening on the left and cover the opening on the right; 
         FIG.  8 B  is a schematic representation of the embodiment of a light barrier of  FIG.  8 A , but with the plug moved to uncover the opening on the right and cover the opening on the left; 
         FIG.  9 A  is a schematic representation of another embodiment of a light barrier of this invention, showing a body having multiple openings therein, each with its own separately actuated plug, actuated to either open or close its associated opening; and 
         FIG.  9 B  is a schematic representation of the light barrier embodiment of  FIG.  9 A , but shown with a different opening opened by movement of an associated plug. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     The present invention modifies a standard BD microscope or other instrument using a BD objective so that in brightfield the BD objective transmits light normally and as described above. In darkfield, the light transmitted through the darkfield channel is limited so that the darkfield illumination is not through the entire 360 degree circumference of the BD objective but rather through only a portion of the circumference. 
     With reference to  FIGS.  4  and  5    a microscope employing brightfield and darkfield functionality in accordance with this invention is shown and designated by the numeral  110 . In this embodiment the microscope  110  is equipped with a camera  112 . Oculars may also be present, such that 112 is to broadly represent oculars and/or a camera. Although the following description will refer to a reflected light microscope, similar techniques apply to transmitted light microscopes or other instruments using BD objectives. The systems generally consist of a light source  114  providing light  124 , a vertical illuminator  116  (light guide), a brightfield/darkfield (BD) switch  118  and a BD objective  120 . As in a standard BD objective  20 , two channels are provided to guide the light to the specimen  1 . The light  124  is directed to a mirror  125  that reflects the light  124  toward the specimen  1  downwardly through the vertical illuminator  116 , the nosepiece  128 , and BD objective  120 . 
     The BD switch  118 , as schematically shown, serves to limit the light  124  to pass either into a brightfield channel  122  ( FIG.  4   ) or darkfield channel  126  ( FIG.  5   ) separated by a shield wall  121 . With the BD switch  118  in a bright field position as in  FIG.  4   , the light  124  is limited to a beam that is reflected off of the mirror  125  as illuminating light  124 ′ to enter the brightfield channel  122 , which directs the illuminating light  124 ′ through the BD objective  120  toward the surface S of the specimen  1  at an angle perpendicular (90 degrees) to the plane of the specimen  1  and allows the reflected light  130  to pass to the oculars or camera  112 . As seen in  FIG.  5 A , when the BD switch  118  is in a darkfield position the light  124  is limited to an annular beam that is reflected off of the mirror  125  to enter the darkfield channel  126 , which is an annular channel directing light coming therethrough toward the specimen at an angle less than 90 degrees and typically 25 to 75 degrees. 
     In some embodiments, the darkfield channel  126  directs illuminating light toward the specimen at an angle less than 90 degrees, in other embodiments, less than 80 degrees, in other embodiments, less than 70 degrees, in other embodiments, less than 80 degrees, in other embodiments, less than 70 degrees, in other embodiments, less than 60 degrees, in other embodiments, less than 50 degrees, in other embodiments, less than 40 degrees, and, in other embodiments, less than 30 degrees. In some embodiments, the darkfield channel  126  directs illuminating light toward the specimen at an angle greater than 20 degrees, in other embodiments, greater than 30 degrees, in other embodiments, greater than 40 degrees, and in other embodiments, greater than 50 degrees. 
     The distance between the distal end of the objective and the specimen is known as the working distance (see  FIG.  5 A ). In some embodiments, the working distance is from 0.05 mm or more to 40 mm or less. In some embodiments, the working distance is from 0.7 mm or more to 30 mm or less, and, in other embodiments, from 1 mm or more to 25 mm or less mm. In some embodiments, the working distance is 10 mm or less, in other embodiments, 5 mm or less, in other embodiments, 3 mm or less, in other embodiment, 2 mm or less, in other embodiments, 1.5 mm or less and, in other embodiments, 1 mm or less. 
     In some embodiments, the field of view of the BD objective  20  is less than 10 mm. In some embodiments, the field of view of the BD objective is less than 5 mm, in other embodiments, less than 2 mm, in other embodiments, less than 1 mm, in other embodiments, less than 500 μm, in other embodiments, less than 200 μm, in other embodiments, less than 100 μm, in other embodiments, less than 50 μm. 
     When viewing a microscopic specimen at, for example, a size of less than 10 μm, the distance of the microscope objective is often less than 5 mm from the surface of the specimen depending on the working distance of the objective. For example a typical working distance, WD, of a 50× objective is less than 2 mm and, for a 100× objective, is typically 1 mm or less. The physical outside diameter of an objective is typically between 20 and 50 mm. By way of example, with a 20 mm diameter specimen and 5 mm WD, the angle of the light projecting off the surface would be approximately 26 degrees. In the more likely case of a WD of 1 mm the angle of light projecting on the specimen would be 6 degrees. Photometric stereo optimally uses illumination at 30 to 80 degrees. In most microscope use cases, then, it would not be possible to determine topographies of specimens using photometric stereo or other imaging techniques requiring oblique lighting due to the low incident of oblique illumination. 
     The present invention uses the darkfield channel of the objective to direct the light onto the surface of the specimen. This allows the light source to be much closer to the vertical axis of illumination. In the above standard illumination the light had to be outside the radius of the objective. The use of the darkfield channel allows the light source to be within the radius of the specimen and essentially be adjacent to the light path. The distance from the vertical axis can now be approximately equal to the WD allowing an angle of illumination to be 45 degrees. This angle may vary slightly with the design of the objective but is typically in the range of 25 to 75 degrees. Thus, the imaging systems according to this invention achieve oblique illumination angles despite the very tight working distances required in many applications. The method taught herein can be used to determine topographies in microscopy applications that could not be achieved by standard methods. 
     It can be seen in  FIG.  4    that the light path in brightfield (illuminating light  124 ′) is projected through the center of the nosepiece  128  and through the brightfield channel  122  of the BD objective  120 . The reflected light  130  is reflected back through the brightfield channel  122 , through the nosepiece  128  and tube lens  132  and is affected by any oculars and/or captured by a camera  112 . It is seen here that the illumination light  124 ′ in brightfield is at 90 degrees to the general resting plane of the specimen  1  and the reflected light  130  that is measured travels parallel to the illumination light  124 ′ but in an opposite direction.  FIG.  4 B  shows a schematic cross sectional view of the specimen  1  and the brightfield illumination light  124 ′ that is projected onto the specimen  1 . The projected brightfield illumination light  124 ′ illuminates the entire field of view. 
       FIG.  5    shows the microscope  110  in darkfield mode. Here the light  124  is blocked by the darkfield switch  118  so that no light passes through the brightfield channel  122  and is instead directed to pass through the darkfield channel  126  as illuminating light  124 ″. As with the embodiment of  FIG.  3    of the prior art, this blocking of the light  124  produces an annular beam (or, in other terms, a hollow cylinder or annular cylinder) of light reflected off of mirror  125  and projected toward the specimen  1 . However, in distinction over the prior art, the entirety of that annular beam of illuminating light  124 ″ does not reach the specimen at an oblique angle determined by the design of the objective  120  and wall of the darkfield channel  126 . Instead, only a portion of the light at from less than the entire 360 degree circumference of the BD objective is delivered down the darkfield channel to reach the specimen, as arced illuminating light  124 *. This arced illuminating light  124 *still illuminates the entire field of view, but, rather than doing so from the entire 360 degree circumference of the objective, does so from a discrete direction of limited degrees (or minutes of arc), i.e., from only a portion of the circumference. In other embodiments, the darkfield projection of arced illuminating light  124 *illuminates the entire field of view from a discrete direction of limited degrees (or minutes of arc), and the darkfield illumination is devoid of any additional illumination that would interfere with the surface shading caused by the obliquely introduced arced illuminating light  124 *. This is accomplished by positioning a light barrier  140  in the path of the illuminating light  124 ″. 
     In some embodiments, such as that shown in  FIG.  6   , the light barrier  140  has a body  142  with a darkfield opening  144  therein so that unwanted illuminating light  124 ″ is blocked and a desired arced illuminating light  124 *passes through the opening to be projected toward the specimen  1  through less that the entire 360 degree circumference practiced in the prior art. The body  142  of the light barrier  140  does not let illuminating light  124 ″ pass through, while the darkfield opening  144  simply defines an open path for the illuminating light  124 ″, which is then defined as arced illuminating light  124 *after being limited by passage through the light barrier opening  144 . The light barrier  140  also defines a brightfield opening  146  for the brightfield channel  122  and illuminating light  124 ′, as well as all reflected light whether from brightfield or darkfield illumination. 
       FIG.  5    shows a schematic cross sectional view of the specimen  1  and the arced of illumination light  124 *that is projected onto the specimen  1 . The projected arced illuminating light  124 *illuminates the entire field of view, but at an oblique angle and from a discrete position. With reference back to  FIG.  5   , it is seen that only the left side of the darkfield channel  126  is shown having arced illuminating light  124 *traveling therethrough, as that reflects the location of the darkfield opening  144  in the light barrier  140 . The illumination thus comes from that direction and shines at an oblique angle across the field of view. 
     In some embodiments, the light barrier  140  is secured in the nosepiece  128 . In other embodiments, the light barrier  140  is secured in the vertical illuminator  116 . It will be appreciated that the light barrier  140  and concepts related herein can be implemented in other ways as well, such as in the BD objective  120 . 
     In some embodiments, such as that in  FIG.  5 A , the light barrier  140  is mounted in the nosepiece  128 , and is secured to a bearing housing  148  that is secured to the nosepiece  128  without intruding upon the darkfield channel  126  and the light traveling therethrough, i.e., it is desirable that the light be unaffected by the encroachment of the bearing housing  148  in the darkfield channel  126 . The bearing housing  148  includes bearings  150  permitting the rotation of the light barrier  140  to position the darkfield opening  144  at a desired position about the circumference of the BD objective  120 , thus defining the arced illuminating light  124 *projected toward the specimen  1 . The rotation is visually represented in  FIG.  6    by the double-headed arrow A. 
     In some embodiments, a driver  152  serves to rotate the light barrier  140  to place the darkfield opening  144  in a desired position. In some embodiments, the driver  152  is a motor that interacts with the light barrier  140  through a belt  154 , but gearing and other interactions can be employed. It will be appreciated that the driver  152  could also be a manually manipulated driver, such as a wheel or knob geared or belted or otherwise associated with the light barrier  140  to rotate it. 
     In some embodiments, a sensor  156  is mounted to the microscope  110  at an appropriate location to identify a zero position for the light barrier  140 . The sensor  156  on the microscope  110  will identify the zero position when the sensor aligns with a reference element  158  on the light barrier  140 . The zero position establishes a known starting position for the light barrier  140  and more particularly the darkfield opening  144  therein, and this known starting position is used for indexing imaging so that each image recorded by the camera  112  has associated with it a known lighting position relative to the specimen. 
     The camera can be any camera useful in imaging systems and specifically used for imaging specimens intended for topographical analysis. These will often employ a CCD or CMOS sensors. 
     It will be appreciated that the control of all elements of the microscope can be implemented in known ways, typically with some or all controls being implemented through various hardware and/or software and/or firmware, all represented and designated herein as a processor  170 . One or more processors can be used and a myriad of hardware such as joysticks, relays, switches among others. The processor  170  can record the images taken from the camera and be programmed with the appropriate algorithms to analyze one or more images and recreate a topographical image of the portion of the specimen imaged. 
     For the topographical imaging techniques implemented by the processor  170 , it is typically necessary or at least helpful to have associated with a particular image the positioning of the incoming oblique light relative to the circumference of the objective. The shading created by the oblique light is dependent upon the position of the incoming light relative to the circumference, and establishing a zero position facilitates the automation of processes for taking multiple images and calculating topographies based upon those multiple images. Once a zero position is established, the processor and associate hardware and/or firmware and/or software can carry out an automated process of providing oblique illumination from a first position about the circumference, taking an image and collecting image data and associating it with the illumination from the first position, then providing oblique illumination from a second position about the circumference, taking an image and collecting image data and associating it with the illumination from the second position positional data; repeating the process as desired to obtain a desired number of imaging data sets from a desired number of illuminating positions. In some embodiments, the sensor  156  is an optical proximity sensor, wherein a light shined by the sensor  156  is blocked by a reference element  158  on the light barrier  140  when the sensor  156  and reference element  158  are aligned. In other embodiments, the sensor  156  magnetic position sensor, working by sensing a magnet serving as a reference element. Mechanical limit switches and Hall effect sensors are other examples. 
     In some embodiments, such as seen in  FIG.  7    the light barrier  140  has a spool-like shape with two opposed walls  160 ,  162 , with a separating sidewall  164 . A belt such as belt  154  (or gearing or other drive mechanisms) can engage the sidewall  164  to drive the light barrier  140 . 
     In some embodiments, such as that shown in  FIGS.  8 A and  8 B , a light barrier  240  has multiple openings represented at darkfield openings  244   a  and  244   b , but any number of openings can be employed taking into account obvious size constraints. The darkfield openings  244   a ,  244   b  join to the perimeter of the of the body  242  of the light barrier so that moveable plugs  245   a  and  245   b  can be employed to selectively block a respective darkfield opening  244   a ,  244   b . In the embodiment of  FIG.  8 A  the darkfield openings  244   a  and  244   b  are opposite one another, and the moveable plugs  245   a  and  245   b  are joined, forming a plug unit  247  such that when the movable plug  245   b  blocks darkfield opening  244   b , the movable plug  245   a  is removed from darkfield opening  244   a  (as in FIG.  8 A) and vice versa (as in  FIG.  8 B ). This allows light to pass through a desired darkfield opening  244   a ,  244   b , providing the arced illuminating light  124 *, and also allows for quick switching of the positioning of the arced illuminating light  124 *, by switching the positioning of the plug unit  247 . It can be appreciated that multiple slits and moveable plugs may be employed, and that each plug could have its own control as opposed to the common control established in the present exemplary embodiment of  FIGS.  8 A and  8 B . 
     In another embodiment, such as that shown in  FIGS.  9 A and  9 B , a light barrier  340  has six darkfield openings  344   a ,  344   b ,  344   c ,  344   d ,  344   e , and  344   f  spaced at 60 degrees apart around the circumference of the body  242  of the light barrier. Any number and position desired could alternatively be employed. The darkfield openings  344   a - f  join to the perimeter of the of the body  342  of the light barrier  340  so that moveable plugs  345   a ,  345   b ,  345   c ,  345   d ,  345   e , and  345   f  can be employed to selectively block a respective darkfield opening  344   a - f . In this embodiment, the movable plugs  345   a - f  each can be actuated independently to block a respective opening. To visually represent the selective movement, plug  345   a  is shown removed from its opening  344   a  in  FIG.  9 A , with all other plugs seated to block their respective openings, while, in  FIG.  9 B , plug  345   b  is shown removed from its opening  344   b , with all other plugs seated to block their respective openings. 
     In some embodiments, such plugs can be moved by linear actuators, solenoid, eccentric, or any other known method of motion control. Linear actuators  349   a ,  349   b ,  349   c ,  349   d ,  349   f  are employed. 
     In any embodiment, the size of the arced illuminating light  124 *may vary as desired based on results achieved and results desired. This entails a choice of the sizing of the darkfield opening  144  (or  244   a ,  244   b ) In some embodiments, the arced illuminating light  124 *ranges from 1 degree or more to 180 degrees or less (60 or more to 10,800 or less minutes of arc). In other embodiments, the arced illuminating light  124 *ranges from 45 degrees or more to 120 degrees or less (2,700 or more to 7,200 or less minutes of arc), in other embodiments, from 30 degrees or more to 45 degrees or less (1,800 or more to 2,700 or less minutes of arc), in other embodiments, from 10 degrees or more to 30 degrees or less (600 or more to 1,800 or less minutes of arc), in other embodiments, from 5 degrees or more to 10 degrees or less (300 or more to 600 or less minutes of arc), and, in other embodiments, from 2 degrees or more to 5 degrees or less (120 or more to 300 or less minutes of arc). The size of the arced illuminating light is dependent upon the size of the darkfield opening  144  relative to the arc of the annular darkfield channel  126  with which it communicates. 
     Another aspect of the invention is to use the oblique lighting BD microscopes described above to create a 3D topography by taking multiple images of a specimen  1  obliquely illuminated with arced illuminating light  124 *from different positions about the 360 circumference of the BD objective  120  using the light barrier  140 , and processing the data from those images in accordance with topographical imaging techniques. The choice of topographical imaging technique is not limited to any particular technique, but, in some embodiments, is selected from shape from shading techniques, photometric stereo techniques, and Fourier ptychography modulation techniques. The processor  170  receives the imaging data from the camera  112  and is programmed through one or more topographical imaging techniques to generate data used to create a topographical representation of the area of the specimen  1  that was imaged. This is represented at output  172 . Using known techniques such as shape from shading algorithms, photometric stereo algorithms, and Fourier ptychography modulation algorithms with the know size, number, and position of the arced illuminating light, the angle of the oblique illumination, a 3D topography can be generated. 
     In some topographical imaging techniques such as shape from shading (SFS), a single obliquely illuminated specimen image generated from arced illuminating light at a single position can be sufficient to generate topographical data and images. In other topographical imaging techniques such as photometric stereo, at least two obliquely illuminated specimen images generated from arced illuminating light at two positions can be sufficient to generate topographical data and images. In other topographical imaging techniques such as Fourier ptychography modulation, at least two obliquely illuminated specimen images generated from arced illuminating light at two positions plus an image from brightfield illumination is needed to generate topographical data, and 10 or more obliquely illuminated specimen images will provide even better data for Fourier ptychography modulation. The existing algorithms and algorithms yet to be developed in this field will provide the ordinarily skilled artisan with the knowledge as to the number of type of images needed. The present invention does not invent or alter the algorithms but rather provides methods and apparatus that allows for their implementation. 
     It will be appreciated that, in some embodiments, the processor  170  (which again, represents any number of appropriate processors, hardware, software, firmware), automates the control of the light barrier, the illumination, the image collection and generation of topographical data and/or images. 
     Thus this invention provides a process for imaging a specimen with an imaging system that employs a BD objective having a darkfield channel and a bright field channel and defining a circumference about the specimen to be imaged. The process includes obliquely illuminating the specimen through the darkfield channel with a first arced illuminating light that obliquely illuminates the specimen through a first arc of the circumference, and taking a first image providing a first image data set of the specimen from the first arced illuminating light reflected off the surface of the specimen. In some embodiments, the process further includes generating a 3D topography of the specimen by processing the first data through a topographical imaging technique. In some embodiments, the arc sizes are selected as described above for the arced illuminating light  124 *. 
     In other embodiments, the process includes, obliquely illuminating the specimen through the darkfield channel with a second arced illuminating light that obliquely illuminates the specimen through a second arc of the circumference of the BD objective different from said first arc, and taking a second image providing a second image data set of the specimen from the second arced of illuminating light reflected off the surface of the specimen. In other embodiments, the process further includes illuminating the specimen through the brightfield channel with brightfield illuminating light, and taking a third image of the specimen from the brightfield illuminating light reflected off the surface of the specimen. In other embodiments, the process further includes repeating said obliquely illuminating step and said taking an image step for any n number of images producing n number of image data sets. In other embodiments, n is from 2 to 12, in other embodiments, from 3 to 9, in other embodiments, from 4 to 7, and in other embodiments, 6. 
     In other embodiments, said obliquely illuminating steps include providing a light barrier in the darkfield channel, the light barrier having a body that does not permit the passage of light therethrough, and a darkfield opening in the body that does permit the passage of light therethrough, and delivering illuminating light into the darkfield channel to the light barrier and through the darkfield opening to provide the arced illuminating light that obliquely illuminates the specimen. 
     In other embodiments, the process includes a processor and associate hardware and/or firmware and/or software controlling the oblique illumination of any said oblique illumination step and controlling any said image taking step. In other embodiment a same or different processor and associate hardware and/or firmware and/or software controls said step of generating a 3D topography. 
     In some embodiments, the light barrier  140  may remain stationary to allow an image to be captured from a single position. In some embodiments, the light barrier  140  may be rotated to allow multiple images to be captured at known, specific positions of the darkfield opening  144 . In some embodiments, the light barrier (such as light barrier  240 ) will have multiple openings and plugs, with the plugs sequentially manipulated to open a pathway for the arced illuminating light  124 *. In some embodiments, the positions are generally symmetrical such as two images captured 180 degrees apart; three images captured at 120 degrees apart, six images captured at 60 degrees apart, and so on. It will be appreciated that these measurements would have the mid-point of each arc of each arced illumination as a reference point, with the measurement made from mid-point to mid-point. It should be appreciated that the invention allows one or more images to be captured using the darkfield oblique light and still allows a brightfield image to be captured at 90 degrees. 
     In light of the foregoing, it should be appreciated that the present invention significantly advances the art by providing an imaging system and topographical imaging 
     method that is structurally and functionally improved in a number of ways. While particular embodiments of the invention have been disclosed in detail herein, it should be appreciated that the invention is not limited thereto or thereby inasmuch as variations on the invention herein will be readily appreciated by those of ordinary skill in the art. The 
     scope of the invention shall be appreciated from the claims that follow.