Abstract:
Techniques and systems for implementing fast, fixed-focal-length lens imaging systems for molecular biology or genetics applications are provided. In particular, techniques and structures are provided for allowing for precise alignment of the optical and imaging components of such imaging systems during assembly with a minimal amount of adjustment.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of priority under 35 U.S.C. §119(e) from pending U.S. Provisional Patent Application Nos. 62/307,214, filed on Mar. 11, 2016, which is hereby incorporated herein by reference in its entirety for all purposes. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates generally to imaging systems for molecular biology or genetics applications and, in particular, to imaging systems utilizing high-speed lenses with large apertures suitable for use in imaging gels or blots. 
       BACKGROUND 
       [0003]    Imaging systems for molecular biology and genetics applications typically provide an optical magnification system, e.g., one or more lenses, that produce an image on a focal plane that is generally aligned with the imaging plane of an imaging sensor. Such imaging sensors are typically sold as self-contained camera units by their respective manufacturers, with the imaging sensor, associated electronics, and cooling systems housed within a housing. The housings typically have a threaded lens mounting feature, and the center of the imaging sensor is generally centered on the center of the threaded lens mount and positioned such that the focal plane of lenses that may be connected to the lens mount may generally align with the imaging plate of the sensor. One or more mounting features are typically located on the exterior surface of the housing to allow the camera unit to be mounted to, for example, a tripod or other support structure. 
         [0004]    Such imaging systems are typically configured to receive a sample, e.g., a gel, blot, or other generally planar specimen, on a sample stage. The lens/camera unit system is generally configured so as to focus the lens on the sample stage to capture images of the sample. 
       SUMMARY 
       [0005]    The present inventors have conceived of an imaging system for molecular biology or genetic analyses that utilizes a fixed-focal-length lens with a large aperture, e.g., having F-numbers of less than or equal to 1.4 (meaning that such lenses have a focal length that is less than or equal to the effective aperture of the lens), to capture images, including under very low lighting conditions. In the course of doing so, the present inventors determined that commercially available camera units required extensive post-installation adjustment in order to correct relatively minor misalignments that would typically be of little or no consequence in zoom lens imaging systems or other smaller-aperture camera systems. Such smaller-aperture imaging systems have a large depth of field, and thus minor misalignments between the lens center axis, the imaging sensor imaging plane, and the sample stage are unnoticeable since the large depth-of-field can absorb any such errors. The present inventors have determined that even small misalignments between the lens center axis, the imaging sensor imaging plane, and the sample stage may produce unacceptable image distortions in a fast-lens imaging system due to the very shallow depth of field of such lenses. Accordingly, the present inventors have conceived of a number of techniques and apparatuses that may be used in such fast-lens imaging systems to provide high-precision placement of optical and image-capture components requiring a minimal amount of post-installation adjustment in order to properly focus the imaging system. 
         [0006]    In molecular biology and genetic analysis applications, a biological sample may be subjected to any of several techniques in which the composition of the sample is reflected in some form of generally planar media, e.g., gels or blots. For example, the molecules in a particular sample may be separated within a gel using a technique such as electrophoresis. By applying an electric field, the molecules of a sample may be caused to migrate through a planar gel; the larger/heavier molecules will move through the gel slower than the smaller/lighter molecules, resulting in a size-based spatial distribution of molecules across the gel. Other factors, such as molecular charge, may also affect the movement of molecules through the gel and thus the spatial distribution of the molecules. Once distributed, molecules may optionally be transferred to a blotting membrane or paper to form a blot. The spatially distributed molecules may then be labeled by adding a labelling agent/compound or agents/compounds that bind to the molecules of interest, and the resulting labeled gel or blot may be imaged to obtain a quantified estimate of the amounts of various molecules that are present in the sample. In some instances, this quantification may involve measuring the amount of light in particular wavelengths that is emitted by the labelled molecules—such light may be due to fluorescence, in which the gel or blot is exposed to light of a particular wavelength that stimulates photoemissions from the labelling compound, bioluminescence, in which the labelling compound may be a bioluminescent compound, and chemiluminescence, in which the labelling compound may produce light during a chemical reaction with the target molecules. The present inventors developed an imaging system that may be used to obtain images of gels or blots, such as those described above, in order to quantify the molecular makeup of such samples; the imaging systems in question may utilize a high-speed lens, as discussed below, in order to adequately capture the emitted luminescence in luminescence-based approachs (the amount of luminescence in chemiluminescence-based approaches may be quite small, e.g., invisible to the human eye). Such imaging systems may also be used for non-luminescent approaches, e.g., color staining or similar techniques. 
         [0007]    In some implementations, an imaging system for molecular biology or genetic analysis may be provided. The imaging system may include a linear translation mechanism including one or more linear guides, a carriage configured to translate along a first axis along the linear guides, and a first mechanical interface feature located on the carriage. The imaging system may also include a camera unit that includes a camera barrel. The camera barrel, in turn may have an interior volume within the camera barrel, a lens mounting feature having a lens mount plane, and a second mechanical interface feature located on the exterior of the camera unit. The camera barrel may also include an imaging sensor that is located within the interior volume of the camera barrel. In such implementations, the imaging sensor may have a plurality of light-sensitive pixels arranged in a planar array that is parallel to the lens mount plane, the first mechanical interface feature and the second mechanical interface feature may interact so as to fix the camera unit in place relative to the carriage such that the first axis is perpendicular to the planar array of light-sensitive pixels, and there may be no positional adjustment mechanisms between the carriage and the camera unit. 
         [0008]    In some such implementations, the camera unit may include a carriage-facing surface that faces towards the carriage, as well as a first raised boss and a second raised boss. The first raised boss and the second raised boss may protrude from the carriage-facing surface, and the first raised boss and the second raised boss may form part of the second mechanical interface feature. In such implementations, the first raised boss and the second raised boss may both be in compressive contact with the carriage and the first raised boss and the second raised boss may be machined so as to have a tolerance of ±0.02 degrees with respect to an axis normal to the planar array of light-sensitive pixels and a tolerance of ±0.03 mm of flatness with respect to one another. 
         [0009]    In some further or alternative implementations, the imaging system may further include a fixed-focal-length lens, having an aperture with an f-number of at least 1.4 or lower, which may be mounted to the lens mounting feature. 
         [0010]    In some further or alternative implementations, the imaging system may include at least two alignment shafts. In such implementations, the first mechanical interface feature may include at least two first alignment holes, each first alignment hole sized to receive a corresponding alignment shaft, and the second mechanical interface feature may include at least two second alignment holes, each second alignment hole corresponding in location to one of the first alignment holes and sized to receive the corresponding alignment shaft for the corresponding first alignment hole. 
         [0011]    In some further such implementations, the alignment shafts may be in the form of shoulder screws with a threaded portion and a shoulder portion having a larger diameter than the threaded portion, the second alignment holes may be threaded holes sized to receive the threaded portion of the corresponding alignment shaft, and the first alignment holes may be sized to have the same diameter as the shoulder portion of the corresponding alignment shaft (or a diameter that is between 0 and 0.0005 inches larger than a diameter of the shoulder portion of the corresponding alignment shaft). 
         [0012]    In some further or alternative implementations, the imaging system may include a mounting fixture. In such implementations, the camera barrel may have a cylindrical outer surface with a center axis, and the cylindrical outer surface may include a plurality of spaced-apart circumferential grooves that extend around the outer circumference of the camera barrel. In such implementations, the camera barrel may also include a mounting fixture surface that is parallel to the center axis and that defines a chord of the cylindrical outer surface, the mounting fixture surface may include at least two first fixture alignment features, the mounting fixture may include at least two second fixture alignment features as well as the second mechanical interface feature, the first fixture alignment features and the second fixture alignment features may interlock so as to fix the camera barrel in place relative to the mounting fixture, and there may be no positional adjustment mechanisms between the camera barrel and the mounting fixture. 
         [0013]    In some further such implementations, the imaging system may further include a seal plate. In such implementations, the imaging sensor may be mounted to an imaging printed circuit board (PCB) that includes a plurality of electrically conductive pins that protrude from a side of the imaging PCB on the opposite side of the imaging PCB from the imaging sensor, the seal plate may have one or more through-holes, and each electrically conductive pin may protrude through one of the through-holes. The camera barrel may also include a ledge surface within the interior volume on which the seal plate rests; the ledge surface may be perpendicular to the mounting fixture surface to within a tolerance of ±0.25 degrees. 
         [0014]    In some further or alternative such implementations, the mounting fixture may further include a carriage-facing surface that faces towards the carriage, a first raised boss and a second raised boss, the first raised boss and the second raised boss protruding from the carriage-facing surface, and a barrel-facing surface that faces towards the camera barrel. In such implementations, the first raised boss and the second raised boss may form part of the second mechanical interface feature and both be in compressive contact with the carriage. In such implementations, the first raised boss and the second raised boss may be machined so as to have a tolerance of ±0.5 degrees with respect to the barrel-facing surface and a tolerance of ±0.5 degrees with respect to one another. 
         [0015]    In some further or alternative such implementations, the cylindrical outer surface may include a plurality of slots, each slot extending along a direction having a component parallel to the center axis, having a depth within ±6% of the average depth of the circumferential grooves, and intersecting with each of the circumferential grooves in the plurality of circumferential grooves. In some such implementations, each slot may extend along a direction parallel to the center axis. 
         [0016]    In some further or alternative implementations, the lens mounting feature may be part of the camera barrel. 
         [0017]    In some additional or alternative implementations, the lens mounting feature may be located in a plate that is located adjacent to the camera barrel, three adjustment screws may be located such that a threaded portion of each adjustment screw is threaded into a corresponding threaded hole located in either the plate or in the camera barrel and a bearing surface of each adjustment screw is in contact with a bearing surface of the other of the plate or the camera barrel, and the plate may be held against the camera barrel by a compression mechanism such that the adjustment screws are compressively loaded. 
         [0018]    In some additional or alternative implementations, the imaging system may further include an enclosure defining a plenum volume. In such implementations, the camera unit may be located within the plenum volume, the enclosure may include a first port and a second port, and the camera unit may be interposed between the first port and the second port. In such implementations, the first port may be configured to connect the plenum volume with a convective cooling system source, and the second port may be configured to connect the plenum with a convective cooling system exhaust. 
         [0019]    In some such implementations, the imaging system may also include a flexible cooling duct fluidically connected with the first port and a flexible exhaust duct fluidically connected with the second port. 
         [0020]    In some alternative or further such implementations, the enclosure may have a side with a plurality of U-shaped slots milled in directions perpendicular to an edge of the side, a plurality of U-shaped bosses may exist proximate to the first mechanical interface feature and the second mechanical interface feature, and the U-shaped bosses and the U-shaped slots may intermesh to locate the enclosure relative to the camera unit. 
         [0021]    In some alternative or further such implementations, the imaging system may further include a reflector assembly including a mirror having a reflective surface arranged at 45°±0.5° to the first axis. 
         [0022]    In some alternative or further such implementations, the imaging system may also include a sample stage having a planar sample surface, the sample stage positioned beneath the reflector assembly and oriented such that the planar sample surface is parallel to the first axis. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The included drawings are for illustrative purposes and serve only to provide examples of possible structures for the concepts disclosed herein. These drawings in no way limit any changes in form and detail that may be made by one skilled in the art without departing from the spirit and scope of the disclosed embodiments. 
           [0024]      FIG. 1  depicts an off-angle view of an example of an imaging system according to some implementations discussed herein. 
           [0025]      FIG. 2  depicts a side view of the imaging system of  FIG. 1 . 
           [0026]      FIGS. 3, 4, and 5  depict simplified representations of an example linear translation mechanism. 
           [0027]      FIG. 6  depicts an isometric exploded view of a subportion of the imaging system of  FIG. 1 . 
           [0028]      FIG. 7  depicts an unexploded isometric view of the subportion of the imaging system of  FIG. 6 . 
           [0029]      FIG. 8  depicts an isometric view of an example camera unit according to some implementations discussed herein. 
           [0030]      FIG. 9  depicts another isometric view of the example camera unit of  FIG. 8 . 
           [0031]      FIG. 10  depicts a rear view of the example camera unit of  FIG. 8 . 
           [0032]      FIG. 11  depicts a front view of the example camera unit of  FIG. 8 . 
           [0033]      FIG. 12  depicts a top view of the example camera unit of  FIG. 8 . 
           [0034]      FIG. 13  depicts a side view of the example camera unit of  FIG. 8 . 
           [0035]      FIG. 14  depicts a section view of the example camera unit of  FIG. 8 . 
           [0036]      FIG. 15  depicts an isometric exploded view of the camera unit of  FIG. 8 . 
           [0037]      FIG. 16  depicts another isometric exploded view of the camera unit of  FIG. 8 . 
           [0038]      FIG. 17  depicts an isometric view of an example of a mounting fixture that may be used to precision-mount the example camera unit of  FIG. 8  within the imaging system of  FIG. 1 . 
           [0039]      FIG. 18  depicts another isometric view of the example mounting fixture of  FIG. 17 . 
           [0040]      FIG. 19  depicts a section view of the subportion of the imaging system shown in  FIG. 6 . 
           [0041]      FIG. 20  depicts another section view of the subportion of the imaging system shown in  FIG. 6 . 
       
    
    
       [0042]    Throughout the drawings, the same reference numerals and characters, or reference numbers sharing the same last two digits, unless otherwise stated or suggested by the text or Figures, are used to denote like features, elements, components, or portions of the illustrated embodiments. Moreover, while the concepts herein will now be described in detail with reference to the drawings, the description is done in connection with the illustrative embodiments. It is intended that changes and modifications can be made to the described embodiments without departing from the true scope and spirit of the disclosed subject matter, as defined by the appended claims. 
       DETAILED DESCRIPTION 
       [0043]    Specific exemplary embodiments of concepts discussed herein will now be described with reference to the accompanying drawings. These concepts may, however, be embodied in many different forms, and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the concepts disclosed herein to those skilled in the art. 
         [0044]    It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element, or intervening elements may be present; the term “coupled” may also refer to two elements that are coupled via a contiguous structure, e.g., a single, molded part may have a “tab” that is coupled with a “body.” Furthermore, “connected” or “coupled” as used herein may include wirelessly connected or coupled. It will be understood that although the terms “first” and “second” are used herein to describe various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another element. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. The symbol “/” is also used as a shorthand notation for “and/or”. 
         [0045]    As mentioned above, the present inventors have developed a fast-lens imaging system. As used herein, the term “fast lens” refers to lenses having a f-number less than or equal to 1.4, meaning that their focal lengths are less than or equal to the lens aperture diameter of such lenses. In their development, the present inventors determined that the typical imaging system paradigm, i.e., purchasing a stock camera unit with a CCD contained within a housing having a lens mount and then mounting that stock camera unit into the imaging system, resulted in an assembly requiring extensive post-installation adjustment of the camera unit in order to properly focus and calibrate the imaging system. As such, the present inventors determined that a new approach to camera unit design would be beneficial, as it would be possible to drastically decrease or, in some cases, completely eliminate camera unit alignment and/or positioning adjustment in such systems. 
         [0046]      FIG. 1  depicts an off-angle view of an example of an imaging system according to some implementations discussed herein. In  FIG. 1 , the imaging system  100  includes a number of components, including a sample stage  155  having a planar sample surface  156 , a reflector assembly  152  having a mirror  153  with a reflective surface  154  oriented at a 45° angle ±0.5° or ±0.25° with respect to the planar sample surface  156  and/or a first axis  104 , and an imaging subassembly that includes an enclosure  141  that contains a camera unit (not shown in  FIG. 1 ). The imaging subassembly may also include linear translation mechanism that may include a carriage  103  that is configured to translate linearly along the first axis  104 , e.g., by sliding along linear guides  102  (a second linear guide  102  is provided as well, although not visible in  FIG. 1  as it is located on the back side of imaging system  100 ). A linear actuator or drive may provide a mechanism for translating the carriage  103  along the first axis  104 . 
         [0047]      FIG. 2  depicts a side view of the imaging system of  FIG. 1 . As can be seen, there are also vertical guides  165  along which the linear guides  102  may be slid in order to raise or lower the linear guides  102 . A slotted track  167 , which may be oriented at an angle with respect to the first axis  104 , may engage with a roller  166  on the carriage  103  such that when the linear guides  102  are raised and lowered vertically, e.g., by a linear actuator or ball screw driven by a motor (not shown), the slotted track  167  causes the carriage  103  (and attached enclosure  141 , with a camera unit within) to translate along the linear guides  102  in a horizontal direction.  FIGS. 3, 4, and 5  depict simplified representations of an example linear translation mechanism (similar to that shown in  FIG. 2 ) showing such bi-axial translation (a ball screw actuator  173  may drive the horizontal linear guides up and down along a set of vertical guides; at the same time, a sloped slotted track may engage with a roller on the carriage that causes the carriage to translate to the right when the horizontal linear guides are lowered, and to translate to the left when the linear guides are raised). In this manner, the carriage  103  may be moved closer to the sample stage  155  and the reflector assembly  152  (which also moves with the linear guides  102 ) simultaneously using only one drive component. In other implementations, separate independent drives may be used to provide such bi-axial translation. In yet other implementations, single-axis translation mechanisms may be used to provide only uniaxial translation, e.g., as may be the case in an imaging system  100  that does not utilize a reflector assembly  152  but instead has a camera unit that is pointed directly at the sample stage  155 . 
         [0048]      FIG. 6  depicts an isometric exploded view of a subportion of the imaging system of  FIG. 1 .  FIG. 7  depicts an unexploded isometric view of the subportion of the imaging system of  FIG. 6 . As can be seen in  FIG. 6 , the enclosure  141  includes a camera unit  107 , a first port  144 , and a second port  145 . The camera unit  107  may be located within a plenum volume  143  of the enclosure  141 ; the enclosure  141  may also include an enclosure lid  142  that may close off one or more open faces of the enclosure  141  so as to create a generally enclosed volume within which the camera unit  107  may be housed. The first port  144  and the second port  145  may be used to route a cooling fluid, e.g., air, through the enclosure  141 . For example, the first port  144  may be connected with a convective cooling system source  146  (not shown, but flow from source is indicated in  FIG. 1  by arrow  146 ), e.g., a facility dry air source, an intake, a fan or blower unit (to push air through the enclosure), etc., by a flexible cooling duct  148  (shown in  FIG. 1 ) and the second port  145  may be connected with a convective cooling system exhaust, e.g., an outlet into the ambient environment, a fan or suction unit (to pull air through the enclosure  141 ), or other type of exhaust (flexible exhaust duct and exhaust system not shown, but generally similar to the cooling-related components discussed above). Cooling fluid that is flowed through the enclosure in this manner may flow around the camera unit  107 , where it may convectively cool the camera unit  107  before exiting the enclosure  141  via the second port  145 . 
         [0049]    The enclosure  141  may also optionally have features that allow the enclosure  141  to interface with features on the camera unit  107 , such as U-shaped slots  150  in a side  151  of the enclosure  141 . 
         [0050]    The camera unit  107  may include a camera barrel  108  and camera electronics  157 . The camera unit  107  may optionally also include a plate  137 , a window retainer  164  (which may hold a window, not separately indicated, in place), and a mounting fixture  127 . 
         [0051]      FIG. 8  depicts an isometric view of an example camera unit according to some implementations discussed herein.  FIG. 9  depicts another isometric view of the example camera unit of  FIG. 8 . As can be seen, the camera unit  107  includes a camera barrel  108  that has a cylindrical outer surface  124 . The cylindrical outer surface  124  may have a number of spaced-apart circumferential grooves  126  (in this case, there are more than 12 such grooves, although other implementations may have as few as 5 grooves or up to 30 grooves) that extend into it, as well as slots  136  (in this example, there are a total of 20 such slots, although other implementations may have as few as 4 slots or as many as 28 slots; the addition of such slots in the depicted design was found to increase the cooling rate such that there was a corresponding 20-25% drop in dark current, which directly impacts the level of noise in the imaging sensor; in low-lighting conditions, such performance improvements may result in significantly higher quality data). These grooves and slots may define a large number, e.g.,  ˜ 200, annular-sector shaped cooling fins that may facilitate convective cooling of the camera unit  107 . It is to be understood that while the slots  136  that are shown extend along a direction parallel to the center axis of the cylindrical outer surface, the slots  136  may alternatively extend along helical paths along the cylindrical outer surface  124 , much like the flutes of a drill bit, although the manufacturing cost of such an arrangement is likely higher. In some implementations, the depths of the slots  136  may be within ±6% of the depth of the circumferential grooves  126 . In addition to such features, the camera barrel  108  may also include a mounting fixture surface  128 , which may be machined so as to be a chord surface of the cylindrical outer surface  124 . The mounting fixture surface  128  may include a first fixture alignment feature  129 , e.g., two precision-machine holes for receiving locating pins on a mating part, that may be used to locate a mating part relative to the camera barrel  108  in a high-precision manner. The mounting fixture surface  128  may also form part of the first fixture alignment feature  129 , e.g., the mounting fixture surface  128  may be machined to a high degree of precision so as to ensure that it is within ±0.02 degrees of parallel with a center axis  125  of the camera barrel  108 . By recessing the mounting fixture surface  128  into the cylindrical outer surface  124 , the entire camera barrel  108  may be machined from a piece of cylindrical stock, e.g., aluminum alloy round stock, in an economical manner. 
         [0052]    The camera unit  107  may also include a plate  137  that may include a lens mounting feature  110 , which may be a threaded lens mount or other standard lens mount interface. The lens mounting feature  110  may inherently define a lens mount plane  111 , as well as potentially the center axis  125 . The lens mount plane  111  is perpendicular to the optical centerline of whatever lens, e.g., such as lens  171  (see  FIGS. 6 and 7 ), is mounted to the lens mounting feature  110 , and the center axis  125  may be aligned with the optical centerline of whatever lens is installed in the lens mounting feature  110 . Generally speaking, the lens mount plane  111  is parallel to a planar array of light-sensitive pixels that are part of the imaging sensor (not shown in this view, but visible in later views) of the camera unit  107 . The plate  137 , and thus the lens mounting feature  110 , may be separate from the camera barrel  108  so as to allow for fine-tuning of the alignment of the lens optical centerline with the center axis  125 . For example, the camera barrel  108  may include two or three adjustment screws that may be used to increase or decrease the distance between the plate  137  and the camera barrel  108  at various locations, thereby changing the relative angle between the plate  137  and the surface of the camera barrel  108  facing the plate  137 . If only two adjustment screws are used, a third point of contact, and thus stability, may be provided by a fixed-length pin or other non-adjustable contact point. The plate  137  may be pressed into contact with such adjustment screws (and fixed-length contact point, if used) by a compressive load exerted on the plate  137 , e.g., by a compression mechanism  140  such as a set of screws that thread into the camera barrel  108 , as shown in  FIG. 8  (adjustment screws are indicated in later Figures). In some implementations, if sufficient precision is used in machining the camera barrel  108 , the lens mounting feature  110  may be machined directly into a surface of the camera barrel  108 , with no adjustment mechanism or plate  137 . 
         [0053]    As can be seen in  FIG. 9 , the camera barrel  108  may have an interior volume  109 , which is sized to receive camera electronics  157  (an input/output (I/O) printed circuit board (PCB)  161  of the camera electronics  157  is visible here). The interior volume  109  may be cylindrical, as shown, in order to keep manufacturing costs low-other interior volume cross-sectional shapes are possible as well, e.g., square cross-sections, but such shapes may introduce additional manufacturing complexity with little or no performance benefit. 
         [0054]    The following Figures provide additional views of the camera unit  107 .  FIG. 10  depicts a rear view of the example camera unit of  FIG. 8 .  FIG. 11  depicts a front view of the example camera unit of  FIG. 8 .  FIG. 12  depicts a top view of the example camera unit of  FIG. 8 .  FIG. 13  depicts a side view of the example camera unit of  FIG. 8 . 
         [0055]    As can be seen in  FIG. 10 , there are three adjustment screws  138 , in this case, ball-tip or round-tip, socket-head set screws, that engage with the plate  137  in order to allow for precise tuning and alignment of the optical centerline of the lens that is eventually mounted in the lens mounting feature  110  with the center axis  125 . 
         [0056]      FIG. 14  depicts a section view of the example camera unit of  FIG. 8 . In  FIG. 14 , additional details are visible, such as the camera electronics  157 , which may include a series of PCBs, such as the I/O PCB  161 , a bulkhead PCB  160 , and an imaging PCB  159 . The I/O PCB  161  may serve as an interface between the camera unit  107  and other, external hardware, such as a power supply and/or personal computer (not shown). The bulkhead PCB  160  may, in combination with a seal plate  132 , provide for a hermetically sealed bulkhead that may seal off a portion of the interior volume  109  of the camera barrel  108 . An imaging sensor  112  with a planar array  113  of light-sensitive pixels may be located within this sealed-off portion of the interior volume  109 ; the sealed-off portion may be purged of ambient atmospheric air during the product process and filled with argon or other low-thermal-conductivity, inert, gas to prevent condensation on the imaging sensor  112  or other surfaces of the camera unit  107 . The imaging sensor  112  may be connected electrically to the imaging PCB  159 , which may, by way of a series of long electrically conductive pins  131  or socket-and-pin assemblies (as shown), communicate electrically with the bulkhead PCB  160 . Such electrically conductive pins may pass through a through-hole  133  that is machined or otherwise formed in the seal plate  132  before passing through solder connection holes in the bulkhead PCB  160 , where each pin may be soldered to the bulkhead PCB  160 . The bulkhead PCB  160  may be bonded to, or simply pressed against, the seal plate  132  and one or more compressive seals, e.g., o-rings (such as are visible near the outer perimeter of the seal plate  132 ), in order to provide an air-tight seal. The penetrations through the bulkhead PCB  160  may be sealed by virtue of the solder that bonds the electrically conductive pins  131  to the bulkhead PCB  160 . The seal plate  132 , which may be machined from aluminum or other comparably high-thermal conductivity material, may also provide a conductive heat flow path to conduct heat generated by the imaging sensor  112  to the camera barrel  108 , where it may be convectively removed by cooling fluid that flows past the cooling fins provided by the circumferential grooves  126  and the slots  136 . A heat pipe  158  and thermoelectric cooler (TEC)  174  may pull the heat generated by the imaging sensor  112  from the imaging sensor  112  and distribute such heat in a generally uniform manner across the seal plate  132  so as to increase heat flow from the imaging sensor  112  to the seal plate  132 . 
         [0057]    The camera barrel  108  may have an aperture through which the imaging sensor  112  may be exposed to light; this aperture may be sealed by a window  162 , which may be transparent to one or more wavelengths of light and, in many cases, may be optically transparent to most or all wavelengths of light. The window  162  may be held in place by a window retainer  164 , and sealed against the camera barrel  108  by a window seal  163 . 
         [0058]      FIG. 15  depicts an isometric exploded view of the camera unit of  FIG. 8 .  FIG. 16  depicts another isometric exploded view of the camera unit of  FIG. 8 . As can be seen, the camera unit  107  is constructed such that there are relatively few components between the first mounting fixture surface  128  and the imaging sensor  112 . In this particular example, the imaging sensor  112  rests on top of the heat pipe  158 , which is, in turn, in contact with the TEC  174 , which, in turn, acts as a heat pump and causes heat from the imaging sensor  112  to flow into the seal plate  132 , which is then clamped to a ledge surface  135  (see  FIG. 16 ) using several screws, allowing the heat to be conducted into the camera barrel  108 . The only remaining component between these interfaces and the first mounting fixture surface  128  is the camera barrel  108  itself. In some implementations, the ledge surface  135  may be perpendicular to within ±0.25 degrees of the mounting fixture surface  128  to facilitate alignment of the imaging sensor with the lens mount feature. If the imaging sensor  112 /seal plate  132  assembly is constructed and assembled so as to precisely align the planar array  113  so as to be parallel to the annular outer surface of the seal plate  132  that interfaces with the ledge surface  135 , which may be done using fixtures/jigs before assembling the remainder of the camera unit  107 , then only two surfaces, the mounting fixture surface  128  and the ledge surface  135 , need to be held to high tolerances relative to one another in order to ensure that the mounting fixture  127  is sufficiently aligned with the planar array  113  of light-sensitive pixels. 
         [0059]      FIG. 17  depicts an isometric view of an example of a mounting fixture that may be used to precision-mount the example camera unit of  FIG. 8  within the imaging system of  FIG. 1 .  FIG. 18  depicts another isometric view of the example mounting fixture of  FIG. 17 . As can be seen from  FIG. 17 , which shows the side of the mounting fixture  127  that faces towards the camera barrel  108  when installed, the mounting fixture  127  may, for example, have a base  168 , e.g., a flat plate, that includes a raised portion  169  that terminates in a barrel-facing surface  172  that contacts the mounting fixture surface  128  when the mounting fixture  127  is assembled with the camera barrel  108 . The barrel-facing surface  172  may include a second fixture alignment feature  130 , which, in this example, includes two precision-ground locating pins that have been inserted or pressed into corresponding holes in the mounting fixture  127 . The second fixture alignment feature  130  may interlock with the first fixture alignment feature  129  that is part of the mounting fixture surface  128  in order to orient the mounting fixture  127  relative to the camera barrel  108 . The base may also include one or more mounting tabs  170  that may include features, e.g., threaded holes or nut plates, to allow the enclosure  141  to be connected with the mounting fixture  127  using, for example, screws. 
         [0060]    The mounting fixture  127  may also include features for mounting and aligning the mounting fixture  127  (and attached camera barrel  108 ) to the carriage  103 . For example, in  FIG. 18 , a carriage-facing surface  114  of the mounting fixture  127  may be seen. The carriage may, for example, include a first mechanical interface feature (not shown here, but see  FIG. 19 ) having, for example, a plurality of first alignment holes that may interface with a second mechanical interface feature  106 , which, in this example implementation, includes two second alignment holes  120 . In this example, the second alignment holes  120  are threaded so as to be able to receive shoulder screws or other precision-ground shafts, although the second alignment holes  120  may also be smooth-walled so as to receive ground pins, similar to the pins used in the example second fixture alignment feature  130  discussed earlier. 
         [0061]    As can be seen, the carriage-facing surface  114  may include several raised bosses, e.g., a first raised boss  115 , a second raised boss  1 AA 16 , and a third raised boss  117 . These raised bosses, which in this example are U-shaped, may not only provide for a gap between the carriage  103  and the base  168  of the mounting fixture  127 , thereby allowing, for example, a wall of the enclosure  141  with U-shaped slots, in this example, to be sandwiched between the mounting fixture  127  and the carriage  103 , but may also serve as a lower-cost interface to ensure proper alignment between the carriage  103  and the camera unit  107 . For example, the third raised boss  117  may be machined such that it is slightly lower than the first raised boss  115  or the second raised boss  116 , even taking into account manufacturing tolerances, thereby causing only the first raised boss  115  and the second raised boss  116  to be in contact with the carriage  103 , while the third raised boss  117  may be separated from the carriage by a small gap. The third raised boss may also, for example, include the second alignment holes  120 , as depicted in this example, although in other implementations, such second alignment holes  120  may be located in the first raised boss  115  and/or the second raised boss  116 , and the third raised boss may be omitted entirely. Thus, in this implementation, the mounting fixture would be located in the X- and Y-directions (directions orthogonal to the center axes of the second alignment holes  120 ) by the second alignment holes  120 , and in the Z-direction by contact between the carriage  103  and the first raised boss  115  and the second raised boss  116 . Moreover, the interface between the first alignment holes on the carriage  103  and the second alignment holes  120  would prevent rotational movement of the camera unit  107  about the Z-axis, and the contact between the carriage  103  and the first raised boss  115  and the second raised boss  116  would prevent rotational movement of the camera unit  107  about the X- and Y-axes. In some implementations, the first raised boss  115  and the second raised boss  116  may be manufactured so as to have, when assembled into the completed camera assembly, a tolerance of ±0.02 degrees with respect to the central axis  125  and a flatness tolerance of ±0.03 mm with respect to one another. 
         [0062]    While the first raised boss  115 , the second raised boss  116 , and the third raised boss  117  are optional, e.g., they could be omitted and the features in each raised boss located instead in the carriage-facing surface  114  directly, the entire carriage-facing surface  114  may need to be machined to a high degree of flatness if the raised boss features are not included, which may be much more expensive. If the mounting fixture is constructed as shown, i.e., with the raised bosses, only the first raised boss  115  and the second raised boss  116  may need to be machined to precise tolerances relative to the barrel-facing surface  172  to ensure proper rotational alignment between the carriage  103  and the camera unit  107  about the X- and Y-axes. This reduces cost, both in terms of machining and later metrology/inspection of the machined features. 
         [0063]      FIG. 19  depicts a section view of the subportion of the imaging system shown in  FIG. 6 .  FIG. 20  depicts another section view of the subportion of the imaging system shown in  FIG. 6 .  FIG. 19  depicts a section that passes through the center axis  125 , whereas  FIG. 20  depicts a section that passes through the first raised boss  115 . 
         [0064]    As can be seen, the carriage  103  may include a first mechanical interface that includes plurality of first alignment holes  119 —in this example, three first alignment holes  119  are provided, but only two are used—the remaining first alignment hole (not indicated, but visible) may be used in other camera unit mounting configurations, if desired. Also visible is the mounting fixture  127 , which may include the second mechanical interface and features thereof, e.g., the second alignment holes  120 , which, in this example, are threaded holes. The first mechanical interface or the second mechanical interface may include features that interlock with corresponding features in the other mechanical interface, e.g., an alignment shaft  118  may be part of one mechanical interface and interlock with features of the other mechanical interface. 
         [0065]    In the depicted implementation, the alignment shafts  118  are provided by shoulder screws  121 , which may have a precision-ground shoulder portion  123 , as well as a threaded portion  122 . The threaded portion  122  of each shoulder screw  121  may engage with the threaded second alignment holes  120  so as to fix the shoulder screws  121  in place relative to the mounting fixture  127 . As noted earlier, the third raised boss  117  may be separated from the carriage  103  by a small gap, e.g., such as at the location “A” (the gap is quite small, e.g., a few thousandths of an inch, and not actually discernible at the depicted scale), in contrast to location “B,” where the mounting fixture  127  is compressed against the mounting fixture surface  128  of the camera barrel  108  and location “C,” where the barrel-facing surface  172  is compressed against the mounting fixture surface  128 , i.e., where no gap exists. As can be seen, the shoulder screws  121  may act more as pins than as compressive members, as the screw heads do not bear directly on the carriage  103 , which could potentially cause the mounting fixture  127  to flex, leading to misalignment between the camera unit  107  and the carriage  103 . 
         [0066]    The various concepts embodied in the above-discussed implementation may be practiced or implemented in a variety of ways in order to achieve the imaging system envisioned by the present inventors. For example, as mentioned previously, a separate plate  137  may be unnecessary, and some implementations may feature a camera barrel  108  that incorporates the lens mounting feature  110  directly into the camera barrel  108  as opposed to in a separate plate  137  that allows for adjustment of the lens mounting feature  110  relative to the camera barrel  108 . In some other or additional implementations, the mounting fixture  127  may be omitted and some or all of the features of the mounting fixture  127  may be machined directly into the camera barrel  108 . Such an approach may eliminate one of the contact interfaces requiring tight tolerancing in order to properly align the camera unit with the carriage, but may, at the same time, require additional machining and/or larger starting material due to a more complex part shape. For example, the camera barrel  108  that is depicted in the example implementation discussed herein may be machined from a piece of round stock that is the same diameter as the camera barrel  108 . However, if the features provided by the mounting fixture  127  were integrated directly into the camera barrel  108 , it would be necessary to start with a larger diameter piece of round stock to accommodate the portions of the mounting fixture that protrude beyond the limits of the cylindrical outer surface  124 . 
         [0067]    The camera barrel  108 , mounting fixture  127 , plate  137 , and seal plate  132  may be manufactured from any suitable material, e.g., aluminum alloy. Various other components, such as screws and linear guides, may be manufactured from steel or other suitable material, e.g., high-hardness and high-strength materials. 
         [0068]    Generally speaking, the camera barrel/mounting fixture/carriage interfaces described herein may be particularly notable due to the deliberate omission of any positional adjustment mechanisms that would allow the precise positioning and alignment of these components relative to one another to be adjusted. In short, these components may be assembled in only one, fixed configuration, thereby simplifying the assembly process by eliminating potentially time-consuming adjustment steps. This is directly contrary to how imaging systems are typically constructed, since such systems typically routinely incorporate adjustment mechanisms for maximum tuneability. 
         [0069]    Although several implementations have been described in detail herein with reference to the accompanying drawings, it is to be understood that this disclosure is not limited to these precise embodiments or implementations, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the disclosure as defined in the appended claims.