Patent Publication Number: US-2023152672-A1

Title: Mounting systems for multi-camera imagers

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the National Stage of International Application No. PCT/US2020/66702, filed Dec. 22, 2020, which claims priority to and the benefit of: International Patent Application No. PCT/US2020/039197, filed Jun. 23, 2020, entitled “Opto-Mechanics of Panoramic Capture Devices with Abutting Cameras;” International Patent Application No. PCT/US2020/039200, filed Jun. 23, 2020, entitled “Multi-camera Panoramic Image Capture Devices with a Faceted Dome;” International Patent Application No. PCT/US2020/039201, filed Jun. 23, 2020, entitled “Lens Design for Low Parallax Panoramic Camera Systems;” U.S. Provisional Patent Application Ser. No. 62/952,973, filed Dec. 23, 2019, entitled “Opto-Mechanics of Panoramic Capture Devices with Abutting Cameras;” U.S. Provisional Patent Application Ser. No. 62/952,983, filed Dec. 23, 2019, entitled “Multi-camera Panoramic Image Capture Devices with a Faceted Dome;” and U.S. Provisional Patent Application Ser. No. 62/972,532, filed Feb. 10, 2020, entitled “Integrated Depth Sensing and Panoramic Camera System.” The three International Applications listed above each claims priority to the three listed US provisional applications, as well as to U.S. Provisional Patent Application Ser. No. 62/865,741, filed Jun. 24, 2019. The entirety of each of the applications listed above is incorporated herein by reference. 
    
    
     This invention was made with US Government support under grant number 2026054 awarded by the National Science Foundation. The Government has certain rights to this invention. 
    
    
     DISCLOSURE 
     Technical Field 
     The present disclosure relates to panoramic low-parallax multi-camera capture devices having a plurality of adjacent and abutting polygonal cameras. The disclosure also relates the opto-mechanical design of cameras that capture incident light from a polygonal shaped field of view to form a polygonal shaped image. 
     Background 
     Panoramic cameras have substantial value because of their ability to simultaneously capture wide field of view images. The earliest such example is the fisheye lens, which is an ultra-wide-angle lens that produces strong visual distortion while capturing a wide panoramic or hemispherical image. While the field of view (FOV) of a fisheye lens is usually between 100 and 180 degrees, the approach has been extended to yet larger angles, including into the 220-270° range, as provided by Y. Shimizu in U.S. Pat. No. 3,524,697. As an alternative, there are mirror or reflective based cameras that capture annular panoramic images, such as the system suggested by P. Greguss in U.S. Pat. No. 4,930,864. While these technologies have continued to evolve, it is difficult for them to provide a full hemispheric or spherical image with the resolution and image quality that modern applications are now seeking. 
     As another alternative, panoramic multi-camera devices, with a plurality of cameras arranged around a sphere or a circumference of a sphere, are becoming increasingly common. However, in most of these systems, including those described in U.S. Pat. Nos. 9,451,162 and 9,911,454, both to A. Van Hoff et al., of Jaunt Inc., the plurality of cameras are sparsely populating the outer surface of the device. In order to capture complete 360-degree panoramic images, including for the gaps or seams between the adjacent individual cameras, the cameras then have widened FOVs that overlap one to another. In some cases, as much as 50% of a camera&#39;s FOV or resolution may be used for camera to camera overlap, which also creates substantial parallax differences between the captured images. Parallax is the visual perception that the position or direction of an object appears to be different when viewed from different positions. Then in the subsequent image processing, the excess image overlap and parallax differences both complicate and significantly slow the efforts to properly combine, tile or stitch, and synthesize acceptable images from the images captured by adjacent cameras. 
     There are also panoramic multi-camera devices in which a plurality of cameras is arranged around a sphere or a circumference of a sphere, such that adjacent cameras are abutting along a part or the whole of adjacent edges. As an example, U.S. Pat. No. 7,515,177 by K. Yoshikawa depicts an imaging device with a multitude of adjacent image pickup units (cameras). Images are collected from cameras having overlapping fields of view, so as to compensate for mechanical errors. 
     More broadly, in a multi-camera device, mechanical variations in the assembly and alignment of individual cameras, and of adjacent cameras to each other, can cause real physical variations to both the cameras themselves, and to the seam widths and parallelism of the camera edges along the seams. These variations can then affect the FOVs captured by the individual cameras, the parallax errors in the images captured by adjacent cameras, the extent of “blind spots” in the FOV corresponding to the seams, the seam widths, and the amount of image overlap that is needed to compensate. Thus, there are opportunities to improve panoramic multi-camera devices and the low-parallax cameras thereof, relative to the optical and opto-mechanical designs, and other aspects as well. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    depicts a 3D view of a portion of a multi-camera capture device, and specifically two adjacent cameras thereof. 
         FIGS.  2 A and  2 B  depict portions of camera lens assemblies in cross-section, including lens elements and ray paths. 
         FIG.  3    depicts a cross-sectional view of a portion of a standard multi-camera capture device showing FOV overlap, Fields of view, overlap, seams, and blind regions. 
         FIG.  4    depicts two polyhedron shapes, that of a regular dodecahedron and a truncated icosahedron, to which a multi-camera capture device can be designed and fabricated. 
         FIG.  5 A  and  FIG.  5 B  depict the optical geometry for fields of view for adjacent hexagonal and pentagonal lenses, as can occur with a device having the geometry of a truncated icosahedron.  FIG.  5 B  depicts an expanded area of  FIG.  5 A  with greater detail. 
         FIG.  5 C  depicts an example of a low parallax (LP) volume located near both a paraxial NP point or entrance pupil and a device center. 
         FIG.  5 D  depicts parallax differences for two adjacent cameras, relative to a center of perspective. 
         FIG.  5 E  depicts front color at an edge of an outer compressor lens element. 
         FIG.  6    depicts distortion correction curves plotted on a graph showing a percentage of distortion relative to a fractional field. 
         FIG.  7    depicts fields of view for adjacent cameras, including both Core and Extended fields of view (FOV), both of which can be useful for the design of an optimized panoramic multi-camera capture device. 
         FIG.  8    depicts an image sensor with a sensor mount having adjustors. 
         FIG.  9    depicts a cross-sectional view of an improved opto-mechanics construction for a multi-camera capture device, and a 3D view of a camera channel thereof. 
         FIG.  10    depicts a cross-sectional view of a seam and two adjacent stepped edge angle compressor lenses, near a seam, and a zoomed in view of a portion (B) thereof. 
         FIG.  11    depicts 3D- and top-down views of a sensor area, masking, and optical fiducial. 
         FIG.  12    depicts a baffle. 
         FIG.  13 A  depicts a cross-section of an improved lens design that shows multi-compressor lens group and that can support a FRU concept. 
         FIG.  13 B  depicts another improved lens design, relative to an offset device center. 
         FIG.  14 A  depicts a 3D view of a multi-camera capture device with fins. 
         FIG.  14 B  depicts a multi-camera capture device with pins. 
         FIG.  15    depicts an electronics system diagram for a multi-camera capture device. 
         FIG.  16    depicts different views of an outer compressor lens element with lens datums, and an associated lens housing with datum features. 
         FIG.  17    depicts a cross-sectional view of a portion of an assembly of an improved multi-camera panoramic image capture device, and a portion thereof in detail. 
         FIG.  18 A  depicts a series of views of components and features of a lens housing and a channel loading support, that can be used during assembly of an improved multi-camera panoramic image capture device. 
         FIG.  18 B- 1    depicts a cross-sectional views of an alternate version of the lens housings and the interaction thereof, at or near a seam, to that shown in  FIG.  10   . 
         FIG.  18 B- 2    depicts a cross-sectional views of an alternate version of the channel to channel datums to those shown in  FIG.  18 A . 
         FIG.  19    depicts a view of an alternate design to that of  FIG.  9    or  FIG.  17   , for the mounting of the camera channels to a central support. 
         FIG.  20    depicts a view of another alternate design for the mounting of the camera channels to a central support. 
         FIG.  21    depicts an alternate configuration for an improved multi-camera projection device. 
         FIG.  22 A  depicts a perspective view of additional systems for the mounting of camera channels to each other and to a central support. 
         FIG.  22 B  depicts an exploded perspective view of a portion of the alternate design of  FIG.  22 A , providing greater detail on the interface of a secondary channel to the primary channel. 
         FIG.  23    depicts a perspective view of a sensor cooling system. 
         FIG.  24    depicts an alternate configuration for an improved multi-camera projection device. 
     
    
    
     DETAILED DESCRIPTION 
     As is generally understood in the field of optics, a lens or lens assembly typically comprises a system or device having multiple lens elements which are mounted into a lens barrel or housing, and which work together to produce an optical image. An imaging lens captures a portion of the light coming from an object or plurality of objects that reside in object space at some distance(s) from the lens system. The imaging lens can then form an image of these objects at an output “plane”; the image having a finite size that depends on the magnification, as determined by the focal length of the imaging lens and the conjugate distances to the object(s) and image plane, relative to that focal length. The amount of image light that transits the lens, from object to image, depends in large part on the size of the aperture stop of the imaging lens, which is typically quantified by one or more values for a numerical aperture (NA) or an f-number (F# or F/#). 
     The image quality provided by the imaging lens depends on numerous properties of the lens design, including the selection of optical materials used in the design, the size, shapes (or curvatures) and thicknesses of the lens elements, the relative spacing of the lens elements one to another, the spectral bandwidth, polarization, light load (power or flux) of the transiting light, optical diffraction or scattering, and/or lens manufacturing tolerances or errors. The image quality is typically described or quantified in terms of lens aberrations (e.g., spherical, coma, or distortion), or the relative size of the resolvable spots provided by the lens, which is also often quantified by a modulation transfer function (MTF). 
     In a typical electronic or digital camera, an image sensor is nominally located at the image plane. This image sensor is typically a CCD or CMOS device, which is physically attached to a heat sink or other heat removal means, and also includes electronics that provide power to the sensor, and read-out and communications circuitry that provide the image data to data storage or image processing electronics. The image sensor typically has a color filter array (CFA), such as a Bayer filter within the device, with the color filter pixels aligned in registration with the image pixels to provide an array of RGB (Red, Green, Blue) pixels. Alternative filter array patterns, including the CYGM filter (cyan, yellow, green, magenta) or an RGBW filter array (W=white), can be used instead. 
     In typical use, many digital cameras are used by people or remote systems in relative isolation, to capture images or pictures of a scene, without any dependence or interaction with any other camera devices. In some cases, such as surveillance or security, the operation of a camera may be directed by people or algorithms based on image content seen from another camera that has already captured overlapping, adjacent, or proximate image content. In another example, people capture panoramic images of a scene with an extended or wide FOV, such as a landscape scene, by sequentially capturing a sequence of adjacent images, while manually or automatically moving or pivoting to frame the adjacent images. Afterwards, image processing software, such as Photoshop or Lightroom, can be used to stitch, mosaic, or tile the adjacent images together to portray the larger extended scene. Image stitching or photo stitching is the process of combining multiple photographic images with overlapping fields of view to produce a segmented panorama or high-resolution image. Image quality improvements, including exposure or color corrections, can also be applied, either in real time, or in a post processing or image rendering phase, or a combination thereof. 
     Unless the objects in a scene are directionally illuminated and/or have a directional optical response (e.g., such as with reflectance), the available light is plenoptic, meaning that there is light travelling in every direction, or nearly so, in a given space or environment. A camera can then sample a subset of this light, as image light, with which it provides a resulting image that shows a given view or perspective of the different objects in the scene at one or more instants in time. If the camera is moved to a different nearby location and used to capture another image of part of that same scene, both the apparent perspectives and relative positioning of the objects will change. In the latter case, one object may now partially occlude another, while a previously hidden object becomes at least partially visible. These differences in the apparent position or direction of an object are known as parallax. In particular, parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. 
     In a stereoscopic image capture or projection system, dual view parallax is a cue, along with shadowing, occlusion, and perspective, that can provide a sense of depth. For example, in a stereo (3D) projection system, polarization or spectrally encoded image pairs can be overlap projected onto a screen to be viewed by audience members wearing appropriate glasses. The amount of parallax can have an optimal range, outside of which, the resulting sense of depth can be too small to really be noticed by the audience members, or too large to properly be fused by the human visual system. 
     Whereas, in a panoramic image capture application, parallax differences can be regarded as an error that can complicate both image stitching and appearance. In the example of an individual manually capturing a panoramic sequence of landscape images, the visual differences in perspective or parallax across images may be too small to notice if the objects in the scene are sufficiently distant (e.g., optically at infinity). An integrated panoramic capture device with a rotating camera or multiple cameras has the potential to continuously capture real time image data at high resolution without being dependent on the uncertainties of manual capture. But such a device can also introduce its own visual disparities, image artifacts, or errors, including those of parallax, perspective, and exposure. Although the resulting images can often be successfully stitched together with image processing algorithms, the input image errors complicate and lengthen image processing time, while sometimes leaving visually obvious residual errors. 
     To provide context,  FIG.  1    depicts a portion of an improved integrated panoramic multi-camera capture device  100  having two adjacent cameras  120  in housings  130  which are designed for reduced parallax image capture. These cameras are alternately referred to as image pick-up units, or camera channels, or objective lens systems. The cameras  120  each have a plurality of lens elements (see  FIG.  2   ) that are mounted within a lens barrel or housing  130 . The adjacent outer lens elements  137  have adjacent beveled edges  132  and are proximately located, one camera channel to another, but which may not be in contact, and thus are separated by a gap or seam  160  of finite width. Some portion of the available light (D), or light rays  110 , from a scene or object space  105  will enter a camera  120  to become image light that was captured within a constrained FOV and directed to an image plane, while other light rays will miss the cameras entirely. Some light rays  110  will propagate into the camera and transit the constituent lens elements as edge-of-field chief rays  170 , or perimeter rays, while other light rays can potentially propagate through the lens elements to create stray or ghost light and erroneous bright spots or images. As an example, some light rays ( 167 ) that are incident at large angles to the outer surface of an outer lens element  137  can transit a complex path through the lens elements of a camera and create a detectable ghost image at the image plane  150 . 
     In greater detail,  FIG.  2 A  depicts a cross-section of part of a camera  120  having a set of lens elements  135  mounted in a housing ( 130 , not shown) within a portion of an integrated panoramic multi-camera capture device  100 . A fan of light rays  110  from object space  105 , spanning the range from on axis to full field off axis chief rays, are incident onto the outer lens element  137 , and are refracted and transmitted inwards. This image light  115  that is refracted and transmitted through further inner lens elements  140 , through an aperture stop  145 , converges to a focused image at or near an image plane  150 , where an image sensor (not shown) is typically located. The lens system  120  of  FIG.  2 A  can also be defined as having a lens form that consists of outer lens element  137  or compressor lens element, and inner lens elements  140 , the latter of which can also be defined as consisting of a pre-stop wide angle lens group, and a post-stop eyepiece-like lens group. This compressor lens element ( 137 ) directs the image light  115  sharply inwards, compressing the light, to both help enable the overall lens assembly to provide a short focal length, while also enabling the needed room for the camera lens housing or barrel to provide the mechanical features necessary to both hold or mount the lens elements and to interface properly with the barrel or housing of an adjacent camera. The image light that transited a camera lens assembly from the outer lens element  137  to the image plane  150  will provide an image having an image quality, that can be quantified by an image resolution, image contrast, a depth of focus, and other attributes, whose quality was defined by the optical aberrations (e.g., astigmatism, distortion, or spherical) and chromatic or spectral aberrations, encountered by the transiting light at each of the lens elements ( 137 ,  140 ) within a camera  120 .  FIG.  2 B  depicts a fan of chief rays  170 , or perimeter rays, incident along or near a beveled edge  132  of the outer lens element  137  of the camera optics ( 120 ) depicted in  FIG.  2 A .  FIG.  2 B  also depicts a portion of a captured, polygonal shaped or asymmetrical, FOV  125 , that extends from the optical axis  185  to a line coincident with an edge ray. 
     In the camera lens design depicted in  FIG.  2 A , the outer lens element  137  functions as a compressor lens element that redirects the transiting image light  115  towards a second lens element  142 , which is the first lens element of the group of inner lens elements  140 . In this design, this second lens element  142  has a very concave shape that is reminiscent of the outer lens element used in a fish-eye type imaging lens. This compressor lens element directs the image light  115  sharply inwards, or bends the light rays, to both help enable the overall lens assembly to provide a short focal length, while also enabling the needed room for the camera lens housing  130  or barrel to provide the mechanical features necessary to both hold or mount the lens elements  135  and to interface properly with the barrel or housing of an adjacent camera. However, with a good lens and opto-mechanical design, and an appropriate sensor choice, a camera  120  can be designed with a lens assembly that supports an image resolution of 20-30 pixels/degree, to as much as 110 pixels/degree, or greater, depending on the application and the device configuration. 
     The resultant image quality from these cameras will also depend on the light that scatters at surfaces, or within the lens elements, and on the light that is reflected or transmitted at each lens surface. The surface transmittance and camera lens system efficiency can be improved by the use of anti-reflection (AR) coatings. The image quality can also depend on the outcomes of non-image light. Considering again  FIG.  1   , other portions of the available light can be predominately reflected off of the outer lens element  137 . Yet other light that enters a camera  120  can be blocked or absorbed by some combination of blackened areas (not shown) that are provided at or near the aperture stop, the inner lens barrel surfaces, the lens element edges, internal baffles or light trapping features, a field stop, or other surfaces. Yet other light that enters a camera can become stray light or ghost light  167  that is also potentially visible at the image plane. 
     The aggregate image quality obtained by a plurality of adjacent cameras  120  within an improved integrated panoramic multi-camera capture device  100  (e.g.,  FIG.  1   ) can also depend upon a variety of other factors including the camera to camera variations in the focal length and/or track length, and magnification, provided by the individual cameras. These parameters can vary depending on factors including the variations of the glass refractive indices, variations in lens element thicknesses and curvatures, and variations in lens element mounting. As an example, images that are tiled or mosaiced together from a plurality of adjacent cameras will typically need to be corrected, one to the other, to compensate for image size variations that originate with camera magnification differences (e.g., ±2%). 
     The images produced by a plurality of cameras in an integrated panoramic multi-camera capture device  100  can also vary in other ways that effect image quality and image mosaicing or tiling. In particular, the directional pointing or collection of image light through the lens elements to the image sensor of any given camera  120  can vary, such that the camera captures an angularly skewed or asymmetrical FOV (FOV↔) or mis-sized FOV (FOV±). The lens pointing variations can occur during fabrication of the camera (e.g., lens elements, sensor, and housing) or during the combined assembly of the multiple cameras into an integrated panoramic multi-camera capture device  100 , such that the alignment of the individual cameras is skewed by misalignments or mounting stresses. When these camera pointing errors are combined with the presence of the seams  160  between cameras  120 , images for portions of an available landscape or panoramic FOV that may be captured, may instead be missed or captured improperly. The variabilities of the camera pointing, and seams can be exacerbated by mechanical shifts and distortions that are caused by internal or external environmental factors, such as heat or light (e.g., image content), and particularly asymmetrical loads thereof. 
     In comparison to the  FIG.  1    system, in a typical commercially available panoramic camera, the seams between cameras are outright gaps that can be 30-50 mm wide, or more. In particular, as shown in  FIG.  3   , a panoramic multi-camera capture device  101  can have adjacent cameras  120  or camera channels separated by large gaps or seams  160 , between which there are blind spots or regions  165  from which neither camera can capture images. The actual physical seams  160  between adjacent camera channels or outer lens elements  137  ( FIG.  1    and  FIG.  3   ) can be measured in various ways; as an actual physical distance between adjacent lens elements or lens housings, as an angular extent of lost FOV, or as a number of “lost” pixels. However, the optical seam, as the distance between outer chief rays of one camera to another can be larger yet, due to any gaps in light acceptance caused by vignetting or coating limits. For example, anti-reflection (AR) coatings are not typically deposited to the edges of optics, but an offsetting margin is provided, to provide a coated clear aperture (CA). 
     To compensate for both camera misalignments and the large seams  160 , and to reduce the size of the blind regions  165 , the typical panoramic multi-camera capture devices  101  ( FIG.  3   ) have each of the individual cameras  120  capture image light  115  from wide FOVs  125  that provide overlap  127 , so that blind regions  165  are reduced, and the potential capturable image content that is lost is small. As another example, in most of the commercially available multi-camera capture devices  101 , the gaps are 25-50+ mm wide, and the compensating FOV overlap between cameras is likewise large; e.g., the portions of the FOVs  125  that are overlapping and are captured by two adjacent cameras  120  can be as much as 10-50% of a camera&#39;s FOV. The presence of such large image overlaps from shared FOVs  125  wastes potential image resolution and increases the image processing and image stitching time, while introducing significant image parallax and perspective errors. These errors complicate image stitching, as the errors must be corrected or averaged during the stitching process. In such systems, the parallax is not predictable because it changes as a function of object distance. If the object distance is known, the parallax can be predicted for given fields of view and spacing between cameras. But because the object distance is not typically known, parallax errors then complicate image stitching. Optical flow and common stitching algorithms determine an object depth and enable image stitching, but with processing power and time burdens. 
     Similarly, in a panoramic multi-camera capture device  100 , of the type of  FIG.  1   , with closely integrated cameras, the width and construction at the seams  160  can be an important factor in the operation of the entire device. However, the seams can be made smaller than in  FIG.  3   , with the effective optical seam width between the FOV edges of two adjacent cameras determined by both optical and mechanical contributions. For example, by using standard optical engineering practices to build lens assemblies in housings, the mechanical width of the seams  160  between the outer lens elements  137  of adjacent cameras might be reduced to 4-6 mm. For example, it is standard practice to assemble lens elements into a lens barrel or housing that has a minimum radial width of 1-1.5 mm, particularly near the outermost lens element. Then accounting for standard coated clear apertures or coating margins, and accounting for possible vignetting, aberrations of the entrance pupil, front color, chip edges, and trying to mount adjacent lens assemblies or housings in proximity by standard techniques. Thus, when accounting for both optics and mechanics, an optical seam width between adjacent lenses can easily be 8-12 mm or more. 
     But improved versions of the panoramic multi-camera capture device ( 300 ) of the type of  FIG.  1   , with optical and opto-mechanical designs that enable significantly smaller seams, and with further improved parallax performance, are possible. As a first example, for the present technology for improved polygonal shaped cameras, during early stages of fabrication of outer lens elements  137 , these lenses can have a circular shape and can be AR coated to at or near their physical edges. When these lenses are subsequently processed to add the polygonal shape defining beveled edges  132  (e.g.,  FIG.  2 B ), a result can be that the AR coatings will essentially extend to the beveled lens edges. The effective optical or coated clear apertures can then defined by any allowances for mechanical mounting or for the standard edge grind that is used in optics manufacturing to avoid edge chipping. With this approach, and a mix of other techniques that will be subsequently discussed, the optical seams can be reduced to 1-5 mm width. 
     Aspects of the present disclosure produce high quality low-parallax panoramic images from an improved multi-camera panoramic capture device ( 300 ), for which portions of a first example are shown in  FIG.  8    and  FIG.  9   . This broad goal can be enabled by developing a systemic range of design strategies to inform both the optical and opto-mechanical lens design efforts, and the opto-mechanical device design and fabrication efforts, as well as strategies for improved image capture and processing. This goal can also be enabled by providing for both initial and ongoing camera and device calibration. In broad terms, the image processing or rendering of images is a method to generate quality images from the raw captured image data that depends on the camera intrinsics (geometric factors such as focal length and distortion), the camera extrinsics (geometric factors such as camera orientation to object space), other camera parameters such as vignetting and transmission, and illumination parameters such as color and directionality. With respect to an improved multi-camera panoramic capture device  300 , the use of fiducials in determining and tracking a center pixel or an image centroid, exposure correction, and knowledge of the camera intrinsics for any given camera  320  in a device, are all assists towards completing reliable and repeatable tiling of images obtained from a plurality of adjacent cameras. Thus the subsequent discussions are broadly focused on providing optical (camera or objective lens) designs that can enable the desired image quality, as well as camera and device assembly approaches, management of key tolerances, camera calibration, knowledge of camera intrisincs and extriniscs, and other factors that can likewise affect the resultant device performance. The improved panoramic multi-camera capture devices of the present invention can be used to support a wide variety of applications or markets, including cinematic image capture, augmented reality or virtual reality (VR) image capture, surveillance or security imaging, sports or event imaging, mapping or photogrammetry, vehicular navigation, and robotics. 
     Before exploring opto-mechanical means for enabling improved panoramic multi-camera capture devices ( 300 ), means for providing cameras  120  that are improved for use in these systems are developed. Accordingly, the goals include providing improved cameras ( 320 ) having both reduced parallax errors and image overlap. As one aspect of the present approach, a goal is to reduce the residual parallax error for the edge chief rays collected respectively by each camera in an adjacent pair. The parallax error is defined as the change in parallax with respect to object distance (e.g., that the chief ray trajectory with respect to a near distance (e.g., 3 feet) from the device, versus a far distance (e.g., 1 mile), is slightly different). For example, as one goal or target for reduced parallax, or to have effectively no parallax error, or to be “parallax-free”, is that the chief rays of adjacent cameras should deviate from parallelism to each other by ≤0.5-2.0 deg., and preferably by ≤0.01-0.1 deg. Alternately, or equivalently, the parallax error, as assessed as a perspective error in terms of location on the image plane, should be reduced to ≤2 pixels, and preferably to ≤0.5 pixel. As another aspect of the present approach, the width of the seams  160  between adjacent cameras (e.g.,  120 ,  320 ) assembled into their own lens housings are to be reduced. The goal is to reduce the width of the seams, both in terms of their absolute physical width, and their optical width or an effective width. For example, a goal is to reduce a seam  160  between adjacent outer lens elements  137  to having a maximum gap or an actual physical seam width in a range of only ≈0.5-3.0 mm, and to then reduce the maximum optical seam width to a range of about only 1-6 mm. As an example, these reduced seams widths can translate to a reduced angular extent of lost FOV of only 0.25-1.0°, or a number of “lost” pixels of only 2-20 pixels. For example, for a device providing 8k pixels around a 360-degree panorama equirectangular image, a loss of only 2-4 pixels at the seams can be acceptable as the residual image artifacts can be difficult to perceive. The actual details or numerical targets for effectively no-parallax error, or for the maximum optical seam width, depend on many factors including the detailed opto-mechanical designs of the improved cameras ( 320 ) and overall device ( 300 ), management of tolerances, possible allowances for a center offset distance or an amount of extended FOV ( 215 ) and the targets for low parallax therein, and the overall device specifications (e.g., diameter, sensor resolution or used sensor pixels within an imaged FOV or a Core FOV  205  ( FIG.  7   )). Further goals, enabled by some combination of the above improvements, are for each camera to reliably and quickly provide output images from an embedded sensor package that are cropped down to provide core FOV images, and then that each cropped image can be readily seamed or tiled with cropped images provided by adjacent cameras, so as to readily provide panoramic output images from an improved multi-camera capture device ( 300 ) in real time. 
     An improved panoramic multi-camera capture device  300 , such as that of  FIG.  13    and  FIG.  15   , can have a plurality of cameras arranged around a circumference of a sphere to capture a 360-degree annular FOV. Alternately, a panoramic multi-camera capture device can have a plurality of cameras arranged around a spherical or polyhedral shape. A polyhedron is a three-dimensional solid consisting of a collection of polygons that are contiguous at the edges. One polyhedral shape, as shown in  FIG.  4   , is that of a dodecahedron  50 , which has 12 sides or faces, each shaped as a regular pentagon  55 , and 20 vertices or corners (e.g., a vertex  60 ). A panoramic multi-camera capture device formed to the dodecahedron shape has cameras with a pentagonally shaped outer lens elements that nominally image a 69.1° full width field of view. Another shape is that of a truncated icosahedron, like a soccer ball, which as is also shown in  FIG.  4   , and has a combination of 12 regular pentagonal sides or faces, 20 regular hexagonal sides or faces, 60 vertices, and 90 edges. More complex shapes, with many more sides, such as regular polyhedra, Goldberg polyhedra, or shapes with octagonal sides, or even some irregular polyhedral shapes, can also be useful. For example, a Goldberg chamfered dodecahedron is similar to the truncated icosahedron, with both pentagonal and hexagonal facets, totaling 42 sides. But in general, the preferred polyhedrons for the current purpose have sides or faces that are hexagonal or pentagonal, which are generally roundish shapes with beveled edges  132  meeting at obtuse corners. Other polyhedral shapes, such as an octahedron or a regular icosahedron can be used, although they have triangular facets. Polyhedral facets with more abrupt or acute corners, such as square or triangular faces, can be easier to fabricate, as compared to facets with pentagonal and or hexagonal facets, as they have fewer edges to cut to provide polygonal edges on the outermost lens element, so as to define a captured polygonal FOV. However, greater care can then be needed in cutting, beveling, and handling the optic because of those acute corners. Additionally, for lens facets with large FOVs and acute facet angles, it can be more difficult to design the camera lenses and camera lens housings for optical and opto-mechanical performance. Typically, a 360° polyhedral camera will not capture a full spherical FOV as at least part of one facet is sacrificed to allow for support features and power and communications cabling, such as via a mounting post. However, if the device communicates wirelessly, and is also hung by a thin cable to a vertex, the FOV lost to such physical connections can be reduced. 
     As depicted in  FIG.  1    and  FIG.  2 B , a camera channel  120  can resembles a frustum, or a portion thereof, where a frustum is a geometric solid (normally a cone or pyramid) that lies between one or two parallel planes that cut through it. In that context, a fan of chief rays  170  corresponding to a polygonal edge, can be refracted by an outer compressor lens element  137  to nominally match the frustum edges in polyhedral geometries. 
     To help illustrate some issues relating to camera geometry,  FIG.  5 A  illustrates a cross-sections of a pentagonal lens  175  capturing a pentagonal FOV  177  and a hexagonal lens  180  capturing a hexagonal FOV  182 , representing a pair of adjacent cameras whose outer lens elements have pentagonal and hexagonal shapes, as can occur with a truncated icosahedron, or soccer ball type panoramic multi-camera capture devices (e.g.,  100 ,  300 ). The theoretical hexagonal FOV  182  spans a half FOV of 20.9°, or a full FOV of 41.8° (□ 1 ) along the sides, although the FOV near the vertices is larger. The pentagonal FOV  177  supports 36.55° FOV (□ 2 ) within a circular region, and larger FOVs near the corners or vertices. Notably, in this cross-section, the pentagonal FOV  177  is asymmetrical, supporting a 20-degree FOV on one side of an optical axis  185 , and only a 16.5-degree FOV on the other side of the optical axis. 
     Optical lenses are typically designed using programs such as ZEMAX or Code V. Design success typically depends, in part, on selecting the best or most appropriate lens parameters, identified as operands, to use in the merit function. This is also true when designing a lens system for an improved low-parallax multi-camera panoramic capture device ( 300 ), for which there are several factors that affect performance (including, particularly parallax) and several parameters that can be individually or collectively optimized, so as to control it. One approach targets optimization of the “NP” point, or more significantly, variants thereof. 
     As background, in the field of optics, there is a concept of the entrance pupil, which is a projected image of the aperture stop as seen from object space, or a virtual aperture which the imaged light rays from object space appear to propagate towards before any refraction by the first lens element. By standard practice, the location of the entrance pupil can be found by identifying a paraxial chief ray from object space  105 , that transits through the center of the aperture stop, and projecting or extending its object space direction forward to the location where it hits the optical axis  185 . In optics, incident Gauss or paraxial rays are understood to reside within an angular range ≤10° from the optical axis, and correspond to rays that are directed towards the center of the aperture stop, and which also define the entrance pupil position. Depending on the lens properties, the entrance pupil may be bigger or smaller than the aperture stop, and located in front of, or behind, the aperture stop. 
     By comparison, in the field of low-parallax cameras, there is a concept of a no-parallax (NP) point, or viewpoint center. Conceptually, the “NP Point” has been associated with a high FOV chief ray or principal ray incident at or near the outer edge of the outermost lens element, and projecting or extending its object space direction forward to the location where it hits the optical axis  185 . For example, depending on the design, camera channels in a panoramic multi-camera capture device can support half FOVs with non-paraxial chief rays at angles &gt;31° for a dodecahedron type system ( FIG.  4   ) or &gt;20° for a truncated icosahedron type system (see  FIG.  4    and  FIG.  5 A ). This concept of the NP point projection has been applied to the design of panoramic multi-camera capture devices, relative to the expectations for chief ray propagation and parallax control for adjacent optical systems (cameras). It is also stated that if a camera is pivoted about the NP point, or a plurality of camera&#39;s appear to rotate about a common NP point, then parallax errors will be reduced, and images can be aligned with little or no parallax error or perspective differences. But in the field of low parallax cameras, the NP point has also been equated to the entrance pupil, and the axial location of the entrance pupil that is estimated using a first order optics tangent relationship between a projection of a paraxial field angle and the incident ray height at the first lens element (see  FIGS.  2 A,  2 B ). 
     Thus, confusingly, in the field of designing of low-parallax cameras, the NP point has also been previously associated with both with the projection of edge of FOV chief rays and the projection of chief rays that are within the Gauss or paraxial regime. As will be seen, in actuality, they both have value. In particular, an NP point associated with the paraxial entrance pupil can be helpful in developing initial specifications for designing the lens, and for describing the lens. An NP point associated with non-paraxial edge of field chief rays can be useful in targeting and understanding parallax performance and in defining the conical volume or frustum that the lens assembly can reside in. 
     The projection of these non-paraxial chief rays can miss the paraxial chief ray defined entrance pupil because of both lens aberrations and practical geometry related factors associated with these lens systems. Relative to the former, in a well-designed lens, image quality at an image plane is typically prioritized by limiting the impact of aberrations on resolution, telecentricity, and other attributes. Within a lens system, aberrations at interim surfaces, including the aperture stop, can vary widely, as the emphasis is on the net sums at the image plane. Aberrations at the aperture stop are often somewhat controlled to avoid vignetting, but a non-paraxial chief ray need not transit the center of the aperture stop or the projected paraxially located entrance pupil. 
     To expand on these concepts, and to enable the design of improved low parallax lens systems, it is noted that the camera lens system  120  in  FIG.  2 A  depicts both a first NP point  190 A, corresponding to the entrance pupil as defined by a vectoral projection of paraxial chief rays from object space  105 , and an offset second NP point  190 B, corresponding to a vectoral projection of a non-paraxial chief rays from object space. Both of these ray projections cross the optical axis  185  in locations behind both the lens system and the image plane  150 . As will be subsequently discussed, the ray behavior in the region between and proximate to the projected points  190 A and  190 B can be complicated and neither projected location or point has a definitive value or size. A projection of a chief ray will cross the optical axis at a point, but a projection of a group of chief rays will converge towards the optical axis and cross at different locations, that can be tightly clustered (e.g., within a few or tens of microns), where the extent or size of that “point” can depends on the collection of proximate chief rays used in the analysis. Whereas, when designing low parallax imaging lenses that image large FOVs, the axial distance or difference between the NP points  190 A and  190 B that are provided by the projected paraxial and non-paraxial chief rays can be significantly larger (e.g., millimeters). Thus, as will also be discussed, the axial difference represents a valuable measure of the parallax optimization (e.g., a low parallax volume  188 ) of a lens system designed for the current panoramic capture devices and applications. As will also be seen, the design of an improved device ( 300 ) can be optimized to position the geometric center of the device, or device center  196 , outside, but proximate to this low parallax volume  188 , or alternately within it, and preferably proximate to a non-paraxial chief ray NP point. 
     As one aspect,  FIG.  5 A  depicts the projection of the theoretical edge of the fields of view (FOV edges  155 ), past the outer lens elements (lenses  175  and  180 ) of two adjacent cameras, to provide lines directed to a common point ( 190 ). These lines represent theoretical limits of the complex “conical” opto-mechanical lens assemblies, which typically are pentagonally conical or hexagonally conical limiting volumes. Again, ideally, in a no-parallax multi-camera system, the entrance pupils or NP points of two adjacent cameras are co-located. But to avoid mechanical conflicts, the mechanics of a given lens assembly, including the sensor package, should generally not protrude outside a frustum of a camera system and into the conical space of an adjacent lens assembly. However, real lens assemblies in a multi-camera panoramic capture device are also separated by seams  160 . Thus, the real chief rays  170  that are accepted at the lens edges, which are inside of both the mechanical seams and a physical width or clear aperture of a mounted outer lens element (lenses  175  and  180 ), when projected generally towards a paraxial NP point  190 , can land instead at offset NP points  192 , and be separated by an NP point offset distance  194 . 
     This can be better understood by considering the expanded area A-A in proximity to a nominal or ideal point NP  190 , as shown in detail in  FIG.  5 B . Within a hexagonal FOV  182 , light rays that propagate within the Gauss or paraxial region (e.g., paraxial ray  173 ), and that pass through the nominal center of the aperture stop, can be projected to a nominal NP point  190  (corresponding to the entrance pupil), or to an offset NP point  190 A at a small NP point difference or offset  193  from a nominal NP point  190 . Whereas, the real hexagonal lens edge chief rays  170  associated with a maximum inscribed circle within a hexagon, can project to land at a common offset NP point  192 A that can be at a larger offset distance ( 194 A). The two adjacent cameras in  FIGS.  5 A ,B also may or may not share coincident NP points (e.g.,  190 ). Distance offsets can occur due to various reasons, including geometrical concerns between cameras (adjacent hexagonal and pentagonal cameras), geometrical asymmetries within a camera (e.g., for a pentagonal camera), or from limitations from the practical widths of seams  160 , or because of the directionality difference amongst aberrated rays. 
     As just noted, there are also potential geometric differences in the projection of incident chief rays towards a simplistic nominal “NP point” ( 190 ). First, incident imaging light paths from near the corners or vertices or mid-edges (mid-chords) of the hexagonal or pentagonal lenses may or may not project to common NP points within the described range between the nominal paraxial NP point  190  and an offset NP point  192 B. Also, as shown in  FIG.  5 B , just from the geometric asymmetry of the pentagonal lenses, the associated pair of edge chief rays  170  and  171  for the real accepted FOV, can project to different nominal NP points  192 B that can be separated from both a paraxial NP point ( 190 ) by an offset distance  194 B and from each other by an offset distance  194 C. 
     As another issue, during lens design, the best performance typically occurs on axis, or near on axis (e.g., ≤0.3 field (normalized)), near the optical axis  185 . In many lenses, good imaging performance, by design, often occurs at or near the field edges, where optimization weighting is often used to force compliance. The worst imaging performance can then occur at intermediate fields (e.g., 0.7-0.8 of a normalized image field height). Considering again  FIG.  5 A ,B, intermediate off axis rays, from intermediate fields (D) outside the paraxial region, but not as extreme as the edge chief rays (10°&lt;□&lt;20.9°), can project towards intermediate NP points between a nominal NP point  190  and an offset NP point  192 B. But other, more extreme off axis rays, particularly from the 0.7-0.8 intermediate fields, that are more affected by aberrations, can project to NP points at locations that are more or less offset from the nominal NP point  190  than are the edge of field offset NP points  192 B. Accounting for the variations in lens design, the non-paraxial offset “NP” points can fall either before (closer to the lens) the paraxial NP point (the entrance pupil) as suggested in  FIG.  5 B , or after it (as shown in  FIG.  2 A ). 
     This is shown in greater detail in  FIG.  5 C , which essentially illustrates a further zoomed-in region A-A of  FIG.  5 B , but which illustrates an impact from vectoral projected ray paths associated with aberrated image rays, that converge at and near the paraxial entrance pupil ( 190 ), for an imaging lens system that was designed and optimized using the methods of the present approach. In  FIG.  5 C , the projected ray paths of green aberrated image rays at multiple fields from a camera lens system converge within a low parallax volume  188  near one or more “NP” points. Similar illustrations of ray fans can also be generated for Red or Blue light. The projection of paraxial rays  173  can converge at or near a nominal paraxial NP point  190 , or entrance pupil, located on a nominal optical axis  185  at a distance Z behind the image plane  150 . The projection of edge of field rays  172 , including chief rays  171 , converge at or near an offset NP point  192 B along the optical axis  185 . The NP point  192 B can be quantitatively defined, for example, as the center of mass of all edge of field rays  172 . An alternate offset NP point  192 A can be identified, that corresponds to a “circle of least confusion”, where the paraxial, edge, and intermediate or mid-field rays, aggregate to the smallest spot. These different “NP” points are separated from the paraxial NP point by offset distances  194 A and  194 B, and from each other by an offset distance  194 C. Thus, it can be understood that an aggregate “NP point” for any given real imaging lens assembly or camera lens that supports a larger than paraxial FOV, or an asymmetrical FOV, is typically not a point, but instead can be an offset low parallax (LP) smudge or volume  188 . 
     Within a smudge or low parallax volume  188 , a variety of possible optimal or preferred NP points can be identified. For example, an offset NP point corresponding to the edge of field rays  172  can be emphasized, so as to help provide improved image tiling. An alternate mid-field (e.g., 0.6-0.8) NP point (not shown) can also be tracked and optimized for. Also the size and position of the overall “LP” smudge or volume  188 , or a preferred NP point (e.g.,  192 B) therein, can change depending on the lens design optimization. Such parameters can also vary amongst lenses, for one fabricated lens system of a given design to another, due to manufacturing differences amongst lens assemblies. Although  FIG.  5 C  depicts these alternate offset “NP points”  192 A,B for non-paraxial rays as being located after the paraxial NP point  190 , or further away from the lens and image plane, other lenses of this type, optimized using the methods of the present approach, can be provided where similar non-paraxial NP points  192 A,B that are located with a low parallax volume  188  can occur at positions between the image plane and the paraxial NP point. 
       FIG.  5 C  also shows a location for a center of the low-parallax multi-camera panoramic capture device, device center  196 . Based on optical considerations, an improved panoramic multi-camera capture device  300  can be preferably optimized to nominally position the device center  196  within the low parallax volume  188 . Optimized locations therein can include being located at or proximate either of the offset NP points  192 A or  192 B, or within the offset distance  194 B between them, so as to prioritize parallax control for the edge of field chief rays. The actual position therein depends on parallax optimization, which can be determined by the lens optimization relative to spherical aberration of the entrance pupil, or direct chief ray constraints, or distortion, or a combination thereof. For example, whether the spherical aberration is optimized to be over corrected or under corrected, and how weightings on the field operands in the merit function are used, can affect the positioning of non-paraxial “NP” points for peripheral fields or mid fields. The “NP” point positioning can also depend on the management of fabrication tolerances and the residual variations in lens system fabrication. The device center  196  can also be located proximate to, but offset from the low parallax volume  188 , by a center offset distance  198 . This approach can also help tolerance management and provide more space near the device center  196  for cables, circuitry, cooling hardware, and the associated structures. In such case, the adjacent cameras  120  can then have offset low parallax volumes  188  of “NP” points ( FIG.  5 D ), instead of coincident ones ( FIGS.  5 A , B). In this example, if the device center  196  is instead located at or proximate to the paraxial entrance pupil, NP point  190 , then effectively one or more of the outer lens elements  137  of the cameras  120  are undersized and the desired full FOVs are not achievable.  FIG.  13 B  depicts the possible positioning of a similar lens system  920  with respect to an offset device center  910 . 
     Thus, while the no-parallax (NP) point is a useful concept to work towards, and which can valuably inform panoramic image capture and systems design, and aid the design of low-parallax error lenses, it is idealized, and its limitations must also be understood. Considering this discussion of the NP point(s) and LP smudges, in enabling an improved low-parallax multi-camera panoramic capture device (lens design example to follow; device  300  of  FIG.  13 A ), it is important to understand ray behavior in this regime, and to define appropriate parameters or operands to optimize, and appropriate target levels of performance to aim for. In the latter case, for example, a low parallax lens with a track length of 65-70 mm can be designed for in which the LP smudge is as much as 10 mm wide (e.g., offset distance  194 A). But alternate lens designs, for which this parameter is further improved, can have a low parallax volume  188  with a longitudinal LP smudge width or width along the optical axis (offset  194 A) of a few millimeters or less. 
     The width and location of the low parallax volume  188 , and the vectoral directions of the projections of the various chief rays, and their NP point locations within a low parallax volume, can be controlled during lens optimization by a method using operands associated with a fan of chief rays  170  (e.g.,  FIGS.  2 A ,B). But the LP smudge or LP volume  188  of  FIG.  5 C  can also be understood as being a visualization of the transverse component of spherical aberration of the entrance pupil, and this parameter can be used in an alternate, but equivalent, design optimization method to using chief ray fans. In particular, during lens optimization, using Code V for example, the lens designer can create a special user defined function or operand for the transverse component (e.g., ray height) of spherical aberration of the entrance pupil, which can then be used in a variety of ways. For example, an operand value can be calculated as a residual sum of squares (RSS) of values across the whole FOV or across a localized field, using either uniform or non-uniform weightings on the field operands. In the latter case of localized field preferences, the values can be calculated for a location at or near the entrance pupil, or elsewhere within a low parallax volume  188 , depending on the preference towards paraxial, mid, or peripheral fields. An equivalent operand can be a width of a circle of least confusion in a plane, such as the plane of offset NP point  192 A or that of offset NP  192 B, as shown in  FIG.  5 C . The optimization operand can also be calculated with a weighting to reduce or limit parallax error non-uniformly across fields, with a disproportionate weighting favoring peripheral or edge fields over mid-fields. Alternately, the optimization operand can be calculated with a weighting to provide a nominally low parallax error in a nominally uniform manner across all fields (e.g., within or across a Core FOV  205 , as in  FIG.  7   ). That type of optimization may be particularly useful for mapping applications. 
     Whether the low-parallax lens design and optimization method uses operands based on chief rays or spherical aberration of the entrance pupil, the resulting data can also be analyzed relative to changes in imaging perspective. In particular, parallax errors versus field and color can also be analyzed using calculations of the Center of Perspective (COP), which is a parameter that is more directly relatable to visible image artifacts than is a low parallax volume, and which can be evaluated in image pixel errors or differences for imaging objects at two different distances from a camera system. The center of perspective error is essentially the change in a chief ray trajectory given multiple object distances—such as for an object at a close distance (3 ft), versus another at “infinity.” 
     In drawings and architecture, perspective, is the art of drawing solid objects on a two-dimensional surface so as to give a correct impression of their height, width, depth, and position in relation to each other when viewed from a particular point. For example, for illustrations with linear or point perspective, objects appear smaller as their distance from the observer increases. Such illustrated objects are also subject to foreshortening, meaning that an object&#39;s dimensions along the line of sight appear shorter than its dimensions across the line of sight. Perspective works by representing the light that passes from a scene through an imaginary rectangle (realized as the plane of the illustration), to a viewer&#39;s eye, as if the viewer were looking through a window and painting what is seen directly onto the windowpane. 
     Perspective is related to both parallax and stereo perception. In a stereoscopic image capture or projection, with a pair of adjacent optical systems, perspective is a visual cue, along with dual view parallax, shadowing, and occlusion, that can provide a sense of depth. As noted previously, parallax is the visual perception that the position or direction of an object appears to be different when viewed from different positions. In the case of image capture by a pair of adjacent cameras with at least partially overlapping fields of view, parallax image differences are a cue for stereo image perception, or are an error for panoramic image assembly. 
     To capture images with an optical system, whether a camera or the human eye, the optical system geometry and performance impacts the utility of the resulting images for low parallax (panoramic) or high parallax (stereo) perception. In particular, for an ideal lens, all the chief rays from object space point exactly towards the center of the entrance pupil, and the entrance pupil is coincident with the center of perspective (COP) or viewpoint center for the resulting images. There are no errors in perspective or parallax for such an ideal lens. 
     But for a real lens, having both physical and image quality limitations, residual parallax errors can exist. As stated previously, for a real lens, a projection of the paraxial chief rays from the first lens element, will point towards a common point, the entrance pupil, and its location can be determined as an axial distance from the front surface of that first element. Whereas, for a real lens capturing a FOV large enough to include non-paraxial chief rays, the chief rays in object space can point towards a common location or volume near, but typically offset from, the center of the entrance pupil. These chief rays do not intrinsically coincide at a single point, but they can be directed through a small low parallax volume  188  (e.g., the LP “smudge”) by appropriate lens optimization. The longitudinal or axial variation of rays within the LP smudge can be determined from the position a chief ray crosses the optic axis. The ray errors can also be measured as a transverse width or axial position of the chief rays within an LP smudge. 
     The concept of parallax correction, with respect to centers of perspective, is illustrated in  FIG.  5 D . A first camera lens  120 A collects and images light from object space  105  into at least a Core FOV, including light from two outer ray fans  179 A and  179 B, whose chief ray projections converge towards a low parallax volume  188 A. These ray fans can correspond to a group of near edge or edge of field rays  172 , as seen in  FIG.  2 B  or  FIG.  5 C . As was shown in  FIG.  5 C , within an LP volume  188 , the vectoral projection of such rays from object space, generally towards image space, can cross the optical axis  185  beyond the image plane, at or near an alternate NP point  192 B that can be selected or preferred because it favors edge of field rays. However, as is also shown in  FIG.  5 C , such edge of field rays  172  need not cross the optical axis  185  at exactly the same point. Those differences, when translated back to object space  105 , translate into small differences in the parallax or perspective for imaged ray bundles or fans within or across an imaged FOV (e.g., a Core FOV  205 , as in  FIG.  7   ) of a camera lens. 
     A second, adjacent camera lens  120 B, shown in  FIG.  5 D , can provide a similar performance, and image a fan of chief rays  170 , including ray fan  179 C, from within a Core FOV  205  with a vectoral projection of these chief rays converging within a corresponding low parallax volume  188 B. LP volumes  188 A and  188 B can overlap or be coincident, or be offset, depending on factors including the camera geometries and the seams between adjacent cameras, or lens system fabrication tolerances and compensators, or on whether the device center  196  is offset from the LP volumes  188 . The more overlapped or coincident these LP volumes  188  are, the more overlapped are the centers of perspective of the two lens systems. Ray Fan  179 B of camera lens  120 A and ray fan  179 C of camera lens  120 B are also nominally parallel to each other; e.g., there is no parallax error between them. However, even if the lens designs allow very little residual parallax errors at the FOV edges, fabrication variations between lens systems can increase the differences. 
     Analytically, the chief ray data from a real lens can also be expressed in terms of perspective error, including chromatic errors, as a function of field angle. Perspective error can then be analyzed as a position error at the image between two objects located at different distances or directions. Perspective errors can depend on the choice of COP location, the angle within the imaged FOV, and chromatic errors. For example, it can be useful to prioritize a COP so as to minimize green perspective errors. Perspective differences or parallax errors can be reduced by optimizing a chromatic axial position (Dz) or width within an LP volume  188  related to a center of perspective for one or more field angles within an imaged FOV. The center of perspective can also be graphed and analyzed as a family of curves, per color, of the Z (axial) intercept position (distance in mm) versus field angle. Alternately, to get a better idea of what a captured image will look like, the COP can be graphed and analyzed as a family of curves for a camera system, as a parallax error in image pixels, per color, versus field. 
     During the design or a camera lens systems, a goal can be to limit the parallax error to a few pixels or less for imaging within a Core FOV  205  ( FIG.  7   ). Alternately, it can be preferable to particularly limit parallax errors in the peripheral fields, e.g., for the outer edges of a Core FOV and for an Extended FOV region (if provided). If the residual parallax errors for a camera are thus sufficiently small, then the parallax differences seen as a perspective error between two adjacent cameras near their shared seam  160 , or within a seam related region of extended FOV overlap imaging, can likewise be limited to several pixels or less (e.g., ≤3-4 pixels). Depending on the lens design, device design, and application, it can be possible and preferable to reduce parallax errors for a lens system further, as measured by perspective error, to ≤0.5 pixel for an entire Core FOV, the peripheral fields, or both. If these residual parallax errors for each of two adjacent cameras are small enough, images can be acquired, cropped, and readily tiled, while compensating for or hiding image artifacts from any residual seams  160  or blind regions  165 . 
     In pursuing the design of a panoramic camera of the type of that of  FIG.  1   , but to enable an improved low-parallax multi-camera panoramic capture device ( 300 ), having multiple adjacent cameras, the choices of lens optimization methods and parameters can be important. A camera lens  120 , or system of lens elements  135 , like that of  FIG.  2 A , can be used as a starting point. The camera lens has compressor lens element(s), and inner lens elements  140 , the latter of which can also be defined as consisting of a pre-stop wide angle lens group, and a post-stop eyepiece-like lens group. In designing such lenses to reduce parallax errors, it can be valuable to consider how a fan of paraxial to non-paraxial chief rays  125  (see  FIG.  2 A ), or a fan of edge chief rays  170  (see  FIG.  2 B ), or localized collections of edge of field rays  172  (see  FIG.  5 C ) or  179  A,B (see  FIG.  5 D ) are imaged by a camera lens assembly. It is possible to optimize the lens design by using a set of merit function operands for a collection or set (e.g.,  31  defined rays) of chief rays, but the optimization process can then become cumbersome. As an alternative, in pursuing the design of an improved low-parallax multi-camera panoramic capture device ( 300 ), it was determined that improved performance can also be obtained by using a reduced set of ray parameters or operands that emphasizes the transverse component of spherical aberration at the entrance pupil, or at a similar selected surface or location (e.g., at an offset NP point  192 A or  192 B) within an LP smudge volume  188  behind the lens system. Optimization for a transverse component of spherical aberration at an alternate non-paraxial entrance pupil can be accomplished by using merit function weightings that emphasize the non-paraxial chief rays. 
     As another aspect, in a low-parallax multi-camera panoramic capture device, the fans of chief rays  170  that are incident at or near a beveled edge of an outer lens element of a camera  120  (see  FIG.  2 B ) should be parallel to a fan of chief rays  170  that are incident at or near an edge  132  of a beveled surface of the outer lens element of an adjacent camera (see  FIG.  1   ). It is noted that an “edge” of an outer lens element  137  or compressor lens is a 3-dimensional structure (see  FIG.  2 B ), that can have a flat edge cut through a glass thickness, and which is subject to fabrication tolerances of that lens element, the entire lens assembly, and housing  130 , and the adjacent seam  160  and its structures. The positional definition of where the beveled edges are cut into the outer lens element depends on factors including the material properties, front color, distortion, parallax correction, tolerances, and an extent of any extra extended FOV  215 . An outer lens element  137  becomes a faceted outer lens element when beveled edges  132  are cut into the lens, creating a set of polygonal shaped edges that nominally follow a polygonal pattern (e.g., pentagonal or hexagonal). 
     A camera system  120  having an outer lens element with a polygonal shape that captures incident light from a polygonal shaped field of view can then form a polygonal shaped image at the image plane  150 , wherein the shape of the captured polygonal field of view nominally matches the shape of the polygonal outer lens element. The cut of these beveled edges for a given pair of adjacent cameras can affect both imaging and the optomechanical construction at or near the intervening seam  160 . 
     As another aspect,  FIG.  5 E  depicts “front color”, which is a difference in the nominal ray paths by color versus field, as directed to an off axis or edge field point. Typically, for a given field point, the blue light rays are the furthest offset. As shown in  FIG.  5 E , the accepted blue ray  157  on a first lens element  137  is DX≈1 mm further out than the accepted red ray  158  directed to the same image field point. If the lens element  137  is not large enough, then this blue light can be clipped or vignetted and a color shading artifact can occur at or near the edges of the imaged field. Front color can appear in captured image content as a narrow rainbow-like outline of the polygonal FOV or the polygonal edge of an outer compressor lens element  437  which acts as a field stop for the optical system. Localized color transmission differences that can cause front color related color shading artifacts near the image edges can be caused by differential vignetting at the beveled edges of the outer compressor lens element  137 , or from edge truncation at compressor lens elements  438  ( FIG.  13 A ), or through the aperture stop  145 . During lens design optimization to provide an improved camera lens ( 320 ), front color can be reduced (e.g., to DX≤0.5 mm width) as part of the chromatic correction of the lens design, including by glass selection within the compressor lens group or the entire lens design, or as a trade-off in the correction of lateral color. The effect of front color on captured images can also be reduced optomechanically, by designing an improved camera lens ( 320 ) to have an extended FOV  215  ( FIG.  7   ), and also the opto-mechanics to push straight cut or beveled lens edges  132  at or beyond the edge of the extended FOV  215 , so that any residual front color occurs outside the core FOV  220 . The front color artifact can then be eliminated during an image cropping step during image processing. The impact of front color or lateral color can also be reduced by a spatially variant color correction during image processing. As another option, an improved camera lens ( 320 ) can have a color dependent aperture at or near the aperture stop, that can, for example, provide a larger transmission aperture (diameter) for blue light than for red or green light. 
     Optical performance at or near the seams can be understood, in part, relative to distortion ( FIG.  6   ) and a set of defined fields of view ( FIG.  7   ). In particular,  FIG.  7    depicts potential sets of fields of view for which potential image light can be collected by two adjacent cameras. As an example, a camera with a pentagonally shaped outer lens element, whether associated with a dodecahedron or truncated icosahedron or other polygonal lens camera assembly, with a seam  160  separating it from an adjacent lens or camera channel, can image an ideal FOV  200  that extends out to the vertices ( 60 ) or to the polygonal edges of the frustum or conical volume that the lens resides in. However, because of the various physical limitations that can occur at the seams, including the finite thicknesses of the lens housings, the physical aspects of the beveled lens element edges, mechanical wedge, and tolerances, a smaller core FOV  205  of transiting image light can actually be imaged. The coated clear aperture for the outer lens elements  137  should encompass at least the core FOV  205  with some margin (e.g., 0.5-1.0 mm). As the lens can be fabricated with AR coatings before beveling, the coatings can extend out to the seams. The core FOV  205  can be defined as the largest low parallax field of view that a given real camera  120  can image. Equivalently, the core FOV  205  can be defined as the sub-FOV of a camera channel whose boundaries are nominally parallel to the boundaries of its polygonal cone (see  FIGS.  5 A and  5 B ). Ideally, with small seams  160 , and proper control and calibration of FOV pointing, the nominal Core FOV  205  approaches or matches the ideal FOV  200  in size. 
     During a camera alignment and calibration process, a series of image fiducials  210  can be established along one or more of the edges of a core FOV  205  to aid with image processing and image tiling or mosaicing. The resulting gap between a core FOV  205  supported by a first camera and that supported by an adjacent camera can result in blind regions  165  ( FIG.  5 A , B). To compensate for the blind regions  165 , and the associated loss of image content from a scene, the cameras can be designed to support an extended FOV  215 , which can provide enough extra FOV to account for the seam width and tolerances, or an offset device center  196 . As shown in  FIG.  7   , the extended FOV  215  can extend far enough to provide overlap  127  with an edge of the core FOV  205  of an adjacent camera, although the extended FOVs  215  can be larger yet. This limited image overlap can result in a modest amount of image resolution loss, parallax errors, and some complications in image processing as were previously discussed with respect to  FIG.  3   , but it can also help reduce the apparent width of seams and blind regions. However, if the extra overlap FOV is modest (e.g., ≤5%) and the residual parallax errors therein are small enough (e.g. ≤0.75 pixel perspective error), as provided by the present approach, then the image processing burden can be very modest. Image capture out to an extended FOV  215  can also be used to enable an interim capture step that supports camera calibration and image corrections during the operation of an improved panoramic multi-camera capture device  300 .  FIG.  7    also shows an inscribed circle within one of the FOV sets, corresponding to a subset of the core FOV  205 , that is the common core FOV  220  that can be captured in all directions from that camera. The angular width of the common core FOV  220  can be useful as a quick reference for the image capacity of a camera. An alternate definition of the common core FOV  220  that is larger, to include the entire core FOV  205 , can also be useful. The dashed line ( 225 ) extending from the common core FOV  220  or core FOV  205 , to beyond the ideal FOV  200 , to nominally include the extended FOV  215 , represents a region in which the lens design can support careful mapping of the chief or principal rays or control of spherical aberration of the entrance pupil, so as to enable low-parallax error imaging and easy tiling of images captured by adjacent cameras. 
     Across a seam  160  spanning the distance between two adjacent usable clear apertures between two adjacent cameras, to reduce parallax and improve image tiling, it can be advantageous if the image light is captured with substantial straightness, parallelism, and common spacing over a finite distance. The amount of FOV overlap needed to provide an extended FOV and limit blind regions can be determined by controlling the relative proximity of the entrance pupil (paraxial NP point) or an alternate preferred plane within a low parallax volume  188  (e.g., to emphasize peripheral rays) to the device center  196  (e.g., to the center of a dodecahedral shape). The amount of Extended FOV  215  is preferably 5% or less (e.g., ≤1.8° additional field for a nominal Core FOV of 37.5°), such that a camera&#39;s peripheral fields are then, for example, ˜0.85-1.05). If spacing constraints at the device center, and fabrication tolerances, are well managed, the extended FOV  215  can be reduced to ≤1% additional field. Within an extended FOV  215 , parallax should be limited to the nominal system levels, while both image resolution and relative illumination remain satisfactory. The parallax optimization to reduce parallax errors can use either chief ray or pupil aberration constraints, and targeting optimization for a high FOV region (e.g., 0.85-1.0 field), or beyond that to include the extra camera overlap regions provided by an extended FOV  215  (e.g.,  FIG.  7   , a fractional field range of ˜0.85-1.05). 
     In addition, in enabling an improved low-parallax multi-camera panoramic capture device ( 300 ), with limited parallax error and improved image tiling, it can be valuable to control image distortion for image light transiting at or near the edges of the FOV, e.g., the peripheral fields, of the outer lens element. In geometrical optics, distortion is a deviation from a preferred condition (e.g., rectilinear projection) that straight lines in a scene remain straight in an image. It is a form of optical aberration, which describes how the light rays from a scene are mapped to the image plane. In general, in lens assemblies used for image capture, for human viewing it is advantageous to limit image distortion to a maximum of +/−2%. In the current application, for tiling or combining panoramic images from images captured by adjacent cameras, having a modest distortion of ≤2% can also be useful. As a reference, in barrel distortion, the image magnification decreases with distance from the optical axis, and the apparent effect is that of an image which has been mapped around a sphere (or barrel). Fisheye lenses, which are often used to take hemispherical or panoramic views, typically have this type of distortion, as a way to map an infinitely wide object plane into a finite image area. Fisheye lens distortion ( 251 ) can be large (e.g., 15% at full field or 90° half width (HW)), as a deviation from f-theta distortion, although it is only a few percent for small fields (e.g., ≤30° HW). As another example, in laser printing or scanning systems, f-theta imaging lenses are often used to print images with minimal banding artifacts and image processing corrections for pixel placement. In particular, F-theta lenses are designed with a barrel distortion that yields a nearly constant spot or pixel size, and a pixel positioning that is linear with field angle θ, (h=f*θ). 
     Thus, improved low-parallax cameras  320  that capture half FOVs of ≤35-40° might have fisheye distortion  251 , as the distortion may be low enough. However, distortion can be optimized more advantageously for the design of improved camera lens assemblies for use in improved low-parallax multi-camera panoramic capture devices ( 300 ). As a first example, as shown in  FIG.  6   , it can be advantageous to provide camera lens assemblies with a localized nominal f-theta distortion  250 A at or near the edge of the imaged field. In an example, the image distortion  250  peaks at ˜0.75 field at about 1%, and the lens design is not optimized to provide f-theta distortion  250  below −0.85 field. However, during the lens design process, a merit function can be constrained to provide a nominally f-theta like distortion  250 A or an approximately flat distortion  250 B, for the imaged rays at or near the edge of the field, such as for peripheral fields spanning a fractional field range of ˜0.9-1.0. This range of high fields with f-theta type or flattened distortion correction includes the fans of chief rays  170  or perimeter rays of  FIG.  2 B , including rays imaged through the corners or vertices  60 , such as those of a lens assembly with a hexagonal or pentagonal outer lens element  137 . Additionally, because of manufacturing tolerances and dynamic influences (e.g., temperature changes) that can apply to a camera  120 , including both lens elements  135  and a housing  130 , and to a collection of cameras  120  in a panoramic multi-camera capture device, it can be advantageous to extend the region of nominal f-theta or flattened distortion correction in peripheral fields to beyond the nominal full field (e.g., 0.85-1.05). This is shown in  FIG.  6   , where a region of reduced or flattened distortion extends beyond full field to ˜1.05 field. In such a peripheral field range, it can be advantageous to limit the total distortion variation to ≤0.5% or less. Controlling peripheral field distortion keeps the image “edges” straight in the adjacent pentagonal shaped regions. This can allow more efficient use of pixels when tiling images, and thus faster image processing. 
     The prior discussion treats distortion in a classical sense, as an image aberration at an image plane. However, in low-parallax cameras, this residual distortion is typically a tradeoff or nominal cancelation of contributions from the compressor lens elements ( 137 , or  437  and  438  in  FIG.  13 A ) versus those of the aggregate inner lens elements ( 140 , or  440  in  FIG.  13 A ). Importantly, the ray re-direction caused by the distortion contribution of the outer compressor lens element also affects both the imaged ray paths and the projected chief ray paths towards the low parallax volume. This in turn means that for the design of at least some low-parallax lenses, distortion optimization can affect parallax or edge of field NP point or center of perspective optimization. 
     The definitions of the peripheral fields or a fractional field range  225  of (e.g., ˜0.85-1.05, or including ≤5% extra field), in which parallax, distortion, relative illumination, resolution, and other performance factors can be carefully optimized to aid image tiling, can depend on the device and camera geometries. As an example, for hexagonal shaped lenses and fields, the lower end of the peripheral fields can be defined as ˜0.83, and for pentagonal lenses, ˜0.8. Although  FIG.  7    was illustrated for a case with two adjacent pentagon-shaped outer lens elements and FOV sets, the approach of defining peripheral fields and Extended FOVs to support a small region of overlapped image capture, can be applied to multi-camera capture device designs with adjacent pentagonal and hexagonal cameras, or to adjacent hexagonal cameras, or to cameras with other polygonal shapes or with adjacent edges of any shape or contour generally. 
     For an Extended FOV  215  to be functionally useful, the nominal image formed onto an image sensor that corresponds to a core FOV  205  needs to underfill the used image area of the image sensor, by at least enough to allow an extended FOV  215  to also be imaged. This can be done to help account for real variations in fabricated lens assemblies from the ideal, or for the design having an offset device center  196 , as well as fabrication variations in assembling an improved low-parallax multi-camera panoramic capture device ( 300 ). But as is subsequently discussed, prudent mechanical design of the lens assemblies can impact both the imaged field of view of a given camera and the seams between the cameras, to limit mechanical displacements or wedge and help reduce parallax errors and FOV overlap or underlap. Likewise, tuning the image FOV (core FOV  205 ) size and position with compensators or with fiducials and image centroid tracking and shape tracking can help. Taken together in some combination, optimization of distortion and low or zero parallax imaging over extended peripheral fields, careful mechanical design to limit and compensate for component and assembly variations, and the use of corrective fiducials or compensators, can provide a superior overall systems solution. As a result, a captured image from a camera can readily be cropped down to the nominal size and shape expected for the nominal core FOV  205 , and images from multiple cameras can then be mosaiced or tiled together to form a panoramic image, with reduced burdens on image post-processing. However, an extended FOV  215 , if needed, should provide enough extra angular width (e.g., q 1 ≤5% of the FOV) to match or exceed the expected wedge or tilt angle q 2 , that can occur in the seams, q 1 ≥q 2 . 
     In designing an improved imaging lens of the type that can be used in a low-parallax panoramic multi-camera capture device ( 100  or  300 ), several first order parameters can be calculated so as to inform the design effort. A key parameter is the target size of the frustum or conical volume, based on the chosen polygonal configuration (lens size (FOV) and lens shape (e.g., pentagonal)) and the sensor package size. Other key parameters that can be estimated include the nominal location of the paraxial entrance pupil, the focal lengths of the compressor lens group and the wide-angle lens group, and the FOV seen by the wide-angle group. 
     But the design optimization for an improved camera lens ( 320 ) for use in an improved low-parallax panoramic multi-camera capture devices ( 300 ) also depends on how the numerous other lens attributes and performance metrics are prioritized. In particular, the relevant system parameters can include the control of parallax or the center of perspective (COP) error at the edges of an imaged field or for inner field locations or both, as optimized using fans of chief rays or spherical aberration of the entrance pupil). These parameters are closely linked with other key parameters including the width and positions of the “LP smudge” or volume  188 , the size of any center offset distance between the entrance pupil or LP smudge and the device center  196 , the target width of the gaps or seams, the extent of blind regions  165 , and the size of any marginal or extended FOV to provide overlap. The relevant performance metrics can include image resolution or MTF, distortion (particularly in the peripheral fields, and distortion of the first compressor lens element and of the compressor lens group), lateral color, relative illumination, front color, and color vignetting, telecentricity, and ghosting. Other relevant design variables can include mechanical and materials parameters such as the number of compressor lens elements, the configuration of the compressor lens group, the wide-angle lens group and eyepiece lens group, glass choices, the allowed maximum size of the first compressor or outer lens element, the sensor package size, the track length, the nominal distance from the image plane to the nearest prior lens element (e.g., working distance), the nominal distance from the image plane to the entrance pupil, the nominal distance from the image plane or the entrance pupil to the polygonal center or device center, manufacturing tolerances and limits, and the use of compensators. 
       FIG.  13 A  provides a cross-sectional view of an alternate and improved opto-mechanical design for an improved camera  320  that can be used in an improved panoramic multi-camera capture device  300 . In this exemplary design, the camera lens  320  has a lens form in which the compressor lens element has been split into a compressor lens group, including first and second compressor lens elements ( 437  and  438 ). The inner lens elements  400  include a wide-angle lens group located prior to the aperture stop  445 , that includes a fourth lens element  442 , and a post-stop eyepiece lens group. As previously, the lens system provides a paraxial NP point  490  that is offset from a non-paraxial chief ray NP point  492  that lie within a low parallax volume  488 . The size or width of this volume, and the location of NP Points of potential interest (e.g., paraxial, mid field, peripheral field, circle of least confusion based) within it, depends on design priorities and parallax optimization (e.g., spherical aberration of the entrance pupil, chief ray fans, distortion). While the lens form of the example camera lens systems designs of  FIG.  2 A  and  FIG.  13 A  are similar, the lenses vary in details and performance, including with their different compressor lens configurations. Because of differences in specifications and optimization methods and priorities, these lenses are also different in cost, performance, and manufacturability. 
     Depending on priorities, these lens systems can be optimized further, and the different variations of the lens form may be individually better suited for different markets or applications. In general, the outermost lens element, or first compressor lens element, has used Ohara SLAH52, SLAH53, and SLAH63 glasses (or equivalent glasses from Schott Glass (e.g., N-LAF36 and N-LASF43)), which are high index, low dispersion flint glasses with visible spectra refractive indices n˜1.80 and an Abbe number Vd˜41.5. It should be understood that other optical materials can be used for the lens elements in the camera lenses  520  generally, including for the compressor lens elements. For example, use of a high index, lower dispersion, mid-crown glass like Ohara SLAL-18 can be helpful for color correction. As another example, lens elements can also be made from optical ceramics such as Alon (n˜1.79, Vd˜57-72) or Spinel, which are extremely durable materials, similar to sapphire, but with excellent optical transparency, low dispersion, and a controllably modifiable isotropic crystalline structure. It should also be understood that the camera lenses of the present approach can also be designed with optical elements that consist of, or include, refractive, gradient index, glass or optical polymer, reflective, aspheric or free-form, Kinoform, fresnel, diffractive or holographic, sub-wavelength or metasurface, optical properties. These lens systems can also be designed with achromatic or apochromatic color correction, or with thermal defocus desensitization. 
     Although  FIG.  13 A  does not depict how the improved camera lens can be mounted within a lens housing, the close proximity of the large outer compressor lens element  437  to the large second compressor lens elements  438  that form a doublet, can require a careful to robustly support these elements in close proximity. As one approach, the first compressor lens element  437  can be positionally centered to the compressor doublet ( 438 ), and the doublet can be centered to a primary circular datum on the inside surface of the lens housing. This datum can be tightly tolerance to a channel centering hub  330 , so as to reduce tolerance buildup between adjacent camera channels. 
     While improving the optical design of the camera lens systems is important for enabling improved low-parallax panoramic multi-camera capture devices ( 300 ), improving the opto-mechanical design can be equivalently important. As suggested previously, the actual performance of a camera  120  can vary from the designed performance due to materials and fabrication variations amongst the individual lens elements  135  and the housing  130  and its constituent components, and the interactions thereof. As a result of such variations, the image quality (e.g., aberrations, including distortion), focal length (EFL) and magnification, working distance or track length, beam pointing or image location, and other attributes of a camera  120  can vary. These variations also mean that the assembly and performance of a given camera varies from that of another camera with nominally the identical opto-mechanical design. For example, the focal length of a set of nominally identical cameras can vary by ±2%, which in turn will cause a similar variation in the lens magnifications and FOVs. This variation can be reduced or eliminated by designing improved camera lenses varifocally to include a focal length compensator, such as with a lens element whose axial position can be adjusted. Alternately, the cameras  120  can be designed such that nominal image from a nominal camera underfills the image sensor, enough so that the image from a camera with a large (e.g., +2%) focal length lens also underfills a sensor, albeit with less margin. During calibration to determine a FOV, the EFL or magnification of a lens can be measured, and the sensor can also be aligned to be in focus for that lens. Image processing software can then be used to compensate the image for the lens variations, including compensating image size for magnification and distortion variations between lenses. 
     Considering the opto-mechanics in greater detail, the axial alignment or focal position of an image sensor, relative to an image plane  150  provided by a camera lens assembly ( 320 ) can be improved by means of an appropriate mechanism. For example,  FIG.  8    and  FIG.  9    show a portion of an improved panoramic multi-camera capture device  300 , in which an image sensor  270  can be assembled into a sensor package  265  that includes a mount  275  which includes a plate  290 , a circular flange, several adjustment screws  280 , flexures, or springs  285 . For example, three adjustment screws can be used to control X translation along with Z-axis rotation, and another set of three screws can be used to control Z-axis translation along with X-Y axes rotations, and an additional screw is used to control Y axis translation. A pair of springs are used to retain a gimbal plate  290 , while also allowing X and Z-axis translations respectively. Other adjustment designs or devices can be used, such as using pins and micrometers or pins and shims, within the tight space constraints that the camera  320  and the overall panoramic multi-camera capture device  300  allows. 
     Fabrication variations for individual cameras, and the opto-mechanical interactions between them, can have significant impact on the design and performance of a multi-camera capture device  300 . During the initial assembly of a multi-camera capture device  300 , the interaction of tolerances and mechanical wedge between a housing  430  of a first camera  320  and a housing  430  of a second adjacent and abutting camera  320  can affect the seams  400 , the pointing of the Core FOV  205  or Extended FOV  215  of individual cameras (causing FOV overlap or underlap), and thus affect a FOV captured by each of the cameras. Furthermore, co-alignment mounting stresses imparted to adjacent cameras by the close proximity mounting can physically distort one or more of the camera housings, and then potentially also distort or skew the optical imaging function of the camera lenses. As a result, a camera lens system can provide an image to the sensor that is shifted or rotated or tilted out of plane. These potential problems, or the risk of their occurrence, can be exacerbated by environmental influences, such as asymmetrical thermal loading or substantial asymmetrical optical loading. 
     To counter such issues, an improved multi-camera capture device  300 , as shown in  FIG.  9   , can include features to provide kinematic type mounting of individual cameras  320  or objective lenses. In particular,  FIG.  9    depicts two views of a dodecahedron multi-camera capture device  300 , including a partial cross-section in which 11 pentagonal cameras  320  are mounted to a central support  325  that occupies the nominal position of a twelfth potential camera channel. Each camera  320  has a separate base lens assembly or housing  430  that consists of a lens mount which mounts the compressor lens ( 437 ) while also mounting the inner lens elements  440  that together comprise a base lens assembly. Although for each camera  320 , the lens elements and housings  430  fit within the nominal conical space or volume, they need not nominally fill that space. Indeed, the abrupt ray bending provided by the compressor lens elements can mean that the inner lens elements  440  and their housings or barrels underfill the available space, and the overall lens housings  430  can taper further inwards, potentially leaving an open inner volume  390  between adjacent lens assemblies. 
     The housings  430  or base lens assemblies of  FIG.  9    also include a turned section, that can be machined on a CNC multi axis (5-axis) machine, and that mates with a tripod-like channel centering hub  330 . The lens housings  430  are preferably fabricated from a material such as stainless steel or invar. The channel centering hubs  330  can be entirely turned on a lathe except for the pentagonal flange, which is completed in a finish operation after the lathe. Being turned on a lathe means that exceptional concentricity and runout can be achieved, helping with the ultimate alignment of the channel. The housing  430  mates with the inside diameter of the channel centering hub  330  which is a key part of a central mount mechanical assembly that is designed to have a fit with it that ranges from a slip fit to a light interference fit, so as to ensure axial alignment without significant variations due to gap tolerances. This same fit reduces perpendicularity errors with respect to the channel axis. 
     The tripods or channel centering hubs  330  also include a turned section or ball pivot  340  that mates with a socket  345  of a spherical socket array  346  provided on the central support  325 . In this system, the camera  320  located in the polar position, opposite the central support  325 , is a rigidly placed reference channel. The center support  325  consists of a cylindrically shaped post with a ball on the top. The geometries for the center support  325  and tripods or centering hubs  330  can be designed to provide more space for power and communications cables, cooling lines, and mechanisms to secure the lens housings  430  or cables. In this example, the ball contains sockets  345 , each of which can receive a ball pivot  340 . The ball pivots  340  are at the ends of extended pins or ball pivot arms  342 . Although this ball and socket portion of the center support  325  mount can be expensive to machine, given the precision expected with respect to the position and depth of the sockets, the advantages are that centerline pointing is controlled, while there is only a single part per device  300  that demands exceptional precision. Whereas, each of the camera channels  320  may be machined with less precision, which eases both the fabrication and replacement costs. 
     The individual camera lens housings  430  of  FIG.  9    can also be provided with external or outside channel to channel datums  335 , located midway along the pentagonal sides or faces  337 . Each of these channel-to-channel datums  335  can comprise two parallel convexly curved slightly protruding bars that are separated by an intervening groove. These datums are designed to provide both single point or localized kinematic contacts or interactions between lens housings, such that the datum features interweave in such a way that only one part or housing will dominate in terms of tolerance. Since they are interwoven, only the variation of one part will influence the distance between each camera channel, and thus influence the angle between the channels. In particular, if one datum  335  is larger it will dominate because the other will not make contact. Thus, only one tolerance contributes for two parts. That the channel to channel datums  335  are interwoven from one camera  320  to another, also limits lateral movement between mating (pentagonal) faces or sides, while allowing limited angular movement of the lens housings  430 . 
     Individually, and in aggregate, the interactions between camera lens housings  430  or base lens assembly&#39;s limits mechanical displacements and wedge or channel pointing errors (roll, pitch and yaw) between cameras due to both the ball and socket arrangement and the datum features ( 335 ). Each camera channel assembly works together with its neighbors to limit channel pointing error. The portion of the base lens assembly ( 430 ) that holds the outer lens element  437  or compressor lens also has internal functional datums that can locate the compressor lens perpendicular relative, to the optical or mechanical channel axis, and it has additional internal datum features that limit axial misalignment. As will be discussed in subsequent detail with respect to  FIG.  16   , an additional set of alignment features provided on the ground edges of the compressor lens can function as a datum and interact with these internal datum features to limit pentagonal rotation about the channel axis as well. 
     The use of the alignment features depicted in  FIG.  9   , and particularly the ball pivot and socket datums ( 350  and  356 ) and the channel to channel datum features  335  reduces the risks of rotation, pivoting, or splay from one camera channel ( 320 ) to another. Thus, these features also help enable the seams  400  between cameras  320  to have more consistent thicknesses, with respect to the design values, than may have happened otherwise. The use of the internal features within the lens housing (e.g., compensators, adjustments screws, and shims) and external features between lens housings (e.g., channel to channel datums, ball and socket datums, and a channel loading support) help control Core FOV or Extended FOV pointing, so that one camera channel can be aligned to another adjacent channel. The combined use of channel to channel datums, ball and socket datums ( FIG.  10   ), and a channel loading support ( FIG.  17   ) also can help desensitize the device to mechanical or thermal loads. 
       FIG.  10    depicts a further design option for improving the opto-mechanical design of the outer lens elements  437 , or compressor lens elements, in proximity to the seams  400  in an improved multi-camera panoramic image capture device  300 . In particular, the edges of an outer lens element  437  can protrude beyond the upper or outer edge of a lens housing  430  such that two adjacent outer lens elements  437  of adjacent cameras  320  can be in near contact at the seams  400 . If these outer lens elements  437  are fabricated at least in part with a somewhat compliant material, then some amount of actual physical contact can be allowed. If, however, these outer lens elements  437  are fabricated with a brittle material, such as glass, then greater care is required. 
     In the configuration of  FIG.  10   , two adjacent outer lens elements  437  that have protruding edges are in near contact at the seams  400 . In a preferred design approach, the opposing edges are provided with a stepped edge angle  365  or structure. In the outermost portion, the two lenses and housing can provide a parallel seam  400  with a width of 1.0 mm or smaller. 
     In the innermost portion, where the inner beveled edges  370  of the adjacent outer lens elements  437  approach each other, the lens housing  430 , channel to channel datums  335  along sidewalls  337 , and flat surface datums  670  can be provided. The edge of each outer lens element  437  then has a stepped edge groove  380  that can be filled with a compliant adhesive. Above that, along the edges  432  or seams  400 , spanning the outermost edge portion of the adjacent outer lens elements  437 , these lens elements can be nearly abutting, and separated by a gap that can be only 0.5 mm wide, or smaller. In practice, the optimization of the seam width can depend on how brittle or compliant the lens material is (glass or polymer), the flexibility of a seam filling adhesive, the use of other protective measures, and the application. 
       FIG.  17    provides greater detail on how these and other features can be used during alignment and assembly. In particular,  FIG.  17    depicts a cross-sectional view of a portion of an improved multi-camera panoramic image capture device  300  of the present approach, in which 11 camera channels  320  are attached to a post or vertical central support  325  through which both wiring and cooling can be provided (see  FIG.  15    for more details).  FIG.  17    in particular depicts a design for the opto-mechanical hardware, albeit assembled without the lens elements (see  FIGS.  9  and  15    for illustrations of opto-mechanical hardware including lens elements).  FIG.  18 A  depicts key elements or components used in this example alignment and assembly approach in yet greater detail. 
     As shown in  FIG.  17   , a top camera  320  can be identified as a primary alignment channel  610 , while all other camera channels  320  shown are identified as secondary channels  615 . In particular, for the primary channel, the ball pivot arm  342  with ball pivot  340  of the channel centering hub  330 , mates into a ball socket datum  356  of the ball socket array  346 , where it can interact with a locking axial retention pin  348  that slips into an indent between the ball pivot arm  342  and the ball pivot  340 , to stop Z-axis (vertical) translation. The central hub or ball socket array  346  is preferably fabricated from stainless steel. An anti-rotation keying pin  349  is press fit into a localized hole provided in the ball pivot arm, so as to stop rotation of the primary camera channel  610  about the z-axis. The ball pivot arm  342  of the primary camera channel  610  has a light press fit into its ball socket datum  356 , so as to prevent rotations about the X and Y axes. 
     Alternately, the ball sockets  345  can have a latch mechanism (not shown) to load a ball pivot  340  against a ball socket datum  356 , as a means to provide both a loading force and a mechanism that has reduced sensitivity to a mechanical loading force being applied to the camera or the device. For example, a latching mechanism can have latches actuated with linkage assemblies. As compared to using a retention pin, a latching mechanism can be more compliant, robust, and reliable, if a camera channel  320  or the device  300  are impacted by a loading force. It is also noted that the lens housings  430  can also have identifying marks to ease alignment of a housing with adjacent lens housings. 
     As previously shown in  FIG.  9   , and shown in yet greater detail in  FIG.  18 A , each camera channel  320  has a pair of peripheral channel to channel datums  335  on each face or sidewall  337 , that are small (localized) and nominally centered along the faces or sides of the lens housing. For a pentagonal lens, each of the five sides would have a pair of datums ( 335 ). These datums are provided with curved surfaces  373  (shown in bold, and extended, for emphasis) so as to enable point to point type contact ( 375 ). In particular, each pair of channel to channel datums  335  has side faces which act as lateral datums between camera channels. They are curved to accommodate relative angular movement between channels. Each side datum only has an effective single point of contact  375  where each of their mating datum radial surfaces meet. Since the radii are very large, the datum surfaces approach a straight line. Thus, any shifting of the camera channels relative to each other that could result in an angular or centerline offset can then only have a minute effect on the relative lateral offset of a given camera channel. 
     As further shown in  FIG.  17   , an improved multi-camera panoramic image capture device  300  can also have a channel loading support  630  that biases all secondary channels  615  against the primary channel  610 . The channel loading support  630  employs peripheral datum pairs that are nominally identical to the channel to channel datums  335  used on each channel. The channel loading support  630  can also have a spring element  635  to facilitate loading of the secondary channels  615  against the primary channel  610 . The channel loading support  630  can also utilize a key feature for anti-rotation, although using a keyed support may impart superfluous constraints. 
     The primary alignment channel  610  (see  FIG.  17   ) is aligned and locked into place when its ball pivot arm  342  and ball pivot  340  are engaged with the pins ( 348 ,  349 ) of the channel centering hub  330 . The secondary camera channels  615  are then added, and are loosely aligned with their ball pivots  340  fit against datums within the sockets of the channel centering hub  330 . When the channel loading support  330  is added, at the seams  400 , it nudges the secondary channels  615  both against the primary channel  610  and each other. The relative size of the ball socket  345  to the ball pivots  340  of the secondary channels are provided so that the secondary channels  615  are constrained by the ball socket  345  in only the Z-direction. 
     Then at the seams  400 , for any two faces of adjacent camera channels ( 610 ,  615 ) to be parallel to each other, the configuration requires that at least three camera channels have their peripheral channel to channel datums  335 , with points of contact  375 , in contact with opposing channel to channel datums  335  with their points of contact  375 . This effectively constrains the secondary channels  615  for three degrees of freedom (DOF). It is recognized that applying traditional kinematic mechanical design principles, in which motion and constraints in 6 DOF can be precisely limited with little crosstalk, can be tricky in a device that can intrinsically locate a multitude of complex polygonal faces (e.g., hexagonal or pentagonal) in close proximity. In a case where more than 3 camera channels are in close proximity, if not in contact, with each other, the camera channels could become over constrained. Because the system can then be only quasi-kinematic, mechanical stresses and strains could then cause component mis-alignment or damage. These potential problems can be overcome by a variety of methods. As one example, the relatively small size and centered locations of the channel to channel datums  335  can limit any angular or spatial misalignment to relatively small amounts. As another example, a compliant material such as RTV can be applied in the seams  400  to absorb some stresses or strains, while the lens housings  430  can be designed and fabricated to be sufficiently rigid to resist deformations, mis-alignments, or damage. Seam width variations, including dynamic ones caused by thermal or mechanical loads, can also be compensated by providing improved cameras  320  that capture image light  415  with an extended FOV  215 . 
     As shown in  FIG.  18 A , a point of contact can occur along a line across the radial surface of a datum. Thus, each channel to channel datum  335  makes “line” contact with an adjacent set of channel to channel datums  335  if the mating surfaces are perfectly parallel. If not, only point contact is made. Typically, the peripheral channel to channel datums  335  only contact an opposing face at one point. For each channel to channel datum pair, only a single datum is likely to contact due to dimensional variations. This is an asset of this design approach, since only a single datum can influence the gap or seam  400  between adjacent camera channels. This approach can be used in various designs for an improved multi-camera panoramic image capture device  300 , including a device with a “soccer ball” or truncated icosahedron ( FIG.  4   ) geometry, where the primary alignment (camera) channel can be an external hexagonally shaped lens. This approach can also be used in the construction of “hemispherical” devices (see  FIG.  21   ). 
       FIG.  18 B- 1    depicts an across seam cross-sectional view of an alternate or refined version of the construction of lens housings  430 , and their interface near a seam  400 , to that shown in  FIG.  10    and  FIG.  18 A . In particular,  FIG.  18 B- 1    depicts portions of two adjacent lens housings  430 , located around a seam  400 , where each housing support an outer compressor lens element  437  and at least a second compressor lens element  438 . The lens housings  430  include internal light traps  457  and sides that extend up into grooves  433  that have been cut into the edges  432  of the outer lens elements  437 . The outer walls of the lens housings  430  are tapered, expanding towards the device center, so as to provider greater mechanical rigidity and robustness. The interaction of two pairs of adjacent channel to channel datums  335  can be seen in cross-section. 
       FIG.  18 B- 2    depicts an alternate cross-sectional view of these same components, but cut along or within a seam  400 , to show the interaction of channel to channel datums  335 . As in  FIG.  18 A , the adjacent pair channel to channel datums  335   a  and  335   b , each have curved surfaces  373  that interact locally to help register or align adjacent camera channels together. In this example, to further reduce the potential for over-constraint, the channel to channel datum pairs are asymmetrical and partially offset and are thus more likely to provide localized point contacts and less likely to cause over-constraint. It is noted that the circular holes  530  provide access through a side wall of a lens housing  430 , to enable application of adhesive or RTV used in mounting an outer lens element  437  to the housing. 
     During assembly and alignment of the camera channels, it is also important to properly position the lens elements within the housings. For example, the compressor lens ( 437 ) can be provided with datum features along edges  432  that interact with a set of mating datum features on the inside of the lens housing  430 . The datum features provided on the lens elements are intended to limit perpendicularity and concentricity error and are designed to be reasonably machined or ground features, or to be mounted onto the ground glass lens bevel surfaces with an adhesive. As shown in  FIG.  16   , these features can include flat datum surfaces  650  fabricated on the bottom face of the compressor lens at the corner, outside the FOV. Other datums, including adjacent flat edges  660 , that can be ground into the round lens element before it was shaped into a pentagon with truncated or beveled edges  370 , can be mated with flat surface datums  670  on the lens mount. As glass is typically mounted to metals with adhesives, these flat edge datums can provide a guiding alignment without risk of over constraint. The outer lens element  437  can also be provided with an anti-clocking datum feature  680 , likely bonded to one of the beveled surfaces. 
     Because of these datum features, the chamfered or beveled finishes on the pentagonal lens surfaces can be fabricated with significantly less precision, thus helping to reduce lens cost. Even though  FIG.  9    depicts a pentagon-shaped compressor lens or outer lens element  437  and housing  430 , these mechanical approaches to reduce mis-alignment errors can also be applied to hexagonally shaped lenses, or lens elements having other polygonal shapes. 
     Alternately, or in addition, the lens housings  430  can be equipped with one or more tab or post like structures (not shown) that can protrude out from a lens housing out of the nominal conical space or volume and interact with similar protruding structures of an adjacent lens housing, or alternately interact with indented structures of an adjacent lens housing. For example, these protruding structures can be provided in the general vicinity of the sensor  270  and sensor package  265 , and be several millimeters in length, and have datum features to help kinematically control a DOF, such as a radial position from the device center, or a tilt or rotation of one camera channel to an adjacent camera channel. A camera assembly can have two such protruding structures, arranged symmetrically or asymmetrically about the lens housing and one oriented orthogonally to the other, to control a different degree of freedom. Alternately, or in addition, the camera channels can have lens housings  430  that include one or more protruding tab, or post structures located within the seams  400 . For example, such datum structures (not shown) can be provided within the seams, at the polygonal outer face of a camera channel, at a vertex  60 , and can protrude out of the nominal conical space or volume and into the seam  400  between the two adjacent channels. Depending on the device design and intended applications, the protruding tab or structures, whether located in the outer seams  400 , or more deeply imbedded, such as near the image sensors, can be either be fabricated from a compliant or a stiff material, or a combination thereof. As another alternative, one or more tabs of a given lens housing  430  need not protrude outside the nominal conical volume or frustum, but clamps that bridge from one tab to a tab of an adjacent lens housing can provide the interface or control to limit a degree of freedom, or to help prevent over constraint or under constraint of one lens housing with another. 
       FIG.  19    depicts an alternate version of the interface of the camera channels to the mounting structure near the device center to that shown in  FIG.  9    and  FIG.  17   . In particular,  FIG.  19    depicts portions of two adjacent camera channels, an upper primary channel  610  in cross-section and a secondary channel  615  in partial perspective. In this case, a tripod or channel centering hub  330  has a socket  545  that provides a concave surface that contacts a nominally matching convex surface of a central hub  550 . The central hub  550  is part of a mount mechanical assembly nominally positioned with its center at the device center, and it can be attached to a support post  750 . A cable  560 , having a ball  565  at an end, can be used to pull or tension the socket  545  against the central hub  550 . The primary channel, and each of the secondary channels, can be held together by similar tensioned cables that descend into the support post, where they are fastened and locked. Alternately, the primary channel  610  can be held in place with a tightened bolt (not shown). As compared to the prior approaches of  FIG.  9    and  FIG.  17   , this approach has exchanged the plurality of balls and sockets for an inverted configuration with a plurality of sockets  545  (one per camera channel) contacting one main ball or hub  550 . The tensioned cables replace the prior approaches that used retention pins, or latches, or springs. The approach of  FIG.  19    can enable numerous camera channels to be simultaneously and robustly pulled into alignment against the ball hub  550 , and about the device center. The ball hub  550  can be machined from a precision ball bearing fabricated from stainless steel. 
     In the examples shown in  FIG.  9   ,  FIG.  10   ,  FIG.  18 A , and  FIG.  18 B , the plurality of adjacent and abutting low parallax cameras have outer lens elements with polygonal edges that capture polygonal FOVs and lens housings that generally fit within limiting volumes, e.g. pentagonally-conical or hexagonally-conical limiting volumes. Once the camera lens housings mechanically clear the image plane or image sensor package and associated cooling hardware, they taper inwards quickly (e.g., via the tripods  330 ) to provide room for a central mounting structure, such as the spherical socket array  346  or the central hub  550 . The camera channel housings  430  interface to each other by means including the channel-to-channel datums  335 . 
       FIG.  22 A  depicts an alternate version for opto-mechanical designs for camera lens housings that generally fit within pentagonally conical or hexagonally conical limiting volumes so as to position and support adjacent and abutting low-parallax camera channels. In particular,  FIG.  22 A  depicts portions of five adjacent imaging lenses or camera channels  1100 , including an upper primary channel  1110 , and four secondary channels  1115 , that are separated by narrow seams  1105 . The camera channels  1100  each include a lens housing  1130 , a polygonal shaped outer lens element  1138 , and a channel centering hub or tripod  1140  that mounts and interfaces to a central hub  1150 . Part of at least one tertiary camera channel  1120  is also depicted.  FIG.  22 B  then depicts an exploded perspective view of a portion of the design of  FIG.  22 A , providing greater detail of the interface of one of the secondary channels  1115  to the primary channel  1110 . 
     In the design of  FIGS.  22 A and  22 B , unlike in the examples above using the channel to channel datums  335 , channel to channel datums include kinematic ball, flat, and vee features. In particular, the primary channel  1110  can include a plurality of balls  1160  (or otherwise partially-spherical or arcuate surface) protruding from faces or sides  1135  of the lens housing  1130 . During assembly of a primary camera channel  1110 , a pair of the balls  1160  can be aligned using fixturing (not shown) so as to protrude from their respective side or face  1135  of housing  1130  by a prescribed amount, within a tolerance. The lens housings  1130  of the secondary channels  1115  can then be fabricated with a corresponding vee slot  1162  and flat  1165 . During assembly of the multi-camera capture device  300 , the primary channel  1110  can be aligned to the central hub  1150  with a pin (not shown) and mounted using a tensioned cable (see  FIG.  19   ) or a bolt to pull the channel centering hub or tripod  1140  into contact with the central hub  1150 . A secondary channel  1115  can then likewise be mounted to the central hub  1150  using a second spring tensioned cable  1155 . As the assembly process occurs, spanning or across the seam  1105 , first of the balls  1160  protrudes to contact the corresponding secondary vee slot  1162  and a second of the balls  1160  protrudes to contact a corresponding one of the flats  1165 . The interaction of the first of the kinematic balls  1160  with the kinematic vee slot  1162  stops movement in two directions, positioning the two camera channels relative to each other with both accuracy and precision. Likewise, the second of the precision balls  1160  on the primary channel can interact with the corresponding flat  1162  of the opposing secondary channel  1115  to stop rotation in a third direction and provide a stable and repeatable relative positioning of the two camera channels to each other. As an example, the balls  1160  can be precision stainless steel balls with a nominal 0.188-inch diameter, and the precision vee slots  1162  can be have a nominal 110-degree angle. 
     The opto-mechanical interface of the multi-camera capture device  300  depicted in  FIGS.  22 A and  22 B  also includes magnets  1170  on the camera lens housings  1130 . For example, on a side face  1135  of the primary channel  1110 , one of the magnets  1170  can be provided near each of the balls  1160 . For example, on a primary channel side face, the two magnets  1170  can be mounted with their north poles facing outwards. Each magnet can be set and glued within a machined pocket to a precise height while being oriented so that the magnet will not interfere with the magnet in the next assembly, and the poles will be attracted. Lens housings  1130  are preferably fabricated from stainless steel, such as alloy  416 , which has magnetic properties, that help collapse the inwards directed magnetic field and enhance the outwards directed (e.g., towards a secondary channel) magnetic field. 
     On an adjacent secondary channel  1115 , two magnets  1170  can be provided adjacent to the vee slot  1162  and the flat  1165 , with their South poles facing outwards. When the two camera channels are brought into proximity, the effect of magnetic attraction between North and South poles will span the seam  1105 . This magnetic attraction can ensure that the two camera channels are pulled towards each other, such that the vee slot  1162  and the flat  1165  are in contact with their respective precision balls  1160 , thus bringing two channels into kinematic alignment and preventing under constraint relative to channel-to-channel separation or rotation. As an example, permanent rare earth magnets, part number D32SH from K&amp;J Magnetics of Pipersville, Pa., that are 3/16″ dia.×⅛″ thick, with a pull force or 1-2 lbs., can be used. With approximate gap across the seam between the magnets  1170  of 0.75 mm, and with the magnets mounted into a lens housing  1130  fabricated from stainless steel, the attracting strength between two magnets can be ˜0.5 lbs. 
     The use of magnets  1170  mounted to the side faces  1135  of the camera channel lens housings  1130  can be configured in various ways. For example, the pair of magnets on the side face  1135  of a primary channel can be oriented for their direction of magnetism as a North-North pair, or a South-South pair, or a North-South pair. In  FIGS.  22 A and  22 B , some magnets  1170  are marked with an “N” to indicate that their north pole is oriented outwards. The magnetic orientations can vary amongst the side faces  1135  of the primary channel  1110 . In alternate configurations, a primary channel face  1135  can have only one magnet or no magnets, while other primary channel faces  1135  are provided with a different number. Magnets can also be positioned in other locations on a side face, and not just adjacent to precision balls  1160 , vee slots  1162 , or flats  1165 . The nominal magnetic strength or pull force need not be identical for magnets on a side face, or from one side face to another, of a camera channel (whether primary or otherwise). 
     As depicted in  FIGS.  22 A and  22 B , magnets  1170  are provided between the primary channel  1110  and the secondary channels  1115 , and on all side faces  1135  of the secondary channels  1115 . Use of magnets between the secondary channels  1115  and tertiary channels  1120  is likewise anticipated. However, use of magnets  1170  between secondary channels  1115  or between tertiary channels  1120  can be optional depending on the design. Likewise, the nominal strength of magnets  1170  used between secondary channels  1115  and tertiary channels  1120 , or between secondary channels  1115 , or between tertiary channels  1120 , need not be identical to those used between the primary channel  1110  and the secondary channels  1115 . In particular, these secondary magnets, in locations other than on or about the primary channel  1110 , can be selected to have lower magnetic strengths. 
     In the nominal system depicted in  FIGS.  22 A and  22 B , the primary channel  110  can be aligned into the central hub  1150  with a pin, and attached to the hub with a bolt. The central hub  1150  can be fabricated from stainless steel (e.g., alloy  440 ). The secondary channels  1115  can be mounted by being pulled to the hub  1150  by the cables  1155 , while also being pulled to the primary channel with magnets  1170 , such that the vee grooves  1162  and the flats  1165  are kinematically in contact with the precision balls  1160  on a side face  1135  of the primary channel  1110 . The tertiary channels  1120  can also have two balls, but in some examples the balls  1120  can be in different locations. For instance, balls on the tertiary channels can be located one on each side and the other in a corner. The tertiary channels  1120  can be pulled to the hub by cables, and pulled to the secondary channel by magnets, while being kinematically aligned by a precision ball to a “V” created by the intersection of two adjacent secondary channels. Tertiary channel rotation is prevented by contact of the other ball against a flat on a secondary channel. 
     In other examples, a mounting plate, channel loading support, or channel nesting plate (not shown) can also be provided with magnets  1170 , springs, flexures, vlier pins, or other devices, to provide underlying support to the tertiary channels. Although the magnets  1170  are shown in  FIG.  22 A  being used in a multi-camera capture device  300  having balls  1160 , vees  1162 , and flats  1165 , magnets can also be used in the prior devices of  FIG.  9   ,  FIG.  10   , and  FIGS.  18 A and  18 B  where the lens housings have the low-profile channel to channel datums  335 . Magnets can also be used on the lens housings for devices ( 300 ) with yet other opto-mechanical configurations, including the example of  FIG.  20    with the nexus internal frame  800 . Moreover, although the example of  FIGS.  22 A and  22 B  show the use of both the magnets  1170  and the ball-based alignment features, in other instances, the magnets can be omitted. Moreover, the magnets  1170  can be used in the absence of the ball-based mounting features. Also, the choice or design of channel-to-channel interfaces or datums can be provided in other combinations. Without limitation, a first interface between the primary channel and a first of the secondary channels can use the ball-based and magnet alignment mechanisms, whereas a second interface between the primary channel and a second of the secondary channels can use only the ball-based features or only the magnets. Likewise, as a design alternative, the ball datum features can be provided on the secondary camera channels, while the vee and flat datum features are provided on the primary and tertiary camera channels. As another alternative, the ball and vee or flat datum features can be mixed in arrangement across or amongst camera channels, whether primary, secondary, or tertiary. For example, a sidewall of the primary channel can have a ball datum feature and a vee-datum feature, while the sidewall of the adjacent and abutting secondary camera channel has a corresponding flat and ball datum features. Moreover, other alignment and/or registration techniques described herein can be used in place of, or in conjunction with, the features illustrated in  FIGS.  22 A and  22 B . 
     It is noted that some or all of the magnets can also be electro-magnets instead of permanent magnets. This can be advantageous for adjusting the magnetic strength in response to environmental or dynamic conditions, such as vibrations or applied mechanical loads. As compared to using screws or latches, the magnets  1170  can be advantageous for this application as they can provide a mechanical holding force across the seams  1105  between adjacent camera channels, in a thin space with thin materials, while causing little mechanical stress or strain. In some improved devices, springs, flexures, or adhesives can be used in combination with, or instead of magnets, to provide a low stress mechanical linkage or connection between the lens housing of adjacent camera channels so at help limit under-constraint between the housings. 
     The precision balls  1160 , vees  1162 , and flats  1165  provide similar alignment functionality to the previously described channel to channel datums  335  (see  FIG.  9   ,  FIG.  10   , and  FIGS.  18 A and  18 B ), and can be an alternate version of the channel-to-channel datums. The prior channel to channel datums  335  have a low profile, and are advantageously positioned near the upper edges of the side faces of the lens housings. These approaches can be particularly useful for multi-camera capture devices  300  or camera channels that are smaller in volume or mass, and that have particularly small seam widths. However, as the mass and size of the multi-camera capture devices  300  and camera channels increases, a more robust approach can be useful, as the risks of mechanical under-constraint or over-constraint of one camera channel to another, or of mechanical failure, increase. The precision balls  1160  and vees  1162  can also be easier to fabricate than the channel-to-channel datums  335 . 
     In  FIGS.  22 A and  22 B , the primary channel  1110  can be precisely located to a central mounting structure, central hub  1150 , with rotation stopped with a precisely located pin. The primary channel  1110  can be secured to the hub  1150  with a screw or bolt, preventing movement. The primary channel  1110  can then be a fixed datum for all the other channels. With the balls  1160 , vees  1162 , and flats  1165 , the lens housings of the secondary channels  1115  are precisely located, with the magnets  1170  providing local holding forces, to the primary channel  1110 . The secondary channels are also held and located then by tensioning cables and mount features against the central hub  1150 . The tertiary channels mount in a similar fashion to the secondary channels, with the underlying channel loading support and magnets helping load the various camera channels towards the primary channel. 
     In some instances, the central hub  1150  can be equipped with magnets, instead of, or in addition to, springs, latches, flexures, cables, or bolts, in providing holding forces to retain camera channels against the central hub  1150 . Central hub magnets can be used to retain the primary camera channel, the secondary camera channels, or the tertiary camera channels, or some combination thereof. As an approach, the central hub  1150  can be fabricated from a magnetic stainless steel (e.g., alloy  416 ) and include pockets into which the magnets are aligned, positioned, and secured. Similarly, magnets can be mounted to alternate central mounting structures, such as the nexus internal frame  800  shown in  FIG.  20   . Alternately, instead of mounting magnets to the central hub, the entire central hub  1150  or nexus frame  800  can be fabricated from or with magnetic material. Using magnets to hold the camera channels to a central hub or nexus or other central structure can reduce the space requirements and mechanical complexity, as compared to using latches or cables. However, the mechanical holding forces used to retain the camera channels against the hub can then be less. This approach can be particularly useful for multi-camera capture devices with lower mass, weight, power, and cost requirements (e.g., low SWaP-C). 
       FIGS.  22 A and  22 B  also depict another design alternative for the lens housings  1130  used in a multi-camera capture device  300 . In particular, each of the side faces  1135  is illustrated as including a lens holding plate  1180 . In the examples depicted in  FIG.  9   ,  FIG.  10   , and  FIGS.  18 A and  18 B , the sidewalls or faces  337  of a lens housing  430  extended all the way up to directly support the outer lens element  437 . In that approach, the sidewalls  337  can be thinner higher up a side wall and holding tolerances along the thin walls can become more difficult and/or expensive. In the approach of  FIGS.  22 A and  22 B , the lens housings  1130  include the lens holding plate  1180  mounted along each of the sidewalls  1135 . Although fabrication of the lens housing can still require tight machining, the side walls  1135  can be thicker because they do not extend as high. There will be less material to machine away, reducing material cost and machining time. Instead, the side walls  1135  are extended by the lens holding plate  1180 , which is a thin part, e.g., made of sheet metal or a thin plastic, that can be attached to a pocket that machined into the side wall. In some examples, the lens holding plate  1180  can be secured in the pocket using a thin double-sided tape, which reduces the seam or gap width lost by mounting these plates otherwise. 
     As another aspect, during camera channel assembly, holes  1185  provided in the lens holding plates  1180  can enable RTV adhesive to be injected between the outer lens element  1138  and the plate  1180 , so as to secure the lens element after it has been aligned. Some of the holes  1185  in a lens holding plate  1180  can align with slots (not shown) that can be fabricated into the beveled edge  370  of the polygonal shaped outer lens element  1138  to provide a locking mechanism to secure a position and orientation of the lens element. 
     The design approaches for the improved multi-camera capture device  300  shown in  FIGS.  22 A and  22 B  have been described relative to camera channel lens housings that generally fit within pentagonally conical or hexagonally conical limiting volumes. However, as noted previously, the shapes of the outer lens elements, and the shapes of the polygonal conical limiting volumes, can have other geometries, such as square or triangular. Generalizing, a camera channel can have a first outer lens having a plurality of first sides corresponding to a polygonal periphery, and the associated lens housing can generally fit within a conical limiting volume having a plurality of sides nominally matching that polygonal periphery. The lens housing can have protruding features such as balls (like the balls  1160  discussed above), fins, or tabs, that protrude outside the nominal limiting volume. 
     It is noted that in the assembly approach depicted in  FIG.  9    and  FIG.  17   , with a primary channel  610 , and secondary channels  615 , and centering hubs  330  interfacing with a central ball socket array  346 , that the available space in the center of the device, into which power and communications cables, cooling lines, and support mechanics must fit can be tight. 
     As shown in  FIG.  13 B , an improved camera  920 , having a track length  980  between the front lens center and the image plane  950 , can be positioned at an offset distance  925  from the image plane  950  to the low parallax volume  992 . As one approach to improve the device center congestion, the camera  920 , its housing  430  (not shown), and the overall improved device  300 , can be designed to provide an axial center offset distance  915  along the optical axis  985  between the low parallax volume  992  and the device center  910 , much as previously discussed with respect to  FIG.  5 C . Designing in an offset distance  915  (e.g., 1-4 mm) can provide extra space for power, communications, or cooling connections, cables, and for mechanical supports for the sensor package  952 , or for other structural members. In the example of the camera system  920  depicted in  FIG.  13 B , the improved low-parallax multi-camera panoramic capture device ( 300 ) can have a dodecahedral format, and then the device center  910  is the center of the nominal dodecahedral polygonal structure. This offset distance must be determined during the process of designing the cameras  920  and overall device  300 , as it interacts with the optimization of the lens near the edges of the FOV. Thus this optimization can depend on, or interacts with, the seam width, the distortion correction, the control of front color, the optimization for reduced parallax for peripheral rays (edge ray  972 ) or image rays  975  generally, or for the extent and sub-structure of the LP volume  992 , the sizing of the lens elements (particularly for the compressor lens group  955 ), or the allowance for an extended FOV  215 . 
     As noted previously, it can be difficult to provide sensor cooling in the confined space between the device center and the image sensor, and particularly within the volume between the channel tripod and the sensor. In some systems, sensors can generate a low enough thermal load so as to be air cooled. But in many systems, the thermal loads are high enough that cooling via a solid conductive pipe or channel or via liquid cooling can be required.  FIG.  23    depicts a portion of a mechanism for liquid cooling the image sensors for each camera channel in examples described herein. More specifically,  FIG.  23    shows a cooling structure  1200  defining an elliptically shaped chamber  1210 , through which cooling fluid can be pumped. A cover plate  1220  can be soldered in place, to seal the chamber  1210 . The elliptical chamber  1210  can increase heat extraction of the fluid before it exits the chamber, e.g., relative to other shapes. The structure  1200  also includes nozzles  1230 , which are illustrated as being threaded to a body of the cooling structure  1200 . In examples, O-rings, gaskets, or the like can be used to seal the nozzles  1230  relative to the body. As also shown, hoses  1240  can be attached to the nozzles  1230 . The nozzles  1230  can be embodied as barbed fittings  1232 . The hoses  1240  can be pressed over the barbed fittings  1232 , and, in some examples, a sleeve  1235  can be disposed over a portion of hose  1240 , e.g., at the barbed fittings  1232 . The sleeve  1235  can function as a clamp that prevents movement of the hose  1240  from the fitting  1232 . 
     Although not illustrated in  FIG.  23   , the hoses  1240  can be in fluid communication with a cooling source, e.g., including a pump. More specifically, one of the two hoses  1240  can be a cooling solution supply and the other can be a return. In examples, the cooling solution can be water, a solution with 30% ethylene glycol, or other cooling agent. Also in examples, the cooling solution can be circulated at about 0.1 m/s. The direction of liquid flow, e.g., in versus out, can be arbitrary and/or reversible. Also in examples, aspects of the cooling apparatus  1210 , including the body of the cooling apparatus, can be fabricated from materials having high thermal conductivity, including but not limited to copper, aluminum, or the like. 
     In operation, heat generated by components of the imaging sensor can be extracted through a circuit board and into a heat sink. The cooling solution circulated through the chamber  1210  draws the heat away from the main camera body. In some examples, the cooling solution can be pumped through a post connected to the underside of the improved multi-camera capture device  300  to a radiator where the heat is dissipated into the air away from the cameras. Air flow is also required to cool other circuit board assemblies that can be mounted within the post. Cool air can be pushed up the post and out over the circuit boards, thus cooling them. The air is then exhausted out the side. 
     As another option to provide more access for cabling, supports, and thermal management hardware, the ball and socket approach of  FIG.  17    can be replaced with an internal frame ( FIG.  20   ) with polygonal faces, with access holes to a hollow center. For an improved multi-camera panoramic image capture device  300  constructed in a dodecahedral pattern, the internal frame would also be dodecahedral with pentagonal faces and it would be oriented with the internal pentagonal faces nominally aligned with the external pentagonal geometry. An internal frame can be machined separately and assembled from 2 or more pieces, or it can be made as a single piece structure by casting or 3D printing. Although, the fabrication of a single piece frame could be more complex, the resulting structure can be more rigid and robust, and support tighter mechanical tolerances. For example, a dodecahedral frame with a hollow center could be cast in stainless steel, and then selectively post-casting machined to provide precision datum features. This internal frame can then be provided with flexures or adjustors on all or most of the pentagonal faces, to provide kinematic type adjustments and to reduce or avoid over constraint during device assembly and use. As before, the available adjustors on these internal faces can be different for the secondary channels as compared to a primary channel. Alternately, an internal frame can be at least in part made with a more compliant material, such as brass or Invar. As the central volume of this internal frame can be at least partially hollow, space can then be provided for the electrical cabling, thermal management hardware, and other support structures. 
       FIG.  20    provides an example of such an internal frame  800 , with numerous pentagonal faces  810  arranged in a dodecahedral pattern with a hollow center. An internal frame  800  can be designed as a mount mechanical assembly for an 11-camera system, with a support post attaching in the 12th position (similar to  FIG.  9    and  FIG.  15   ). A polygonal internal frame, or half or partial internal frame can also be used in a partial or hemispheric system, where the camera assemblies, including images sensors are mounted to the frame. Alternately, a hemispherical system (e.g., see  FIG.  21   ) with an internal frame  800  can use a central hollow space (e.g., a nexus) to enable image light to cross through in reaching image sensors on the far side, including by transiting intervening relay lens systems ( 725 ). As shown in  FIG.  20   , a pentagonal face ( 810 A) can have three adjustors  820 , such as set screws or flexures, oriented nominally 120° apart, that can interact with features on the camera housing and thus be used to help align a given camera channel. As previously, the mounting and adjustments for secondary channels can have a different design or configuration than those for a primary channel. As another alternative (not shown), one or more pentagonal faces  810 A,  810 B, or  810 C can be provided with one or more adjustors that can be used to nudge the respective camera channel against a precision v-groove structure (also not shown). These-v-groove structures can be fabricated into, or protruding from, an inside edge of a pentagonal vertex  60  of a pentagonal face. The internal frame approach can be used with other polygonal device structures, such as that for an icosahedron. 
       FIG.  11    depicts an advantageous hardware configuration in the region of the sensor  270 , cover glass  272 , and the accompanying sensor package  265  (which can include electronics, cooling and mounting). The cover glass  272  can seal or protect the sensor from the environment. The cover glass  272  can also provide UV or IR cut filtering by means of a thin film interference or dichroic coating, or that function can be provided on a separate window, external filter  295 . The UV or IR cut filter reduces the level of the non-visible light incident, that is accompanying the image light  415 , to the sensor  270 . Alternately, or in additionally, UV and IR cut filtering can be provided with a coating applied to a lens element, including to the outer surface of outer lens element  437  ( FIG.  9   ). The cover glass or filter  295  can also be a UV light absorbing glass and provide UV filtering by a combination of absorption and coating reflectance. 
     It is recognized that in providing an improved multi-camera panoramic image capture device  300  with outer lens elements  437  having inner beveled edges  370  ( FIGS.  10  and  16   ), that the centering tolerances can be worse as compared to typical lens elements fabricated with conventional cylindrical edges. Such decentering can in turn effect the centering of the FOV captured by the entire camera lens system  320 . As one approach for compensation of such errors, the positioning of the effective image centroid or center pixel can be determined either optically or electronically ( FIG.  11   ). As another approach, an improved lens housing  430  can be designed to provide a compensating lateral adjustment for one or more internal lens elements. For example, means to adjust the positioning or tilt of an intermediate inner lens element, such as for a lens element located between the stop and the image sensor, can be provided. The adjustment means can include or use micrometers, pins, shims, flexures, or springs. Z-axis compensators to adjust focus or magnification differences can also be provided within each camera channel by similar mechanisms. The mechanisms to enable compensation can be built in, or internal to the device or a camera, or external, or a combination thereof. 
     Although the opto-mechanics of  FIGS.  8 - 10    and  FIGS.  16 - 20    can reduce alignment errors for the sensors  270 , the camera housings  430 , and one or more cameras  320 , these design improvements, and other comparable ones, may not provide sufficient accuracy for all configurations or applications of an improved multi-camera capture device  300 . As another, or complimentary approach, an optical fiducial system can be provided. In particular, as shown in  FIG.  11   , a light source  460  can direct light  462  for an optical fiducial into a window or filter  295 , within a camera  320  of an improved multi-camera panoramic image capture device  300 . The optical fiducial light  462  can be coupled into an edge of the filter  295  and propagates by total internal reflection (TIR) to an output coupler  465 , by which it is directed towards the sensor  270 , where it provides one or more illuminated spots or areas that function as optical fiducials  475 . The optical fiducial light  462  can be low power infrared (IR) light, such as at 785 or 835 nm, and the output coupler  465  can be one or more lenslets, a prismatic feature, or a diffraction grating. The illuminated areas that function as optical fiducials  475  can be focused spots that are only a few sensor pixels wide. The optical fiducial light  462  can be provided by a light source  460  that is mounted in a mechanically stable position relative to the image sensor  270 . Fiducial light  462  that remains within the optical substrate of the filter  295 , and is light guided towards the opposite edge, can be absorbed by an absorber  470 , which can for example be provided with a black paint coating. 
       FIG.  11    depicts one advantageous approach for providing an optical fiducial  475  that enables FOV tuning for a camera  320 , and thus helps limit parallax errors and image overlap or underlap for adjacent cameras in an improved panoramic multi-camera capture device  300 . But in general, an optical fiducial can be provided by a light source located proximate to the sensor. As another example, a light source could be mounted on or near the sensor plane, and direct light outwards towards or through the cover glass, so that it reflects off of an optical element, and back towards the image sensor. The light source would be positioned outside the used active area of the sensor, as would a reflective coating. The reflective coating can be a localized metallic or dielectric coating positioned outside the clear aperture that is used by transiting image light. As discussed previously, the light source can then provide at least one illuminating spot of light onto active sensor pixels located outside, but proximate to, the active area used by image light, thereby providing an optical fiducial  475 . This concept can also be extended, and optical fiducials can be attached to, or interact with, other components within the system, including lens elements or lens housing structures. As such, the relative motion of particular lens elements or sub-groups thereof, could be monitored to inform the image tracking, cropping, or correction efforts. Additionally, if one or more lens sub-groups or compensators can be actively driven, such as with motors, the resulting data can be useful to inform those corrections. 
     As shown in  FIG.  12   , a camera  320  for an improved multi-camera panoramic image capture device  300  can also be equipped with a mask or an internal baffle  455 , which can be located between an outer lens element  437 , or compressor lens, and the subsequent inner lens elements  440 . As suggested by  FIG.  9    and  FIG.  16   , the beveled edges  370  of the outer lens element  137  can be fabricated through a curved outer lens surface, at a set distance from, and parallel to, the nominal edge chief rays  170  that are incident along a straight pentagonal outer edge. The beveled edges  370  can have a curved bevel shapes or profiles. However, it is easier and cheaper to fabricate the outer lens elements  437 , and mount them within lens housings  430 , if the ground edges ( 370 ) have straight bevels or chamfers. This however means that the volume of optical glass along a straight edge of a pentagonal (or hexagonal) outer lens element  437  that can accept light, that then may become stray light, or image light that complicates image mosaicing or tiling, can vary along the beveled lens edges. The baffle  455 , provided in  FIG.  12   , can provide a sharp polygonal edged aperture (e.g., pentagonal or hexagonal) following the shape of the outer lens element  437  and the core FOV  205 , and also a blackened surface for blocking and absorbing light outside the intended FOV. Alternatively, the light absorbing baffle  455  can be painted or coated on an internal lens element surface. Thus, the baffle  455  or mask can also define the edges of the transiting image light and thus cast an edge shadow  495  onto the image sensor  270  (see  FIG.  11   ). 
     The optical fiducial light  462  and the shadow  495  cast by the baffle  455  can be used both individually and in combination to provide an improved multi-camera capture device  300 , with reduced parallax errors and reduced image overlap or underlap between cameras. As shown in  FIG.  11   , incident image light  415  can provide an illuminated image area  450  that is incident to an image sensor that has an active area length and width. For example, a camera  320  that collects uniform image light within a nominally pentagon-shaped core FOV  205  can then provide a pentagon-shaped illuminated area  450  on the sensor  270 . This image or illuminated area  450  can underfill a width of the sensor  270 , to a greater or lesser extent, depending on the shapes of the illuminated area and the sensor. To be a useful datum, all or most of the projected edge shadow  495  can define boundaries of an illuminated area of active pixels within an underfilled sensor area. In some examples, the edge shadow  495  fills most (e.g., ≥97%) of the active area width. The baffle  455  is acting like a field stop. In cameras  320  without a baffle, the outer lens element can act like the field stop and define the polygonal FOV. 
     Within the illuminated areas corresponding to the edge shadow  495 , there is a smaller illuminated area  450  corresponding to the core FOV  205 , and between them, there can be an intermediate extended FOV  215 . The extended FOV  215  can be large enough to almost match the size of the edge shadow  495 . The difference can be optimized depending on the expected mechanical alignment tolerances for the lens assembly and for positioning the baffle  455 , and the optical sharpness or transition width of the projected shadow. Underfill of the sensor active area width allows the core FOV  205 , an image centroid, the extended FOV  215 , and edge shadow  495  to shift position on the sensor without being clipped. It can be beneficial during a calibration process to establish an image centroid  480  that can then be tracked versus time and exposure conditions. In particular, an initial distance or offset  485  can be determined during a calibration process and stored as a pixel count. Then, if the illuminated image area  450  shifts during or after assembly of the camera  320  into a multi-camera capture device  300 , whether due to mechanical or thermal reasons, a new location of an image centroid  480  and the shape, size, and position of the core FOV  205  can be determined and compared to prior saved calibration data. 
     However, in completing this process, a boundary of the illuminated area  450  that corresponds to the desired image data must be determined. The edge shadow  495  cast by the baffle  455 , much as suggested in  FIG.  7   , can then provide a useful series of fiducial edges or points  210  proximate to, but a bit larger than, the core FOV  205 . The shape and position of the shadow or occlusion cast by the baffle  455  can be determined during a bench test of a given camera  320 , prior to assembly of that camera  320  into a given multi-camera capture device  300 . Similar calibration data can be obtained after that assembly, and then again over time as the camera and device are used, to track changes in the shadow positioning that might occur due to environmental or mechanical initiated changes in the internal mounting or positioning of the lens elements (e.g.,  437 ,  440 ) or the baffle  455 . 
     In greater detail, the FOV edge defining baffle  455  and the optical fiducial  475  (see  FIGS.  11  and  12   ), can be used in combination to monitor or longitudinally track the position of the image centroid  480  and image area edges, to aid image mosaicing or tiling. In particular, for the purposes of aligning a camera lens  320  for both center and rotation with respect to an image sensor  270 , a method of projecting an optical fiducial or casting an optical occlusion onto the image sensor  270 , can be used either individually or in combination. 
     Essentially the baffle  455  or mask casts a multi-edged shadow onto the sensor  270 , and the shape of the baffle will be sampled from around the periphery of the projected image or illuminated area  450  captured by the sensor  270  in software or hardware. The shadow edge can be relatively sharp, but can still create a gradient fall off, potentially spanning at least several pixels, between the illuminated area  450  and the dark surround of the projected shadow. The data for the sampled edges or fiducials from around the edges of the occluded area and the shadow gradients can then be used to derive an image centroid  480  of the lens projection. The baffle  455  or occluding shadow  495  can also have an added feature to indicate and derive rotation if needed. A calibration step can be initially used to derive a relationship of the shadow  495  to the lens center and rotation. Additionally, the dimensions and shape of the mask can be accurately measured before installation and compared to the size and shape of the projected shadow  495 . The derived relationship of the size, shape, and centroid of the projected shadow  495  can account for an expected or measured difference in the shape and size of the edge shadow  495  compared to the shape and size of the baffle. Other factors that can affect the edge shadow  495 , such as mask tilt, and an impact of lens distortion in a fractional field portion (e.g., 0.85-1.01) corresponding to the outer portion of a core FOV  205  and an extended FOV  215 , can also be accounted for. 
     Additionally, as previously described, an optical fiducial  475  can be projected using IR or visible light onto an unused portion of the sensor  270 . The pattern formed by the fiducial can then be used to derive the location of the fiducial and be calibrated to the image centroid  480 , and the lens center and rotation. A calibration step is initially used to derive the relationship of the optical fiducial  475  to the lens center and rotation and correlated to the distortion characteristics calculated in the calibration process. Additionally, a series of calibration images of the fiducial shadow  495  provided by baffle  455  can be used to locate more distant features (e.g., the corners), and thus to confirm or determine the planarity of the lens to sensor mechanical alignment. Sensor alignment or planarity can be modified using the adjustments previously described in  FIG.  8   . The combined fiducial method, of using both an optical fiducial  475  and a projected fiducial shadow  495  has the advantage of being more robust in diverse lighting conditions where the edge of the occlusion cast method may be inconsistent or hard to detect. 
     The method for calibrating with optical fiducials (or with electronic fiducials) and shadow occlusions can be used for a given camera to accurately align the modeled lens distortion derived from a calibration step to the calibrated core FOV  205 . The resulting correction data can be stored in matrices or other forms in an on-board look up table (LUT) on a local board that is part of the sensor package, for each camera and sensor. When an image is captured, this correction data can be used to crop a larger image, corresponding to an extended FOV  215 , during an initial or interim capture step, down to an image corresponding to a real current core FOV  205 . Likewise, other available data, such as for exposure and color corrections, that can be stored locally, can also be applied in real time to the cropped, core FOV sized image, before it is transmitted to a system computer for further image processing, including image seaming or tiling to assemble a panoramic image. 
     More broadly, in general, during either a real time or post processing step of modifying image data captured by one or more cameras  320  of an improved multi-camera panoramic capture device  300 , a method for calibrating optical fiducials and shadow occlusions can be used for a given camera to accurately align the modeled lens distortion derived from a calibration step to the captured image. Then an image can be accurately undistorted as needed, and also corrected to account for other camera intrinsics (e.g., lens focal length, or sensor parameters). This method can be replicated for the multiple cameras  320  of a multi-camera capture device  300  to enable accurate mosaicing or tiling of multiple images together. By matching knowledge of the camera intrinsics accurately to the captured images, the quality of the mosaicing across the boundaries or seams between images captured by adjacent cameras will increase the combined image quality and reduce the errors from the image being misaligned to the calibrated intrinsics initially calculated. As such, the speed of the mosaicing or tiling increases because little or no time can be spent on compute intensive (e.g., optical flow) image feature-based methods to correct for mismatches in alignment, distortion, and lens intrinsics. 
       FIG.  11    also shows that outer portions of the active area or pixel areas of a rectangular image sensor  270  can be covered or shielded by masks  455 . In the case that the sensor  270  is much larger than the image illuminated area  450 , use of masks  455  prevents stray light from otherwise being incident to the underlying dark areas. As a result, these pixel values will essentially be “zero” at all times, and their output can be ignored or dumped, which can speed image processing and compression times. Also, it is possible to replace or substitute the light source  460  and optical fiducial  475  with an offset value  485  for an electronic fiducial calculated as a difference in a calibrated location of the centroid  480  to a sensor edge or mask edge. Use of an electronic fiducial can be simpler and cheaper to implement, as compared to the optical fiducial  475 , but depending on the mechanical design of the camera housing  430 , or a use case for the improved multi-camera capture device  300 , it may or may not be as mechanically or functionally robust. 
     Variations in brightness from scene to scene, or camera to camera, can affect the image content incident within an illuminated area  450  corresponding to a core FOV  205 . In particular, image quality and image mosaicing or tiling can vary with content; such as dark scenes to one camera, and a bright scene to an adjacent camera, affecting image mosaicing and exposure levels. These variations not only make it hard to detect image or shadow edges, but also to make it difficult to determine image centroid values to use during image seaming. Furthermore, these exposure variations can make mosaiced images appear tiled along or across the edges. While either an electronic or optical fiducial can be used to help determine image centroids and image edges, an optical fiducial can also be used to enable electronic exposure control correction. Additional exposure correction can be provided by matching the center or average values of adjacent cameras and scenes, to help the mosaiced images blend or match better. 
     The masks  455  depicted as part of a sensor portion of a camera  320  can be eliminated or reduced if the sensor  270  has a configuration closer to that of the core FOV  205  or the shape of the image illuminated area  450 . Replacing a rectangular sensor with an alternate one that is square, or nearly so, makes more effective use of the available space. In particular, much smaller portions of the conical volume that a camera lens assembly can nominally be designed to fit within are lost in supporting unused sensor area. The illuminated area  450  can land on a sensor with a more appropriate active area, and thus increase the effective resolution (in pixels at the sensor, or in pixels/degree relative to the core FOV  205 ). However, use a of square image sensor can still provide space or pixels to support use of an optical fiducial  475 . Alternately, the rectangular image sensor can be replaced with a sensor having an active area optimized for the camera shape, such as to have a hexagonal or pentagonal shape. Having a shape optimized sensor can further ease the optical design, thus making it easier to fit the camera assembly within the nominal conical volume or frustum, and to optimize the “NP point” location and size. Use of a shaped optimized sensor can provide greater freedom for the optical design optimization trade-offs or balance for factors including the relative distance between the image sensor and the NP point, image quality, pupil aberrations, image distortion, and ray constraints for reduced parallax. As a result, the optical resolution (e.g., from the lens) and angular resolution (from the sensor) can be further optimized, and exceed 100 px/deg. However, the design can still have the core FOV  205  underfill the optimized shape sensor, to allow room for image capture of an extended FOV, and to avoid loss of potential image content due to image shifts and rotations. The underfill, if large enough, can still also allow space to provide an optical fiducial  475 . 
     It is noted that for many image sensors  270 , the image light is incident directly onto the sensor pixels. However, many commercially available image sensors are further equipped with an integrated lenslet array, overlaying, and aligned to, the pixel array. A given lenslet directs its portion of incident image light to the corresponding underlying pixel. This approach can reduce optical crosstalk between pixels, as the incident image light is more likely to be photo-electrically converted into an electrical signal within the incident pixel than may have been true otherwise. As the pixels have become progressively smaller, this approach has become increasingly common, as a means to improve or maintain image resolution (MTF). Such sensors with integrated lenslet arrays can be used in the cameras  320  of the improved multi-camera capture devices  300 . 
     Alternately, an overlaying lenslet array can provide an array of lenslets, where any given lenslet directs light onto a plurality of image sensor pixels. In this case, direct image resolution can be lost, but with a benefit of gaining a light field capability to provide either stereo image capture or increased depth of focus image capture. This type of light field capability can be designed into a panoramic multi-camera capture device  300 , but much of the benefit can then be lost to FOV overlap ( FIG.  3   ). In such systems, the optical designs also can have the entrance pupils at the front or outer lens elements, which can lead to information loss. However, introducing light field capabilities into an improved panoramic multi-camera capture device  300  that has a plurality of adjacent abutting cameras  320  with reduced parallax errors, whether from improved kinematic design, improved opto-mechanical design at the seams  400 , or the use of electronic or optical fiducials or shadow edge masks, can improve the performance and value of captured light field data for such systems. Particularly, in such a system, cameras  320  with light field imaging can capture a portion of the available plenoptic light to provide images with an improved depth of focus and object perspective, without either the information loss or complicated image fusing that results from parallax errors. 
     As noted previously, the width of the seams  400  can be a critical parameter in the design of an improved multi-camera capture device  300 , as the seam width affects the parallax error, size of blind regions  165 , the size of any compensating image overlap ( FIG.  3   ), and the image processing and mosaicing or tiling time. For example, in cases where an expensive multi-camera capture device  300  is used in controlled environments, narrower seams with small tolerances could be allowed or tolerated. However, a local collision or stress of expensive brittle materials (e.g., glass) should be avoided, as chipping and other damage can result. There are of course other external damage risks, including those from external materials coming in contact with the outer lens elements  437 . Thus, as a multi-camera capture device  300  can be an expensive unit, opto-mechanical designs that provide risk mitigation, or protection of the cameras or the device, can be beneficial. 
     As one remedy, a seam  400  can be filled with a compliant material, such as an RTV or silicone type adhesive. As another remedy, the optical design of the camera lenses can include an outer lens element  437  that is designed to be a polymer or plastic material, such as Zeonex, that is less brittle than is glass. The combined use of a polymer outer lens element  437  and seams  400  filled with compliant materials can further reduce risks. Use of a compliant adhesive within the seams  400  between the lens housings  430  can also counter under-constraint between adjacent camera channels  320 . 
     However, in optical designs, glass usually provides better and more predictable performance than do polymer materials. As one approach, the outer lens element  437  may be designed with a common, more robust and less expensive optical glass, such as BK7. The outer lens elements, whether glass or polymer, can also be overcoated with scratch resistant AR coatings, and oleophobic or hydrophobic coatings. A compliant seam filling adhesive should likewise resist penetration or contamination by water, oils, or other common materials. 
     It can be advantageous to design the camera lenses  320  with lens elements  435  that include an outer lens element  437 , or compressor lens, is more of a meniscus type lens element than previously suggested ( FIG.  2 A ). As an example, as shown in  FIG.  13 A , the compressor lens element has been split into a compressor lens group, including a first compressor lens element ( 437 ) and compressor lens elements  438  that are combined as a doublet. The outer lens element  437  can then more freely be designed to have a partially meniscus type shape, while still providing both some beam or image light compression or re-direction towards a wide angle lens group that include a fourth lens element  442 , and the chief light collection to reduce parallax. If the outer lens element is more meniscus like, or generally has a long focal length, it can be flatter, and protrude less above the lens housing  430 . Thus, it can also be less likely to accept light rays  410  at extreme angles from object space  405 , but from outside the nominal field of view  425 , that can successfully reach an image sensor  270  as visible or detectable ghost light. In such a lens design, a second compressor lens element  438 , or doublet, provides further optical power, and re-directs the transiting image light inwards towards an inner fourth lens element  442 . 
     Additionally, the camera lenses  320  can be opto-mechanically designed so that the outer lens element  437  can be a field replaceable unit (FRU). One way to aid this approach is to design that lens element to have a more meniscus like shape. The optical mechanical design can be designed to enable an outer lens element  437  to be mounted so that it can also be readily removed and replaced if it is damaged. For example, the outer lens element can be directly mounted into the camera lens housing  430 , using datum features such as those shown in  FIG.  16   , but then be removable using one or more extraction tools. A desolvable adhesive (e.g., glyptal) or hot glue, with a transition temperature above terrestrial extremes, can also be used. A replacement outer lens element can then be mounted in its place. Alternately, the outer lens element can also be in an assembly, mounted to a sub-housing portion that can be removed from the main camera housing  430 . In either case, providing a lens design in which the outer lens element has a partial meniscus or long focal length design then reduces the sensitivity of the design, relative to image quality and image location on the sensor, to an inaccurate alignment of a substitute outer lens element. Potentially then, a cast or molded optical element, whether made with a polymer (e.g., acrylic) or a glass (e.g., B270), can also be used. Camera re-calibration using the previously discussed optical or electronic fiducials, or the shadow  495  of a baffle  455 , further reduces the risks associated with outer lens replacement. 
     As another alternative for an improved multi-camera capture device  300 , an entire camera  320  can also be designed to be modular, or a potential FRU. In such a case, the camera  320 , including the housing  430 , and the accompanying lens elements including the outermost compressor lens element  437 , can be removed and replaced as a unit. For example, the pressure from the channel loading support  630  can be released or reduced, and the ball pivot of a camera channel can then be released from a ball socket  345 , and a replacement camera channel can be inserted in its place. Thereafter, the pressure from the channel loading support  630  can be restored. As the relative positions of the camera channels can shift slightly during this re-assembly process, a process of FOV centering or calibration with fiducials may have to be repeated thereafter. Depending on the complexity of the design, FRU replacement of modular camera lens assemblies may occur in the field, in a service center, or in the factory, but with relative ease and alacrity. 
     An improved multi-camera capture device  300 , and the cameras  320  therein, can also be protected by a dome or a shell (not shown) with nominally concentric inner and outer spherical surfaces through which the device can image. The addition of an outer dome can be used to enclose the nearly spherical device of  FIG.  15   , or for a nearly hemispheric device like that of  FIG.  21   , or a device having an alternate geometry or total FOV, within an interior volume. The dome can consist of a pair of mating hemispheric or nearly hemispheric domes that interface at a joint, or be a single nearly hemispheric shell (e.g., for  FIG.  21   ). The transparent dome or shell material can be glass, plastic or polymer, a hybrid or reinforced polymer material, or a robust optical material like ceramic, sapphire, or Alon. The optically clear dome or shell can help keep out environmental contaminants, and likewise if damaged, function as a FRU and be replaced. It can be easier to replace a FRU dome than an entire camera  320  or a FRU type outer lens element or outer lens element assembly. The dome or shell can also be enhanced with AR, oleophobic, or hydrophobic coatings on the outer surface, and AR coatings on the inner surface. Although the use of a dome or shell can reduce the need or burden of also using a carrying case or shipping container, such enclosures can still be useful. Alternately, or in addition, the dome or shell can be faceted, and provide a series of contiguous adjacent lens elements, which can function as the outer lens elements for the associated adjacent camera systems  320 . This approach can have the potential advantages of reducing the widths of both the intervening seams  160  (e.g., seam widths ≤0.5 mm) and their associated blind regions  165  and enabling the device center  196  to be coincident with the low parallax volumes  188 . 
     As yet other alternatives, shown in  FIGS.  14 A and  14 B , an improved multi-camera capture device  300 , and the cameras  320  and their housings  430  therein, can be designed to enable providing protective fins  510  that protrude from the seams  400 , or protective posts  520  that protrude from the vertices ( 60 ) or corners where a plurality of adjacent cameras meet. These fins  510  or posts  520  would protrude into object space  405 , but can be designed to be outside the captured FOV, by protruding less than the extent of a blind region  165 , and they could prevent direct contact by some objects from the outside environment. These fins or posts can also be designed to be rigid enough, with the right aspect ratios of height to thickness, to reduce their risk of buckling. Alternately, the fins or posts can be designed with a somewhat compliant material so as to rebound from a contacting force, or a combination, such as compliant fins and rigid posts can be used in tandem. The posts and fins can be supported by compliant mounting that is imbedded with the seams  400 , so that these protective features can revert towards their native designed shape without damaging the cameras  320  or multi-camera capture device  300  during an impact event. Use of darkened fins that protrude, by perhaps a few or tens of millimeters, from the seams  400 , can also provide a benefit of reducing acceptance of light rays at extreme incidence angles relative to a camera lens, that can become ghost light that successfully reaches an image sensor  270 . Use of fins or posts will only protect the cameras  320  and the multi-camera capture device  300  from a moderate force or impact, and thus for some designs and applications, there could be sufficient value. These fins  FIG.  14 A  or posts of  FIG.  14    B can also be sacrificial elements or detachable FRUs themselves. Once they have done their job, or if damaged, they can then be substituted by plugging in replacements (e.g., perhaps into receptacle sockets designed specifically for that purpose). 
     A prior example was given in which a proposed width of a seam  400  was rather narrow. But to clarify, relative to the design and performance of a multi-camera capture device  300 , for chief rays  170  transiting adjacent cameras  320 , and for a given object distance, it can be unnecessary to hold the beam to beam separation to complete zero. Rather, a goal can be to have at most a pixel of missing information (or a few pixels, depending on the application) at the object distance of interest. Depending on the allowed seam width and pixel loss, the cameras  320 , and multi-camera capture device  300 , can be more or less robust, or more or less tolerant of both fabrication tolerances and protective design approaches, including those discussed previously. 
     In particular, some fabrication tolerances of the cameras  320  (e.g., see  FIG.  9   ), housings  430 , outer lens elements  437 , and seams  400  can be tolerated or accommodated. In part, the use of the optical or electronic fiducials, or a shadow cast by a baffle, enables greater tolerance or flexibility in collecting low parallax error images from adjacent cameras  320  with little FOV overlap, as these corrective approaches can enable a “centered” image to be found. However, a multi-camera capture device  300  can also be tolerant of some image loss. For example, for a 5 foot object distance, and a device whose cameras support an aggregate 32 Megapixel resolution (an  8   k  output equirectangular image), a 1 pixel width seam  400  can equate to a 1.2 mm sized gap. If an improved multi-camera capture device  300  is designed to hold the mechanical seams to 3 mm after construction, then the cameras can be designed for a 1.5 mm gap while allowing some FOV overlap (□□). The device can have a mechanical design that with tolerances, allows a matching pointing error of at most □□. After the cameras are assembled, the actual rays that are collected parallel to the edge surface that are shared between the camera lenses may shift, but will always be within the pointing error. Thus, a gap or seam  400  can be constrained to be at most 3 mm wide. For some camera designs, and markets or applications, wider seams can be tolerated, in either absolute size (e.g., 4.5 mm seam widths) or in lost image content (e.g., 2-20 pixels per seam). Lost pixels can be compensated for by increasing the FOV overlap or extended FOV  215 , between adjacent cameras, to capture overlapped content but at a cost of some parallax errors and some increase in the image processing burden. Although, for modest amounts of extended FOV (e.g., ≤5%), the residual parallax errors (e.g.,  FIG.  8 B ) can still be modest. The smaller the seams  400 , and the better the knowledge of the position of an image centroid  480 , and an image size and shape, then the larger the core FOV  205  can be on the sensor, and the less lens capacity and sensor area can then be devoted to providing a yet larger extended FOV  215 . 
     The seams  400  can be nominally identically wide at the interfaces between abutting adjacent cameras for all cameras  320  in an improved multi-camera capture device  300 . Careful camera and camera housing design, and camera to camera mounting ( FIGS.  9  and  10   ) can help this to occur. But nonetheless, the seam widths can vary, either upon device assembly, or during dynamic environmental conditions. For example, on one side of a first camera, a seam width between that camera and an adjacent one can be only 0.75 pixels wide, while simultaneously a seam width between the first camera and another adjacent camera can be 3.25 pixels wide. The seam widths can also vary non-uniformly. The resulting images to the sensors can be shifted or rotated relative to expectations. Thus, such variations can increase the parallax errors for the images captured by these adjacent cameras, and complicate image mosaicing or tiling. However, with the use of electronic or optical fiducials ( 475 ), or shadows cast by internal baffles  455 , an image centroid and image edges ( FIGS.  11  and  12   ) can be monitored for each camera to enable a quick reference to the nominally calibrated or expected conditions. This reference or correction data can also be compared from one camera to another, with a goal to define effective image centroids and image edges for each camera that effectively best reduces parallax errors for all cameras, either individually, or in aggregate (e.g., average). This information can then be used during image processing to quickly and robustly determine image edges and enable efficient image mosaicing or tiling. 
     As discussed previously, with respect to  FIG.  15   , a useful configuration for a multi-camera capture device can be to design and fabricate a generally spherical system, having a plurality of camera lenses distributed in a dodecahedron or truncated icosahedron arrangement. However, an issue that can occur with an improved multi-camera capture device  300  of the types of  FIG.  15   , is that with the plurality of camera channels and respective image sensors confined within a nominally spherical shape, there is little room to include other components or capabilities. Thus, for some applications, devices with a generally hemispherical configuration, with potential room underneath for other hardware, can be valuable. However, because the outer lens elements and cameras are typically polygonal in shape, a hemispherical device can have a jagged or irregular circumference. Also, in such systems, one or more of the cameras can be designed with folds (e.g., using mirrors or prisms) so that the optical paths extend through the bottom irregular circumferential surface. This construction can provide more room for use of modular sensor units that can be swapped in and out. 
     However, for a “hemispheric” version of a truncated icosahedron, there are 6 camera channels with pentagonal faces, and 10 with hexagonal faces, and it can be difficult to provide space for the opto-mechanics to fold so many optical paths.  FIG.  21    depicts an alternative version of an improved multi-camera capture device  700  in which image light collected by the respective camera objective lens systems  720  is directed along a nominally straight optical path, through the nominal image plane, and then through an image relay optical system ( 725 ) to a more distant image sensor located in a sensor housing  730 . The original image plane provided by an objective or camera lens system is essentially a real intermediate image plane within the larger optical system. It can be re-imaged with a magnification (e.g., 1:1 or 2.75:1) to a subsequent image plane (not shown) where an image sensor is located. Thus, advantageously, the image sensors can be larger, and provide a higher pixel count, and the relay lens systems  725  can re-image the image provided by the objective lenses ( 720 ) at an appropriate magnification to nominally fill the more distant sensor with a projected image.  FIG.  21    depicts an upper “hemispheric” portion of a truncated icosahedron, with a semi-internal view that reveals portions of two camera objective lens systems  720 , each with an associated relay system  725  that extends outside the nominal conical space or volume. Image light from the respective cameras  720  crosses through a central volume or nexus  710  on its way through the respective relay lens systems  725 . The relay lens systems  725  can include field lenses (not shown) after the image plane of the camera lenses, but before the nexus, to help contain the space needed for transiting image light. The optics of the relay lens systems  725  can also be coherently designed with the cameras  720 , so as to correct or compensate for aberrations thereof. 
     To provide a hollow central volume or nexus  710  for the imaging light rays from the adjacent camera channels to cross one another and transit the respective relay lens systems  725 , an internal frame  800  (e.g., see  FIG.  20   ) with polygonal faces having access holes to allow the image light to transit the hollow center. As previously suggested, an internal polygonal frame can have flexures or adjustors provided on all or most of the polygonal faces, to provide kinematic or quasi-kinematic adjustments and to reduce or avoid over constraint during device assembly and use. However, in this case the hollow space or central volume of this internal frame is primarily provided so as to allow image light rays to transit the central nexus  710 , and secondarily can also providing room for electrical cabling and thermal management hardware. Alternately, mirrors (not shown) can also be used in the relay lens paths to redirect the image light so that the overall opto-mechanical structure is more compact. The improved multi-camera capture device  700  also includes a support structure  740 , a support post  750 , and cabling  760  for supplying power and extracting signal (image) data. The support structure  740  can provide more substantial support of the camera housings  730  than is illustrated in  FIG.  21   . 
     Another alternative configuration for a multi-camera capture device  300  of the present approach is depicted in  FIG.  24   . This exemplary device is a dodecahedron with both upper- and lower-most (in the illustrated orientation) camera channels removed. Thus, the illustrated device is an annular multi-camera capture system  1300  with two interlocking rings, e.g., an upper ring  1320  and a lower ring  1325 , of camera channels. As shown, the upper-most camera channel has been replaced with a channel alignment ring  1330  that can have the external features of a lens housing as discussed above, such as magnets, precision balls, or the like. However, the channel alignment ring  1330  may lack internal lens mounting features and lens elements. The upper ring  1320  of camera channels can still be mounted against the channel alignment ring  1330 , e.g., in a manner as was previously described with respect to  FIGS.  22 A and  22 B . As such, the channel alignment ring  1330  still can provide the primary datums for assembly of the entire device. The underlying channel loading support (not shown) can still provide alignment and support to the lower ring  1325  of camera channels as previously. Other annular versions of a multi-camera capture device  1300  can be developed which are based on more complex geometric shapes, such as the truncated icosahedron ( FIG.  4   ) or a Goldberg polyhedron. In such cases, as compared to the regular dodecahedron, there can be more cameras in a given annular ring of camera channels, each capturing a smaller FOV than the example lenses of  FIG.  2 A  or  FIGS.  13 A and  13 B . The annular multi-camera capture device  1300  can have just one ring of adjacent low-parallax camera channels that each capture polygonal FOVs, or be multi-tier, with multiple adjacent rings of camera channels, as illustrated. As suggested in  FIG.  24   , an upper or lower ring structure can still provide the primary alignment datums. However, as an alternative, a camera channel  1310  within an annular ring (e.g., the upper ring  1320 ) can be used to provide the primary alignment datums for the other cameras in that ring and in adjacent rings. As another variant, one or more additional primary alignment datum camera channels can be used, for example on the opposite side (180°) of the ring, or in an adjacent ring of camera channels, to help limit the stack up of alignment tolerances around the overall device  1300 . 
     It should be understood that the opto-mechanical approaches of the present invention, including those as described in  FIGS.  9 ,  10 ,  17 ,  18 A,  18 B,  21 ,  22 A,  22 B , and/or  24  for a multi-camera capture device  300  with plurality of adjacent and abutting cameras with outer lens elements that have at least one polygonal edge, can be extended or applied for other multi-camera devices in which the individual cameras do not capture or image FOVs with polygonal edges. The individual cameras, can for example, image circular FOVs and not be designed for reduced parallax errors at or near the edges of these circular FOVs. 
       FIG.  15    depicts an electronics system diagram for an improved multi-camera capture device  300 . In this example, a dodecahedron type device has 11 cameras  320 , and an electro-mechanical interface in the twelfth camera position. Image data can be collected from each of the 11 cameras, and directed through an interface input-output module, through a cable or bundle of cables, to a portable computer that can provide image processing, including live image cropping and mosaicing or tiling, as well as camera and device control. The output image data can be directed to an image display, a VR headset, or to further computers, located locally or remotely. Electrical power and cooling can also be provided as needed. 
     Also, as suggested previously, the performance of a multi-camera capture device, relative to both the opto-mechanics and image quality, can be affected by both internal or external environmental factors. Each of the image sensors  270 , and the entirety of the sensor package  265 , with the data interface and power support electronics can be localized heat sources. To reduce the thermal impact on the camera lenses, and the images they provide, the mechanical design for an improved multi-camera capture device  300  can isolate the sensors  270  thermally from the lens opto-mechanics. To further help reduce thermal gradients between the sensors and their electronics, and the optics, micro-heat pipes or Peltier devices can be used to cool the sensors and re-direct the heat. The heat can be removed from the overall device by either active or passive cooling provided through the electro-mechanical interface in the twelfth camera position, shown in  FIG.  15   . This cooling can be provided by convection or conduction (including liquid cooling) or a combination thereof. 
     As also suggested previously, outside ambient or environmental factors can also affect performance of a multi-camera capture device. These factors can include the effects of the illuminating ambient light, or thermal extremes or changes in the environment. For example, as sun light is typically highly directional, a scenario with outdoor image capture can result in the cameras on one side of the device being brightly illuminated, while the other cameras seeing plenoptic illumination from the scene are in shadows. In such instances, the captured images can show dramatic exposure variations, which can then be modified by exposure correction, which can be provided locally (see  FIG.  15   ). In an improved multi-camera capture device  300 , light from an optical fiducial  475  can also be used for exposure correction of captured images. Light or pixel signals from a portion of the peripheral image region, between the edges of the core FOV  205  and the extended FOV  215 , can also be used for exposure correction, prior to the image being cropped down to the size of the real current core FOV  205 . It is also noted that as extended FOV  215  of a first camera can overlap at least in part with an extended FOV  215  of an adjacent camera, that light level and color comparisons can be made for content or signals that are simultaneously captured by both cameras. The signals or pixel data from these overlapping regions can be used to determine exposure variations between the two cameras, by having a common reference point (e.g., a matched feature point—using SIFT, SURF or a similar algorithm for finding common feature points in the overlap region). 
     It is noted that the peripheral image or exposure data can also be retained for use in later post image processing. Additionally, exposure correction can also be enabled by imbedding optical detectors in the seams  400 , or vertices, between outer lens elements  437 . These abrupt exposure differences can also cause spatial and temporal differences in the thermal loading of some image sensors  270 , as compared to others, within a multi-camera capture device  300 . The previously discussed sensor cooling, whether enabled by heat pipes, heat sinks, liquid cooling, or other means, can be designed to account for such differences. The performance can be validated by finite element analysis (FEA). 
     Alternately, one or more camera systems can be protected by the attachment of a shield or mask to cover the polygonal shape, from seam to seam, and vertex to vertex, of the outer lens element thereof. Such shields can be provided to cover a single camera lens system, or multiple systems. These shields can be shaped to generally conform to the outer surface shape of the outer lens elements, and they can be used to prevent saturated exposure or overexposure from bright directional light (e.g., solar), or to prevent contamination from a localized directional environmental source. While these caps are nominally detachable, for some user applications, they may remain in use for a prolonged time period. Overly bright exposure, from the sun or other light sources can also be controlled with an image sensor having electronic shuttering or drains, or a physical shutter or an electro-optical neutral density, photochromic, or electrochromic filter, that can, for example be designed into a camera  320 , within for example the grouping of inner lens elements  440 . Signals to initiate or control electronic or secondary shuttering can be obtained from the image sensor or from other internal or external optical detectors. As another robustness improvement, one or more camera channels can use dichroic color filter arrays integrated into the image sensor package instead of the standard dye-based CFAs. 
     Environmental influences can also cause a multi-camera capture device to be heated or cooled asymmetrically. The previously discussed nominally kinematic mounting or linkage of adjacent camera housings  430  (see  FIGS.  9 - 10    and  FIGS.  17 - 18   ) for an improved multi-camera capture device  300  can help reduce this impact, by trying to deflect or average mechanical stresses and limit mechanical displacements. However, it can be additionally beneficial to provide channels or materials to communicate or shift an asymmetrical thermal load to be shared more evenly between or by cameras  320  and their housings  430 . With respect to  FIG.  9   , this can mean that the spaces around the lens housing  430  and the channel centering hub  330 , such as the inner volume  390 , can be at least partially filled with compliant but high thermal contact, thermally conductive materials (e.g., Sil-Pad (from Henkel Corporation) or CoolTherm (Lord Corporation, Cary N.C.)) to help spatially average an asymmetrical thermal load or difference. Alternately, or additionally, thermal conductive straps or tapes, such as an adhesive tape in the 88xx series from 3M (St. Paul, Minn.) can be used. However, at the same time, some of the effect of thermal changes, relative to the imaging performance of the camera lenses  320 , can be mitigated by both judicious selection of optical glasses and a thermal mounting of the optical elements within the lens housing  430 . Taken in combination, an effective design approach can be to enable thermal communication or crosstalk between lenses  320  and their housings  430  to environmental influences, but to simultaneously isolate the lenses and housings from the sensors  270  and their electronics. 
     An improved camera  320  for use in an improved multi-camera image capture device  300  can also use a tunable lens element to correct for thermally or mechanically induced focus changes (e.g., defocus). This tunable lens can preferentially be located amongst the inner lens elements  440 , and can be a liquid crystal or elastic polymer type device, such as an electrically actuated focus tunable lens from Optotune (Dietikon, SW). 
     The emphasis has been on developing improved cameras  320 , that have a polygonal shaped outer lens element and capture and image light from a polygonal FOV, for use in an improved multi-camera image capture device  300 . Multiple such adjacent cameras can be used in a nominally spherical device or hemispherical device. However, devices  300  can be developed that have a yet smaller number of cameras and that cover a yet smaller total FOV. For example, systems with only four or six low-parallax, adjacent polygonal cameras can be suitable for some market applications. Additionally, a single camera having a polygonal shaped outer lens element that captures image light with reduced parallax or perspective error, from a nominally matching polygonal shaped FOV can be use in isolation, such as for security or surveillance applications. For example, a single camera, optomechanically designed to fit within the form of ⅛ th  of an octahedron can be mounted in a ceiling corner of a room, and capture image content of the room environment with little or no blind regions. Likewise, the emphasis has been on the development of improved camera lens systems  320  for which parallax errors can be reduced within at least a core FOV  205 , while modest extended FOVs  215  (e.g., ≤5% extra) and image capture overlap with adjacent cameras can also be provided. Similarly, it is noted that the present approach can be extended to support possible applications having yet larger overlapping FOVs (e.g., 10-25% extra, or ≈ 4-10° extra FOV for dodecahedral systems with a nominal Core FOV of 37.45°) of image capture between adjacent cameras, and simultaneous parallax error or perspective error control within at least a core FOV. The camera designs can be extended even further, to provide yet larger overlapping FOVs (e.g., 10-20° extra), but without benefit of reduce parallax for angles much beyond the designed core FOV. 
     As noted previously, the present approach can be used to design low parallax lens systems for a variety of applications. A method of device development can be outlined, for example, as follows: 
     1. Define for a customer or an application space, a polygonal device configuration, a resolution, an expected extent of the seams and blind regions, and a minimum object distance. The minimum object distance is the closest distance at which instant image stitching or image combining of low parallax overlapped images can be applied if image processing is acceptable. At this distance, estimate a maximum total gap or seam width for which the image losses or differences are generally imperceptible to a human viewer. For example, for an 8k equirectangular projected image, an expected image loss of 1/40th % of the output image (along the equator) equates to seams that are 2 pixels wide each. An alternate minimum object distance, for which even modest image processing is not acceptable, and which is further away, can be defined. 
     2. Design the imaging lenses, while controlling parallax and front color. The design can be further modified to provide an extra or extended FOV in which the parallax can be controlled. This extra FOV can provide margin for the rainbow tinting of the residual front color to be located outside of the Core FOV with some margin. 
     3. Design the lens and device opto-mechanics. Determine an expected seam width and the expected thickness and wedge variations between and within the seams, from fabrication and assembly tolerance variations. Determine an expected extended FOV overlap to cover the expected mechanical and optical seam widths to be as high or greater than the maximum expected opto-mechanical wedge and thickness variations so that parallel chief rays between adjacent lens systems can be selected without underlap (fields of view that diverge). 
     4. Update the lens design to provide field of view overlap along the seams between the outer compressor lens elements, to exceed both the maximum expected mechanical variations and residual front color, while controlling parallax therein. 
     In conclusion, aspects of this disclosure provide improved panoramic multi-camera capture devices having low parallax cameras in which the opto-mechanics synergistically enable image capture by the cameras. An intervening mechanical seam between two adjacent cameras can have a real width and thus impact the ray splitting or the extent of blind regions and number of lost pixels or the value of having an extended FOV. The present application provides several means, structures, and configurations to provide robust and controlled alignment of multiple adjacent cameras within a panoramic device, in part so that the seams can be reliably reduced in width. 
     In order to push chief rays to the edge of a polygonal surface, aberrations of the entrance pupil, and particularly spherical aberration and axial chromatic aberration of the pupil, should be optimized or reduced. For context, the entrance pupil and exit pupil, which are projected images of the aperture stop in object space and image space respectively, are usually academic curiosities, representing the virtual images of the aperture stop that a person can see when looking into a lens. 
     In a typical optical system, to provide good image quality, aberrations matter at an image plane, with the typical goal to have small net sums of the individual surface contributions, even though values at individual internal surfaces, whether positive or negative, can be magnitudes larger. Whereas, aberrations at the aperture stop often do not matter much, other than positioning the stop correctly and defining the lens system f-number while minimizing clipping or vignetting of the ray bundles versus field. It is noted that if an object was located at the aperture stop, pupil aberrations would affect the apparent image quality of the image of that object as seen by the person viewing the entrance or exit pupil, although these pupil aberrations are not necessarily representative of the image quality at the image plane. 
     In low-parallax lenses, on the other hand, pupil aberrations, and particularly entrance pupil aberrations, matter. First, to begin to properly design the lens to control parallax, the entrance pupil must be positioned behind the image plane. Secondly, the aiming of peripheral chief rays from the outer compressor lens element, and towards the low parallax volume, must be controlled. As noted previously, optimizing spherical aberration of the entrance pupil can be an effective way to limit parallax errors. In that context, modest over-corrected or under-corrected optimizing spherical aberration of the entrance pupil can occur, meaning that the non-paraxial chief ray NP points can lead or follow the paraxial NP point respectively. Additionally, axial chromatic aberration of the entrance pupil creates color differences that can affect optimization of spherical aberration of the entrance pupil. Front color, which can be considered to be an artifact of this axial chromatic aberration, and the axial chromatic aberration itself, can be reduced by judicious choice and use of high and low dispersion optical materials within the lens design. Although optimization of the spherical aberration of the entrance pupil or chief ray pointing provides fine control for the non-paraxial, chief ray NP point position and parallax reduction, distortion from the compressor lens group also has an increasing influence, versus increasing field, on the projected chief ray pointing towards a location behind the lens and towards the low parallax volume. The magnitude and characteristics of the distortion, which also defines the chief ray height on the outer surface of the outer compressor lens element, can be significantly determined by the use of aspheric surfaces within the compressor lens group. 
     Although this discussion has emphasized the design of improved multi-camera image capture devices  300  for use in broadband visible light, or human perceivable applications, these devices can also be designed for narrowband visible applications (modified using spectral filters, ultraviolet (UV), or infrared (IR) optical imaging applications). Polarizers or polarizer arrays can also be used. Additionally, although the imaging cameras  320  have been described as using all refractive designs, the optical designs can also be reflective, or catadioptric and use a combination of refractive and reflective optical elements.