Improved low parallax lens design

Abstract

The lens geometry of the low parallax imaging device includes a plurality of imaging lens elements arranged to capture and image a polygonal field of view, the lens geometry including a group of compression lens elements and a group of wide-angle lens elements.

Description

Technical Field

[0001] The present disclosure relates to a panoramic low-parallax multi-camera capture device having a plurality of polygonal cameras abutting adjacent to each other. The present disclosure also relates to a lens design of a camera that captures incident light from a polygonal-shaped field of view and forms an image of a polygonal shape with improved parallax and front color performance.

Background Art

[0002] (Cross-reference to Related Applications) This application claims the benefit of priority of (1) U.S. Provisional Patent Application No. 63 / 185,042, filed May 6, 2021, entitled "Low Parallax Lens Design with Improved Performance", and (2) International Patent Application No. PCT / US21 / 17284, filed Feb. 9, 2021, entitled "Panoramic Camera System for Enhanced Sensing", each of which is incorporated herein by reference.

[0003] Panoramic cameras are of great value because of their ability to simultaneously capture wide-field images. The earliest such example is the fisheye lens, which is an ultra-wide-angle lens that captures a wide panoramic or hemispherical image while causing strong visual distortion. The field of view (FOV) of a fisheye lens is typically between 100 degrees and 180 degrees, but the technique has been extended to even larger angles, including ranges up to 220 - 270 degrees, as presented by Y. Shimizu in U.S. Patent No. 3,524,697.

[0004] As an alternative, panoramic multi-camera devices, in which multiple cameras are positioned around or circumferentially around a sphere, are becoming increasingly popular. However, in most of these systems, including those described in U.S. Patents 9,451,162 and 9,911,454 by A. Van Hoff et al. of Jaunt Inc., multiple cameras are mounted spaced apart on the exterior of the device. To capture a complete 360-degree panoramic image, including the gaps or seams between adjacent individual cameras, the cameras have an expanded FOV that overlaps with each other in this case. In some cases, as much as 50% of the camera's FOV or resolution may be used for inter-camera overlap, which also results in considerable parallax between the captured images. Parallax is the visual perception that the position or orientation of an object appears different when viewed from different positions. In this case, both excessive image overlap and parallax differences complicate and significantly delay the subsequent image processing required to properly combine, tile, or stitch and combine an acceptable image from images captured by adjacent cameras.

[0005] There are also panoramic multi-camera devices in which multiple cameras are arranged around or circumferentially around a sphere, with adjacent cameras touching along part or all of the adjacent edges. For example, K. Yoshikawa's U.S. Patent No. 7,515,177 describes an imaging device that includes a number of adjacent imaging units (cameras). Images are collected from cameras with overlapping fields of view, in order to compensate for mechanical errors.

[0006] There is still room for improvement in the lens design and functionality of imaging lens systems that can be used in low-parallax panoramic multi-camera devices. Potential optical improvements may also have direct and indirect benefits or synergies to the optical-mechanical design of individual camera lens systems and the overall device, particularly in relation to issues at or near seams between adjacent cameras. [Brief explanation of the drawing]

[0007] [Figure 1] This is a 3D diagram showing a portion of a multi-camera capture device, specifically two adjacent cameras. [Figure 2A] This is a cross-sectional view of a portion of a camera lens assembly, including lens elements and ray paths. [Figure 2B] This is a cross-sectional view of a portion of a camera lens assembly, including lens elements and ray paths. [Figure 3] This is a cross-sectional view of a portion of a standard multi-camera capture device, showing FOV overlap, field of view, overlaps, seams, and blind areas. [Figure 4A] This figure shows the optical geometry of the fields of view of adjacent hexagonal and pentagonal lenses that may occur in a device with a truncated icosahedron geometry. [Figure 4B] This shows a more detailed view of the enlarged area in Figure 4A. [Figure 4C] This figure shows an example of low parallax (LP) located near the paraxial NP point or both the entrance pupil and the device center. [Figure 4D] This figure shows the parallax difference of the camera channel relative to the near and far center. [Figure 4E] This figure shows the front color at the edge of the outer compressor lens element. [Figure 5] This figure shows the fields of view of adjacent cameras, including both core and extended field of view (FOV), which can both be useful in designing an optimized panoramic multi-camera capture device. [Figure 6] This is a cross-sectional view of an exemplary objective lens. [Figure 7] The lens design method according to the present invention is shown in a flowchart. [Figure 8A] This is a cross-sectional view of a two-element compressor lens group, each designed separately according to a lens design method. [Figure 8B] This is a cross-sectional view of the principal rays directed towards a temporary aperture diaphragm created by a compressor lens element, which is separately designed according to the lens design method. [Figure 9A] This figure shows an improved imaging lens system designed using the lens design method shown in Figure 7, in which both parallax and front color are reduced. [Figure 9B] Figure 9A is a cross-sectional view of the lens with low parallax. [Figure 9C] Figure 9A shows a graph plotted on a graph representing the residual parallax error as the principal ray angle of view error in degrees relative to the field of view in degrees for the lens shown. The graph shows the parallax correction curve plotted on the graph representing the residual parallax error as the principal ray angle of view error in degrees relative to the field of view in degrees. [Figure 9D] This figure shows the residual front color of the lens in Figure 9A. [Figure 9E] This is a table showing the lens prescription for the lens in Figure 9A. [Figure 9F] Figure 9A is a graph showing the thermal sensitivity of the lens. [Figure 10A] Figure 7 shows a cross-sectional view of an exemplary improved imaging lens system designed according to the new lens design method. [Figure 10B] Another illustrative cross-sectional view of an improved imaging lens system. [Figure 11A] Another illustrative cross-sectional view of an improved imaging lens system. [Figure 11B] This is a cross-sectional view of the pre-aperture stop portion of an additional exemplary improved imaging lens system. [Figure 11C] Another illustrative cross-sectional view of an improved imaging lens system. [Figure 11D] Figure 11C is an illustrative cross-sectional view of an improved imaging lens system with low parallax. [Modes for carrying out the invention]

[0008] As is generally understood in the field of optics, a lens or lens assembly typically comprises a system or device having a plurality of lens elements that are attached to and cooperate within a lens barrel or housing to produce an optical image. An imaging lens captures a portion of the light coming from an object or objects existing in object space at some distance from the lens system. Thus, the imaging lens can form an image of these objects on an output "plane", and this image has a finite size that depends on the magnification determined by the focal length of the imaging lens and the conjugate distances to the object and the image plane with respect to that focal length. The amount of image light passing from the object to the image through the lens depends strongly on the size of the aperture stop of the imaging lens, which is typically quantified by one or more values for the numerical aperture (NA) or the F-number (F# or F / #).

[0009] The image quality obtained by an imaging lens depends on a number of characteristics of the lens design, including the selection of the optical materials used in the design, the size, shape (or curvature) and thickness of the lens elements, the relative spacing between the lens elements, the spectral bandwidth, polarization, the optical loading (power or beam) of the transmitted light, optical diffraction or scattering, and / or lens manufacturing tolerances or errors. Image quality is typically described or quantified in terms of lens aberrations (e.g., spherical aberration, coma, astigmatism, distortion), or the relative size of the resolvable spots obtained by the lens. The resolution obtained by an imaging lens is typically quantified by the modulation transfer function (MTF).

[0010] In a typical electronic or digital camera, an image sensor, which is usually a CCD or CMOS device, is nominally placed at the image plane.

[0011] In typical use, a camera images the environment and the objects within it. If the camera is moved to a different location nearby and used to capture another image of a part of the same scene, both the apparent viewpoint of the object and its relative positioning change. In the latter case, where one object may partially obscure another, previously hidden objects become at least partially visible. These apparent differences in the position or orientation of the objects are known as parallax. In particular, parallax is the apparent displacement or difference in the position of an object seen along two different lines of sight, and is measured by the angle of inclination or half-angle between these two lines. In panoramic image capture applications, the parallax difference can be considered an error that complicates both image stitching and image appearance, potentially resulting in visual differences, image artifacts, exposure differences, and other errors. The resulting images can often be successfully stitched together using image processing algorithms, but the input image errors complicate and lengthen the image processing time and, in some cases, leave visually apparent residual errors.

[0012] To present the situation, FIG. 1 shows a portion of an improved integrated panoramic multi-camera capture device 100 having two adjacent cameras 120 within a housing 130 designed for parallax-reduced image capture. These cameras are also referred to as camera channels or objective lens systems. Each camera 120 has a plurality of lens elements (see FIG. 2) mounted within a lens barrel or housing 130. The adjacent outer lens elements 137 have adjacent beveled edges 132 and are installed in proximity from one camera channel to the other, but need not be in contact, and are thus separated by a gap or seam 160 of finite width. Some portion of the available light (λ) from the scene or object space 105, i.e., some of the light rays 110, enters the cameras 120 and becomes image light directed towards the image plane, captured within a restricted FOV, while other light rays completely miss the cameras.

[0013] More specifically, Figure 2A shows a cross-section of a portion of a camera 120 having a set of lens elements 135 mounted within a housing (130, not shown) within a portion of an integrated panoramic multi-camera capture device 100. A fan-shaped ray 110 from object space 105, ranging from the on-axis principal ray to the full-field off-axis principal ray, enters the outer lens element 137, is refracted, and is transmitted inward. Each principal ray is shown with adjacent rays on both sides, representing a localized beam of light. This image light 115, passing through the aperture diaphragm 145 and then through the inner lens element 140, is refracted and transmitted, converging into a focused image at or near the image plane 150 where an image sensor (not shown) is typically located. The lens system 120 in Figure 2A can also be defined as having a lens configuration consisting of the outer lens element 137 or compressor lens element and the inner lens element 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) sharply compresses the image light 115 inward, helping the entire lens assembly achieve a short focal length, while also providing the necessary space in the camera lens housing or barrel to obtain the mechanical functions required both to hold or mount the lens element and to properly interface with the adjacent camera lens barrel or housing. The image light that passes through the camera lens assembly from the outer lens element 137 to the image plane 150 results in an image of quality that can be quantified by image resolution, image contrast, depth of field, and other attributes, the quality of which is defined by optical aberrations (e.g., astigmatism, distortion, or spherical aberration) and chromatic or spectral aberrations that occur in the light passing through each of the lens elements (137, 140) in the camera 120. Figure 2B shows the fan-shaped principal rays 170, or peripheral rays, incident along or near the bevel edge 132 of the outer lens element 137 of the camera optical component (120) shown in Figure 2A. Figure 2B also shows a portion of the captured polygonal or asymmetrical FOV 125 extending from the optical axis 185 to a line coinciding with the end rays.

[0014] Images generated by the multiple cameras of the integrated panoramic multi-camera capture device 100 may be affected by the directional positioning or collection of image light passing through the lens elements to the image sensor of any given camera 120, causing the cameras to capture an angularly distorted or asymmetrical FOV (FOV⇔) or a missized FOV (FOV±). Lens positioning variations may occur during the manufacturing of the cameras (e.g., lens elements, sensors, and housings) or during the assembly of the multiple cameras into the integrated panoramic multi-camera capture device 100, causing the alignment of individual cameras to be distorted due to misalignment or mounting stress. These camera positioning errors, combined with the presence of seams 160 between the cameras 120, may result in some of the available landscape or panoramic FOV being missed or improperly captured. Camera positioning and seam variations may be exacerbated by mechanical shifts and distortions caused by internal or external environmental factors such as heat or light (e.g., image content), and especially by their asymmetrical loading.

[0015] To help illustrate some issues related to camera geometry, Figure 4A shows a cross-section 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 are pentagonal and hexagonal, as can occur in truncated icosahedron or soccer ball-shaped panoramic multi-camera capture devices (e.g., 100, 300). The theoretical hexagonal FOV 182 extends to a half-FOV of 20.9° along the edges, or a full FOV of 41.8° (θ1), but the FOV is larger near the vertices. The pentagonal FOV 177 supports a 36.55° FOV (θ2) within a circular region and supports 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 the optical axis 185 and only a 16.5-degree FOV on the other side of the optical axis.

[0016] When designing the lens system for an improved low-parallax multi-camera panoramic capture device (300), there are several factors that affect performance (particularly parallax) and several parameters that can be optimized individually or collectively to control it. One technique for parallax control during lens optimization is to target the "NP" point, or more importantly, its deformed form. As background, the field of optics has the concept of the entrance pupil, which is the projection of the aperture diaphragm as seen from object space, or a hypothetical aperture through which imaging rays from object space appear to propagate before refraction by the first lens element. In standard techniques, the position of the entrance pupil can be found by identifying the paraxial principal ray from object space 105 passing through the center of the aperture diaphragm, and projecting or extending its object space direction forward to the position where it strikes the optical axis 185. In optics, the incident Gaussian ray or paraxial ray is generally understood to correspond to a ray that lies within an angular range of 10° or less from the optical axis and is directed toward the center of the aperture diaphragm, and also defines the position of the entrance pupil. Depending on the characteristics of the lens, the entrance pupil may be larger or smaller than the aperture diaphragm, and may be located in front of or behind the aperture diaphragm.

[0017] In contrast, the field of low parallax cameras has the concept of the no-parallax (NP) point, or viewpoint center. Conceptually, an NP point associated with the paraxial entrance pupil can be useful in formulating initial specifications for designing or describing a lens. In contrast, an NP point associated with the non-paraxial edge principal rays can be useful in targeting and understanding parallax performance, as well as defining the conical volume or frustum in which a lens assembly can exist. The projection of principal rays, especially non-paraxial principal rays, can miss the entrance pupil for paraxial principal ray definition due to both lens aberrations and the practical geometry associated with these lens systems. In relation to the former, in a well-designed lens, image quality at the image plane is usually prioritized by limiting the effect of aberrations on resolution, telecentricity, and other attributes. Within a lens system, since the emphasis is on the net sum at the image plane, aberrations at intermediate planes, including the aperture diaphragm, can vary widely. While aberrations in aperture diaphragms are often controlled to some extent to avoid vignetting, the non-paraxial principal rays do not need to pass through the center of the aperture diaphragm or the center of the projected paraxial entrance pupil.

[0018] To extend these concepts and enable the design of improved low-parallax lens systems, it should be noted that the camera lens system 120 in Figure 2A shows both a first NP point 190A corresponding to the entrance pupil defined by the vector projection of a paraxial principal ray from object space 105, and an offset second NP point 190B corresponding to the vector projection of a non-paraxial principal ray from object space. Both of these virtual ray projections cross the optical axis 185 at a position behind both the lens system and the image plane 150. As will be discussed later, the behavior of rays between projection points 190A and 190B, and in the regions adjacent to them, can be complex, and neither the projected position nor the point has an explicit value or size. The projection of a principal ray crosses the optical axis at a point, but the projection of a group of principal rays crosses at different positions (e.g., within a few microns or tens of microns) that can converge toward the optical axis and become densely packed, and the range or size of that “point” may depend on the aggregate of nearby principal rays used for analysis. In contrast, when designing a low-parallax imaging lens for imaging a large FOV, the axial distance or difference between NP points 190A and 190B, obtained by the projected paraxial and non-paraxial principal rays, can be significantly large (e.g., millimeters). Therefore, as will be discussed later, the axial difference is a useful measure of parallax optimization (e.g., low parallax amount 188) of the lens system designed for current panoramic capture devices and applications. As will also be seen later, the design of an improved device (300) can be optimized to position the geometric center of the device, i.e., the device center 196, outside but near or inside this low parallax amount 188, preferably in the vicinity of the non-paraxial principal ray NP point.

[0019] In one aspect, Figure 4A shows a virtual projection of the theoretical edge of the field of view (FOV edge 155) passing through the outer lens elements (lenses 175 and 180) of two adjacent cameras to obtain a line directed toward a common point (190). These lines represent the theoretical limits of a complex “conical” optical mechanical lens assembly, which are typically pentagonal or hexagonal limit quantities. Again, ideally, in a difference-negligible multi-camera system, the entrance pupils or NP points of adjacent cameras are in the same position. However, to avoid mechanical interference, the mechanism of a given lens assembly, including the sensor package, should generally not protrude outside the frustum of the camera system and into the frustum space of adjacent lens assemblies. However, in reality, the lens assemblies of a multi-camera panoramic capture device are also separated by a seam 160. Therefore, the actual principal rays 170 received at the lens edge, which are located inside both the mechanical seam and the physical width or opening of the mounted outer lens elements (lenses 175 and 180), if projected overall toward the paraxial NP point 190, can instead land at the offset NP point 192 and be separated by an NP point offset distance 194.

[0020] This can be better understood by considering the enlarged region AA adjacent to the nominal or ideal point NP190, as shown in detail in Figure 4B. Figures 4A to 4C move toward a relatively finer scale, and it should be understood that, for example, not all the details presented in Figure 4C are visible in Figure 4A or 4B. In Figure 4B, within the hexagonal FOV 182, rays propagating within the Gaussian or paraxial region and passing through the nominal center of the aperture diaphragm (e.g., paraxial rays 173) can be projected to the nominal NP point 190 (corresponding to the entrance pupil), or to offset NP point 190A with a small NP point difference or offset 193 from the nominal NP point 190. In contrast, the actual hexagonal lens edge principal rays 170 associated with the largest inscribed circle within the hexagon can be projected to land on a common offset NP point 192A, which may be at a larger offset distance (194A). The two adjacent cameras in Figures 4A and 4B may or may not share a corresponding NP point (e.g., 190). Distance offsets can occur due to a variety of reasons, including geometrical matters between the cameras (adjacent hexagonal and pentagonal cameras), geometric asymmetry within the cameras (e.g., in the case of the pentagonal camera), limitations from the practical width of the seam 160, or due to directional differences between aberration rays.

[0021] As mentioned above, there are also potential geometric differences in the hypothetical projection of the incident principal rays toward the extremely simplified nominal "NP point" (190). Firstly, the incident imaging light path from the corners, vertices, or near the central edge (central chord) of the hexagonal or pentagonal lens may or may not project to a common NP point within the described range between the nominal paraxial NP point 190 and the offset NP point 192B. Also, as shown in Figure 4B, due to the geometric asymmetry of the pentagonal lens alone, the associated pair of edge principal rays 170 and 171 for the actually received FOV can be projected to a different nominal NP point 192B, which can be separated from the paraxial NP point (190) by only an offset distance 194B and by only an offset distance 194C from each other.

[0022] Another issue is that during lens design, the best performance usually occurs on-axis or near-on-axis (e.g., below 0.3 field of view (normalized)) around the optical axis 185. In many lenses, good imaging performance by design often occurs at or near the edge of the field of view, where optimization weighting is often used to enforce compliance. Thus, the worst imaging performance may occur in the intermediate field of view (e.g., 0.7-0.8 of the normalized image field of view height). Considering Figures 4A and 4B again, off-axis rays from the intermediate field of view (θ) outside the paraxial region, but not as extreme as the edge principal rays (10°<θ<20.9°), can be projected toward the intermediate NP point between the nominal NP point 190 and the offset NP point 192B. However, other, more extreme off-axis rays, particularly those from the 0.7–0.8 intermediate field of view, which are more affected by aberrations, can be projected onto NP points located more or less offset from the nominal NP point 190 than from the field-edge offset NP point 192B. Considering variations in lens design, non-paraxial offset "NP" points can be located either in front of (closer to the lens than) the paraxial NP point (entry pupil) or behind it (illustrated in Figure 2A), as suggested in Figure 4B.

[0023] This is shown in more detail in Figure 4C, which essentially shows a further enlarged area AA of Figure 4B, but illustrates the effect of vector projection ray paths associated with aberrational image rays converging to the paraxial entrance pupil (190) and its vicinity for imaging lens systems designed and optimized using the method of this technique. In Figure 4C, the projection ray paths of green aberrational image rays in multiple fields of view from the camera lens system converge within a low parallax amount 188 near one or more "NP" points. Similar ray sector diagrams can also be generated for red or blue light. The virtual projection of the paraxial ray 173 can converge to the nominal paraxial NP point 190 located on the nominal optical axis 185 at a distance Z behind the image plane 150, or to its vicinity, or to the entrance pupil. The virtual projection of the field edge rays 172, including the principal ray 171, converges to the offset NP point 192B or its vicinity along the optical axis 185. The NP point 192B can be quantitatively defined, for example, as the centroid of all field edge rays 172. An alternative offset NP point 192A corresponding to the “circle of least confusion” can be identified, in which case the paraxial rays, edge rays, and mid- or central field rays converge at the minimum spot (off-axis). These different “NP” points are separated from each other by offset distances 194A and 194B from the paraxial NP point, and by an offset distance 194C. Thus, it can be understood that the “NP point” of any given actual imaging lens assembly or camera lens set supporting a larger paraxial FOV or asymmetric FOV is usually not a point, but may be an offset low parallax (LP) smudge or quantity 188. The NP points of the central field rays and field edge principal rays are usually located further from the image plane than the paraxial entrance pupil or paraxial NP point, but this is not always the case. In lens design, these details may depend on both design specifications and optimization priorities.

[0024] Within the smudge or low parallax amount 188, various possible optimal or preferred NP points can be identified. For example, offset NP points corresponding to the edges of field rays 172 can be highlighted to help achieve improved image tiling. Alternative central field (e.g., 0.6–0.8) NP points (not shown) can also be tracked and optimized. Furthermore, the size and position of the overall "LP" smudge or amount 188, or preferred NP points within it (e.g., 192B), may also vary depending on lens design optimization. Such parameters may also vary between lenses due to manufacturing differences between lens assemblies, from one lens system to another manufactured for a given design. Figure 4C shows these alternative offset "NP points" 192A,B for non-paraxial rays located behind the paraxial NP point 190, or further away from the lens and image plane, but it is also possible that other lenses of this type, optimized using the method of this technique, may be provided, in which case similar non-paraxial NP points 192A,B, positioned with a low parallax amount 188, may occur between the image plane and the paraxial NP point.

[0025] Figure 4C also shows the location of the center of the low parallax multi-camera panoramic capture device, device center 196. Based on optical considerations, the improved panoramic multi-camera capture device 300 can preferably be optimized to nominally position the device center 196 within a low parallax amount 188. The optimized position therein may be at or near either offset NP point 192A or 192B, or within an offset distance 194B between them, in order to prioritize parallax control for the principal rays at the edge of the field of view. The actual position therein depends on parallax optimization, which can be determined by lens optimization related to spherical aberration of the entrance pupil, or direct principal ray constraint, or distortion, or a combination thereof. For example, whether spherical aberration is optimized to be overcorrected or undercorrected, and how much weighting is used for the field operand of the merit function, may affect the positioning of the non-paraxial "NP" point relative to the peripheral or central field of view. The "NP" point positioning may also depend on control of manufacturing tolerances and residual variability in lens system manufacturing. The device center 196 can also be positioned near the low parallax amount 188, but offset by a center offset distance 198 from it. This technique also helps with tolerance control and allows more space near the device center 196 for cables, circuits, cooling hardware, and associated structures. In such a case, the adjacent camera 120 can have the "NP" point offset low parallax amount 188 (Figure 4C) instead of the matching one (Figures 4A, 4B). In this example, if the device center 196 were located or near the paraxial entrance pupil, NP point 190, then one or more of the outer lens elements 137 of camera 120 would be substantially undersized, and the desired full FOV would not be achievable.

[0026] The width and position of the low parallax quantities 188, the vector directions of the projections of various principal rays, and the NP point positions within those low parallax quantities can be controlled during lens optimization by using operands associated with the sectors of the principal rays 170 (e.g., Figures 2A and 2B). However, the LP smudge or LP quantity 188 in Figure 4C can also be understood as a visualization of the lateral component of the spherical aberration (PSA) of the entrance pupil, and this parameter can be used in an alternative, but equivalent, design optimization method to using the principal ray sectors. In particular, during lens optimization, for example using Code V, the lens designer can create a special user-defined function or operand for the lateral component of the spherical aberration of the entrance pupil (e.g., ray height), which can then be used in various ways. For example, the operand value can be calculated as the sum of squared residuals (RSS) of values ​​over the entire FOV or local field of view, using either equal or unequal weighting for the field of view operands. For the latter case of localized field of view selection, the value can be calculated depending on whether the paraxial, central, or peripheral field of view is selected for the entrance pupil or a position near it, or somewhere else within the low parallax amount 188. The equivalent operand can be the width of the circle of least disturbance in a plane, such as the plane of offset point NP 192A or that of offset NP 192B, as shown in Figure 4C. The optimization operand can also be calculated with weightings to reduce or limit parallax error non-uniformly across the entire field of view, with unbalanced weightings favoring the peripheral or edge field of view over the central field of view. Alternatively, the optimization operand can be calculated with weightings that nominally uniformly yield nominally low parallax error across the entire field of view (e.g., within or across the core FOV 205, as shown in Figure 5). This type of optimization may be particularly useful in mapping type application examples.

[0027] Whether or not low parallax lens design and optimization methods use operands based on the spherical aberration (PSA) of the principal ray or entrance pupil, the resulting data can also be analyzed in relation to changes in imaging perspective. In particular, parallax errors with respect to field of view and color can also be analyzed using the calculation of the center of far-to-far (COP), a parameter that is more directly related to visible image artifacts than the amount of low parallax, and can be evaluated as the image pixel error or difference when an object is imaged at two different distances from the camera system. The COP error is essentially the change in the principal ray trajectory at a given number of object distances, such as an object at a close distance (3 feet (91.44 cm)) to another object at "infinity".

[0028] Perspective works by representing light from a scene through an imaginary rectangle (realized as a plane in the drawing) to the observer's eye as if the observer were looking through a window and drawing what they saw directly onto the windowpane. In drawings and architecture, in drawings using linear or point perspective, objects appear smaller as their distance from the observer increases. In stereoscopic image acquisition or projection using pairs of adjacent optical systems, perspective, along with dual-view parallax, shading, and occlusion, provides visual cues that create a sense of depth. In image acquisition using pairs of adjacent cameras with at least partially overlapping fields of view, parallax image differences provide cues for stereoscopic image perception or errors in panoramic image assembly.

[0029] Analytically, principal ray data from actual lenses can also be expressed as a function of the field of view in terms of perspective error, including chromatic error. In this case, perspective error can be analyzed as the positional error in the image between two objects located at different distances or directions. Perspective error may depend on the choice of COP position, the angle within the imaging FOV, and chromatic error. For example, it may be useful to prioritize the COP to minimize green perspective error. Perspective or parallax error can be reduced by optimizing the position (Δz) or width of the color axis within LP quantity 188 relative to the near center for one or more fields of view within the imaging FOV. The near center can also be graphed and analyzed for each color as a group of curves of Z(axis) intercept position (distance in mm) relative to the field of view. Alternatively, to better understand how the captured image looks, the COP can also be graphed and analyzed for each color as a group of curves of the camera system as parallax error per image pixel relative to the field of view.

[0030] During the design of the camera lens system, the goal may be to limit the parallax error of imaging within the core FOV 205 (Figure 5) to a few pixels or less. Alternatively, it may be preferable to particularly limit the parallax error in the peripheral field of view, for example, at the outer edge of the core FOV and in the extended FOV region (if provided). If the residual parallax errors of the cameras are so small as to this extent, the parallax difference seen as a perspective error between two adjacent cameras near their shared seam 160 or within the seam-related region of extended FOV overlap imaging can also be similarly limited to a few pixels or less (e.g., 3-4 pixels or less). Depending on the lens design, device design, and application, it is possible and preferable to further reduce the parallax error of the lens system, as determined by the perspective error, to 0.5 pixels or less across the entire core FOV, the peripheral field of view, or both. If these residual parallax errors of each of the two adjacent cameras are so small as to this extent, images can be captured, cropped, and easily tiled while compensating for or hiding image artifacts from any residual seam 160 or blind region 165.

[0031] In pursuing the design of a panoramic camera of the type shown in Figure 1, lens optimization methods and parameter selection may be important to enable an improved low-parallax multi-camera panoramic capture device (300) with multiple adjacent cameras. A camera lens 120, i.e., a system of lens elements 135, like that of Figure 2A, can be used as a starting point. This camera lens has a compressor lens element and an inner lens element 140, the latter of which can also be defined as consisting of a front aperture wide-angle lens group and a rear aperture eyepiece-like lens group. When designing such a lens to reduce parallax errors, it may be useful to consider how the sector 125 from the paraxial principal rays to the non-paraxial principal rays (see Figure 2A), or the sector 170 of the edge principal rays (see Figure 2B), or the local cluster 172 of the field edge rays (see Figure 4C) are imaged by the camera lens assembly. Lens design can be optimized by using a set of merit function operands for a set or set of principal rays (e.g., 31 defined rays), although this can make the optimization process 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 could also be obtained by using a reduced set of ray parameters or operands that emphasize the lateral component of spherical aberration at the entrance pupil or at a similarly selected surface or location within the LP smudge amount 188 behind the lens system (e.g., at offset NP points 192A or 192B). Optimization of the lateral component of spherical aberration (PSA) at the alternative non-paraxial entrance pupil can be achieved by using merit function weighting that emphasizes the non-paraxial principal rays.

[0032] In another embodiment, in a low parallax multi-camera panoramic capture device, the sector of the principal ray 170 incident on or near the bevel edge of the outer lens element of camera 120 (see Figure 2B) must be parallel to the sector of the principal ray 170 incident on or near the bevel surface edge 132 of the outer lens element of an adjacent camera (see Figure 1). Note that the “edge” of the outer lens element 137 or compressor lens is a three-dimensional structure (see Figure 2B) that may have a flat edge cut through the glass thickness, and is subject to the manufacturing tolerances of its lens element, the entire lens assembly, and the housing 130, as well as adjacent seams 160 and their structure. The determination of where the bevel edge is cut into the outer lens element depends on factors including material properties, front color, distortion, parallax correction, tolerances, and the extent of any extra extended FOV 215. The outer lens element 137 becomes a faceted outer lens element when the bevel edge 132 is cut into the lens to create a set of polygonal edges nominally following a polygonal pattern (e.g., pentagons or hexagons). Throughout this specification, the terms “polygonal edges,” “polygonal edges,” “polygonal lens edges,” and similar terms may be used to refer to one or more edges of a polygonal lens configured to image a polygonal field of view, for example, as discussed above, which are configured to image a polygonal image corresponding to that field of view.

[0033] In another aspect, Figure 4E shows "front color," which is the difference in nominal ray paths by color relative to the field of view when directed to an off-axis or edge field of view point. Typically, for a given field of view point, the blue ray is the furthest offset. As shown in Figure 4E, the incoming blue ray 157 to the first lens element 137 is ΔX ≈ 1 mm further away than the incoming red ray 158 directed to the same image plane point. If the lens element 137 is not large enough, this blue light may be clipped or vignetted, and color shading artifacts may occur at or near the edge of the imaging field of view. Front color may appear in the captured image content as a thin, rainbow-like contour of the polygonal FOV, or as the polygonal edge of the outer compressor lens element acting as a field aperture of the optical system. Local color transmittance differences that can cause front color-related color shading artifacts near the edges of the image may be caused by differential vignetting at the beveled edge of the outer compressor lens element 137, or by edge trimming in the compressor lens element, or by the aperture diaphragm 145. During lens design optimization to achieve an improved camera lens (320), front color can be reduced as part of the color correction of the lens design, including by the selection of glass in the compressor lens group or the overall lens design, or as a trade-off in lateral color correction (e.g., to a ΔX(BR) width of 0.5 mm or less). The effect of front color on the captured image can also be reduced optically by designing the improved camera lens (320) to have an extended FOV 215 (Figure 5), and by designing the optical mechanism to push the straight-cut or beveled lens edge 132 at or beyond the edge of the extended FOV 215, so that any residual front color occurs outside the core FOV 220. In this way, any residual front color artifacts can be removed during the image cropping step in image processing.

[0034] Figure 4D shows the difference between near and far centers 280 as an error or difference in image pixels for the field of view and color (R, G, B) for low parallax lenses of the type shown in Figures 2A and 2B, but with improved optical design and performance. In this example, imaging of two objects was analyzed, one at a distance of 3 feet (91.44 cm) from an improved low parallax multi-camera panoramic capture device (300) with an improved low parallax camera lens 320, and the other at a distance of "infinity" (∞) from the device. Figure 4D shows parallax errors of <1 pixel for red and green and about 1.5 pixels for blue from the axis to near the edge of the field of view (e.g., up to about 34 degrees). Parallax errors can also be quantified in angular units (e.g., fractions of degrees per color). Due to parallax optimization, the R, G, B curves of the difference between near and far centers 280 have similar shapes, but there are small offset and gradient differences between them. These differences are manifestations of residual color differences in the lenses, including lateral color, axial color, and front color. Parallax errors in blue light can exceed 1.5 pixels at extreme points of view (e.g., vertices). However, within the designed FOV, and especially in green light, it is preferable to further limit the perspective or parallax error to the sub-pixel level (e.g., 0.5 pixels or less) for imaging in the peripheral field of view. If the residual parallax error between adjacent cameras is sufficiently small, the captured images obtained from the core FOV can be easily and quickly cropped and tiled together. Similarly, if the residual parallax error in the extended FOV capturing content at or near the seam is similarly sufficiently small, and the two adjacent cameras are properly aligned with each other, the superimposed captured image content from the two cameras can be quickly cropped or averaged and included in the output panoramic image.

[0035] The optical performance at or near the seam can also be understood in part in relation to the defined set of fields of view (Figure 5). In particular, Figure 5 shows the potential set of fields of view from which potential image light can be collected by two adjacent cameras. As an example, a camera with a pentagonal outer lens element, with or without a dodecahedron or truncated icosahedron or other polygonal lens camera assembly, and with the seam 160 separating it from the adjacent lens or camera channel, can image an ideal FOV 200 extending to the vertex (60) or to the polygonal edge of the frustum or conical volume where the lens resides. However, due to various physical constraints that may arise at the seam, including the finite thickness of the lens housing, the physical characteristics of the beveled edge of the lens element, mechanical wedge, and tolerances, a smaller core FOV 205 of transmitted image light may actually be imaged. The coated opening for the outer lens element 137 must encompass at least the core FOV 205 with some margin (e.g., 0.5–1.0 mm). Since the lenses can be manufactured with AR coating before beveling, the coating can extend to the seams. The core FOV 205 can be defined as the largest low-parallax field of view that a given actual camera 120 can image. Equivalently, the core FOV 205 can be defined as a sub-FOV of the camera channel, whose boundary is nominally parallel to the boundary of its polygonal pyramid (see Figures 4A and 4B). Ideally, with a small seam 160 and proper control and calibration of FOV positioning, the nominal core FOV 205 will approach or match the size of the ideal FOV 200.

[0036] To compensate for the blind area 165 and the associated loss of image content from the scene, the camera can be designed to support an extended FOV 215 or offset device center 196, which can provide an extra FOV sufficient to account for the seam width and tolerance. As shown in Figure 5, the extended FOV 215 can extend far enough to obtain overlap 127 with the edge of the adjacent camera's core FOV 205, but the extended FOV 215 can be even larger. This limited image overlap may result in a moderate amount of image resolution loss, parallax error, and some complexity in image processing, as discussed earlier with respect to Figure 3, but it may also help reduce the apparent width of the seam and blind area. However, if the extra overlapping FOV is moderate (e.g., 5% or less) and the residual parallax error within it is small enough to be achieved by this method (e.g., perspective error of 0.75 pixels or less), the burden on image processing can be quite moderate. Image acquisition up to an extended FOV of 215 can also be used to enable intermediate acquisition steps that support camera calibration and image correction during the operation of the improved panoramic multi-camera capture device 300. Figure 5 also shows the inscribed circle in one of the FOV sets, corresponding to a subset of the core FOV 205, which is the common core FOV 220 that can be acquired in all directions from that camera. The angular width of the common core FOV 220 may be useful as a quick reference for the image capacity of the camera. An alternative definition of the common core FOV 220, larger to include the entire core FOV 205, may also be useful. The dashed line (225) extending from the common core FOV 220 or core FOV 205 beyond the ideal FOV 200, nominally including the extended FOV 215, represents the region where the lens design can support careful mapping of the principal ray or principal ray, or control of spherical aberration of the entrance pupil, to enable low parallax error imaging and easy tiling of images captured by adjacent cameras.

[0037] To reduce parallax and improve image tiling across the entire seam 160 spanning the distance between two adjacent usable openings between two adjacent cameras, it may be advantageous if the image light is captured with substantial linearity and parallelism over a finite distance and at common intervals. The amount of extended FOV to be designed can take into account the expected optical and mechanical seam widths and the nominal object viewing distance. For example, a finite mechanical seam width may require less extended FOV to cover the seam if the imaged object is always far from the multi-camera device. Generally, the mechanical seam width is 8 mm or less, preferably 4 mm or less. The amount of FOV overlap required to form the extended FOV and limit the blind area can be determined by controlling the relative proximity of the entrance pupil (paraxial NP point) or an alternative preferred plane within a low parallax amount 188 (for example, to enhance peripheral rays) to the device center 196 (e.g., the center of the dodecahedron shape). The amount of extended FOV 215 is preferably 5% or less, such that the camera's peripheral field of view is, for example, about 0.85–1.05 (e.g., an additional field of view of 1.8° or less for a nominal core FOV of 37.5°). If spacing constraints at the device center and manufacturing tolerances are properly controlled, the extended FOV 215 can be reduced to an additional field of view of 1% or less. Within the extended FOV 215, parallax should be limited to the nominal system level, while both image resolution and relative contrast remain sufficient. Parallax optimization to reduce parallax errors can be used, including principal ray constraints or pupil aberration constraints and targeting optimization in or beyond the high FOV region (e.g., 0.85–1.0 field of view), to include the extra camera overlap region obtained by the extended FOV 215 (e.g., a small field of view within approximately 0.85–1.05, as shown in Figure 5).

[0038] Given the problems that front color (e.g., Figure 4E) can cause, it may be advantageous to develop improved design methods and further reduce its size (e.g., to 0.2 mm or less, preferably 0.1 mm or less). Front color is observed at or near the polygonal edge of the image on the image plane, and it is caused by chromatic aberration of the entrance pupil, which appears in the outer compressor lens element as spatial color difference or beam height difference of red, green, and blue light. The outer compressor lens element and its polygonal edge essentially function as a soft-focus or out-of-focus field aperture. When light entering from near the polygonal edge propagates through the lens, blue light crosses an outer path compared to green and red, and can be vignetted unless the designer takes care to define the aperture. In contrast, red light crosses an inner path compared to green and blue, and is relatively less attenuated. As a result, the retained red light is adjacent to the green light along the outer edge, and the blue light is further inward, before it reaches the in-lens field of view or core FOV, which has normal white light transmittance, resulting in a rainbow-colored image plane artifact. In addition, this front color problem inevitably means an increase in the distance between adjacent camera channels. These gaps are undesirable, and therefore, it is important to minimize the front color.

[0039] During the design of low parallax cameras or objective lens systems, front color has been difficult to control. This problem begins as soon as the incident light is refracted by the first compressor element. Therefore, low-dispersion elements must be used. At the same time, the highest possible refractive index must also be used to minimize the curvature of this large element. These conflicting pressures may lead to the selection of optical materials such as OHARA S-LAH53 in the upper left corner of the glass map. However, the glass selection in this region of the glass map is rather limited. An improved solution may be found by using unconventional optical materials such as the optical ceramic ALON from Surmet (Burlington, Massachusetts) for the front lens element. However, it may not be desirable to make such a large element from such a material. ALON has a similar refractive index to S-LAH53, but with much lower dispersion. To compensate for the use of the S-LAH53 front element, a doublet L2-3 was added so that the doublet would have a three-element compressor group that helps correct residual color issues and thereby enable a reduction in front color (see objective lens in Figure 1). An example of such a low parallax and low front color camera lens 120 is shown in Figure 6, where the outer compressor element 137 uses SLAH-53 and the inner compressor lens element 138 uses SBAH28 for element 138A and STIH53 for element 138B, all from Ohara Glass. However, the design is further complicated by the simultaneous requirement that in order to control or limit parallax, the three compressor elements must also achieve very small entrance pupil spherical aberration (PSA). Furthermore, at the same time, the entire lens system must have small lateral color (LC) aberration and distortion aberrations in the image.

[0040] When designing low-parallax cameras or low-parallax objective lens systems, such as those shown in Figure 1 or Figure 6, it can be difficult to simultaneously achieve the three objectives of low parallax, low front color, and low lateral color. Typically, front color and lateral color are inversely proportional, with decreasing one increasing the other. In the design of low-parallax lenses supporting a dodecahedron shape, where each camera channel supports a maximum half-FOV of approximately 37.4 degrees, there appears to be insufficient freedom in the three-element compressor lens group, potentially leaving a compromise of 0.4-0.6 mm for front color (measured on the outer compressor lens element). However, in practice, smaller residual front color values ​​of 0.1 mm or less are preferable for blue-red separation.

[0041] As mentioned earlier, one way to solve this is to use unconventional optical materials such as ALON. Among the inner lens elements 140, it was found that preferred glass for some lens elements is located in the upper left corner of the glass map. Using ALON for these very small elements is beneficial. As another alternative, increasing lateral color may be acceptable. However, this can quickly reach an unacceptable value equivalent to several image pixels. As a third alternative, when the objective lens is paired with a relay imaging system, the lateral color of the objective lens can be sacrificed to allow for a reduction in front color. This means that the lateral color in the first or first aerial image can become "unacceptable," but the relay system corrects the final performance loss in the final image. In this case, the optimization of pupillary spherical aberration (PSA) and front color is controlled by the compressor lens group of the objective lens, resulting in performance losses (e.g., lateral color, distortion, and telecentricity) in the first or intermediate image, which are then compensated for in the relay lens design. Advantageously, imaging relays are not subject to any of the spatial constraints found in objective lenses. However, this application must enable the use or space for an objective lens and relay lens system combination in at least one imaging channel of a panoramic multi-camera device.

[0042] One way to simplify these lens systems might be to replace the optical material used in the large front compressor lens elements from glass to plastic. However, current and past optical plastics or polymers are very limited, and there are no high refractive index, low dispersion materials that are nearly equivalent to S-LAH53 or ALON. Bonded plastic doublets can also be undesirable, especially for lens elements of the size of compressor lens elements.

[0043] To overcome these problems, new and enhanced techniques or methods have been developed for designing low-parallax lenses with better simultaneous parallax and front color performance. These improved techniques apply to lenses with refractive compressor lens elements using glass, plastic or polymer materials, optical ceramics, or combinations thereof. They also apply to lenses using lens elements with free-form surfaces, or surfaces with subwavelength or metamaterial structures.

[0044] As one embodiment of this new method, a new lens design method 600 shown in Figure 7 can be used, in which the lens system is designed by separating and designing compressor lens elements or lens groups first (steps 610-640), and then combining the compressor lens with other lens elements (step 650) to design a complete low parallax, low front color camera or objective lens system 300 (steps 660-670). More specifically, in step 610, primary target data such as focal length and spectral operating bandwidth are provided for the first compressor lens element 237 (see Figure 8A). In particular, primary data on the position of the aperture diaphragm, the position of the entrance pupil, and the angles of view of the compressor and wide-angle groups can be based on, inferred from, or derived from either the overall system specification or previous designs for this type of lens system.

[0045] Furthermore, as a first-line technique, the initial primary data presented in step 610 can also be temporarily restricted to a quasi-monochromatic wavelength bandwidth (for example, with green having a 20 nm bandwidth). This temporarily removes front color, lateral color, and any other chromatic aberrations. Next, during the initial compressor optimization step 615, the first compressor lens element 237 can be designed in terms of shape and size to guide incident light toward a temporary aperture diaphragm 292, which is also an aberration-free entrance pupil, located near the position of the final LP smudge, and the principal ray converges toward a position 245 nominally corresponding to where the final aperture diaphragm of the complete lens is located. Of course, it is possible to swap the roles of 245 and 292 since they are conjugate to each other. During the initial compressor optimization step 615, an essentially single-lens element monochromatic compressor with an acceptable PSA is designed. This compressor can be designed separately, or, if available, can be designed while incorporating some or all of the front aperture elements of the wide-angle lens group (140). In the latter case, it is beneficial or preferable if the formulation of the wide-angle lens elements is frozen or fixed during this front aperture compressor lens group design stage (steps 610-640).

[0046] During this initial compressor optimization step 615, the lens position, size, curvature, and power of the first compressor lens element 237 can be found to resolve all monochromatic aberrations. This first lens element typically has a shape like the first lens element 237 shown in Figure 8A, but further has a meniscus shape, which can achieve very low pupillary aberration (PSA) resulting from a specific shape factor of a single compressor element. There are various ways to set up this lens and perform non-imaging optimizations while using the improved lens design method 600 in Figure 7. If the shape of this first compressor lens element 237 is too extreme to be manufactured or robustly mounted by the curvature check step 620, the design can be modified by the design modification step 630, for example, to reduce the curvature of the element. If the lens curvature is corrected in step 630 and it is deemed acceptable, the design process can proceed to the color correction step 640. For example, to realize compressor lens elements 237 with less extreme shapes, the optical material, glass, plastic, or ceramic can be changed to a high refractive index material. The design bandwidth can also be expanded (for example, up to 50 nm). Alternatively, or additionally, the compressor lens group can be extended to include both the first compressor lens element 237 and the second compressor lens element 238. In this front group of compressor lens elements 230, the image of the object is not produced properly, and therefore the optimization is set to satisfy only the internal constraints specified by the lens designer.

[0047] However, acknowledging the expectation that color correction will ultimately be required, particularly in the visible light spectrum, a compressor lens group 230 having at least two compressor lens elements 237 and 238, as shown in Figure 8A, may be required. Next, in step 640, the compressor lens group design can be further modified by optical material selection to further expand the design spectral bandwidth (e.g., up to 200-300 nm) and to make this doublet colorless. To achieve colorlessness, lens materials (e.g., refractive index and dispersion) are selected, and the bending or curvature of the lens elements, thickness, and intervening space are designed to direct the light of a given field of view forward with the smallest spectral or color difference in the position and vector direction of these rays as they exit the colorless lens group. Optimization during step 640 can also be performed by optimizing only a two-element compressor group to achieve good control of both spherical pupil aberration (PSA) and axial chromatic pupil aberration. During the modified compressor design step 640, the design spectrum can be extended to cover the entire intended wavelength range while correcting for front color. A third lens element or flint lens element may be added as needed. During design step 640, the primary compressor design target and the design itself can also be modified as needed. Design steps 610-640 are non-imaging optimizations of this separated lens element group (230). Controlling axial chromatic pupil aberration essentially corrects for colorless incident pupil spherical aberration and is an effective mechanism for controlling front color.

[0048] In designing lenses, particularly their color correction, using the new method 600, the goal is that, when correcting for parallax and front color, the projection of the principal rays of light at or near the lower and upper ends of the imaged spectral bandwidth nominally falls within the same small amount of low parallax or LP smudge. In a color-corrected imaging system with a spectral bandwidth of 200 nm, the lower and upper end wavelengths or colors may be, for example, 450 nm and 650 nm. In contrast, in a color-corrected imaging system with a spectral bandwidth of 300 nm, the lower and upper end wavelengths or colors may be, for example, 400 nm and 700 nm. As another example, in a system imaging LWIR light and spectrally corrected for it, the imaged and corrected spectral bandwidth may be 6 μm wide, with the lower and upper end wavelengths at 8 μm and 14 μm, respectively.

[0049] As an example, in one design, the first and second compressor lens elements in Figure 8A may include two optical plastics, with a low refractive index E48R and a higher refractive index OKPA2, respectively. Figure 8B shows the principal ray color spread near the final aperture 245, where the periphery principal rays 270 are tightly controlled and the inner principal rays 272 are more offset from each other. The transient aperture 292 and LP smudge 285 have their roles reversed in this isolated lens design process (steps 610-640), and the entrance pupil becomes virtual, aberrant, as opposed to actual, aberrant. The contributions of these compressor lens elements 237 and 238 to other optical aberrations may increase, as these lens elements are designed with little or no emphasis on them. Note that the color spread of the periphery principal rays 270 across or near the entire field of view is very small, meaning that the front color is well controlled. However, color spreading in lower fields of view (principal ray 272) is not corrected, and there is no need for correction in the compressor lens elements.

[0050] Next, to optimize the entire objective lens for imaging, the optimized compressor group 230 is combined with lens elements that include or have wide-angle group or inner lens elements (step 650). Now, considering the complete lens in Figure 9A, when the wide-angle group lens element 340 is added, the aperture diaphragm 345 shifts along the optical axis 185 and returns to its original position in the lens far from the vertex of the first compressor lens element, but the projected paraxial entrance pupil and non-paraxial equivalent remain in the same nominal positions as the original lens in Figure 8A. However, adjustments may then be necessary to ensure that the image plane is far enough in front of the entrance pupil position and LP smudge position so that the image plane or sensor package remains within an acceptable conical volume or frustum. These other lens groups are then designed to achieve the desired imaging function and image quality, some of which include correcting the optical aberrations introduced by the compressor group, including lateral color and distortion (step 660). The compressor lens elements can be frozen, for example, left unchanged, during this lens design optimization step (660). A very large number of elements within these lens groups, along with lens surfaces having aspherical profiles, can result in good image quality on the image plane. During the final full lens optimization step 670, the design of the compressor lens elements can be allowed some freedom to modify to support the imaging design efforts, as long as front color and parallax performance are not significantly sacrificed. Figure 9A shows an exemplary low-parallax objective or camera lens of this type designed for a dodecahedron device. However, in practice, this lens design method 600 has been used to achieve new low-parallax lens designs using standard optical glass or polymer materials, with low residual parallax performance equivalent to or better than previous designs, but with improved front color and improved lateral color performance.

[0051] The improved lens design method 600 in Figure 7 can be modified depending on the design problem or as the lens designer's experience in designing this type of low parallax, low front color lens increases. For example, in some situations where the target wavelength band is limited or the available optical materials have sufficiently low dispersion, the resulting lens design may have a compressor lens group with a single lens element instead of a doublet (e.g., Figure 9A) or having three or more lens elements.

[0052] In particular, Figure 9A shows an improved low parallax, low front color camera lens or objective lens 300, designed by the improved method 600 and usable with the multi-camera capture device 100. This lens is designed for a dodecahedron system and therefore supports polygonal edges with field edge angles ranging from approximately 31 to 37 degrees from the central edge to the vertices. The lens system 300 images light collected from the field of view 325, including the principal rays 370 and the field edge principal rays 372, onto the image plane 350 through the compressor lens group 330 and the inner lens elements or wide-angle group 340, and the aperture diaphragm 345. The inner lens elements or wide-angle lens group 340 can also be considered as the front-diaphragm wide-angle lens group and the rear-diaphragm eyepiece-like lens group. The virtual projection 380 of the edge principal rays 372 is directed towards the edge principal ray NP point 392 located behind the image plane 350.

[0053] More specifically, Figure 9B shows a cross-sectional view of the periphery principal ray NP point 394 or the LP smudge amount near it of the lens in Figure 9A. The paraxial entrance pupil 390 is located approximately 26.7 mm behind the sensor or image plane 350. This figure shows that the peripheral principal rays along the polygonal rim converge to an amount offset from but near the paraxial entrance pupil 390 or to the non-paraxial NP point 394. The lower and central field rays converge to 392. Tight projection convergence of the peripheral principal rays is necessary to reduce parallax. In this example, the projection of many central field principal rays 374 actually converges to the position of the central field NP point 392 behind the paraxial entrance pupil 390, or near it, but closer to it than the peripheral ray NP point 394. However, in this design example, all projected principal rays are contained within the smallest amount located near the periphery principal ray field NP point 394. As this example demonstrates, considering various scenarios can be useful when analyzing parallax correction.

[0054] It may also be useful to define an observation plane and then graph the residual parallax error across that plane. As shown in the figure, the low-angle (less than 10 degrees) and intermediate-angle (e.g., 10-25 degrees) principal rays converge to a narrow area in front of the selected observation plane. The lowest-angle rays converge to a position very close to the paraxial entrance pupil and the selected observation plane. Rays along the polygonal edges converge to a point in front of or beyond the observation plane. This introduces some residual parallax error, which is quantified in Figure 9C as principal ray angle error versus field of view. The position of the observation or evaluation plane shown in Figure 9B was adjusted only slightly to produce balanced results for the green principal ray. This exemplary graph of residual parallax 310, given as angle error versus field of view, numerically shows a maximum residual difference of ±0.3 degrees over a half-field of view ranging from 0 to 37.4 degrees.

[0055] More specifically, in this example, the true negligible difference occurs near the central chord point along the polygonal edge (0.0 degree error at 33.6 degrees). The residuals from the true negligible difference are nearly balanced near the chord center point, with a principal ray deviation of -0.3 degrees at the vertex (37 degrees), a deviation of +0.18 degrees at the central edge (31.4 degrees), and a residual error of +0.27 degrees at the central field of view (approximately 24 degrees). Depending on the lens design, the magnitude of residual parallax and the curve shape can vary or be further optimized. The parallax difference between adjacent cameras in a stereo camera system or a typical multi-camera panoramic system is usually measured in degrees (e.g., 5-20 degrees), and these values ​​are approximately 100 × lower, which can significantly reduce parallax-related image artifacts. Other similar graphs can be created by recalculating this data under different conditions. For example, a graph of residual parallax error in pixels against position along the image plane can also be very useful.

[0056] In the example lens design in Figure 9A, the front color, measured for the outer compressor lens element 337 and measured as the local distance Dx between the red and blue rays, was reduced to just 0.084 mm, as shown in Figure 9D. The local distance between the green and blue rays is virtually zero. This is small compared to the estimated geometric beam size of 2.2 mm on the first compressor lens element 337. Since the lens design substantially controls the front color, the three curves of RGB residual parallax in Figure 9C are substantially at the top of each other across the range of the polygonal edge. In particular, the graph in Figure 9C shows parallax measurements indicating that the spectrally corrected or RGB color-corrected projection 380 of the principal rays is properly corrected across the polygonal edge corresponding to a field of view of approximately 31–37 degrees from the central edge to the vertex. In Figure 9C, this is indicated by the fact that the RGB curves are closely clustered or nearly overlapping (e.g., within 0.07 degrees of each other) over a field of view of 31–37 degrees along the edge of the polygon.

[0057] Image resolution (pixels or pixels / mm) in a sensor can also be recast into object space as pixels / degree. Typically, these low parallax lenses can support resolutions of 20-400 pixels / degree, depending on the design and the sensor used, although higher or lower values ​​are also possible. Adjacent principal rays of adjacent pixels are angularly offset, but their geometric beam sizes overlap. Therefore, residual front color along the polygonal lens edge can be interrelated with the influence on multiple image pixels of the sensor. It can affect the total imaging FOV, image tiling, and residual image artifacts along the polygonal edge. Thus, reducing the size of the front color on the outer surface of the lens to 0.084 mm or 0.2 mm, respectively, as illustrated by the improved design method 600 in Figure 7 and by the examples in Figures 9A-F and 11B-D, can lead to minimizing the influence on the image plane. In particular, considering the image plane, such small angular differences lead to front color image artifacts of 0.7 pixels or less, preferably 0.2 pixels or less in width, making it possible to almost completely eliminate front color rainbow image artifacts. This residual portion can then be easily removed if necessary. Of course, converting the residual angular principal error to image pixels on the image plane also depends on the resolution and pixel size of the image sensor. Therefore, while the measure is very useful, it can also be relative.

[0058] When interpreted together, Figures 9C and 9D show that this exemplary lens design, created by applying the improved lens design method 600 of Figure 7, exhibits virtually no residual chromatic aberration with respect to both front color and distance or parallax correction. The amount of residual parallax error and residual front color can contribute to design choices regarding how much extended FOV 215 is given beyond the core FOV 205. The improved front color performance is also useful because it helps the optical-mechanical design reduce seam width and avoid chromatic vignetting near the polygonal edges of the compressor lens.

[0059] Figure 9E shows the optical design of the exemplary low parallax, low front color imaging lens 300 shown in Figure 9A. It consists of nine lens elements, as well as a filter plate and a detector window near the image plane. Element 1 uses optical plastic E48R, and lens elements 2 and 9 are both designed using optical plastic OKPA2. Element 4 has both an aspherical and a conical surface. Lens elements 8-9 each have one aspherical surface. The entire imaging lens has a focal length of 4.87 mm and an aperture value of F / 2.8. Its half-field of view is 37.4°, and it supports an image half-diagonal of 3.74 mm. The overall track length of the imaging lens along the optical axis from the front vertex to the image plane is 122.8 mm, and the LP smudge is located approximately 25.6 mm behind the image sensor.

[0060] The imaging lens design in Figure 9A also functions well against classical lens design metrics, as detailed in the formulation in Figure 9E. In particular, imaging resolution with an MTF of over 50% is achieved at the Nyquist frequency of 100 lp / mm across the entire field of view. This lens has residual pincushion distortion of less than 1.5% on the image plane across the entire field of view. The relative contributions within the design to this low distortion can be examined using surface contribution data. In this exemplary design, the compressor lens element contributes positive third-order distortion (+2.38), and the wide-angle group lens element provides a counteracting negative distortion (-2.09), resulting in a net total surface contribution of +0.29 for the entire lens. Similar calculations can be performed for the fifth-order distortion surface contribution, which again indicates that the wide-angle group is designed to nominally counteract the positive distortion contribution of the compressor lens group. Combined, the third and fifth total contributions contribute to the aforementioned 1.5% distortion across the field of view.

[0061] This lens design also exhibits residual lateral color on the image plane of <0.7 microns (mm) between blue and red, <1.7 mm between blue and green, and <2 mm between green and red. Since all of these values ​​are subpixels, the residual lateral color is essentially inconspicuous for the intended 2.5 mm sensor pixel size. Relative light intensity (RI) is also high across the entire imaging field of view, dropping to only about 63% at the edges of the field of view. Figure 9F also shows that the thermal behavior of this imaging lens has been considered. The through-focus MTF curve at 100 lp / mm, acquired over a 40°C temperature range, shows low thermal sensitivity. A previous version of this lens design had a fourth lens element using optical plastic, but that version exhibited considerable thermal sensitivity for out-of-field angles in the range of 30–37.4°.

[0062] Figure 10A shows an alternative exemplary lens design to that of Figure 9A. In this example, the improved objective lens 300 has two compressor lens elements 337 and 338 that use low-refractive-index and high-refractive-index pairs (Δn approximately 0.17) of optical plastics (PMMA and OKPA2) for color correction, but they have substantially different lens element shapes than those presented in Figure 9A. Figure 10B shows an additional alternative exemplary lens 300 to that of Figure 9A, which has compressor lens elements whose shapes are intermediate with those of Figures 9A and 10A, but the low-refractive-index lens element using E48R comes before the high-refractive-index lens element (Δn approximately 0.07) using OKP4. These various designs differ in detail in terms of aberration control or image quality, the number of conical or aspherical surfaces, the presence of wide-angle group lens elements 340 similar to those in modern smartphone camera lenses, their parallax performance, their sensitivity to ghosting and thermal defocus, and / or other factors. However, the lenses in Figures 9A, 10A, and 10B were all designed to include an improved compressor lens group by applying the new lens design method 600 in Figure 7.

[0063] All of these exemplary lenses 300 have a compressor lens element (group 330) that uses an optical polymer, but this compressor lens element further enhances control of both parallax and front color. Doing so brings greater freedom to the surface shape, lowers the unit cost of the lens, and reduces the total weight of the lens. However, compared to other low parallax lens designs with all-glass compressor lens elements, using very high refractive index materials for some elements of the wide-angle group may be beneficial to offset the refractive power loss of the compressor group due to the switch from high refractive index front glass elements to low refractive index polymers.

[0064] It should be noted that lenses similar to those in Figures 9A, 10A, and 10B, which have a two-element shape for the compressor lens group 330, can be designed using the improved method 600 in Figure 7 to provide enhanced control over parallax and front color optimization, while using glass lens elements instead of optical polymer lens elements for the compressor lens elements. In yet another alternative configuration, these two compressor elements (337 and 338) can be composed of glass lens elements and optical polymer lens elements, in either order.

[0065] As another example, Figure 11A shows an alternative imaging lens 300 designed using the improved method 600 of Figure 7, which requires a larger image size but a smaller field of view (maximum approximately 24 degrees) compared to the exemplary lenses in Figures 9A-F and 10A-B. In this example, the curvature of the front surface of the first compressor lens element 337 was too strong, so a two-element compressor group 330 using optical plastic was not feasible. Subsequently, a viable design using a three-element compressor group 330 with optical plastic was obtained. However, a two-element compressor solution was obtained by changing the first compressor lens element 337 to a medium refractive index, low dispersion glass (e.g., Ohara SLAL-19 (n approximately 1.72)). Optical plastic OKPA2 was used for the second compressor lens element 338. Notably, this design solution weighed 1290g, 980g heavier than the three-element plastic solution. However, its thermal sensitivity was lower than that of the three-element plastic solution.

[0066] As yet another example, Figure 11B shows the portion of an alternative imaging lens 300, designed using the improved method 600 of Figure 7, with a virtual projected principal ray 380, in front of the aperture diaphragm (345). Next, Figure 11C shows the complete lens system, including the wide-angle lens element 340 located behind the aperture diaphragm 345. Figure 11C also shows the field edge virtual projection 380 of the principal ray directed to the edge principal ray NP point 392. This lens 300 is similar to that in Figure 6, but like the exemplary lens 300 in Figure 11A, the maximum field of view is approximately 24 degrees.

[0067] During the design of this exemplary lens, the lens design method 600 was modified. Essentially, an intermediate step 645 was included between steps 650 and 660, during which the first three front aperture wide-angle group lens elements of the intended wide-angle (WA) group 340 were included (e.g., Figure 11B), but were not permitted to change, and the design of the three-element compressor group 330 was further modified. For example, the design of the second or third compressor lens element could be modified to reduce chromatic aberration such as front color or color difference in the PSA. The space required for the three plastic elements was 5 mm larger than in the precedent of Figure 11A, which included only one glass lens element and one plastic lens element. The R / #, a metric of lens shape at the front of the first compressor lens element 337, was reduced from R / 0.508 (nearly hemispherical) to R / 0.55 by using an extra compressor element (339). Therefore, in this modification method, including step 645, the compressor group 330 design takes into account all contributions to the aberration of the entrance pupil. For final lens design optimization, the three resulting compressor lens elements were then combined with all the lens elements of the entire WA group 340.

[0068] The objective lens 300 obtained in Figure 11C consists of 11 lens elements. Elements 1-3 are made of plastic (E48R, E48R, OKPA2). Element 5 has an aspherical and a conical surface. Elements 9-10 each have one aspherical surface. The lens has a focal length of 14.9 mm and an aperture value of F2.8. Its half-field of view is 23.8°, and it supports an image half-diagonal of 6.55 mm. The track length is 119.7 mm, and the LP smudge is located approximately 29.2 mm behind the image sensor or image plane 350.

[0069] Figure 11D shows the principal rays across the entire field of view near the paraxial entrance pupil 390 for the exemplary objective lens 300 in Figure 11C. In this case, the amount of LP smudge is very small, and there is almost no positional shift (crossing of optical axes 185) in the field of view. As a result, the residual angular disparity in the field of view of this lens is very small, less than 0.03° for green light and less than 0.07° for red or blue light. Also, compared to the example in Figure 9B, the paraxial (390), mid-field (392), and field edge (394) NP points are densely clustered, although there is some subtle variation. Distortion, which again benefits from the wide-angle group contribution that largely offsets that of the compressor lens group, is less than 1.3% across the entire imaging field of view. Lateral color smaller than 0.7 μm is again subpixel. The corrected front color of less than 0.2 mm between red and blue light is again small compared to the estimated geometric beam size of 6.5 mm on the first compressor lens. The image resolution measured by MTF is over 40% for the entire field of view of 200 lp / mm. The relative light intensity (RI) at the edge of the imaging field of view is approximately 75%. The total weight of all lens elements of lens 300 in Figure 11B is estimated to be 311 grams.

[0070] Compared to the exemplary lenses in Figures 9A-F and 11B, the reduction in the total field of view in the lenses in Figures 11A and 11B-D facilitated the design of both the compressor lens element group and the wide-angle group. However, the relative increase in the size of the image sensor was offset to some extent, adding some burden to the design of the wide-angle group.

[0071] However, broadly speaking, applying the improved lens design method 600 shown in Figure 7 enabled a significant improvement in lens performance compared to conventional lens design methods for low-parallax camera lenses or objective lenses. The meniscus lens shape is used to position the entrance pupil or LP smudge behind the sensor surface and limit residual parallax. In particular, more precise control of the meniscus shape of the outer compressor lens element suppresses parallax by directly reducing the spherical aberration (PSA) of the entrance pupil in or near the entrance pupil or LP smudge (see Figures 4C and 8B). PSA can be estimated in various ways in lens design software, including the mean RMS lateral deviation or radius of the principal ray across the surface in the LP smudge (e.g., low parallax amount 188), or lateral error (LP smudge radius) versus field of view. As an example, in the low-parallax imaging lens 300 shown in Figures 9A-F, the mean PSA of 12 fields of view, measured as the RMS lateral principal ray error in the LP smudge, was only 0.18 mm. As another example, in the low parallax imaging lens 300 shown in Figures 11B-D, the estimated PSA averaged across the field of view was only 0.023 mm. A good design target value is that for lenses designed to image a half-FOV of approximately 20-40 degrees, the average PSA across the field of view is 0.30 mm or less, when measured as the RMS lateral principal ray error in the LP smudge.

[0072] In addition, compared to conventional low parallax lenses, applying the improved lens design method 600 in Figure 7 significantly reduced front color artifacts. In particular, both exemplary lenses reduced it to a front color of 0.2 mm or less, compared to the 0.5-0.6 mm values ​​commonly seen in conventional low parallax lens designs. Furthermore, these improved results were obtained by using low refractive index (e.g., n(vis) to 1.60 or less) crown glass, while at least the first compressor lens element 337 has an Abbe number or v number of 55 or more, without requiring high refractive index flint glass or special materials such as ALON. Alternatively, the first compressor lens element can be a medium to high refractive index glass (n between 1.6 and 1.8) with a dispersion in the v number range of 40 or more, near the relevant crown / flint boundary (the crown has a v number of 50 or more).

[0073] In some new lens designs, including those shown in Figures 9A-F, the first compressor lens element is a low refractive index (n(vis) approximately 1.55) plastic crown (E48R). The use of low refractive index crown glass or optical plastic, due to its low dispersion, greatly helps reduce front color compared to using high refractive index flint glass. In that case, front color can be further suppressed by adding a second, and possibly third, compressor lens element, along with the appropriate selection of optical material (dispersion). In addition, the use of low refractive index crown material (e.g., BK-7) can significantly improve costs compared to using high refractive index flint glass, along with its polygonal edge shape, for (usually) larger compressor lens elements, especially the first compressor lens element. Furthermore, the use of low refractive index plastic for one or more compressor lens elements can dramatically reduce the lens element weight, as well as the lens system weight and cost. In these low parallax lenses 300, second and third compressor lenses are typically required to assist in front color correction. However, although the presented example had two or three lens elements within the compressor lens element group 330, low parallax lens systems 300 having only one lens element or four or more lens elements can also be developed using the improved design method 600.

[0074] Furthermore, as mentioned above, the reduction of residual parallax error and residual front color enabled by the improved lens design method 600 in Figure 7 can also separately improve camera channel and multi-camera device designs. For example, the improvement can reduce the amount by which the extended FOV 215 is given beyond the core FOV 205, thereby helping the optical-mechanical design reduce the seam width and avoid color vignetting near the polygonal edge of the compressor lens.

[0075] However, as mentioned above, the compressor lens elements, particularly the first lens element, make a large positive contribution to reducing image distortion in order to reduce parallax (e.g., PSA) and front color. In this case, the rest of the lens, especially the wide-angle lens group, is responsible for substantially offsetting the negative distortion contribution.

[0076] As described above, the improved low parallax imaging lens system (300) is designed using the improved method 600 shown in Figure 7, in which the preliminary design of the compressor lens group 330 is obtained separately by optimizing it for rays directed toward the transient aperture diaphragm, which is also an aberration-free entrance pupil. After the initial design of the compressor lens group 330 is obtained, the entire lens 300, including the wide-angle group, can be designed and optimized. The advantage of this improved method is that the compressor lens element group 330 is designed to suppress parallax and front color so that it does what it is supposed to do without burdening or overburdening it with other design objectives. Thus, once the entire lens 300 is designed, the wide-angle group 340 must correct, to some extent, any primary attributes or aberrations that the compressor group 330 has ruined. As a specific example, the surface contribution to distortion of the compressor group 330, particularly the first compressor lens element 337, usually gives a large positive distortion. When a compressor is allowed to change shape without considering other aberrations in order to minimize PSA and suppress parallax, it exhibits a meniscus shape. The position of the entrance pupil behind the intended image plane is key to driving this shape. The addition of second and / or third compressor lens elements (338 and 339) reduces front color but has little effect on distortion. Measured by the contribution of their distortion aberration planes, the wide-angle group 340 then introduces nearly equivalent large distortions of opposite signs, resulting in small net residual distortion across the intended field of view.

[0077] The improved lens design method 600 in Figure 7 can also enable more precise control over lateral color than before. By optimizing the compressor lens elements separately to suppress parallax and front color (steps 610-640), improved targeting of the compressor lens elements, and by more informed material selection, both front and lateral color can be reduced to lower levels. In particular, the surface contribution of the compressor group to lateral color is lower than previously seen. Secondly, when the wide-angle group is designed and optimized while the compressor group is frozen (step 660), the wide-angle group 340 can more accurately offset the lateral color contribution of the compressor lens elements 330, resulting in a lower final lateral color than seen with conventional design methods. Overall, the compressor group 300 contributes a large positive lateral color plane contribution, and the wide-angle group 340 contributes a large negative lateral color plane contribution. In combination, these two elements can be combined to achieve a negligible total lateral color. Compared to before, optimizing for low front color is no longer a trade-off that causes high lateral color. Of course, the resulting lateral color, ranging from low to negligible, can then be traded off to a more normal level while refining the design of the wide-angle lens group 340, which is beneficial for reducing other lens aberrations.

[0078] It should be noted that step 650, in which the separated compressor group 330 is attached to the wide-angle lens group 340, can be somewhat tricky. When the lens element power, lens element spacing, and principal ray angle are varying or different, the two groups may not immediately align or mate properly with each other. In such cases, several standard lens design strategies available in lens design software (e.g., Code V or Zemax) may be used to match the two lens groups before beginning the overall optimization.

[0079] In contrast, when starting with conventional methods of designing lenses, all or most of the intended functional characteristics are present from the outset and represented by the lens elements distributed therein. When designing a low parallax lens system, this means that the initial lens design includes at least some compressor lens elements (group 330) and lens elements of wide-angle group 340, which are located both around the aperture 345. However, while conventional methods can have the correct type of lens elements in the nominally correct positions within the lens, this does not guarantee that the compressor group will do what it is supposed to do. Essentially, the optimization merit function has too much equal treatment and does not yield satisfactory results. An inappropriate kind of competition may be set up between the compressor lens element group and the wide-angle lens element group.

[0080] As an alternative to the partially sequential design method 600 in Figure 7, a more classical lens design technique or method can be adapted to achieve equivalent results. Instead, the entire lens, including the compressor lens elements (group 330) and the wide-angle group 340 lens elements located both before and after the aperture diaphragm 345, can be kept together and optimized simultaneously. However, in this case, the lens design merit function can only be modified to include several compressor group constraints that target parallax and front color control. These constraints can be enabled using operands and weighting coefficients of the Code V or Zemax merit function, and these operands and weighting coefficients affect only the compressor lens elements and / or their surface contributions to aberrations, or their collective, and not the wide-angle group lens elements. This alternative lens design method can also use different weightings at different stages of lens design, or it can have two optimization scripts, one applied during the initial compressor group optimization stage, and the second applied thereafter during the optimization of the entire lens, targeting image plane image quality. The optimization script may also have different weightings for the compressor lens element than for other lens elements to address most standard lens aberrations. Low parallax, low front color objective lens designs can be produced by these alternative methods, which are equivalent to the partially sequential design method 600 in Figure 7.

[0081] The design of the exemplary objective lens 300 in Figures 11B–D has also been modified to accommodate various application examples where different size, weight, performance, and cost (SWaP-C) expectations exist. For example, while the objective lens 300 in Figure 11C has a track length of 119.7 mm and a focal length of 14.9 mm, a similar, also manufacturable, much smaller lens was obtained from Figure 11C, however, with a track length of 9.3 mm and a focal length of 1.12 mm. Both lenses function at the same f / # and wavelength. This second lens is essentially the same design form as the original lens, but the number of lens elements can be reduced as all geometric aberrations decrease with decreasing focal length. When the lens size is reduced to a point where plastic lens elements nominally comparable to those used in mobile phones are feasible, greater degrees of freedom in lens shape become possible, including the use of aspherical or free-form profiles. Such changes also allow lenses to be designed using fewer lens elements.

[0082] To improve front color or residual parallax, as is evident from the improvement of lateral color by applying the partially sequential design method 600 in Figure 7, or a variation or equivalent thereof, discussed previously, this new technique can achieve or enable other complementary improvements. Most simply, it can thus facilitate the reduction of the magnitude of other lens aberrations. Also, as mentioned above, in this type of low parallax lens, the outer compressor lens element 337 and its polygonal edge essentially function as a soft-focus or out-of-focus field aperture, which is magnified by a finite beam width, parallax variation, and residual front color. Therefore, by applying the partially sequential design method 600 in Figure 7, or a variation or equivalent thereof such as the alternative method described above, front color and residual parallax can be reduced, which also helps to make the out-of-focus field aperture sharper. This can be beneficial in both mechanical design and the image cropping and tiling steps. In addition, the lens system may also include a mechanical field diaphragm, such as a plate having a polygonal aperture aligned with the polygonal edge of the compressor element.

[0083] This type of low parallax low front color lens 300 can also be paired with an imaging relay lens system. This imaging relay can enable the use of a larger image sensor, a beam splitter with a secondary image sensor or optical sensor, and a zooming optical component. Alternatively, the improved objective lens 300 can also be paired with an optical fiber relay using a coherent fiber bundle. These improved lenses 300 can also be used in various configurations of multi-camera panoramic capture devices, including spherical and hemispherical systems, conical systems that image a field of view smaller than the hemispherical total field of view, or annular systems that image a field of view that is wide horizontally and narrow vertically (e.g., halo or visor systems). Depending on the design requirements, the system geometry can be octahedron, dodecahedron, icosahedron, or utilize more complex Goldberg polyhedron shapes and patterns, but pentagonal and hexagonal faceted polyhedra are generally preferred because they facilitate the manufacture of camera channels. In some application geometry, camera channels with square or rectangular outer lens elements may be useful. Multi-camera devices can also be manufactured, in which case the outer compressor lens elements are integrated adjacent to each other to form a faceted dome or partial dome. In faceted dome systems, it may be easier to reduce the seam width to, for example, 2 mm or less, preferably 0.5 mm or less. Depending on the lens channel alignment tolerance, the extended FOV 215 can also be reduced.

[0084] This discussion highlighted the design of improved multi-camera image capture devices and associated objective lenses 300 for use in broadband visible light or human-perceptible applications. However, these devices can also be designed for narrowband visible applications (modified using spectral filters), or multispectral, ultraviolet (UV), or infrared (IR) optical imaging applications. In the infrared spectrum, improved low parallax and low front color lenses can be designed for shortwave (SWIR), mediumwave (MWIR), or longwave (LWIR) spectra. In such cases, the image spectral bandwidth can extend to several microns. As the available materials vary across different spectra, the ease or difficulty of the design can change. Nevertheless, using improved design methods, residual front color in these spectral bands can also be reduced to less than 0.1 mm in width. Polarizers or polarizer arrays can also be used. In addition, although the imaging cameras 300 have all been described as using refractive designs, the optical designs can also be reflective or catadioptric, and combinations of refractive and reflective optical elements can also be used. It should also be understood that the camera lens 300 of this method can be designed using optical elements comprising, or including, refractive, gradient refractive index, glass or optical polymer, reflective, aspherical or free-form, quinoform, Fresnel, diffractive or holographic, and subwavelength or metasurface optical properties. These lens systems can also be designed with colorless or apochromatic color correction, or with thermal defocus sensitivity suppression.

Claims

1. An imaging lens for use in a low parallax multi-camera imaging system, A compressor lens element group comprising a truncated polygonal lens element having a meniscus lens shape and equipped with a crown optical material, wherein the compressor lens element group is configured to refract at least a portion of incident light having a spectral bandwidth as image light within a polygonal field of view, and the image light includes a principal ray of the field of view which is a ray of light received along the edge of the compressor lens element group, A wide-angle lens group configured to receive the image light from the compressor lens group, direct the image light towards the image plane, and form a polygonal image corresponding to the polygonal field of view, Equipped with, The projection of the principal rays at the edge of the field of view, contained in the incident light, converges to a low parallax point located behind the image plane, so that the light within the spectral bandwidth converges at the low parallax point. The compressor lens element group is configured to limit parallax and front color in order to reduce color-dependent vignetting at the edges of the truncated polygonal lens element. The aforementioned compressor lens element group introduces positive lateral color, The wide-angle lens element group is configured to provide a negative lateral color that offsets the positive lateral color, thereby forming an imaging lens.

2. The imaging lens according to claim 1, wherein the meniscus shape of the truncated polygonal lens element minimizes pupillary aberration (PSA) within a low parallax range.

3. The imaging lens according to claim 2, wherein the average PSA of the imaging field, measured as the RMS lateral principal ray error within the amount of the low parallax point, is 0.30 mm or less.

4. The imaging lens according to claim 3, wherein the spectral difference of the incident light converging at the low parallax point is determined by a combination of the compressor lens element and one or more front aperture diaphragm lens elements of the wide-angle lens element group.

5. The imaging lens according to claim 1, wherein the compressor lens element group is configured to contribute to positive distortion, and the wide-angle lens element group is configured to contribute to negative distortion.

6. The imaging lens according to claim 1, wherein the compressor lens element group includes a second compressor lens element, and the truncated polygonal lens element and the second compressor lens element are color-corrected to be colorless in order to control or limit the front color.

7. The imaging lens according to claim 1, wherein the distance between the entrance pupil and the low parallax point reduces the parallax error of the non-paraxial principal ray received near one of the plurality of edges.

8. The imaging lens according to claim 1, wherein the compressor lens element group has a visible refractive index of 1.6 or less and an Abbe number of 55 or more.

9. The imaging lens according to claim 1, wherein the compressor lens element group has a visible refractive index of 1.6 or more and 1.8 or less and an Abbe number of 40 or more.

10. The imaging lens according to claim 1, which provides visible light imaging with a spectral bandwidth of 200 nm or more, and the compressor lens element group limits the residual front color along the edge of the truncated polygonal lens element to 0.2 mm or less.

11. The imaging lens according to claim 1, which provides visible light imaging with a spectral bandwidth of 200 nm or more, wherein the compressor lens element group limits the residual front color along the edge of the polygonal image of the image on the image plane to 0.7 or less of the image pixel size.

12. The imaging lens according to claim 1, wherein the compressor lens element group comprises two compressor lens elements combined to provide a color-corrected projection of the principal rays within the spectral bandwidth such that the projection of the paraxial principal rays converges to an entrance pupil located behind the image plane, and the projection of the non-paraxial principal rays converges to a near center optimized to be located close to the entrance pupil such that the near error is reduced over the spectral bandwidth of at least the non-paraxial principal rays received at or near the edge of the molded lens element.

13. The imaging lens according to claim 1, wherein control of both front color and parallax along the edge of the polygonal image reduces the required width of the extended field of view provided by the imaging lens.

14. The imaging lens according to claim 13, wherein the expanded field of view is preferably less than 5% of the nominal field of view width, and more preferably less than 1%.

15. The imaging lens according to claim 1, wherein the control of both front color and parallax along the edge of the polygonal image contributes to reducing the width of the seam between the imaging lens and adjacent imaging lenses in a multi-lens device to a mechanical width of 8 mm or less.

Images