Abstract:
A series of optical elements is used to produce multiple simultaneous adjoining images on a single image plane. A first, intermediate, image is produced using the first telecentric imaging lens. This intermediate image is produced at a plane coincident with an adjustable-size rectangular field stop. The rectangular field stop is mounted in a sub-housing that allows its free rotation. A second telecentric lens collimates the light from the intermediate image. This collimated light is next passed through an optical splitting means, which uses the principal of refraction to separate the light into multiple components. The optical splitting means is mounted in a sub-housing that allows its free rotation. From here, the light next passes through a third and final lens, which produces a second, final, image on a single, planar detection device. The final image consists of a plurality of identical copies of the intermediate image.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority of U.S. Provisional Application No. 60/303,243 filed on Jul. 5, 2001, which is herein incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    This invention relates generally to imaging systems and more particularly to an imaging system that produces multiple images of a single object scene onto a single detector array. These multiple images are spatially displaced from one another on a single detector array in the image plane.  
           [0003]    In some specialized applications, such as long-range multi-spectral imaging, there is a great desire to produce several images of a given object scene simultaneously on a single detector array (such as a CCD). For applications such as multi-spectral imaging, each of these separate images is passed through a different colored filter. Presently, multi-spectral imaging is typically performed either with rotating filter wheels (which are unable to record more than a single image simultaneously) or with a plurality of imaging and detection systems (which inherently are unable to image onto a single detector array).  
           [0004]    Multi-spectral systems that rely on rotating filter wheels produce images through various filters, one-at-a-time, and in succession. In cases where it is important to produce differently-filtered images simultaneously, filter-wheel-dependent multi-spectral systems are inadequate.  
           [0005]    U.S. Pat. No. 5,194,959 describes a multi-spectral imaging system that produces differently-filtered images simultaneously on three different imaging sensors. One major drawback with this system is that three imaging sensors, which can often be quite expensive, are required. In addition, in cases where high-performance and/or low-contrast imaging is to be performed, it is desirable to compare images formed on a single imaging sensor. The reason for this is that every imaging sensor, no matter how similar, is different in some way than every other imaging sensor. For example, something as simple as a slight difference in temperature stability between two imaging sensors can make very fine comparisons of images made on the two imaging sensors practically impossible. For many multi-spectral applications, it is absolutely necessary to produce multiple images on a single imaging sensor.  
           [0006]    U.S. Pat. Nos. 4,933,751, 5,024,530, 5,642,191, 5,729,011, and 5,926,283 each describe an apparatus and/or method for producing multiple images simultaneously on a single imaging sensor. All of these prior art patents have shortcomings which are directly addressed in the invention described herein.  
           [0007]    U.S. Pat. Nos. 4,933,751 and 5,926,283 describe apparatuses that require mirror reflection of the optical beam in so-called “off-axis” or “perpendicular” directions. Because of the convoluted orientation of the multiple off-axis mirrors in these designs, complex positioning systems are required., These patents also describe apparatuses that do not to minimize vignetting.  
           [0008]    U.S. Pat. No. 5,729,011 describes an apparatus that positions both the image-separating prism and the filter array at a point in the optical train where the light is converging. Positioning of the prism at a point in the optical train where light is converging introduces a number of aberrations and degrades image quality. Furthermore, positioning of the filter array at a point in the optical train where light is converging necessarily causes light to be incident on the filters at a wide range of angles (corresponding to the angles at which the light is converging). It is well-known in the field of interference filters that filters&#39; spectral transmission properties vary greatly with angle. Furthermore, this apparatus does not minimize vignetting.  
           [0009]    U.S. Pat. No. 5,642,191 describes an apparatus that positions the filter at a point in the optical train where the light is converging. This presents the same shortfalls presented in the case where a filter array is placed in a converging beam. Furthermore, splitting of the image into only two images is anticipated, and means are not shown for the more complex case where four or more images are to be produced. Furthermore a system of two, concentrically located prisms is required, which is more complicated to align than a single prism would be.  
           [0010]    U.S. Pat. No. 5,024,530 describes an apparatus that does not prevent light from each of the multiple images from spilling over into neighboring images. Furthermore, splitting of the image into only two images is anticipated, and means are not shown for the more complex case where four or more images are to be produced.  
           [0011]    It is therefore an object of this invention to produce multiple images of the same object scene simultaneously and adjoining one another on a single detector plane.  
           [0012]    It is another object of this invention to effect such imaging with an optical system that exhibits no vignetting.  
           [0013]    It is another object of this invention to effect such imaging with an optical system that requires no off-axis optical elements.  
           [0014]    It is another object of this invention to effect such imaging with an optical splitting means that comprises a single refractive prism.  
           [0015]    It is another object of this invention to effect such imaging without the use of mirrors.  
           [0016]    It is another object of this invention to effect such imaging with an optical system that allows adjustment of the size of each image constituting the multiple images.  
           [0017]    It is another object of this invention to effect such imaging with an optical system that allows adjustment of orientation and placement of the multiple images.  
         SUMMARY OF THE INVENTION  
         [0018]    The objects set forth above as well as further and other objects and advantages of the present invention are accomplished by the embodiments of the invention described herein below.  
           [0019]    The present invention uses a series of optical elements to produce multiple simultaneous adjoining images on a single image plane. A first, intermediate, image is produced using the first telecentric imaging lens. This intermediate image is produced at a plane coincident with an adjustable-size rectangular field stop. The rectangular field stop is mounted in a sub-housing that allows its free rotation. A second telecentric lens collimates the light from the intermediate image. This collimated light is next passed through an optical splitting means, which uses the principal of refraction to separate the light into multiple components. The optical splitting means is mounted in a sub-housing that allows its free rotation. From here, the light next passes through a third and final lens, which produces a second, final, image on a final imaging plane. A single, planar detection device (such as film or a CCD array) is located at a plane substantially coincident with the final imaging plane. The final image consists of a plurality of identical copies of the intermediate image, each of which may be composed of a different component, or set of components, of the original incident light. The plurality of identical copies of the intermediate image may be arranged such that their edges are adjoining or nearly-adjoining. Size of the multiple identical copies of the intermediate image may be adjusted by adjusting the size of the rectangular field stop. Orientation of the multiple identical copies of the intermediate image may be adjusted by adjusting the rotation of the rectangular field stop. Placement of the multiple identical copies of the intermediate image on the final imaging plane may be adjusted by adjusting the rotation of the optical splitting means.  
           [0020]    For a better understanding of the present invention, together with other and further objects thereof, reference is made to the accompanying drawings and detailed description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]    [0021]FIG. 1 is a schematic illustration of the components of the present invention.  
         [0022]    [0022]FIG. 2 is a schematic illustration depicting the concept of forming a plurality of nearly-identical images on a single imaging plane.  
         [0023]    [0023]FIG. 3 is a schematic illustration of a side view of a first preferred embodiment of the present invention.  
         [0024]    [0024]FIG. 4 is a schematic illustration of a top view of a first preferred embodiment of the present invention.  
         [0025]    [0025]FIG. 5 is a schematic illustration of the present invention depicting the concept of a vignetting optical system.  
         [0026]    [0026]FIG. 6 is a schematic illustration of the present invention depicting the concept of a non-vignetting optical system.  
         [0027]    [0027]FIG. 7 is a schematic illustration of the present invention depicting the concept of telecentric imaging.  
         [0028]    [0028]FIG. 8 is a schematic illustration of the present invention depicting the concept of non-telecentric imaging.  
         [0029]    [0029]FIG. 9 is a schematic illustration of the present invention depicting a telecentric imager and telecentric collimator.  
         [0030]    [0030]FIG. 10 is a schematic illustration of the present invention depicting a non-telecentric imager and non-telecentric collimator.  
         [0031]    [0031]FIG. 11 is a schematic illustration of the present invention of a preferred embodiment of a filter plane.  
         [0032]    [0032]FIG. 12 is a pictorial illustration of a preferred embodiment of a beam-separating prism.  
         [0033]    [0033]FIG. 13 is a schematic illustration of the present invention of a preferred embodiment of a filter plane with a preferred embodiment of a beam-separating prism shown overlaid.  
         [0034]    [0034]FIG. 14 is schematic illustration of the present invention of a second preferred embodiment of the invention.  
         [0035]    [0035]FIG. 15 is a schematic illustration of the present invention of a second preferred embodiment of a filter plane.  
         [0036]    [0036]FIG. 16 is a schematic illustration of the present invention of a second preferred embodiment of a filter plane with a second preferred embodiment of a beam-separating prism plane shown overlaid.  
         [0037]    [0037]FIG. 17 is a pictorial illustration of a preferred embodiment of an individual wedge-prism. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0038]    The basic concept of the present invention involves telecentrically forming a first image of a distant object, masking the edges of the first image, collimating light from the first image, filtering and then beam-separating the collimated light, and then forming a plurality of separate images on a single imaging plane. FIG. 1 shows a schematic diagram of the present invention.  
         [0039]    Referring to FIG. 1, optical radiation  10  from a distant object (not shown) is incident on a first telecentric imaging lens  12  (also referred to as the first telecentric optical sub-system). The first telecentric imaging lens  12  focuses the optical radiation  14  and forms a first image at a plane substantially coincident with a rectangular aperture  16 . After focusing to an image at a plane substantially coincident with a rectangular aperture  16 , optical radiation next diverges  18  and is incident on a second telecentric imaging lens  20  (also referred to as the second telecentric optical sub-system). The second telecentric imaging lens  20  is positioned at a distance from the rectangular aperture  16  that causes the optical radiation to be substantially collimated  22  after passing through the second telecentric imaging lens  20 . The collimated beam of optical radiation  22  is next incident on a beam-separating sub-system  24 . The beam-separating sub-system  24  comprises a filter plane  26  and a beam-separating prism plane  28 . After the collimated beam of optical radiation  22  passes through the beam-separating sub-system  24 , it emerges as a plurality of collimated beams of optical radiation  30 , each traveling at an angle with respect to the original direction of propagation of the collimated beam of optical radiation  22 . The plurality of collimated beams of optical radiation  30  next passes through a third imaging lens  32  (also referred to as the third optical sub-system), which third imaging lens  32  forms a plurality of images on a final imaging plane  34 . The plurality of images are nearly identical in form, with the only exception being that each is formed with optical radiation that has passed through a different filter in the filter plane  26 .  
         [0040]    [0040]FIG. 2 shows a schematic of the principle of forming a plurality of (four in this case) nearly identical images  36 ,  38 ,  40 , and  42  of a single object  44  on a single imaging plane  46 . Note that each of the plurality of images  36 ,  38 ,  40 , and  42  has passed through a different filter in the filter plane  26 , but is otherwise identical in form to the other images.  
         [0041]    [0041]FIG. 3 shows a pictorial cross-section of a first preferred embodiment of the apparatus  48 . The components of this first preferred embodiment  48  include an adjustable-diameter iris  50 , an objective lens  52 , an adjustable-size rectangular field stop  54 , a collimating lens  56 , a filter plane  58 , a beam-separating prism  60 , and a focusing lens group  62 , which focusing lens group  62  comprises a focusing lens  64 , and a field-flattening meniscus lens  66 . The adjustable-diameter iris  50  and objective lens  52  are mounted in a sub-housing  68  by conventional means (not shown), which sub-housing  68  is held firmly in place with a locking bolt  70 . The rectangular field stop  54  is mounted in a sub-housing  72  by conventional means (not shown), which sub-housing  72  is held firmly in place to the housing  74  with a locking bolt  76 . The filter plane  58  and the beam-separating prism  60  are mounted in a sub-housing  78  by conventional means (not shown), which sub-housing  78  is held firmly in place to the housing  74  with a locking bolt  80 . All of the components of the apparatus  48  are mounted to the housing  74  such that their centerline is coincident with an optical axis  82 . All of the components of the apparatus  48  are contained within or connected to a housing  74 , which in this case is made of aluminum, but may be made of any durable material such as plastic, wood, or metal.  
         [0042]    As illustrated in FIG. 3, optical radiation  84  from a distant object (not shown) passes through the adjustable-diameter iris  50  and a series of lenses and filters to form a plurality of images on a detector plane  86 . Optical radiation includes, for example, ultraviolet, visible, and near-infrared electromagnetic radiation with wavelength(s) in the range from 0.3 micron to 2 microns.  
         [0043]    Referring again to FIG. 3, optical radiation  84  from a distant object (not shown) passes through the adjustable-diameter iris  50  (preferably by Thorlabs, part #SM1D12) and is focused by objective lens  52  (preferably by Newport, 50 mm focal length, part #PAC040) to form an intermediate, real image at a plane substantially coincident with an adjustable-size rectangular field stop  54  (preferably by Coherent, part #61-1137). The adjustable-diameter iris  50  and objective lens  52  (an embodiment of the first telecentric optical sub-system) are mounted in a sub-housing  68 , which sub-housing  68  is connected with the system housing  74  in such a way that the sub-housing  68  may be moved along the optical axis  82 . For example, the adjustable-diameter iris  50  and objective lens  52  may be firmly mounted in a round sub-housing  68 , and the round sub-housing  68  may have attached to it a locking bolt  70 , which locking bolt  70  passes through a slot  88  (illustrated in FIG. 4) in the housing  74 . Provided that the slot  88  in the housing  74  is aligned parallel to the optical axis  82 , and the slot  88  in the housing  74  has a width slightly larger than the width of the locking bolt  70 , the sub-housing  68  will then be restricted to move only in a direction parallel to the optical axis  82 . Furthermore, the locking bolt  70  is attached to the sub-housing  68  such that when the locking bolt  70  is tightened, the sub-housing  68  will be firmly attached to the housing  74  and the sub-housing  68  will then be restricted from moving along the optical axis  82 . By setting the size of the adjustable iris  50  to preferably 8 mm, and by locating the adjustable iris  50  50 mm from the objective lens  52 , a non-vignetting, telecentric imaging situation is obtained. A non-vignetting, telecentric imaging situation ensures that substantially all optical radiation  84  collected by the objective lens  52  will be passed without loss through the entirety of the system  48 .  
         [0044]    Vignetting is an effect occurring in some optical imaging systems that causes off-axis objects to appear dimmer than on-axis objects. As illustrated in FIG. 5, an off-axis object emits or reflects optical radiation A that passes through a non-telecentric lens  90  and is redirected as A′ upon an imaging plane  92 . The optical radiation A″ exits the imaging plane  92  and is directed towards a non-telecentric lens  94 . Some, but not all, of the optical radiation A″ is passed through the system as denoted by rays A′″. Because some of the rays A do not pass through lens  94 , passage of the rays A through the system is impeded and the total amount of optical radiation through the system is lessened, and therefore the system is said to suffer from vignetting.  
         [0045]    [0045]FIG. 6 shows an example of an off-axis object emitting or reflecting optical radiation B that passes through a telecentric lens  96  and is redirected as B′ upon an imaging plane  98 . The optical radiation B″ exits the imaging plane  98  and is directed towards a telecentric lens  100 . All of the optical radiation B″ is passed through the system as denoted by rays B′″. Because the passage of all of the rays B through the system is not impeded, the total amount of optical radiation through the system is conserved and the system is said to not suffer from vignetting.  
         [0046]    As illustrated in FIG. 3, the adjustable-diameter iris  50  is located at a position ahead of the objective lens  52 . The distance between the iris  50  and the objective lens  52  is substantially equivalent to the focal length of the objective lens  52 . Locating the iris  50  at this position ensures telecentricity (to be discussed in detail below) of the objective lens  52  in image space. As illustrated in FIG. 3, an intermediate image of the distant object is formed by the objective lens  52  at a plane substantially coincident with an adjustable-size rectangular field stop  54 . Because of the image-space telecentricity of the objective lens  52 , optical radiation  102  emerges from the adjustable-size rectangular field stop  54  in a telecentric manner ensuring that vignetting (to be discussed in detail below) of the image is minimized.  
         [0047]    [0047]FIG. 7, FIG. 8, FIG. 9, and FIG. 10 are provided herein to aid in the explanation of the processes of vignetting and telecentric systems. FIG. 7 shows a schematic diagram of the action of a telecentric imaging lens  104  aligned along an optical axis  106 . Incoming optical radiation  108  from a distant off-axis source (not shown) is focused to an image  110  by the telecentric imaging lens  104  to an imaging plane  112 .  
         [0048]    [0048]FIG. 8 shows a schematic diagram of the action of a non-telecentric imaging lens  114  aligned along an optical axis  116 . Incoming optical radiation  118  from a distant off-axis source (not shown) is focused to an image  120  by the non-telecentric imaging lens  114  to an imaging plane  122 . Note the difference in angles between the focused rays  110  emerging from the telecentric imaging lens  104  of FIG. 7 and the focused rays  120  emerging from the non-telecentric imaging lens  114  of FIG. 8.  
         [0049]    [0049]FIG. 9 shows a schematic diagram of the telecentric imaging lens  104  and imaging plane  112 , wherein rays of optical radiation  110  converging on the imaging plane  112  are further collimated with the use of a second telecentric collimating lens  124 . Rays of optical radiation  126  exit the telecentric collimating lens  124 . Because the objective lens  104  and collimating lens  124  are both telecentric, and are designed and matched so as to co-act telecentrically together, all incident rays of optical radiation  108  are passed through the system and emerge unimpeded as-optical radiation rays  126 , and therefore the system does not suffer from vignetting.  
         [0050]    [0050]FIG. 10 shows a schematic diagram of a non-telecentric imaging lens  114  and imaging plane  122 , wherein rays of optical radiation converging on the imaging plane  122  are further collimated with the use of a second non-telecentric collimating lens  128 . Rays of optical radiation  130  exit the second non-telecentric collimating lens  128 . Because the objective lens  114  and collimating lens  128  are not telecentric, and are not designed and matched so as to co-act telecentrically together, a significant portion of the incident rays of optical radiation  118  are prevented from emerging  130  from the system. Because the passage of some of the rays  132  through the system is impeded, the total amount of optical radiation through the system is lessened, compared to the telecentric-lens-case presented in FIG. 9, and the system is said to suffer from vignetting.  
         [0051]    Returning to FIG. 3, collimating lens  56  receives diverging optical radiation  102  from the intermediate image, which image having been formed by objective lens  52  at a plane substantially coincident with the rectangular field stop  54 , and produces a collimated beam of optical radiation  136 . The size of the rectangular field stop  54  may be adjusted. Furthermore, the rectangular field stop  54  is mounted in a sub-housing  72 , which sub-housing  72  is connected with the system housing  74  in such a way that the sub-housing  72  may be rotated by conventional means (not shown) about the optical axis  82 . For example, the rectangular field stop  54  may be firmly mounted in a round sub-housing  72 , and the round sub-housing  72  may be fitted into a round groove  134  in the system housing  74  (as shown in FIG. 4). In this way, the sub-housing  72  is free to rotate about the optical axis  82  within the groove  134  in the housing  74 , but is restricted from any other motion. Furthermore, a locking bolt  76  is attached to the sub-housing  72  such that when the locking bolt  76  is tightened, the sub-housing  72  will be firmly attached to the housing  74  and the sub-housing  72  will then be restricted from rotating about the optical axis  82 .  
         [0052]    Collimated optical radiation  136  next strikes the filter plane  58 . As shown in FIG. 11, the filter plane  58  is itself comprised of a plurality of optical filters  138  (four in this case). The filters  138  may be of any type, including but not necessarily limited to, wavelength-selective bandpass filters, polarization filters, or neutral density filters. As shown in FIG. 11, the beam of collimated optical radiation  136 , which beam  136  is incident on the filter plane  58 , has a cross-sectional shape that is substantially round. As the beam of collimated optical radiation  136  passes through the filter plane  58 , each of a plurality of (four in this case) separate portions (to be discussed in detail below) of the collimated beam  136  passes through one of a plurality of (four in this case) filters  138 .  
         [0053]    [0053]FIG. 11 shows a cross-sectional schematic diagram of the plurality of (four in this case) filters  138  that comprise the filter plane  58 . Note that the cross-sectional area of the collimated beam of optical radiation  136  is substantially circular in shape, and is centered on the optical axis  82 , as it passes through the filter plane  58 . Note that the top-left quadrant of the collimated beam of optical radiation  136  passes through filter A, the top-right quadrant of the collimated beam of optical radiation  136  passes through filter B, the bottom-left quadrant of the collimated beam of optical radiation  136  passes through filter C, and the bottom-right quadrant of the collimated beam of optical radiation  136  passes through filter D. Immediately after passing through filter plane  58 , the beam of collimated optical radiation  136  next passes through the beam-separating prism  60 . The beam-separating prism  60  is an optical element, or an arrangement of a plurality of optical elements, with a plurality of (four in this case) facets on one side, and a single flat facet on the other side. For the present preferred embodiment, the beam-separating prism  60  is preferably a single optical element made of BK7 glass, but any transmitting, refracting material (such as plastic, water, or other types of glass) may be used. For the present preferred embodiment, the multi-faceted side of the beam-separating prism  60  preferably has four identical facets, each with a wedge angle of 8.92 degrees. The beam-separating prism  60  causes the four quadrants of the beam of collimated optical radiation, each of which has passed through a different filter  138  in the filter plane  58 , to bend in toward the optical axis  82 .  
         [0054]    [0054]FIG. 12 shows a drawing of the beam-separating prism  60 , and clearly shows the vertices  140  of the beam-separating prism  60 , which vertices  78  separate the multiple sections (four in this case) of the prism  60 . FIG. 13 shows a cross-sectional schematic diagram of the plurality of (four in this case) filters  138  that comprise the filter plane  58 , superimposed in front of the beam-separating prism  60 . Note that the cross-sectional area of the collimated beam of optical radiation  136  is substantially circular in shape, and is centered on the optical axis  82 , as it passes through the beam-separating prism  60 . As shown in FIG. 13, each of the vertices  140  of the beam-separating prism  60  is aligned so that it is substantially parallel with each of the corresponding interfaces between the individual filters  138  (which filters are labeled A, B, C, and D in FIG. 13) that comprise the filter plane  58 .  
         [0055]    Returning to FIG. 3, the filter plane  58  and the beam-separating prism  60  are mounted in a sub-housing  78 , which sub-housing  78  is connected with the system housing  74  in such a way that the sub-housing  78  may be rotated about the optical axis  82 . For example, the filter plane  58 , which filter plane  58  comprises a plurality of separate filters  138 , and the beam-separating prism  60  may be firmly mounted in a round sub-housing  78 , and the round sub-housing  78  may be fitted into a round groove  142  in the system housing  74  (as shown in FIG. 4). In this way, the sub-housing  78  is free to rotate about the optical axis  82  within the groove  142  in the housing  74 , but is restricted from any other motion. Furthermore, a locking bolt  80  is attached to the sub-housing  78  such that when the locking bolt  80  is tightened, the sub-housing  78  will be firmly attached to the housing  74  and the sub-housing  78  will then be restricted from rotating about the optical axis  82 .  
         [0056]    After the beam of collimated optical radiation  136  has passed through the beam-separating prism  60 , it next passes through the final imaging lens group  62 . After the beam of collimated optical radiation  136  has passed through the beam separating prism  60 , the beam of collimated optical radiation  136  effectively becomes a plurality of (four in this case) differently-directed collimated beams of optical radiation  144 . With this plurality of (four in this case) differently-directed collimated beams of optical radiation  144 , the final imaging lens group  62  is used to form a plurality of (four in this case) images on the detector plane  86  (preferably a CCD detector, such as by Pulnix, part #TM1040). Imaging lens group  62  preferably comprises an achromatic doublet  64  (manufactured by Newport, part #PAC040) and a field-flattening meniscus lens  66  (preferably made of BK7 glass, preferably having a center thickness of 2.3 mm, preferably having a convex radius of curvature of 12.49 mm, preferably having a concave radius of curvature of 29.54 mm, and preferably having a diameter of 12.7 mm).  
         [0057]    The method of operation for this embodiment involves simply aiming the optical system at a reflecting or emitting source of optical radiation. Adjustment of the size of each of the plurality of (four in this case) images is effected through the adjustment of the size of the rectangular field-stop  54 . Adjustment of the orientation of the plurality of (four in this case) images on the CCD detector  86  is effected through rotation about the optic axis  82  of the rectangular field-stop  54 , which field stop  54  is mounted in a rotatable sub-housing  72  with a locking bolt  76  provided for just this purpose. Adjustment to the placement of the plurality of (four in this case) images on the CCD detector  86  is effected through rotation about the optic axis  82  of the filter plane  58  and beam-separating prism  60 , which filter plane  58  and prism  60  are mounted in a rotatable sub-housing  78  with a locking bolt  80  provided for just this purpose. Focus of the images is effected through movement of objective lens  52  in a direction, along the optical axis  82 , towards or away from the rectangular field-stop  54 . Ultimately, the electronic signal from the CCD detector  86  must be collected and then used to create a display elsewhere (such as on a display monitor, or in a computer&#39;s memory). The present invention concerns only creating multiple images on a single imaging plane. Methods for displaying and/or processing the multiple images are outside the scope of the present invention.  
         [0058]    [0058]FIG. 14 shows a pictorial cross-section of a second preferred embodiment  146  of the apparatus. The components of this second preferred embodiment  146  include an objective lens  148 , an adjustable-size rectangular field stop  150 , a collimating lens  152 , a filter plane  154 , a beam-separating prism plane  156 , and a focusing lens  158 . The objective lens  148  in this second preferred embodiment  146  is a compound lens, and therefore comprises a plurality of (seven in this case) optical elements, which optical elements are mounted in a single sub-housing  160 . Optical elements mounted in the sub-housing  160  preferably include a first lens element  162 , a second lens element  164 , a third lens element  166 , a primary mirror  168 , a secondary mirror  170 , a fourth lens element  172 , and a fifth lens element  174 . The sub-housing  160  is held firmly in place with a locking bolt  176 . The rectangular field stop  150  is mounted in a sub-housing  178 , which sub-housing  178  is held firmly in place with a locking bolt  180 . The collimating lens  152  in this second preferred embodiment  146  is a compound lens, and therefore comprises a plurality of (seven in this case) optical elements, which optical elements are mounted in a single sub-housing  182 . Optical elements mounted in the sub-housing  182  preferably include a first lens element  184 , a second lens element  186 , a first mirror  188 , a second mirror  190 , a third lens element  192 , a fourth lens element  194 , and a fifth lens element  196 . The filter plane  154  and beam-separating prism plane  156  are mounted in a sub-housing  198 , which sub-housing  198  is held firmly in place with a locking bolt  200 . The focusing lens  158  in this second preferred embodiment  146  is a compound lens, and therefore comprises a plurality of (seven in this case) optical elements, which optical elements are mounted in a single sub-housing  202 . Optical elements mounted in the sub-housing  202  preferably include a first lens element  204 , a second lens element  206 , a third lens element  208 , a primary mirror  210 , a secondary mirror  212 , a fourth lens element  214 , and a fifth lens element  216 . All of the components of the apparatus  146  are mounted along an optical axis  218  and are contained within or connected to a housing  220 , which in this case is made of aluminum, but may be made of any durable material such as plastic, wood, or metal.  
         [0059]    As illustrated in FIG. 14, a single beam of optical radiation  222  from a distant object (not shown) passes through a series of lenses and filters to form a plurality of (four in this case) images on a detector plane  224 . Optical radiation includes, for example, ultraviolet, visible, and near-infrared electromagnetic radiation with wavelength(s) in the range from 0.3 micron to 2 microns. As illustrated with arrows in FIG. 14, the order in which optical radiation  222  passes through the optical elements is as follows. First, optical radiation  222  passes through the first lens element  162 , then the second lens element  164 , and then the third lens element  166  of the objective lens  148 . Next, optical radiation is reflected from the primary mirror  168  and then the secondary mirror  170  of the objective lens  148 . Next, optical radiation passes through the fourth lens element  172  and then the fifth lens element  174  of the objective lens  148 . Optical radiation next passes through the rectangular aperture  150 , and then it passes through the first lens element  184  and then the second lens element  186  of the collimating lens  152 . Next optical radiation reflects from the first mirror  188  and then the second mirror  190  of the collimating lens  152 . Next optical radiation passes through the third lens element  192 , then the fourth lens element  194 , and then the fifth lens element  196  of the collimating lens  152 . Next, optical radiation passes through the filter plane  154  and then the beam-separating prism plane  156 . Note that the order of placement of the two beam-separating elements, namely the filter plane  154  and the beam-separating prism plane  156 , may be reversed without affecting the principle of the present invention. Next, optical radiation passes through the first lens element  204 , then the second lens element  206 , and then the third lens element  208  of the focusing lens  158 . Next, optical radiation is reflected from the primary mirror  210  and then the secondary mirror  212  of the focusing lens  158 . Next, optical radiation passes through the fourth lens element  214  and then the fifth lens element  216  of the focusing lens  158 . Optical radiation finally exits the housing  220  of the apparatus  146  and forms a plurality of (four in this case) images on the detector plane  224 .  
         [0060]    Referring again to FIG. 14, optical radiation  222  from a distant object (not shown) is focused by the objective lens  148  to form an intermediate, real image at a plane substantially coincident with an adjustable-size rectangular field stop  150  (preferably by Coherent, part # 61 - 1137 ). The objective lens  148  comprises a plurality of (seven in this case) optical elements, which optical elements are mounted in a single sub-housing  160 , which sub-housing  160  is connected with the system housing  220  in such a way that the sub-housing  160  may be moved along the optical axis  218 . For example, the objective lens  148  may be firmly mounted in a round sub-housing  160 , and the round sub-housing  160  may have attached to it a locking bolt  176 , which locking bolt  176  passes through a slot  226  in the housing  220 . Provided that the slot  226  in the housing  220  is aligned parallel to the optical axis  218 , and the slot  226  in the housing  220  has a width slightly larger than the width of the locking bolt  176 , the sub-housing  160  will then be restricted to move only in a direction along the optical axis  218 . In this way, the sub-housing  160  is free to move along the optical axis  218 , but is restricted from any other motion. Furthermore, the locking bolt  176  is attached to the sub-housing  160  such that when the locking bolt  176  is tightened, the sub-housing  160  will be firmly attached to the housing  220  and the sub-housing  160  will then be restricted from moving along the optical axis  218 . By carefully designing the objective lens  148  so that the exit pupil is located a very large distance to the left of the objective lens (a well-understood practice in the art of optical design), a non-vignetting, telecentric imaging situation may be obtained. As explained previously, a non-vignetting, telecentric imaging situation ensures that substantially all optical radiation collected by the objective lens  148  will be passed without loss through the entirety of the system  146 .  
         [0061]    Because of the image-space telecentricity of the objective lens  148 , optical radiation emerges from the adjustable-size rectangular field stop  150  in a telecentric manner (this ensures that vignetting of the image is substantially eliminated).  
         [0062]    Referring again to FIG. 14, collimating lens  152  collimates the optical radiation from the intermediate image, which intermediate image having been formed by objective lens  148  at a plane substantially coincident with the rectangular field stop  150 . The size of the rectangular field stop  150  may be adjusted. Furthermore, the rectangular field stop  150  is mounted in a sub-housing  178 , which sub-housing  178  is connected with the system housing  220  in such a way that the sub-housing  178  may be rotated about the optical axis  218 . For example, the rectangular field stop  150  may be firmly mounted in a round sub-housing  178 , and the round sub-housing  178  may be fitted into a round groove  228  in the system housing  220 . In this way, the sub-housing  178  is free to rotate about the optical axis  218  within the groove  228  in the housing  220 , but is restricted from any other motion. Furthermore, a locking bolt  180  is attached to the sub-housing  178  such that when the locking bolt  180  is tightened, the sub-housing  178  will be firmly attached to the housing  220  and the sub-housing  178  will then be restricted from rotating about the optical axis  218 .  
         [0063]    Collimated optical radiation next strikes the filter plane  154 . As shown in FIG. 15, the filter plane  154  is itself comprised of a plurality of optical filters  230  (four in this case). The filters  230  may be of any type, including but not necessarily limited to, wavelength-selective bandpass filters, polarization filters, or neutral density filters. As shown in FIG. 11, the beam of collimated optical radiation  232 , which beam  232  is incident on the filter plane  154 , has a cross-sectional shape that is generally round, but is confined to an area between two concentric circles, as shown in FIG. 15. As the beam of collimated optical radiation  232  passes through the filter plane  154 , each of a plurality of (four in this case) separate portions of the collimated beam  232  passes through one of a plurality of (four in this case) filters  230 .  
         [0064]    [0064]FIG. 15 shows a cross-sectional schematic diagram of the plurality of (four in this case) filters  230  that comprise the filter plane  154 . Also shown in FIG. 15 is a shaded circle representing the cross-sectional area of the collimated beam of optical radiation  232 , as it passes through the filter plane  154 . Note that the cross-sectional area of the collimated beam of optical radiation  232  is generally round, but is confined to an area between two concentric circles, as shown in FIG. 15. The reason for this is that the collimating lens  152  comprises a secondary mirror  188 , which secondary mirror  188  obscures the central portion of the collimated beam  232 . Note that, as depicted in FIG. 15, the top-left quadrant of the collimated beam of optical radiation  232  passes through filter W, the top-right quadrant of the collimated beam of optical radiation  232  passes through filter X, the bottom-left quadrant of the collimated beam of optical radiation  232  passes through filter Y, and the bottom-right quadrant of the collimated beam of optical radiation  232  passes through filter Z. Immediately after passing through filter plane  154 , the beam of collimated optical radiation  232  next passes through the beam-separating prism plane  156 .  
         [0065]    The beam-separating prism plane  156  comprises a plurality of (four in this case) wedge-prisms  234 , arranged as shown in FIG. 16. The individual wedge-prisms  234  are designed so that they are thickest toward the outermost edge of the prism plane  156  (farthest away from the optical axis  176 ) and they are thinnest at the innermost edge of the prism plane  156  (the innermost edge is defined here as the edge that is closest to the optical axis  218 ). A sketch of a single wedge-prism  234  is shown in FIG. 17. For the present preferred embodiment, the prism is preferably made of BK7 glass, but any transmitting, refracting material (such as plastic, water, or other types of glass) may be used. The beam-separating prism plane  156  causes the four quadrants of the beam of collimated optical radiation  232 , each quadrant of the beam having passed through a different filter  230  in the filter plane  154 , to bend or refract in a direction that is generally away from the optical axis  218 .  
         [0066]    [0066]FIG. 16 shows a drawing of the beam-separating prism plane  156 , and clearly shows the plurality of (four in this case) individual wedge prisms  234  that comprise the beam-separating prism plane  156 . FIG. 16 also shows a cross-sectional schematic diagram of the plurality of (four in this case) filters  230  that comprise the filter plane  154 , which filter plane  154  is drawn superimposed in front of the beam-separating prism plane  156 . Also shown in this figure is a shaded area representing the cross-sectional area of the collimated beam of optical radiation  232 , as it passes through the filter plane  154 . As shown in FIG. 16, each of the individual wedge prisms  234  comprising the beam-separating prism plane  156  is aligned so that its edges are aligned substantially parallel to the edges of the individual filters  230  (which filters are labeled W, X, Y, and Z in FIG. 16) that comprise the filter plane  154 .  
         [0067]    Returning to FIG. 14, the filter plane  154 , which filter plane  154  is shown in FIG. 15 as comprising a plurality of (four in this case) separate filters  230 , and the beam-separating prism plane  156 , which beam-separating prism plane  156  is shown in FIG. 16 as comprising a plurality of (four in this case) individual wedge prisms  234 , are mounted in a sub-housing  198 , which sub-housing  198  is connected with the system housing  220  in such a way that the sub-housing  198  may be rotated about the optical axis  218 . For example, the filter plane  154 , which filter plane  154  comprises a plurality of (four in this case) separate filters  230 , and the beam-separating prism plane  156 , which beam-separating prism plane  156  comprises a plurality of (four in this case) individual wedge prisms  234 , may be firmly mounted in a round sub-housing  198 , and the round sub-housing  198  may be fitted into a round groove  236  in the system housing  220 . In this way, the sub-housing  198  is free to rotate about the optical axis  218  within the groove  236  in the housing  220 , but is restricted from any other motion. Furthermore, a locking bolt  200  is attached to the sub-housing  198  such that when the locking bolt  200  is tightened, the sub-housing  198  will be firmly attached to the housing  220  and the sub-housing  198  will then be restricted from rotating about the optical axis  218 .  
         [0068]    After the beam of collimated optical radiation has passed through the beam-separating prism plane  156 , it next passes through the focusing lens  158 . After the beam of collimated optical radiation has passed through the beam separating prism plane  156 , the beam of collimated optical radiation effectively becomes a plurality of (four in this case) differently-directed collimated beams of optical radiation. With this plurality of (four in this case) differently-directed collimated beams of optical radiation, the focusing lens  158  is used to form a plurality of (four in this case) images on the detector plane  224  (preferably a CCD detector).  
         [0069]    The method of operation for this embodiment involves simply aiming the optical system at a target. Adjustment of the size of each of the plurality of (four in this case) images is effected through the adjustment of the size of the rectangular field-stop  150 . Adjustment of the orientation of the plurality of (four in this case) images on the CCD detector  224  is effected through rotation about the optic axis  218  of the rectangular field-stop  150 , which field stop  150  is mounted in a rotatable sub-housing  178  with a locking bolt  180  provided for just this purpose. Adjustment to the placement of the plurality of (four in this case) images on the CCD detector  224  is effected through rotation about the optic axis  218  of the filter plane  154  and beam-separating prism plane  156 , which filter plane  154  and prism plane  156  are mounted in a rotatable sub-housing  198  with a locking bolt  200  provided for just this purpose. Focus of the images is effected through movement of objective lens  148  in a direction, along the optical axis  218 , towards or away from the rectangular field-stop  150 . Ultimately, the electronic signal from the CCD detector  224  must be collected and then used to create a display elsewhere (such as on a display monitor, or in a computer&#39;s memory). The present invention concerns only creating multiple images on a single imaging plane. Methods for displaying and/or processing the multiple images are outside the scope of the present invention.  
         [0070]    Although the invention has been described with respect to various embodiments, it should be realized this invention is also capable of a wide variety of further and other embodiments within the spirit and scope of the appended claims.