Patent Abstract:
An optical system of the present invention produces multiple simultaneous adjoining images on a single image plane. The optical system includes a first optical sub-system, a second optical sub-system, an aperture stop located between the first optical sub-system and the second optical sub-system, and a beam separating sub-system located at a plane substantially coincident with the aperture stop. The beam separating sub-system can receive electromagnetic radiation from the first optical sub-system and can separate the received electromagnetic radiation into multiple beams of electromagnetic radiation. The second optical sub-system images the multiple beams of electromagnetic radiation received from the beam separating sub-system into multiple images on an image plane. The beam separating sub-system includes one or more beam separating components and a mid-system filter system. An output filter, overlaid on the imaging plane, prevents light from any one of the images from passing through to the portion of the image plane corresponding to any one of the other images.

Full Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application claims priority of U.S. Provisional Application No. 60/363,997 filed on Mar. 14, 2002, which is incorporated by reference herein. 

   BACKGROUND OF THE INVENTION 
   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. 
   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). 
   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. 
   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, especially through a large range of illumination levels. 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. 
   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. 
   U.S. Pat. Nos. 4,933,751 and 5,926,283 describe apparatuses that require mirror reflection of the optical beam in “off-axis” or “perpendicular” directions. Because of the convoluted orientation of the multiple off-axis mirrors in these designs, complex positioning systems are required. 
   U.S. Pat. No. 5,729,011 describes an apparatus that positions the image-separating prism at a point in the optical train where the light is converging. Whereas positioning of the prism at a point in the optical train where light is collimated would produce sharp, well-resolved images, positioning of the prism at a point in the optical train where light is converging introduces a number of aberrations and degrades image quality. Therefore an apparatus that positions the prism at a point in the optical train where light is converging is inferior to one that takes care to position the prism in a collimated-light space. 
   U.S. Pat. Nos. 5,642,191 and 5,024,530 describe apparatuses in which 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, these patents require several imaging lens systems in order to create a first image, collimate the light, and then to form a second image. These multiple imaging lens systems more costly, larger, and cause more imaging aberrations than the single imaging lens system described in the present invention. 
   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. 
   It is another object of this invention to effect such imaging with an optical system that exhibits no vignetting (obscuration of a portion of the light reaching the detector). 
   It is another object of this invention to effect such imaging with an optical system that requires no off-axis optical elements. 
   It is another object of this invention to effect such imaging with a single optical imaging lens system. 
   It is another object of this invention to effect such imaging without the need for mirrors. 
   SUMMARY OF THE INVENTION 
   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. 
   The present invention uses a series of optical elements (an optical system) to produce multiple simultaneous adjoining images on a single image plane. A beam separating sub-system of this invention is located at a plane substantially coincident with the aperture stop of a color-corrected imaging lens. The image produced by this optical system consists of a plurality of identical images of the object, wherein each of these images may be composed of a different component, or set of components, of the original incident light. A filter of this invention, overlaid on the imaging plane, prevents light from any one of the images from passing through to the portion of the imaging plane corresponding to any one of the other images. 
   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 
       FIG. 1  is a schematic illustration of a first preferred embodiment of the present invention; 
       FIG. 2   a  is a schematic illustration of a first preferred embodiment of the first prism; 
       FIG. 2   b  is a schematic side-view illustration of a first preferred embodiment of the first prism; 
       FIG. 2   c  is a schematic front-view illustration of a first preferred embodiment of the first prism; 
       FIG. 3  is a schematic illustration of a first preferred embodiment of the first filter set; 
       FIG. 4   a  is a schematic illustration of a first preferred embodiment of the second prism; 
       FIG. 4   b  is a schematic side-view illustration of a first preferred embodiment of the second prism; 
       FIG. 4   c  is a schematic front-view illustration of a first preferred embodiment of the second prism; 
       FIG. 5  is a schematic illustration of a first preferred embodiment of the second filter set; 
       FIG. 6  is a schematic illustration of a second preferred embodiment of the present invention; 
       FIG. 7   a  is a schematic illustration of a second preferred embodiment of the first prism; 
       FIG. 7   b  is a schematic side-view illustration of a second preferred embodiment of the first prism; 
       FIG. 7   c  is a schematic front-view illustration of a second preferred embodiment of the first prism; 
       FIG. 8  is a schematic illustration of a second preferred embodiment of the first filter set; 
       FIG. 9   a  is a schematic illustration of a second preferred embodiment of the second prism; 
       FIG. 9   b  is a schematic side-view illustration of a second preferred embodiment of the second prism; 
       FIG. 9   c  is a schematic front-view illustration of a second preferred embodiment of the second prism; 
       FIG. 10  is a schematic illustration of a second preferred embodiment of the second filter set; 
       FIG. 11  is a schematic illustration of a side view of a typical imaging lens system; 
       FIG. 12  is a schematic illustration of a cutaway side view of the top portion of a typical imaging lens system; 
       FIG. 13  is a schematic illustration of a front view of an image plane; 
       FIG. 14  is a schematic illustration of a cutaway side view of the top portion of an imaging lens system with a prism and filter group inserted at the aperture stop; 
       FIG. 15  is a schematic illustration of a front view of another image plane; 
       FIG. 16   a  is a schematic illustration of a form for the filter and prism group; 
       FIG. 16   b  is a schematic illustration of another form for the filter and prism group; 
       FIG. 16   c  is a schematic illustration of yet another form for the filter and prism group; 
       FIG. 17  is a schematic illustration of yet another form for the filter and prism group; 
       FIG. 18  is a schematic illustration of a cutaway side view of the top portion of an imaging lens system with another prism and filter group inserted at the aperture stop; 
       FIG. 19  is a schematic illustration of a front view of yet another image plane; 
       FIG. 20   a  is a schematic illustration of yet another form for the filter and prism group; 
       FIG. 20   b  is a schematic illustration of yet another form for the filter and prism group; 
       FIG. 20   c  is a schematic illustration of yet another form for the filter and prism group; 
       FIG. 21   a  is a schematic illustration of a perspective view of a multiple-faceted prism with four facets; 
       FIG. 21   b  is a schematic illustration of a front-view of a multiple-faceted prism with four facets; 
       FIG. 21   c  is a schematic illustration of a side-view of a multiple-faceted prism with four facets; 
       FIG. 22  is a schematic illustration of four images being formed simultaneously on a single image plane; 
       FIG. 23   a  is a schematic illustration of a perspective view of a multiple-faceted prism with nine facets; 
       FIG. 23   b  is a schematic illustration of a front-view of a multiple-faceted prism with nine facets; 
       FIG. 23   c  is a schematic illustration of a side-view of a multiple-faceted prism with nine facets; 
       FIG. 24  is a schematic illustration of nine images being formed simultaneously on a single image plane; 
       FIG. 25  is a schematic illustration of a front-view of a 4-part filter; 
       FIG. 26  is a schematic illustration of a cutaway side view of the top portion of an imaging lens system with a prism and filter group inserted at the aperture stop and a matching filter set inserted at the imaging plane; and, 
       FIG. 27  is a schematic illustration of a front-view of a matching 4-part filter. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In the following descriptions of the present invention, the terms “light”, “optical radiation” and “electromagnetic radiation” may be used interchangeably, and these terms both include, but are not limited to, for example, ultraviolet, visible, and infrared electromagnetic radiation with wavelength(s) in the range from 0.2 micron to 20 microns. Similarly, the term “optical system”, as used herein, includes systems to operate on “electromagnetic radiation”, wherein such operations include, but are not limited to, directing, receiving, or filtering “electromagnetic radiation”. The term “color corrected”, as used herein, refers to a system designed to substantially correct for chromatic aberrations. 
   The basic concept of the present invention involves forming a plurality of separate images on a single imaging plane simultaneously.  FIG. 1  shows a schematic diagram of a first preferred embodiment of the present invention  10 . 
     FIG. 1  shows a schematic diagram cut-away view of a color-corrected imaging lens, consisting of a first lens group  12 , a second lens group  14 , and an aperture stop  16 . Also shown is a filter and prism group  18  inserted at a location substantially coincident with the aperture stop  16 . The filter and prism group  18  (also referred to as a beam separating sub-system) is comprised of a first prism  20 , a filter set  22 , and a second prism  24 . Also shown is a second filter set  26  (also referred to as a filtering sub-system), located at a plane that is very close in proximity to the image plane  28  of the optical system  10 . Note that all of these optical elements are aligned along an optical axis  30 . Note also that the positive direction of the optical axis  30  points to the right on the page, as shown in  FIG. 1 . Note also that the “up” direction is defined as pointing up on the page, as denoted by the y-axis  31  shown in  FIG. 1 . 
   The introduction of the filter and prism group  18  into the optical system  10 , at a location substantially coincident with the aperture stop  16  of the system  10 , as shown in  FIG. 1  causes the optical system  10  to form multiple images simultaneously on the image plane  28 . The purpose of the second filter set  26  is to exclude light from one of these multiple images from becoming incident on the portion of the imaging plane corresponding to any of the other images. In this way, the filters comprising the second filter set  26  are said to be matched, as defined herein below, to the filters in the first filter set  22 . 
   Embodiments of the system of this invention are described herein below. Although the embodiments are described for specific wavelength ranges, resulting in the selection of specific component parameters, it should be noted that system of this invention is not limited to those parameter ranges. In the embodiments described herein below, although the characteristics of elements of the embodiment are stated with specificity, it should be noted that the specific value of any of the characteristics of any element of the embodiment is provided to within engineering tolerances. Engineering tolerances as utilized herein include the tolerances within which elements can be procured and the tolerances within which the design performs the desired function. 
     FIG. 2   a  depicts a drawing of the first preferred embodiment of the first prism  20 , and clearly shows the vertices  32  of the first prism  20 , which vertices  32  separate the multiple sections  34  (four in this case) of the first prism  20 .  FIG. 2   b  shows a side view of the first prism  20  and clearly shows the flat side  36  of the prism  20  and the optic axis  30 . In this first preferred embodiment of the invention  10 , the angle between any one of the vertices  32  and the flat side  36  of the first prism  20  is preferably 8.1 degrees. The center thickness of the first prism  20 , measured along the optic axis  30 , is 5.0 mm. The first prism  20  is centered on the optic axis  30 . The first prism  20  is preferably made of glass with an optical index of 1.439 and an Abbe dispersion V-number of 95, such as O&#39;Hara glass S-FPL53. The first prism  20  is preferably square in shape, when viewed along a direction parallel to the optic axis  30 , and preferably measures 20 mm across each side.  FIG. 2   c  shows a front view of the first prism  20  and clearly shows the vertices  32  of the first prism  20 , which vertices  32  separate the multiple flat sections  34  (four in this case) of the first prism  20 . The drawing of the first prism  20  in  FIG. 2   c  is made from the point of view where the positive direction of the optic axis  30  is pointing into the page, away from the reader. Note that the “up” direction is defined as pointing up on the page, as denoted by the y-axis  31  shown in  FIG. 2   c . Note that the first prism  20  may comprise four separate pieces of glass, each piece of glass comprising one of the sections  34 , wherein the four pieces of glass are held together, mechanically or with an adhesive, so that they comprise a first prism  20 . It should be noted that the first prism  20  may be also comprised of a single optical element, where the element has multiple flat sections  34  (facets) located opposite from a single substantially flat facet  36 . 
     FIG. 3  shows a drawing of a front view of the first preferred embodiment of the first filter plane  22  and clearly shows the vertices  38  of the first filter plane  22 , which vertices  38  separate the multiple separate filters  40  (four in this case) of the first filter plane  22  (also referred to as a filter system). The drawing of the filter plane  22  in  FIG. 3  is made from the point of view where the positive direction of the optic axis  30  is pointing into the page, away from the reader. Note that the “up” direction is defined as pointing up on the page, as denoted by the y-axis  31  shown in  FIG. 3 . The first filter plane  22  is preferably square in shape, when viewed along a direction parallel to the optic axis  30 , and preferably measures 28 mm across each side. Note that the four filters  40  that comprise the first filter plane  22  are marked A, B, C, and D in  FIG. 3 . The first filter plane  22  is centered on the optic axis  30 . Note that the vertices  38  of the first filter plane  22  and the vertices  32  of the first prism  20  are aligned to be substantially overlapping one another when viewed in a direction along the optic axis  30 . The filters comprising the first filter plane  22  are preferably 3.00 mm thick and are preferably made of glass with an optical index of 1.517 and an Abbe dispersion V-number of 64.2, such as Schott glass BK7. Each of the filters  40  may transmit only a certain specific band or bands of wavelengths. Each of the filters  40  may transmit only a certain polarization state or states of light. Each of the filters  40  may transmit only a certain fraction of light. Each of the filters  40  may transmit some combination of wavelengths and/or polarization states. 
     FIG. 4   a  shows a drawing of the first preferred embodiment of the second prism  24 , and clearly shows the vertices  42  of the second prism  24 , which vertices  42  separate the multiple sections  44  (four in this case) of the second prism  24 .  FIG. 4   b  shows a side view of the second prism  24  and clearly shows the flat side  46  of the prism  24  and the optic axis  30 . In this first preferred embodiment of the invention  10 , the angle between any one of the vertices  42  and the flat side  46  of the second prism  24  is 8.1 degrees. The center thickness of the second prism  24 , measured along the optic axis  30 , is preferably 5.0 mm. The second prism  24  is centered on the optic axis  30 . Note that the vertices  42  of the second prism  24  and the vertices  38  of the first filter plane  22  are aligned to be substantially overlapping one another when viewed in a direction along the optic axis  30 . The second prism  24  is preferably made of glass with an optical index of 1.439 and an Abbe dispersion V-number of 95, such as O&#39;Hara glass S-FPL53. The second prism  24  is preferably square in shape, when viewed along a direction parallel to the optic axis  30 , and preferably measures 20 mm across each side.  FIG. 4   c  shows a front view of the second prism  24  and clearly shows the vertices  42  of the second prism  24 , which vertices  42  separate the multiple flat sections  44  (four in this case) of the second prism  24 . The drawing of the second prism  24  in  FIG. 4   c  is made from the point of view where the positive direction of the optic axis  30  is pointing into the page, away from the reader. Note that the “up” direction is defined as pointing up on the page, as denoted by the y-axis  31  shown in  FIG. 4   c . Note that the second prism  24  may comprise four separate pieces of glass, each piece of glass comprising one of the sections  44 , wherein the four pieces of glass are held together, mechanically or with an adhesive, so that they comprise a second prism  24 . It should be noted that the second prism  24  may be also comprised of a single optical element, where the element has multiple flat sections  44  (facets) located opposite from a single substantially flat facet  46 . 
     FIG. 5  shows a drawing of the first preferred embodiment of the second filter plane  26  (also referred to as a second filter system), and clearly shows the vertices  48  of the second filter plane  26 , which vertices  48  separate the multiple separate filters  50  (four in this case) of the second filter plane  26 . The second filter plane  26  is preferably square in shape, when viewed along a direction parallel to the optic axis  30 , and preferably measures 40 mm across each side. Note that the four filters  50  are marked A′, B′, C′, and D′ in  FIG. 5 . The second filter plane  26  is centered on the optic axis  30 . Note that the vertices  48  of the second filter plane  26  and the vertices  32  of the second prism  24  are aligned to be substantially overlapping one another when viewed in a direction along the optic axis  30 . The filters comprising the second filter plane  26  are preferably 3.0 mm thick and are preferably made of glass with an optical index of 1.517 and an Abbe dispersion V-number of 64.2, such as Schott glass BK7. Each of the filters  50  may transmit only a certain specific band or bands of wavelengths. Each of the filters  50  may transmit only a certain polarization state or states of light. Each of the filters  50  may transmit only a certain fraction of light. Each of the filters  50  may transmit some combination of wavelengths and/or polarization states. Note that the actions of the filters  50  are chosen such that filter A′ in the second filter plane  26  will transmit light that has been transmitted through filter A in the first filter plane  22 , but will not transmit light that has been transmitted through filters B, C, or D in the first filter plane  22 . Likewise, filter B′ in the second filter plane  26  will transmit light that has been transmitted through filter B in the first filter plane  22 , but will not transmit light that has been transmitted through filters A, C, or D in the first filter plane  22 . Likewise, filter C′ in the second filter plane  26  will transmit light that has been transmitted through filter C in the first filter plane  22 , but will not transmit light that has been transmitted through filters A, B, or D in the first filter plane  22 . Likewise, filter D′ in the second filter plane  26  will transmit light that has been transmitted through filter D in the first filter plane  22 , but will not transmit light that has been transmitted through filters A, B, or C in the first filter plane  22 . 
   Referring again to  FIG. 1 , the first lens group  12  is preferably comprised of a first lens element  52 , a second lens element  54 , and a third lens element  56 . 
   The first lens element  52  is preferably made of glass with an optical index of 1.529 and an Abbe dispersion V-number of 77.0, such as Schott glass PK51A. The shape of the first surface  58  of the first lens element  52  is preferably convex spherical, with a radius of curvature of 120.00 mm. The shape of the second surface  60  of the first lens element  52  is preferably convex spherical, with a radius of curvature of 950.00 mm. The center thickness of the first lens element  52  is preferably 18.80 mm. The first lens element  52  preferably measures 66 mm in diameter. The center distance, measured along the optic axis  30 , between the first lens element  52  and the second lens element  54  is preferably 50.00 mm. 
   The second lens element  54  is preferably made of glass with an optical index of 1.439 and an Abbe dispersion V-number of 95.0, such as O&#39;Hara glass S-FPL53. The shape of the first surface  62  of the second lens element  54  is preferably convex spherical, with a radius of curvature of 58.00 mm. The shape of the second surface  64  of the second lens element  54  is preferably convex spherical, with a radius of curvature of 971.00 mm. The center thickness of the second lens element  54  is preferably 15.00 mm. The second lens element  54  preferably measures 38 mm in diameter. The center distance, measured along the optic axis  30 , between the second lens element  54  and the third lens element  56  is preferably 8.57 mm. 
   The third lens element  56  is preferably made of glass with an optical index of 1.613 and an Abbe dispersion V-number of 44.3, such as Schott glass KZFSN4. The shape of the first surface  66  of the third lens element  56  is preferably concave spherical, with a radius of curvature of 140.00 mm. The shape of the second surface  68  of the third lens element  56  is preferably concave spherical, with a radius of curvature of 50.00 mm. The center thickness of the third lens element  56  is preferably 1.500 mm. The third lens element  56  preferably measures 26 mm in diameter. The center distance, measured along the optic axis  30 , between the third lens element  56  and the first prism  20  is preferably 5.00 mm. 
   The first prism  20  is preferably oriented, as shown in  FIG. 1 , with its convex side closest to the third lens element  56 . The flat surface  36  of the first prism  20  is preferably in contact with the first filter plane  22 . The first filter plane  22  is preferably in contact with the flat surface  46  of the second prism  24 . The aperture stop  16  is preferably located at the plane between the first filter plane  22  and the flat surface  46  of the second prism. The aperture stop  16  is preferably a circular aperture with a diameter of 17.0 mm. 
   The second lens group  14  is preferably comprised of a fourth lens element  70 , a fifth lens element  72 , a sixth lens element  74 , a seventh lens element  76 , an eighth lens element  78 , and a ninth lens element  80 . 
   The second prism  24  is preferably oriented, as shown in  FIG. 1 , with its convex side closest to the fourth lens element  70 . The center distance, measured along the optic axis  30 , between the second prism  24  and the fourth lens element  70  is preferably 7.30 mm. 
   The fourth lens element  70  is preferably made of glass with an optical index of 1.613 and an Abbe dispersion V-number of 44.3, such as Schott glass KZFSN4. The shape of the first surface  82  of the fourth lens element  70  is preferably concave spherical, with a radius of curvature of 29.00 mm. The shape of the second surface  84  of the fourth lens element  70  is preferably concave spherical, with a radius of curvature of 122.00 mm. The center thickness of the fourth lens element  70  is preferably 6.00 mm. The fourth lens element  70  preferably measures 30 mm in diameter. The center distance, measured along the optic axis  30 , between the fourth lens element  70  and the fifth lens element  72  is preferably 1.70 mm. 
   The fifth lens element  72  is preferably made of glass with an optical index of 1.439 and an Abbe dispersion V-number of 95.0, such as O&#39;Hara glass S-FPL53. The shape of the first surface  86  of the fifth lens element  72  is preferably convex spherical, with a radius of curvature of 130.00 mm. The shape of the second surface  88  of the fifth lens element  72  is preferably convex spherical, with a radius of curvature of 33.00 mm. The center thickness of the fifth lens element  72  is preferably 11.00 mm. The fifth lens element  72  preferably measures 38 mm in diameter. The center distance, measured along the optic axis  30 , between the fifth lens element  72  and the sixth lens element  74  is preferably 3.70 mm. 
   The sixth lens element  74  is preferably made of glass with an optical index of 1.613 and an Abbe dispersion V-number of 44.3, such as Schott glass KZFSN4. The shape of the first surface  90  of the sixth lens element  74  is preferably concave spherical, with a radius of curvature of 139.00 mm. The shape of the second surface  92  of the sixth lens element  74  is preferably convex spherical, with a radius of curvature of 64.30 mm. The center thickness of the sixth lens element  74  is preferably 6.00 mm. The sixth lens element  74  preferably measures 44 mm in diameter. The center distance, measured along the optic axis  30 , between the sixth lens element  74  and the seventh lens element  76  is preferably 0.50 mm. 
   The seventh lens element  76  is preferably made of glass with an optical index of 1.439 and an Abbe dispersion V-number of 95.0, such as O&#39;Hara glass S-FPL53. The shape of the first surface  94  of the seventh lens element  76  is preferably convex spherical, with a radius of curvature of 65.00 mm. The shape of the second surface  96  of the seventh lens element  76  is preferably convex spherical, with a radius of curvature of 187.00 mm. The center thickness of the seventh lens element  76  is preferably 17.2 mm. The seventh lens element  76  preferably measures 46 mm in diameter. The center distance, measured along the optic axis  30 , between the seventh lens element  76  and the eighth lens element  78  is preferably 8.87 mm. 
   The eighth lens element  78  is preferably made of glass with an optical index of 1.439 and an Abbe dispersion V-number of 95.0, such as O&#39;Hara glass S-FPL53. The shape of the first surface  98  of the eighth lens element  78  is preferably convex spherical, with a radius of curvature of 44.00 mm. The shape of the second surface  100  of the eighth lens element  78  is preferably concave spherical, with a radius of curvature of 31.00 mm. The center thickness of the eighth lens element  78  is preferably 20.000 mm. The eighth lens element  78  preferably measures 46 mm in diameter. The center distance, measured along the optic axis  30 , between the eighth lens element  78  and the ninth lens element  80  is preferably 1.50 mm. 
   The ninth lens element  80  is preferably made of glass with an optical index of 1.529 and an Abbe dispersion V-number of 77.0, such as Schott glass PK51A. The shape of the first surface  102  of the ninth lens element  80  is preferably convex spherical, with a radius of curvature of 30.00 mm. The shape of the second surface  104  of the ninth lens element  80  is preferably concave spherical, with a radius of curvature of 38.00 mm. The ninth lens element  80  preferably measures 40 mm in diameter. The center thickness of the ninth lens element  80  is preferably 20.00 mm. The center distance, measured along the optic axis  30 , between the ninth lens element  80  and the second filter plane  26  is preferably 6.17 mm. 
   The center distance, measured along the optic axis  30 , between the second filter plane  26  and the imaging plane  28  is preferably 0.526 mm. 
     FIG. 6  shows a schematic diagram of a second preferred embodiment of the present invention  200 . Note that the only difference between the first preferred embodiment of the present invention  10  and the second preferred embodiment of the present invention  200  is that the filter and prism group  18  of the first embodiment of the present invention  10  has been changed in the second embodiment of the present invention  200 . All other elements of the two embodiments are identical. 
     FIG. 6  shows a schematic diagram cut-away view of a color-corrected imaging lens, consisting of a first lens group  202 , a second lens group  204 , and an aperture stop  206 . Also shown is a filter and prism group  208  inserted at a location substantially coincident with the aperture stop  206 . The filter and prism group  208  is comprised of a first prism  210 , a filter set  212 , and a second prism  214 . Also shown is a second filter set  216 , located at a plane that is very close in proximity to the image plane  218  of the optical system  200 . Note that all of these optical elements are aligned along an optical axis  220 . Note also that the positive direction of the optical axis  220  points to the right on the page, as shown in  FIG. 6 . Note also that the “up” direction is defined as pointing up on the page, as denoted by the y-axis  221  shown in  FIG. 6 . 
   The introduction of the filter and prism group  208  into the optical system  200 , at a location substantially coincident with the aperture stop  206  of the system  200 , as shown in  FIG. 6  causes the optical system  200  to form multiple images simultaneously on the image plane  218 . The purpose of the second filter set  216  is to exclude light from one of these multiple images from becoming incident on the portion of the imaging plane corresponding to any of the other images. In this way, the filters comprising the second filter set  216  are said to be matched to the filters in the first filter set  212 . 
     FIG. 7   a  shows a drawing of the second preferred embodiment of the first prism  210 , and clearly shows the vertices  222  of the first prism  210 , which vertices  222  separate the multiple sections  224  (four in this case) of the first prism  210 .  FIG. 7   b  shows a side view of the first prism  210  and clearly shows the flat side  226  of the prism  210  and the optic axis  220 . In the second preferred embodiment of the invention  200 , the angle between any one of the vertices  222  and the flat side  226  of the first prism  210  is 8.1 degrees. The center thickness of the first prism  210 , measured along the optic axis  220 , is 5.0 mm. The first prism  210  is centered on the optic axis  220 . The first prism  210  is preferably made of glass with an optical index of 1.439 and an Abbe dispersion V-number of 95, such as O&#39;Hara glass S-FPL53. The first prism  210  is preferably square in shape, when viewed along a direction parallel to the optic axis  220 , and preferably measures 20 mm across each side.  FIG. 7   c  shows a front view of the first prism  210  and clearly shows the vertices  222  of the first prism  210 , which vertices  222  separate the multiple sections  224  (four in this case) of the first prism  210 . The drawing of the first prism  210  in  FIG. 7   c  is made from the point of view where the positive direction of the optic axis  220  is pointing into the page, away from the reader. Note that the “up” direction is defined as pointing up on the page, as denoted by the y-axis  221  shown in  FIG. 7   c . Note that the first prism  210  may comprise four separate pieces of glass, each piece of glass comprising one of the sections  224 , wherein the four pieces of glass are held together, mechanically or with an adhesive, so that they comprise a first prism  210 . 
     FIG. 8  shows a drawing of the second preferred embodiment of the first filter plane  212 , and clearly shows the vertices  228  of the first filter plane  212 , which vertices  228  separate the multiple separate filters  230  (four in this case) of the first filter plane  212 . The drawing of the filter plane  212  in  FIG. 8  is made from the point of view where the positive direction of the optic axis  220  is pointing into the page, away from the reader. Note that the “up” direction is defined as pointing up on the page, as denoted by the y-axis  221  shown in  FIG. 8 . The first filter plane  212  is preferably square in shape, when viewed along a direction parallel to the optic axis  220 , and preferably measures 28 mm across each side. Note that the four filters  230  that comprise the first filter plane  212  are marked A, B, C, and D in  FIG. 3 . The first filter plane  212  is centered on the optic axis  220 . Note that the vertices  228  of the first filter plane  212  and the vertices  222  of the first prism  210  are aligned to be substantially overlapping one another when viewed in a direction along the optic axis  220 . The filters comprising the first filter plane  212  are preferably 3.00 mm thick and are preferably made of glass with an optical index of 1.517 and an Abbe dispersion V-number of 64.2, such as Schott glass BK7. Each of the filters  230  may transmit only a certain specific band or bands of wavelengths. Each of the filters  230  may transmit only a certain polarization state or states of light. Each of the filters  230  may transmit only a certain fraction of light. Each of the filters  230  may transmit some combination of wavelengths and/or polarization states. 
     FIG. 9   a  shows a drawing of the second preferred embodiment of the second prism  214 , and clearly shows the vertices  232  of the second prism  214 , which vertices  232  separate the multiple sections  234  (four in this case) of the second prism  214 .  FIG. 9   b  shows a side view of the second prism  214  and clearly shows the flat side  236  of the prism  214  and the optic axis  220 . In this second preferred embodiment of the invention  200 , the angle between any one of the vertices  232  and the flat side  236  of the second prism  214  is 8.1 degrees. The center thickness of the second prism  214 , measured along the optic axis  220 , is preferably 5.0 mm. The second prism  214  is centered on the optic axis  220 . Note that the vertices  232  of the second prism  214  and the vertices  228  of the first filter plane  212  are aligned to be substantially overlapping one another when viewed in a direction along the optic axis  220 . The second prism  214  is preferably made of glass with an optical index of 1.439 and an Abbe dispersion V-number of 95, such as O&#39;Hara glass S-FPL53. The second prism  214  is preferably square in shape, when viewed along a direction parallel to the optic axis  220 , and preferably measures 20 mm across each side.  FIG. 9   c  shows a front view of the second prism  214  and clearly shows the vertices  232  of the second prism  214 , which vertices  232  separate the multiple sections  234  (four in this case) of the second prism  214 . The drawing of the second prism  214  in  FIG. 9   c  is made from the point of view where the positive direction of the optic axis  220  is pointing into the page, away from the reader. Note that the “up” direction is defined as pointing up on the page, as denoted by the y-axis  221  shown in  FIG. 9   c . Note that the second prism  214  may comprise four separate pieces of glass, each piece of glass comprising one of the sections  234 , wherein the four pieces of glass are held together, mechanically or with an adhesive, so that they comprise a second prism  214 . 
     FIG. 10  shows a drawing of the second preferred embodiment of the second filter plane  216 , and clearly shows the vertices  238  of the second filter plane  216 , which vertices  238  separate the multiple separate filters  240  (four in this case) of the second filter plane  216 . The second filter plane  216  is preferably square in shape, when viewed along a direction parallel to the optic axis  220 , and preferably measures 40 mm across each side. Note that the four filters  240  are marked A′, B′, C′, and D′ in  FIG. 10 . The second filter plane  216  is centered on the optic axis  220 . Note that the vertices  238  of the second filter plane  216  and the vertices  222  of the second prism  214  are aligned to be substantially overlapping one another when viewed in a direction along the optic axis  220 . The filters comprising the second filter plane  216  are preferably 3.0 mm thick and are preferably made of glass with an optical index of 1.517 and an Abbe dispersion V-number of 64.2, such as Schott glass BK7. Each of the filters  240  may transmit only a certain specific band or bands of wavelengths. Each of the filters  240  may transmit only a certain polarization state or states of light. Each of the filters  240  may transmit only a certain fraction of light. Each of the filters  240  may transmit some combination of wavelengths and/or polarization states. Note that the actions of the filters  240  are chosen such that filter A′ in the second filter plane  216  will transmit light that has been transmitted through filter A in the first filter plane  212 , but will not transmit light that has been transmitted through filters B, C, or D in the first filter plane  212 . Likewise, filter B′ in the second filter plane  216  will transmit light that has been transmitted through filter B in the first filter plane  212 , but will not transmit light that has been transmitted through filters A, C, or D in the first filter plane  212 . Likewise, filter C′ in the second filter plane  216  will transmit light that has been transmitted through filter C in the first filter plane  212 , but will not transmit light that has been transmitted through filters A, B, or D in the first filter plane  212 . Likewise, filter D′ in the second filter plane  216  will transmit light that has been transmitted through filter D in the first filter plane  212 , but will not transmit light that has been transmitted through filters A, B, or C in the first filter plane  212 . 
   Referring again to  FIG. 6 , the first lens group  202  is preferably comprised of a first lens element  242 , a second lens element  244 , and a third lens element  246 . 
   The first lens element  242  is preferably made of glass with an optical index of 1.529 and an Abbe dispersion V-number of 77.0, such as Schott glass PK51A. The shape of the first surface  248  of the first lens element  242  is preferably convex spherical, with a radius of curvature of 120.00 mm. The shape of the second surface  250  of the first lens element  242  is preferably convex spherical, with a radius of curvature of 950.00 mm. The center thickness of the first lens element  242  is preferably 18.80 mm. The first lens element  242  preferably measures 66 mm in diameter. The center distance, measured along the optic axis  220 , between the first lens element  242  and the second lens element  244  is preferably 50.00 mm. 
   The second lens element  244  is preferably made of glass with an optical index of 1.439 and an Abbe dispersion V-number of 95.0, such as O&#39;Hara glass S-FPL53. The shape of the first surface  252  of the second lens element  244  is preferably convex spherical, with a radius of curvature of 58.00 mm. The shape of the second surface  254  of the second lens element  244  is preferably convex spherical, with a radius of curvature of 971.00 mm. The center thickness of the second lens element  244  is preferably 15.00 mm. The second lens element  244  preferably measures 38 mm in diameter. The center distance, measured along the optic axis  220 , between the second lens element  244  and the third lens element  246  is preferably 8.57 mm. 
   The third lens element  246  is preferably made of glass with an optical index of 1.613 and an Abbe dispersion V-number of 44.3, such as Schott glass KZFSN4. The shape of the first surface  256  of the third lens element  246  is preferably concave spherical, with a radius of curvature of 140.00 mm. The shape of the second surface  258  of the third lens element  246  is preferably concave spherical, with a radius of curvature of 50.00 mm. The center thickness of the third lens element  246  is preferably 1.500 mm. The third lens element  246  preferably measures 26 mm in diameter. The center distance, measured along the optic axis  220 , between the third lens element  246  and the first prism  210  is preferably 5.00 mm. 
   The first prism  210  is preferably oriented, as shown in  FIG. 6 , with its concave side closest to the third lens element  246 . The flat surface  226  of the first prism  210  is preferably in contact with the first filter plane  212 . The first filter plane  212  is preferably in contact with the flat surface  236  of the second prism  214 . The aperture stop  206  is preferably located at the plane between the first filter plane  212  and the flat surface  236  of the second prism. The aperture stop  206  is preferably a circular aperture with a diameter of 17.0 mm. 
   The second lens group  204  is preferably comprised of a fourth lens element  260 , a fifth lens element  262 , a sixth lens element  264 , a seventh lens element  266 , an eighth lens element  268 , and a ninth lens element  270 . 
   The second prism  214  is preferably oriented, as shown in  FIG. 6 , with its concave side closest to the fourth lens element  260 . The center distance, measured along the optic axis  220 , between the second prism  214  and the fourth lens element  260  is preferably 7.30 mm. 
   The fourth lens element  260  is preferably made of glass with an optical index of 1.613 and an Abbe dispersion V-number of 44.3, such as Schott glass KZFSN4. The shape of the first surface  272  of the fourth lens element  260  is preferably concave spherical, with a radius of curvature of 29.00 mm. The shape of the second surface  274  of the fourth lens element  260  is preferably concave spherical, with a radius of curvature of 122.00 mm. The center thickness of the fourth lens element  260  is preferably 6.00 mm. The fourth lens element  260  preferably measures 30 mm in diameter. The center distance, measured along the optic axis  220 , between the fourth lens element  260  and the fifth lens element  262  is preferably 1.70 mm. 
   The fifth lens element  262  is preferably made of glass with an optical index of 1.439 and an Abbe dispersion V-number of 95.0, such as O&#39;Hara glass S-FPL53. The shape of the first surface  276  of the fifth lens element  262  is preferably convex spherical, with a radius of curvature of 130.00 mm. The shape of the second surface  278  of the fifth lens element  262  is preferably convex spherical, with a radius of curvature of 33.00 mm. The center thickness of the fifth lens element  262  is preferably 11.00 mm. The fifth lens element  262  preferably measures 38 mm in diameter. The center distance, measured along the optic axis  220 , between the fifth lens element  262  and the sixth lens element  264  is preferably 3.70 mm. 
   The sixth lens element  264  is preferably made of glass with an optical index of 1.613 and an Abbe dispersion V-number of 44.3, such as Schott glass KZFSN4. The shape of the first surface  280  of the sixth lens element  264  is preferably concave spherical, with a radius of curvature of 139.00 mm. The shape of the second surface  282  of the sixth lens element  264  is preferably convex spherical, with a radius of curvature of 64.30 mm. The center thickness of the sixth lens element  264  is preferably 6.00 mm. The sixth lens element  264  preferably measures 44 mm in diameter. The center distance, measured along the optic axis  220 , between the sixth lens element  264  and the seventh lens element  266  is preferably 0.50 mm. 
   The seventh lens element  266  is preferably made of glass with an optical index of 1.439 and an Abbe dispersion V-number of 95.0, such as O&#39;Hara glass S-FPL53. The shape of the first surface  284  of the seventh lens element  266  is preferably convex spherical, with a radius of curvature of 65.00 mm. The shape of the second surface  286  of the seventh lens element  266  is preferably convex spherical, with a radius of curvature of 187.00 mm. The center thickness of the seventh lens element  266  is preferably 17.2 mm. The seventh lens element  266  preferably measures 46 mm in diameter. The center distance, measured along the optic axis  220 , between the seventh lens element  266  and the eighth lens element  268  is preferably 8.87 mm. 
   The eighth lens element  268  is preferably made of glass with an optical index of 1.439 and an Abbe dispersion V-number of 95.0, such as O&#39;Hara glass S-FPL53. The shape of the first surface  288  of the eighth lens element  268  is preferably convex spherical, with a radius of curvature of 44.00 mm. The shape of the second surface  290  of the eighth lens element  268  is preferably concave spherical, with a radius of curvature of 31.00 mm. The center thickness of the eighth lens element  268  is preferably 20.000 mm. The eighth lens element  268  preferably measures 46 mm in diameter. The center distance, measured along the optic axis  220 , between the eighth lens element  268  and the ninth lens element  270  is preferably 1.50 mm. 
   The ninth lens element  270  is preferably made of glass with an optical index of 1.529 and an Abbe dispersion V-number of 77.0, such as Schott glass PK51A. The shape of the first surface  292  of the ninth lens element  270  is preferably convex spherical, with a radius of curvature of 30.00 mm. The shape of the second surface  294  of the ninth lens element  270  is preferably concave spherical, with a radius of curvature of 38.00 mm. The ninth lens element  270  preferably measures 40 mm in diameter. The center thickness of the ninth lens element  270  is preferably 20.00 mm. The center distance, measured along the optic axis  220 , between the ninth lens element  270  and the second filter plane  216  is preferably 6.17 mm. 
   The center distance, measured along the optic axis  220 , between the second filter plane  216  and the imaging plane  218  is preferably 0.526 mm. 
   Following is a description of the concept of the invention, which description should provide the reader with enough information to allow the realization of a wide variety of further other embodiments within the spirit and scope of the invention. 
   The basic concept of the invention involves inserting a prism and filter group into an imaging lens system at a location substantially coincident with the aperture stop of the imaging lens system and inserting a matched filter plane at a location close in proximity to the imaging plane of the imaging lens system. 
     FIG. 11  shows a side view of a typical imaging lens system  300 . This lens system  300  comprises a first lens group  302 , a second lens group  304 , an aperture stop  306 , and an imaging plane  308 . All the components of the imaging lens system are centered on an optic axis  310 . Note that the positive direction of the optical axis  310  points to the right on the page, as shown in  FIG. 11 . Note also that the “up” direction is defined as pointing up on the page, as denoted by the y-axis  312  shown in  FIG. 11 . 
     FIG. 12  shows a cutaway side view of the top portion of the same imaging system. Only the portion of the lens system  300  above the optic axis  310  is shown in  FIG. 12 . Light rays  314  from a distant, on-axis object are shown entering the lens system  300 . As the light rays  314  pass through the first lens group  302 , the aperture stop  306 , and the second lens group  304 , they are imaged and come to a focal point  316  on the image plane  308 . As is well understood in the field of imaging optics, the light rays  314  from a distant on-axis object are imaged with a rotationally-symmetric imaging lens system  300  and come to a focus at a point  316  that is substantially coincident with the intersection of the imaging plane  308  and the optic axis  310 . 
     FIG. 13  shows a front view of the image plane  308  corresponding to the imaging setup shown in  FIG. 12 . The drawing of the image plane  308  in  FIG. 13  is made from the point of view where the positive direction of the optic axis  310  is pointing into the page, away from the reader. Note that the “up” direction is defined as pointing up on the page, as denoted by the y-axis  312  shown in  FIG. 13 . An example of an image  317  is shown formed on the image plane  308 . In this case, the image  317  is formed such that it is centered on the optic axis  310 . Note that the on-axis image point  316  is shown as substantially coincident with the intersection of the imaging plane  308  and the optic axis  310 . 
     FIG. 14  shows a cutaway side view of the top portion of the same imaging system that was shown in  FIG. 12 , this time with a prism and filter group  318  inserted at a location substantially coincident with the aperture stop  306 . The prism and filter group  318  comprises a first prism  320 , a first filter plane  322 , and a second prism  324 . The first prism  322  and second prism  326  act together to bend the light rays  314  in such a way that they come to focus at a point  326  on the image plane  308 , which point is moved away from the optic axis  310 . 
     FIG. 15  shows a front view of the image plane  308  corresponding to the imaging setup shown in  FIG. 14 . The drawing of the image plane  308  in  FIG. 15  is made from the point of view where the positive direction of the optic axis  310  is pointing into the page, away from the reader. Note that the “up” direction is defined as pointing up on the page, as denoted by the y-axis  312  shown in  FIG. 15 . An example of an image  328  is shown formed on the image plane  308 . In this case, the image  328  is formed such that it is centered at a point well removed from the optic axis  310 . Note that the on-axis image point  326  is shown as a point well removed from the optic axis  310 . Note that the insertion of the prism and filter group  318 , as shown in  FIG. 14 , is the reason for the change in position of the image  328  and the on-axis image point  326  on the image plane  308 . 
   The filter and prism group  318  shown in  FIG. 14  is one of many possible embodiments of a filter and prism group that could effect the movement of the image  328  as demonstrated above. 
     FIG. 16   a  shows another embodiment for the filter and prism group  330 , as it might be inserted into the system shown in  FIG. 12 , at a location substantially coincident with the aperture stop  306 . Note that in  FIG. 16   a , the optic axis  310  is shown and that the positive direction is toward the right on the page. Note also that the “up” direction is defined as pointing up on the page, as denoted by the y-axis  312  shown in  FIG. 16   a . In  FIG. 16   a , the filter and prism group  330  comprises a first prism  332 , a filter  334 , and a second prism  336 , none of which elements are touching one another. 
     FIG. 16   b  shows yet another embodiment for the filter and prism group  338 , as it might be inserted into the system shown in  FIG. 12 , at a location substantially coincident with the aperture stop  306 . Note that in  FIG. 16   b , the optic axis  310  is shown and that the positive direction is toward the right on the page. Note also that the “up” direction is defined as pointing up on the page, as denoted by the y-axis  312  shown in  FIG. 16   b . In  FIG. 16   b , the filter and-prism group  338  comprises one prism  340  and a filter  342 . The prism  340  filter  342  are not in contact with each other in this 
     FIG. 16   c  shows still yet another embodiment for the filter and prism group  344 , as it might be inserted into the system shown in  FIG. 12 , at a location substantially coincident with the aperture stop  306 . Note that in  FIG. 16   c , the optic axis  310  is shown and that the positive direction is toward the right on the page. Note also that the “up” direction is defined as pointing up on the page, as denoted by the y-axis  312  shown in  FIG. 16   c . In  FIG. 16   c , the filter and prism group  344  comprises a first prism  346 , a filter  348 , and a second prism  350 . Note that in this case the first prism  346  and the filter  348  are in contact with one another. Note also that the angle of the first prism  346  is different than the angle of the second prism  350 . 
   It should be noted that there are numerous possible configurations for the filter and prism group that are within the scope of the invention. 
     FIG. 17  shows yet another form for the filter and prism group  352 , as it might be inserted into the system shown in  FIG. 12 , at a location substantially coincident with the aperture stop  306 . Note that in  FIG. 17 , the optic axis  310  is shown and that the positive direction is toward the right on the page. Note also that the “up” direction is defined as pointing up on the page, as denoted by the y-axis  312  shown in  FIG. 17 . In  FIG. 17 , the filter and prism group  352  comprises a first prism  354 , a filter  356 , and a second prism  358 . Note that in this case the direction of angles on the first prism  354  and the second prism  358  are opposite the directions of angles of the prisms shown in  FIG. 14 ,  FIG. 16   a ,  FIG. 16   b , and  FIG. 16   c . The effect of inserting this filter and prism group  352  into an optical system like the one shown in  FIG. 12  is shown in  FIG. 18 . 
     FIG. 18  shows a cutaway side view of a portion of the same imaging system that was shown in  FIG. 12 , this time with a prism and filter group  352  inserted at a location substantially coincident with the aperture stop  306 . The prism and filter group  352  comprises a first prism  354 , a first filter plane  356 , and a second prism  358 . Note that the angle of the second prism  358  is labeled as θ in  FIG. 18 . The first prism  354  and second prism  358  act together to bend the light rays  314  in such a way that they come to focus at a point  360  on the image plane  308 , which point is moved away from the optic axis  310 . Note that the on-axis focus point  360  is moved down away from the optic axis  310 , whereas the insertion of an oppositely-angled filter and prism group  318  previously caused the on-axis image point  326  to move up away from the optic axis  310  as shown previously in  FIG. 14 . 
     FIG. 19  shows a front view of the image plane  308  corresponding to the imaging setup shown in  FIG. 18 . The drawing of the image plane  308  in  FIG. 19  is made from the point of view where the positive direction of the optic axis  310  is pointing into the page, away from the reader. Note that the “up” direction is defined as pointing up on the page, as denoted by the y-axis  312  shown in  FIG. 19 . An example of an image  362  is shown formed on the image plane  308 . In this case, the image  362  is formed such that it is centered at a point well removed from the optic axis  310 . Note that the on-axis image point  360  is shown as a point well removed from the optic axis  310 . Note that the insertion of the prism and filter group  352 , as shown in  FIG. 18 , is the reason for the change in position of the image  362  and the on-axis image point  360  on the image plane  308 . Note also that because the angles of the faces on the prisms  354  and  358  (as shown in  FIG. 18 ) are opposite the angles of the faces on the prisms  320  and  324  (as shown in  FIG. 14 ), the direction of movement of the image  317  and on-axis image point  316  is also opposite. 
   The filter and prism group  352  shown in  FIG. 18  is one of many possible embodiments of a filter and prism group that could effect the movement of the image  362  as demonstrated above. 
     FIG. 20   a  shows another form for the filter and prism group  364 , as it might be inserted into the system shown in  FIG. 12 , at a location substantially coincident with the aperture stop  306 . Note that in  FIG. 20   a , the optic axis  310  is shown and that the positive direction is toward the right on the page. Note also that the “up” direction is defined as pointing up on the page, as denoted by the y-axis  312  shown in  FIG. 20   a . In  FIG. 20   a , the filter and prism group  364  comprises a first prism  366 , a filter  368 , and a second prism  370 , none of which elements are touching one another. 
     FIG. 20   b  shows yet another form for the filter and prism group  372 , as it might be inserted into the system shown in  FIG. 12 , at a location substantially coincident with the aperture stop  306 . Note that in  FIG. 20   b , the optic axis  310  is shown and that the positive direction is toward the right on the page. Note also that the “up” direction is defined as pointing up on the page, as denoted by the y-axis  312  shown in  FIG. 20   b . In  FIG. 20   b , the filter and prism group  372  comprises one prism  374  and a filter  376 . The prism  374  and filter  376  are not in contact with each other in this case. 
     FIG. 20   c  shows yet another embodiment for the filter and prism group  378 , as it might be inserted into the system shown in  FIG. 12 , at a location substantially coincident with the aperture stop  306 . Note that in  FIG. 20   c , the optic axis  310  is shown and that the positive direction is toward the right on the page. Note also that the “up” direction is defined as pointing up on the page, as denoted by the y-axis  312  shown in  FIG. 20   c . In  FIG. 20   c , the filter and prism group  378  comprises a first prism  380 , a filter  382 , and a second prism  384 . Note that in this case the first prism  380  and the filter  382  are in contact with one another. Note also that the angle of the first prism  380  is different than the angle of the second prism  384 . 
   It should be noted that there are numerous possible configurations for the filter and prism group that are within the scope of the invention. 
   It should also be noted that movement of the images  317 ,  328 ,  362  in the image plane  308  occurs in the plane of the slope angle θ of the prism or prisms used in the filter and prism groups  318 ,  352 . It should also be noted that the amount of movement of the images  317 ,  328 ,  362  in the image plane  308  is proportional to the size of the slope angle θ of the prism or prisms used in the filter and prism groups  318 ,  352 . Thus, if more movement of the image  328 ,  362  is desired, then a larger slope angle θ of the prisms  320 ,  324 ,  354 ,  358  would be called for. 
   By using multiple-faceted prisms, it is possible to create multiple images in the image plane.  FIG. 21   a  shows a perspective drawing of what such a multiple-faceted prism  386  would look like with four facets  388 .  FIG. 21   b  shows a front view of what such a multiple-faceted prism  386  would look like with four facets  388 .  FIG. 21   c  shows a side view of what such a multiple-faceted prism  386  would look like with four facets  388 . Note that each of the facets  388  comprises a flat plane that is not parallel to the back face  390  of the prism  386 . Instead, each facet  388  forms an angle θ with respect to the back face  390  of the prism  386 . 
     FIG. 22  shows an example of the image formation that would occur at the imaging plane  308  if a 4-faceted prism  386  were placed at a location substantially coincident with the aperture stop  306  of an imaging system  300  like the one shown in  FIG. 11 . Note that four identical copies of the same image  392  are formed on the image plane  308 , at locations centered on the four on-axis image points  394 . Each of these identical images  392  is formed by light that has passed through one of the facets  388  on the prism  386 . Note that the location on the image plane  308  of each of the four on-axis image points  394  is controlled by the angle θ of each of the facets  388  on the prism  386 . 
     FIG. 23   a  shows a perspective drawing of what a multiple-faceted prism  396  would look like with nine facets  398 ,  400 ,  402 .  FIG. 23   b  shows a front view of what such a multiple-faceted prism  396  would look like with nine facets  398 ,  400 ,  402 .  FIG. 23   c  shows a side view of what such a multiple-faceted prism  386  would look like with nine facets  398 ,  400 ,  402 . Note that each of the facets  398 ,  400 ,  402  comprises a flat plane that is not parallel to the back face  404  of the prism  396 . Note that the facets  398 ,  400 ,  402  of the prism  396  make different angles with respect to the back face  404  of the prism  396 , wherein the angles of the facets  398 ,  400 ,  402  depend on the placement of the facets  398 ,  400 ,  402 . For example the center facet  398  is parallel to the back face  404  of the prism  396 . The four edge facets  400  form an angle θ′ with the back face  404  of the prism  396 . The four corner facets  402  form an angle with the back face  404  of the prism  396  that is larger than θ′. 
     FIG. 24  shows an example of the image formation that would occur at the imaging plane  308  if a 9-faceted prism  396  were placed at a location substantially coincident with the aperture stop  306  of an imaging system  300  like the one shown in  FIG. 11 . Note that nine identical copies of the same image  406 ,  408 ,  410  are formed on the image plane  308 , at locations centered on the nine on-axis image points  412 ,  414 ,  416 . Each of these identical images  406 ,  408 ,  410  is formed by light that has passed through one of the facets  398 ,  400 ,  402  on the prism  396 . Note that the location on the image plane  308  of each of the nine on-axis image points  412 ,  414 ,  416  is controlled by the angle of each of the facets  398 ,  400 ,  402  on the prism  396 . Thus, the center image  406  is centered on the center on-axis image point  412 , which on-axis image point  412  is coincident with the intersection of the optic axis  310  and the image plane  308 . The center image  406  is formed by light that has passed through the center facet  398  of the prism  396  as shown in  FIG. 23   a ,  FIG. 23   b ,  FIG. 23   c . Likewise, the edge images  408  are centered on the edge on-axis image points  414 . The edge images  408  are formed by light that has passed through the edge facets  400  of the prism  396  as shown in  FIG. 23   a ,  FIG. 23   b ,  FIG. 23   c . Similarly, the corner images  410  are centered on the corner on-axis image points  416 . The corner images  410  are formed by light that has passed through the corner facets  402  of the prism  396  as shown in  FIG. 23   a ,  FIG. 23   b ,  FIG. 23   c.    
   Referring to  FIG. 22  and  FIG. 24  it can be seen that if each of the images  392 ,  406 ,  408 ,  410  is large, then light from the multiple images  392 ,  406 ,  408 ,  410  will overlap on the image plane  308 . Because this is a typically undesirable effect, it is important to prevent light from any one of the images  392 ,  406 ,  408 ,  410  from becoming incident on the part of the image plane  308  corresponding to any other of the images  392 ,  406 ,  408 ,  410 . The method for achieving this goal is through the process of matching filters. The process for matching filters is explained below. 
   The process for matching filters involves first choosing a filter for the filter and prism group  352  as shown in  FIG. 18 . For example, let us examine the case where the prisms  354 ,  358  in the filter and prism group  352  comprise 4-faceted prisms like the ones shown in  FIG. 21   a ,  FIG. 21   b ,  FIG. 21   c . In this case, the filter  356  in the filter and prism group  352  would comprise a 4-part filter  356  like the one shown in  FIG. 25 . Four individual filters  420 ,  422 ,  424 ,  426  comprise the 4-part filter  356  as shown in  FIG. 25 . Each filter  420 ,  422 ,  424 ,  426  in the 4-part filter  356  is chosen so as to transmit only a portion of the light, and furthermore each filter  420 ,  422 ,  424 ,  426  is chosen so as to transmit a portion of light that is not transmitted by any of the other filters  420 ,  422 ,  424 ,  426 . In this way, each of the four filters  420 ,  422 ,  424 ,  426  is said to be exclusive of the other four filters  420 ,  422 ,  424 ,  426 . 
   For the sake of clarity in this explanation, a specific example set of filters  420 ,  422 ,  424 ,  426  will be examined herein. However, it should be noted that there exists a practically infinite number of sets of exclusive filters  420 ,  422 ,  424 ,  426  that satisfy the scope of the present invention. 
   For example, the filter  420  in  FIG. 25  might transmit only light with wavelengths between 425 nm and 450 nm. Also for example, the filter  422  in  FIG. 25  might transmit only light with wavelengths between 500 nm and 525 nm. Also for example, the filter  424  in  FIG. 25  might transmit only light with wavelengths between 575 nm and 600 nm. Also for example, the filter  426  in  FIG. 25  might transmit only light with wavelengths between 650 nm and 675 nm. 
   Referring again to  FIG. 18 , it is apparent that the insertion of the filter and prism group  352  into the optical system as shown in  FIG. 18  causes the on-axis image point to move to the opposite side of the optic axis  310  from the side of the axis that the prisms  354 ,  358  are on. 
     FIG. 26  shows the same optical imaging system shown in  FIG. 18 , this time with a second filter plane  428  inserted at a plane that is very near the image plane  308 . 
   The second filter plane  428  comprises a 4-part filter  428  like the one shown in  FIG. 27 . Four individual filters  430 ,  432 ,  434 ,  436  comprise the 4-part filter  428  as shown in  FIG. 27 . Each filter  430 ,  432 ,  434 ,  436  in the 4-part filter  428  is chosen so as to transmit only a portion of the light, and furthermore each filter  430 ,  432 ,  434 ,  436  is chosen so as to transmit a portion of light that is transmitted by the corresponding filter  420 ,  422 ,  424 ,  426  in the first filter plane  356 , and furthermore each filter  430 ,  432 ,  434 ,  436  is chosen so as to prevent transmission of a portion of light that is transmitted by the any of the other three non-corresponding filters  420 ,  422 ,  424 ,  426  in the first filter plane  356 . In this way, each of the four filters  430 ,  432 ,  434 ,  436  in the second filter plane  428  is said to be matched to a specific one of the other four filters  420 ,  422 ,  424 ,  426  in the first filter plane  356 . 
   For the sake of clarity in this explanation, a specific example set of filters  430 ,  432 ,  434 ,  436  will be examined herein. The example chosen below is meant to continue with the example set of filters  420 ,  422 ,  424 ,  426  outlined above. However, it should be noted that there exists a practically infinite number of sets of exclusive filters  430 ,  432 ,  434 ,  436  that satisfy the scope of the present invention. 
   For example, the filter  430  in  FIG. 27  might transmit only light with wavelengths between 410 nm and 465 nm. Also for example, the filter  432  in  FIG. 27  might transmit only light with wavelengths between 485 nm and 440 nm. Also for example, the filter  434  in  FIG. 27  might transmit only light with wavelengths between 560 nm and 615 nm. Also for example, the filter  436  in  FIG. 27  might transmit only light with wavelengths between 635 nm and 690 nm. Note that each filter  430 ,  432 ,  434 ,  436  in the second filter plane  428  is chosen so as to transmit only light that has been transmitted through the corresponding filter  420 ,  422 ,  424 ,  426  in the first filter plane  356 , and to prevent transmission of light that has been transmitted through any of the three other non-corresponding filters  420 ,  422 ,  424 ,  426  in the first filter plane  356 . Thus filter  430  in the second filter plane  428  corresponds to filter  420  in the first filter plane  356 , and filter  432  in the second filter plane  428  corresponds to filter  422  in the first filter plane  356 , and filter  434  in the second filter plane  428  corresponds to filter  424  in the first filter plane  356 , and filter  436  in the second filter plane  428  corresponds to filter  426  in the first filter plane  356 . 
   It should be noted that although embodiments of the present invention have been described in specific terms corresponding to a color corrected (chromatic aberration corrected) system for a pre-selected range of wavelengths, other embodiments are possible for different ranges of wavelengths. Embodiments are also possible where the filters in each of the filter planes transmit only certain polarization states or a combination of wavelength and polarization state or other radiation condition. Such embodiments would differ in specific components from the embodiments disclosed above. 
   Although the invention has been described with respect to a plurality of preferred 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 invention.

Technology Classification (CPC): 0