Abstract:
A lens having an axis of symmetry, including a transparent circumferential surface, circumferentially extending about the axis of symmetry, the transparent surface having optical power in planes which include the axis of symmetry, a first reflective surface, symmetric with respect to the axis of symmetry and being operative to reflect light passing through the transparent surface and a second reflective surface, symmetric with respect to the axis of symmetry and axially spaced from the transparent surface and being operative to reflect light reflected by the first reflective surface.

Description:
SUMMARY OF THE INVENTION 
       [0001]    The present invention seeks to provide improved lenses and optical system having an extremely wide field of view. 
         [0002]    There is thus provided in accordance with a preferred embodiment of the present invention a lens having an axis of symmetry, including a transparent circumferential surface, circumferentially extending about the axis of symmetry, the transparent surface having optical power in planes which include the axis of symmetry, a first reflective surface, symmetric with respect to the axis of symmetry and being operative to reflect light passing through the transparent surface and a second reflective surface, symmetric with respect to the axis of symmetry and axially spaced from the transparent surface and being operative to reflect light reflected by the first reflective surface. 
         [0003]    Preferably, the lens is formed of at least one of glass and plastic. Additionally or alternatively, the transparent circumferential surface receives light from a 360-degree field of view about the axis of symmetry. 
         [0004]    Preferably, the first transparent circumferential surface is transparent to radiation at a specific range of wavelengths. Additionally or alternatively, the transparent circumferential surface is operative to refract light onto the first reflective surface. 
         [0005]    Preferably, the lens also includes an additional circumferential surface disposed between the transparent circumferential surface and the second reflective surface. Additionally, the transparent circumferential surface has a first curvature and the additional circumferential surface has a second curvature, the second curvature being generally different than the first curvature. 
         [0006]    Preferably, the additional circumferential surface is operative to enhance an axial field of view of the lens. Additionally or alternatively, the additional circumferential surface smoothly joins the transparent circumferential surface. 
         [0007]    Preferably, at least one of the first and second reflective surfaces is a convex reflective surface. Alternatively, each of the first and second reflective surfaces is a convex reflective surface. Preferably, the second reflective surface directs light generally along the axis of symmetry. 
         [0008]    Preferably, at least one of the first and second reflective surfaces is annular. Alternatively, each of the first and second reflective surfaces is annular. 
         [0009]    Preferably, the second reflective surface also includes a curved portion which has a transparent surface and which is symmetric with respect to the axis of symmetry, operative to refract rays from a field of view which is at least partially different than the 360-degree field of view. Additionally, the curved portion has a curvature which is different than a curvature of the second reflective surface. Additionally or alternatively, the transparent surface of the curved portion is transparent to radiation at a specific range of wavelengths. 
         [0010]    Preferably, the first reflective surface also includes a central area which has a transparent surface and which is symmetric with respect to the axis of symmetry. Additionally, the central area has a curvature which is different than a curvature of the first reflective surface. Additionally or alternatively, the transparent surface of the central area is transparent to radiation at a specific range of wavelengths. 
         [0011]    Preferably, the specific range of wavelengths includes visible wavelengths. Alternatively or additionally, the specific range of wavelengths includes infrared wavelengths. 
         [0012]    Preferably, the lens also includes at least one additional lens arranged to direct light axially through the lens. Additionally, the lens also includes a shield element operative to protect the at least one additional lens. Preferably, a field of view of the at least one additional lens at least partially overlaps a field of view of the lens, providing stereoscopic viewing of at least one object lying in the overlapped portions of the field of view of the at least one additional lens and the field of view of the lens. 
         [0013]    Preferably, the lens also includes at least one aberration correcting lens arranged to correct aberrations of light passing through the lens. 
         [0014]    Preferably, the lens also includes at least one of a first base portion and a second base portion. Additionally, the first base portion is disposed about the first reflective surface. Alternatively or additionally, the second base portion is disposed about the second reflective surface. 
         [0015]    Preferably, at least one of the first base portion and the second base portion is integrally formed with the lens. Alternatively, at least one of the first base portion and the second base portion is mounted onto the lens. 
         [0016]    Preferably, at least one of the first base portion and the second base portion is operative to mount the lens onto additional optical elements forming an optical system. Alternatively or additionally, at least one of the first base portion and the second base portion is operative to mount the lens onto at least one mechanical element. 
         [0017]    Preferably, light passing through the lens is directed onto an imaging element. Additionally, the imaging element includes a CCD array. 
         [0018]    Preferably, the lens also includes a non-axially symmetric reflecting surface having optical power for focusing light from a region limited in azimuth and elevation through the lens. Additionally, the non-axially symmetric reflecting surface includes a convex surface. Alternatively, the non-axially symmetric reflecting surface includes a generally planar surface. Preferably, the additional circumferential surface is operative to refract light received by the lens onto the non-axially symmetric reflecting surface. 
         [0019]    Preferably, the lens is operative to enable illumination of a field of view from a source of light located in an image plane. 
         [0020]    Preferably, the lens also includes at least one light pipe, operative to illuminate the field of view of the lens. Additionally, the light pipe includes at least one inclined edge surface. Preferably, the light pipe includes optical fibers. Alternatively or additionally, the light pipe includes a hollow light pipe. 
         [0021]    Preferably, the light pipe is disposed about the first reflective surface. Preferably, the at least one inclined edge surface is operative to scatter light rays emitted from the light pipe. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which: 
           [0023]      FIGS. 1A ,  1 B and  1 C are, respectively, simplified rearward facing and forward facing pictorial illustrations and a sectional illustration of a circumferential field of view lens constructed and operative in accordance with a preferred embodiment of the present invention,  FIG. 1C  being taken along section lines IC-IC in  FIG. 1A ; 
           [0024]      FIGS. 2A and 2B  and  2 C are, respectively, simplified rearward facing and forward facing exploded pictorial illustrations and a sectional exploded view illustration of an optical system employing the lens of  FIG. 1  in accordance with a preferred embodiment of the present invention,  FIG. 2C  being taken along section lines IIC-IIC in  FIG. 2A ; 
           [0025]      FIGS. 3A and 3B  which are respectively, a simplified assembled view illustration and a sectional assembled view illustration of the optical system of  FIGS. 2A-2C ,  FIG. 3B  being taken along section lines IIIB-IIIB in  FIG. 3A ; 
           [0026]      FIG. 4  is a simplified sectional illustration of a variation of the optical system of  FIG. 2A-3B , employing the lens of  FIG. 1  in accordance with a preferred embodiment of the present invention; 
           [0027]      FIGS. 5A ,  5 B and  5 C are, respectively, simplified rearward facing and forward facing pictorial illustrations and a sectional illustration of a circumferential field of view lens constructed and operative in accordance with another preferred embodiment of the present invention,  FIG. 5C  being taken along section lines VC-VC in  FIG. 5A ; 
           [0028]      FIGS. 6A and 6B  are, respectively, a simplified pictorial illustration and a sectional illustration of a circumferential field of view lens constructed and operative in accordance with yet another preferred embodiment of the present invention,  FIG. 6B  being taken along section lines VIB-VIB in  FIG. 6A ; 
           [0029]      FIGS. 7A and 7B  are, respectively, a simplified pictorial illustration and a sectional illustration of an optical system constructed and operative in accordance with another preferred embodiment of the present invention,  FIG. 7B  being taken along section lines VIIB-VIIB in  FIG. 7A ; and 
           [0030]      FIG. 8  is a simplified illustration of an optical system constructed and operative in accordance with still another preferred embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0031]    Reference is now made to  FIGS. 1A ,  1 B and  1 C, which are, respectively, simplified rearward facing and forward facing pictorial illustrations and a sectional illustration of a circumferential field of view lens constructed and operative in accordance with a preferred embodiment of the present invention. As seen in  FIGS. 1A-1C , there is provided a lens  100  including a lens body  101 , preferably formed of plastic, glass or any other suitable material which is transparent to radiation at a wavelength range of interest, which is symmetric about an axis of rotation  102 . 
         [0032]    Preferably the lens  100  includes a curved circumferential surface  104 , having optical power, which receives light from a 360 degree field of view about axis  102 , limited by rays  105  and  106 , which are seen with particular clarity in  FIG. 1C . Surface  104  refracts the light, as shown, onto an adjacent, preferably convex, annular reflective coating  107  formed onto a correspondingly shaped surface  108  of lens body  101 . The light is reflected from convex reflective coating  107  onto an oppositely facing, preferably convex, reflective coating  110  formed onto a correspondingly shaped surface  112  of lens body  101 , as shown by ray  113 , which is seen with particular clarity in  FIG. 1C . 
         [0033]    It is a particular feature of the present invention that surface  112  and reflective coating  110  are substantially spaced along axis  102  from annular reflective coating  107  formed on surface  108 , and thus from curved circumferential surface  104 . In the illustrated embodiment, this spacing, which enhances the axial field of view of the lens defined by rays  105  and  106 , is provided by configuring the lens body  101  to define an intermediate circumferential surface  120 , which is preferably curved, intermediate curved circumferential surface  104  and surface  112 . Intermediate circumferential surface  120  typically has a different curvature than the curvature of surface  104 , and need not collect light from the field of view of interest. 
         [0034]    Light reflected from convex reflective coating  110  preferably passes out of the lens  100  through a central portion  122  of surface  108  which is transparent to radiation at the wavelength range of interest and which is not coated by reflective coating  107 . 
         [0035]    Optionally, a rear base portion  124  is provided around surface  108 , to enable mounting of the lens  100  onto additional elements of an optical system, such as additional lenses, or other suitable mechanical elements, as described hereinbelow with reference to  FIGS. 2 and 3 . Rear base portion  124  may be integrally formed with the remainder of lens  100  or may be mounted onto the lens by any suitable means. Alternatively or additionally, a forward base portion (not shown) may be provided around surface  112  for a similar purpose. 
         [0036]    It will be appreciated that rays of light could enter the lens  100  through central portion  122 , which is transparent to radiation at a wavelength range of interest, be reflected by reflective coating  110  and pass out of the lens through central portion  122 . This can be avoided if reflective coating  110  is formed with a central annular aperture, such that a central transparent portion  127  is formed on surface  112 . Central transparent portion  127  enables rays of light from a forward field of view of the lens  100  to enter the lens  100  and pass through lens body  101  and central portion  122 . Alternatively, lens body  101  may be formed with a bore extending therethrough (not shown), which enables passage of light rays from the center of surface  112  to the center of surface  108 . It is appreciated that provision of transparent portion  127  or the bore extending through lens body  101  eliminates the reflection of light rays entering lens  100  at central portion  122 . 
         [0037]    It is appreciated that in certain cases, depending on the materials used for forming the lens body  101 , total internal reflection of certain light rays may occur, thus obviating the need for some or all of the reflective coatings. 
         [0038]    Reference is now made to  FIGS. 2A ,  2 B and  2 C, which are, respectively, simplified rearward facing and forward facing pictorial exploded view illustrations and a sectional exploded view illustration of an optical system employing the lens of  FIG. 1  in accordance with a preferred embodiment of the present invention, and to  FIGS. 3A and 3B , which are, respectively, a simplified assembled view illustration and a sectional assembled view illustration of the optical system of  FIGS. 2A-2C . As seen in  FIGS. 2A-3B , there is provided a lens  200  including a lens body  201 , preferably formed of glass or any other suitable material which is transparent to radiation at a wavelength range of interest, which is symmetric about an axis of rotation  202 . 
         [0039]    Preferably the lens  200  includes a curved circumferential surface  204 , having optical power, which receives light from a 360 degree field of view about axis  202 . Lens  200  preferably provides a circumferential field of view of at least approximately 90 degrees, as indicated by rays  205  and  206 , which are seen with particular clarity in  FIG. 2C . Surface  204  refracts the light, as shown, onto an adjacent, preferably convex, annular reflective coating  207  formed onto a correspondingly shaped surface  208  of lens body  201 . The light is reflected from convex reflective coating  207  onto an oppositely facing, preferably convex, reflective coating  210  formed onto a correspondingly shaped surface  212  of lens body  201 , as shown by ray  213 , which is seen with particular clarity in  FIG. 2C . 
         [0040]    It is a particular feature of the present invention that surface  212  and reflective coating  210  are substantially spaced along axis  202  from annular reflective coating  207  formed on surface  208 , and thus from curved circumferential surface  204 . In the illustrated embodiment, this spacing, which enhances the axial field of view of the lens  200  defined by rays  205  and  206 , is provided by configuring the lens body  201  to define an intermediate circumferential surface  220 , which is preferably curved, intermediate curved circumferential surface  204  and surface  212 . Intermediate circumferential surface  220  typically has a different curvature than the curvature of surface  204 , and need not collect light from the field of view of interest. 
         [0041]    Light reflected from convex reflective coating  210  preferably passes out of the lens  200  through a central portion  222  of surface  208  which is transparent to radiation at the wavelength range of interest and which is not coated by reflective coating  207 . 
         [0042]    Lens  200  is preferably formed with a rear base portion  224  and a forward base portion  225 , which are provided around surfaces  208  and  212  respectively, and which enable mounting of lens  200  onto additional elements of the optical system or other suitable mechanical elements, as described hereinbelow. Rear base portion  224  and forward base portion  225  may be integrally formed with the remainder of lens  200  or may be mounted onto the lens  200  by any suitable means. 
         [0043]    Light from a forward field of view, limited by rays  226  and  228 , preferably is refracted by a lens  230  towards a central portion  232  of surface  212 , interiorly of annular reflective coating  210 , through the lens body  201  and out through central portion  222  of surface  208 , interiorly of annular reflective coating  207 , as shown by ray  234 , which is seen with particular clarity in  FIG. 2C . 
         [0044]    Preferably, lens  230  is protected by a forward facing generally hemi-spherical shield  236  which is transparent to radiation at a wavelength range of interest, which ensures that the lens  230  will not be damaged, but does not corrupt the optical path of rays in the forward field of view. Alternatively, shield  236  may be obviated, leaving lens  230  exposed. Typically, lens  230  and shield  236  are mounted onto lens  200  at forward base portion  225 , as seen in  FIGS. 3A and 3B . 
         [0045]    One or more lenses  240 , which may include focusing lenses and optical correction lenses operative to correct for aberrations such as astigmatism, may lie along an optical path of the light leaving the lens body  201  via central portion  222  and may direct the light onto an imaging sensor  242 , such as a CCD array or any other suitable imaging sensor. Typically, lenses  240  and imaging sensor  242  are mounted onto lens  200  at rear base  224 , as seen in  FIGS. 3A and 3B . The complete field of view which may be imaged by imaging sensor  242  forms a hemisphere. 
         [0046]    It is appreciated that in certain cases, depending on the materials used for forming the lens body  201 , total internal reflection of certain light rays may occur, thus obviating the need for some or all of the reflective coatings. 
         [0047]    It will be appreciated that the optical system of  FIGS. 2A-3B  includes a “dead space”, designated by reference numeral  248 , which is not imaged by imaging sensor  242 , as seen in  FIG. 2C . 
         [0048]    Reference is now made to  FIG. 4 , which is a simplified sectional illustration of a variation of the optical system of  FIG. 2 , employing the lens of  FIG. 1  in accordance with yet another preferred embodiment of the present invention.  FIG. 4  illustrates a structure including a lens which is similar to lens  200  ( FIGS. 2A-3B ), that at least partially eliminates the “dead space”  248  ( FIG. 2C ), by providing an annular recess located in part of the central portion  232  ( FIG. 2C ), preferably centered about the axis  202  ( FIG. 2C ). 
         [0049]    Accordingly, there is provided in the embodiment of  FIG. 4 , a lens  300  including a lens body  301 , preferably formed of glass or any other suitable material which is transparent to radiation at the wavelength range of interest, which is symmetric about an axis of rotation  302 . 
         [0050]    Preferably the lens  300  includes a curved circumferential surface  304 , having optical power, which receives light from a 360-degree field of view about axis  302 . Lens  300  preferably provides a circumferential field of view of at least approximately 90 degrees, as indicated by rays  305  and  306 . Surface  304  refracts the light, as shown, onto an adjacent, preferably convex, annular reflective coating  307  formed onto a correspondingly shaped surface  308  of lens body  301 . The light is reflected from convex reflective coating  307  onto an oppositely facing, preferably convex, reflective coating  310  formed onto a correspondingly shaped surface  312  of lens body  301 , as shown by ray  313 . Convex surface  312  preferably includes a curved portion  314  having a different curvature than the curvature of surface  312 . Curved portion  314  is not coated by reflective coating  310  and enables the provision of a wider forward field of view relative to the field of view shown in  FIG. 2C  by rays  226  and  228 . 
         [0051]    It is a particular feature of the present invention that surface  312 , including curved portion  314 , and reflective coating  310  are substantially spaced along axis  302  from annular reflective coating  307  formed on surface  308 , and thus from curved circumferential surface  304 . In the illustrated embodiment, this spacing, which enhances the axial field of view of the lens  300  defined by rays  305  and  306 , is provided by configuring the lens body  301  to define an intermediate circumferential surface  320 , which is preferably curved, intermediate curved circumferential surface  304  and surface  312 . Intermediate circumferential surface  320  typically has a different curvature than the curvature of surface  304 , and need not collect light from the field of view of interest. 
         [0052]    Light reflected from convex reflective coating  310  preferably passes out of the lens  300  through a central portion  322  of surface  308  which is transparent to radiation at a wavelength range of interest and which is not coated by reflective coating  307 . 
         [0053]    Lens  300  is preferably formed with a rear base portion  324  and a forward base portion  325 , which are provided around surfaces  308  and  312  respectively, and which enable mounting of lens  300  onto additional elements of the optical system or other suitable mechanical elements, as described hereinbelow. Rear base portion  324  and forward base portion  325  may be integrally formed with the remainder of lens  300  or may be mounted onto the lens  300  by any suitable means. 
         [0054]    Light from a forward field of view, limited by rays  326  and  328 , preferably is refracted by a lens  330  through curved portion  314  and/or through a central portion  332  of surface  312 , interiorly of annular reflective coating  310 , through the lens body  301  and out through central portion  322  of surface  308 , interiorly of annular reflective coating  307 , as shown by ray  334 . 
         [0055]    Preferably, lens  330  is protected by a forward facing generally hemi-spherical shield  336  which is transparent to radiation at a wavelength range of interest and which ensures that the lens  330  will not be damaged, but does not corrupt the optical path of rays in the forward field of view. Alternatively, shield  336  may be obviated, leaving lens  330  exposed. Typically, lens  330  and shield  336  are mounted onto lens  300  at forward base portion  325 . 
         [0056]    One or more lenses  340 , which may include focusing lenses and optical correction lenses operative to correct for aberrations such as astigmatism, may lie along an optical path of the light leaving the lens body  301  via central portion  322  and may direct the light onto an imaging sensor  342 , such as a CCD array or any other suitable imaging sensor. Typically, lenses  340  and imaging sensor  342  are mounted onto lens  300  at rear base  324 . The complete field of view which may be imaged by imaging sensor  342  forms a hemisphere. 
         [0057]    It is appreciated that in certain cases, depending on the materials used for forming the lens body  301 , total internal reflection of certain light rays may occur, thus obviating the need for some or all of the reflective coatings. 
         [0058]    It is further appreciated that the optical system of  FIG. 4  includes a “dead space”, designated by reference numeral  348 , which is not imaged by imaging sensor  342 . As described hereinabove, curved portion  314  enables the provision of a wider forward field of view than the field of view shown in  FIG. 2C  by rays  226  and  228 , thus dead space  348  is smaller than dead space  248  shown in  FIGS. 2C and 3B . 
         [0059]    Reference is now made to  FIGS. 5A ,  5 B and  5 C, which are, respectively, simplified rearward facing and forward facing pictorial illustrations and a sectional illustration of a circumferential field of view lens constructed and operative in accordance with another preferred embodiment of the present invention. As seen in  FIGS. 5A-5C , there is provided a lens  400  including a lens body  401 , preferably formed of plastic, glass or any other suitable material which is transparent to radiation at a wavelength range of interest, which is symmetric about an axis of rotation  402  and includes an asymmetric surface  403 . 
         [0060]    Preferably the lens  400  includes a curved circumferential surface  404 , having optical power, which receives light from a 360 degree field of view about axis  402  limited by rays  405  and  406 , seen with particular clarity in  FIG. 5C . Surface  404  refracts the light, as shown, onto an adjacent, preferably convex, annular reflective coating  407  formed onto a correspondingly shaped surface  408  of lens body  401 . The light is reflected from convex reflective coating  407  onto an oppositely facing, preferably convex, reflective coating  410  formed onto a correspondingly shaped surface  412  of lens body  401 , as shown by ray  413 , which is seen with particular clarity in  FIG. 5C . 
         [0061]    It is a particular feature of the present invention that surface  412  and reflective coating  410  are substantially spaced along axis  402  from annular reflective coating  407  formed on surface  408 , and thus from curved circumferential surface  404 . In the illustrated embodiment, this spacing, which enhances the axial field of view of the lens  400  defined by rays  405  and  406 , is provided by configuring the lens body  401  to define an intermediate circumferential surface  420 , which is preferably curved, intermediate curved circumferential surface  404  and surface  412 . Intermediate circumferential surface  420  typically has a different curvature than the curvature of surface  404 . 
         [0062]    Light reflected from convex reflective coating  410  preferably passes out of the lens  400  through a central portion  422  of surface  408  which is transparent to radiation at a wavelength range of interest and which is not coated by reflective coating  407 . 
         [0063]    Optionally, a rear base portion  424  may be provided around surface  408 , to enable mounting of the lens onto additional elements of an optical system such as additional lenses or other suitable mechanical elements, as described hereinabove with reference to  FIGS. 2 and 3 . Rear base portion  424  may be integrally formed with the remainder of lens  400  or may be mounted onto the lens  400  by any suitable means. Alternatively or additionally, a forward base portion (not shown) may be provided around surface  412  for a similar purpose. 
         [0064]    It is appreciated that in certain cases, depending on the materials used for forming the lens body  401 , total internal reflection of certain light rays may occur, thus obviating the need for some or all of the reflective coatings. 
         [0065]    The embodiment of  FIGS. 5A-5C  is particularly characterized in that surface  403  of lens body  401  comprises a generally planar, but preferably somewhat convex surface. Surface  403  is preferably provided with a reflective coating  428  which is operative to reflect incoming light from a given azimuthal and elevational region and to direct it through the center of central portion  422  of surface  408 , as seen by ray  430 . The preferred convexity of surface  403  provides magnification of the image of the given azimuthal and elevational region so as to provide an image configuration on an image plane of the general type designated by reference numeral  432 . 
         [0066]    It is appreciated that in the embodiment of  FIGS. 5A-5C  the intermediate circumferential surface  420  is operative to collect light. Light collected by intermediate circumferential surface  420 , such as ray  430 , is refracted by the intermediate circumferential surface  420  and is directed to surface  403 . Intermediate circumferential surface  420  may optionally be formed to provide additional focusing of the ray  430 , or to refract the collected rays, thus changing the field of view of surface  403  of lens  400 . 
         [0067]    Reference is now made to  FIGS. 6A and 6B , which are, respectively, a simplified pictorial illustration and a sectional illustration of a circumferential field of view lens constructed and operative in accordance with yet another preferred embodiment of the present invention. As seen in  FIGS. 6A and 6B , similarly to the embodiment of  FIG. 1 , there is provided a lens  500  including a lens body  501 , preferably formed of plastic, glass or any other suitable material which is transparent to radiation at a wavelength range of interest, which is symmetric about an axis of rotation  502 . 
         [0068]    Preferably the lens  500  includes a curved circumferential surface  504 , having optical power, which receives light from a 360 degree field of view about axis  502  limited by rays  505  and  506 , seen with particular clarity in  FIG. 6B . Surface  504  refracts the light, as shown, onto an adjacent, preferably convex, annular reflective coating  507  formed onto a correspondingly shaped surface  508  of lens body  501 . The light is reflected from convex reflective coating  507  onto an oppositely facing, preferably convex, reflective coating  510  formed onto a correspondingly shaped surface  512  of lens body  501 , as shown by ray  513 , which is seen with particular clarity in  FIG. 6B . 
         [0069]    It is a particular feature of the present invention that surface  512  and reflective coating  510  are substantially spaced along axis  502  from annular reflective coating  507  formed on surface  508 , and thus from curved circumferential surface  504 . In the illustrated embodiment, this spacing, which enhances the axial field of view of the lens  500  defined by rays  505  and  506 , is provided by configuring the lens body  501  to define an intermediate circumferential surface  520 , which smoothly joins curved circumferential surface  504  at the location of ray  505  and extends to surface  512 . Intermediate circumferential surface  520  typically has a different curvature the curvature of surface  504 , and need not collect light from the field of view of interest. 
         [0070]    Light reflected from convex reflective coating  510  preferably passes out of the lens  500  through a central portion  522  of surface  508  which is transparent to radiation at a wavelength range of interest and which is not coated by reflective coating  507 , and is focused by the optical power of the central portion  522  onto an image plane. 
         [0071]    Optionally, a rear base portion  524  may be provided around surface  508 , to enable mounting of the lens  500  onto additional elements of an optical system such as additional lenses or other suitable mechanical elements, as is described hereinabove with reference to  FIGS. 2 and 3 . Rear base portion  524  may be integrally formed with the remainder of lens  500  or may be mounted onto the lens  500  by any suitable means. Alternatively or additionally, a forward base portion (not shown) may be provided around surface  512  for a similar purpose. 
         [0072]    It is appreciated that in certain cases, depending on the materials used for forming the lens body  501 , total internal reflection of certain light rays may occur, thus obviating the need for some or all of the reflective coatings. 
         [0073]    It is appreciated that the lenses and optical systems described hereinabove with reference to  FIGS. 1A-6B  are equally applicable for light traveling in both opposite directions, i.e. receiving light from a scene and directing it to an image plane, as specifically described hereinabove, as well as illuminating a field of view from a source of light located at the image plane. 
         [0074]    Reference is now made to  FIGS. 7A and 7B , which are, respectively, a simplified pictorial illustration and a sectional illustration of an optical system constructed and operative in accordance with another preferred embodiment of the present invention. In the embodiment of  FIGS. 7A and 7B , at least one light pipe  600 , which may be hollow or may alternatively include optical fibers, is arranged to surround a rear surface of a lens  602  which is similar to lens  100  shown in  FIGS. 1A-1C , and to have an inclined prism-like edge surface  604  located at a periphery of lens  602 . 
         [0075]    The light pipe  600  directs light from one or more light sources (not shown), which are preferably located at a rear end of light pipe  600 . Light directed from the light sources is refracted by prism-like edge surface  604  of light pipe  600 , and is thus scattered to illuminate at least part of the field of view of lens  602 , as indicated by light rays  607  seen in  FIG. 7B . 
         [0076]    In a second operative orientation of the embodiment of  FIGS. 7A and 7B , shown in  FIG. 7B  by dashed lines, a forward portion of light pipe  600  can be directed somewhat outwardly. In this orientation, the light scattered by prism-like edge surface  604  illuminates a different field of view of lens  602 , as indicated by light rays  608  seen in  FIG. 7B . 
         [0077]    In the illustrated embodiment, lens  602  comprises a lens body  610 , preferably formed of plastic, glass or any other suitable material which is transparent to radiation at a wavelength range of interest, which is symmetric about an axis of rotation  612 . 
         [0078]    Preferably the lens  602  includes a curved circumferential surface  614 , having optical power, which receives light from a 360-degree field of view about axis  612  limited by rays  615  and  616 , which are seen with particular clarity in  FIG. 7B . Surface  614  refracts the light, as shown, onto an adjacent, preferably convex, annular reflective coating  617  formed onto a correspondingly shaped surface  618  of lens body  610 . The light is reflected from convex reflective coating  617  onto an oppositely facing, preferably convex, reflective coating  620  formed onto a correspondingly shaped surface  622  of lens body  610 , as shown by ray  623 , which is seen with particular clarity in  FIG. 7B . 
         [0079]    It is a particular feature of the present invention that surface  622  and reflective coating  620  are substantially spaced along axis  612  from annular reflective coating  617  formed on surface  618 , and thus from curved circumferential surface  614 . In the illustrated embodiment, this spacing, which enhances the axial field of view of the lens  602  defined by rays  615  and  616 , is provided by configuring the lens body  610  to define an intermediate circumferential surface  630 , which is preferably curved, intermediate curved circumferential surface  614  and surface  622 . Intermediate circumferential surface  630  typically has a different curvature than the curvature of surface  614 . 
         [0080]    Light reflected from convex reflective coating  620  preferably passes out of the lens  602  through a central portion  632  of surface  618  which is transparent to radiation at a wavelength range of interest and which is not coated by reflective coating  617 . The light leaving the lens body  610  via central portion  632  is preferably directed onto an imaging sensor  634 , such as a CCD array or any other suitable imaging sensor, which is disposed rearwardly of lens  602 . 
         [0081]    Reference is now made to  FIG. 8 , which is a simplified illustration of an optical system constructed and operative in accordance with still another preferred embodiment of the present invention. As seen in  FIG. 8 , there is provided a lens  700  including a lens body  701 , preferably formed of glass or any other suitable material which is transparent to radiation at a wavelength range of interest, which is symmetric about an axis of rotation  702 . 
         [0082]    Preferably the lens  700  includes a curved circumferential surface  704 , having optical power, which receives light from a 360-degree field of view about axis  702 . Lens  700  preferably provides a circumferential field of view of at least approximately 90 degrees, as indicated by rays  705  and  706 . Surface  704  refracts the light, as shown, onto an adjacent, preferably convex, annular reflective coating  707  formed onto a correspondingly shaped surface  708  of lens body  701 . The light is reflected from convex reflective coating  707  onto an oppositely facing, preferably convex, reflective coating  710  formed onto a correspondingly shaped surface  712  of lens body  701 , as shown by ray  713 . 
         [0083]    It is a particular feature of the present invention that surface  712  and reflective coating  710  are substantially spaced along axis  702  from annular reflective coating  707  formed on surface  708 , and thus from curved circumferential surface  704 . In the illustrated embodiment, this spacing, which enhances the axial field of view of the lens  700  defined by rays  705  and  706 , is provided by configuring the lens body  701  to define an intermediate circumferential surface  720 , which is preferably curved, intermediate curved circumferential surface  704  and surface  712 . Intermediate circumferential surface  720  typically has a different curvature than the curvature of surface  704 , and need not collect light from the field of view of interest. 
         [0084]    Light reflected from convex reflective coating  710  preferably passes out of the lens  700  through a central portion  722  of surface  708  which is transparent to radiation at a wavelength range of interest and which is not coated by reflective coating  707 . 
         [0085]    Lens  700  may optionally be formed with a rear base portion which may be provided around surface  708 , and which may enable mounting of lens  700  onto additional elements of an optical system or other suitable mechanical elements. Alternatively or additionally, a forward base portion (not shown) may be provided around surface  712  for a similar purpose. 
         [0086]    Light from a forward field of view, limited by rays  726  and  728 , preferably is refracted by a lens  730  through a central portion  732  of surface  712 , interiorly of annular reflective coating  710 , through the lens body  701  and out through central portion  722  of surface  708 , interiorly of annular reflective coating  707 , as shown by ray  734 . 
         [0087]    Lens  730  is optionally and preferably protected by a forward facing generally hemi-spherical shield  736  which is transparent to radiation at a wavelength range of interest and which ensures that the lens  730  will not be damaged, but does not corrupt the optical path of rays in the forward field of view. Alternatively, shield  736  may be obviated, leaving lens  730  exposed. Typically, lens  730  and shield  736  are mounted onto lens  700  at forward base thereof. 
         [0088]    It is appreciated that in the illustrated embodiment, the forward field of view limited by rays  726  and  728  at least partially overlaps the circumferential field of view limited by rays  705  and  706 , thus providing stereoscopic viewing of objects lying in overlapped portions  740  of the fields of view. 
         [0089]    It is appreciated that a wavelength range of interest may include the wavelength range of visible wavelengths, the wavelength range of infrared wavelengths, or any other wavelength range. 
         [0090]    It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes combinations and subcombinations of various features described hereinabove as well as modifications thereof which would occur to a person skilled in the art upon reading the foregoing description, and which are not in the prior art.