Abstract:
The invention relates to apparatus and methods for increasing visual acuity through the use of a bioptic telescope which is at least partially embedded in a spectacle lens. In one embodiment, the telescope includes a vision lens having a vision axis and a first surface for placement substantially in front of an eye of a user. The telescope further includes a plurality of optical elements defining an optical path for viewing an object in front of the first surface. At least one of the plurality of optical elements is positioned such that at least a portion of the optical path is located within the vision lens in a plane substantially orthogonal to the vision axis.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to optical devices for improving visual acuity, and more specifically to a telescope system integrated into a spectacle lens. 
     BACKGROUND OF THE INVENTION 
     Magnification is useful for individuals who have resolution loss due to defects in the optics of the eye or of the retina, specifically of the fovea (i.e., the central part of the retina) which provides detail vision for reading, facial recognition and other fine discrimination tasks. Bioptic telescope systems have been prescribed for use by the visually impaired for many years. These multi-element devices provide magnified images of objects at further distances as compared to single element lenses that can only provide magnification at very close working distances. 
     Typically, bioptic telescopes are mounted toward the top of a pair of eyeglasses frames with the telescope eyepiece positioned directly above the pupil of the wearer&#39;s eye. This positioning allows the wearer to look under the eyepiece using their unaided vision, and to tip their head downward to sight through the telescope eyepiece to see the magnified image. Bioptic telescopes are available in small, compact Galilean designs that provide narrow fields of view (e.g., about 5 degrees in a 3.0× magnifier) and generally provide relatively dim images. Alternative bioptic telescopes are available in large, heavy Keplerian designs that provide brighter images and fields of view at least twice as wide (e.g., 12 degrees in a 4.0× magnifier) as Galilean designs. Bioptic telescopes are typically mounted through a spectacle (carrier) lens by drilling a hole through it. 
     Although these types of visual aids can be effectively used in a variety of settings, a large number of visually impaired people reject them. The obvious and unsightly appearance of these prosthetic devices has been identified as one major reason for the reluctance of the visually impaired to use bioptic telescopes. 
     Previous attempts to improve the cosmetic appearance of bioptic telescopes include the use of very small Galilean telescopes, small mostly behind-the-spectacle-lens Keplerian telescopes, and horizontal telescopes folded above the spectacle lenses. While each of these devices improves the cosmetics of bioptic telescopes, they remain obtrusive and continue to be generally rejected. In addition, conventional attempts at minimization invariably result in optical compromises such as reductions in field-of-view or image brightness, or both. 
     Low magnification telescopes can be created by combining a high negative power contact lens or intra-ocular (i.e., surgically implanted) lens with a high positive power spectacle lens. While such telescopes are limited in magnification and severely restrict the field-of-fixation they offer an advantage in cosmetic appearance. However, patients also reject these devices due to the unsightly appearance of the high power spectacle lens. A fully implanted intra-ocular telescopic lens is available. It offers the potential of normally looking spectacles and eyes at the cost of a serious surgical procedure, severely reduced field-of-view (but wide open field-of-fixation), dim image, and possible difficulties with future eye care. 
     What is needed is a low vision bioptic telescope that provides a relatively wide field-of-view, high-magnification, and a bright-image while being cosmetically appealing and permitting the wearer&#39;s eye to appear natural. 
     SUMMARY OF THE INVENTION 
     The invention relates to bioptic telescopes for increasing visual acuity. In one embodiment, the illustrative telescope includes a vision lens having a vision axis and a first surface for placement substantially in front of an eye of a user. In alternative embodiments, the vision lens can be a carrier lens or a spectacle lens. The telescope further includes a plurality of optical elements defining an optical path for viewing an object in front of the first surface of the vision lens. Additionally, at least one of the plurality of optical elements is positioned such that at least a portion of the optical path is located within the vision lens in a plane substantially orthogonal to the vision axis. In another embodiment, the vision lens further includes a second surface and at least one of the plurality of optical elements is positioned substantially between the first surface and the second surface of the vision lens. 
     In one embodiment, the user&#39;s eye simultaneously views the object through the vision lens and the plurality of optical elements. In another embodiment, the vision lens is a spectacle lens. The telescope further includes an eyeglass frame adapted to retain the spectacle lens. In another embodiment, at least a portion of one of the plurality of optical elements is embedded in the vision lens. In alternative embodiments, at least one of the plurality of optical elements is a lens, a mirror, or a holographic element. 
     In one embodiment, the plurality of optical elements includes an objective lens, an ocular lens, and a plurality of planar mirrors, the plurality of planar mirrors is adapted to direct the optical path between the objective lens and the ocular lens. The telescope can be a Galilean or Keplerian type telescope. In another embodiment, at least one of the plurality of planar mirrors is located completely within the lens. 
     The invention is further related to a vision enhancing system. The vision enhancing system includes a spectacle lens having a vision axis and a first surface for placement substantially in front of an eye of a user. The system further includes a telescope in communication with the spectacle lens for viewing an object in front of the first surface of the spectacle lens. The telescope includes an objective lens having an objective lens axis which is substantially parallel to the vision axis. The telescope further includes an ocular lens in optical communication with the objective lens and having an ocular lens axis which is substantially parallel to the vision axis. The telescope further includes a plurality of optical elements defining an optical path between the objective lens and the ocular lens. At least one of the plurality of optical elements is positioned such that at least a portion of the optical path is located within the spectacle lens in a plane substantially orthogonal to the vision axis. 
     In one embodiment, the spectacle lens further includes a second surface and at least one of the plurality of optical elements is positioned substantially between the first surface and the second surface of the spectacle lens. In another embodiment, the user&#39;s eye simultaneously views the object through the spectacle lens and the telescope. In yet another embodiment, an eyeglass frame is adapted to retain the spectacle lens. In still another embodiment, at least a portion of one of the plurality of optical elements is embedded in the spectacle lens. In yet another embodiment the telescope is either a Galilean or Keplerian type telescope. 
     The invention also relates to a method for constructing a telescope. The method includes the steps of mounting a lens having a vision axis and including a first surface to a frame such that the lens is positioned substantially in front of an eye of a user. The method further includes the step of arranging a plurality of optical elements relative to the lens, such that the plurality of optical elements defines an optical path for viewing an object in front of the first surface. At least one of the plurality of optical elements is positioned such that at least a portion of the optical path is located within the lens in a plane substantially orthogonal to the vision axis. In another embodiment, the step of arranging the plurality of optical elements includes placing an objective lens in optical communication with the lens. In another embodiment, the step of arranging the plurality of optical elements includes placing an ocular lens in optical communication with the lens. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and further advantages of the invention may be better understood by referring to the following description taken in conjunction with the accompanying drawings, in which: 
     FIG.  1 A &amp; FIG. 1B are diagrams of an illustrative Galilean telescope system mounted in an eyeglasses frame and the corresponding view seen by a user through the system, respectively; 
     FIG. 1C is a diagram of another illustrative Galilean telescope system mounted in an eyeglasses frame; 
     FIG. 2A, FIG.  2 B &amp; FIG. 2C are schematic diagrams of illustrative Galilean telescopes according to the present invention; 
     FIG.  3 A &amp; FIG. 3B are diagrams of an illustrative Keplerian telescope system mounted in an eyeglasses frame and the corresponding view seen by a user through the system, respectively; 
     FIG.  4 A &amp; FIG. 4B are schematic diagrams of illustrative Keplerian telescope systems according to the present invention; 
     FIG. 5 is a diagram illustrating a telescope having two lenses; and 
     FIGS. 6A-6C are diagrams of various methods for attaching and/or embedding optical elements to a carrier lens. 
    
    
     DETAILED DESCRIPTION 
     In one embodiment, the invention relates to a telescopic device built in part or completely into a carrier lens for increasing visual acuity. In one embodiment, the carrier lens is a spectacle lens. The carrier lens is also referred herein as a “vision lens.” 
     Although the telescope is visible to observers other than the wearer, it does not attract attention due to its compact design. For example, the visibility of the telescope to observers is similar to that of bifocal or trifocal segments in spectacle lenses. In one embodiment, the telescope can be used to simultaneously view the magnified image and the unmagnified image of the same area. This feature improves user orientation and navigation. 
     FIG. 1A is an illustrative embodiment of a Galilean telescope system  100  embedded in a spectacle lens  102 . The spectacle lens  102  is mounted in an eyeglass frame  104  and includes a vision axis which is substantially in the Z-direction. In one embodiment, the vision axis is oriented coincident to the axis of the pupil  108  of a user&#39;s eye  112 . An ocular mirror  204  is suitably positioned such that it is in front of at least a portion of the user&#39;s pupil  108 . An objective mirror  202  is in optical communication with the ocular mirror  204  and is located at a predetermined distance S from the ocular mirror  202 . A magnified image  108 ′ of the pupil  108  is shown on the objective mirror  202  for clarity. The mirrors  202  and  204  are embedded into the spectacle lens and are adapted to direct an image (not shown) between an ocular lens (not shown) and an objective lens (not shown) such that an optical path between the ocular lens and the objective lens is substantially orthogonal to the vision axis of the spectacle lens  102 . In one embodiment, the objective lens and the ocular lens are mounted to the surface of the spectacle lens  102 . In another embodiment, at least a portion of the optical path traverses the spectacle lens  102  in a direction that is perpendicular to the vision axis. The width of the mirrors  202  and  204  limits the field-of-view of the telescope  100  in the Y-direction. Skilled artisans will appreciate that the maximum width of the mirrors  202  and  204  is related to the thickness of the spectacle lens  102 . The field-of-view in the X-direction can be made relatively large since the length of the mirrors  202  and  204  is limited only by the diameter of the spectacle lens  102 . In one embodiment, a combination of curved mirrors (not shown) is embedded into the spectacle lens  102 . The curved mirrors perform the function of the objective and ocular lenses in addition to folding the optical path. In another embodiment, the objective and/or the ocular lenses can be replaced with a holographic element adapted to perform the same function. Techniques for embedding optical components in a carrier lens will be discussed in more detail with respect to FIGS. 6A-6C. 
     FIG. 1B illustrates the user&#39;s view  120  through the telescopic system of FIG.  2 A. The Galilean telescope system  100  allows for the simultaneous viewing of magnified  124  and unmagnified  122  images. Due to the geometry of telescope  100 , the simultaneous viewing feature superimposes the magnified image  124  over the unmagnified image  122 . The spectacle lens  102  can be adapted to conform to the user&#39;s vision-correcting prescription such that the unmagnified image  122  is substantially in focus to the user&#39;s eye  112 . By providing simultaneous views of the magnified  124  and unmagnified  122  images, the user can easily locate an object  126  or determine his position relative to the object  126 . 
     FIG. 1C is a diagram of an illustrative Galilean telescope system  100 ′ embedded in the spectacle lens  102 . In this embodiment, the ocular mirror  204 ′ is suitably positioned such that it is above the user&#39;s pupil  108 . The objective mirror  202 ′ is in optical communication with the ocular mirror  204 ′ and is located at a predetermined distance S from the ocular mirror  204 ′. Since the objective mirror  202 ′, in the normal mode of operation, does not reflect the image of the pupil  108 , this embodiment can be more cosmetically appealing. The mirrors  202 ′ and  204 ′ are embedded into the spectacle lens. The mirrors  202 ′ and  204 ′ are adapted to direct an image (not shown) between the ocular lens (not shown) and the objective lens (not shown) as discussed with reference to FIG.  1 A. In another embodiment, a combination of curved mirrors (not shown) is embedded into the spectacle lens  102 . The curved mirrors perform the function of the lenses in addition to folding the optical path. In another embodiment, objective and/or ocular lenses can be replaced with a holographic element adapted to perform the same function. 
     In operation, the system  100 ′ functions as follows. In the normal mode of operation, the user observes an unmagnified image through the spectacle lens  102 . The spectacle lens can be a prescription lens adapted to correct the user&#39;s vision. To magnify the image, the user tilts his head forward and rotates his eye  112  upward until the ocular mirror  204 ′ is in front of at least a portion of his pupil  108 . In one embodiment, the user simultaneously observes the magnified and unmagnified images as shown in FIG.  1 B. 
     FIG. 2A is a diagram of a Galilean telescope  100  according to one embodiment of the invention. The telescope  100  includes an ocular lens  106  and an objective lens  110 . Planar mirrors  202  and  204  are embedded in the carrier lens  102 . In one embodiment, the mirror  202  is referred to as the objective mirror. In another embodiment, the mirror  204  is referred to as the ocular mirror. Each of the mirrors  202  and  204  is oriented at a suitable angle to direct light between the ocular lens  106  and the objective lens  110 . In one embodiment, the ocular lens  106  and the objective lens  110  are glued to the carrier lens  102 . The mirrors  202  and  204  function as a periscope to fold the optical path from the objective lens  110  to the ocular lens  106 . At least a portion of the optical path lies within the carrier lens  102  substantially in the Y-direction. 
     In one embodiment (FIG.  2 A), the ocular lens  106  is a negative or concave lens. In another embodiment (FIG.  2 C), the ocular lens  106  is a positive or convex lens. The ocular lens  106  is mounted behind the carrier lens  102  slightly above the pupil  108  such that the user can simultaneously see the magnified and unmagnified views. In one embodiment, the position of the ocular lens  106  is near the nasal area of the carrier lens  102 . However, skilled artisans will appreciate that the position of the ocular lens  106  is not limited to the region near the nasal area of the carrier lens  102 . The objective lens  110  is mounted in front of the carrier lens  102 . The objective lens  110  shown in FIG. 2A is a positive or convex lens. In another embodiment (FIG.  2 C), the objective lens  110  is a negative or concave lens. The position of the objective lens  110  is determined at least in part by the ocular lens  106 . The separation between the ocular lens  106  and the objective lens  110  is predetermined to create substantially an afocal telescope from the two lenses  106  and  110 . In one embodiment, the objective lens  110  is positioned at substantially the same vertical or X-position as the ocular lens  106 . In another embodiment, the objective lens  110  is separated from the ocular lens  106  in the horizontal or Y-position by a distance S as shown in FIG.  1 A. Since the mirrors  202  and  204  fold the optical path inside the carrier lens  102  and not in the air, the computation of the focal lengths of the lenses  106  and  110  is modified accordingly. In yet another embodiment, the powers of the objective lens  110  and/or the ocular lens  106  can be configured to provide minification instead of magnification if desired (e.g., to expand the field-of-view of patients having tunnel vision due to glaucoma). In another embodiment (not shown), the objective lens  110  and/or the ocular lens  106  can be holographic elements adapted to provide the necessary minification. 
     FIG. 2B illustrates an embodiment of the telescope  100 ′ having optical elements in the form of curved mirrors  206  and  208  embedded into the carrier lens  102 . The mirrors  206  and  208  are of sufficient curvature to replace the ocular lens  106  and the objective lens  110 . Skilled artisans will appreciate that curved mirrors form images much like lenses. Since the curved mirrors  206  and  208  are totally embedded in the carrier lens  102 , this embodiment of the telescope  100 ′ is substantially invisible to a casual observer making it more cosmetically acceptable to patients. One advantage of this embodiment is that the curved mirrors  206  and  208  do not suffer from chromatic aberrations inherent in lenses. 
     As previously discussed, the field-of-view in the Y-direction of the telescopes of FIG.  2 A and FIG. 2B is limited by the width w of the mirror  202 . Thus, the field-of-view in the Y-direction is related to the thickness t of the carrier lens  102 . The field-of-view in the X-direction can be made relatively large since the dimension of the mirror  202  in the X-direction is only limited by the X-dimension of the carrier lens  102 . To increase the field-of-view in the Y-direction, the objective lens  110  can be positioned below the ocular lens  106  in the X-direction (not shown). In this embodiment, the thickness t of the carrier lens  102  limits the field-of-view in the X-direction and increases the field-of-view in the Y-direction. The field-of-view in the Y direction is limited by the physical dimension of the objective lens  110  or by the extent of the carrier lens  102  on the nasal side of the pupil  108 . 
     FIG. 3A illustrates a Keplerian telescope  300  according to the present invention. The Keplerian telescope  300  uses a positive power lens for both the objective lens (not shown) and the ocular lens (not shown). An ocular mirror  304  is suitably positioned such that it is in front of at least a portion of the user&#39;s pupil  108 . An objective mirror  302  is in optical communication with the ocular mirror  304  and is located at a predetermined distance S from the ocular mirror  302 . A magnified image  108 ′ of the pupil  108  is shown on the objective mirror  302  for clarity. The image generated by the Keplerian telescope  300  is reversed and can be corrected to permit terrestrial use. This correction is achieved by the addition of two mirrors  312  and  314 . In one embodiment, the telescope  300  includes two mirrors  312  and  314  oriented at substantially right angles to each other near the bottom of the carrier lens  102 . The two mirrors  312  and  314  contribute to a longer optical path which is necessary for the design of the Keplerian telescope  300 . 
     The telescope  300  also includes an ocular lens (not shown), and an objective lens (not shown). In another embodiment, the design uses a high power lens for the objective lens and a low power lens for the ocular lens to provide minimization as opposed to magnification. The width of the mirrors  302  and  304  limits the field-of-view of the telescope  300  in the X-direction. Skilled artisans will appreciate that the maximum width of the mirrors  302  and  304  in this embodiment is related to the thickness of the spectacle lens  102 . The field-of-view in the Y-direction can be made relatively large since the length of the mirrors  302  and  304  is limited only by the diameter of the spectacle lens  102 . The telescope  300  having a large field-of-view in the Y-direction allows the user to observe a larger horizontal region in front of him than that of the telescope  100  of FIG.  1 A. 
     FIG. 3B illustrates the user&#39;s view  120  through the telescopic system of FIG.  3 A. The Keplerian telescope system  300  allows for the simultaneous viewing of magnified  124  and unmagnified  122  images. By appropriately tilting the ocular mirror  304 , the position of the magnified image  124  can be shifted to a desired location. In FIG. 3B, the ocular mirror  304  is tilted such that the magnified image  124  is shifted above the unmagnified image  122 . Alternatively, the objective mirror  302  can be tilted to shift the position of the magnified image  124 . The shifting of the magnified image  124  prevents the superposition of the magnified image  124  over the unmagnified image  122  as seen in FIG.  1 B. The spectacle lens  102  can be adapted to conform to the user&#39;s vision-correcting prescription such that the unmagnified image  122  is substantially in focus to the user&#39;s eye  112 . The field-of-view  124 ′ of the magnified image  124  is shown for clarity. By providing simultaneous views of the magnified  124  and unmagnified  122  images, the user can easily locate an object  126  or determine his position relative to the object  126 . 
     FIG. 4A illustrates three views of the Keplerian telescope  300  built into a carrier lens  102 . In one embodiment, the telescope  300  includes an ocular lens  306  and an objective lens  310 . The ocular lens  306  and the objective lens  310  can be glued to the carrier lens  102 . In one embodiment, the ocular lens  306  is located at a position on the carrier lens  102  such that the user can simultaneously view both the magnified and unmagnified images. The telescope also includes an ocular mirror  304  and an objective mirror  302 . The objective mirror  302  directs an image into the telescope  300  and the ocular mirror  304  directs the image into the ocular lens  306 . In one embodiment, the ocular mirror  304  and the objective mirror  302  are embedded into the carrier lens  102 . The telescope  300  also includes two planar mirrors  312  and  314 . In one embodiment, the two planar mirrors  312  and  314  are embedded in the carrier lens  102 . In another embodiment, one or more field lenses (not shown) can be placed in the optical path of the telescope  300 . In another embodiment (not shown), at least one of the optical elements can be replaced with a holographic element. 
     The telescope  300  operates as follows. A user deploying the telescope  300  can simultaneously view both the unmagnified and magnified images. Since the carrier lens  102  is relatively shallow in thickness t, the optical elements that provide the imaging must be relatively small while providing nearly perfect imaging, desired magnification, and producing the image inversion. In one embodiment, the ocular lens  306  and the objective lens  310  are chromatically corrected. In another embodiment, additional field lens elements (not shown) can be added to chromatically compensate the ocular lens  306  and/or the objective lens  310 . 
     The mirror  302  directs light entering the objective lens  310  in the negative X-direction to the mirror  312 , which directs the light to the mirror  314  in the Y-direction. The mirror  314  then directs the light in the positive X-direction to the mirror  304 , which then directs the light through the ocular lens  306  in the Z-direction. In one embodiment, the mirror  312  is disposed at substantially a right angle to the mirror  314 . A distance scale (not shown) can be provided on or embedded in the carrier lens  102  for estimating distance. The distance scale is located such that a user can simultaneously view the distance scale and the magnified image. This can be useful in many applications, such as estimating the distance to the Pin while playing golf. 
     As previously discussed, the telescope  300  allows a user to simultaneously view the magnified image and the unmagnified image. In one embodiment, the simultaneous vision concept requires that the magnified image seen through the telescope  300  be visible simultaneously with the unmagnified image and be projected above the unmagnified view as shown in FIG.  3 B. Alternatively, the magnified image can be shifted in other directions. However, shifting the magnified image above the unmagnified image is preferred because the magnified image occupies an area of the carrier lens  102  that is less likely to include obstacles. In alternative embodiments, the shifting of the magnified image is accomplished by appropriately tilting the ocular mirror  304  and/or the objective mirror  302 . The telescope  300  according to the present invention achieves the simultaneous view in part because there is no opaque frame or mounting structure to block the unmagnified view from reaching the pupil  108 . Furthermore, by tilting the ocular mirror  304  slightly, the magnified image can be projected to appear to be above the unmagnified image. The Keplerian telescope  300  including a field-of-view having limited height is especially suited to the mode of operation in which the magnified view appears above the unmagnified view. 
     FIG. 4B illustrates three views of a Keplerian telescope  300 ′ having curved mirrors embedded into a carrier lens  102 . In one embodiment, the telescope  300 ′ includes a curved ocular mirror  408  and a curved objective mirror  406 . The curved mirrors  408  and  406  behave as lenses and do not suffer from the chromatic aberrations inherent in lenses. In one embodiment, the curved ocular mirror  408  is located at a position on the carrier lens  102  such that the user can simultaneously view both the magnified and unmagnified images. The telescope  300 ′ also includes two mirrors  412  and  414 . The mirrors  412  and  414  can be curved to improve the performance of the telescope  300 ′. In this embodiment, the curved mirrors  412  and  414  act as field lenses without the aberrations inherent in standard lenses. Additionally, the mirrors  412  and  414  invert the magnified image for terrestrial use. In alternative embodiments, one or more of the curved mirrors  406 ,  408 ,  412 , and  414  are embedded into the carrier lens  102 . In other embodiments, the telescope  300 ′ includes additional optical elements (not shown) disposed in the optical path of the telescope  300 ′. 
     Design considerations for the telescope  300  of FIG. 4A will be discussed next. The optical path length {overscore (L)} in the Keplerian telescope  300  is equal to the sum of the focal lengths of the objective lens  310  and the ocular lens  306 . 
     
       
           {overscore (L)}=f′   ob   +f′   oc   (1)  
       
     
     The power or magnification M of the telescope  300  is given by the ratio of the focal length of the objective lens  310  to the focal length of the ocular lens  306 .              M   =            f   ob   ′                 f   oc   ′                    (   2   )                                
     The optical path length {overscore (L)} can be expressed as follows. 
     
       
           {overscore (L)} =( M+ 1) f′   oc   (3)  
       
     
     Thus, for a given focal length of an ocular lens  306 , a longer optical path length {overscore (L)} can achieve higher magnification M. Skilled artisans will appreciate that the optical path length {overscore (L)} is computed using the refractive index n of the medium (e.g., for a plastic carrier lens having n≈1.5). The refractive index n of the medium affects the focal lengths of the lenses  310  and  306 . For example, in one embodiment, the physical length L of the optical path is greater by fifty percent in the medium of the carrier lens  102  than it would be in a design using an air medium. Thus, the optical path length {overscore (L)} in this embodiment can be expressed as follows:                L   _     =       L   n     =       t   +   El   +   S   +   E2     n               (   4   )                                
     where t is the thickness of the carrier lens  102  and L is the physical length of the optical path. Another consideration in the design of the Keplerian telescope  300  is the eye relief (i.e., the distance from the ocular lens  106  to the eye  112 ). This parameter affects both the field-of-view and the light efficiency of the telescope  300 . In one embodiment, the exit pupil (i.e., the image of the objective lens  110  through the ocular lens  106 ) is coincident with the entrance pupil  108  of the eye  112  (e.g., e=15 mm behind the carrier lens  102 ). This provides maximum efficiency and field-of-view. If a field lens is not included in the embodiment, the exit pupil can be expressed as follows.              e   =         f   oc   ′     +       f   oc     ′                 2         f   ob   ′         =       f   oc   ′            M   +   1     M                 (   5   )                                
     Thus, the optical path length {overscore (L)} can be expressed as follows. 
     
       
           {overscore (L)}=e·M   (6)  
       
     
     The field-of-view of the telescope  300  can be calculated with reference to FIG.  5 . FIG. 5 illustrates a telescope  500  having an objective lens  310 ′ and an ocular lens  306 ′. The intermediate image  502  is disposed at a distance F′ ob  from the objective lens  310 ′ and a distance F oc  from the ocular lens  306 ′. This arrangement is said to be afocal since the two lenses  310 ′ and  306 ′ are separated by a distance equal to the sum of their focal lengths. The size of the intermediate image  502  of the largest viewable image at F′ ob  is shown as y′ The visual field is therefore given by 2y′/f′ oc , where f′ oc  is the focal length of the ocular lens  306 ′. The field-of-view is typically defined for the point of half illumination, under the assumption of a small pupil  108 . The field-of-view can be expressed as:                2        y   ′       =       f   oc   ′            D   oc     e               (   7   )                                
     Hence, the focal length f′ oc  and the diameter D oc  of the ocular lens  306 ′ as well as the eye relief e, determine the size of the field-of-view. Depending on the size of the pupil  108 , a range of field-of-views can be derived as follows.                2        y   ′       =       f   oc   ′              D   oc     ±     D   eye       e               (   8   )                                
     This range is centered about the half-illumination field. It will be appreciated by skilled artisans that the half-illumination field refers to the size of the field for which the illumination near the edge of the field decreases to one-half of the illumination near the center of the field. 
     FIG. 6A illustrates one technique available to embed optical elements or optical components into a carrier lens  600 . In one embodiment, a wedge-shaped cut  602  having the desired angles and dimensions is made into the carrier lens  600 . An interior surface  604  of the wedge-shaped cut  602  is then coated with metallic or dielectric layers, for example. The coated interior surface  604  functions as a planar mirror. To reinforce the carrier lens  600 , a wedge-shaped section  606  having the proper dimensions can be inserted and glued into the wedge-shaped cut  602 . Although not required to practice the invention, the wedge-shaped section  606  reinforces the carrier lens  600  and protects the coated interior surface  604  from debris, for example. The wedge-shaped section  606  can be fabricated from a suitable material. The material can be substantially transparent such that the affixed wedge-shaped section  606  appears to be integral to the carrier lens  600 . In alternative embodiments, the material is a flexible material such as silicon sealant, glue such as epoxy resin, or resin from which the carrier lens  600  is made. 
     In another embodiment, a curved-shaped cut  608  having the desired dimensions is made into the carrier lens  600 . An interior surface  610  is then coated with metallic or dielectric layers, for example. The interior surface  610  functions as a curved mirror. An optional curve-shaped section  611  can be affixed to the interior surface  610 . Skilled artisans will appreciate that cuts of any shape or orientation can be made in the carrier lens without departing from the scope of the invention. 
     FIG. 6B illustrates another technique available to embed optical elements or optical components into a carrier lens  600 . In one embodiment, thin plates  612 ,  613  and  614  are molded into the carrier lens  600  at desired positions. The plates  612 ,  613 , and  614  can be coated with a metallic film, for example. In another embodiment, a precise cutout  614  can be made into the carrier lens. A mirror or other optical component can be inserted into the cutout  614  and affixed to the carrier lens. 
     FIG. 6C illustrates a technique available to affix optical components to a carrier lens  600 . In one embodiment, a convex lens  616  and a concave lens  618  are glued to the carrier lens  600  using suitable optical glue. In another embodiment (not shown) the lenses  616  and  618  are injected molded into the carrier lens  600 . Skilled artisans will appreciate that other techniques of embedding, attaching, and combining optical elements can be used without departing from the spirit and scope of the invention. 
     In another embodiment, one or more field lenses (not shown) are included in the Keplerian telescope  300 . Skilled artisans will appreciate that the introduction of field lenses distributes optical power, thus, reducing the need for high power at the ocular lens  306 . In addition, field lenses can also increase the field-of-view of the telescope  300 . These optical elements can be formed within the carrier lens  102  by various techniques such as injection molding. 
     Having described and shown the preferred embodiments of the invention, it will now become apparent to one of skill in the art that other embodiments incorporating the concepts may be used and that many variations are possible which will still be within the scope and spirit of the claimed invention. These embodiments should not be limited to disclosed embodiments but rather should be limited only by the spirit and scope of the following claims.