Abstract:
A thin lens consists of a first optical element which comprises a first refracting surface, wherein incoming light passes through the first refracting surface on a first optical axis. A reflecting surface changes a direction of the incoming light from the first optical axis to a second optical axis. Incoming light on the second optical axis passes through a second refracting surface. A second optical element comprises a first refracting surface, wherein incoming light passes through the first refracting surface on the second optical axis. A reflecting surface changes a direction of the incoming light from the second optical axis to a third optical axis. Incoming light on the third optical axis passes through a second refracting surface. The third optical axis is approximately parallel to, and in opposite direction from, the first optical axis.

Description:
FIELD OF THE INVENTION 
   The invention pertains to a compact, thin lens for portable devices including an image capture device. 
   BACKGROUND OF THE INVENTION 
   For portable devices such as cellular phone cameras and laptop computer cameras, it is desirable to reduce costs as much as possible and to keep the thickness of the portable device as thin as possible. Folding the optical path of a lens is an excellent way to change the form factor of the optical assembly. Consequently, a folded optical assembly is an attractive alternative for the image capture device in a portable apparatus. It is the goal of the present invention to provide a low cost folded optical assembly for an image capture device wherein the thickness of the optical assembly is less than 7 mm. 
   Examples of folded optical assemblies can be found in U.S. Pat. Nos. 6,898,023 (Takeuchi), 6,900,950 (Nagata), and U.S. Patent Application Publication No. 2006/0092524 (Konno). Takeuchi discloses a zoom lens assembly with a series of refractive elements and a prism to fold the optical path. Takeuchi&#39;s folded zoom lens assembly is over 7 mm in thickness and it would be relatively expensive since it is composed of five lenses, one prism, and one filter. In addition, the third lens group moves as the lens zooms so guidance is required on this lens group. As a result, the zoom lens assembly described by Takeuchi is relatively thick and relatively expensive. 
   Nagata discloses a folded lens assembly, shown in  FIG. 1 , that is composed of a series of two refractive surfaces ( 100  and  160 ) and three reflective surfaces ( 110 ,  140 , and  150 ) to create an optical path with three folds. Refractive surfaces  120  and  130  are typically parallel surfaces and as such do not have optical power but they could have refractive functionality. Element  170  is a cover glass and infrared filter which does not have optical power. A problem with the design described by Nagata is that multiple free form surfaces are used. The free form surfaces are required to generate optical power from the three curved reflective surfaces ( 110 ,  140 , and  150 ) used in the Nagata lens design to focus the image on the sensor  180 . Free form surfaces are not rotationally symmetric and as such the mold components for molding the lenses are not manufacturable with rotationally based tooling processes such as diamond turning or traditional grinding and polishing so that manufacturing costs are substantially increased. 
   Konno discloses a folded zoom lens assembly, shown in  FIG. 2 , that includes a series of five refractive lenses ( 230 ,  240 ,  250 ,  255  and  260 ) and two prism elements ( 210  and  270 ) to fold the optical path as and focus an image on the sensor  285 . Element  275  is a cover glass and infrared filter which does not have optical power. This folded zoom lens assembly would also be relatively expensive since the embodiments described include glass lens elements and prisms. In addition, the lens elements between the two prisms are movable to provide the zoom function which requires complicated guidance mechanisms. 
   Therefore a need persists for a low cost folded optical assembly for an image capture device wherein the thickness dimension of the optical assembly is thin. 
   SUMMARY OF THE INVENTION 
   Briefly, according to one aspect of the present invention a thin lens consists of a first optical element which comprises a first refracting surface, wherein incoming light passes through the first refracting surface on a first optical axis. A reflecting surface changes a direction of the incoming light from the first optical axis to a second optical axis. Incoming light on the second optical axis passes through a second refracting surface. A second optical element comprises a first refracting surface, wherein incoming light passes through the first refracting surface on the second optical axis. A reflecting surface changes a direction of the incoming light from the second optical axis to a third optical axis. Incoming light on the third optical axis passes through a second refracting surface. The third optical axis is approximately parallel to, and in opposite direction from, the first optical axis. 
   The invention describes a low cost folded optical assembly for an image capture device that has a thickness that is less then 7 mm. The low cost folded optical assembly includes two plastic prisms with optical power to provide good optical performance in a very thin form factor at a low cost. 
   These and other objects, features, and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a ray trace schematic of a prior art folded lens. 
       FIG. 2  is a ray trace schematic of another prior art folded lens. 
       FIG. 3  is a ray trace schematic of a moderate angle field of view lens (62 mm equivalent focal length (EFL) for a 35 mm sensor) in a Z-shaped layout. 
       FIG. 4  is a ray trace schematic of a moderate angle field of view lens (62 mm EFL) in a U-shaped layout. 
       FIG. 5  is a schematic cross section of the elements for the U-shaped layout folded lens from  FIG. 4 . 
       FIG. 6  is a modulation transfer function (MTF) chart for the lens shown in  FIGS. 4 and 5 . 
       FIG. 7  is a ray trace schematic of a wider angle field of view lens (50 mm EFL) in a Z-shaped layout. 
       FIG. 8  is a ray trace schematic of a wider angle field of view lens (50 mm EFL) in a U-shaped layout. 
       FIG. 9  is a schematic cross section of the elements for the U-shaped layout folded lens shown in  FIG. 8 . 
       FIG. 10  is a MTF chart for the lens shown in  FIGS. 8 and 9 . 
       FIG. 11  is a ray trace schematic of a telephoto (107 mm EFL) in a Z-shaped layout. 
       FIG. 12  is a ray trace schematic of a telephoto lens (107 mm EFL) in a U-shaped layout. 
       FIG. 13  is a schematic cross section of the elements for the U-shaped layout lens shown in  FIG. 12 . 
       FIG. 14  is a MTF chart for the lens shown in  FIGS. 12 and 13 . 
       FIG. 15  is schematic cross section of molded-in alignment features at the interface between the two elements for the lens shown in  FIGS. 8 and 9 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present description is directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. 
   For portable devices with image capture devices such as cellular phones, laptop computers, and personal digital assistants, compact size is required for portability. In particular, thinness is desirable both to reduce size and increase portability, and also to improve the perceived style and improve the heat transfer from the device thereby improving reliability by reducing the operating temperature. 
   Folded lens designs provide an excellent method to reduce the length of an optical assembly. The challenge is to deliver high modulation transfer function values out to the Nyquist frequency with a small number of plastic elements that have rotationally symmetric surfaces to keep manufacturing costs low. 
   The invention is based on lens designs with two plastic elements that are mated together to align the elements with each other. A planar reflective surface is used in each element to turn the optical path by approximately 90 degrees in each element. As such, the planar reflective surfaces do not impart any optical power. The optical power is then delivered by the two refractive surfaces in each element. By confining the optical power to the refractive surfaces and using a planar reflective surface to turn the optical power by 90 degrees in each element, the light rays pass through the refractive surfaces symmetrically so that rotationally symmetric surfaces can be used throughout the lens design. The use of rotationally symmetric surfaces substantially reduces the manufacturing cost of the tooling to make the lens elements. In addition, the first element has positive optical power to reduce the lateral size of the light bundle and the second element has negative optical power to aid in color correction. 
   In addition, the lens elements are laid out so that the image sensor plane is parallel to the lens aperture of the first lens surface, which receives the incoming light. The advantage of this orientation of the image sensor is that the long dimensions of the image sensor are placed in the lateral dimension of the image capture device so that the image sensor does not add substantially to the thickness of the image capture device. 
     FIG. 3  shows a two element folded lens design with a Z-shaped layout wherein the incoming light is parallel to the optical axis  355  of the light at the image sensor  360  and the direction of the incoming light is the same as the direction of the light at the image sensor  360 . In the Z-shaped layout, the image sensor  360  is located on the back side of the image capture device on the opposite side from the lens aperture which receives the incoming light, with the image sensor  360  facing the front. 
   Within the scope of the invention, a new lens layout is proposed in the shape of a U (see  FIG. 4 ) wherein the incoming light is parallel to the optical axis  455  of the light at the image sensor  460  but the direction of the incoming light is opposite to the direction of the light at the image sensor  460 . In the U-shaped layout, the image sensor  460  is located on the front side of the image capture device, on the same side if the device as the lens aperture that receives the incoming light, with the image sensor  460  facing the back of the camera or device. 
   By arranging the optical path in a U-shaped layout, the thickness of the lens assembly is reduced compared to a Z-shaped layout because the two horizontal portions of the optical path do not both add to the thickness dimension. As can be seen in  FIG. 3 , in a Z-shaped layout, the horizontal portion of the optical path from the cover glass  305  to the first reflective surface  310  and the horizontal portion of the optical path from the second reflective surface  340  to the image sensor  360  both add to the thickness dimension of the lens assembly. In contrast, as can be seen in  FIG. 4 , in a U-shaped layout the horizontal portion of the optical path from the cover glass  305  to the first reflective surface  410  and the horizontal portion of the optical path from the second reflective surface  440  to the image sensor  460  do not both add to the thickness dimension since the optical path folds back on itself. Consequently, the U-shaped layout is always thinner than the Z-shaped layout. 
   Both the Z-shaped layout and the U-shaped layout can be applied to fixed focal length lenses or adjustable focal length (zoom) lenses to reduce the thickness of the lens assembly. For the case of the adjustable focal length lens, the two elements  510  and  520  move relative to one another (in a vertical direction as shown in  FIG. 5 ) for zooming. A moderate zoom ratio is attainable with this approach. 
   To further reduce the cost of the lens assembly and reduce the volume of the lens, the invention is directed to fixed focal length lens designs. A combination of two fixed focal length lenses as described by the invention, a wide angle lens (or moderate angle lens) and a telephoto lens, can be used together in an image module to provide a zoom action with composite imaging. The technique of composite imaging to achieve a zoom action with composite imaging is disclosed in commonly-assigned copending U.S. patent application Ser. No. 11/461,574, filed Aug. 1, 2006. 
   An exemplary embodiment of the invention for a compact fixed focal length lens with a moderate angle field of view in a U-shaped layout is shown in  FIG. 4 . (For comparison, a similar lens design with a Z-shaped layout is shown in  FIG. 3 .) This design includes two prism type elements  510  and  520  with power on one or more refractive surfaces each to produce a very small and thin form factor. In addition, the U-shaped layout keeps the image sensor  460  in an orientation such that the image sensor does not add substantially to the thickness of the lens assembly or the image module that would be produced with the lens assembly. The lens design of the invention also provides space on either side of the image sensor  460  (above and below the image sensor  460  as shown in  FIG. 4 ) that can be occupied by the capacitors and other circuitry associated with the image sensor  460  without adding to the thickness of the lens assembly or image module. The thicknesses of the two lens assemblies are indicated in  FIGS. 3 and 4  wherein the thickness dimension t is shown as being the distance from the front vertex of the lens to the face of the image sensor. A cross-sectional view of the two lens elements  510  and  520  for the U-shaped layout is shown in  FIG. 5  along with the cover glass  350  and the image sensor  460 . 
   Table 1, below, shows the thickness benefit provided by the U-shaped layout as disclosed as the invention as compared to a Z-shaped layout for the moderate angle field of view lens discussed above along with thickness data for a wider angle field of view lens and a telephoto angle field of view lens. The ray trace schematics and cross sectional schematics for the wider angle field of view lens in both a Z-shaped layout and a U-shaped layout are shown in  FIGS. 7 ,  8  and  9  while the ray trace schematics and cross sectional schematics for the telephoto angle field of view lens in both a Z-shaped layout and a U-shaped layout are shown in  FIGS. 11 ,  12  and  13 . 
   
     
       
             
           
             
             
             
             
           
         
             
               TABLE 1 
             
           
           
             
                 
             
             
               Thickness comparison of different lens designs 
             
           
        
         
             
                 
               Lens type 
               Lens layout 
               Thickness (mm) 
             
             
                 
                 
             
             
                 
               Moderate angle 
               Z 
               3.84 
             
             
                 
               Moderate angle 
               U 
               3.28 
             
             
                 
               Wider angle 
               Z 
               3.15 
             
             
                 
               Wider angle 
               U 
               2.56 
             
             
                 
               Telephoto 
               Z 
               6.34 
             
             
                 
               Telephoto 
               U 
               5.69 
             
             
                 
                 
             
           
        
       
     
   
   The modulation transfer function chart for the moderate angle field of view lens is shown in  FIG. 6 . The modulation transfer function provided by the two element folded lens design is quite good out beyond 250 line pairs/mm. Which corresponds to the Nyquist frequency for an image sensor with 0.002 mm sized pixels. Wherein, the Nyquist frequency is the highest frequency that the sensor can reliably detect and is defined as
 
 N= 1/(2 p )
 
Wherein N is the Nyquist frequency expressed in line pairs/mm and p is the pixel size in mm. The Nyquist charts for the wider angle field of view lens and the telephoto angle field of view lens are shown in  FIGS. 10 and 14  respectively.
 
   There are two types of aberrations that need to be controlled in a lens system; the monochromatic and the color aberrations. Monochromatic aberrations are generally controlled by lens shape and aspheric surfaces can aid greatly in their control. Color aberrations are more typically controlled by the choice of materials used in the optical elements. For compact systems, the fewest number of elements is the most desirable. However, to control color, at least two different optical materials must be used. Consequently, a two element lens is the minimum possible configuration for a color corrected refractive lens system. The invention includes two elements ( 510  and  520 ) that can be different materials to enable color correction and four surfaces ( 400 ,  420 ,  430 ,  450 ) that can be aspheric shape if needed to correct for monochromatic aberrations. 
   Because the invention describes two element lenses that are very small in size, very tight alignment tolerances of the elements with respect to one another are typically required to deliver good modulation transfer function performance. To this end, the invention includes molded-in alignment features  1510  in the plastic elements  1520  and  1530 , at the interface between the two elements, that force the elements  1520  and  1530  into alignment with one another when they are assembled. Preferably, the alignment features  1510  are rotationally symmetric so they can be machined along with the optical surfaces. Also the guiding surfaces on the alignment features  1510  are preferably angled or tapered to allow the surfaces of the alignment features  1510  to come together easily at first and then get progressively tighter as the elements  1520  and  1530  are moved together into position.  FIG. 15  shows a set of alignment features  1510  associated with the two elements  1520  and  1530  of one of the lens designs discussed previously. 
   In addition to alignment features, other mounting features can also be molded into the two elements. These features can be associated with mounting the lens into the portable device structure or as guidance of the lens during movement for autofocus. 
   Example 1 
   Ray trace schematics for a lens with moderate angle field of view designed as an example of the invention is shown in a Z-shaped layout in  FIG. 3  and a U-shaped layout in  FIG. 4 . The optical performance and the optical surfaces are the same for both the Z-shaped layout and the U-shaped layout. A description of the lens design including surface curvatures, lateral distances, aperture sizes and materials is given in Table 2 below. The lens is designed for an f# of 3.2, a pixel size of 0.002 mm and a sensor with two mega pixels. The modulation transfer function chart is shown in  FIG. 6 . The difference between the Z-shaped layout and the U-shaped layout versions of the lens are in the thickness dimension of the lens assembly, as can be seen in Table 1 and in  FIGS. 3 and 4 , the Z-shaped layout lens is 3.84 mm thick while the U-shaped layout lens is only 3.28 mm thick. For clarification, a cross sectional schematic of the U-shaped layout lens assembly with elements  510  and  520  along with cover glass  305  and image sensor  460  is shown in  FIG. 5 . Based on the sensor size and the thickness, this design is well suited to use in a cell phone or a laptop computer or other application where thinness and moderate angle field of view is important. 
   
     
       
             
           
             
             
             
             
             
             
             
             
           
             
           
             
             
             
             
             
             
             
           
         
             
               TABLE 2 
             
             
                 
             
             
               Lens description for Example 1 with a 62 mm focal length 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
                 
                 
                 
               Thickness or 
               Aperature 
               Aperture 
                 
             
             
               Element # 
               Surface # 
               Radius 
               Shape 
               Separation 
               Dimension 
               Shape 
               Material 
             
             
                 
             
             
               1 
               1 
               Infinite 
               Flat 
               0.3000 
               2.041 
               Circular 
               NBK7 Schott 
             
             
               1 
               2 
               Infinite 
               Flat 
               0.1000 
               1.931 
               Circular 
             
             
               2 
               3 
               3.542 
               Asphere 1 
               1.3000 
               1.875 
               Circular 
               Zeonex-E48R 
             
             
               2 
               4 
               Infinite 
               Flat 
               −2.5667 
               3.035 
               Circular 
               Reflective 
             
             
               2 
               5 
               1.834 
               Asphere 2 
               −0.1000 
               2.574 
               Circular 
             
             
               3 
               6 
               2.369 
               Asphere 3 
               −2.7595 
               2.467 
               Circular 
               Polycarbonate 
             
             
               3 
               7 
               Infinite 
               Flat 
               1.3300 
               4.166 
               Circular 
               Reflective 
             
             
               3 
               8 
               3.642 
               Asphere 4 
               0.6667 
               3.709 
               Circular 
             
             
               Image 
                 
               Infinite 
               Flat 
                 
               4.002 
             
             
                 
             
           
        
         
             
               Aspheric Constants 
             
             
               Z = (VY{circumflex over ( )}2/SQRT(1 + (1 − (1 + K)(C{circumflex over ( )}2Y{circumflex over ( )}2)))) + AY{circumflex over ( )}4 + BY{circumflex over ( )}6 + CY{circumflex over ( )}8 + DY{circumflex over ( )}10 
             
           
        
         
             
               Asphere # 
               V 
               K 
               A 
               B 
               C 
               D 
             
             
                 
             
             
               Asphere 1 
               2.8240E−01 
               0.0000E+00 
               −3.0971E−03 
               −8.3905E−04 
               5.6459E−04 
               −6.3323E−04 
             
             
               Asphere 2 
               5.4520E−01 
               0.0000E+00 
                6.6605E−03 
               −1.9118E−02 
               5.4267E−03 
               −1.2105E−03 
             
             
               Asphere 3 
               4.2210E−01 
               0.0000E+00 
                3.6153E−02 
               −1.7355E−02 
               5.9225E−03 
               −1.0372E−03 
             
             
               Asphere 4 
               2.7460E−01 
               0.0000E+00 
               −1.3189E−02 
               −1.3661E−03 
               5.9801E−04 
               −4.8621E−05 
             
             
                 
             
           
        
       
     
   
   Example 2 
   Ray trace schematics for a lens with a wider angle field of view designed as an example of the invention is shown in a Z-shaped layout in  FIG. 7  and a U-shaped layout in  FIG. 8 . As in the lenses in Example 1, the optical performance and the optical surfaces are the same for both the Z-shaped layout and the U-shaped layout. A description of the lens design including surface curvatures, lateral distances, aperture sizes and materials is given in Table 3 below. The lens is designed for an f# of 3.2, a pixel size of 0.002 mm and a sensor with two mega pixels. The modulation transfer function chart is shown in  FIG. 10 . The difference between the Z-shaped layout and the U-shaped layout versions of the lens are in the thickness dimension of the lens assembly, as can be seen in Table 1 and in  FIGS. 7 and 8 , the Z-shaped layout lens is 3.15 mm thick while the U-shaped layout lens is only 2.56 mm thick. For clarification, a cross sectional schematic of the U-shaped layout lens assembly with elements  910  and  920  along with cover glass  305  and image sensor  460  is shown in  FIG. 9 . Based on the sensor size and the thickness, this design is well suited to use in a cell phone or a laptop computer or other application where thinness and a wider angle field of view is important. 
   
     
       
             
           
             
             
             
             
             
             
             
             
           
             
           
             
             
             
             
             
             
             
           
         
             
               TABLE 3 
             
             
                 
             
             
               Lens description for Example 2 with a 62 mm focal length 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
                 
                 
                 
               Thickness or 
               Aperature 
               Aperture 
                 
             
             
               Element # 
               Surface # 
               Radius 
               Shape 
               Separation 
               Dimension 
               Shape 
               Material 
             
             
                 
             
             
               1 
               1 
               Infinite 
               Flat 
               0.3000 
               1.732 
               Circular 
               NBK7 Schott 
             
             
               1 
               2 
               Infinite 
               Flat 
               0.1000 
               1.596 
               Circular 
             
             
               2 
               3 
               2.182 
               Asphere 1 
               1.2000 
               1.444 
               Circular 
               Zeonex-E48R 
             
             
               2 
               4 
               Infinite 
               Flat 
               −1.8700 
               2.339 
               Circular 
               Reflective 
             
             
               2 
               5 
               1.270 
               Asphere 2 
               −0.1728 
               2.015 
               Circular 
             
             
               3 
               6 
               1.164 
               Asphere 3 
               −1.0500 
               1.941 
               Circular 
               Polycarbonate 
             
             
               3 
               7 
               Infinite 
               Flat 
               1.0500 
               3.880 
               Circular 
               Reflective 
             
             
               3 
               8 
               2.837 
               Asphere 4 
               0.5000 
               3.311 
               Circular 
             
             
               Image 
                 
               Infinite 
               Flat 
                 
               3.496 
             
             
                 
             
           
        
         
             
               Aspheric Constants 
             
             
               Z = (VY{circumflex over ( )}2/SQRT(1 + (1 − (1 + K)(C{circumflex over ( )}2Y{circumflex over ( )}2)))) + AY{circumflex over ( )}4 + BY{circumflex over ( )}6 + CY{circumflex over ( )}8 + DY{circumflex over ( )}10 
             
           
        
         
             
               Asphere # 
               V 
               K 
               A 
               B 
               C 
               D 
             
             
                 
             
             
               Asphere 1 
               4.5820E−01 
               0.0000E+00 
               −5.6310E−03 
               −2.5584E−03 
               1.9920E−03 
               −6.4583E−03 
             
             
               Asphere 2 
               7.8720E−01 
               0.0000E+00 
                2.3760E−02 
               −2.1772E−02 
               1.9544E−01 
               −7.2848E−02 
             
             
               Asphere 3 
               8.5920E−01 
               0.0000E+00 
                1.4551E−01 
               −4.4757E−01 
               4.4868E−01 
               −1.8946E−01 
             
             
               Asphere 4 
               3.5250E−01 
               0.0000E+00 
               −1.3026E−01 
                4.6514E−02 
               −1.3216E−02  
                1.4327E−03 
             
             
                 
             
           
        
       
     
   
   Example 3 
   Lenses with a telephoto angle field of view lens and a larger image sensor were designed as yet a further example of the invention. Ray trace schematics for a telephoto lens designed as an example of the invention are shown in a Z-shaped layout in  FIG. 11  and a U-shaped layout in  FIG. 12 . As in the lenses in Examples 1 and 2, the optical performance and the optical surfaces are the same for both the Z-shaped layout and the U-shaped layout. A description of the lens design including surface curvatures, lateral distances, aperture sizes and materials is given in Table 4 below. In this case, the lens is designed for an f# of 3.2, a pixel size of 0.003 mm and a sensor with two mega pixels. The modulation transfer function chart is shown in  FIG. 14 . The difference between the Z-shaped layout and the U-shaped layout versions of the lens are in the thickness dimension of the lens assembly, as can be seen in Table 1 and in  FIGS. 11 and 12 , the Z-shaped layout lens is 6.34 mm thick while the U-shaped layout lens is only 5.69 mm thick. For clarification, a cross sectional schematic of the U-shaped layout lens assembly is shown with elements  1310  and  1320  along with cover glass  305  and image sensor  460  in  FIG. 13 . Based on the sensor size and the thickness, this design is also well suited to use in a cell phone or a laptop computer or other application where thinness and a telephoto angle field of view is important. 
   
     
       
             
           
             
             
             
             
             
             
             
             
           
             
           
             
             
             
             
             
             
             
           
         
             
               TABLE 4 
             
             
                 
             
             
               Lens description for Example 3 with a 107 mm focal length 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
                 
                 
                 
                 
               Thickness or 
               Aperature 
               Aperture 
                 
             
             
               Element # 
               Surface # 
               Radius 
               Shape 
               Separation 
               Dimension 
               Shape 
               Material 
             
             
                 
             
             
               1 
               1 
               Infinite 
               Flat 
               0.3000 
               4.784 
               Circular 
               NBK7 Schott 
             
             
               1 
               2 
               Infinite 
               Flat 
               0.1000 
               4.72 
               Circular 
             
             
               2 
               3 
               8.008 
               Asphere 1 
               2.7500 
               4.688 
               Circular 
               Zeonex-E48R 
             
             
               2 
               4 
               Infinite 
               Flat 
               −7.0040 
               6.754 
               Circular 
               Reflective 
             
             
               2 
               5 
               4.273 
               Asphere 2 
               −0.1000 
               4.905 
               Circular 
             
             
               3 
               6 
               4.93  
               Asphere 3 
               −9.0612 
               4.767 
               Circular 
               Polycarbonate 
             
             
               3 
               7 
               Infinite 
               Flat 
               2.0000 
               6.51 
               Circular 
               Reflective 
             
             
               3 
               8 
               8.628 
               Asphere 4 
               1.0000 
               5.622 
               Circular 
             
             
               Image 
                 
               Infinite 
               Flat 
                 
               6.001 
             
             
                 
             
           
        
         
             
               Aspheric Constants 
             
             
               Z = (VY{circumflex over ( )}2/SQRT(1 + (1 − (1 + K)(C{circumflex over ( )}2Y{circumflex over ( )}2)))) + AY{circumflex over ( )}4 + BY{circumflex over ( )}6 + CY{circumflex over ( )}8 + DY{circumflex over ( )}10 
             
           
        
         
             
               Asphere # 
               V 
               K 
               A 
               B 
               C 
               D 
             
             
                 
             
             
               Asphere 1 
               1.2490E−01 
               0.0000E+00 
               −1.1073E−04 
               −5.7443E−06 
               5.8261E−07 
               −7.2893E−08 
             
             
               Asphere 2 
               2.3410E−01 
               0.0000E+00 
               −3.5903E−04 
               −2.7866E−04 
               2.7053E−05 
               −1.5048E−06 
             
             
               Asphere 3 
               2.0290E−01 
               0.0000E+00 
                1.2061E−03 
               −2.4682E−04 
               2.7606E−05 
               −1.4681E−06 
             
             
               Asphere 4 
               1.1590E−01 
               0.0000E+00 
               −6.5592E−04 
                1.1303E−04 
               −2.3992E−05  
                2.3945E−06 
             
             
                 
             
           
        
       
     
   
   Example 4 
   The lens described in Example 2 is modified as shown in  FIG. 15  to include alignment features  1510 . In this case, alignment features  1510  guide the two lens elements  1520  and  1530  into a position during assembly wherein the refractive and reflective surfaces are aligned relative to one another. In a preferred embodiment, the alignment features are manufactured at the same time as the refractive and reflective surfaces to improve the accuracy of the relative alignment. The lens elements  1510  and  1520  are then molded to produce the refractive and reflective surfaces along with the alignment features. Other alignment features can likewise be manufactured within the scope of the invention along with the refractive and reflective surfaces to aid in aligning the lens into a structural element or to aid in alignment with the image sensor or an autofocus element. 
   The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope of the invention. 
   
     
       
             
             
           
         
             
               PARTS LIST 
             
             
                 
             
           
           
             
               100 
               refractive surface 
             
             
               110 
               reflective surface 
             
             
               120 
               refractive surface 
             
             
               130 
               refractive surface 
             
             
               140 
               reflective surface 
             
             
               150 
               reflective surface 
             
             
               160 
               refractive surface 
             
             
               170 
               infrared filter and cover glass for sensor 
             
             
               180 
               image sensor 
             
             
               210 
               prism element 
             
             
               230 
               refractive element 
             
             
               240 
               refractive element 
             
             
               250 
               refractive element 
             
             
               255 
               refractive element 
             
             
               260 
               refractive element 
             
             
               270 
               prism element 
             
             
               275 
               infrared filter and cover glass for sensor 
             
             
               285 
               image sensor 
             
             
               305 
               cover glass 
             
             
               310 
               reflective surface S2 for moderate angle 
             
             
                 
               lens design with Z-shaped layout 
             
             
               340 
               reflective surface S5 for moderate angle 
             
             
                 
               lens design with Z-shaped layout 
             
             
               355 
               optical axis 
             
             
               360 
               image sensor 
             
             
               400 
               refractive surface 
             
             
               410 
               reflective surface 
             
             
               420 
               refractive surface 
             
             
               430 
               refractive surface 
             
             
               440 
               reflective surface 
             
             
               450 
               refractive surface 
             
             
               455 
               optical axis perpendicular to image sensor 
             
             
               460 
               image sensor 
             
             
               510 
               first element 
             
             
               520 
               second element 
             
             
               910 
               element 
             
             
               920 
               element 
             
             
               1310 
               element 
             
             
               1320 
               element 
             
             
               1510 
               alignment features 
             
             
               1520 
               element 
             
             
               1530 
               element