Abstract:
Liquid lens cells are used in a compound variable power optical system that forms an intermediate image between the object and the final image. A first variable power optical component is located between the object and an intermediate real image. The first variable power optical component varies power to change the magnification of the intermediate real image. A second variable power optical component is located between the intermediate real image and the final image. The second variable power optical component varies power to change the magnification of the final image. At least one of the first and second variable power optical components is stationary on the optical axis and comprises at least two liquids with different refractive properties and at least one variable shape contact surface between the two liquids, with variations in the shape of the contact surface producing a change of optical power in the optical system.

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/753,639, filed Apr. 2, 2010, entitled “VARIABLE POWER OPTICAL SYSTEM,” which is set to issue as U.S. Pat. No. 8,638,496 on Jan. 28, 2014, which claims the benefit of priority of U.S. Provisional 61/168,523 filed Apr. 10, 2009. Each of the applications referenced in this paragraph is hereby incorporated by reference in its entirety so as to make part of this specification. 
    
    
     BACKGROUND 
     The present invention relates to variable power optical systems. 
     Some zoom lens designs group the lens used in the design, with one group being used largely for zooming, a second group being used largely for keeping an image in focus, and a third group used to keep the image plane stationary. A fourth group may also be used to form a sharp image. The focusing group may be adjusted for focusing the zoom lens at any focal length position without the need to refocus for other focal lengths of the zoom lens. The zooming group (or “variator”) causes significant magnification change during zooming. The lens group that stabilizes the image plane may also be used to provide magnification. 
     Desirable features in a zoom lens include high zoom ratio and a wide angle field of view. As the zoom range of a lens system increases, generally the length and weight also increases. Consumer products such as cellular telephones or point-and-shoot cameras are often small and lightweight, so zoom lenses included in those products are constrained by size and weight. Moreover, as the focal length range of a lens system increases, generally focusing problems also increase usually at the wide field of view zoom positions. 
     SUMMARY 
     Liquid lens cells comprise two or more fluids in a chamber. The fluids contact to form a surface that is variable by, for example, through electrical nodes. A fluid may be, for example, one or more gases, one or more liquids, or a mixture of one or more solids and one or more liquids. Using liquid lens cells to replace one or more moving lens groups results in additional configuration options for the optical path. Liquid cells can be used in a compound zoom lens system to take advantage of these properties. Many point and shoot cameras and cell phone cameras do not have large amounts of space for a long lens. Using liquid cells in combination with folds or redirection of the radiation axis allows for better zoom lens systems in these small camera packages. Larger cameras can also benefit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A-1D  are optical diagrams of a compound zoom lens system employing six liquid lens cells, with a surface of the liquids being varied to provide a range of zoom positions. 
         FIGS. 2A-2D  are optical diagrams of a compound zoom lens system employing five liquid lens cells, with a surface of the liquids being varied to provide a range of zoom positions. 
         FIGS. 3A-3D  are optical diagrams of a compound zoom lens system employing five liquid lens cells, with a surface of the liquids being varied to provide a range of zoom positions. 
         FIGS. 4A-4D  are optical diagrams of a compound zoom lens system employing four liquid lens cells, with a surface of the liquids being varied to provide a range of zoom positions. 
         FIGS. 5A-5D  are optical diagrams of a compound zoom lens system employing three liquid lens cells, with a surface of the liquids being varied to provide a range of zoom positions. 
         FIGS. 6A-6D  are optical diagrams of a compound zoom lens system employing three liquid lens cells, with a surface of the liquids being varied to provide a range of zoom positions. 
         FIGS. 7A-7D  are optical diagrams of a compound zoom lens system employing two liquid lens cells, with a surface of the liquids being varied to provide a range of zoom positions. 
         FIGS. 8A-8D  are optical diagrams of a compound zoom lens system employing a moving lens group and two liquid lens cells, with a surface of the liquids being varied to provide a range of zoom positions. 
         FIG. 9  illustrates a block diagram of a camera with a zoom lens. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, reference is made to the accompanying drawings. It is to be understood that other structures and/or embodiments may be utilized without departing from the scope of the invention. 
     Liquid lens cells can modify an optical path without relying upon mechanical movement of the liquid cell. A liquid lens cell comprising first and second contacting liquids may be configured so that a contacting optical surface between the contacting liquids has a variable shape that may be substantially symmetrical relative to an optical axis of the liquid lens cell. A plurality of lens elements could be aligned along a common optical axis and arranged to collect radiation emanating from an object side space and delivered to an image side space. The liquid lens cell could be inserted into an optical path formed by the plurality of lens elements that are aligned along the common optical axis. The optical axis of the liquid lens cell could be parallel to the common optical axis, or it could be at an angle or decentered to the common optical axis. 
     Presently contemplated liquid lens systems will have a difference in refractive index of about 0.2 or more, preferably at least about 0.3, and in some embodiments at least about 0.4. Water has a refractive index of about 1.3, and adding salt may allow varying the refractive index to about 1.48. Suitable optical oils may have a refractive index of at least about 1.5. Even by utilizing liquids with higher, lower or higher and lower refractive indices, for example a higher refractive index oil, the range of power variation remains limited. This limited range of power variation usually provides less magnification change than that of a movable lens group. Therefore, in a simple variable power optical system, to provide zooming while maintaining a constant image surface position most of the magnification change may be provided by one movable lens group and most of the compensation of defocus at the image surface during the magnification change may be provided by one liquid cell. 
     It should be noted that more movable lens groups or more liquid cells, or both, may be utilized. Examples of one or more moving lens groups used in combination with one or more liquid cells is described in U.S. patent application Ser. No. 12/246,224 titled “Liquid Optics Zoom Lens and Imaging Apparatus,” filed Oct. 6, 2008, and incorporated by reference in its entirety. 
     The size and properties of lens elements used in a system introduce constraints to be considered in designing the lens system. For example, the diameter of one or more lens elements may limit the size of an image formed on an image surface. For lens systems with variable properties, such as a variable power optical system, the optics may change based on variation of the lens elements. Thus, a first lens element may constrain a lens system in a first zoom configuration, while a second lens element constrains the lens system in a second zoom configuration. As an example, the rim rays for a light beam may approach the outer edge of a lens element at one extreme of the zoom range, while being a significant distance from the outer edge of the same lens element at the other extreme of the zoom range. 
       FIGS. 1A-1D  illustrate optical diagrams of a simplified compound variable power optical system that forms an intermediate image  108  and a final image  107 . As illustrated the stop  109  is located just after liquid lens cell  104  in the relay portion of the lens. The variable power optical system may be used, for example, with a camera.  FIG. 1A  illustrates the zoom ratio in the wide position, and  FIG. 1D  illustrates the zoom ratio in the telephoto position. 
     The variable power optical system illustrated in  FIGS. 1A-1D  has no moving lens groups. Instead, the zooming and a constant focus at the final image is accomplished through six liquid lens cells  101 ,  102 ,  103 ,  104 ,  105  and  106 , with each liquid lens cell having a variable surface  111 ,  112 ,  113 ,  114 ,  115  and  116 . A control system may be used to control the variable shape of the contacting optical surface in liquid lens cells  101 ,  102 ,  103 ,  104 ,  105  and  106 . 
     It is to be understood that liquid lens cells could each comprise multiple surfaces, with the surfaces being controllable and/or fixed. In some embodiments, the liquid lens cells could comprise a combination of two or more liquid cells. A plate may be placed between the combined cells. The plate may have an optical power that may be set as desired for the design. The liquid lens cells may also have plates on the exterior surfaces. In some embodiments, the plates on the exterior surfaces may provide optical power or a folding function. The plates and other lens elements can be spherical or aspherical to provide improved optical characteristics. 
     The individual lens elements may be constructed from solid-phase materials, such as glass, plastic, crystalline, or semiconductor materials, or they may be constructed using liquid or gaseous materials such as water or oil. The space between lens elements could contain one or more gases. For example normal air, nitrogen or helium could be used. Alternatively the space between the lens elements could be a vacuum. When “Air” is used in this disclosure, it is to be understood that it is used in a broad sense and may include one or more gases, or a vacuum. The lens elements may have coatings such as an ultraviolet ray filter. 
     Liquids in a liquid lens cell may have a fixed volume, and the shape of the outer surface of the liquid lens cell may be fixed. In the accompanying figures, some of the liquid lens cells are illustrated in a way that suggest variation in the volume of liquids and/or variation in the shape of the outer surface of the liquid lens cell. This also means the vertex points of the surfaces shift axially. The illustrations were generated with computer software without placing constraints on volume or shape of the liquid lens cells. The accompanying figures illustrate the concepts of using liquid lens cells in a variable power optical system, and appropriate modifications may be made for the various liquid lens cells that may be used. 
     The lens elements illustrated in  FIGS. 1A-1D  are arranged to form an intermediate image  108 . Although the location and size of the intermediate image  108  changes as the zoom position changes, it remains between liquid lens cells  101  and  102 . Although  FIGS. 1A-1D  illustrate an objective optics group followed by a relay optics group, multiple relay optics groups could also be used to achieve higher magnifications. Additional magnification can be achieved with high refractive index fluids. 
     Using liquid lens cells to replace one or more moving lens groups results in additional configuration options for the optical path. Replacing moving lens groups with liquid lens cells facilitates additional design possibilities. For example, a linear optical design may result in a lens that is longer than desired. The use of liquid lens cells instead of a moving group facilitates the use of optical elements such as folds to redirect the radiation axis and reduce the physical length of a lens. Although the overall length of the optical path through the lens may remain the same, the liquid lens cells may provide strategic space for folding that reduces the length in one or more directions. This allows longer overall lens lengths to be used in smaller camera packages. For example, many point and shoot cameras and cell phone cameras do not have large amounts of space for a long lens. Using liquid cells in combination with folds allows for better lens systems in these small camera packages. Larger cameras can also benefit from reducing the camera package length that would be required for a lens system that did not use folds. Using liquid lens cells may also allow for a smaller diameter, especially towards the front of the lens design and especially for wide field of view positions. Folding in combination with a relatively small front diameter, as compared to conventional moving group zoom lens designs, may provide for more compact and ergonomically shaped camera packages. 
       FIGS. 2A-2D  illustrate optical diagrams of a simplified compound variable power optical system using five liquid cells  121 ,  122 ,  123 ,  124 , and  125 , with each liquid lens cell having a variable surface  131 ,  132 ,  133 ,  134 , and  135 . The stop  129  is located just after liquid cell  123  in the relay optics group. The optical system forms an intermediate image  128  and a final image  127 . 
       FIGS. 3A-3D  illustrate optical diagrams of a simplified compound variable power optical system using five liquid cells  121 ,  122 ,  123 ,  124 , and  125 , with each liquid lens cell having a variable surface  131 ,  132 ,  133 ,  134 , and  135 . This design is similar to the design illustrated in  FIGS. 2A-2D , but the stop  129  is located in the objective optics group. This may improve the image quality and may allow for liquid cells with smaller diameters, but may also reduce the relative illumination. 
       FIGS. 4A-4D  illustrate optical diagrams of a simplified compound variable power optical system using four liquid cells  141 ,  142 ,  143 , and  144 , with each liquid lens cell having a variable surface  151 ,  152 ,  153 , and  154 . The stop  149  is located in the relay lens group. The optical system forms an intermediate image  148  and a final image  147 . 
       FIGS. 5A-5D  illustrate optical diagrams of a simplified compound variable power optical system using three liquid cells  161 ,  162 , and  163 , with each liquid lens cell having a variable surface  171 ,  172 , and  173 . The stop  169  is located in the relay lens group. The optical system forms an intermediate image  168  and a final image  167 . 
       FIGS. 6A-6D  illustrate optical diagrams of a simplified compound variable power optical system using three liquid cells  161 ,  162 , and  163 , with each liquid lens cell having a variable surface  171 ,  172 , and  173 . The stop  169  is located in the objective lens group. The optical system forms an intermediate image  168  and a final image  167 . 
       FIGS. 7A-7D  illustrate optical diagrams of a simplified compound variable power optical system using two liquid cells  181  and  182 , with each liquid lens cell having a variable surface  191  and  192 . The stop  189  is located in the objective lens group. The optical system forms an intermediate image  188  and a final image  187 . 
       FIGS. 8A-8D  illustrate optical diagrams of a simplified compound variable power optical system using two liquid cells  201  and  202 , with each liquid lens cell having a variable surface  211  and  212 . The illustrated embodiment also has a moving lens group  203 . An intermediate image is formed at image surface  208 , between the liquid cells  201  and  202 . The configuration of optical elements results in a final image  207  that is larger than the final images obtained in earlier embodiments. This allows the use of a larger image sensor, such as sensors 11 mm to 28 mm and above. A moving lens group is used near the sensor because the diameter of a liquid cell may not be sufficiently large to achieve the desired performance. Of note, the final image  207  is also larger than the rim rays at the liquid lens cell variable surface  211  and  212 . 
     For each of the lens designs shown in  FIGS. 1-8 , a listing produced by the CodeV optical design software version 9.70 commercially available from Optical Research Associates, Pasadena, Calif. USA is attached hereto as part of this specification and incorporated by reference in its entirety. 
     The lens designs shown in  FIGS. 1-8  provide a relatively high zoom ratio, as can be seen from the range of focal lengths of the lens designs listed in TABLE 1. For example, the lens designs in  FIGS. 1-8  respectively provide zoom ratios of about 4.4× (F4/F1=−15.6497/−3.5462), 3.3× (−23.9964/−7.2007), 3.3× (−23.9985/−7.2005), 3.3× (−23.9965/−7.2), 3× (−22.046/−7.351), 3× (−22.0489/−7.3514), 2.8× (−21.9962/−7.8524), and 2.8× (−55.7271/−20.0878). 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Effective Focal Length for Lens Designs 
               
             
          
           
               
                 Lens Design Figure 
                 Position 1 
                 Position 2 
                 Position 3 
                 Position 4 
               
               
                   
               
             
          
           
               
                 FIG. 1 
                 −3.5462 
                 −5.4545 
                 −8.9999 
                 −15.6497 
               
               
                 FIG. 2 
                 −7.2007 
                 −10.3000 
                 −15.4998 
                 −23.9964 
               
               
                 FIG. 3 
                 −7.2005 
                 −10.2999 
                 −15.4999 
                 −23.9985 
               
               
                 FIG. 4 
                 −7.2000 
                 −10.2999 
                 −15.4990 
                 −23.9965 
               
               
                 FIG. 5 
                 −7.3510 
                 −10.2999 
                 −15.4979 
                 −22.0460 
               
               
                 FIG. 6 
                 −7.3514 
                 −10.3000 
                 −15.5003 
                 −22.0489 
               
               
                 FIG. 7 
                 −7.8524 
                 −10.3484 
                 −15.8485 
                 −21.9962 
               
               
                 FIG. 8 
                 −20.0878 
                 −25.9451 
                 −40.0379 
                 −55.7271 
               
               
                   
               
             
          
         
       
     
       FIG. 9  illustrates a block diagram of a camera  100  with a zoom lens  102 .  FIG. 9  also illustrates a lens control module  104  that controls the movement and operation of the lens groups in lens  102 . The control module  104  includes electronic circuitry that controls the radius of curvature in the liquid lens cell. The appropriate electronic signal levels for various focus positions and zoom positions can be determined in advance and placed in one or more lookup tables. Alternatively, analog circuitry or a combination of circuitry and one or more lookup tables can generate the appropriate signal levels. In one embodiment, one or more polynomials are used to determine the appropriate electronic signal levels. Points along the polynomial could be stored in a lookup table or the polynomial could be implemented with circuitry. The lookup tables, polynomials, and/or other circuitry may use variables for zoom position, focus position, temperature, or other conditions. 
     Thermal effects may also be considered in the control of the radius of curvature of surface between the liquids. The polynomial or lookup table may include an additional variable related to the thermal effects. 
     The control module  104  may include preset controls for specific zoom settings or focal lengths. These settings may be stored by the user or camera manufacturer. 
       FIG. 9  further illustrates an image capture module  106  that receives an optical image corresponding to an external object. The image is transmitted along an optical axis through the lens  102  to the image capture module  106 . The image capture module  106  may use a variety of formats, such as film (e.g., film stock or still picture film), or electronic image detection technology (e.g., a CCD array, CMOS device or video pickup circuit). The optical axis may be linear, or it may include folds. 
     Image storage module  108  maintains the captured image in, for example, on-board memory or on film, tape or disk. In one embodiment, the storage medium is removable (e.g., flash memory, film canister, tape cartridge or disk). 
     Image transfer module  110  provides transferring of the captured image to other devices. For example, the image transfer module  110  may use one or a variety of connections such as, for example, a USB port, IEEE 1394 multimedia connection, Ethernet port, Bluetooth wireless connection, IEEE 802.11 wireless connection, video component connection, or S-Video connection. 
     The camera  100  may be implemented in a variety of ways, such as a video camera, a cell phone camera, a digital photographic camera, or a film camera. 
     The liquid cells in the focus and zoom groups could be used to provide stabilization, as described in U.S. patent application Ser. No. 12/327,666 titled “Liquid Optics Image Stabilization,” filed Dec. 3, 2008, incorporated by reference in its entirety. By using non-moving lens groups, folds may be used to reduce the overall size as described in U.S. patent application Ser. No. 12/327,651 titled “Liquid Optics with Folds Lens and Imaging Apparatus,” filed Dec. 3, 2008, incorporated by reference in its entirety. One or more moving lens groups may be used in combination with one or more liquid cells as described in U.S. patent application Ser. No. 12/246,224 titled “Liquid Optics Zoom Lens and Imaging Apparatus,” filed Oct. 6, 2008, incorporated by reference in its entirety. 
     It is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the invention as defined by the appended claims.