Patent Publication Number: US-2007097506-A1

Title: Image stabilizing optical system

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application claims the priority benefit of Taiwan application serial no. 94138536, filed on Nov. 3, 2005. All disclosure of the Taiwan application is incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an optical system. More particularly, the present invention relates to an optical system with image stabilizing capability.  
      2. Description of the Related Art  
      With continuous improvement of image-sensing devices, micro-storage medium, and the reduced production cost, a digital camera market continues to expand, leading to a greater demand for more expensive single lens cameras. However, a user did not hold the camera steady when taking a picture, the image captured by the camera will be fuzzy due to the shake. In particular, when a high magnification telescopic lens is used for capturing an image, minor vibration can cause significant fuzziness in the final picture. Hence, a means of minimizing the shaking of cameras for producing a clearer image is always a major research topic for camera manufacturers.  
      As shown in  FIG. 1A , there is no shaking in a period that the camera shutter is opened, then the light from a target point A 10  is steadily focused on an image point M 10  on an image-sensing device  30 . However, there is some shaking in the period that the camera shutter is opened, the focus point of the light from the target point A 10  shifts from the image point M 10  to another image point M 12  as shown in  FIG. 1B . In the way, the image obtained by the image-sensing device (or a film negative)  30  is fuzzy. To minimize the fuzziness in the image due to shakes, one conventional method is to provide a mechanism for moving the lens  20  as soon as the camera shakes as shown in  FIG. 1C . Thus, the light from the target point A 10  remains to be focused on the image point M 10  of the image-sensing device  30 . In another conventional method, the image-sensing device  30  is moved instead to compensate for the shaking.  
      All in all, regardless of the technique used for counteracting the shakes, sophisticated mechanism needs to be installed on either the image-sensing device or the lens so that a real-time correction for any motion in the camera can be effected. These sophisticated mechanism not only is expensive, slow to respond and difficult to assemble, but also produces considerable noise due to mechanical friction, reducing its overall reliability. Moreover, if the correcting mechanism is driven by electric power, the power consumption of the camera increases, which is shorten the working time of the battery.  
     SUMMARY OF THE INVENTION  
      Accordingly, at least one objective of the present invention is to provide an image stabilizing optical system suitable for reducing fuzzy image due to system shakes.  
      To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides an image stabilizing optical system with an optical axis. The optical system includes at least a first lens group and a light deflection element. The first lens group includes a plurality of lenses lined along the optical axis. The light deflection element is disposed along the optical axis and located inside or outside the first lens group. The light deflection element comprises two substrates and a liquid crystal layer between the substrates. Furthermore, two electrode layers are respectively disposed on surfaces of the substrates that contact the liquid crystal layer. An electric field applied to the liquid crystal layer to vary the refractive index of the liquid crystal layer is controlled by the electrode layers. An included angle exists between the substrates.  
      The image stabilizing optical system further includes a second lens group disposed along the optical axis on one side of the first lens group. The second lens group is suitable for moving along the optical axis to zoom in or zoom out.  
      The image stabilizing optical system further includes an image-sensing device disposed along the optical axis and on the image-forming surface of the first lens group. The light deflection element is used for stabilizing the image on the image-sensing device. The light deflection element could be disposed between the first lens group and the image-sensing device. The image-sensing device is a complementary metal-oxide-semiconductor (CMOS) or a charge coupled device (CCD).  
      The image stabilizing optical system further includes a controller electrically connected to the light deflection element for controlling the electric field strength applied to the liquid crystal layer. The controller includes a displacement-sensing module and a microprocessor, for example. The displacement-sensing module is used for detecting displacement of the optical system. The microprocessor is electrically connected to the displacement-sensing module and the light deflection element for changing the electric field strength applied to the liquid crystal layer according to a detection result obtained by the displacement-sensing module. The displacement-sensing module comprises a horizontal displacement sensor and a vertical displacement sensor.  
      The first lens group in the image stabilizing optical system is also adapted to moving along the optical axis for zooming in or zooming out. The liquid crystal layer is a nematic liquid crystal layer, for example. The electrode layers are made of a material such as indium tin oxide (ITO) or indium zinc oxide (IZO), for example.  
      In brief, the image stabilizing optical system in the present invention utilizes an electric field applied to the liquid crystal layer of the light deflection element to change the refractive index and produce the light deflection effect. Therefore, without any moving element, the present invention compensates for the shifted image resulted from a shaky optical system so that fuzzy images are prevented.  
      It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings,  
       FIGS. 1A through 1C  are schematic diagrams showing a stabilizing mechanism inside a conventional camera.  
       FIG. 2  is a diagram showing the image stabilizing optical system according to a first embodiment of the present invention.  
       FIG. 3  is a diagram showing the light deflection element in the image stabilizing optical system according to a third embodiment of the present invention.  
      FIGS.  4 ˜ 6  are diagrams showing the image stabilizing optical systems according to another three kinds of embodiments of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.  
      The image stabilizing image system in the present invention comprises at least a lens group and a light deflection element. The lens group includes at least one lens and the lens and the light reflection element are lined along an optical axis. To simplify the description, four lens groups are used in the embodiment.  
      As shown in  FIG. 2 , the image stabilizing optical system  200  in the present invention has an optical axis  205 . The image stabilizing optical system  200  includes a first lens group G 1  and a light deflection element  210 . The first lens group G 1  has a plurality of lenses L 10  disposed on and lined along the optical axis  205 . The light deflection element  210  is also disposed along the optical axis  205  and located inside the first lens group G 1  or outside the first lens group G 1 . In the present embodiment, the light deflection element  210  is located outside the first lens group G 1 . However, the light deflection element  210  is also disposed between any two lenses L 10  or between the lenses of other lens group or between lens groups themselves. In general, there is no specific limitation on the position of the light deflection element  210 .  
      As shown in  FIG. 3 , the light deflection element  210  comprises a pair of substrates  212  and a liquid crystal layer  214  disposed between the substrates  212 . Two electrode layers  216  are respectively disposed on surfaces of the substrates  212  that contact the liquid crystal layer  214 . An electric field is applied to the liquid crystal layer  214  through the electrode layers  216  so that the liquid crystal molecules inside the liquid crystal layer  214  change their alignment direction according to the strength of the electric field. Because the liquid crystal molecules have a single axis with double refraction property (that is, having mutually perpendicular fast axis and slow axis in a single axle direction), the refractive index of the liquid crystal layer will vary when the liquid crystal molecules change direction controlled by the electric field. Furthermore, an included angle  0  exists between the substrates  212 . In other words, the two substrates  212  are not parallel to each other, but rather form a wedge-shaped panel. The electrode layers  216  are made of indium tin oxide (ITO), indium zinc oxide (IZO) or some other transparent conductive materials, for example. The liquid crystal layer  214  is a nematic liquid crystal layer or a liquid crystal layer in other types, for example. The substrate  212  is a glass substrate or other transparent substrate, for example.  
      As shown in  FIGS. 2 and 3 , the refractive index of the light deflection element  210  is different from the refractive index of the external medium (for example, air). Furthermore, the light deflection element  210  has a wedge shape so that light passing through the light deflection element  210  is deflected. The relation of the included angle θ between the two substrate  212 , the refractive index n, of the liquid crystal layer  214 , the refractive index n 2  of the external medium and the deflection angle δ after penetrating through the light deflection element  210  is given by: δ=(n 1 −n 2 )θ. In the present embodiment, the external medium (air) has a refractive index 1, so that δ=(n 1 −1)θ. Based on this relation, changing the electric field strength applied to the liquid crystal layer  214  varies the refractive index n, of the liquid crystal layer  214  when the image stabilizing optical system  200  shakes. Hence, the light is deflected to prevent a shifted image from causing a fuzzy image.  
      Since the image stabilizing optical system  200  prevents any shifting in the image through controlling the electric field strength applied to the light deflection element  210  alone, there is no need to move the first lens group G 1  or the image-sensing device  220  (described hereafter) as in the conventional technique. In other words, the image stabilizing optical system  200  in the present invention not only eliminates the cost of producing complicated driving mechanism and minimizes the difficulties in assembling them, but also avoids the noise resulting from mechanical friction and lower reliability due to the mechanical elements. Moreover, considerable energy for driving the mechanism is saved. In addition, the light deflection element  210  provides a faster response and operates with better reliability than the moving mechanism used in the conventional technique.  
      In the present invention, the number of light deflection elements  210  used inside the optical system  200  is not limited. In general, the number of light deflection elements  210  depends on the actual requirements. In addition, the image stabilizing optical system  200  further includes a second lens group G 2  or even a third lens group G 3  and/or a fourth lens group G 4  disposed on the optical axis  205 . The number of lens groups changes according to the actual design. Furthermore, at least two of the lens groups G 1 ˜G 4  are adapted to moving along the optical axis  205  for zooming in or zooming out purpose such as magnification or reduction.  
      The image stabilizing optical system  200  further includes an image-sensing device  220  disposed on the optical axis  205  and located in an image-forming surface after the light passed through all the lens groups. The image-sensing device  220  is used for detecting the light that passed through the lens groups G 1 ˜G 4  and arrived at the light deflection element  210  and converting the light into image signals. Meanwhile, through the light deflection element  210 , the image falling on the image-sensing device  220  is stabilized. The image-sensing device  220  is a complementary metal-oxide-semiconductor (CMOS), a charge-coupled device (CCD) or other types of image-sensing device.  
      In addition, the image stabilizing optical system  200  further includes a controller  230  electrically connected to the light deflection device  210  for controlling the electric field strength applied to the liquid crystal layer  214 . More specifically, the controller  230  comprises a displacement-sensing module  240  and a microprocessor  250 . The displacement-sensing module  240  is a device for sensing any displacement of the image stabilizing optical system  200  and the microprocessor  250  controls the electric field strength applied to the liquid crystal layer  214  according to the detection result obtained by the displacement-sensing module  240 . Moreover, the displacement-sensing module  240  comprises a horizontal displacement sensor  242  and a vertical displacement sensor  244  so that the amount of horizontal and vertical displacement in the image stabilizing optical system  200  is measured separately.  
      In the aforementioned embodiment, the light deflection element  210  is located outside the first lens group G 1 . However, the light deflection element  210  could be disposed between the first lens group G 1  and the image-sensing device  220  and other positions as illustrated in the following embodiments.  
      As shown in  FIG. 4 , the light deflection element  210  in the image stabilizing optical system  400  of the present embodiment is disposed between the fourth lens group G 4  and the image-sensing device  220 . Because the fourth lens group G 4  and the image-sensing device  220  are separated from each other by a distance, the insertion of F the light deflection element  210  between them is not necessary to increase the overall length of the image stabilizing optical system  400 . Thus, the demand for an optical system with a simpler configuration is met.  
      As shown in  FIG. 5 , the light deflection element  210  in the image stabilizing optical system  500  of the present embodiment is disposed between the second lens group G 2  and the third lens group G 3 . In practice, the light deflection element  210  is also disposed between the first lens group G 1  and the second lens group G 2  or between the third lens group G 3  and the fourth lens group G 4 . Obviously, if additional lens groups are installed in the image stabilizing optical system  500 , the light deflection element  210  is disposed between any two of the lens groups according to the design.  
      As shown in  FIG. 6 , the light deflection element  210  in the image stabilizing optical system  600  of the present embodiment is disposed between the lens L 31  and the lens L 32  of the third lens group G 3 . Similarly, because there is already a gap separating the lens L 31  from the lens L 32  inside the third lens group G 3 , the insertion of the light deflection element  210  between them is not necessary to increase the overall length of the image stabilizing optical system  600 . Hence, the demand for an optical system with a simpler configuration is met. In addition, the sensitivity to any shifting is higher within the third lens group G 3  (for example, between the lens L 31  and the second lens L 32 ). Therefore, image shifting can be corrected much faster when the light deflection element  210  is disposed in this position. As a result, the image stabilizing optical system  600  has higher shaking compensation sensitivity. Obviously, the light deflection element  210  is disposed anywhere within the lens groups.  
      In summary, the image stabilizing optical system in the present invention utilizes an electric field applied to the liquid crystal layer of the light deflection element to change the refractive index and deflect the light when the optical system shakes.: Hence, the image-sensing device is prevented from receiving a shifted and fuzzy image. Because the present invention requires no moving parts to compensate for the shifted image resulting from shakes the cost for producing the components of a complicated mechanism and the time for assembling the components together are entirely eliminated. Moreover, without any moving mechanical components, less noise is produced and the optical system has better reliability. Meanwhile, the light deflection element also consumes less power and has a quicker response to motion.  
      It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.