TECHNICAL FIELD  
       [0001]     The present invention generally relates to assembling and testing devices and methods for employing the same and, more particularly, to an assembling and testing device for assembling and testing lens units and a method of assembling and testing lens units.  
       BACKGROUND  
       [0002]     With the rapid development of multimedia technology, use of digital devices such as digital still cameras (“still cameras”) and digital video cameras (“video cameras”) has become wide-spread in many countries. Furthermore, more and more mobile phones and PDAs (personal digital assistants) are combined with digital lens units. Therefore, lens units are in great demand. Nowadays, lens units are still very expensive due to the high rejection during quality control.  
         [0003]     Generally, when assembling lenses, lens pieces, spacers, aperture pieces and other elements are pressed into a barrel so as to form a lens unit. Then modulation transfer function (MTF) testing is applied to test clarity and contrast of the lens unit. Before pressing the lens pieces, spacers, aperture pieces and other elements into the barrel, pressing parameters such as pressure and pressing velocity are predetermined so as to obtain flawless lens units. However, if the pressing parameters are changed during assembly, many flawed lens units may be produced before the change in pressing parameters is discovered.  
         [0004]     What is needed, therefore, is an assembling and testing device, which overcomes the above-described problems.  
       SUMMARY  
       [0005]     In one aspect thereof, an apparatus for assembling and testing a lens unit having a barrel and a lens group includes an assembling device, a testing device and a mounting member. The assembling device is used to assemble the lens group into the barrel to form the lens unit. The testing device is used to test the assembled lens unit. The mounting member is configured for carrying the lens unit in a manner so as to move the lens unit along a circle from a first position where the assembling device performs the assembling to a second position where the testing device performs the testing.  
         [0006]     In another aspect thereof, a method of assembling and testing lens units having a barrel and a lens group comprising the following steps: mounting a first barrel on a mounting member; rotating the mounting member; pressing a first lens group into the first barrel to form a first lens unit and mounting a second barrel on the mounting member at substantially the same time; testing the first lens unit using a testing device, pressing a second lens group into the second barrel to form a second lens unit, and mounting a third barrel on the mounting member at substantially the same time.  
         [0007]     Other advantages and novel features of preferred embodiments of the present invention will become more apparent from the following detailed description thereof when taken in conjunction with the accompanying drawing: 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0008]     Many aspects of the assembling and testing devices can be better understood with reference to the following drawing. The components in the drawing are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the assembling and testing devices. Moreover, in the drawing, like reference numerals designate corresponding parts throughout the view.  
         [0009]      FIG. 1  is a schematic, cross-sectional view in accordance with an embodiment of an assembling and testing device for lenses. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0010]     An assembling and testing device is provided for assembling a lens unit and testing MTF of the lens unit.  
         [0011]     Referring to  FIG. 1 , an embodiment of an assembling and testing device  100  for assembling and testing a lens unit  20  includes a pressing device  22 , a testing device (not labeled) and a mounting device  30 . The testing device includes a lampshade  24 , a light source  26 , a connecting member  27 , a MTF plate  28 , a supporting member  32 , a screen  34  and a reflective element  36 .  
         [0012]     The lens unit  20  includes a barrel  202 , at least one spacer  203  and a lens group  204  mounted in the barrel  202 . The barrel  204  is a hollow cylinder. The lens group  202  includes at least one lens mounted in the barrel  204 . The at least one spacer  203  are mounted between any two adjacent lenses. In this embodiment, two lenses and one spacer  203  are provided. The lens has an optical portion in the middle and a non-optical portion at a periphery of the optical portion. The spacer  203  is mounted between the two lenses. The lens and the spacer  203  are pressed into the barrel  202  to form the lens unit  20 .  
         [0013]     The pressing device  22  has a pressing end  220  defining a V-shaped cutout  222  to prevent the pressing end  220  from touching the optical portion of the lenses. The lampshade  24  is a hollow cylinder having a closed end and an open end. The light source  26  is located in the lampshade  24 .  
         [0014]     The connecting member  27  is a hollow cylinder having a hole  270  running through two ends thereof for allowing propagation of light therethrough. The connecting member  27  has a top surface  272 . The lampshade  24  is disposed on the connecting member  27 . The open end of the lampshade  24  faces the connecting member  27 .  
         [0015]     The MTF plate  28  is a patterned plate having a black-and-white striped pattern thereon. The MTF plate  28  is disposed on the top surface  272  of the connecting member  27  and between the connecting member  27  and the light source  26 .  
         [0016]     The mounting member  30  is a dish-shaped plate. Three light holes  302  are defined in the mounting member  30  in a pattern of an equilateral triangle wherein each light hole  302  defines a light path therethrough. That is, an angle defined by a hypothetical line connecting a center of the mounting member  30  and a center of one light hole  302  and a hypothetical line connecting the center of the mounting member  30  and a center of an adjacent light hole  302  is 120 degrees. A mounting hole  304  is defined in the center of the mounting member  30 . The pressing device  22  is positioned corresponding to a light path of one of the light holes  302 , and the connecting member  27  and the lampshade  24  are positioned corresponding to a light path of another one of the light holes  302 . That is, the pressing device  22  is set above one light hole  302 . The connecting member  27  and the lampshade  24  are set above another light hole  302  and have a central axis identical to that of the light hole  302 . During operation of the assembling and testing device  100 , the lens unit  20  is firmly mounted on the mounting member  30 , with the lens unit  20  positioned corresponding to the light path of one of the light holes  302 .  
         [0017]     The supporting member  32  is a hollow cuboid including a top board  320 , a bottom board  321  opposite to the top board  320  and an open side  326  adjacent to the top board  320  and the bottom board  321 . The top board  320  defines an opening  322  and forms a pole  324  engaged in the mounting hole  304  of the mounting member  30  allowing the mounting member  30  to rotate relative to the supporting member  32 . A distance between a center of the opening  322  and an axis of the pole  324  is equal to that between a center of each light hole  302  and a center of the mounting hole  304 . A mounting post  328  is formed in the supporting member  32  corresponding to the position of the opening  322 .  
         [0018]     The screen  34  is disposed at the open side  326  of the supporting member  32 . The reflective element  36  having a reflective surface  362  is fixed at an end of the mounting post  328 . The reflective surface  362  faces the opening  322  and the screen  34 . The reflective surface  362  is slanted at an angle of  45  degrees with respect of the screen  34 .  
         [0019]     When the assembling and testing device  100  works, firstly, one barrel  202  is fixedly mounted on the mounting member  30 . An axis of the barrel  202  is shares the same axis as one of the light holes  302 . Secondly, the mounting member  30  is automatically or manually rotated through an angle of 120 degrees so that the barrel  202  is under the pressing device  22 . The pressing device  22  presses the lens group  204  and the spacer  203  into the barrel  202  to form a lens unit  20 . Thirdly, the mounting member  30  is further rotated through an angle of  120  degrees so that the lens unit  20  corresponds to the light source  26  and the MTF plate  28 . Light from the light source  26  passes through the MTF plate  28  and the lens unit  20 , and is reflected by the reflective element  36  to radiate onto the screen  34 . The MTF of the lens unit  20  can be measured because the images on the screen  34  can show whether the lens unit  20  is flawed or not. Thereby, the MTF of the lens unit  20  is tested immediately after the lens unit  20  being produced.  
         [0020]     Therefore, we can know immediately whether the pressing parameters of the pressing device  22  are suitable or not, and the production of a mass of ineligible lens units  20  can be avoided. The three processes may be carried out at the same time to assemble and test three lens units  20  simultaneously That is, pressing a second lens group into a second barrel by the pressing device and testing a third lens unit by the testing device whilst a first barrel is mounted on the mounting member. Thus, an efficiency is highly improved.  
         [0021]     In alternative embodiments, the number of light hole  302  may be any such as one, two or four. The lampshade  24  and the connecting member  27  may be omitted.  
         [0022]     It is believed that the embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.
An apparatus ( 100) for assembling and testing a lens unit ( 20) having a barrel ( 202) and a lens group ( 204) includes an assembling device ( 22), a testing device and a mounting member ( 30). The assembling device is used to assemble the lens group into the barrel to form the lens unit. The testing device is used to test the assembled lens unit. The mounting member is configured for carrying the lens unit in a manner so as to move the lens unit along a circle from a first position where the assembling device performs the assembling to a second position where the testing device performs the testing.