Abstract:
A telecentric zoom lens having telecentric forming aperture optically and preferably mechanically intermediate an objective lens and a zoom group. The aperture is fixed along an optical axis and selected to provide a constant speed on an image side of the lens system. The location of the aperture relative to the zoom group maintains telecentricity of the lens in object space.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to zoom lenses and more particularly, to a telecentric zoom lens having a telecentric forming aperture mechanically intermediate an objective lens and a zoom group.  
         BACKGROUND OF THE INVENTION  
         [0002]    Telecentric optical systems are often employed in a measuring projector. The measuring projector allows a measurement of various values by illuminating the profile of an object to be measured, projecting the profile onto a screen, enlarging the projected image by a projection optical system and comparing the projection with a reference figure on the screen. For such systems, it is preferable that the projection be telecentric. That is, a principal ray passes through the optical system parallel with the optical axis.  
           [0003]    However, the need exists for a telecentric zoom lens system having a reduced level of distortion in low tolerance applications. A further need exists for a telecentric zoom lens that has inherent color correction and reduced aberrations. A need also exists for a telecentric zoom lens that provides a constant speed on an image side of the lens. The need also exists for a method and apparatus of constructing such a telecentric zoom lens.  
         SUMMARY OF THE INVENTION  
         [0004]    The present invention provides a telecentric zoom lens having a constant speed on an image side of the lens. Generally, the telecentric zoom lens includes a plurality of optical elements located along an optical axis. The optical elements include an objective lens having an object side and an image side; a zoom group moveable along the optical axis; and a telecentricity forming aperture mechanically intermediate the objective lens and the zoom group and thus optically intermediate the objective lens and the zoom group. Thus, the lens is telecentric in object space. In a further configuration, it is contemplated that the telecentricity forming aperture is a variable aperture. It is also contemplated, the telecentric zoom lens may include a first decollimator optically intermediate the objective lens and the telecentricity forming aperture.  
           [0005]    More particularly, the present telecentric lens system includes a plurality of optical elements located on the optical axis, and specifically, a first collimator; a first decollimator, a zoom lens group, a second collimator, second decollimator, and a variable aperture optically intermediate the first decollimator and the zoom group. Further, it is contemplated that the zoom group may include a variator and a compensator. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]    [0006]FIG. 1 is a side elevational view of a first configuration of the lens system in a first position.  
         [0007]    [0007]FIG. 2 is a side elevational view of a first configuration of the lens system in a second position.  
         [0008]    [0008]FIG. 3 is a side elevational view of a first configuration of the lens system in a third position.  
         [0009]    [0009]FIG. 4 is a side elevational view of a first configuration of the lens system in a fourth position.  
         [0010]    [0010]FIG. 5 is a side elevational view of a first configuration of the lens system in a fifth position.  
         [0011]    [0011]FIG. 6 is a side elevational view of a second configuration of the lens system in a first position.  
         [0012]    [0012]FIG. 7 is a side elevational view of a second configuration of the lens system in a second position.  
         [0013]    [0013]FIG. 8 is a side elevational view of a second configuration of the lens system in a third position.  
         [0014]    [0014]FIG. 9 is a side elevational view of a second configuration of the lens system in a fourth position.  
         [0015]    [0015]FIG. 10 is a side elevational view of a second configuration of the lens system in a fifth position.  
         [0016]    [0016]FIG. 11 is a side elevational view of a third configuration of the lens system in a first position.  
         [0017]    [0017]FIG. 12 is a side elevational view of a third configuration of the lens system in a second position.  
         [0018]    [0018]FIG. 13 is a side elevational view of a third configuration of the lens system in a third position.  
         [0019]    [0019]FIG. 14 is a side elevational view of a third configuration of the lens system in a fourth position.  
         [0020]    [0020]FIG. 15 is a side elevational view of a third configuration of the lens system in a fifth position.  
         [0021]    [0021]FIG. 16 is a side elevational view of a fourth configuration of the lens system in a first position.  
         [0022]    [0022]FIG. 17 is a side elevational view of a fourth configuration of the lens system in a second position.  
         [0023]    [0023]FIG. 18 is a side elevational view of a fourth configuration of the lens system in a third position.  
         [0024]    [0024]FIG. 19 is a side elevational view of a fourth configuration of the lens system in a fourth position.  
         [0025]    [0025]FIG. 20 is a side elevational view of a fourth configuration of the lens system in a fifth position. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0026]    Referring to FIG. 1, the present invention includes a telecentric zoom lens. For purposes of the description, the term “object” or “front side” of an optical element is used to describe those elements or surfaces that are nearer to the viewed object. The term “image” or “rear side” is used to describe those sides or surfaces of the optical element that are nearer the image that passes through the lens system. The term telecentric generally means a parallel relationship between the optical axis of the optical system and a principal ray entering or exiting the optical system.  
         [0027]    The telecentric zoom lens includes a plurality of optical elements disposed along an optical axis A. The telecentric zoom lens includes an objective lens and a zoom group. The telecentric zoom lens system may include a first collimator FC, a first decollimator, FD a zoom group, ZG a second collimator SC, and a second decollimator SD along the optical axis.  
         [0028]    The objective lens is the first collimator. The first collimator may be defined by variety of optical surfaces, as set forth in Tables 1-4. The first collimator causes the rays from an on axis point in the object plane to orient substantially parallel to the optical axis.  
         [0029]    The first decollimator is disposed along the optical axis on the image side of the objective lens. The first decollimator causes the rays to converge on the image side of the first decollimator.  
         [0030]    A telecentric aperture TA is located along the optical axis rearward of the first decollimator and located at a fixed position along the optical axis. The telecentric aperture is preferably variable. The range of variance in the telecentric aperture TA is sufficient to provide a constant speed on the image side. The variable telecentric-causing aperture TA may be any of a variety of aperture varying mechanisms such as leaves, plates or diaphragms. Either a motor or cam controls actuation of the variable aperture. By employing a variable aperture it has been found the speed of the lens system on the image side can be controlled  
         [0031]    The zoom group is located along the optical axis rearward of the telecentric aperture. The telecentric causing aperture is optically intermediate the zoom group and the objective lens. Although the telecentric causing aperture is also shown as mechanically and physically intermediate the zoom group and the objective lens, it is contemplated that the physical location of the telecentric causing aperture may be changed while retaining its being optically intermediate the objective lens and the zoom group. Although the zoom group may have a variety of configurations, it is contemplated the zoom group includes a variator and a compensator. The zoom group may be any combination of negative and positive elements. That is, the variator may be negative and the compensator negative; the variator negative and the compensator positive; the variator positive and the compensator negative; and the variator positive and the compensator positive. Configuration  1  &amp;  4 , wherein the variator is negative and the compensator is negative, and configuration  2  &amp;  3  wherein the variator is negative and the compensator is positive are preferred. Representative optical services of the variator and compensator parameters are set forth in Tables 1-4.  
         [0032]    Relative motion of the zoom group components may be accomplished by any of a variety of known mechanisms such as stepper motors and linear actuators. A preferred mechanism is a mechanical cam.  
         [0033]    The second collimator is optically rearward of the zoom group and specifically the compensator. Configurations  1 , 3  and  4  include the second collimator. The second configuration does not include the second collimator as the output from the zoom group (compensator) is collimated. Preferably, the second collimator is constructed to reduce distortion.  
         [0034]    The second decollimator is on the image side of the second collimator. Each of the four configurations includes a second decollimator. The second decollimator focuses the light to the image plane.  
         [0035]    The optical elements may be formed from any appropriate material including plastics, resins as well as, glass and composites. A preferred material is glass.  
         [0036]    It is further contemplated that each air interface surface of the lens elements may be provided with an anti-reflective coating. Typical anti-reflective coatings include magnesium fluoride. The objective lens may have a broadband anti-reflective coating.  
         [0037]    Configuration  1  includes a negative-negative zoom group with a working f-number 20 in a camera format of ½ inch.  
         [0038]    In the first configuration, surfaces  1  to  8  are the first collimator FC, surfaces  9  to  14  are the first decollimator FD, surfaces  16  to  18  are the variator V in zoom group, surfaces  19 - 21  are the compensator C in the zoom group, surfaces  22  to  26  are the second collimator SC and surfaces  27  to  31  are the second decollimator SD.  
                                                                                       Surface   Radius   Thickness   Nd   V#   Diameter               OBJ       77.19       1   −281.5500   4.00   1.45600   90.34   32.00       2   −57.2600   0.50           33.00       3   Infinity   3.80   1.61310   44.36   34.00       4   103.6500   4.25   1.45600   90.34   34.00       5   −95.2500   0.50           34.20       6   Infinity   3.80   1.61310   44.36   34.50       7   115.8000   4.25   1.45600   90.34   34.50       8   −119.6000   39.00           34.70       9   95.2603   3.00   1.61310   44.36   38.00       10   43.0696   7.00   1.49695   81.60   38.00       11   −175.2769   0.50           38.00       12   45.0330   3.00   1.61310   44.36   38.00       13   33.8820   6.50   1.45600   90.34   38.00       14   157.5993   13.79           38.00       STOP   Infinity   11.00       16   −96.3272   1.60   1.80080   35.00   10.00       17   −11.0564   1.00   1.78574   44.20   10.00       18   29.4655   10.97           10.00       19   −97.0317   1.00   1.78574   44.20   10.00       20   5.4658   3.25   1.80080   35.00   10.00       21   26.7295   51.75           10.00       22   730.8634   6.00   1.61262   58.70   40.00       23   −56.0953   0.50           40.00       24   123.3747   8.00   1.48749   70.21   40.00       25   −52.4897   3.00   1.80610   33.27   40.00       26   −258.4570   5.00           40.00       27   697.4209   5.00   1.64839   53.00   41.00       28   −78.9875   3.00   1.80518   25.39   41.00       29   −223.3974   0.50           41.00       30   156.2192   4.00   1.72904   54.70   41.00       31   −1479.0530   127.51           41.00                    IMA       Zoom Data                0.75x   1.33x   2.00x   4.22x   7.50x               S15   11   21.317   26.16429   29.96268   30.12291       S18   10.96782   4.999894   5.663429   16.85393   32.59501       S21   51.74994   47.40086   41.88991   26.90104   10.99979                  
 
         [0039]    Configuration  2  has a negative positive zoom group with a working f-number of 20 and a camera format of ½ inch.  
         [0040]    In the second configuration, surfaces  1  to  8  are the first collimator FC, surfaces  9  to  13  are the first decollimator FD, surfaces  15  to  19  are the variator V in the zoom group, surfaces  20 - 25  are the compensator C in the zoom group and surfaces  27  to  29  are the second decollimator SD. This configuration does not employ a second collimator SC as the compensator C puts out collimated light.  
                                                                                       Surface   Radius   Thickness   Nd   V#   Diameter               OBJ       77.34       1   −283.7479   4.00   1.45600   90.34   34.00       2   −57.4479   0.50           34.00       3   Infinity   2.50   1.61310   44.36   34.80       4   103.1262   5.00   1.45600   90.34   34.80       5   −92.3134   0.50           35.20       6   Infinity   2.50   1.61310   44.36   35.60       7   115.3065   5.00   1.45600   90.34   35.60       8   −124.7165   35.80           35.60       9   66.9775   5.00   1.55220   67.03   35.00       10   −93.1287   3.00   1.65412   39.62   35.00       11   182.9913   0.50           34.90       12   62.7445   4.00   1.49695   81.60   33.50       13   121.7067   22.92           33.50       STOP   Infinity   0.00       15   15.9237   2.00   1.78785   47.40   11.00       16   5.1692   2.50   1.80080   35.00   9.00       17   12.2617   1.30           8.00       18   −17.6645   2.00   1.77236   49.60   9.40       19   59.5758   41.51           9.40       20   −255.2385   4.50   1.78574   44.20   27.80       21   −29.2736   3.50   1.84635   23.80   28.50       22   −63.5616   0.50           31.00       23   262.2000   4.10   1.69350   53.33   30.80       24   −37.2864   2.50   1.75487   52.30   29.30       25   −147.4509   45.91           31.50       26   Infinity   3.00           29.00       27   185.5856   4.25   1.61791   63.40   33.00       28   −57.9111   2.50   1.80610   33.27   33.00       29   −121.8555   148.67           33.50                    IMA       Zoom Data                0.80x   1.44x   2.50x   4.50x   7.90x               S14   0.0000   32.94485   50.92825   61.57181   67.20934       S19   41.51364   38.24532   32.50898   21.85882   3.980362       S25   45.91399   16.23737   3.995184   3.998487   16.23795                  
 
         [0041]    Configuration  3  has a negative positive zoom group with a working f-number of 20 in a camera format of ½ inch.  
         [0042]    In the third configuration, surfaces  1  to  8  are the first collimator FC, surfaces  9  to  13  are the first decollimator FD, surfaces  15  to  17  are the variator V of the zoom group, surfaces  18 - 21  are the compensator C in the zoom group, surfaces  22  to  24  are the second collimator SC and surfaces  25  to  27  are the second decollimator SD.  
                                                                                       Surface   Radius   Thickness   Nd   V#   Diameter               OBJ       78.39       1   −293.2219   4.00   1.52855   76.98   36.00       2   −61.5946   0.50           36.00       3   Infinity   2.50   1.61310   44.36   36.00       4   104.8174   5.00   1.49695   81.60   36.00       5   −94.0966   0.50           36.00       6   Infinity   2.50   1.61310   44.36   36.00       7   72.8788   5.00   1.49695   81.60   36.00       8   −188.2986   41.80           36.00       9   73.2881   5.00   1.49695   81.60   34.00       10   −125.6413   2.50   1.80349   30.40   34.00       11   −462.3412   0.50           34.00       12   94.6181   5.00   1.48656   84.47   34.00       13   230.8875   18.63           34.00       STOP   Infinity   3.56       15   −27.6135   2.25   1.80318   46.38   9.00       16   6.9900   2.75   1.85025   32.17   9.00       17   24.2769   41.67           9.00       18   −505.7763   2.00   1.79935   42.20   21.00       19   −118.3258   5.00   1.69680   55.41   21.00       20   −26.3939   3.50   1.80349   30.40   21.00       21   −47.4743   32.89           22.00       22   87.2833   5.00   1.79619   43.20   29.00       23   −53.8974   2.75   1.87800   38.48   29.00       24   140.8270   1.00           29.00       25   142.0000   3.75   1.58304   59.40   29.00       26   −62.2000   2.25   1.66663   33.00   29.00       27   −203.0000   164.00           29.00                    IMA       Zoom Data                0.80x   1.42x   2.53x   4.50x   8.00x               S14   3.564761   29.43371   44.92315   53.94762   59.06097       S17   41.66636   38.75392   32.98541   22.17358   1.999626       S21   32.88991   9.933404   0.212473   1.999916   17.06044                  
 
         [0043]    Configuration  4  has a negative-negative zoom group with a working f-number of 20 in a camera format: ½ inch.  
         [0044]    In the fourth configuration, surfaces  1  to  8  are the first collimator FC, surfaces  9  to  13  are the first decollimator FD, surfaces  16  to  18  are the variator V in the zoom group, surfaces  19 - 21  are the compensator C in the zoom group, surfaces  22  to  27  are the second collimator SC and surfaces  28  to  30  are the second decollimator SD.  
                                                                             Surface   Radius   Thickness   Nd   V#   Diameter                                OBJ       77.19                   1   −281.5500   4.00   1.45600   90.34   32.00       2   −57.2600   0.50           33.00       3   Infinity   3.80   1.61310   44.36   34.00       4   103.6500   4.25   1.45600   90.34   34.00       5   −95.2500   0.50           34.20       6   Infinity   3.80   1.61310   44.36   34.50       7   115.8000   4.25   1.45600   90.34   34.50       8   −119.6000   45.00           34.70       9   175.8591   6.00   1.48656   84.47   34.00       10   −68.5279   4.00   1.61293   36.96   34.00       11   −399.7037   0.50           34.00       12   66.4254   4.00   1.48656   84.47   34.00       13   −1219.1600   17.31           32.00       STO   Infinity   0.00       15   Infinity   49.20       16   −62.6972   2.25   1.80400   46.57   12.00       17   17.6723   2.75   1.76182   26.52   12.00       18   71.3495   22.97           12.00       19   −58.4378   4.00   1.82223   37.45   10.00       20   −6.0108   2.50   1.81550   44.54   10.80       21   52.7099   7.00           13.00       22   735.5523   6.25   1.75500   52.32   38.00       23   −44.2291   4.25   1.80349   30.40   39.00       24   −61.6877   0.50           40.00       25   155.5579   6.71   1.61800   63.33   40.00       26   −52.9482   3.50   1.83400   37.16   40.00       27   15685.880   5.00           40.00       28   89.3700   4.00   1.80440   39.59   40.00       29   51.8700   6.50   1.52855   76.98   40.00       30   −195.0000   153.11           40.00                  
 
         [0045]    [0045]                                                                                   IMA       Zoom Data                0.75x   1.33x   2.00x   4.22x   7.50x                        S15   11.0000   27.8863   37.0673   47.0086   49.1975       S18   24.7087   10.1201   5.0000   9.1381   22.9692       S21   43.4578   41.1600   37.0992   23.0198   6.9999                    
         [0046]    While the invention has been described with reference to preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation of material to the teachings of the invention without departing from the scope of the invention. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope and spirit of the appended claims.