Abstract:
A wide-angle zoom lens system includes a positive first lens group, a negative second lens group, a positive third lens group and a positive fourth lens group, in this order from the object. Upon zooming from the short focal length extremity to the long focal length extremity, a distance between the positive first lens group and the negative second lens group increases, a distance between the negative second lens group and the positive third lens group decreases, and a distance between the positive third lens group and the positive fourth lens group decreases. The wide-angle zoom lens system satisfies the following conditions:
 
6.3&lt; f 1/ fw &lt;8.0  (1)
 
7.0&lt; f 1/| f 2|&lt;9.0 ( f 2&lt;0)  (2)
 
2.5&lt; f 3/ fw &lt;4.5  (3)
wherein f1: the focal length of the positive first lens group; f2: the focal length of the negative second lens group; f3: the focal length of the positive third lens group; and fw: the focal length of the entire wide-angle zoom lens system at the short focal

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a wide-angle zoom lens system which is suitable for a single-lens reflex (SLR) camera, and especially suitable for a digital single-lens reflex camera.  
         [0003]     2. Description of the Prior Art  
         [0004]     In a digital SLR camera, the size of the imaging device is smaller than a frame size of the film for a silver-halide SLR camera. Therefore an optical system having a wider angle-of-view (shorter focal length) is necessary.  
         [0005]     Various types of the above wide-angle zoom lens system have been known. In particular, as a wide-angle zoom lens system with a higher zoom ratio of 10 or more, the wide-angle zoom lens system of a four-lens-group arrangement, in which the positive, negative, positive and positive lens groups are provided in this order from the object, has been generally known.  
         [0006]     The wide-angle zoom lens systems mentioned above have been designed for the image-plane size corresponding to the 135 (35mm) film format. Therefore the maximum angle-of-view at the short focal length extremity is inevitably smaller, e.g., approximately 75°. Furthermore, in the case of a digital SLR camera having a smaller image plane (the imaging device), e.g., an APSC size image sensor, the angle-of-view at short focal length extremity is at most 55°.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention is to provide a wide-angle zoom lens system of the four-lens-group arrangement, i.e., the positive, negative, positive and positive lens groups, in this order from the object; and the wide-angle zoom lens system is suitable for a digital SLR camera having a smaller imaging device, has an angle-of-view of approximately 80° at the short focal length extremity, and has a zoom ratio exceeding 8.  
         [0008]     According to an aspect of the present invention, there is provided a wide-angle zoom lens system including a first lens group having a positive refractive power (hereinafter, a positive first lens group), a second lens group having a negative refractive power (hereinafter, a negative second lens group), a third lens group having a positive refractive power (hereinafter, a positive third lens group) and a fourth lens group having a positive refractive power (hereinafter, a positive fourth lens group), in this order from the object.  
         [0009]     Upon zooming from the short focal length extremity to the long focal length extremity, a distance between the positive first lens group and the negative second lens group increases, a distance between the negative second lens group and the positive third lens group decreases, and a distance between the positive third lens group and the positive fourth lens group decreases.  
         [0010]     The wide-angle zoom lens system satisfies the following conditions:
 
6.0 &lt;f 1 /fw&lt; 8.0  (1)
 
7.0 &lt;f 1 /|f 2|&lt;9.0 ( f 2&lt;0)  (2)
 
2.5 &lt;f 3/ fw&lt; 4.5  (3)
 
 wherein 
 
         [0011]     f 1  designates the focal length of the positive first lens group;  
         [0012]     f 2  designates the focal length of the negative second lens group;  
         [0013]     f 3  designates the focal length of the positive third lens group; and  
         [0014]     fw designates the focal length of the entire wide-angle zoom lens system at the short focal length extremity.  
         [0015]     The wide-angle zoom lens system preferably satisfies the following condition:
 
1.0 &lt;f 3/ f 4&lt;2.5  (4)
 
 wherein 
 
         [0016]     f 3  designates the focal length of the positive third lens group; and  
         [0017]     f 4  designates the focal length of the positive fourth lens group.  
         [0018]     The positive third lens group of the wide-angle zoom lens system preferably includes a positive  3   a -sub-lens group and a negative  3   b -sub-lens group, in this order from the object.  
         [0019]     The wide-angle zoom lens system preferably satisfies the following conditions:
 
1.0 &lt;f 4/ f 3 a&lt; 2.0  (5)
 
0.2 &lt;f 2/ f 3 b&lt; 0.5  (6)
 
 wherein 
 
         [0020]     f 4  designates the focal length of the positive fourth lens group;  
         [0021]     f 2  designates the focal length of the negative second lens group;  
         [0022]     f 3   a  designates the focal length of the positive  3   a -sub-lens group (&gt;0); and  
         [0023]     f 3   b  designates the focal length of the negative  3   b -sub-lens group(&lt;0).  
         [0024]     According to another aspect of the present invention, there is provided a wide-angle zoom lens system including a positive first lens group, a negative second lens group, a positive third lens group and a positive fourth lens group, in this order from the object.  
         [0025]     Upon zooming from the short focal length extremity to the long focal length extremity, a distance between the positive first lens group and the negative second lens group increases, a distance between the negative second lens group and the positive third lens group decreases, and a distance between the positive third lens group and the positive fourth lens group decreases.  
         [0026]     The positive third lens group includes a positive  3   a -sub-lens group and a negative  3   b -sub-lens group, in this order from the object.  
         [0027]     The wide-angle zoom lens system preferably satisfies the following conditions:
 
1.0 &lt;f 3/ f 4&lt;2.5  (4)
 
1.0 &lt;f 4/ f 3 a&lt; 2.0  (5)
 
0.2 &lt;f 2/ f 3 b&lt; 0.5  (6)
 
         [0028]     wherein  
         [0029]     f 3  designates the focal length of the positive third lens group;  
         [0030]     f 4  designates the focal length of the positive fourth lens group;  
         [0031]     f 2  designates the focal length of the negative second lens group;  
         [0032]     f 3   a  designates the focal length of the positive  3   a -sub-lens group (&gt;0); and  
         [0033]     f 3   b  designates the focal length of the negative  3   b -sub-lens group(&lt;0).  
         [0034]     In the positive third lens group, the negative  3   b -sub-lens group, which is positioned on the image-side of the positive  3   a -sub-lens group, preferably includes cemented lens elements having a positive lens element and a negative lens element.  
         [0035]     The present disclosure relates to subject matter contained in Japanese Patent Application No. 2005-304966 (filed on Oct. 19, 2005) which is expressly incorporated herein in its entirety. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0036]     The present invention will be discussed below in detail with reference to the accompanying drawings, in which:  
         [0037]      FIG. 1  is a lens arrangement of the wide-angle zoom lens system, at the short focal length extremity, according to a first embodiment of the present invention;  
         [0038]      FIGS. 2A, 2B ,  2 C,  2 D and  2 E show aberrations occurred in the lens arrangement shown in  FIG. 1 ;  
         [0039]      FIG. 3  is a lens arrangement of the wide-angle zoom lens system, at the long focal length extremity, according to the first embodiment of the present invention;  
         [0040]      FIGS. 4A, 4B ,  4 C,  4 D and  4 E show aberrations occurred in the lens arrangement shown in  FIG. 3 ;  
         [0041]      FIG. 5  is a lens arrangement of the wide-angle zoom lens system, at the short focal length extremity, according to a second embodiment of the present invention;  
         [0042]      FIGS. 6A, 6B ,  6 C,  6 D and  6 E show aberrations occurred in the lens arrangement shown in  FIG. 5 ;  
         [0043]      FIG. 7  is a lens arrangement of the wide-angle zoom lens system, at the long focal length extremity, according to the second embodiment of the present invention;  
         [0044]      FIGS. 8A, 8B ,  8 C,  8 D and  8 E show aberrations occurred in the lens arrangement shown in  FIG. 7 ;  
         [0045]      FIG. 9  is a lens arrangement of the wide-angle zoom lens system, at the short focal length extremity, according to a third embodiment of the present invention;  
         [0046]      FIGS. 10A, 10B ,  10 C,  10 D and  10 E show aberrations occurred in the lens arrangement shown in  FIG. 9 ;  
         [0047]      FIG. 11  is a lens arrangement of the wide-angle zoom lens system, at the long focal length extremity, according to the third embodiment of the present invention;  
         [0048]      FIGS. 12A, 12B ,  12 C,  12 D and  12 E show aberrations occurred in the lens arrangement shown in  FIG. 11 ;  
         [0049]      FIG. 13  is a lens arrangement of the wide-angle zoom lens system, at the short focal length extremity, according to a fourth embodiment of the present invention;  
         [0050]      FIGS. 14A, 14B ,  14 C,  14 D and  14 E show aberrations occurred in the lens arrangement shown in  FIG. 13 ;  
         [0051]      FIG. 15  is a lens arrangement of the wide-angle zoom lens system, at the long focal length extremity, according to the fourth embodiment of the present invention;  
         [0052]      FIGS. 16A, 16B ,  16 C,  16 D and  16 E show aberrations occurred in the lens arrangement shown in  FIG. 15 ; and  
         [0053]      FIG. 17  is the schematic view of the lens-group moving paths for the wide-angle zoom lens system according to the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0054]     The wide-angle zoom lens system of the present invention, as shown in the zoom path of  FIG. 17 , includes a positive first lens group  10 , a negative second lens group  20 , a positive third lens group  30 , and a positive fourth lens group  40 , in this order from the object.  
         [0055]     Upon zooming from the short focal length extremity (W) to the long focal length extremity (T), all the lens groups ( 10 ,  20 ,  30  and  40 ) move monotonically toward the object.  
         [0056]     While the zooming is being performed, the distance between the positive first lens group  10  and the negative second lens group  20  increases; the distance between the negative second lens group  20  and the positive third lens group  30  decreases; the distance between the positive third lens group  30  and the positive fourth lens group  40  decreases; and the distance between the positive fourth lens group  40  and the image plane monotonically increases.  
         [0057]     A diaphragm S is provided in front of the positive third lens group  30 , and is arranged to move together with the positive third lens group  30 .  
         [0058]     Condition ( 1 ) specifies the ratio of the focal length of the positive first lens group  10  to the focal length of the entire wide-angle zoom lens system at the short focal length extremity.  
         [0059]     If f 1 /fw exceeds the upper limit of condition ( 1 ), the refractive power of the positive first lens group  10  becomes too weak. Consequently, the size of the entire wide-angle zoom lens system becomes larger.  
         [0060]     If f 1 /fw exceeds the lower limit of condition ( 1 ), the refractive power of the positive first lens group  10  becomes too strong. Consequently, spherical aberration, in particular, occurs largely.  
         [0061]     Condition ( 2 ) specifies the ratio of the focal length of the positive first lens group  10  to the focal length of the negative second lens group  20 , i.e., the ratio of the refractive power with respect to the positive first lens group  10  and the negative second lens group  20 .  
         [0062]     If f 1 /|f 2 | exceeds the upper limit of condition ( 2 ), the refractive power of the negative second lens group  20  becomes stronger. Consequently, light rays emit from the negative second lens group  20  largely diverge; and subsequently, the diverged light rays are converged by the positive third lens group  30  and the positive fourth lens group  40 . Therefore spherical aberration largely occurs in the positive third lens group  30  and the positive fourth lens group  40 .  
         [0063]     If f 1 /|f 2 | exceeds the lower limit of condition ( 2 ), the negative refractive power of the negative second lens group  20  becomes too weak. Consequently, the correcting of aberrations occurred in other lens groups (the positive first lens group  10 , the positive third lens group  30  and the positive fourth lens group  40 ) becomes difficult.  
         [0064]     Condition ( 3 ) specifies the ratio of the focal length of the positive third lens group  30  to the focal length of the entire wide-angle zoom lens system at the short focal length extremity.  
         [0065]     If f 3 /fw exceeds the upper limit of condition ( 3 ), the positive refractive power of the positive third lens group  30  becomes too weak, so that the traveling distance of the positive third lens group  30  becomes longer. Consequently, the size of the entire wide-angle zoom lens system becomes larger. As an alternative, the positive refractive power of the positive fourth lens group  40  could be made stronger; however, in such a case, coma and distortion largely occur, and the correcting thereof becomes difficult.  
         [0066]     If f 3 /fw exceeds the lower limit of condition ( 3 ), the positive refractive power of the positive third lens group  30  becomes too strong. Consequently, spherical aberration and coma largely occur, and the correcting thereof becomes difficult.  
         [0067]     Condition ( 4 ) specifies the ratio of the focal length of the positive third lens group  30  to the focal length of the positive fourth lens group  40 , i.e., the ratio of the refractive power with respect to the positive third lens group  30  and the positive fourth lens group  40 .  
         [0068]     The third lens group  30  and the fourth lens group  40  both of which have a positive refractive power are arranged to function as a master lens (group) and the compensator lens (group), respectively; and condition ( 4 ) is to determine distribution (burden) of the positive refractive power over the third lens group  30  and the fourth lens group  40 .  
         [0069]     If f 3 /f 4  exceeds the upper limit of condition ( 4 ), the positive refractive power of the positive fourth lens group  40  becomes too strong. Consequently, coma and distortion largely occur, and the correcting thereof becomes difficult.  
         [0070]     If f 3 /f 4  exceeds the lower limit of condition ( 4 ), the positive refractive power of the positive third lens group  30  becomes too strong. Consequently, the correcting of spherical aberration becomes difficult.  
         [0071]     Condition ( 5 ) and condition ( 6 ) specify the positive third lens group  30  in the case where the positive third lens group  30  includes a positive  3   a -sub-lens group and a negative  3   b -sub-lens group, in this order from the object. The negative  3   b -sub-lens group includes cemented lens elements having a positive lens element and a negative lens element, or a negative lens element and a positive lens element, which are cemented to each other, in this order from the object.  
         [0072]     Furthermore, it should be understood that condition ( 5 ) relates to the fourth lens group  40  and the  3   a -sub-lens group, both of which has a positive refractive power; and condition ( 6 ) relates to the second lens group  20  and the  3   b -sub-lens group, both of which has a negative refractive power.  
         [0073]     Condition ( 5 ) specifies the ratio of the focal length of the positive fourth lens group  40  to the focal length of the positive  3   a -sub-lens group, i.e., the ratio of the refractive power with respect to the positive fourth lens group  40  and the positive  3   a -sub-lens group.  
         [0074]     If f 4 /f 3   a  exceeds the upper limit of condition ( 5 ), the refractive power of the positive  3   a -sub-lens group becomes too strong. Consequently, the correcting of spherical aberration cannot suitably be done.  
         [0075]     If f 4 /f 3   a  exceeds the lower limit of condition ( 5 ), the refractive power of the positive fourth lens group  40  becomes too strong. Consequently, coma and distortion largely occur, and the correcting thereof becomes difficult.  
         [0076]     Condition ( 6 ) specifies the ratio of the focal length of the negative second lens group  20  to the focal length of the negative  3   b -sub-lens group, i.e., the ratio of the refractive power with respect to the negative second lens group  20  and the negative  3   b -sub-lens group.  
         [0077]     Only the second lens group  20  and the  3   b -sub-lens group are the negative lens groups in the wide-angle zoom lens system; therefore by satisfying condition ( 6 ), the negative refractive power in the wide-angle zoom lens system can be maintained in a well balanced manner.  
         [0078]     If f 2 /f 3   b  exceeds the upper limit of condition ( 6 ), the negative refractive power of the negative  3   b -sub-lens group becomes too strong. Consequently, spherical aberration is overcorrected.  
         [0079]     If f 2 /f 3   b  exceeds the lower limit of condition ( 6 ), the negative refractive power of the negative second lens group  20  becomes too strong. Consequently, fluctuations in aberrations due to zooming becomes intolerably larger.  
         [0080]     Specific numerical data of the embodiments will be described hereinafter.  
         [0081]     In the diagrams of spherical aberration and the sine condition, SA designates spherical aberration, and SC designates the sine condition.  
         [0082]     In the diagrams of chromatic aberration (axial chromatic aberration) represented by spherical aberration the solid line and the two types of dotted lines respectively indicate spherical aberrations with respect to the d, g and C lines.  
         [0083]     In the diagrams of lateral chromatic aberration, the two types of dotted lines respectively indicate magnification with respect to the g and C lines; however, the d line as the base line coincides with the ordinate.  
         [0084]     In the diagrams of astigmatism, S designates the sagittal image, and M designates the meridional image.  
         [0085]     The tables, FNO. designates the f-number, f designates the focal length of the entire zoom lens system, W designates the half angle-of-view (°), fB designates the back focal distance, r designates the radius of curvature, d designates the lens-element thickness or a distance between lens elements (lens groups) which is variable upon zooming, N d  designates the refractive index of the d-line, and v designates the Abbe number. The values for the distance “d” are indicated in the order of the short focal length extremity, an intermediate focal length and the long focal length extremity.  
         [0086]     In addition to the above, an aspherical surface which is symmetrical with respect to the optical axis is defined as follows:
 
 x=cy   2 (1+[1+ K}c   2   y   2 ] 1/2 )+A4 y   4   +A 6 y   6   +A 8 y   8   +A 10 y   10 
 
 wherein: 
    c designates a curvature of the aspherical vertex (1/r);     y designates a distance from the optical axis;     K designates the conic coefficient; and     A4 designates a fourth-order aspherical coefficient;     A6 designates a sixth-order aspherical coefficient;     A8 designates a eighth-order aspherical coefficient; and     A10 designates a tenth-order aspherical coefficient.    
 
       Embodiment 1  
       [0094]      FIG. 1  is the lens arrangement of the wide-angle zoom lens system, at the short focal length extremity, according to the first embodiment of the present invention.  FIGS. 2A through 2E  show aberrations occurred in the lens arrangement shown in  FIG. 1 .  
         [0095]      FIG. 3  is the lens arrangement of the wide-angle zoom lens system, at the long focal length extremity, according to the first embodiment of the present invention.  FIGS. 4A through 4E  show aberrations occurred in the lens arrangement shown in  FIG. 3 .  
         [0096]     Table 1 shows the numerical data of the first embodiment.  
         [0097]     The wide-angle zoom lens system of the first embodiment includes a positive first lens group  10 , a negative second lens group  20 , a diaphragm S, a positive third lens group  30 , and a positive fourth lens group  40 , in this order from the object.  
         [0098]     The positive first lens group  10  includes a negative meniscus lens element having the convex surface facing toward the object, a positive biconvex lens element and a positive meniscus lens element having the convex surface facing toward the objects in this order from the object.  
         [0099]     The negative second lens group  20  includes a negative meniscus lens element (the most object-side negative meniscus lens element) having the convex surface facing toward the object, a negative biconcave lens element, a positive biconvex lens element, and cemented lens elements having a negative meniscus lens element having the convex surface facing toward the image and a positive meniscus lens element having the convex surface facing toward the image, in this order from the object. Here, note that the most object-side negative meniscus lens element is provided with an aspherical layer made of a synthetic resin material on the most object-side surface thereof.  
         [0100]     The positive third lens group  30  includes the positive  3   a -sub-lens group and the negative  3   b -sub-lens group, in this order from the object.  
         [0101]     The positive  3   a -sub-lens group includes a positive biconvex lens element, and cemented lens elements having a positive biconvex lens element and a negative biconcave lens element, in this order from the object.  
         [0102]     The negative  3   b -sub-lens group includes cemented lens elements having a positive meniscus lens element having the convex surface facing toward the image and a negative biconcave lens element, in this order from the object.  
         [0103]     The positive fourth lens group  40  includes a positive biconvex lens element, another positive biconvex lens element and a negative meniscus lens element having the convex surface facing toward the image, in this order from the object.  
         [0104]     The diaphragm S is provided 1.10 in front of the positive third lens group  30  (surface No.  17 ).  
                                                           TABLE 1                           FNO. = 1: 3.5-5.0-5.8       f = 16.48-50.00-131.27       W = 41.8-15.6-6.1       fB = 39.44-63.68-76.29            Surf. No.   r   d   Nd   ν                     1   135.739   2.20   1.84666   23.8        2   75.977   0.23   —   —        3   77.159   7.70   1.49700   81.6        4   −3283.505   0.20   —   —        5   62.945   5.37   1.77250   49.6        6   151.258   2.10-32.80-61.87   —   —        7*   124.403   0.10   1.52700   43.7        8   65.008   1.10   1.83500   42.8        9   12.786   7.23   —   —       10   −34.461   1.50   1.82123   44.0       11   78.832   0.11   —   —       12   36.104   4.77   1.84666   23.8       13   −30.189   0.50   —   —       14   −24.634   1.00   1.82955   43.8       15   −571.302   2.20   1.80518   25.4       16   −156.983   25.95-9.85-3.06   —   —       17   19.297   3.44   1.48750   70.2       18   −56.037   0.50   —   —        19*   24.853   3.19   1.48749   70.2       20   −26.657   1.20   1.83312   35.0       21   121.075   2.00   —   —       22   −50.018   1.69   1.80518   25.4       23   −20.283   0.80   1.80400   46.6       24   85.511   4.68-2.41-1.49   —   —       25   46.496   4.01   1.48750   70.2       26   −22.068   0.50   —   —        27*   781.528   2.30   1.60276   52.1       28   −39.535   0.00   —   —       29   −40.570   0.00   1.84617   23.9       30   −580.231   —   —   —                 The symbol * designates the aspherical surface which is rotationally symmetrical with respect to the optical axis.             
 
         [0105]     Aspherical surface data (the aspherical surface coefficients not indicated are zero (0.00)):  
                                               Surf.                       No.   K   A4   A6   A8                    7   0.00     0.22678 × 10 −4     −0.49468 × 10 −7       0.65495 × 10 −10         19   0.00   −0.28095 × 10 −5         27   0.00   −0.39652 × 10 −4     −0.74562 × 10 −7     −0.57795 × 10 −9                    
 
       Embodiment 2  
       [0106]      FIG. 5  is the lens arrangement of the wide-angle zoom lens system, at the short focal length extremity, according to a second embodiment of the present invention.  FIGS. 6A through 6E  show aberrations occurred in the lens arrangement shown in  FIG. 5 .  
         [0107]      FIG. 7  is the lens arrangement of the wide-angle zoom lens system, at the long focal length extremity, according to the second embodiment of the present invention.  FIGS. 8A through 8E  show aberrations occurred in the lens arrangement shown in  FIG. 7 .  
         [0108]     Table 2 shows the numerical data of the second embodiment.  
         [0109]     With respect to the positive first lens group  10 , the positive third lens group  30  and the positive fourth lens group  40 , the basic lens arrangements thereof are the same as those of the first embodiment.  
         [0110]     On the other hand, the negative second lens group  20  includes a negative meniscus lens element (the most object-side negative meniscus lens element in the negative second lens group  20 ) having the convex surface facing toward the object, a negative biconcave lens element, a positive biconvex lens element and a negative meniscus lens element having the convex surface facing toward the image, in this order from the object. Here, note that the most-object side negative meniscus lens element in the negative second lens group  20  is provided with an aspherical layer made of a synthetic resin material on the most object-side surface thereof.  
         [0111]     The diaphragm S is provided 1.10 in front of the positive third lens group  30  (surface No.  16 ) on the optical axis.  
                                                           TABLE 2                           FNO. = 1: 3.5-4.9-5.8       f = 16.50-50.10-131.33       W = 41.7-15.6-6.1       fB = 39.53-62.60-76.31            Surf. No.   r   d   Nd   ν                     1   139.682   2.20   1.84666   23.8        2   75.992   0.25   —   —        3   78.391   7.70   1.49700   81.6        4   −4570.944   0.20   —   —        5   62.352   5.46   1.77250   49.6        6   161.088   2.10-33.56-61.06   —   —        7*   115.906   0.10   1.52700   43.7        8   67.072   1.10   1.83481   42.7        9   12.527   7.23   —   —       10   −34.164   1.50   1.83481   42.7       11   81.139   0.11   —   —       12   34.699   4.78   1.84666   23.8       13   −30.340   0.63   —   —       14   −24.084   2.44   1.79936   45.6       15   −137.360   26.73-10.45-3.07   —   —       16   19.085   3.97   1.48700   70.2       17   −54.588   0.50   —   —        18*   25.073   3.26   1.48755   70.3       19   −27.145   1.20   1.83243   38.0       20   121.546   1.00   —   —       21   −50.404   1.80   1.78523   32.9       22   −14.753   0.90   1.80400   46.6       23   88.783   4.27-2.19-1.47   —   —       24   46.867   4.93   1.49001   82.1       25   −22.237   0.50   —   —        26*   819.574   2.30   1.60547   41.8       27   −40.146   0.00   —   —       28   −40.271   1.00   1.84699   23.8       29   −633.719   —   —   —                 The symbol * designates the aspherical surface which is rotationally symmetrical with respect to the optical axis.             
 
         [0112]     Aspherical surface data (the aspherical surface coefficients not indicated are zero (0.00)):  
                                               Surf. No.   K   A4   A6   A8                    7   0.00     0.22966 × 10 −4     −0.47132 × 10 −7       0.59900 × 10 −10         18   0.00   −0.21485 × 10 −5         26   0.00   −0.39778 × 10 −4     −0.77766 × 10 −7     −0.57543 × 10 −9                     
 
       Embodiment 3  
       [0113]      FIG. 9  is the lens arrangement of the wide-angle zoom lens system, at the short focal length extremity, according to the third embodiment of the present invention.  FIGS. 10A through 10E  show aberrations occurred in the lens arrangement shown in  FIG. 9 .  
         [0114]      FIG. 11  is the lens arrangement of the wide-angle zoom lens system, at the long focal length extremity, according to the third embodiment of the present invention.  FIGS. 12A through 12E  show aberrations occurred in the lens arrangement shown in  FIG. 11 .  
         [0115]     Table 3 shows the numerical data of the third embodiment.  
         [0116]     With respect to the positive first lens group  10 , the negative second lens group  20  and the positive third lens group  30 , the basic lens arrangements thereof are the same as those of the first embodiment.  
         [0117]     However, unlike the first embodiment, the cemented lens elements of the negative second lens group  20  in the third embodiment includes a positive planoconvex lens element and a negative planoconcave lens element, in this order from the object. The flat surfaces of these lens elements are cemented to each other to form a bonding surface.  
         [0118]     The positive fourth lens group  40  includes a positive biconvex lens element, cemented lens elements having a negative meniscus lens element having the convex surface facing toward the object and a positive biconvex lens element, and a negative meniscus lens element having the convex surface facing toward the image, in this order from the object.  
         [0119]     The diaphragm S is provided 1.10 in front of the positive third lens group  30  (surface No.  17 ) on the optical axis.  
                                                           TABLE 3                           FNO. = 1: 3.5-4.9-5.8       f = 16.49-50.03-131.11       W = 41.8-15.6-6.1       fB = 39.51-63.18-75.85            Surf. No.   r   d   Nd   ν                     1   139.704   2.00   1.84666   23.8        2   74.874   1.08   —   —        3   77.759   7.71   1.49700   81.6        4   −3648.112   0.20   —   —        5   62.118   5.46   1.77660   48.8        6   161.181   1.60-32.61-60.90   —   —        7*   97.665   0.10   1.52700   43.7        8   53.300   1.10   1.83481   42.7        9   12.519   7.23   —   —       10   −34.129   1.39   1.83481   42.7       11   82.239   0.11   —   —       12   34.564   5.28   1.84666   23.8       13   −30.655   0.63   —   —       14   −23.942   1.26   1.81465   45.8       15   ∞   1.96   1.69564   37.4       16   −115.577   26.64-10.23-2.96   —   —       17   19.359   3.24   1.48761   70.2       18   −56.381   0.50   —   —        19*   25.719   3.26   1.49007   83.9       20   −26.504   1.20   1.83381   37.8       21   115.503   1.00-1.00-1.00   —   —       22   −49.336   2.00   1.77790   28.3       23   −14.943   0.90   1.80396   44.5       24   86.790   4.17-2.21-1.49   —   —       25   46.170   5.05   1.49486   82.3       26   −21.962   0.50   —   —        27*   793.078   1.00   1.61049   37.2       28   200.000   2.45   1.61400   58.4       29   −38.636   0.50   —   —       30   −40.199   1.00   1.82471   28.5       31   −2323.563   —   —   —                 The symbol * designates the aspherical surface which is rotationally symmetrical with respect to the optical axis.             
 
         [0120]     Aspherical surface data (the aspherical surface coefficients not indicated are zero (0.00)):  
                                               Surf. No.   K   A4   A6   A8                    7   0.00     0.22412 × 10 −4     −0.44784 × 10 −7       0.61590 × 10 −10         19   0.00   −0.14370 × 10 −5       0.14514 × 10 −7         27   0.00   −0.37748 × 10 −4     −0.72698 × 10 −7     −0.49718 × 10 −9                     
 
       Embodiment 4  
       [0121]      FIG. 13  is the lens arrangement of the wide-angle zoom lens system, at the short focal length extremity, according to a fourth embodiment of the present invention.  FIGS. 14A through 14E  show aberrations occurred in the lens arrangement shown in  FIG. 13 .  
         [0122]      FIG. 15  is the lens arrangement of the wide-angle zoom lens system, at the long focal length extremity, according to the fourth embodiment of the present invention.  FIGS. 16A through 16E  show aberrations occurred in the lens arrangement shown in  FIG. 15 .  
         [0123]     Table 4 shows the numerical data of the fourth embodiment.  
         [0124]     The basic lens arrangement is the same as the second embodiment.  
         [0125]     The diaphragm S is provided 1.10 in front of the positive third lens group  30  (surface No.  16 ) on the optical axis.  
                                                           TABLE 4                           FNO. = 1: 3.5-4.9-5.8       f = 16.48-50.00-131.00       W = 41.7-15.6-6.1       fB = 39.44-63.47-76.49            Surf. No.   r   d   Nd   ν                     1   141.414   2.20   1.84666   23.8        2   76.120   0.34   —   —        3   78.986   7.70   1.49700   81.6        4   −8737.731   0.20   —   —        5   62.495   6.10   1.77250   49.6        6   166.603   2.20-32.60-60.96   —   —        7*   182.863   0.10   1.52700   43.7        8   82.725   1.25   1.83481   42.7        9   12.408   7.23   —   —       10   −33.422   1.40   1.83481   42.7       11   78.062   0.11   —   —       12   35.441   4.77   1.84666   23.8       13   −29.134   0.63   —   —       14   −24.425   1.91   1.78049   43.3       15   −113.666   27.12-10.32-3.06   —   —       16   18.742   3.92   1.48749   70.2       17   −52.119   0.50   —   —        18*   25.791   3.35   1.48751   70.2       19   −27.003   1.20   1.83400   42.7       20   121.370   0.80-0.80-0.80   —   —       21   −51.087   2.38   1.75795   29.9       22   −15.098   1.00   1.80399   39.8       23   94.184   4.25-2.21-1.49   —   —       24   47.419   5.13   1.49700   81.6       25   −22.856   0.50   —   —        26*   712.144   2.26   1.58014   41.8       27   −39.605   0.00   —   —       28   −40.788   1.00   1.84699   23.8       29   −556.426   —   —   —                 The symbol * designates the aspherical surface which is rotationally symmetrical with respect to the optical axis.             
 
         [0126]    
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 5 
               
               
                   
                   
               
               
                   
                   
               
               
                   
                 Embod. 1 
                 Embod. 2 
                 Embod. 3 
                 Embod. 4 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                 Cond. (1) 
                 6.74 
                 6.65 
                 6.61 
                 6.66 
               
               
                 Cond. (2) 
                 7.80 
                 7.60 
                 7.47 
                 7.58 
               
               
                 Cond. (3) 
                 3.43 
                 3.49 
                 4.09 
                 3.48 
               
               
                 Cond. (4) 
                 1.63 
                 1.63 
                 2.01 
                 1.61 
               
               
                 Cond. (5) 
                 1.23 
                 1.28 
                 1.16 
                 1.30 
               
               
                 Cond. (6) 
                 0.37 
                 0.38 
                 0.39 
                 0.39 
               
               
                   
               
             
          
         
       
     
         [0127]     Aspherical surface data (the aspherical surface coefficients not indicated are zero (0.00)):
 
Surf. No. K A4 A6 A8
 
7 0.00 0.25348×10 −4  −0.53825×10 −7  0.58240×10 −10  
 
18 0.00 −0.18060×10 −5 
 
26 0.00 −0.41047×10 −4  −0.71683×10 −7  −0.67512×10 −9 
 
         [0128]     The numerical values of each condition for each embodiment are shown in Table 5.  
         [0129]     As can be understood from Table 6, the first through fourth embodiments satisfy conditions ( 1 ) through ( 6 ). Furthermore, as can be understood from the aberration diagrams, the various aberrations are adequately corrected.  
         [0130]     According to the above description, a wide-angle zoom lens system of a four-lens-group arrangement, i.e., negative, positive, negative and positive lens groups, in this order from the object, having the following features can be obtained:  
         [0131]     (i) being suitable for a digital SLR camera having a smaller imaging device;  
         [0132]     (ii) the angle-of-view of approximately 80° at the short focal length extremity; and  
         [0133]     (iii) a zoom ratio exceeding 8.  
         [0134]     Obvious changes may be made in the specific embodiments of the present invention described herein, such modifications being within the spirit and scope of the invention claimed. It is indicated that all matter contained herein is illustrative and does not limit the scope of the present invention.