Abstract:
The invention provides a zoom optical system comprising at least three lens groups and designed to implement zooming by varying a separation between the respective lens groups. The zoom optical system includes, on an image plane side with respect to a stop, a lens group comprising a plurality of lenses and having positive refracting power throughout. The lens group having positive refracting power includes an air double-convex positive lens in it.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a small-format zoom optical system having improved imaging capabilities, and an imaging apparatus incorporating the same. 
         [0002]    In recent years, a bifocal changeover type imaging lens has been proposed for a small-format zoom imaging lens having fewer driving mechanisms (see JP(A) 2007-93961). The optical system set forth in Patent Publication 1 comprises three groups of negative/positive/positive profile, and is designed to implement zooming by moving only the second lens group in the optical axis direction. And unlike a commonly used zoom lens, what is required there is only to satisfy bifocal imaging capabilities at the wide-angle end and telephoto ends so that during zooming the first and third lens groups can remain fixed, making it possible to simplify the mechanism involved. 
       SUMMARY OF THE INVENTION 
       [0003]    For the zoom optical system of the invention comprising at least three lens groups and designed to implement zooming by varying the separation between the respective lens groups, it is preferable to include on an image plane side with respect to a stop a lens group comprising a plurality of lenses and having positive refracting power throughout, and include an air double-convex lens within the lens group having positive refracting power. 
         [0004]    The requirements for, and advantages of such arrangement are now explained. 
         [0005]    In the inventive zoom optical system, the air lens of double-convex shape, i.e., a lens concave on its image plane side and a lens concave on its object side are located in the zoom group forming part of the imaging lens and having positive refracting power while the concave surfaces are opposite to each other so that the front principal point of the zoom lens group can be shift toward the object side, and the spacing or the so-called principal point separation between the front principal point and the rear principal point of the zoom lens group can be spread wide. 
         [0006]    That is, an object image can be transferred to the image plane without giving rise to significant movement of the zoom lens group in the optical axis direction. Thus, the desired high magnifications can be ensured by limited movement of the lens group in the optical axis direction. It follows that sensible tradeoffs can be offered between lens size reductions all along lens length and high zoom ratios. 
         [0007]    In addition, the principal point separation of the zoom lens group is spread so wide that the focal lengths of the lens groups located before and after it can be made long. This is preferable because power is kept low and lens thickness is reduced, contributing to size reductions and making it possible to use low refractive index vitreous material, and because sensibility to decentration remains low as well 
         [0008]    Preferably, the air double-convex lens should satisfy the following Condition (1): 
         [0000]      −0.5≦( Ra 1+ Ra 2)/( Ra 1− Ra 2)≦0.5  (1)
 
         [0000]    where Ra 1  is the radius of curvature of the surface of the air lens on the object side, and Ra 2  is the radius of curvature of the surface of the air lens on the image plane side. 
         [0009]    Condition (1) is indicative of the shaping factor of the double-convex air lens formed in the second lens group. 
         [0010]    Exceeding the upper limit to Condition (1) will cause the radius of curvature of the surface of the air lens on the object side to become too large to locate the front principal point more on the object side. Being short of the lower limit to Condition (1) will cause the radius of curvature of the image plane of the air lens to become too large, resulting in location of the rear principal point more on the object side. In either case, the principal point separation of the zoom lens group will become narrow, rendering it difficult to offer a sensible tradeoff between full length reductions and high zoom ratios. Keeping the shaping factor well in the range of Condition (1) is thus preferable because fluctuations of spherical aberrations and coma can be well corrected. 
         [0011]    If Condition (1) is reduced down to the following Condition (1-1), it is then possible to achieve full length reductions while keeping more satisfactory performance. 
         [0000]      −0.2≦( Ra 1+ Ra 2)/( Ra 1− Ra 2)≦0.2  (1-1)
 
         [0012]    Preferably, the second lens group should satisfy the following Condition (2): 
         [0000]      0.2 ≦|f 2|/{( fw·ft ) 1/2 }≦1.0  (2)
 
         [0000]    where f 2  is the focal length of the second lens group, fw is the focal length of the optical system at the wide-angle end, and ft is the focal length of the optical system at the telephoto end. 
         [0013]    Condition (2) is indicative of the focal length of the second lens group. 
         [0014]    Generally, the stronger the refracting power of the second lens group, the smaller the amount of movement of the second lens group during zooming becomes, so that the full length of the optical system can be curtailed. 
         [0015]    However, increasing refracting power will generally render correction of aberrations difficult. 
         [0016]    Being short of the lower limit to Condition (2) is not preferable because spherical aberrations and coma become worse. Exceeding the upper limit to Condition (2) is again not preferable because there is an increase in the amount of movement of the second lens group during zooming. 
         [0017]    If Condition (2) is reduced down to the following Condition (2-1), it is then possible to achieve full length reductions while keeping more satisfactory performance. 
         [0000]      0.3 ≦|f 2|/{( fw·ft ) 1/2 }≦0.6  (2-1)
 
         [0018]    Preferably, the third lens group should satisfy the following Condition (3): 
         [0000]      0.2( R 4 a+R 4 b )/( R 4 a−R 4 b )≦5.0  (3)
 
         [0000]    where R 4   a  is the radius of curvature of the surface of the third lens group on the object side, and R 4   b  is the radius of curvature of the surface of the third lens group on the image plane side. 
         [0019]    Condition (3) is indicative of the shaping factor of a positive lens in the third lens group. 
         [0020]    Exceeding the upper limit, or being short of the lower limit, to Condition (3) is not preferable because of a worsening of distortion and field curvature. Keeping the shaping factor well in the range of Condition (3) enables the positions of the principal points of the third lens group to shift on the image side while aberration fluctuations are kept in good conditions, making full length reductions possible. 
         [0021]    If Condition (3) is reduced down to the following Condition (3-1), it is then possible to achieve full length reductions while keeping more satisfactory performance. 
         [0000]      1.0≦( R 4 a+R 4 b )/( R 4 a−R 4 b )≦2.5  (3-1)
 
         [0022]    Preferably, the second lens group should include two back-to-back lenses of negative refracting power. 
         [0023]    If two back-to-back negative lenses are located in the zoom lens group, then the principal points spread wide upon seeing through the combined concave lenses and the front principal point of the zoom lens group can be located more on the object side. 
         [0024]    Preferably, the second lens group should comprise at least four lenses: lenses having positive, positive, negative and negative refracting powers as viewed in order from the object side. 
         [0025]    If the zoom lens group is built up of lenses having positive, positive, negative and negative refracting powers as viewed in order from the object side, it is then possible to locate the principal points of the zoom lens group on the most object side with a reduced number of lenses. 
         [0026]    Preferably, the first lens group should remain fixed during zooming from the wide-angle end toward the telephoto end or upon imaging from imaging at infinity to close-range imaging. 
         [0027]    As the full length remains fixed during zooming, it makes sure the strength of an associated lens barrel easily and simplifies the construction of the lens barrel, leading to size reductions. 
         [0028]    In the imaging apparatus of the invention comprising an imaging device located on the image side of the zoom optical system and having an imaging plane capable of converting an optical image to electric signals, it is preferable that the zoom optical system is any one of the zoom optical systems as recited above. 
         [0029]    More preferably, the requirements as recited above should be satisfied simultaneously in any desired combinations. 
         [0030]    Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification. 
         [0031]    The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the invention will be indicated in the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]      FIG. 1  is illustrative in section of the optical system according to Example 1. 
           [0033]      FIG. 2  is illustrative in section of the optical system according to Example 1. 
           [0034]      FIG. 3  is illustrative in section of the optical system according to Example 2. 
           [0035]      FIG. 4  is illustrative in section of the optical system according to Example 2. 
           [0036]      FIG. 5  is an aberration diagram for the optical system according to Example 1. 
           [0037]      FIG. 6  is an aberration diagram for the optical system according to Example 1. 
           [0038]      FIG. 7  is an aberration diagram for the optical system according to Example 2. 
           [0039]      FIG. 8  is an aberration diagram for the optical system according to Example 2. 
           [0040]      FIG. 9  is a front perspective view illustrative of the outside shape of a digital camera. 
           [0041]      FIG. 10  is a rear perspective view illustrative of the outside shape of the digital camera. 
           [0042]      FIG. 11  is a sectional view illustrative of the construction of the digital camera. 
           [0043]      FIG. 12  is a front perspective view illustrative of a personal computer with its cover shut open. 
           [0044]      FIG. 13  is a sectional view of an image-taking optical system in the personal computer. 
           [0045]      FIG. 14  is a side view of the state of  FIG. 12 . 
           [0046]      FIG. 15  is a front view of a cellular phone. 
           [0047]      FIG. 16  is a side view of the cellular phone. 
           [0048]      FIG. 17  is a sectional view of an image-taking optical system in the cellular phone. 
       
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0049]    The optical systems of Examples 1 and 2 are now explained. 
         [0050]      FIG. 1  is illustrative in section of the optical system of Example 1 at the wide-angle end and in close proximity to the wide-angle end, and  FIG. 2  is illustrative in section of the optical system of Example 1 at the telephoto end and in close proximity to the telephoto end. More specifically,  FIG. 1(   a ) is a sectional view of the optical system of Example 1 at the wide-angle end;  FIG. 1(   b ) is a sectional view of the optical system of Example in close proximity to the wide-angle end;  FIG. 2(   a ) is a sectional view of the optical system of Example 1 at the telephoto end; and  FIG. 2(   b ) is a sectional view of the optical system of Example 1 in close proximity to the telephoto end. 
         [0051]    As shown in  FIGS. 1 and 2 , the optical system of Example 1 includes, in order from the object side, a first lens group G 1  of negative refracting power, a second lens group G 2  of positive refracting power, and a third lens group G 3  of positive refracting power. 
         [0052]    The first lens group G 1  is made up of a cemented lens in which a negative meniscus lens L 1  convex on its objet side and a positive meniscus lens L 2  convex on its object side are cemented together in order from the object side, and has a negative refracting power throughout. The first lens group G 1  remains fixed during zooming. 
         [0053]    The second lens group G 2  is made up of, in order from the object side, a double-convex positive lens L 3 , a cemented lens in which a double-convex positive lens L 4  and a double-concave negative lens L 5  are cemented together, and a negative meniscus lens L 6  concave on its object side, and has positive refracting power throughout. 
         [0054]    The third lens group G 3  is made up of one lens: a positive meniscus lens L 7  concave on its object plane. The third lens group G 3  remains fixed during zooming. 
         [0055]    CG and I stand for a cover glass and an image plane, respectively. 
         [0056]    From the wide-angle state shown in  FIG. 1(   a ) to the telephoto end state shown in  FIG. 2(   a ), the second lens group G 2  moves to the object side. The zoom ratio from the wide-angle end to the telephoto end is 2.55, and the optical full length remains constant at 8.9 mm. 
         [0057]    Upon image taking of a close-range object point at the wide-angle end, the second lens group G 2  moves to the object side for focusing, as shown in  FIG. 1(   b ). 
         [0058]    Upon image taking of a close-range object point at the telephoto end, the second lens group G 2  moves to the image side for focusing, as shown in  FIG. 2(   b ). 
         [0059]    Nine aspheric surfaces are used: one for the object-side surface of the negative meniscus lens L 1  in the first lens group G 1 , one for the image-side surface of the positive meniscus lens L 2  in the first lens group G 1 , two for both surfaces of the double-convex positive lens L 3  located on the most object side of the second lens group G 2 , one for the image-side surface of the double-concave negative lens L 5  in the second lens group G 2 , two for both surfaces of the negative meniscus lens L 6  in the second lens group G 2 , and two for both surfaces of the positive meniscus lens L 7  in the third lens group G 3 . 
         [0060]      FIG. 3  is illustrative in section of the optical system of Example 2 at the wide-angle end and in close proximity to the wide-angle end, and  FIG. 4  is illustrative in section of the optical system of Example 2 at the telephoto end and in close proximity to the telephoto end. More specifically,  FIG. 3(   a ) is a sectional view of the optical system of Example 2 at the wide-angle end;  FIG. 3(   b ) is a sectional view of the optical system of Example 2 in close proximity to the wide-angle end;  FIG. 4(   a ) is a sectional view of the optical system of Example 2 at the telephoto end; and  FIG. 4(   b ) is a sectional view of the optical system of Example 2 in close proximity to the telephoto end. 
         [0061]    As shown in  FIGS. 3 and 4 , the optical system of Example 2 includes, in order from the object side, a first lens group G 1  of negative refracting power, a second lens group G 2  of positive refracting power and a third lens group G 3  of positive refracting power. 
         [0062]    The first lens group G 1  is made up of a cemented lens in which a negative meniscus lens L 1  convex on its object side and a positive meniscus lens L 2  convex on its object side are cemented together in order from the object side, and has negative refracting power throughout. 
         [0063]    The second lens group G 2  is made up of, in order from the object side, a double-convex positive lens L 3 , a cemented lens in which a double-convex positive lens L 4  and a double-concave negative lens L 5  are cemented together, and a negative meniscus lens L 6  concave on its object side, and has positive refracting power throughout. 
         [0064]    The third lens group G 3  is made up of one lens: a positive meniscus lens L 7  concave on its object side. The third lens group G 3  remains fixed during zooming. 
         [0065]    CG and I stand for a cover glass and an image plane, respectively. 
         [0066]    From the wide-angle end state shown in  FIG. 3(   a ) to the telephoto end state shown in  FIG. 4(   a ), the first lens group G 1  moves to the object side, and the second lens group G 2  moves to the object side. The cover glass CG moves to the object side, too. The zoom ratio from the wide-angle end to the telephoto end is 2.8. 
         [0067]    Upon image-taking of a close-range object point at the wide-angle end, the second lens group G 2  moves to the object side for focusing, as shown in  FIG. 3(   b ). 
         [0068]    Upon image taking of a close-range object point at the telephoto end, the second lens group G 2  moves to the image side for focusing, as shown in  FIG. 4(   b ). 
         [0069]    Nine aspheric surfaces are used: one for the object-side surface of the negative meniscus lens L 1  in the first lens group L 1 , one for the image-side surface of the positive meniscus lens L 2  in the first lens group G 1 , two for both surfaces of the double-convex positive lens L 3  located on the most object side of the second lens group G 2 , one for the image-side surface of the double-concave negative lens L 5  in the second lens group G 2 , two for both surfaces of the negative meniscus lens L 6  in the second lens group G 2 , and two for both surfaces of the positive meniscus lens L 7  in the third lens group G 3 . 
         [0070]    Numeral data on Examples 1 and 2 are given below. In these numeral data, r is the radius of curvature of each lens surface, d is a lens thickness and an air separation, Nd and νd are d-line (λ=587.6 nm) refractive index and Abbe constant, and ER is an effective diameter. Fno and ω are an F-number and a half angle of view (°), respectively. 
         [0071]    In the following specifications for Numeral Examples 1 and 2, the surfaces followed by (Aspheric Surface) are the ones of aspheric shape. Aspheric surface shape is represented by the following formula (9): 
         [0000]        X ( H )=( H   2   /r )/{1+[1−(1 +K )·( H   2   /r   2 )] 1/2   }+A 4 H   4   +A 6 H   6   +A 8 H   8   +A 10 H   10   +A 12 H   12  
 
         [0000]    where H is a height vertical to an optical axis, X(H) is an amount of displacement at height H in the optical axis direction provided that the origin is defined by a vertex, r is the paraxial radius of curvature, K is the conic constant, and A2, A4, A6, A8, A10 and A12 are the 2 nd -, 4 th -6 th -, 8 th -, 10 th - and 12 th -order aspheric coefficients. 
       Numeral Example 1 
       [0072]      
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
               
             
               
               
               
             
               
             
               
               
               
               
             
               
               
               
             
               
               
               
               
             
           
               
                   
               
             
             
               
                 Unit mm 
               
               
                   
               
               
                 Surface Data 
               
             
          
           
               
                 Surface No. 
                 r 
                 d 
                 nd 
                 νd 
                 ER 
               
               
                   
               
               
                  1 (Aspheric Surface) 
                 284.077 
                 0.30 
                 1.69350 
                 53.20 
                 1.81 
               
               
                  2 
                 3.822 
                 0.28 
                 1.63387 
                 23.38 
                 1.61 
               
               
                  3 (Aspheric Surface) 
                 3.814 
                 D3 
                 1.00000 
                   
                 1.58 
               
               
                  4 (Stop) 
                 ∞ 
                 0.00 
                 1.00000 
                   
                 1.58 
               
               
                  5 (Aspheric Surface) 
                 2.077 
                 0.76 
                 1.59201 
                 67.02 
                 0.95 
               
               
                  6 (Aspheric Surface) 
                 −24.100 
                 0.10 
                 1.00000 
                   
                 1.04 
               
               
                  7 
                 2.224 
                 0.56 
                 1.83400 
                 37.16 
                 1.05 
               
               
                  8 
                 −9.331 
                 0.21 
                 1.61000 
                 25.60 
                 1.00 
               
               
                  9 (Aspheric Surface) 
                 1.619 
                 D9 
                 1.00000 
                   
                 0.90 
               
               
                 10 (Aspheric Surface) 
                 −2.350 
                 0.27 
                 1.54454 
                 55.90 
                 0.88 
               
               
                 11 (Aspheric Surface) 
                 −17868.043 
                 D11 
                 1.00000 
                   
                 1.05 
               
               
                 12 (Aspheric Surface) 
                 −5.803 
                 1.42 
                 1.54454 
                 55.90 
                 2.00 
               
               
                 13 (Aspheric Surface) 
                 −1.777 
                 D13 
                 1.00000 
                   
                 2.22 
               
               
                 14 
                 ∞ 
                 0.30 
                 1.51633 
                 64.14 
                 2.50 
               
               
                 15 
                 ∞ 
                 D15 
                 1.00000 
                   
                 2.50 
               
               
                 Image Plane 
                 ∞ 
               
               
                   
               
             
          
           
               
                 Aspheric Data 
               
               
                   
               
             
          
           
               
                 1 st  Surface 
                   
                   
                   
                   
                   
               
             
          
           
               
                 K = −1.000, 
               
               
                 A4 = −3.27261E−02, A6 = 7.59290E−03, A8 = −4.42538E−04, A10 = −6.84510E−05 
               
             
          
           
               
                 3 rd  Surface 
                   
                   
                   
                   
                   
               
               
                 K = −1.000, 
                   
                   
                   
                   
                   
               
             
          
           
               
                 A4 = −4.03320E−02, A6 = 1.10490E−02, A8 = −3.36010E−04, A10 = −3.26020E−04 
               
             
          
           
               
                 5 th  Surface 
                   
                   
                   
                   
                   
               
               
                 K = 0.000, 
                   
                   
                   
                   
                   
               
             
          
           
               
                 A4 = −2.68318E−02, A6 = −2.49567E−02, A8 = 7.31686E−03, A10 = −1.52062E−02 
               
             
          
           
               
                 6 th  Surface 
                   
                   
                   
                   
                   
               
               
                 K = 0.000, 
                   
                   
                   
                   
                   
               
             
          
           
               
                 A4 = −4.27094E−02, A6 = −2.02273E−02, A8 = 1.03398E−03, A10 = −7.25287E−03 
               
             
          
           
               
                 9 th  Surface 
                   
                   
                   
                   
                   
               
               
                 K = 0.000, 
                   
                   
                   
                   
                   
               
             
          
           
               
                 A4 = 7.35129E−02, A6 = 8.47754E−04, A8 = 7.68574E−02 
               
             
          
           
               
                 10 th  Surface 
                   
                   
                   
                   
                   
               
               
                 K = 0.000, 
                   
                   
                   
                   
                   
               
             
          
           
               
                 A4 = −1.44219E−01, A6 = 8.68545E−03, A8 = 1.08777E−01, A10 = −1.08300E−01 
               
             
          
           
               
                 11 th  Surface 
                   
                   
                   
                   
                   
               
               
                 K = −1.000, 
                   
                   
                   
                   
                   
               
             
          
           
               
                 A4 = −6.99290E−02, A6 = 8.61586E−02, A8 = −1.22815E−02, A10 = −6.73050E−03 
               
             
          
           
               
                 12 th  Surface 
                   
                   
                   
                   
                   
               
               
                 K = 0.000, 
                   
                   
                   
                   
                   
               
             
          
           
               
                 A4 = −2.97803E−02, A6 = 9.93186E−03, A8 = −1.40598E−03, A10 = −4.49689E−07 
               
             
          
           
               
                 13 th  Surface 
                   
                   
                   
                   
                   
               
               
                 K = −0.491, 
                   
                   
                   
                   
                   
               
             
          
           
               
                 A4 = 5.60354E−03, A6 = 1.33571E−03, A8 = 3.98382E−04, A10 = −7.33348E−05 
               
               
                   
               
               
                 Zoom Data 
               
               
                   
               
             
          
           
               
                 Zoom Ratio 
                 2.55 
                   
                   
                   
                   
               
               
                   
               
             
          
           
               
                   
                 Wide-Angle  
                 Close Proximity to  
                 Telephoto 
                 Close Proximity to 
               
               
                   
                 End 
                 the Wide-Angle End 
                 End 
                 the Telephoto End 
               
               
                   
               
               
                 Focal Length 
                 3.12 
                 3.40 
                 7.96 
                 7.74 
               
               
                 Fno 
                 2.81 
                 2.98 
                 4.97 
                 4.92 
               
               
                 Angle of View (2 ω) 
                 75.33 
                 68.32 
                 31.85 
                 32.74 
               
               
                 Image Height 
                 2.25 
                 2.25 
                 2.25 
                 2.25 
               
               
                 Full Lens Length 
                 8.90 
                 8.90 
                 8.90 
                 8.90 
               
               
                 BF 
                 0.90 
                 0.90 
                 0.90 
                 0.90 
               
               
                 Entrance Pupil 
                 2.22 
                 2.11 
                 0.54 
                 0.64 
               
               
                   
               
             
          
           
               
                 Postition 
               
               
                   
               
               
                 Exit Pupil Position A (Exit Pupil Position from the Last Lens Surface) 
               
             
          
           
               
                   
                 −10.39 
                 −14.16 
                 16.52 
                 17.42 
               
             
          
           
               
                 Exit Pupil Position B (Exit Pupil Position from the Image Plane) 
               
             
          
           
               
                   
                 −11.19 
                 −14.96 
                 15.72 
                 16.62 
               
             
          
           
               
                 Front Principal Point Position 
               
             
          
           
               
                   
                 4.47 
                 4.74 
                 12.53 
                 11.96 
               
             
          
           
               
                 Rear Principal Point Position 
               
             
          
           
               
                   
                 −2.82 
                 −3.21 
                 −7.65 
                 −7.56 
               
               
                 D3 
                 2.83 
                 2.60 
                 0.20 
                 0.30 
               
               
                 D9 
                 0.78 
                 0.78 
                 0.78 
                 0.78 
               
               
                 D11 
                 0.48 
                 0.72 
                 3.12 
                 3.01 
               
               
                 D13 
                 0.30 
                 0.30 
                 0.30 
                 0.30 
               
               
                 D15 
                 0.30 
                 0.30 
                 0.30 
                 0.30 
               
               
                   
               
             
          
           
               
                 Individual Lens Data 
               
             
          
           
               
                 Lens 
                 Starting Surface 
                 Focal Length 
               
               
                   
               
               
                 L1 
                 1 
                 −5.59 
               
               
                 L2 
                 2 
                 227.80 
               
               
                 L3 
                 5 
                 3.27 
               
               
                 L4 
                 7 
                 2.20 
               
               
                 L5 
                 8 
                 −2.25 
               
               
                 L6 
                 10 
                 −4.32 
               
               
                 L7 
                 12 
                 4.18 
               
               
                   
               
             
          
           
               
                 Zoom Lens Group Data 
               
               
                   
               
             
          
           
               
                 Group 
                 Starting Surface 
                 Focal Length 
                 Lens Arragement Length 
               
               
                   
               
               
                 G1 
                 1 
                 −5.5661 
                 0.5800 
               
               
                 G2 
                 4 
                 2.3649 
                 1.6274 
               
               
                 G3 
                 10 
                 −4.3153 
                 0.2726 
               
               
                 G4 
                 12 
                 4.1830 
                 2.0245 
               
               
                   
               
             
          
           
               
                 Group 
                 Front Principal Point Position 
                 Rear Principal Point Position 
               
               
                   
               
               
                 G1 
                 0.3382 
                 −0.0101 
               
               
                 G2 
                 −0.2279 
                 −1.0366 
               
               
                 G3 
                 −0.0000 
                 −0.1765 
               
               
                 G4 
                 1.1820 
                 −0.1358 
               
               
                   
               
             
          
           
               
                   
                 Wide-Angle 
                 Intermediate  
                 Telephoto  
               
               
                 Group 
                 Magnification 
                 Magnification 
                 Magnification 
               
               
                   
               
               
                 G1 
                 0.0000 
                 0.0000 
                 0.0526 
               
               
                 G2 
                 −0.4065 
                 −0.7426 
                 −0.4472 
               
               
                 G3 
                 1.5404 
                 2.1504 
                 1.5951 
               
               
                 G4 
                 0.8952 
                 0.8951 
                 0.8952 
               
               
                   
               
             
          
         
       
     
       Numeral Example 2 
       [0073]      
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
             
               
               
               
               
               
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
               
             
               
               
               
               
               
             
               
             
               
               
               
             
               
             
               
               
               
               
             
               
               
               
             
               
               
               
               
             
           
               
                   
               
             
             
               
                 Unit mm 
               
               
                   
               
               
                 Surface Data 
               
             
          
           
               
                 Surface No. 
                 r 
                 d 
                 nd 
                 νd 
                 ER 
               
               
                   
               
               
                  1 (Aspheric Surface) 
                 275.896 
                 0.30 
                 1.69350 
                 53.20 
                 1.83 
               
               
                  2 
                 3.904 
                 0.28 
                 1.63387 
                 23.38 
                 1.64 
               
               
                  3 (Aspheric Surface) 
                 3.625 
                 D3 
                 1.00000 
                   
                 1.61 
               
               
                  4 (Stop) 
                 ∞ 
                 −0.10 
                 1.00000 
                   
                 0.85 
               
               
                  5 (Aspheric Surface) 
                 2.082 
                 0.77 
                 1.59201 
                 67.02 
                 0.88 
               
               
                  6 (Aspheric Surface) 
                 −24.177 
                 0.10 
                 1.00000 
                   
                 0.98 
               
               
                  7 
                 2.237 
                 0.56 
                 1.83400 
                 37.16 
                 1.00 
               
               
                  8 
                 −9.389 
                 0.21 
                 1.61000 
                 25.60 
                 0.94 
               
               
                  9 (Aspheric Surface) 
                 1.627 
                 D9 
                 1.00000 
                   
                 0.90 
               
               
                 10 (Aspheric Surface) 
                 −2.333 
                 0.27 
                 1.54454 
                 55.90 
                 0.94 
               
               
                 11 (Aspheric Surface) 
                 −13612.925 
                 D11 
                 1.00000 
                   
                 1.09 
               
               
                 12 (Aspheric Surface) 
                 −6.222 
                 1.42 
                 1.54454 
                 55.90 
                 2.00 
               
               
                 13 (Aspheric Surface) 
                 −1.750 
                 D13 
                 1.00000 
                   
                 2.22 
               
               
                 14 
                 ∞ 
                 0.30 
                 1.51633 
                 64.14 
                 2.50 
               
               
                 15 
                 ∞ 
                 D15 
                 1.00000 
                   
                 2.50 
               
               
                 Image Plane 
                 ∞ 
                   
                   
                   
                   
               
               
                   
               
             
          
           
               
                 Aspheric Data 
               
               
                   
               
             
          
           
               
                 1 st  Surface 
                   
                   
                   
                   
                   
               
               
                 K = −1.000, 
                   
                   
                   
                   
                   
               
             
          
           
               
                 A4 = −3.61788E−02, A6 = 9.84129E−03, A8 = −9.01148E−04, A10 = −4.87278E−05 
               
             
          
           
               
                 3 rd  Surface 
                   
                   
                   
                   
                   
               
               
                 K = −1.000, 
                   
                   
                   
                   
                   
               
             
          
           
               
                 A4 = −4.39300E −02, A6 = 1.27250E−02, A8 = −9.19580E−05, A10 = −5.33170E−04 
               
             
          
           
               
                 5 th  Surface 
                   
                   
                   
                   
                   
               
               
                 K = 0.000, 
                   
                   
                   
                   
                   
               
             
          
           
               
                 A4 = −3.42899E−02, A6 = −4.60442E−02, A8 = 2.41371E−02, A10 = −3.36031E−02 
               
             
          
           
               
                 6 th  Surface 
                   
                   
                   
                   
                   
               
               
                 K = 0.000, 
                   
                   
                   
                   
                   
               
             
          
           
               
                 A4 = −7.20113E−02, A6 = −2.65029E−02, A8 = −1.13623E−03, A10 = −5.51827E−03 
               
             
          
           
               
                 9 th  Surface 
                   
                   
                   
                   
                   
               
               
                 K = 0.000, 
                   
                   
                   
                   
                   
               
             
          
           
               
                 A4 = 1.34179E−01, A6 = 2.12632E−02, A8 = 1.91144E−01 
               
             
          
           
               
                 10 th  Surface 
                   
                   
                   
                   
                   
               
               
                 K = 0.000, 
                   
                   
                   
                   
                   
               
             
          
           
               
                 A4 = −7.40533E−02, A6 = 7.78628E−02, A8 = 1.07051E−01, A10 = −5.08971E−02 
               
             
          
           
               
                 11 th  Surface 
                   
                   
                   
                   
                   
               
               
                 K = −1.000, 
                   
                   
                   
                   
                   
               
             
          
           
               
                 A4 = −3.31306E−02, A6 = 8.65468E−02, A8 = 8.12362E−04, A10 = −1.95356E−02 
               
             
          
           
               
                 12 th  Surface 
                   
                   
                   
                   
                   
               
               
                 K = 0.000, 
                   
                   
                   
                   
                   
               
             
          
           
               
                 A4 = −2.56061E−02, A6 = 6.27279E−03, A8 = −9.11807E−04, A10 = 3.62897E−06 
               
             
          
           
               
                 13 th  Surface 
                   
                   
                   
                   
                   
               
               
                 K = −0.515, 
                   
                   
                   
                   
                   
               
             
          
           
               
                 A4 = 9.31569E−03, A6 = 8.69481E−04, A8 = 3.44678E−05, A10 = −1.09508E−05 
               
               
                   
               
               
                 Zoom Data 
               
               
                   
               
             
          
           
               
                 Zoom Ratio 
                 2.77 
                   
                   
                   
                   
               
               
                   
               
             
          
           
               
                   
                 Wide-Angle 
                 Close Proximity to 
                 Telephoto 
                 Close Proximity to 
               
               
                   
                 End 
                 the Wide-Angle End 
                 End 
                 the Telephoto End 
               
               
                   
               
               
                 Focal Length 
                 3.10 
                 3.43 
                 8.57 
                 8.47 
               
               
                 Fno 
                 2.84 
                 3.04 
                 5.43 
                 5.43 
               
               
                 Angle of View(2 ω) 
                 75.28 
                 67.39 
                 29.48 
                 30.10 
               
               
                 Image Height 
                 2.25 
                 2.25 
                 2.25 
                 2.25 
               
               
                 Full Lens Length 
                 9.01 
                 9.01 
                 9.66 
                 9.66 
               
               
                 BF 
                 0.92 
                 0.92 
                 1.04 
                 1.04 
               
               
                 Entrance Pupil 
                 2.25 
                 2.13 
                 0.63 
                 0.70 
               
               
                   
               
             
          
           
               
                 Position 
               
               
                   
               
               
                 Exit Pupil Position A (Exit Pupil Position from the Last Lens Surface) 
               
             
          
           
               
                   
                 −11.23 
                 −16.89 
                 11.82 
                 12.10 
               
             
          
           
               
                 Exit Pupil Position B (Exit Pupil Position from the Image Plane) 
               
             
          
           
               
                   
                 −12.05 
                 −17.71 
                 10.89 
                 11.17 
               
             
          
           
               
                 Front Principal Point Position 
               
             
          
           
               
                   
                 4.55 
                 4.89 
                 15.95 
                 15.50 
               
             
          
           
               
                 Rear Principal Point Position 
               
             
          
           
               
                   
                 −2.77 
                 −3.22 
                 −8.13 
                 −8.17 
               
               
                 D3 
                 2.96 
                 2.69 
                 0.30 
                 0.38 
               
               
                 D9 
                 0.80 
                 0.80 
                 0.80 
                 0.80 
               
               
                 D11 
                 0.51 
                 0.79 
                 3.71 
                 3.63 
               
               
                 D13 
                 0.30 
                 0.30 
                 0.30 
                 0.30 
               
               
                 D15 
                 0.32 
                 0.32 
                 0.44 
                 0.44 
               
               
                   
               
             
          
           
               
                 Individual Lens Data 
               
               
                   
               
             
          
           
               
                 Lens 
                 Starting Surface 
                 Focal Length 
               
               
                   
               
               
                 L1 
                 1 
                 −5.71 
               
               
                 L2 
                 2 
                 −131.48 
               
               
                 L3 
                 5 
                 3.27 
               
               
                 L4 
                 7 
                 2.21 
               
               
                 L5 
                 8 
                 −2.26 
               
               
                 L6 
                 10 
                 −4.29 
               
               
                 L7 
                 12 
                 4.02 
               
               
                   
               
             
          
           
               
                 Zoom Lens Group Data 
               
               
                   
               
             
          
           
               
                   
                   
                   
                 Lens Arragement  
               
               
                 Group 
                 Starting Surface 
                 Focal Length 
                 Length 
               
               
                   
               
               
                 G1 
                 1 
                 −5.3218 
                 0.5800 
               
               
                 G2 
                 4 
                 2.3761 
                 1.5412 
               
               
                 G3 
                 10 
                 −4.2857 
                 0.2726 
               
               
                 G4 
                 12 
                 4.0193 
                 2.0223 
               
               
                   
               
             
          
           
               
                   
                 Front Principal 
                 Rear Principal 
               
               
                 Group 
                 Point Position 
                 Point Position 
               
               
                   
               
               
                 G1 
                 0.3391 
                 −0.0093 
               
               
                 G2 
                 −0.3259 
                 −1.0430 
               
               
                 G3 
                 −0.0000 
                 −0.1765 
               
               
                 G4 
                 1.1519 
                 −0.1740 
               
               
                   
               
             
          
           
               
                   
                 Wide-Angle 
                 Intermediate 
                 Telephoto 
               
               
                 Group 
                 Magnification 
                 Magnification 
                 Magnification 
               
               
                   
               
               
                 G1 
                 0.0000 
                 0.0000 
                 0.0504 
               
               
                 G2 
                 −0.4249 
                 −0.8112 
                 −0.4707 
               
               
                 G3 
                 1.5608 
                 2.3444 
                 1.6253 
               
               
                 G4 
                 0.8769 
                 0.8470 
                 0.8769 
               
               
                   
               
             
          
         
       
     
         [0074]      FIGS. 5 to 8  are aberration diagrams for Examples 1 and 2 upon focusing at infinity. More specifically,  FIG. 5(   a ) is an aberration diagram for Example 1 at the wide-angle end;  FIG. 5(   b ) is an aberration diagram for Example 1 in close proximity to the wide-angle end;  FIG. 6(   a ) is an aberration diagram for Example 1 at the telephoto end;  FIG. 6(   b ) is an aberration diagram for Example 1 in close proximity to the telephoto end;  FIG. 7(   a ) is an aberration diagram for Example 2 at the wide-angle end;  FIG. 7(   b ) is an aberration diagram for Example 2 in close proximity to the wide-angle end;  FIG. 8(   a ) is an aberration diagram for Example 2 at the telephoto end; and  FIG. 8(   b ) is an aberration diagram for Example 2 in close proximity to the telephoto end. 
         [0075]    Spherical aberration and chromatic aberration of magnification are indicated by numerals at the respective wavelengths: 486.1 nm (F-line: one-dotted line), 587.6 nm (d-line: broken line), and 656.3 nm (C-line: solid line). Astigmatism is provided with the sagittal image surface as a solid line and the meridional image surface as a dotted line, and FNO and FIY are indicative of an F-number and an image height, respectively. 
         [0076]    Set out below are the values of Conditions (1), (2) and (3) in Examples 1 and 2. 
         [0000]    
       
         
               
               
               
             
               
               
               
             
           
               
                   
               
               
                 Conditions 
                 Example 1 
                 Example 2 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 (1) 
                 −0.18 
                 −0.18 
               
               
                 (2) 
                 0.47 
                 0.67 
               
               
                 (3) 
                 1.88 
                 1.78 
               
               
                   
               
             
          
         
       
     
         [0077]    With the inventive zoom optical system as embodied above, it is possible to offer a sensible tradeoff between size reductions in the full lens length direction and high zoom ratios. It is also possible to achieve cost reductions because the necessary power is kept so low that the lenses can be made thin and low refractive index vitreous material can be used, resulting in size reductions. Sensitivity to decentration can remain low too. Moreover, it is possible to provide an imaging apparatus incorporating such a zoom optical system. 
         [0078]    Such an imaging apparatus as mentioned above may be used with image-taking apparatus designed to form an object image through a zoom optical system and receive that image at a CCD or other imaging device, inter alia, digital cameras, video cameras, personal computers typical of information processors, and phones, especially convenient-to-carry-around cellular phones, as embodied below. 
         [0079]      FIGS. 9 to 11  are illustrative in conception of an arrangement having the zoom optical system built in an image-taking optical system  41  of a digital camera. More specifically,  FIG. 9  is a front perspective view of the outside shape of a digital camera  40 ;  FIG. 10  is a rear perspective view of the same; and  FIG. 11  is a sectional view of the arrangement of the digital camera  40 . The digital camera  40  here includes an image-taking optical system  41  having an image-taking optical path  42 , a finder optical system  43  having a finder optical path  44 , a shutter  45 , a flash  46 , a liquid crystal display monitor  47 , and so on. As the shutter  45  located on top of the camera  40  is pressed down, it causes an image to be taken through the image-taking optical system  41 , for instance, the zoom optical system of Example 1. An object image taken by the image-taking optical system  41  is then formed on the imaging plane of CCD  49  through a cover glass CG having a near-infrared cut coating functioning as a low-pass filter. The object image received at CCD  49  is then displayed via a processing means  51  on the liquid crystal display monitor  47  mounted on the back of the camera. The processing means  51  is also connected with a recording means  52  so as to record the taken electronic image in it. It is to be noted that the recording means  52  may be provided separately from the processing means  51  or, alternatively, the electronic image may be recorded and written in a recording medium such as a memory card or MO. If a silver halide film is located in place of CCD  49 , the digital camera may be constructed in the form of a silver halide camera. 
         [0080]    Further, a finder objective optical system  53  is located on the finder optical path  44 . An object image formed by the finder objective optical system  53  is formed on the field frame  57  of an image-erecting Porro prism  55 . In the rear of the Porro prism  55 , there is an eyepiece optical system  59  located so as to guide an erected orthoscopic image to a viewers eyeball E. It is to be noted that a cover member  50  is located on the entrance side of the image-taking optical system  41 , and the finder objective optical system  53  as well as on the exit side of the eyepiece optical system  59 . 
         [0081]    The thus assembled digital camera  40  can have higher performance and smaller size because the image-taking optical system  41  has high performance and small-format size. 
         [0082]    Although a plane-parallel plate is located as the cover member  50  in the example of  FIG. 11 , it is to be understood that any powered lens may be used. 
         [0083]    Referring then to  FIGS. 12 to 14 , there is a personal computer shown that is one typical example of an information processor having a zoom optical system built in as an objective optical system. More specifically,  FIG. 12  is a front perspective view of a personal computer  300  with its cover shut open;  FIG. 13  is a sectional view of an image-taking optical system  303  in the personal computer  300 ; and  FIG. 14  is a side view of the state of  FIG. 12 . As shown in  FIGS. 12 ,  13  and  14 , the personal computer  300  includes a keyboard  301  via which an operator enters information from outside, an information processing means and recording means (not shown), a monitor  302  for showing information to the operator, and an image-taking optical system  303  for taking an operators own image and the surrounding images. For the monitor  302  here, use may be made of a transmission type liquid crystal display designed to implement illumination from back by a backlight (not shown), a reflection type liquid crystal display designed to reflect light from front to display images, or the like. While the image-taking optical system  303  is shown to be built in the right upper portion of the monitor  302 , it is to be understood that it may be located anywhere, for instance, around the monitor  302  or around the keyboard  301 . 
         [0084]    The image-taking optical system  303  includes, on an image-taking optical path  304 , an objective lens  112  comprising a (roughly shown) zoom optical system and an imaging device chip  162  for receiving an image, each built in the personal computer  300 . 
         [0085]    Here a cover glass CG functioning as a low-pass filter is additionally applied onto the imaging device chip  162  to form an integrated-form imaging unit  160 , and the imaging unit  160  is detachably fitted over the rear end of the lens barrel  113  of the objective lens  112  in one-touch operation; so any centering alignment or surface separation adjustment of the objective lens  112  and imaging device chip  162  may be dispensed with, resulting in simplified assembling. The lens barrel  113  is provided at its end with a cover glass  114  for protection of the objective lens  112 . 
         [0086]    An object image received at the imaging device chip  162  is then entered into the processing means of the personal computer  300  via a terminal  166  so that it is displayed on the monitor  302  as an electronic image. An image  305  taken of the operator is shown typically in  FIG. 12 . The image  305  may be remotely displayed on a personal computer at other communication end through the processing means via the Internet or a phone line. 
         [0087]      FIG. 15  is illustrative of one typical example of the information processing means having a zoom optical system built in as an image-taking optical system: a phone, especially a convenient-to-carry-around cellular phone.  FIG. 15  is a front view of a cellular phone  400 ;  FIG. 16  is a side view of the same; and  FIG. 17  is a sectional view of an image-taking optical system  405 . As shown in  FIGS. 15 ,  16  and  17 , the cellular phone  400  includes a microphone  401  via which the voice of the operator is entered as information in it, a speaker  402  via which the voice of a person at the other end is produced, an input dial  403  via which the operator enters information, a monitor  404  for displaying the image taken of the operator or the person at the other end as well as information such as telephone numbers, an image-taking optical system  405 , an antenna  406  for transmission and reception of communication waves, and processing means (not shown) for image information, communication information, input signals, and so on. The monitor  404  here is a liquid crystal display device. The locations of the parts are not always limited to what is shown in  FIGS. 15 ,  16  and  17 . The image-taking optical system  405  includes an objective lens  112  comprising an image-formation optical system (roughly shown) located on an image-taking optical path  407  and an imaging device chip  162  for receiving an object image, each built in the cellular phone  400 . 
         [0088]    Here a cover glass CG functioning as a low-pass filter is additionally applied onto the imaging device chip  162  to form an integrated-form imaging unit  160 , and the imaging unit  160  is detachably fitted over the rear end of the lens barrel  113  of the objective lens  112  in one-touch operation; so any centering alignment or surface separation adjustment of the objective lens  112  and imaging device chip  162  may be dispensed with, resulting in simplified assembling. The lens barrel  113  is provided at its end with a cover glass  114  for protection of the objective lens  112 . 
         [0089]    An object image received at the imaging device chip  162  is entered in processing means (not shown) via a terminal  166  so that it is displayed as an electronic image on the monitor  404  and/or a monitor at the other end. To transmit an image to the person at the other end, the processing means may include a signal processing function of converting information about the object image received at the imaging device chip  162  into transmittable signals. 
         [0090]    The foregoing examples or embodiments may be variously modified pursuant to what is recited in the appended claims.