# Patent

## Title
Zoom lens system

## Abstract

A compact zoom lens system allowing excellent image quality regardless of an object distance, is disclosed. The disclosed zoom lens system comprises, in order from an object side to an image side, a first, a second, and a third lens units having a positive, a positive, and a negative optical powers, respectively. The spacings between the first and second lens units and between the second and third lens units are changed during zooming. The second lens unit is constituted by, in order from the object to image side, a first lens subunit having a positive or negative optical power and a second lens subunit having a positive optical power. At least the second lens subunit is moved toward the object side to change the spacing between the first and second lens subunits during focusing on an object at a short distance from an object at infinity at least one zoom position.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a zoom lens system, and more particularly, to a zoom lens system preferable for use as an image-taking optical system of a camera.
2. Description of the Related Art
In recent years, more compact image-taking optical systems with higher performance are needed as image-taking systems for cameras.
Especially for an image-taking optical system of a lens shutter camera, a reduced size of such a camera is becoming possible with the aid of technical progress of associated mechanisms and electrical circuits, so that a zoom lens system achieving a higher zoom ratio and a smaller size at the same time is desired as an optical system of the camera.
As an image-taking optical system for a lens shutter camera, Japanese Patent Application Laid-Open No. H8(1996)-262325 (corresponding to U.S. Pat. No. 5,721,643), Japanese Patent Application Laid-Open No. H9(1997)-120028 (corresponding to U.S. Pat. No. 5,793,535) and the like have proposed a zoom lens which is formed of three lens units having a positive refractive power, a positive refractive power, and a negative refractive power, respectively, in order from an object side.
Japanese Patent Application Laid-Open No. H9(1997)-15499 (corresponding to U.S. Pat. No. 5,587,840) and Japanese Patent Application Laid-Open No. H10(1998)-031155 have also proposed a zoom lens which provides a zoom ratio of approximately three to four and is formed of four lens units having a negative, a positive, a positive, and a negative refractive powers, in order from an object side.
In addition, Japanese Patent Application Laid-Open No. H4(1992)-338910, Japanese Patent Application Laid-Open No. H8(1996)-220438 and the like have proposed a focusing method for reducing variations in aberration when images of an object at a short distance are taken.
Japanese Patent Application Laid-Open No. H3(1991)-249614 (corresponding to U.S. Pat. No. 5,172,273) has proposed a zoom lens system which is formed of four lens units having a positive, a positive, a positive, and a negative refractive powers in order from an object side, as well as a method of moving a second lens unit and a third lens unit together and a method of moving a fourth lens unit as a focusing method using one or more lens units other than a first lens unit.
When attempts are made to realize a zoom lens system which provides a higher zoom ratio and has a smaller size, however, optical performance is likely to change at the time of focusing. It is difficult to achieve favorable optical performance over the entire zoom range while such changes in optical performance are suppressed.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a compact zoom lens system which can maintain excellent image quality even in an image-taking for a short distance object by appropriately setting a zoom lens structure and lens unit arrangement and making improvements to how lens units are moved at the time of focusing.
According to an illustrative embodiment, the present invention provides a zoom lens system which comprises, in order from an object side to an image side, a first lens unit having a positive optical power, a second lens unit having a positive optical power, and a third lens unit having a negative optical power. The spacing between the first lens unit and the second lens unit and the spacing between the second lens unit and the third lens unit are changed during zooming. The second lens unit comprises, in order from the object side to the image side, a first lens subunit having a positive or negative optical power and a second lens subunit having a positive optical power. At least the second lens subunit is moved toward the object side such that the spacing between the first lens subunit and the second lens subunit is changed during focusing on an object at a short distance from an object at infinity at least one zoom position.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the structure of lenses of a zoom lens system of Numerical Example 1;
FIGS. 2(A), 2(B), and 2(C) show various types of aberration in the zoom lens system of Numerical Example 1 at the wide-angle end, intermediate zoom position, and telephoto end, respectively, when the zoom lens system is focused on an object at infinity;
FIGS. 3(A) and 3(B) show various types of aberration in the zoom lens system of Numerical Example 1 at the wide-angle end and telephoto end, respectively, when an object located at a distance of 80 centimeters is brought into focus (in a direct driving method) with the spacing being changed between a first lens subunit and a second lens subunit;
FIGS. 4(A) and 4(B) show various types of aberration in the zoom lens system of Numerical Example 1 at the wide-angle end and telephoto end, respectively, when an object located at a distance of 80 centimeters is brought into focus (in a zoom cam method) with the spacing being changed between the first lens subunit and the second lens subunit;
FIGS. 5(A) and 5(B) show various types of aberration in the zoom lens system of Numerical Example 1 at the wide-angle end and telephoto end, respectively, when an object located at a distance of 80 centimeters is brought into focus (in the direct driving method) without changing the spacing between the first lens subunit and the second lens subunit, as a comparative example;
FIGS. 6(A) and 6(B) show various types of aberration in the zoom lens system of Numerical Example 1 at the wide-angle end and telephoto end, respectively, when an object located at a distance of 80 centimeters is brought into focus (in the zoom cam using method) without changing the spacing between the first lens subunit and the second lens subunit, as a comparative example;
FIG. 7 shows the structure of lenses of a zoom lens system of Numerical Example 2;
FIGS. 8(A), 8(B), and 8(C) show various types of aberration in the zoom lens system of Numerical Example 2 at the wide-angle end, intermediate zoom position, and telephoto end, respectively, when the zoom lens system is focused on an object at infinity;
FIGS. 9(A) and 9(B) show various types of aberration in the zoom lens system of Numerical Example 2 at the wide-angle end and telephoto end, respectively, when an object located at a distance of 80 centimeters is brought into focus (in the direct driving method) with the spacing being changed between a first lens subunit and a second lens subunit;
FIGS. 10(A) and 10(B) show various types of aberration in the zoom lens system of Numerical Example 2 at the wide-angle end and telephoto end, respectively, when an object located at a distance of 80 centimeters is brought into focus (in the zoom cam using method) with the spacing being changed between the first lens subunit and the second lens subunit;
FIGS. 11(A) and 11(B) show various types of aberration in the zoom lens system of Numerical Example 2 at the wide-angle end and telephoto end, respectively, when an object located at a distance of 80 centimeters is brought into focus (in the direct driving method) without changing the spacing between the first lens subunit and the second lens subunit, as a comparative example;
FIGS. 12(A) and 12(B) show various types of aberration in the zoom lens system of Numerical Example 2 at the wide-angle end and telephoto end, respectively, when an object located at a distance of 80 centimeters is brought into focus (in the zoom cam using method) without changing the spacing between the first lens subunit and the second lens subunit, as a comparative example;
FIG. 13 shows the structure of lenses of a zoom lens system of Numerical Example 3;
FIGS. 14(A), 14(B), and 14(C) show various types of aberration in the zoom lens system of Numerical Example 3 at the wide-angle end, intermediate zoom position, and telephoto end, respectively, when the zoom lens system is focused on an object at infinity;
FIG. 15 shows various types of aberration in the zoom lens system of Numerical Example 3 at the wide-angle end when an object located at a distance of 80 centimeters is brought into focus (in the direct driving method) with the spacing being changed between a first lens subunit and a second lens subunit;
FIG. 16 shows various types of aberration in the zoom lens system of Numerical Example 3 at the wide-angle end when an object located at a distance of 80 centimeters is brought into focus (in the zoom cam using method) with the spacing being changed between the first lens subunit and the second lens subunit;
FIGS. 17(A) and 17(B) show various types of aberration in the zoom lens system of Numerical Example 3 at the wide-angle end and telephoto end, respectively, when an object located at a distance of 80 centimeters is brought into focus (in the direct driving method) without changing the spacing between the first lens subunit and the second lens subunit, as a comparative example;
FIGS. 18(A) and 18(B) show various types of aberration in the zoom lens system of Numerical Example 3 at the wide-angle end and telephoto end, respectively, when an object located at a distance of 80 centimeters is brought into focus (in the zoom cam using method) without changing the spacing between the first lens subunit and the second lens subunit, as a comparative example;
FIG. 19 shows the structure of lenses of a zoom lens system of Numerical Example 4;
FIGS. 20(A), 20(B), and 20(C) show various types of aberration in the zoom lens system of Numerical Example 4 at the wide-angle end, intermediate zoom position, and telephoto end, respectively, when the zoom lens system is focused on an object at infinity;
FIGS. 21(A) and 21(B) show various types of aberration in the zoom lens system of Numerical Example 4 at the wide-angle end and telephoto end, respectively, when an object located at a distance of 80 centimeters is brought into focus (in the direct driving method) with the spacing being changed between a first lens subunit and a second lens subunit;
FIGS. 22(A) and 22(B) show various types of aberration in the zoom lens system of Numerical Example 4 at the wide-angle end and telephoto end, respectively, when an object located at a distance of 80 centimeters is brought into focus (in the zoom cam using method) with the spacing being changed between the first lens subunit and the second lens subunit;
FIGS. 23(A) and 23(B) show various types of aberration in the zoom lens system of Numerical Example 4 at the wide-angle end and telephoto end, respectively, when an object located at a distance of 80 centimeters is brought into focus (in the direct driving method) without changing the spacing between the first lens subunit and the second lens subunit, as a comparative example;
FIGS. 24(A) and 24(B) show various types of aberration in the zoom lens system of Numerical Example 4 at the wide-angle end and telephoto end, respectively, when an object located at a distance of 80 centimeters is brought into focus (in the zoom cam using method) without changing the spacing between the first lens subunit and the second lens subunit, as a comparative example;
FIG. 25 shows the structure of lenses of a zoom lens system of Numerical Example 5;
FIGS. 26(A), 26(B), and 26(C) show various types of aberration in the zoom lens system of Numerical Example 5 at the wide-angle end, intermediate zoom position, and telephoto end, respectively, when the zoom lens system is focused on an object at infinity;
FIG. 27 shows various types of aberration in the zoom lens system of Numerical Example 2 at the telephoto end when an object located at a distance of 80 centimeters is brought into focus (in the direct driving method) with the spacing being changed between a first lens subunit and a second lens subunit;
FIGS. 28(A) and 28(B) show various types of aberration in the zoom lens system of Numerical Example 5 at the wide-angle end and telephoto end, respectively, when an object located at a distance of 80 centimeters is brought into focus (in the zoom cam using method) with the spacing being changed between the first lens subunit and the second lens subunit;
FIGS. 29(A) and 29(B) show various types of aberration in the zoom lens system of Numerical Example 5 at the wide-angle end and telephoto end, respectively, when an object located at a distance of 80 centimeters is brought into focus (in the direct driving method) without changing the spacing between the first lens subunit and the second lens subunit, as a comparative example;
FIGS. 30(A) and 30(B) show various types of aberration in the zoom lens system of Numerical Example 5 at the wide-angle end and telephoto end, respectively, when an object located at a distance of 80 centimeters is brought into focus (in the zoom cam using method) without changing the spacing between the first lens subunit and the second lens subunit, as a comparative example;
FIG. 31 schematically shows trajectories in zooming and movements in focusing of lenses in a method in which the first lens subunit and the second lens subunit are moved by an electrical means (the direct driving method);
FIG. 32 schematically shows trajectories in zooming and moving trajectories in focusing at respective zoom positions in a method in which the focus lens unit is moved in focusing by using part of a zoom cam; and
FIG. 33 schematically shows the structure of a compact camera.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
An embodiment of a zoom lens system of the present invention is hereinafter described with reference to the drawings. The zoom lens system disclosed in the embodiment is particularly preferable as an image-taking optical system for a compact camera. The zoom lens system has a zoom ratio of approximately 4.5 and can provide excellent image quality even when images of an object at a short distance are taken.
FIGS. 1, 7, 13, 19, and 25 are section views showing zoom lens systems in Numerical Examples 1 to 5, later described, respectively. In the section views of the lenses, L1 shows a first lens unit having a positive refractive power (that is, an optical power is the reciprocal of a focal length), L2 shows a second lens unit having a positive refractive power as a whole, and L3 shows a third lens unit having a negative refractive power. The second lens unit L2 is formed of a first lens subunit L2A having a positive or negative refractive power and a second lens subunit L2B having a positive refractive power. SP shows an aperture stop, and IP shows an image plane on which a silver haloid film or the like is located.
FIGS. 2, 8, 14, 20, and 26 show various types of aberration when the zoom lens systems in Numerical Examples 1 to 5 are focused on an object at infinity.
The first lens subunits L2A in Numerical Examples 1 to 3 have a negative refractive power, while the first lens subunits L2A in Numerical Examples 4 and 5 have a positive refractive power.
The zoom lens systems of the embodiment perform zooming by changing the spacing between the first lens unit L1 and the second lens unit L2 and the spacing between the second lens unit L2 and the third lens unit L3.
In each of the zoom lens systems of Numerical Examples 1, 2, and 4, the spacing between the first lens subunit L2A and the second lens subunit L2B is also changed during zooming. Specifically, each of the zoom lens systems of Numerical Examples 1 and 2 is a four-unit zoom lens which has lens units having a positive, a negative, a positive, and a negative refractive powers in order from an object side to an image side. The zoom lens system of Numerical Example 4 is a four-unit zoom lens which has four lens units having a positive, a positive, a positive, and a negative refractive powers in order from an object side to an image side.
In each of the zoom lens systems of Numerical Examples 3 and 5, the spacing between the first lens subunit L2A and the second lens subunit L2B is not changed during zooming. Specifically, each of the zoom lens systems of Numerical Examples 3 and 5 is a three-unit zoom lens which has lens units having a positive, a positive, and a negative refractive powers in order from an object side to an image side.
The spacing between the first lens subunit L2A and the second lens subunit L2B is changed during zooming as in the zoom lens systems of Numerical Examples 1, 2, and 4 to allow well-balanced correction of spherical aberration and off-axis aberration. Thus, it can be expected that the zoom lens systems provide higher quality images over the entire zoom range.
In the zoom lens systems of the embodiment, the first lens subunit L2A and the second lens subunit L2B are moved toward the object side to achieve focusing on an object at a short distance from an object at infinity. At least one zoom position in the zoom range, at least the second lens subunit L2B is moved toward the object side to change the air spacing between the first lens subunit L2A and the second lens subunit L2B to achieve focusing on an object at a short distance from an object at infinity.
Thus, the second lens subunit L2B is mainly responsible for the function of correcting the image plane position at the time of focusing. In addition, variations in aberration due to changes in object distance can be reduced by appropriately setting the relative positions of the first lens subunit L2A and the second lens subunit L2B, so that excellent image quality can be realized over the entire object distance range.
Especially at the wide-angle end, it is desirable to move the respective lens units relatively on an optical axis such that the air spacing between the first lens subunit L2A and the second lens subunit L2B is increased during focusing on an object at a short distance from an object at infinity. Since this causes the first lens subunit L2A to approach the first lens unit L1, off-axis rays are incident on peripheral portions of the first lens subunit L2A to positively allow correction of curvature of field.
At the telephoto end, particularly, it is desirable to move at least the second lens subunit L2B such that the air spacing between the first lens subunit L2A and the second lens subunit L2B is reduced during focusing on an object at a short distance from an object at infinity. This enables favorable correction of positive spherical aberration occurring when an object at a finite distance is brought into focus as compared with focusing on an object at infinity.
Methods of moving the lens units during focusing include driving of only the focus lens unit separately with an electrical driving means (a direct driving method), and driving of the focus lens unit by using a cam mechanism which moves each lens unit during zooming (a zoom cam using method). Any of them can be used in the zoom lens systems of the embodiment. FIG. 31 schematically shows loci during zooming and movements during focusing of the respective lens units in the former method. FIG. 32 schematically shows trajectories zooming and moving trajectories in focusing at respective zoom positions in the later method.
In the method shown in FIG. 32, focus cams for a certain zoom position are formed at a region F between an infinite object position at the certain zoom position and an infinite object position at the next zoom position, and the cams are used to achieve focusing on an object at a short distance from an object at infinity at the certain zoom position. In this event, as apparent from FIG. 32, not only the first lens subunit L2A and the second lens subunit L2B, but also the first lens unit L1 and the third lens unit L3 are simultaneously moved on the optical axis. The use of such focusing performed by utilizing part of the driving cam for zooming advantageously realizes a simplified mechanism.
In the embodiment, the first lens unit L1 is formed of a meniscus negative lens having a concave surface toward the object side and a positive lens disposed on the image side of the meniscus negative lens and having a convex surface with a higher refractive power on the object side than on the image side. The first lens unit L1 of the structure described above is used to efficiently correct spherical aberration and distortion.
The first lens subunit L2A has a positive lens and a negative lens for reducing variations of chromatic aberration during zooming. In addition, the positive lens and the negative lens are formed into a cemented lens to provide higher effects of color correction.
The second lens subunit L2B has a lens component (a negative lens or a negative cemented lens) having a negative refractive power on the object side and a positive lens having an aspheric surface on the image side to satisfactorily correct spherical aberration over the entire zoom range. Also, the aperture stop SP is provided in the second lens subunit L2B to reduce the size of the entire zoom lens system and favorably correct off-axis aberration. The aperture stop SP is desirably disposed at a position near the center of the optical system to strike a balance between the front lens diameter and rear lens diameter to provide excellent optical performance.
The third lens unit L3 has a positive lens having an aspheric surface and a negative lens disposed on the image side of the positive lens and having a concave surface with a higher refractive power on the object side than on the image side. This structure enables efficient correction of off-axis aberration to be performed by the small number of the lenses.
Next, description is made for desirable conditions of the zoom lens systems of the embodiment.
To achieve a small optical system which can provide excellent image quality even with a high zoom ratio, it is desirable to satisfy the following expressions at the wide-angle end:

0.3<|F3/Fw|<0.7   (1)

1.0<β3w<2.0   (2)

where Fw represents a focal length of the entire zoom lens system at the wide-angle end, F3 represents a focal length of the third lens unit L3, and β3w represents a lateral magnification of the third lens unit L3 at the wide-angle end. The expressions (1) and (2) relate to the refractive power of the third lens unit L3 at the wide-angle end.

If the negative refractive power of the third lens unit L3 is so low as to result in the value of F3/Fw larger than the upper limit of the expression (1), or if the lateral magnification of the third lens unit L3 at the wide-angle end is so large as to cause the value of β3w larger than the upper limit of the expression (2), the variable magnification action of the third lens unit L3 is reduced during zooming. This inevitably increases the amounts of movement of the respective lens units during zooming to provide a desired zoom ratio, resulting in an increase in the overall length of the lens system. Thus, it is not preferable.
On the other hand, if the lower limit of the expression (1) or (2) is not reached, an action of the telephoto system is increased in the entire lens system to extremely reduce a back focal distance. In addition, the outer diameter of the third lens unit L3 is increased to ensure a certain amount of peripheral light, and at the same time, curvature of field and astigmatism occur. Thus, it is not preferable.
To achieve a reduced size of the lens system and favorable image quality even in image-taking of an object at a short distance, the following expression is preferably satisfied:

0.03<|F2b/F2a|<0.4   (3)

where F2a represents a focal length of the first lens subunit L2A, and F2b represents a focal length of the second lens subunit L2B.

If the positive refractive power of the second lens subunit L2B is so low as to result in the value of F2b/F2a larger than the upper limit of the expression (3), the negative refractive power of the third lens unit L3 must be reduced in order to provide a desired focal length at the wide-angle end. The variable magnification action is reduced in movement over a certain distance during zooming, and at the same time, the amount of movement of the second lens subunit L2B is increased during focusing on an object at a finite distance. As a result, the size of the lens system is increased.
On the other hand, the value of F2b/F2a less than the lower limit is not preferable since the positive refractive power of the second lens subunit L2B is extremely increased to cause significant higher order spherical aberration which is difficult to correct.
Limiting the numerical range of the expression (3) to the following is desirable since the aforementioned effects are provided more prominently:

0.03<|F2b/F2a|<0.2   (3a)

In addition, on the premise that the entire second lens unit L2 has a predetermined focal length, setting may be advantageously made such that the first lens subunit L2A has a negative refractive power and the second lens subunit L2B has a higher positive refractive power in order to reduce the amount of movement of the focus lens unit to achieve a reduced size of the lens system. This can reduce the amount of movement for focusing at a certain finite distance.
In the embodiment, the third lens unit L3 includes a single plastic lens having an aspheric surface, but a plurality of plastic lenses may be used to further reduce cost.
To improve optical performance, another aspheric surface may be used, or a diffractive optical element or a refraction distribution type lens may be used.
It is also possible that the lens units or a portion of the lens units is decentered to correct image position displacement due to camera shake or the like.
Next, numeric data of Numerical Examples 1 to 5 are shown.
In each of Numeric Examples 1 to 5, f represents a focal length, Fno an F number, and ω half of the field angle. Also, i represents the order of an optical surface from the object side, Ri the radius of curvature of an i-th optical surface (an i-th surface), Di a spacing between an i-th surface and an i+1-th surface, Ni and νi the refractive index and the Abbe's number of the material of an i-th optical member for the d line.
An aspheric shape is represented by: 



  x
  =
  
    
      
        
          (
          
            1
            /
            R
          
          )
        
        ⁢
        
          h
          2
        
      
      
        1
        +
        
          
            {
            
              1
              -
              
                
                  (
                  
                    1
                    +
                    k
                  
                  )
                
                ⁢
                
                  
                    (
                    
                      h
                      /
                      R
                    
                    )
                  
                  2
                
              
            
            }
          
        
      
    
    +
    
      Ah
      2
    
    +
    
      Bh
      4
    
    +
    
      Ch
      6
    
    +
    
      Dh
      7
    
    +
    
      Eh
      10
    
  




where k represents the conic constant, A, B, C, D, E aspheric coefficients, x a displacement in the optical axis direction at a height h from the optical axis relative to the plane vertex, and R a paraxial radius of curvature. For example, “e−Z” means “10−Z.”

Table 1 shows numerical values calculated with the aforementioned expressions in the respective Numerical Examples.
Numerical Example 1










f = 39.13-174.73  Fno = 5.76-13.18  2ω = 57.9-14.1°























R1 =
−33.851
D1 =
0.90
N1 =
1.805181
ν1 = 25.4



R2 =
−53.249
D2 =
0.15



R3 =
  21.532
D3 =
2.70
N2 =
1.487490
ν2 = 70.2



R4 =
−95.618
D4 =
variable



R5 =
−22.243
D5 =
0.80
N3 =
1.800999
ν3 = 35.0



R6 =
  84.168
D6 =
1.80
N4 =
1.846660
ν4 = 23.8



R7 =
−28.535
D7 =
variable



R8 =
−34.916
D8 =
2.20
N5 =
1.516330
ν5 = 64.1



R9 =
−10.225
D9 =
0.80
N6 =
1.834000
ν6 = 37.2



R10 =
−31.256
D10 =
1.48



R11 =
variable
D11 =
1.20



R12 =
  60.753
D12 =
3.10
N7 =
1.519480
ν7 = 61.8



* R13 =
−14.243
D13 =
variable



R14 =
−56.334
D14 =
2.70
N8 =
1.583060
ν8 = 30.2



* R15 =
−29.802
D15 =
2.73



R16 =
−10.581
D16 =
1.20
N9 =
1.651597
ν9 = 58.5



R17 =
220.776















focal length












variable separation
39.13
82.68
174.73







D4
2.35
10.00
13.76



D7
1.02
0.90
1.54



 D13
12.75
5.23
0.82











aspheric coefficient




















13-th surface:
k = 0
A = 0
B =
  5.72717e−05
C =
  2.84551e−07
D =
−9.50949e−09
E =
  1.14519e−10


15-th surface:
k = 0
A = 0
B =
−9.52128e−05
C =
−3.93955e−07
D =
  7.34778e−10
E =
−5.70709e−11









Numerical Example 2










F = 39.08-174.76  Fno = 5.76-13.18  2ω = 57.9-14.1°























R1 =
−32.489
D1 =
0.90
N1 =
1.846660
ν1 = 23.9



R2 =
−47.759
D2 =
0.15



R3 =
  22.054
D3 =
2.70
N2 =
1.487490
ν2 = 70.2



R4 =
−92.359
D4 =
variable



R5 =
−24.841
D5 =
0.80
N3 =
1.772499
ν3 = 49.6



R6 =
235.686
D6 =
1.60
N4 =
1.755199
ν4 = 27.5



R7 =
−27.374
D7 =
variable



R8 =
−34.607
D8 =
2.30
N5 =
1.518229
ν5 = 58.9



R9 =
 −9.669
D9 =
0.80
N6 =
1.834000
ν6 = 37.2



R10 =
−43.928
D10 =
1.78



R11 =
stop
D11 =
1.20



R12 =
  49.790
D12 =
3.10
N7 =
1.583126
ν7 = 59.4



* R13 =
−14.330
D13 =
variable



R14 =
−95.746
D14 =
2.80
N8 =
1.583060
ν8 = 30.2



* R15 =
−29.846
D15 =
2.58



R16 =
−10.474
D16 =
1.20
N9 =
1.712995
ν9 = 53.9



R17 =
216.915















focal length












variable separation
39.08
82.64
174.76







D4
3.13
10.44
13.50



D7
0.98
0.82
1.92



 D13
12.15
5.00
0.84











aspheric coefficient




















13-th surface:
k = 0
A = 0
B =
  5.43833e−05
C =
  3.65425e−07
C =
−9.33234e−09
E =
  9.66944e−11


15-th surface:
k = 0
A = 0
B =
−1.08577e−04
C =
−4.13973e−07
D =
−8.98172e−10
E =
−5.71439e−11









Numerical Example 3










f = 39.20-174.48  Fno = 5.76-13.18  2ω = 57.8-14.1°























R1 =
 −35.689
D1 =
0.90
N1 =
1.805181
ν1 = 25.4



R2 =
 −56.236
D2 =
0.15



R3 =
   21.872
D3 =
2.70
N2 =
1.487490
ν2 = 70.2



R4 =
−106.884
D4 =
variable



R5 =
 −22.591
D5 =
0.80
N3 =
1.800999
ν3 = 35.0



R6 =
   88.749
D6 =
1.80
N4 =
1.846660
ν4 = 23.8



R7 =
 −27.877
D7 =
1.32



R8 =
 −35.528
D8 =
2.20
N5 =
1.516330
ν5 = 64.1



R9 =
 −9.968
D9 =
0.80
N6 =
1.834000
ν6 = 37.2



R10 =
 −31.609
D10 =
1.48



R11 =
stop
D11 =
1.20



R12 =
   68.985
D12 =
3.10
N7 =
1.519480
ν7 = 61.8



* R13 =
 −13.819
D13 =
variable



R14 =
 −57.289
D14 =
2.70
N8 =
1.583060
ν8 = 30.2



* R15 =
 −30.479
D15 =
2.73



R16 =
 −10.654
D16 =
1.20
N9 =
1.651597
ν9 = 58.5



R17 =
 225.539















focal length












variable separation
39.20
82.48
174.48







D4
2.35
9.76
14.21



 D13
12.75
5.34
0.90











aspheric coefficient





















13-th surface:
k =
  1.18363e−07
A = 0
B =
  5.55010e−05
C =
  3.08495e−07
D =
−9.39367e−09
E =
  1.14901e−10


15-th surface:
k =
−1.60824e−07
A = 0
B =
−9.20055e−05
C =
−3.71847e−07
D =
  7.86843e−10
E =
−5.77324e−11









Numerical Example 4










f = 39.15-174.94  Fno = 5.76-13.60  2ω = 57.9-14.1°























R1 =
 −63.771
D1 =
0.90
N1 =
1.846660
ν1 = 23.8



R2 =
−115.864
D2 =
0.15



R3 =
   18.211
D3 =
2.40
N2 =
1.487490
ν2 = 70.2



R4 =
   82.119
D4 =
variable



R5 =
−118.574
D5 =
1.50
N3 =
1.805181
ν3 = 25.4



R6 =
 −39.840
D6 =
0.80
N4 =
1.834807
ν4 = 42.7



R7 =
 −57.201
D7 =
variable



R8 =
 −14.224
D8 =
0.80
N5 =
1.834000
ν5 = 37.2



R9 =
 −41.325
D9 =
2.17



R10 =
stop
D10 =
1.20



* R11 =
   25.178
D11 =
3.00
N6 =
1.516330
ν6 = 64.1



* R12 =
 −15.433
D12 =
variable



* R13 =
−123.957
D13 =
2.60
N7 =
1.583060
ν7 = 30.2



* R14 =
 −36.063
D14 =
2.31



R15 =
 −11.819
D15 =
1.20
N8 =
1.712995
ν8 = 53.9



R16 =
 511.691















focal length












variable separation
39.15
82.66
174.94







D4
2.00
10.15
13.91



D7
2.01
1.70
2.65



 D12
13.09
5.26
0.59











aspheric coefficient



















11-th surface:
k =
  1.15860e+01
A = 0
B =
  1.79904e−05
C = 2.35770e−06
D = −4.82302e−08
E =
  2.76220e−09


12-th surface:
k =
−4.14162e−01
A = 0
B =
  1.57084e−04
C = 4.27373e−06
D = −9.03446e−08
E =
  4.56037e−09


13-th surface:
k =
  3.72751e+01
A = 0
B =
−2.10313e−05
C = 8.77397e−07
D = −1.15189e−08
E =
−2.44649e−11


14-th surface:
k =
  1.68205e+00
A = 0
B =
−1.00065e−04
C = 4.16150e−07
D = −8.04747e−10
E =
−1.25287e−10









Numerical Example 5










f = 39.18-174.83  Fno = 5.76-13.60  2ω = 57.8-14.1°























R1 =
 −70.593
D1 =
0.90
N1 =
1.846660
ν1 = 23.8



R2 =
−128.524
D2 =
0.15



R3 =
   18.056
D3 =
2.40
N2 =
1.487490
ν2 = 70.2



R4 =
   72.766
D4 =
variable



R5 =
 −99.500
D5 =
1.30
N3 =
1.805181
ν3 = 25.4



R6 =
 −40.390
D6 =
0.70
N4 =
1.834807
ν4 = 42.7



R7 =
 −53.667
D7 =
2.21



R8 =
 −14.202
D8 =
0.80
N5 =
1.834000
ν5 = 37.2



R9 =
 −40.691
D9 =
2.16



R10 =
stop
D10 =
1.20



* R11 =
   25.132
D11 =
3.00
N6 =
1.516330
ν6 = 64.1



* R12 =
 −15.614
D12 =
variable



* R13 =
−129.309
D13 =
2.90
N7 =
1.583060
ν7 = 30.2



* R14 =
 −34.181
D14 =
2.31



R15 =
 −11.774
D15 =
1.20
N8 =
1.712995
ν8 = 53.9



R16 =
 422.631















focal length












variable separation
39.18
82.93
174.83







D4
1.97
10.09
14.70



 D12
13.09
4.97
0.36











aspheric coefficient



















11-th surface:
k =
  1.15856e+01
A = 0
B =
  1.89321e−05
C = 2.35471e−06
D = −4.82828e−08
E =
  2.66760e−09


12-th surface:
k =
−4.14522e−01
A = 0
B =
  1.59175e−04
C = 4.27353e−06
D = −9.32039e−08
E =
  4.56052e−09


13-th surface:
k =
  3.72751e+01
A = 0
B =
−2.09291e−05
C = 8.79812e−07
D = −1.23836e−08
E =
−1.76404e−11


14-th surface:
k =
  1.68201e+00
A = 0
B =
−1.00645e−04
C = 4.08676e−07
D = −7.88733e−10
E =
−1.24762e−10























TABLE 1







ex-
numerical
numerical
numerical
numerical
numerical



pression
example 1
example 2
example 3
example 4
example 5






















{circle around (1)}
|F3/Fw|
0.469
0.456
0.469
0.521
0.528


{circle around (2)}
β3w
1.563
1.584
1.560
1.498
1.482


{circle around (3)}
|F2b/
0.138
0.076
0.100
0.285
0.275



F2a|









Table 2-1 shows movement amounts of the focus lens unit (the second lens unit L2) when an object located at a distance of 80 centimeters is brought into focus after focusing on an object at infinity by the direct driving method shown in FIG. 31 without changing the spacing between the first lens subunit L2A and the second lens subunit L2B.
Table 2-2 shows movement amounts of the focus lens unit (the second lens unit L2), the first lens unit L1, and the third lens unit L3 when an object located at a distance of 80 centimeters is brought into focus after focusing on an object at infinity by the zoom cam using method shown in FIG. 32 without changing the spacing between the first lens subunit L2A and the second lens subunit L2B.
Table 2-3 shows movement amounts of the focus lens unit (the first lens subunit L2A and the second lens subunit L2B) when an object located at a distance of 80 centimeters is brought into focus after focusing on an object at infinity by the direct driving method shown in FIG. 31 with the spacing being changed between the first lens subunit L2A and the second lens subunit L2B.
Table 2-4 shows movement amounts of the focus lens unit (the first lens subunit L2A and the second lens subunit L2B), the first lens unit L1, and the third lens unit L3 when an object located at a distance of 80 centimeters is brought into focus after focusing on an object at infinity by the zoom cam using method shown in FIG. 32 with the spacing being changed between the first lens subunit L2A and the second lens subunit L2B.













TABLE 2-1







numerical
numerical
numerical
numerical
numerical



example 1
example 2
example 3
example 4
example 5





















movement
−1.072
−1.030
−1.067
−1.068
−1.097


amount of


second lens


unit at


wide-angle


end


movement
−1.921
−1.826
−1.888
−1.745
−1.800


amount of


second lens


unit at


telephoto


end






















TABLE 2-2







numerical
numerical
numerical
numerical
numerical



example 1
example 2
example 3
example 4
example 5





















movement
−1.445
−0.693
−1.446
−1.441
−0.931


amount of


first and


third lens


units at


wide-angle


movement
−1.806
−1.386
−1.807
−1.801
−0.155


amount of


second lens


unit at


wide-angle


end


movement
−6.703
−1.761
−6.596
−6.159
−0.256


amount of


first and


third lens


units at


telephoto


end


movement
−8.379
−3.522
−8.245
−7.699
−0.427


amount of


second lens


unit at


telephoto


end






















TABLE 2-3







numerical
numerical
numerical
numerical
numerical



example 1
example 2
example 3
example 4
example 5





















movement
−1.655
−2.435
−1.613
−0.188
—


amount of


first lens


subunit at


wide-angle


end


movement
−1.136
−1.130
−1.113
−1.263
—


amount of


second lens


subunit at


wide-angle


end


movement
−1.120
−0.634
—
−0.621
−1.172


amount of


first lens


subunit at


telephoto


end


movement
−1.812
−1.719
—
−2.029
−1.953


amount of


second lens


subunit at


telephoto


end






















TABLE 2-4







numerical
numerical
numerical
numerical
numerical



example 1
example 2
example 3
example 4
example 5





















movement
−1.383
−1.472
−1.597
−0.737
−0.075


amount of


first and


third lens


units at


wide-angle


end


movement
−3.009
−3.907
−2.833
−0.459
−0.140


amount of


first lens


subunit at


wide-angle


end


movement
−1.910
−1.956
−1.972
−1.652
−1.347


amount of


second lens


subunit at


wide-angle


end


movement
−2.265
—
—
−0.945
−0.207


amount of


first and


third lens


units at


telephoto


end


movement
−3.322
—
—
−1.535
−1.301


amount of


first lens


subunit at


telephoto


end


movement
−3.993
—
—
−2.941
−2.169


amount of


second lens


subunit at


telephoto


end









FIGS. 3, 9, 15, 21, and 27 show various types of aberration of the zoom lens systems in Numerical Examples 1 to 5 when an object located at a distance of 80 centimeters is brought into focus by the direct driving method shown in FIG. 31 with the spacing being changed between the first lens subunit L2A and the second lens subunit L2B. FIGS. 4, 10, 16, 22, and 28 show various types of aberration of the zoom lens systems in Numerical Examples 1 to 5 when an object located at a distance of 80 centimeters is brought into focus by the zoom cam using method shown in FIG. 32 with the spacing being changed between the first lens subunit L2A and the second lens subunit L2B.
As a comparative example, FIGS. 5, 11, 17, 23, and 29 show various types of aberration of the zoom lens systems in Numerical Examples 1 to 5 when an object located at a distance of 80 centimeters is brought into focus by the direct driving method shown in FIG. 31 without changing the spacing between the first lens subunit L2A and the second lens subunit L2B. Similarly, as a comparative example, FIGS. 6, 12, 18, 24, and 30 show various types of aberration of the zoom lens systems in Numerical Examples 1 to 5 when an object located at a distance of 80 centimeters is in brought into focus by the zoom cam using method shown in FIG. 32 without changing the spacing between the first lens subunit L2A and the second lens subunit L2B.
The comparison between the aberration graphs of the embodiment and the comparative examples reveals that at least the second lens subunit L2B is moved toward the object side to change the spacing between the first lens subunit L2A and the second lens subunit L2B to achieve focusing on an object at a short distance from an object at infinity, thereby favorably correcting, especially off-axis curvature of field, at the wide-angle end, and spherical aberration at the telephoto end.
Next, description is made for an embodiment of a compact camera of a lens shutter type which employs the zoom lens system of the present invention as an image-taking optical system with reference to FIG. 33.
In FIG. 33, reference numeral 10 shows a compact camera body, 11 an image-taking optical system realized by the zoom lens system of the present invention, 12 an electronic flash contained in the camera body, 13 an external finder system which has an optical axis different from that of the image-taking optical system 11, and 14 a shutter button.
The zoom lens of the present invention can be applied to an optical apparatus such as a lens shutter camera to realize an optical apparatus which has a small size and high optical performance.
While preferred embodiment has been described, it is to be understood that modification and variation of the present invention may be made without departing from the scope of the following claims.

## Claims

1. A zoom lens system comprising in order from an object side to an image side:
a first lens unit having a positive optical power; 
a second lens unit having a positive optical power, the second lens unit having, in order from the object side to the image side, a first lens subunit having one of a positive optical power and a negative optical power, and a second lens subunit having a positive optical power; and 
a third lens unit having a negative optical power, 
wherein a spacing between the first lens unit and the second lens unit and a spacing between the second lens unit and the third lens unit are changed during zooming, and 
at least the first lens unit and the third lens unit are moved toward the object side, and in the second lens unit, the second lens subunit is moved toward the object side such that the spacing between the first lens subunit and the second lens subunit is changed during focusing on an object at a short distance from an object at infinity in at least one zoom position.

2. The zoom lens system according to claim 1, wherein the spacing between the first lens subunit and the second lens subunit is increased during focusing on an object at short distance from an object at infinity at a wide-angle end.

3. The zoom lens system according to claim 1, wherein the spacing between the first lens subunit and the second lens subunit is reduced during focusing on an object at a short distance from an object at infinity at a telephoto end.

4. The zoom lens system according to claim 1, wherein the following expressions are satisfied:


0.3<|F3/Fw|<0.7 



1.0<β3w<2.0 


where Fw represents a focal length of the entire zoom lens system at a wide-angle end, F3 represents a focal length of the third lens unit, and β3w represents a lateral magnification of the third lens unit at the wide-angle end.

5. The zoom lens system according to claim 1, wherein the following expression is satisfied:


0.03<|F2b/F2a|<0.4 


where F2a represents a focal length of the first lens subunit, an F2b represents a focal length of the second lens subunit.

6. The zoom lens system according to claim 1, wherein the spacing between the first lens subunit and the second lens subunit is changed during zooming.

7. The zoom lens system according to claim 1, wherein the first lens subunit comprises, in order from the object side to the image side, a neniscus negative lens element which has a concave surface toward the object side and a positive lens element which has a convex surface with a higher optical power on the object side than on the image side.

8. The zoom lens system according to claim 1, wherein the first lens subunit comprises a positive lens and a negative lens.

9. The zoom lens system according to claim 1, wherein the second lens subunit comprises, in order from the object side to the image side, a lens component having a negative optical power, an aperture stop, and a positive lens element having an aspheric surface on the image side.

10. The zoom lens system according to claim 1, wherein the third lens unit comprises, in order from the object side to the image side, a positive lens element having an aspheric surface and a negative lens element having a concave surface with a higher optical power on the object side than on the image side.

11. A camera comprising:
the zoom lens system according to claim 1; and 
a finder system which has an optical axis different from an optical axis of the zoom lens system.