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Zoom lens and image pickup apparatus

  • US 20100214665A1
  • Filed: 02/08/2010
  • Published: 08/26/2010
  • Est. Priority Date: 02/18/2009
  • Status: Abandoned Application
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Assignment
First Claim
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1. A zoom lens comprisinga first lens group having negative refractive power,a second lens group having positive refractive power, anda third lens group having positive refractive power which are arranged in order from an object side to an image side, whereinwhen a positional lens state is changed from a wide angle end state to a telephoto end state, said second lens group moves toward an object in an optical axis direction and both said first lens group and said third lens group move in said optical axis direction to reduce said spacing between said first lens group and said second lens group and to increase the spacing between said second lens group and said third lens group;

  • short distance focusing is performed by the movement of said third lens group in the optical axis direction at the time of changing the object position;

    said first lens group includes a negative lens and a positive lens which are arranged in this order from an image side to an object side;

    said third lens group includes a positive lens;

    both surfaces of said negative lens of said first lens group are aspherical surfaces, respectively;

    both surfaces of said positive lens of said third lens group are aspherical surfaces, respectively; and

    the following conditional expressions (1) to (4) are satisfied;


    0.10<

    ASPa1<

    0.36;

     

     

    (1)
    −

    0.05<

    ASPa    2<

    −

    0.02;

     

     

    (2)
    0<

    ASPb1<

    0.20; and

     

     

    (3)
    0.04<

    ASPb2<

    0.15, wherein 

     

    (4)
    ASPa1=(ZAa1−

    ZRa    1)/{Ca1(Na−

    1)·

    f1},
    ASPa2=(ZAa2−

    ZRa    2)/{Ca2(1·

    Na    )·

    f1},
    AsPb1=(ZAb1−

    ZRb1)/{Cb1(Na−

    1)·

    f3},
    AsPb2=(ZAb2−

    ZRb    2)/{Cb2(1−

    Na    )·

    f3},Da is defined as a thickness of said negative lens on said optical axis of said first lens group,Db is defined as a thickness of said positive lens on said optical axis of said first lens group,Ya=4Da,Yb=2Db,ZRa1 is defined as a coordinate in the optical axis direction at a height corresponding to Ya from the optical axis of an object-side paraxial curvature surface of said negative lens in said first lens group,ZRa2 is defined as a coordinate in the optical axis direction at a height corresponding to Ya from the optical axis on the image side of said negative lens in said first lens group,ZAa1 is defined as a coordinate in the optical axis direction at a height corresponding to Ya from the optical axis of an object-side aspherical surface of said negative lens in said first lens group,ZAa2 is defined as a coordinate in the optical axis direction at a height corresponding to Ya from the optical axis of an image-side aspherical surface of said negative lens in said first lens group,Ca1 is defined as a paraxial curvature of the object-side aspherical surface of said negative lens in said first lens group,Ca2 is defined as a paraxial curvature of the image-side aspherical surface of said negative lens in said first lens group,Na is defined as a refractive index to the e-line of said negative lens in said first lens group,f1 is defined as a focal length of said first lens group,ZRb1 is defined as a coordinate in the optical axis direction at a height corresponding to Yb from the optical axis of an object-side paraxial curvature surface of said positive lens in said first lens group,ZRb2 is defined as a coordinate in the optical axis direction at a height corresponding to Yb from the optical axis on the image side of said positive lens in said first lens group,ZAb1 is defined as a coordinate in the optical axis direction at a height corresponding to Yb from the optical axis of an object-side aspherical surface of said positive lens in said first lens group,ZAb2 is defined as a coordinate in the optical axis direction at a height corresponding to Yb from the optical axis of an image-side aspherical surface of said positive lens in said first lens group,Cb1 is defined as a paraxial curvature of the object-side aspherical surface of said positive lens in said first lens group;

    Cb2 is defined as a paraxial curvature of the image-side aspherical surface of said positive lens in said first lens group;

    Nb is defined as a refractive index to the e-line of said positive lens in said first lens group, andf3 is defined as a focal length of said third lens group.

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