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Four-group endoscope objective lens

  • US 6,994,668 B2
  • Filed: 12/18/2003
  • Issued: 02/07/2006
  • Est. Priority Date: 12/25/2002
  • Status: Active Grant
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Petitions
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Forward Citations
2
Assignments
First Claim
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1. An endoscope objective lens formed of only four lens groups, in order along an optical axis from the object side, as follows:

  • a first lens group having negative refractive power;

    a second lens group having positive refractive power;

    a diaphragm;

    a third lens group having positive refractive power; and

    a fourth lens group having positive refractive power;

    whereinsaid first lens group includes a first lens element having negative refractive power and the image side lens surface of said first lens element is concave;

    said second lens group includes a lens component that includes second and third lens elements;

    said third lens group includes a fourth lens element having positive refractive power and said fourth lens element has its lens surface of smaller radius of curvature on its image side;

    said fourth lens group includes a lens component that includes a fifth lens element having positive refractive power and a sixth lens element that is a meniscus lens element having negative refractive power; and

    the following conditions are satisfied;


    1.50<

    |d/f    1|<

    2.50
    0.96<

    f/h    <

    1.04
    2.00<

    f    2+3/f<

    25.0
    15.0<

    |ν

    2–

    ν

    3|
    10.0<

    (f×

    (ν

    5–

    ν

    6))/(|R|×

    Bf    )whered is the distance along the optical axis between the concave lens surface of said first lens element and said diaphragm;

    f1 is the focal length of said first lens group;

    f is the focal length of the endoscope objective lens;

    h is the maximum height of an image formed by the endoscope objective lens;

    f2+3 is the focal length of said second lens group;

    ν

    2 is the Abbe number of said second lens element;

    ν

    3 is the Abbe number of said third lens element;

    ν

    5 is the Abbe number of said fifth lens element;

    ν

    6 is the Abbe number of said sixth lens element;

    |R| is the absolute value of the radius of curvature of the adjoining lens surfaces of said fifth lens element and said sixth lens element; and

    Bf is the back focal length of the endoscope objective lens.

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