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Imaging-optical system

  • US 7,158,314 B2
  • Filed: 03/09/2005
  • Issued: 01/02/2007
  • Est. Priority Date: 03/10/2004
  • Status: Expired due to Fees
First Claim
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1. An imaging-optical system comprising a negative first lens group, a positive second lens group and a positive third lens group, in this order from an object,wherein a zooming operation is performed by moving said positive second lens group and said positive third lens group while an object distance to said object is being varied without varying a distance from the most object-side surface of said negative first lens group to the imaging plane;

  • wherein an in-focus state of said imaging-optical system is maintained while the focal length of said imaging-optical system is being varied through said zooming operation;

    wherein said negative first lens group comprises cemented lens elements, and said cemented lens elements are positioned at the most object-side of said negative first lens group; and

    wherein said cemented lens elements satisfy the following condition;


    0.9<

    Ra/fw<

    2.0whereinRa designates the radius of curvature of a bonding surface of said cemented lens elements of said negative first lens group; and

    fw designates the focal length of said imaging-optical system at the short focal length extremity.

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