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Variable focal length optical system

  • US 5,999,329 A
  • Filed: 11/26/1997
  • Issued: 12/07/1999
  • Est. Priority Date: 12/26/1995
  • Status: Expired due to Term
First Claim
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1. A variable focal length optical system consisting of, in succession from an object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, a third lens unit having a negative refractive power, and a fourth lens unit having a positive refractive power,wherein when a focal length of the entire lens system is changed while maintaining a constant image plane position, said second lens unit moves in an optical axis direction, said third lens unit moves in the optical axis direction to compensate for variations in image plane position upon movement of said second lens unit, and said first and fourth lens units are fixed in position in the optical axis direction,an aperture stop is disposed at a position on an object side of a position closest to the image side of said third lens unit,said third lens unit is constituted by a negative sub unit disposed on the object side, and a positive sub unit disposed on the image side of said negative sub unit,said negative sub unit includes at least one negative lens, and said positive sub unit includes at least one positive lens, andsaid negative and positive sub units are disposed to be separated by a gap.

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