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Objective lens system for endoscopes

  • US 5,119,238 A
  • Filed: 10/12/1990
  • Issued: 06/02/1992
  • Est. Priority Date: 10/13/1989
  • Status: Expired due to Term
First Claim
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1. An objective lens system for endoscopes, comprising, in order from the object side:

  • a front lens unit including a negative lens component and a positive lens component;

    an aperture stop; and

    a rear lens unit having a positive refractive power;

    whereinsaid aperture stop is disposed substantially at a front focal point of said rear lens unit; and

    at least said rear lens unit includes an aspherical surface satisfying the following condition (1);

    
    
    space="preserve" listing-type="equation">E'"'"'(n.sub.i-1 -n.sub.i)>

    0 (1)wherein the reference symbol E'"'"' represents the aspherical surface coefficient of fourth order, the reference symbol ni-1 designates the refractive index of a medium disposed on the object side of said aspherical surface, and the reference symbol ni denotes the refractive index of the medium disposed on the image side of said aspherical surface.

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