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Objective lens system for endoscopes

  • US 5,359,456 A
  • Filed: 10/15/1992
  • Issued: 10/25/1994
  • Est. Priority Date: 10/15/1991
  • Status: Expired due to Term
First Claim
Patent Images

1. An objective lens system for endoscopes comprising, in order from the object side:

  • a front lens unit having a negative refractive power, an aperture stop, and a rear lens unit having a positive refractive power;

    wherein said front lens unit includes a graded refractive index lens component, and wherein said graded refractive index lens component satisfies the following conditions (6) and (7) when a refractive index and an Abbe'"'"'s number of said graded refractive index lens component are approximated by formulae (1) through (5) mentioned below;

    
    
    space="preserve" listing-type="equation">N.sub.d (r)=N.sub.0.sbsb.d +N.sub.1.sbsb.d r.sup.2 +N.sub.2.sbsb.d r.sup.4 +N.sub.3.sbsb.d r.sup.6 (

         1)
    
    
    space="preserve" listing-type="equation">N.sub.F (r)=N.sub.0.sbsb.F +N.sub.1.sbsb.F r.sup.2 +N.sub.2.sbsb.F r.sup.4 +N.sub.3.sbsb.F r.sup.6 (

         2)
    
    
    space="preserve" listing-type="equation">N.sub.C (r)=N.sub.0.sbsb.C +N.sub.1.sbsb.C r.sup.2 +N.sub.2.sbsb.C r.sup.4 +N.sub.3.sbsb.C r.sup.6 (

         3)
    
    
    space="preserve" listing-type="equation">ν

    .sub.0.sbsb.d =(1-N.sub.0.sbsb.d)/(N.sub.0.sbsb.F -N.sub.0.sbsb.C)(4)
    
    
    space="preserve" listing-type="equation">ν

    .sub.1.sbsb.d =N.sub.1.sbsb.d /(N.sub.1.sbsb.F -N.sub.1.sbsb.C)(6)
    
    
    space="preserve" listing-type="equation">N.sub.1.sbsb.d <

    0 (6)
    
    
    space="preserve" listing-type="equation">0≦

    ν

    .sub.0.sbsb.d ≦

    ν

    .sub.1.sbsb.d (

         7)wherein the reference symbols Nd (r), NF (r) and NC (r) represent refractive index of said graded refractive index lens component for the d-line, F-line and C-line respectively when a radial distance as measured from an optical axis is designated by r, the reference symbols N0.sbsb.d, N1.sbsb.d, N2.sbsb.d and N3.sbsb.d denote refractive index distribution coefficient for the d-line, the reference symbols N0.sbsb.F, N1.sbsb.F, N2.sbsb.F and N3.sbsb.F represent refractive index distribution coefficients for the F-line, the reference symbols N0.sbsb.C, N1.sbsb.C, N2.sbsb.C and N3.sbsb.C designate refractive index distribution coefficients for the C-line, and the reference symbols ν

    0.sbsb.d and ν

    1.sbsb.d denote Abbe'"'"'s numbers.

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