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Objective for an endoscope

  • US 4,755,029 A
  • Filed: 05/19/1987
  • Issued: 07/05/1988
  • Est. Priority Date: 05/22/1986
  • Status: Expired due to Term
First Claim
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1. An objective for an endoscope comprising a GRIN lens whose surface on the object side is arranged as a planar surface or convex surface and whose surface on the image side is arranged as a convex surface, and an aperture stop located on the object side of said GRIN lens, said GRIN lens being arranged that the refractive index n thereof is expressed by the formula shown below when the refractive index of the central portion thereof is represented by reference symbol n0 and the radial distance from the optical axis is represented by reference symbol r, said objective for an endoscope fulfilling the conditions (1), (2) and (3) shown below:

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    space="preserve" listing-type="equation">n.sup.2 (r)=n.sub.0.sup.2 {1-(gr).sup.2 +h.sub.4 (gr).sup.4 +h.sub.6 (gr).sup.6 + . . . } ##EQU2## where, reference symbol g represents a parameter showing the degree of the gradient of the refractive index, reference symbols h.sub.4, h.sub.6, . . . respectively represent the coefficients of distribution of refractive indices in the terms of the fourth order, sixth order and so on, reference symbol I represents the image height, reference symbol φ

    represents the outer diameter of the GRIN lens, reference symbol Z represents the thickness of the central portion of the GRIN lens, and reference symbol R.sub.1 and R.sub.2 respectively represent radii of curvature of the surface on the object side and surface on the image side of the GRIN lens.

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