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Field curvature corrector

  • US 5,559,637 A
  • Filed: 02/04/1994
  • Issued: 09/24/1996
  • Est. Priority Date: 02/04/1994
  • Status: Expired due to Term
First Claim
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1. An optical system which (a) forms an image of an object, (b) has a positive power, and (c) has a limiting principal ray associated with the system'"'"'s maximum field of view, said system comprising:

  • at least one positive lens element; and

    a field curvature corrector unit having a positive power and at least one aspheric surface;

    wherein;

    (i) the exact field curvature (EFC) of said field curvature corrector unit computed along at least one principal ray of the optical system is positive, where the exact field curvature of the field curvature corrector unit is given by;

    
    
    space="preserve" listing-type="equation">EFC=-Σ

    (n'"'"'-n)c/nn'"'"'where the summation is taken over the surfaces of the unit, and for each of said surfaces, n is the index of refraction on the object side of the surface, n'"'"' is the index of refraction on the image side of the surface, and c is the curvature of the surface at the intersection of the surface with the principal ray, c being positive if the center of curvature is on the image side of the surface; and

    (ii) the system is free of lens elements having a negative power which provide substantial correction of the field curvature of the lens system.

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