Lens systems for use in fingerprint detection

  • US 5,900,993 A
  • Filed: 05/09/1997
  • Issued: 05/04/1999
  • Est. Priority Date: 05/09/1997
  • Status: Expired due to Term
First Claim
Patent Images

1. An optical system having an optical axis, said system forming an image of an object and comprising:

  • a) a prism having a first surface for contacting the object and a second surface, said first surface being oriented with respect to the optical axis at an angle greater than the angle of total internal reflection of the surface;

    b) an aperture stop;

    c) a first lens unit having a positive power between the aperture stop and the prism for forming a telecentric entrance pupil;

    d) a second lens unit having a positive power on the image side of the aperture stop for forming a real image of the object; and

    e) a third lens unit between the first and second lens units, said third lens unit having cylindrical power, said cylindrical power being substantially afocal.

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