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Optical projector/reader

  • US 3,941,467 A
  • Filed: 10/29/1074
  • Issued: 03/02/1976
  • Est. Priority Date: 10/29/1974
  • Status: Expired due to Term
First Claim
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1. Viewing apparatus comprising:

  • prism means for magnifying a light image passing through it,means for projecting a diverging light beam image through the prism means,viewing screen means for displaying light projected through the prism means onto the viewing screen means, the prism means including a prism having an index of refraction n1, a transparent entrant surface, a flat transparent exit surface facing the viewing screen means, a light transmitting medium having an index of refraction n2 interposed between the viewing screen means and the exit surface, where n2 <

    n1, a first reflecting surface opposite to the entrant surface and forming a predetermined, acute angle with the exit surface such that a major portion of the light beam passing through the entrant surface is reflected by the first reflecting surface to the exit surface at an incident angle greater than the critical angle sin-1 n2 /n1for total internal reflection by the exit surface, and a second reflecting surface angularly facing the exit surface for returning the light beam reflected internally by the exit surface back to the exit surface at an incident angle which is less than the critical angle sin-1 n2 /n1such that the returned light beam passes through the exit surface to impinge on the viewing screen means.

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