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Projection lens systems having reduced spherochromatism

  • US 5,329,363 A
  • Filed: 06/15/1993
  • Issued: 07/12/1994
  • Est. Priority Date: 06/15/1993
  • Status: Expired due to Term
First Claim
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1. A projection lens system for use with a cathode ray tube comprising in order from the system'"'"'s image side:

  • (a) a first lens unit comprising in order from the lens system'"'"'s image side;

    (i) a first lens element having a positive power on axis and at least one aspheric surface which causes said positive power to become negative in the vicinity of the lens element'"'"'s clear aperture; and

    (ii) a second lens element of weak optical power;

    (b) a second lens unit which comprises a third lens element which provides the majority of the lens system'"'"'s positive optical power, the dispersion of the first lens element being greater than the dispersion of the third lens element and being greater than the dispersion of all other lens elements, if any, of the second lens unit; and

    (c) a third lens unit of negative power which is associated with the cathode ray tube during use of the lens system and which provides most of the correction for the field curvature of the lens system.

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