Claims
- 1. A projection lens system for use with a cathode ray tube, said projection lens system having a long conjugate side and a short conjugate side and comprising in order from its long conjugate side:(a) a first lens unit which primarily corrects aperture dependent aberrations, said first lens unit having a short conjugate side and comprising at least one aspherical surface; (b) a second lens unit having a positive optical power; (c) a corrector lens unit comprising at least one aspherical surface; and (d) a third lens unit which is associated with the cathode ray tube during use of the lens system and which provides correction for the field curvature of the lens system, said third lens unit having a long conjugate side; wherein the lens system includes at least one diffractive optical surface which at least partially corrects the axial color of the lens system and which is located between the short conjugate side of the first lens unit and the long conjugate side of the third lens unit.
- 2. The projection lens system of claim 1 wherein the diffractive optical surface is formed on a diffractive optical element which comprises two optical surfaces, one of said optical surfaces being plano and the other of said optical surfaces being the diffractive optical surface.
- 3. The projection lens system of claim 1 wherein:(i) the projection lens system has an aperture stop and a focal length f0, and (ii) the distance between the diffractive optical surface and the aperture stop is less than 0.1·f0.
- 4. The projection lens system of claim 3 wherein the distance between the diffractive optical surface and the aperture stop is less than 0.05·f0.
- 5. A projection television system comprising a cathode ray tube and a projection lens system for projecting light from the cathode ray tube onto a screen to form an image, said projection lens system comprising the projection lens system of claim 1.
- 6. A projection television system comprising three cathode ray tubes and three projection lens systems, one projection lens system being associated with each of the cathode ray tubes for projecting light from that tube onto a common screen to form an image, each projection lens system comprising the projection lens system of claim 1.
CROSS REFERENCE TO RELATED APPLICATIONS
This application is the U.S. national phase under 35 USC §371 of International Application No. PCT/US99/26645, filed Nov. 12, 1999, which was published in English under PCT Article 21(2) on May 18, 2000 as International Publication No. WO 00/28353. This application claims the benefit under 35 USC §119(e) of U.S. Provisional Application No. 60/108,143 filed Nov. 12, 1998, the contents of which in its entirety is hereby incorporated by reference.
PCT Information
Filing Document |
Filing Date |
Country |
Kind |
PCT/US99/26645 |
|
WO |
00 |
Publishing Document |
Publishing Date |
Country |
Kind |
WO00/28353 |
5/18/2000 |
WO |
A |
US Referenced Citations (11)
Foreign Referenced Citations (2)
Number |
Date |
Country |
0 517 409 |
Dec 1992 |
EP |
1 075 150 |
Feb 2001 |
EP |
Non-Patent Literature Citations (2)
Entry |
Warren J. Smith, Modern Optical Engineering, Second Edition, McGraw-Hill, Inc., New York, New York, 1990, pp. 372-375. |
W.C. Sweatt, “Mathematical Equivalence between a Holographic Optical Element and an Ultra High Index Lens,” Journal of the Optical Society of America, 69:486-487, 1979. |
Provisional Applications (1)
|
Number |
Date |
Country |
|
60/108143 |
Nov 1998 |
US |