G - Physics – 02 – B
Patent
G - Physics
02
B
88/99
G02B 13/18 (2006.01) G02B 13/16 (2006.01)
Patent
CA 1257124
12 ABSTRACT: Projection lens system. A lens system is provided which is suitable for back-pro- jecting an enlarged image of a TV cathode ray tube (CRT). To achieve a compact cabinet design 1 for such a projection television set, a short projection throw and a wide projection angle are required, to- gether with a wide aperture (F/1) for a bright projected picture and with a definition which may need to be good enough to resolve 1249 line television pictures. The lens system comprises a concave CRT face- plate FP and three lens elements L1, L2, L3. L2 and L3 are each of positive power and L1, most remote from the CRT, is a weak lens. At least one of the element surfaces is aspheric. The powers of the elements are chosen so that -0.20 K < K1 < +0.15 K +0.62 K < K2 < +0.80 K and +0.55 K < K3 < +0.67 K where K1 is the power of the first weak element remote from the object surface, K2 is the power of the second element, K3 is the power of the third element adjacent to the CRT surface and K is the total power of the projection lens. Projection angles upto ? 40 degrees are obtained. (Figures 1 and 2).
497497
Fetherstonhaugh & Co.
Koninklijke Philips Electronics N.v.
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