| 摘要 |
<p>16 A lens system is provided which is suitable for back-projecting 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, together 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. L1 and L3 are each of positive power and each have one aspheric surface. L2 is between L1 and L3 and also has one aspheric surface. The powers of the elements are chosen so that 0.50K < K1 < 0.90K -0.35K < K2 < 0.20K, and 0.70K < K3 < 1.0K where K1 is the power of the first element remote from the object surface, K2 is the power of the second low power element, K3 is the power of the third element adjacent to the object surface and K is the total power of the projection lens.</p> |
