| 摘要 |
Projection lens systems for use in CRT projection televisions are provided. The lens systems include a negative lens unit (U4) which is associated with the CRT during use of the lens system and four lens elements (L1, L2, L3, CR) on the image side of the negative lens unit (U4). Three of those lens elements (L1, L2, L3) are arranged as follows from the long conjugate to the short conjugate of the lens system: a first lens element (L1) which has a weak optical power and at least one aspherical surface; a second lens element (L2) which has a positive focal length and provides most of the optical power of the lens system; and a third lens element (L3) which has a positive focal length and at least one aspherical surface. The last lens element of the system is a corrector lens element (CR) which is located adjacent to the second lens element (L2) and has a weak optical power, at least one aspherical surface, and is substantially flat. The lens systems achieve wide fields of view, low f-numbers, and low levels of thermal focus drift.
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