| 摘要 |
PURPOSE:To compact a projection lens by making f1/f2 which is the ratio of two focal lengths smaller than the conventional ratio when the focal length of the 1st lens is denoted as f1 and that of the 2nd lens is denotes as f2. CONSTITUTION:The optical power of the whole lens system is determined nearly by the 1st lens L1 and the 2nd lens L2, and the 3rd lens L3 is arranged nearby a CRT and serves as a field flattener. An inequality 1 holds, where f1 is the focal length of the 1st lens L1 and f2 is the focal length of the 2nd lens L2. The inequality L1 is concerned in the distribution of the optical power of the 1st lens L1 and the 2nd lens L2; the lens is disad- vantageous to compacting when exceeding the upper limit and advantageout to the compacting when exceeding the lower limit, but becomes difficult to compensate its coma aberration because the optical power of the 1st lens L1 becomes too large and also becomes difficult to manufacture because the thickness of the 1st lens L1 increases.
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