| 摘要 |
PROBLEM TO BE SOLVED: To provide a projection lens for a projection optical device having short entire length and back focus including a protection glass and possessing a high modulation transfer function (MTF). SOLUTION: The projection lens for the projection optical device projecting a video obtained by an optical modulator for generating an image by changing the respective reflecting directions of a plurality of reflection elements to a screen has a 1st lens group having negative refractive power and having a focal distance f1 and a 2nd lens group having positive refractive power and having a focal distance f2 in order from the screen side. The 1st lens group includes a doublet consisting of a negative lens and a positive lens, and the 2nd lens group includes a doublet consisting of a negative lens and a positive lens. The lens nearest to the optical modulator in the 2nd lens group is a negative lens, and the 1st and the 2nd lens groups form a retrofocus type lens as a whole. When the entire length of the lens is defined as L and the back focus thereof is defined as BF, following three conditions: ¾f1¾≥f2, 8×BF≥7×L and MTF≥45% are satisfied. COPYRIGHT: (C)2004,JPO&NCIPI
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