| 摘要 |
PROBLEM TO BE SOLVED: To provide a compact, high-performance projection optical system having a short projecting distance equal to or less than 1m, capable of enlarging and projecting an image with variable power. SOLUTION: The projection optical system PO for power-variably enlarging and projecting the image formed on a display element surface So on the screen surface includes, in order from the enlargement side, a first negative group Gr1, a second negative group Gr2, a third positive group Gr3 and a fourth positive group Gr4, all of which function as a zooming group, further, a positive lens CL as a fifth group Gr5 is disposed on the most reduction side. The projection optical system satisfies conditional expressions of 0.2<f1/f2<0.8 (wherein, f1: focal length of the first group Gr1, f2: focal length of the second group Gr2), 0.1<Yd/Lb<0.5 (wherein Lb: the shortest distance between the positive lens CL and a lens located adjacent to the positive lens CL on the enlargement side, Yd: the maximum image height) and 45°<ωkw<70°(wherein,ωkw: the maximum half angle of view at a wide angle end W in the closest projection state). COPYRIGHT: (C)2008,JPO&INPIT
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