| 摘要 |
PROBLEM TO BE SOLVED: To prevent the degradation in performance of a projected image by performing focus adjustment so that a projected luminous flux doesn't pass a local part degrading the performance of a plastic lens even when using the plastic lens for various projectors. SOLUTION: A projection lens is focused by moving a front lens group 15 in a direction of an optical axis. A focus ring 21 is helicoidally engaged with an outer periphery of a front holding frame 20 holding the front lens group 15 and is rotated only by a certain angle for a lens barrel main body 22 holding the other lens groups, in a rotation stop state. The front holding frame 20 is supported rectilinearly movably by action of a rectilinear key 24 and a rectilinear groove 25 between the front holding frame 20 and the lens barrel main body 22. When the focus ring 21 is rotated, the front holding frame 20 is rectilinearly moved in the direction of the optical axis. The front lens group 15 is integrally built in the front holding frame 20 in such fixed direction that the projected luminous flux passes only an area other than the local part degrading the performance. COPYRIGHT: (C)2007,JPO&INPIT
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