| 摘要 |
PROBLEM TO BE SOLVED: To provide a fixed-focus lens which can improve the quality of image formation. SOLUTION: The fixed focus lens for projecting an image-forming light flux by a light valve on a screen includes a first lens group, a second lens group, and a third lens group, arranged in this order. The third lens group is arranged close to the light valve. The first lens group has negative refractive power and includes at least one aspherical mirror. The second lens group has positive refractive power and includes at least one lens. The third lens group has positive refractive power and includes at least four lenses. When the shortest distance between the first lens group and the second lens group is defined as S1-2 and the effective focal length of the third lens group is defined as F3, S1-2 and F3 satisfy S1-2/F3>1.51. The effective focal length of the lens approaching closest to the screen in the first lens group is defined as F11 and the effective focal length of the fixed focus lens is defined as F, F11 and F satisfy F11/F<-18.5. COPYRIGHT: (C)2008,JPO&INPIT
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