| 摘要 |
A fixed-focus lens suitable for projecting an image beam from a light valve onto a screen is provided. The fixed-focus lens comprises a first lens group, a second lens group, and a third lens group arranged in sequence. The third lens group is disposed near the light valve. The first lens group having a negative refractive power comprises at least an aspheric lens. The second lens group having a positive refractive power comprises at least a lens. The third lens group having a positive refractive power comprises at least four lenses. A shortest distance between the first and second lens groups is S<SUB>1-2</SUB>, the effective focal length of the third lens group is F<SUB>3</SUB>, and S<SUB>1-2</SUB>/F<SUB>3</SUB> >1.51 . The effective focal length of the lens closest to the screen in the first lens group is F<SUB>11</SUB>. The effective focal length of the fixed-focus lens is F, and F<SUB>11</SUB>/F<-l8.5.
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