Patent ID: 7505209

Claim:
A fixed-focus lens, suitable for projecting an image beam from a light valve onto a screen, comprising: a first lens group, disposed between the light valve and the screen, the first lens group having a negative refractive power and comprising: a first lens, having a negative refractive power, the first lens being an aspheric lens; a second lens, disposed between the first lens and the second lens group, and having a negative refractive power; and a third lens, disposed between the second lens and the second lens group, and having a negative refractive power; a second lens group, disposed between the first lens group and the light valve, the second lens group having a positive refractive power and comprising: a fourth lens, having a positive refractive power; and a third lens group, disposed between the second lens group and the light valve, the third lens group having a positive refractive power and comprising: a fifth lens, having a positive refractive power; a sixth lens, disposed between the fifth lens and the light valve, and having a negative refractive power; a seventh lens, disposed between the sixth lens and the light valve, and having a positive refractive power; an eighth lens, disposed between the seventh lens and the light valve, and having a negative refractive power; and a ninth lens, disposed between the eighth lens and the light valve, and having a positive refractive power; wherein the shortest distance between the first lens group and the second lens group is S 1-2 , the effective focal length of the third lens group is F 3 , and S 1-2 /F 3 >1.51, the effective focal length of the lens closest to the screen in the first lens group is F 11 , the effective focal length of the fixed-focus lens is F, and F 11 F<−18.5.