Patent ID: 7944623

Claim:
A fixed-focus lens, adapted to be disposed between a magnified side and a reduced side, the fixed-focus lens comprising: a first lens group, disposed between the magnified side and the reduced side and having a negative refractive power, the first lens group comprising a first lens, a second lens, and a third lens arranged in sequence from the magnified side to the reduced side, wherein the first lens is an aspherical lens, and refractive powers of the first lens, the second lens, and the third lens are all negative; a second lens group, disposed between the first lens group and the reduced side and having a positive refractive power, the second lens group comprising a fourth lens, a fifth lens, a sixth lens, a seventh lens, and an eighth lens arranged in sequence from the magnified side to the reduced side, wherein refractive powers of the fourth lens, the fifth lens, the sixth lens, the seventh lens, and the eighth lens are respectively negative, positive, positive, negative, and positive; and a third lens group, disposed between the second lens group and the reduced side and having a positive refractive power, the third lens group comprising a ninth lens, a tenth lens, an eleventh lens, a twelfth lens, and a thirteenth lens arranged in sequence from the magnified side to the reduced side, wherein refractive powers of the ninth lens, the tenth lens, the eleventh lens, the twelfth lens, and the thirteenth lens are respectively positive, negative, positive, negative, and positive, wherein the fixed-focus lens satisfies |F 1 /F|<1.35, 3.5<|F 2 /F|<4.5, and 4|F 3 /F|<5, wherein F 1 is an effective focal length of the first lens group, F 2 is an effective focal length of the second lens group, F 3 is an effective focal length of the third lens group, and F is an effective focal length of the fixed-focus lens.