| 摘要 |
A fixed-focus lens disposed between an enlarged side and a reduced side is provided. An f-number of the fixed-focus lens is smaller than or equal to 2. The fixed-focus lens includes a first lens group and a second lens group. The first lens group includes a first lens, wherein the first lens is an aspheric lens. The second lens group, disposed between the first lens group and the reduced side, has a positive dioptre. The second lens group includes a second lens, wherein the second lens is an aspheric lens. The fixed-focus lens focuses by moving the first and the second lens group and satisfies 0.1<|f/f1|<1, 0.2<|f/f2|<1.5, and 1.5<L/BEL<3.5, where f, L, and BFL are respectively a focal length, a total length, and a back focal length of the fixed-focus lens, and f1 and f2 are respectively an effective focal length of the first and the second lens group. |
