| 摘要 |
An optical system for endoscope of the present invention comprises a first lens group having negative refraction, a second lens group having positive refraction, a third lens group having positive refraction and a fourth lens group having positive refraction, sequentially from an object side. A first minimum effective diameter between the first and second lens groups exists, in which the bundle of rays passing through the first lens group is minimized. A second minimum effective diameter between the third and fourth lens groups exists, in which the bundle of rays passing through the third lens group is minimized. A first image formation surface is disposed between the second and third lens groups, on which an object image is picked up. A second image formation surface is disposed on the rear of the fourth lens group, on which the object image is picked up once more. An angle of a chief ray incident on the first and second image formation surfaces ranges from 0 to 2 degrees based on the axis of the optical system. |
