| 摘要 |
Introduced is a fast lens for near infrared ray which has wide angle of view and assures a small F-number as obtaining aberration correction by assembling a spherical lens and an aspheric lens. The fast lens for near infrared ray comprises a first lens, a second lens, a third lens, a fourth lens and an iris which are arranged sequentially to an image from a target object. The first lens is a meniscus lens which has a negative refractive index and has a convex surface which is facing the target object to photograph. The second lens includes at least one aspherical surface having a positive refractive index. The third lens is a meniscus lens or a biconvex lens which has a positive refractive index and a convex surface facing the side where the image is formed. The fourth lens has a negative refractive index, and is a meniscus lens having a concave surface facing the side where the image is formed. The iris is arranged between the second lens and the third lens. Here, the focal length (f1) of the first lens and the focal length (f2) of the second lens satisfy the relation in which f1/f2 is greater than -1.3 and is less than -1.1. |
