| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical system for infrared radiation in which an aberration can be corrected excellently even at a wide angle of view in spite of double-lens configuration, in particular, to provide an optical system for infrared radiation capable of ensuring an image plane without enlarging a Petzval sum even when a wide angle of view from 40° to 110° is obtained.SOLUTION: An optical system for infrared radiation comprises two lenses of a first lens having negative refractive power and a second lens having positive refractive power in order from a subject side. The first lens has a shape turning a concave face toward an image side and the second lens has a shape turning a convex face toward the subject side. When a distance on an optical axis from the image-side face of the first lens to the subject-side face of the second lens is defined as (d) and a focal distance of the overall system is defined as (f), a conditional expression 2.1≤d/f≤11 is satisfied. |
