| 摘要 |
PROBLEM TO BE SOLVED: To reduce Narcissus and also excellently correct aberration, to reduce F value, to widen a viewing angle, and to secure a necessary back focus by using this infrared ray lens comprising a 1st lens group having a convex meniscus lens directing its concave toward an object side arranged nearest to the object and having a negative refractive power, and a 2nd lens group with a positive refractive power. SOLUTION: This infrared ray lens is comprised of a 1st lens group G1 with a negative refractive power consisting of, sequentially from a object side, a convex meniscus lens L1 direction its concave toward the object, a concave meniscus lens L2 directing its convex toward the object, and a convex lens L3 , and a 2nd lens group G2 with a positive refractive power consisting of at least two lenses, and focuses the light flux transmitting this lens to form an image on a detection plane 2 via a cold aperture 1. Moreover, this lens satisfies the following condition.|fG2 /fG1|<0.40...(1) Here, fG1 : focal length of the 1st lens group, and fG2 : focal length of the 2nd lens group.
|
