JPS6488414A - Lens for infrared rays - Google Patents

Abstract

PURPOSE:To completely obstruct infrared rays radiated by the inside surface of a lens barrel and the inside of an image pickup device and to prevent the generation of an unnecessary noise and the saturation of charge by providing an aperture diaphragm on the outside of an emitting side of an infrared-ray use lens. CONSTITUTION:The titled lens is constituted of a first convex meniscus lens L1 whose convex face is turned to an object side, a second concave meniscus lens L2, a third convex meniscus lens L3 whose concave face has been turned to the object side, a fourth concave meniscus lens L4, a fifth convex meniscus lens L5, and a sixth convex meniscus lens L6 whose convex face is turned to the object side, in order from the object side. Also, the surface of an image field side of the third lens L3 is formed aspherically, a cooled aperture diaphragm 2 is placed after the sixth lens L6, the first image forming face and the second image forming face are provided on a space extending from the second lens L2 to the third lens L3, and after the aperture diaphragm, respectively, and infrared-ray transmission materials for forming each lens are silicon, germanium, silicon, germanium, silicon and silicon in order. In such a way, the radiation from the inside surface of a lens barrel and the inside of an image pickup device can all be obstructed, and the generation of noise and the saturation of charge can be prevented.