LARGE APERTURE LENS SYSTEM Russian patent published in 2009 - IPC G02B9/34 G02B13/14 

FIELD: instrument engineering.

SUBSTANCE: invention can be used in thermal imagery devices. Lens system consists of four single lenses in the beam directions: the first lens - positive meniscus facing with its concavity the image, the second lens - negative meniscus facing with its concavity the image, the third lens - negative meniscus made from zinc selenide and facing with its convexity the image, the thickness of which is within 0.03 to 0.3 of the value by module of curvature radius of the first optical surface of the third lens, and the fourth lens - positive meniscus facing with its convexity the image. Between the first and the second lenses there located is a plate glass made from zinc selenide. The first, the second and the fourth lenses are made from germanium. Curvature radius of the first optical surface of the third lens by module is less than curvature radius of the second optical surface of the third lens.

EFFECT: enlarging focal distance, relative aperture, and decreasing the ratio of distance from the first optical surface to back focus to focal distance of the whole lens system at high image quality.

2 cl, 1 dwg