INFRARED LENS SYSTEM WITH SMOOTHLY CHANGING FOCAL DISTANCE Russian patent published in 2009 - IPC G02B15/16 G02B13/14 

FIELD: instrument engineering.

SUBSTANCE: lens system consists of five in-series located elements. The fixed first element consists of positive and negative lenses. The second and third movable elements are installed with the possibility of being moved along optical axis. The second element contains a negative lens, and the third one is made in the form of a negative concave-convex lens. The fourth fixed element is made in the form of a positive concave-convex lens, and the fifth fixed element includes the first and the second positive convex-concave lenses. The second surface of the first lens is aspherical. Negative lens of the movable second element is double concave.

EFFECT: decreasing length of infrared lens system relative to its maximum focal distance with simultaneous increase of changing interval of focal distance at maintaining image quality.

2 cl, 1 dwg