OBJECTIVE LENS WITH VARIABLE FOCAL DISTANCE FOR OPERATION IN TWO INFRARED SPECTRAL REGIONS Russian patent published in 2012 - IPC G02B15/14 G02B9/60 G02B13/14 

FIELD: physics.

SUBSTANCE: objective lens consists of a first fixed positive component, a second movable negative component, a third movable positive component, a fourth fixed positive component and a fifth fixed negative component. The first, third, fourth and fifth components are in form of menisci whose concave surfaces face the image plane. The second component is in form of a single biconcave lens. The first and fifth components are made from optical germanium with refraction index n=4. The second and fourth components are made from material with refraction index n₂=n₄=2.44 and the third component is made from material with refraction index n=2.78. The concave outer surfaces of the first and fourth components are aspherical. Radii of curvature of the surfaces of the objective lens and thickness of the first and fifth components satisfy relationships given in the claim.

EFFECT: high quality of the image formed in two spectral ranges with small weight and size parameters.

6 dwg, 2 tbl