LARGE-APERTURE LENS Russian patent published in 2010 - IPC G02B9/34 G02B13/14 

FIELD: physics.

SUBSTANCE: objective can be used for operation in the far-infrared range in thermal imaging devices. The objective has four lenses along the beam path: the first is a single positive meniscus whose concave surface faces the image, the second is a single negative meniscus whose concave surface faces the image, the third is a single negative meniscus whose convex surface faces the image, the fourth is a single positive meniscus whose convex surface faces the object. The modulus of the radius of curvature of the first optical surface of the fourth lens is less than that of the second optical surface. The first and fourth lenses are made from germanium, the second and third are made from optical oxygen-free infrared glass with refraction index for wavelength 10 mcm greater than 2.5 and less than 3.1. Radii of curvature of the lenses are linked by relationships given in the formula of invention.

EFFECT: improved technological effectiveness and transmission, increased focal distance and aperture ratio with high image quality.

1 dwg, 2 tbl