OBJECTIVE LENS FOR INFRARED SPECTRUM Russian patent published in 2016 - IPC G02B13/14 G02B9/34 

FIELD: optics.

SUBSTANCE: lens can be used in thermal imagers sensitive in spectral range from 8 to 12 mqm. Lens has four menisci, from which first, second and fourth menisci on beam path are positive, and third one is negative. All meniscus by concave surfaces face image plane. First and fourth menisci are made from germanium, and second and third are from zinc selenide. Third meniscus is made movable along optical axis. Following ratios are implemented: φ₁:φ₂:φ₃:φ₄=(0.75÷0.83):(0.3÷0.64):-(0.69÷1.5):(1.30÷1.77), where φ₁, φ₂, φ₃, φ₄ is relative optical power of first, second, third and fourth menisci, D2/f′=0.18÷0.42; D6/f=0.34÷0.60, where D2 is air gap between first and second menisci, f′ is equivalent focal distance of lens; D6 is air gap between third and fourth menisci.

EFFECT: high aperture ratio of lens while maintaining high image contrast and constant focal distance in range of temperatures from -40 to +50 °C.

1 cl, 3 dwg, 1 tbl