TELEPHOTO LENS FOR SPECTRUM IR Russian patent published in 2019 - IPC G02B13/14 G02B9/16 

FIELD: physics.

SUBSTANCE: lens can be used in thermal imagers sensitive in spectral range from 8 to 12 mcm. Telephoto lens has three menisci, of which the first and third are positive and the second is negative. All meniscus lenses face the image plane with their concave surfaces. First meniscus is made of germanium, the rest – from oxygen-free glass IKS-25. Second surface of the first meniscus is aspherical. Second meniscus is movable along the optical axis. Following ratios are met: ϕ₁:ϕ₂:ϕ₃=(1.4÷1.7):-(3.0÷5.0):(2.6÷4.5), where ϕ₁, ϕ₂, ϕ₃ are relative optical powers of first, second and third menisci, respectively; D2/f'=0.38÷0.50, D4/f'=0.18÷0.28, where D2 is air gap between first and second menisci; D4 is the air gap between the third and fourth menisci; f' is equivalent telephoto lens focal distance. Shape of the aspherical surface is determined by the equation given in the claim.

EFFECT: reduced relative length of telephoto lens and providing invariance of focal length value during thermal stabilization while maintaining high image contrast in temperature range from -40 °C to +50 °C.

1 cl, 3 dwg, 2 tbl