FIELD: physics.;SUBSTANCE: lens has three components arranged in series on the beam path. The first and third components are positive menisci made from the same material whose concave surfaces face the image plane. The second component is negative with optical power of -(0.15-0.5) and comprises a negative meniscus and an additional negative and a positive meniscus with relative optical power values which are quasiequal on modulus, respectively lying on both sides of the negative meniscus. The menisci of the second component face the image plane with their concave surfaces; two of them are made from material different from material of the first and third components and have in spectral ranges 3-5 mcm and 8-12 mcm, average dispersion coefficients which differ by more than fivefold, with quasiequal partial dispersion coefficients values. Menisci on the beam path have the following optical power values, respectively: (0.6-0.7); -(0.6-0.9); -(0.1-0.25); (0.5-0.7); (0.65-0.85).;EFFECT: widening the operating spectral range from 3 mcm to 12 mcm, providing a fixed position of the image plane for operating spectral ranges of 3-5 mcm and 8-12 mcm, high energy concentration factor in a spot with diameter of 0,015 mcm.;2 cl, 6 dwg
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