DOUBLE LENS Russian patent published in 2016 - IPC G02B9/10 G02B11/02 

FIELD: photography.

SUBSTANCE: lens consists of, located on beam path, a negative meniscus whose convex side faces object, and a biconvex lens, with ratios: 2,0 < R₁/R₂ < 3,0; 0,9<R₂/R₃<1,1; d₂/f′ < 0,002; where R₁, R₂, R₃, R₄ - radii of first, second, third and fourth surfaces lenses on beam path, respectively; d₂ - air gap between lenses; f′ is focal distance; ν₁ and ν₂ - dispersion coefficients of glass of first and second lenses respectively; p₁ and p₂ - relative partial dispersion glass of first and second lenses respectively.

EFFECT: technical result is increase in focal length while maintaining high quality of image, improving performance by reducing temperature equalisation time of objective lens with ambient temperature, improving manufacturability.

2 cl, 1 dwg, 2 tbl