Active athermalization of dual-infrared zoom lenses

For medium- and long-wavelength dual-band infrared refractive and refractive-diffractive thermal imaging zoom lenses of simple design, we show that it is possible to maintain superb and practically unchanged optical characteristics across the temperature range from $ -40$ to $+40^{\circ}$C in the entire range of focal length variation. Athermalization for any focal length is achieved by moving one double-lens component or a single lens along the optical axis of the lens. Considering that these optical components are not involved in the zooming process, it becomes possible to both compensate for thermal defocusing and focus the lens on the object of interest using the same focusing mechanism, while maintaining the size and tightness of the optical system.