Opto-mechanical design for a lightweight long-wave infrared athermalized focusing lens

To address the integrated requirements of hand-held optoelectronic devices for lightweight construction, stable imaging across wide temperature ranges, and ergonomic operability, this paper designs a long-wave infrared athermalized frontgroup manual focusing lens. In the optical system design, a two-element separated germanium lens configuration is adopted, optimized with aspheric and diffractive surfaces. The lens mass is only 26.6 g, with modulation transfer function (MTF) exceeding 0.2 at 42 lp/mm across the -40°C to +50°C operational range. The mechanical structure proposes a threaded mechanism for front-group manual focusing to achieve active athermalization. By driving the displacement of the first lens through a precision threaded mechanism, rapid target switching between 15 m and 3 km and thermal defocus compensation are simultaneously realized. Magnesium alloy barrels are selected for lightweight design, with structural components weighing 49.4 g, resulting in a total opto-mechanical system mass of 76.0 g. This design integrates wide-temperature stability, operational convenience, and mass production potential, providing a high-performance solution for hand-held infrared detection equipment in complex environments.