Different from visible light, infrared optical systems need to consider various effects in order to change the F-number of the system, such as the effect of stray light in the system before and after variable F number, and the effect of cold reflection on the system, which are all effects to be considered. This paper analyzes the technology of infrared variable F number, summarizes the research progress, and the key technology of thermal aperture variable F-number.
A secondary imaging convergence system is designed for a cooled infrared optical system with three Germanium lenses. An optimal design method for low stray radiation is proposed. Compared with the traditional method, stray light analysis shows that the new design method can suppress stray radiation by 23.87% more than the traditional method.