With the principle of mechanical passive athermalization, a method of making the dual field-of-view (DFOV) switching
zoom system for passive athermalization is presented. The long effective focal length (EFL) and short EFL have the
same focus shift values of temperature by optical material combination of switching groups. So the long EFL and short
EFL of this system achieve the best temperature compensation simultaneously by moving the compensated lens with the
same distance, and the system has the best images and parfocality in a large working temperature.
A DFOV switching zoom system is designed. It has a relative aperture of f/4.0, 100% cold shield efficiency, the EFL of
180mm/60mm at 3.7-4.8μm. The movement of compensated lens can be achieved with four layers of aluminum/titanium
materials. Compared with the MTF of a normal switching zoom system without athermalization, this system needn't
move the compensated lens repeatedly to obtain the best images from -30°C to 70°C and enhances the performance of
target tracking and recognition.