Long Focal Length Variable F-Number Infrared System With Secondary Mirror Switching Cassegrain Mirror Zoom

To address the development requirements of long focal length, wide field of view, and high transmittance optical systems for next-generation airborne electro-optical platforms, this study focuses on the infrared optical system of a new-type pod-based electro-optical platform. Through optical system design, structural design, and finite element analysis, we conduct research on optical design techniques for variable F-number optical systems with multipath multiplexing and optical performance stability under dynamic multi-physical field coupling. Key technologies are validated, prototypes developed, and performance tests completed. By integrating the secondary mirror of the Cassegrain reflection system with the transmissive front group, we achiev a compact design that combines large aperture, long focal length, and wide field of view zoom capabilities. The prototype demonstrates a long focal length transmittance of 91.8% and a first-order modal frequency of 242 Hz, while maintaining excellent imaging performance under actual airborne operating conditions.