Design of Airborne Miniaturized Middle Wavelength Infrared Continuous Zoom Optical System

To satisfy the requirements of an airborne electro-optical system for miniaturized and lightweight optical system of an infrared thermograph, a 22^× continuous zoom optical system of 30–660 mm was realized by combining front-end afocal extender and back-end continuous zoom optical system. The total optical length of the system was 244 mm, and the total length/maximum focal length ratio was 0.37. The system had a small optical length and large zoom ratio, which makes the system suitable for large airborne electro-optical pod systems for long-distance detection. Upon removing the front afocal extender, the back-end system could achieve a 22^× continuous zoom optical system of 15 to 330 mm. The total optical length of the system was 138 mm, and the total length/maximum focal length ratio was 0.42. The system can be used as a continuous zoom optical system in small-and medium-sized airborne electro-optical pod systems for close-range target detection. The design results exhibit that the system can capture images effectively in both states: at the characteristic frequency of 33 lp/mm corresponding to the detector, all the MTF values of the central field view were approximately 0.3, close to the diffraction limit, all the MTF values of the 0.7 field view were approximately 0.2, and all the MTF values of the edge field view were approximately 0.15, which satisfies the application requirements.