Design of a four-mirror optical system with wide field of view

Reflective optics is used widely in space optical systems for their achromatization, large aperture and lightweight compared with refractive systems. Four-mirror system especially off-axis system is desired for its excellent imaging performance and compact structure. Aberration theory of coaxial four-mirror system based on PW method is analyzed and the design procedure is proposed to get the initial four-mirror system in this paper. A large field off-axis four-mirror system is designed based on the theory and the design process. The system contains four conic aspheric mirrors. It has a 2 degrees x0.32 degrees rectangular field of view. The MTF of the system is diffraction-limited and the distortion is less than 0.1%. The structure of the system is compact and the ratio of total axis length to focal length is about 1/3.9. The excellent imaging performance and compact structure make it adaptable to space remote sensing systems.