Design of Coaxial Four-Mirror System for Large-Scale Stereoscopic Mapping Camera

In order to improve spatial resolution and geometric precision of the large-scale stereoscopic mapping camera, four-mirror coaxial optical system with ultra-low distortion and well symmetry is researched. The design method of the four-mirror system with ultra-low distortion based on primary aberration is explored. The basic structural parameters are calculated according to magnification and obscuration ratio of each mirror. The conic parameters are calculated according to primary aberration coefficient. The procedure for calculating initial structural parameters is programmed. Then a four-mirror system is designed with an focal length of 12 m, a field of view of 2° × 0.1°, and the wavelength range of 0.45–0.9 μm. The results indicate that the modulation transfer function (MTF) of the whole field is approached to the diffraction limit at Nyquist 71.5l p/mm, and the relative distortion is less than 0.01%. The design structure of four-mirror system can be widely used in the surveying and mapping cameras for high spatial resolution imaging.