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With the development of space optical technology,space camera is required to be characterized by both high resolution of ground sample distance and ability of multi-spectral imaging.Thus the optical system design must be satisfied with the demand of large field of view and small distortion.Based on the on-axis three-mirror-anastigmat system,a new type of optical system was designed,which is characterized by small central obscuration,low optical distortion and reasonable arrangement of panchromatic and multi-spectral CCD.The results indicate that the field angel reaches 1.6°,the system line central obscure coefficient is lower 1/3,the optical system distortion is less than 0.5%,MTF is superior to 0.47 at 50 lp/mm,the image quality reaches the limit of optical diffraction,when the focal length is 12 000 mm,focal ratio is 12,and the spectrum band is from 450 to 900 nm.So the proposed optical system can meet the demand of high resolution multi-spectral space cameras.

An example of 8× ratio visible zoom system with mechanic compensator was designed.The focal length and angle of vision of the system were 6.5~52 mm and 6.6°~52°,respectively.The modulation transfer function(MTF) is above 0.6 within the whole focal range at spatial frequency of 75 lp/mm,and approaches the diffraction limit.RMS value of spot diameter was investigated.The cam curves after optimization was given.The system has the advantages of simple structure,high image quality,short zoom path and smooth zoom locus etc.