针对地球环境遥感的大视场和宽 光谱的应用需求，在同轴三反光学系统的基础上，通过 视场离轴实现了无中心遮拦，并设计了一种焦 距为120 mm、F数为3.5、工作波长为0.4 ～ 1.65 m、像元尺 寸为7.5 m以及采用Cook三片式结构的光学系统。在没有使用自由曲 面的情况下，实现了30°×4°的大视场。其中，主镜为六 次双曲面，次镜为二次扁椭圆面，三镜为四次扁椭圆 面。在全视场范围内，该系统在奈奎斯特频率处的调制传递 函数(Modulation Transfer Function, MTF)大于0.6，接 近衍射极限。其弥散斑直径的均方根值小于探测器的像元尺 寸，畸变小于2.5%，说明本文系统具有优良的成像性能。

To meet the application needs of wide field and wide spectrum of earth environment remote sensing, a center without obstructing is realized by means of field off-axis on the basis of coaxial three-mirror optical systems. An optical system with a Cook three-mirror structure is designed. The optical system has its focal length of 120 mm, F number of 3.5, operating wavelength of 0.4 to 1.65 m and pixel size of 7.5 m. it realizes the 30°×4° large field of view without any free-form surfaces. In the optical system, the primary mirror is a 6 times hyperboloid; the second mirror is a secondary flat ellipse and the third mirror is a 4 times flat ellipse. The system has its Modulation Transfer Function (MTF) greater than 0.6 at the Nyquist freaquency in the whole field of view, which is close to the diffraction limit. Its RMS dispersion spot diameter is less than the pixel size of the detector and its distortion is less than 2.5%. These results show that the system has excellent imaging performance.