为解决超短焦投影系统中自由曲面反射镜的设计难题, 提出一种适用于大视场成像光学系统的自由曲面设计方法, 即多视场优化迭代法.该方法以一个反射平面作为设计起始面, 基于多视场下物像的对应关系, 并根据反射面的法线方向, 通过加权优化迭代计算得到自由曲面反射面的形貌.采用基于该方法得到的自由曲面优化设计了一种折反式超短焦投影物镜, 可将0.65 inch的数字微镜器件芯片在230 mm投影距离处放大为100 inch的投影画面.物镜的调制传递函数在0.43 lp/mm处优于0.4, 最大畸变优于1%.该方法简单易行, 可为大视场成像系统中自由曲面的设计提供有益参考.

In order to solve the design problem of freeform mirror in ultra-short-focus projection system, a method of freeform surface design for large field of view imaging optical system is proposed, which is called multi-field optimization iteration method. In this method, a reflection plane is used as the design starting surface. Based on the corresponding relationship between objects and images in multi-field, and according to the normal direction vectors of the reflector, the freeform surface is obtained by weighted iterative optimization. Based on the freeform surface obtained by this method, a refractive-reflective combined ultra-short-focus projection objective is designed, which can magnify the 0.65 inch digital micromirror device chip to 100 inch projection screen at the projection distance of 230 mm. The modulation transfer function of the objective system is better than 0.4 at 0.43 lp/mm and the maximum distortion is less than 1%. This method is simple and feasible, which can provide useful reference for the design of freeform surface in large field of view imaging system.