为了实现接近衍射极限的分辨率，工作在极紫外波段的Schwarzschild物镜要求其光学元件的面形精度达到约1 nm(RMS值)；而在物镜的装配过程中，装卡产生的应力会影响光学元件的面形精度，定量计算装卡应力对元件面形的影响是获得高分辨率成像的关键。在光学设计、公差分析的基础上，采用有限元模型系统地分析了应力对Schwarzschild物镜光学元件面形精度的影响。结果表明：采用自行设计的物镜结构，应力对主镜面形的影响可以达到0.7 nm，而对副镜的影响可以忽略；应力所产生的光学元件面形变化会使系统的几何传递函数(5000 lp/mm)从0.76下降到0.61。

To closely achieve diffraction-limited resolution, the surface shape of extreme ultraviolet (EUV) Schwarzschild objective requires about 1 nm (RMS value). But the mounting stress generated during the assembling process will affect the surface shape of optical components. Making quantitative calculation of mounting stress is a key point to obtain high-resolution images. On the basis of optical design and tolerance analysis, the influence of mounting stress on the surface shape of Schwarzschild objective is analyzed through the finite element model. The calculated results of the already designed structure show that, the surface shape error of primary mirror could reach to 0.7 nm (RMS value), but the influence on secondary could be ignored; the value of geometric optical transfer function (5000 lp/mm) decreased from 0.76 to 0.61 due to the surface shape error.