离焦检测技术的研究是光学加工与检测行业的一项重要课题。像散法由于操作简单、灵敏度高等优点，被广泛应用于离焦检测技术中。然而，基于像散法的离焦检测系统设计有待完善。基于像散法的基本理论，综合考虑系统像面光斑大小合理性和光学元件可加工性等因素对像散离焦检测系统进行灵敏度分析。设置合适的参数，并使用光学设计软件Zemax对光学元件几何参数进行优化。为了计算实际光斑的能量非均匀与非标准椭圆的性质带来的误差，采用MATLAB对该系统进行光线追迹。根据光线追迹的结果，完成对零信号像面的校准工作，提高了测量精度。

Research on defocus detection is an important issue in optical manufacture and testing. Astigmatism method is widely applied in the defocus detection due to the advantages of simple operation and high sensitivity. However, the design of defocus detection system based on astigmatism method is under improvement. The sensitivity analysis of the measurement system based on the basic theory of astigmatism method is carried on considering factors such as system components machinability and spot size rationality. The suitable parameters are determined and geometric parameters of optical components are optimized by the optical design software Zemax. The MATLAB is used for ray tracing to calculate the error caused by facular energy heterogeneity and non-standard elliptic property. Calibration of image plane with zero signal has been completed and the accuracy of measurement has been improved.