传统刀口仪检测光学元件面形具有设备简单、非接触性测量等优点，但传统刀口仪只能定性评价面形质量，且人为因素较大。在传统刀口检测原理的基础上，建立了面形缺陷与阴影图相对应关系的数学模型。为了验证该模型的正确性，对口径150 mm的凹透镜进行了数值模拟研究。设置模拟的缺陷参数，利用建立的数学模型得到对应的阴影图；用波像差理论对该阴影图进行分析处理，得到该元件的面形缺陷；将分析得到的缺陷参数与预先设置的面形缺陷进行比较，二者吻合很好。

The traditional knife-edge test has advantages such as simple requirement on the instrument and non-contact measurement etc. But it can only give a rough test to the surface shape and will be heavily affected by human factors. On the basis of traditional knife-edge test, a mathematical model according to the relationship between surface defects and shadow images is developed. To verify the model, a concave lens of 150 mm caliber is studied by numerical simulation method. Firstly, defects parameters are set, then the shadow image is acquired through the mathematical model. After that, the shadow image is analyzed based on wave front error, and then the surface shape defects are obtained. Finally, by comparing the obtained parameters and the pre-set parameters, it is found that the two match well.