非球面可以由其法线汇来表征，即可以由法线距和法线角的关系来描述。提出了一种基于相位测量偏折术(PMD)的非球面反射镜法线向量检测方法。在PMD测量系统中，将待测镜沿光轴方向作相对移动。在移动过程中，由CCD相机扫描待测镜，观察并记录下随待测镜移动而发生变化的条纹图，通过相位分布计算得到非球面法线距和法线角的关系，即非球面的法线汇，再由法线汇计算得到非球面面形直角坐标分布。在该方法中，可以用法线汇来描述非球面的面形，同时也可以通过几何计算转换到直角坐标系进行评价。

The aspheric normal intersects the optical axis at different points with different angles and the surface can be expressed by the normal. The method based on phase measuring deflectometry (PMD) for testing the surface normal is presented. The aspheric surface under test shifts accurately along the optical axis relative to the measurement system. The camera observes the patterns reflected off the testing mirror at every scanning position while scanning the testing aspheric surface along the optical axis. Through the phase distributions, the relation between the intersection point and the angle of the surface normal with the optical axis can be gotten. In this method, the surface can also be expressed in the orthogonal coordinate.