提出一种新的零朗奇检测法用于测量大口径非球面镜的面形。利用光线追迹和正弦条纹的相位信息设计补偿正弦光栅。使用透射液晶显示屏显示补偿正弦光栅并作为相移装置。一个离轴点光源发出的光被镜面反射后通过补偿正弦光栅，摄像机记录携带镜面偏差信息的相移条纹图。通过对相移条纹图的分析确定被测镜面的实际横向像差以及对应的理想横向像差，然后基于朗奇检测的几何原理得到被测镜面的偏差梯度，对其积分获得被测镜面的偏差，进而重建被测镜面的三维面形。与传统的零朗奇检测法相比，这种方法可以消除补偿光栅上每个条纹带边缘的锯齿形状，而且可以获得镜面上足够多的待测点信息。计算机模拟和初步实验验证了该方法的可行性。

A new null Ronchi test method is presented to measure the shape of a large-aperture aspheric mirror. Null sinusoidal gratings are designed by using ray tracing and phase information of sinusoidal fringes. A transmission type liquid crystal display (T-LCD) screen generates null sinusoidal gratings and controls phase shift. An off-axis point source illuminates the whole mirror surface and a camera captures the phase-shifted fringe patterns containing the information of deviations of the mirror. By analyzing these fringe patterns, the actual transverse aberration and the corresponding ideal one are obtained. Then, the slopes of the deviations of the mirror are determined based on the geometric principle of the Ronchi test. The shape of the mirror is reconstructed after restoring the deviations of the mirror by integrating. Compared with the traditional null Ronchi test, the method eliminates the jagged edge of bands on the null gratings, and acquires the information of enough tested point. Simulations and a preliminary experiment validate the feasibility of this method.