基于立式Fizeau 型干涉仪曲率半径测量系统，提出了一种简捷的离焦补偿算法，该算法对猫眼和共焦零位置的离焦量进行补偿，达到了提高曲率半径测精度的目的。从理论的角度分析了待测面波前像差中的离焦量与待测面位置偏移量之间的线性关系，并得到了两者之间变化的斜率。结果表明，猫眼和共焦零位置附近离焦量的大小与待测面位置偏移量之间为线性关系，且拟合直线的斜率与理论值相一致。同时，当待测面在共焦位置存在离焦时，利用离焦补偿算法使曲率半径测量精度提高了一个数量级。

Based on vertical Fizeau interferometer for radius of curvature (ROC) measurement system, a simple null position power compensation algorithm for defocus at cat′s eye position and confocal position is proposed to improve the measurement accuracy of ROC. The linear relationship between defocus of the wave- front aberration and the offset of tested surface is theoretically analyzed. And the theory line slope between the two is got. The results show that between power value at cat′ s eye and confocal null position and tested surface position offset is the linear relation. And the fitting line slope of experiment is consistent with the theoretical value. Furthermore, radius of curvature measurement precision is improved by an order of magnitude with using the defocus compensation algorithm when the tested surface with some defocus at confocal position.