在反射式望远镜系统误差校正过程中,常以点目标的清晰度函数作为成像质量的评价指标。通过优化算法对存在误差的参量进行校正,使清晰度函数达到极值。平均半径作为点目标成像的清晰度函数由于具有适用范围大、动态特性好的特点而得到广泛的应用。然而,在实际工作过程中,由于探测器噪声等因素的影响,平均半径计算值与理论值存在一定的偏差,从而对校正过程产生影响。对噪声下平均半径的计算误差以及阈值对误差的影响进行了理论和仿真分析,结果表明存在最优阈值使计算误差达到最小,并对不同噪声强度下仿真的最优阈值数据进行拟合,给出了最优阈值拟合公式,分析表明该公式能够较准确的计算最优阈值。 In the process of error correction of the reflective telescope system, the sharpness function of point target is often used as the evaluation index of imaging quality. Through the optimization algorithm to correct the error parameters, the sharpness function reaches the extreme value. The average radius as the sharpness function of point-target imaging has been widely used due to its wide range of applications and good dynamic characteristics. However, during the actual working process, due to the influence of the detector noise and other factors, there is a certain deviation between the calculated value of the mean radius and the theoretical value, which affects the calibration process. The calculation error of the average radius under the noise and the influence of the threshold on the error are analyzed theoretically and simulatively. The results show that the optimal threshold exists to minimize the calculation error, and the optimal threshold data of the simulation under different noise intensities are fitted to Out of the optimal threshold fitting formula, the analysis shows that the formula can calculate the optimal threshold more accurately.