等晕角是反映大气湍流特性的重要参数之一，对自适应光学系统设计和补偿效果分析有着重要的作用。介绍了一种新型的三环结构变迹镜，并将其应用于高精度等晕角测量。给出了测量原理和实验测量方法，进行了夜间等晕角的测量。理论推导结果表明：利用三环结构变迹镜对光强调制，能够很好地拟合大气湍流随高度分布的加权特性，并提高等晕角的测量精度。测量结果表明：西安城区夜间的等晕角变化范围为5~10 μrad，与同纬度地区的等晕角值比较一致。针对现有实验系统存在的问题提出了改进方案。

Isoplanatic angle is one of important atmospheric turbulence parameters which has play a significant role in system design and compensation effect of adaptive optics. A apodized mask with triple concentric annuluses is introduced and applied to high precision measurement of isoplanatic angles. Principle and measurement technique are presented, and isoplanatic angle is measured at night in Xi′an. The conclusion of theoretical derivation shows that the apodized mask can modulate irradiance of star light received as a “5/3” power of height and improve measurement precision. The measurement results shows that isoplanatic angles in a range 5~10 μrad at night in Xi′an agree with that in the same latitude regions. The suggestions for improving experimental device are proposed.