大变倍比连续变焦红外成像系统能够同时应用于大视场下的目标搜索和小视场下的高精度跟踪测量。由于变倍比很大，在整个变焦范围内均保持良好的成像质量就成了其设计验证的难点。为了解决这一问题，本文利用调制传递函数对变焦距像面的变化量进行测量和验证。红外成像系统整机调制传递函数的主要测试方法有斜狭缝法和斜刃边法。在对两者的测试特点和影响要素进行分析比较后，选取斜刃边法作为红外成像系统整机调制传递函数的测试手段。通过用调制传递函数对现有的大变倍比测试样品在各特征焦距下的离焦曲线进行标定，得到了最优像面位置。与理论设计值相比较，最大偏差为36 m。依据该数据对调焦补偿进行了修正。复测后，该偏差的最大值降至5 m。

A continuous zoom infrared imaging system with a large zoom ratio can be used for target searching in a large field of view and for high precision tracking in a small field of view at the same time. Because of the large zoom ratio, to keep good imaging quality throughout the zoom range becomes the difficulty for design and validation. To solve this problem, the Modulation Transfer Function (MTF) is used to measure and validate the variation of the zoom image plane. There are two mainmethods for measuring the MTF of an infrared imaging system: a slit method and a sloping edge method. After analysis and comparison of the characteristics and influence factors of both methods, the sloping edge method is chosen. By using the MTF to calibrate the defocus curve of the existing test sample with a large zoom ratio at each focal length, the optimal image plane position is obtained. Compared with the theoretical design value, its maximum deviation is 36 m. The focusing compensation is modified according to the data. Finally, the maximum deviation is reduced to 5 m.