相机焦面定位精度决定了相机的成像质量，对其测试方法须作专门研究。介绍了一种基于图像频谱的定焦测试方法，最少仅利用同一目标的两个离焦图像，即可推算出相机成像面的离焦量。算法基于相机对任意目标所拍摄的离焦图像，并且在相机镜头装调质量达到设计要求的情况下，对成像目标无要求。利用两幅图像的相似性，通过数值分析的手段，避免了对图像频谱的直接分解，具有所得结果有可靠、稳定、精度高、易操作的特点。

The imaging quality of camera severely depends on the precision of location of focal plane, and correlation research on the testing method is carried out. A testing method of locating focal length based on the image spectrum is presented, which can make use of at least two defocusing pictures from the same target to calculate the defocusing amount of camera image plane. And on the condition that the camera lens is aligned well with the design requirement,the target is random. In the process of numerical calculation using the similarity of two images, the image spectrum can avoid direct decomposition and make the testing easy, stable, reliable and with high precision.