We use single-lens imaging system to analyze whether the specific function of 4f lenses system in the particle field in-line holographic diagnosis (ie, the magnification of 4f lenses system is the same constant for each position of the particles) is unique or not to 4f lenses system. The experimental results show that when the positions of the recording surface and the lens are relatively fixed, the hologram recorded by the single-lens optical system can also be precisely reproduced by the plane wave, and its magnification has nothing to do with the object distance of the object. So we can see that the above advantages of 4f in particle field in-line holographic diagnosis are not unique to the 4f. That is to say, we record the particle field by a single-lens imaging system without different reproduction or particle size calibration methods.