Fig. 1. Ideal optical imaging system

Fig. 2. Distribution of typical power spectrum

Fig. 3. Output signal of spatial filter

Fig. 4. Schematic diagram of aerial camera image plane detection by spatial filtering effect

Fig. 5. Principle diagram of linear CCD image plane detection

Fig. 6. Out-of-phase differential detection algorithm

Fig. 7. Implementation process of out-of-phase differential focusing method

Fig. 8. Experimental acquisition of images

Fig. 9. Focusing curves in different imaging scenarios