Fig. 1. Evaluation curve of star spot by gradient algorithm

Fig. 2. Gray distribution of star facula

Fig. 3. Structure diagram of focusing module

Fig. 4. Schematic diagram of focusing system

Fig. 5. Star-following device equipped with focusing syst

Fig. 6. Systematic imaging of HIP11767 in focusing process.

Fig. 7. Evaluation results of different functions

Fig. 8. Atmospheric coherence length measurement with an autofocus device and improved algorithms