Inertial confinement fusion（ICF） needs micro-target in high precision assembly

and the online monitoring system based on machine vision is the primary means of target measuring.Precise optical focusing is the premise of stable

high-precision measurements.An active auto-focus method based on 3D precise shift platform is proposed.The system achieves fast and precise focus.Suitable definition evaluation function is selected through experiment.Searching strategy uses long step to find the region

small step to find the precision focus point.It is proved that the precision is better than 10μm

and the overall time is about 30s.The issue that using long time and not entirely clear of manual focus is overcomed.