  Fast and accurate auto-focus in adverse conditions remains an arduous task.
The emergence of event cameras has opened up new possibilities for addressing
the challenge. This paper presents a new high-speed and accurate event-based
focusing algorithm. Specifically, the symmetrical relationship between the
event polarities in focusing is investigated, and the event-based focus
evaluation function is proposed based on the principles of the event cameras
and the imaging model in the focusing process. Comprehensive experiments on the
public event-based autofocus dataset (EAD) show the robustness of the model.
Furthermore, precise focus with less than one depth of focus is achieved within
0.004 seconds on our self-built high-speed focusing platform. The dataset and
code will be made publicly available.
