Systems and methods for continuous automatic focus are disclosed. In some aspects, an object to focus on is selected from a field of view of a camera. At least one region of the field of view that includes the object is monitored for change. Regions of the field of view that do not include the object may not be monitored, thus improving efficiency and speed. If a change in the image content of the monitored region(s) occurs, the method may trigger a focus event. If the object moves to different region(s) of the field of view, the method detects the movement and adjusts the regions of the image being monitored to maintain focus on the object. In some aspects, the size of the object is also monitored. If the size of the object changes, a focus event may be triggered, depending on whether the amount of change exceeds predetermined parameters.