Continuous autofocus for movies

The continuous autofocus feature, or continuous AF, can be extremely helpful for video recording. This technology keeps moving subjects in focus – something particularly useful when shooting sports, animals, urban life, or just any non-stationary subject.

Also known as full-time servo, continuous autofocus works by tracking the subject's movement trajectory and constantly readjusting the focus fast enough to prevent blurring from happening. The camera system can do so by capturing, retaining, and analyzing information regarding the subject’s positioning.

One of the disadvantages of continuous AF is more substantial battery consumption. Another drawback relates to potential focus inaccuracies; since the tracking process includes movement prediction, the system may be caught by surprise by an unexpected movement direction. However, as AI technology evolves, so does the continuous autofocus feature.

Before recording a video, the user must remember to select the desired feature. Camera manufacturers may name their continuous autofocus functionalities in different ways. As an example, Nikon calls the feature full-time servo AF, or AF-F, whereas Canon has named the feature AI Servo – short for Artificial Intelligence Servo Automatic Focusing. Some cameras offer several choices within their continuous autofocus modes. A number of Canon EOS products, for instance, include continuous AF presets that differ in terms of how the camera responds to changes in subject speed and new subjects entering the frame.

As a significant number of consumers rely exclusively on their smartphones to record videos (from private to professional use), plenty of manufacturers have incorporated the continuous AF feature, which can be expected especially in high-end and mid-range phones.