For filming a fast-moving object like a car, what specific autofocus mode should you use to keep it sharp throughout the video?

For filming a fast-moving object like a car, you should use Continuous Autofocus. This autofocus mode, often labeled as AF-C on cameras from manufacturers like Nikon and Sony, or AI Servo AF on Canon cameras, is specifically designed to track subjects that are in motion. When Continuous Autofocus is engaged, the camera's focus system constantly monitors the distance to the subject and continuously adjusts the lens's focus to keep that subject sharp. As the car moves closer to or further away from the camera, or across the frame, the autofocus system predicts its movement and updates the focus in real-time. This continuous adjustment ensures that the fast-moving car remains in sharp focus throughout the entire video clip, unlike a Single Autofocus mode which would lock focus once and not readjust for movement.