I’ve always had difficulty photographing birds in flight with a compact digital camera, even if it had a long telephoto zoom. A bit frustrating, because I enjoy the challenge.
As a result, any digital single lens reflex camera I buy must have predictive autofocus. A standard focus mode on most DSLRs, predictive autofocus is not a common feature on compact digital cameras.
When predictive autofocus is engaged, the camera focuses continually, even while the shutter button is pressed down halfway. This assumes that focus is locked accurately at the start. This is different than most compact cameras, where continual autofocus locks when the shutter button is pressed to the halfway point.
Predictive autofocus is particularly useful when tracking moving subjects. It “predicts” where the subject will be, continually refocuses and locks focus when the shutter button is fully depressed. It not only follows a subject as it moves within the frame, but as it moves away from or towards the camera.
No wonder many action, sports and wildlife photographers like predictive autofocus.
Predictive Autofocus is also known as:
- AI Servo (Canon)
- Continuous Servo Autofocus (Nikon)
- Focus Tracking (Olympus)
Update: Using a Servo mode on a DSLR takes a lot of practice. Using a fast focusing lens will significantly improve performance and accuracy.