AI servo

AI Servo is an auto focus mode found on higher end Canon cameras, although the same principal is used with Nikon cameras, known as "Continuous Focus" [ [http://www.dpreview.com/learn/?/Glossary/Camera_System/af_servo_01.htm AF Servo: Camera System: Glossary: Learn: Digital Photography Review ] ] . Also referred to as focus tracking, it is used to track a subject as it moves around the frame, or toward and away from the camera. When in use, the lens will constantly maintain its focus on the subject, hence why it is commonly used for sports and action photography. AI refers to artificial intelligence, the algorithms that constantly predict where a subject is about to be.

High end cameras have extremely fast autofocus systems with good tracking performance. These are typically much faster than a person is able to focus manually, and coupled with camera bodies that shoot several frames per second. While sports and wildlife photography were possible in the manual focus era, good autofocus systems have dramatically improved the photographer's productivity. Before servo focus the photographer would generally pre-focus on an area where he/she thought the best action would take place; today he/she can follow the entire sequence of events, and select the best later.

References