A sharply focused image
Today Canon is one of the largest manufacturers of digital cameras. While their products range from small, inexpensive point-and-shoot models, Canon also produces a full line of professional digital SLRs. These cameras feature several high-tech systems to make taking better photographs easier and to improve image quality. AI Servo is one of Canon's more advanced systems, available on only its highest-end models.
Description
AI Servo (sometimes called AI Servo AF) is an autofocus system intended to help a Canon camera users produce clean, sharp images of a subject in motion. The "AI" in the name refers to "artificial intelligence" since the system uses multiple pieces of information including the lighting conditions, the speed of the subject, and the trajectory of its motion to determine points of focus. For this reason, Canon refers to AI Servo as a predictive autofocus feature.
Applications
Like most autofocus systems, AI Servo is most useful in certain types of photography. Sports photography is among these, with the predictive autofocus able to track a fast-moving athlete or ball. Nature photography is another field that benefits from AI Servo since animals may move suddenly and there may be very few opportunities to capture the desired image. On Canon's cameras, AI Servo is paired with the ability to shoot multiple frames per second, meaning that even in cases of a fast-moving subject it may be possible to produce several sharp images.
Technical Function
Canon's AI Servo functions by using two separate CPUs to control focus. This means focus can be attained more quickly, and more data can be used in predicting where focus will need to occur. As the autofocus system is used, information from each focus decision is stored in the camera and used to increase the precision of all future focus decisions. AI Servo also relies on a series of autofocus points that run through the image sensor's autofocus ellipse, or the space within which the camera can determine autofocus points, allowing it to track a moving subject virtually anywhere within the frame.
Use
Using Canon's AI Servo is meant to be intuitive and simple. AI Servo works best when the photographer has been tracking the subject for at least one second. AI Servo functions in two different modes: single focus point, which is useful when tracking a single moving object within a larger field of moving objects, and autofocus point selection (AFPS) which allows AI Servo to identify the moving subject and focus on it accordingly. Additional settings can be modified by advanced users to customize AI Servo even further.
Availability
Canon has made AI Servo available as a feature on its most advanced cameras for several years. As of 2009, Canon offers two digital SLRs that use the newest version of AI Servo technology, known as AI Servo II AF. They are the Eos 7D and Eos-1D Mark IV models. Both are priced over $1,000, as have most AI Servo-equipped models in the past. Similar predictive autofocus systems are available from other camera manufacturers and opinions vary as to which is best, though users of Canon AI Servo report generally good results.
Tags: Canon Servo, predictive autofocus, autofocus points, autofocus system, autofocus systems, digital SLRs, moving subject