What's the difference between AF Tracking and AI Servo?

Started 4 months ago | Discussions thread
J Peters Contributing Member • Posts: 510
Re: What's the difference between AF Tracking and AI Servo?

Different manufacturers call their features different things, but on a Canon (assuming default settings because these things are customisable):

AF tracking will follow an object you've locked onto (typically a face) as it moves around the frame, or as you move the camera. The most commonly used alternative is single-point focus where you select a point within the frame to focus on, but it stays in that position - It's then up to you to either move the camera, or move the focus point again to keep it on top of the subject if necessary.

With AI Servo OFF (alternative is called One-Shot on my camera), the focus is locked when you half-press the shutter button. If the object/person continues to move before you fully press the shutter, they will likely move out of focus. With the non-tracking modes this (lock on half press) is useful for still subjects as you can lock the focus and recompose.

With AI Servo ON the camera does not lock the focus when you half-press the shutter. So you can half-press to get the camera ready to shoot and lock the exposure, and it will continue to focus right up until you take the shot.

AF Tracking and AI Servo therefore do different things, and can be used singly or together.

Turning both on sounds like a great idea for moving subjects, but like most automated features it can be both a blessing and a pain. If the object is moving very fast, tracking may not be able to keep up and may latch onto something else. Servo mode likewise, if your subject briefly moves behind something in the foreground, it can pull the focus right back and latch onto the foreground item. Experiment and see what works for you.

As an asides, if you use AI servo with burst mode (where you hold the button down to get a bunch of quick shots) then the camera will do FOCUS-SHOOT-FOCUS-SHOOT-FOCUS-SHOOT...   With the AI Servo off it would do FOCUS-SHOOT-SHOOT-SHOOT...   The former is slower but more likely to keep a moving subject in focus from the first shot to the last.

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