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

[stevet1]

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

Steve Thomas

[Waddizzle]

Tracking and focusing are two entirely different concepts, but they are joined at the hip.

Focusing is pretty straight forward.  In One Shot AF mode, you put the enabled AF point on the subject, half press the shutter, and the camera should lock focus and beep.  In AI Servo AF mode, the camera focuses, but it does not lock until you fully press the shutter button.  AI Servo AF mode is designed to allow the camera to stay focused on a subject, whose distance to the camera is constantly changing.

You the photographer are primarily responsible for tracking your subject, which means keeping the AF point on the subject as they move.  This often omes into play during sports and wildlife photography shoots.  You must move the camera to not only keep the subject in the viewfinder, but also covered by the active AF point.

In AF Tracking modes, the camera can automatically reselect AF points as your subject moves around the viewfinder.  This is a more advanced mode of using the camera.  The user must go into the menus and tell the camera which AF point to use as the initial AF Tracking point,

[kvbarkley]

Do you mean AF Face tracking?

AI Servo uses the viewfinder focus chip, while the AF Face Tracking uses the on-sensor focus sites + sensor info.

[jrhoffman75]

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@stevet1 wrote:

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

Steve Thomas

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The general answer is that AI Servo monitors the subject (where the focus point is) and calculates the velocity  of the subject. Then it uses that information to determine where the subject will be when the shutter actually fires. There is a time delay between  when the shutter button is pushed and when the shutter actually opens. If the velocity is great enough there could be a noticable focusing error if the adjustment wasn't made.  Velocity * time = distance. AI Servo, when selected, will work with a single or multiple focus points. cameras that don't have the tracking capability still have AI Servo.

Focus Tracking will follow the the subject as it moves through the area of the selected focus points. Generally only works when the fully auto AF selection option is active. Once the subject is acquired the foucs point will follow that subject as it moves across the viewfinder.

I can only address the 1D series, but for those cameras subject tracking will work in viewfinder mode - the sensor isn't involved since the mirror is down.

In LiveView there is improved subject tracking since the focus points cover more of the view area and there are more focus points.