AI Servo AF is an indispensable function for focus tracking of moving subjects. The basic principle of AI Servo AF is anticipating focus by predicting the distance of a moving subject in the next frame from a continuous sequence of previous distances. Canon developed an advanced algorithm for AI Servo AF II (as used in the EOS-1D Mark IV) which enhanced prediction accuracy by ignoring focus readings when errors occur, such as when subjects move out of the AF area or obstructions appear.
The 61-point AF system1 and 65-point AF system2 incorporates AI Servo AF III, achieving even higher levels of stability and precision. AI Servo AF III is the result of algorithm adjustments and the inclusion of three setting parameters based on evaluation feedback from worldwide professional photographers. The system is able to respond to subjects with complex trajectories, as is often the case in sports, enabling capturing of movements that go against predictions.
3 AI Servo AF Parameters in AF Configuration Tool
3 AI Servo AF Parameters of AI Servo AF III
| Tracking Sensitivity
This is the parameter that can be set to track a subject that the AF point had been following until a different subject (or
background) got in the way.
The [Locked on: -2/-1] setting excludes subjects that come into the AF point as obstacles, and continues to focus on the original subject .
Selecting -2 results in the targeted subject being tracked for a longer time before focus changes to subject now in the AF point.
The [Responsive: +1/+2] setting determines that subjects that come into the AF point are new subjects to be focused, and quickly focuses. It is also effective when you want to quickly focuson subjects that are hidden and appear suddenly.
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| Accel./decel. Tracking
This is a tracking setting for subjects that experience significant changes in speed, move or stop suddenly.
The default setting is [0], which is suited for shooting subjects that move at steady speeds, .
[+1/+2] is suited to shooting subjects that stop/change direction suddenly or accelerate/decelerate suddenly, enabling it to continue to focus on the subject. +2 can handle greater changes in speed than +1, however, it can also be more prone to be affected by slight movements of the subject causing temporarily unstable focus accuracy.
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AF pt auto switching
The parameter is used for setting characteristics of AF point switching when the subject has a lot of movements. This pa-rameter is only for switching between multiple AF points, so it is unavailable when using AF area selection modes [Single-point Spot AF] and [Single-point AF].
The [0] setting is a standard setting for moderate switching of AF
points.
The [+1/+2] settings are used when shooting subjects with er-ratic movement which could happen in any directions. When a
manually selected AF point (AF point being focused during Zone AF) leaves the subject, it will rapidly switch to surrounding AF points to capture the subject.
Use the [+] setting when you want the camera to automatically decide (switch) to use a new AF point, and the [0] setting is used when you want to place emphasis on manually selected AF points to track the subject.
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*Illustrated with EOS-1D X screens, screens sand functions of EOS-1D C, EOS 5D Mark III and EOS 7D Mark II may differ.
1 Applicable to EOS-1D X, EOS-1D C and EOS 5D Mark III
2 Applicable to EOS 7D Mark II only
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