The behavior of Canon's AI Servo AF autofocus can be modified by choosing one of six presets, and can be customized further by adjusting the Tracking sensitivity, Acceleration/deceleration tracking and AF point auto-switching parameters.

If I set the three parameters to the same value on two different cases, do they both behave the same?

e.g. would Case 1 be equal to Case 6 if I set Tracking sensitivity, Acceleration/deceleration tracking and AF point auto-switching to the exact same values on both cases or would they behave differently still?


I thought I read somewhere a while back that they are much like Canon's "Picture Styles" and the '0' defaults are not necessarily the same starting points for each AF case, just as the same "fine tuning" settings are not the same with different "Picture Styles." Recently I had a discussion where that was challenged and I couldn't immediately find where I had previously come across the idea.

They might be fine tuning controls for each Case preset:

This article from Canon USA for the EOS 7D Mark II seems to be saying the above after introducing the six AI Servo AF cases offered by the 7D Mark II:

Note: Each of these can be further fine-tuned by adjusting the parameters manually (see below).

This statement is echoed on page 3 of the EOS 7D Mark II AF Setting Guidebook

Blessed with the same AI Servo AF III focus-tracking system as the top-of-the-line EOS-1D X camera, the default AI Servo AF settings will handle most moving subjects with great success. But for challenging situations, critical users can turn to the AF Configuration Tool, in the AF menu. Six separate “Cases” there tailor the EOS 7D Mark II for different and specific types of subjects and subject movement. And, each can be further fine-tuned in three distinct ways, via the “Detail Settings” within the AF Configuration Tool menu.

On the other hand:

A careful reading of other resources published by Canon, such as the Canon EOS 1D X Mark II AF Setting Guidebook seem to lean in the other direction.

By selecting from six presets (Case 1 - Case 6), it is possible to set the AI Servo AF characteristics to most accurately suit the subject's movement, and scene conditions. It is also possible for fine control to adjust each parameter separately.

Canon also published an EOS 5D Mark III AF Setting Guidebook but apparently they did not make one for the EOS 5D Mark IV. The 5D Mark III AF Settings Guidebook says:

These six presets are combinations of the following three parameters, [Tracking sensitivity], [Accel./decel. tracking], and [AF pt auto switching].

The 5D Mark IV and the 1D X Mark II AF systems are very similar, and I would expect both to behave the same in this respect. In fact, I'd expect all of the Canon bodies that offer AI Servo AF "cases" to do it the same way. But I've yet to find a definitive answer to this question in the materials I've read from Canon, and I've been looking for it for a while now.

If Chuck Westfall were still around, I'm sure he'd know the answer and be willing to reveal it. He certainly wasn't shy about extolling the virtues of Canon's products. And though he was an upper level executive for Canon USA, he wasn't as reticint as most executives about also discussing the abilities we might want but that Canon, for whatever reason, had not included in the latest model. Unfortunately, Chuck passed away in May of 2018.

My practice has been to develop certain settings, either the default ones or modified slightly, for each case and leave them there, then use whatever case I find most appropriate. This allows me to get a "feel" for how each case will act. Whether changing cases and then setting the parameters to what they were in the previous case would be identical or different isn't really that crucial to me. Concentrating on learning how each case as I've set it up acts in different shooting scenarios has been more productive for me.

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Yes, they will behave on the same way because at the end autofocus depend of those three parameters (and focus points selected).

I base my answer on Canon EOS 5D Mark III (do not have Mark IV).

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