Canon’s 7D Mark 2 has a powerful and effective autofocus system, with a comprehensive set of controls and adjustments for setting it up. It shares quite similar menu and setup options to those found on the much more expensive 5D Mark 3, 5DSR and 1DX series cameras.
This AF system is sophisticated, but well organised.
The very first AF menu tab shows what Canon call the six AF Cases. On the 7D Mark 2, the AF Cases consist of six different combinations (presets) of the three different parameters that all have an effect on how Ai Servo performs. These parameters are 1. Tracking Sensitivity, 2. Accelerate/Decelerate Tracking and 3. AF Point Auto Switching.
Canon used sport scenarios to describe each case, in an effort to make it easier to choose. I shoot wildlife rather than sports. I also much prefer to work with the three parameters on their own, and gather my own understanding of their function, rather than modifying the cases in place.
I have been working in this way with the 5D Mark 3, 5DSR and 1DX bodies for some years now. The first step is to move the three parameters into the Green My Menu tab. That way I can access them instantly, and individually.
This takes less time to do than it does to type out this text. Simply go the green menu tab called My Menu, and select Configure.
Select the option “Select items to register”
Scroll downwards in this vertical listing of the entire camera menu until you reach Tracking Sensitivity
Press the Set button
Scroll down one more line, and select Accel/decel.tracking
Scroll down one more line, select AF pt auto switching
Once you have carried out the selection of the three parameters as illustrated, your My Menu tab should like the image below.
Having the three parameters available like this enables me to make quick and easy changes.
This setting controls how long the camera will ‘wait’ before refocusing, when a new subject/object moves between the camera and the original subject, or the active focus point is moved off of the subject. An example of this is when you are tracking a bird, and the bird passes behind a branch, momentarily. With this setting on Responsive (+2), it is more likely that the AF will quickly lock onto the branch. If this setting is on Locked-On (-2), it is likely that the camera will hold the focus for longer, without attempting to re-focus for long enough that the bird can once again be located once the obstruction has passed by and out of the line of sight.
Another example of how this parameter can be of use, is for those times when you are tracking a moving subject with an active AF point on that subject, and you accidentally move the camera so that the active AF point drops off of the subject. With Tracking sensitivity set to -1 or -2, there will be more time available for you to re-locate the subject, without the lens having focused on the background. The image above is an example of such an instance. My Single AF point was right in the middle of the frame, but the camera did not immediately try to focus on the blue sky background.
Canon do mention that with Tracking Sensitivy set to the Locked-On side of the slider, it may take the AF a little longer to re-aquire focus if focus is lost. Canon also state that initial AF acquisition is not affected by setting Tracking sensitivity to Locked-On (-1 or -2). Despite what Canon have stated, it is my feeling that having the camera set toward Locked-On, either -1 or -2, may result in slightly slower AF response if a subject is coming directly toward the camera at high speed. If I expect to be shooting oncoming subjects a lot, I may keep the Tracking Sensitivity on 0 or +1.
Tracking sensitivity is definitely the most important of the three parameters described here in that it can make a noticeable difference to how stable AF tracking is if you move it towards the negative settings, or Locked-On side of the slider. It can also speed up the AF systems responsiveness if you move it toward the plus or Responsive side of the slider.
In my experience, I find myself more likely to slow down Tracking Sensitivity (-1 or -2) when I am using focal lengths of 500mm and upward, and only if I feel that I am dropping focus off the subject too often. When I am working with lenses with shorter focal lengths, 400mm or less, I may leave Tracking Sensitivity on 0 or even +1 if I am expecting really fast, approaching subjects. With shorter focal lengths, it is much easier to keep the focus point/points on the subject, and also easy enough to relocate the subject even if I do move the point away momentarily.
This setting allows the AF to be optimized to capture fast-moving subjects that might suddenly stop, or move in a random direction, or rapidly speed up or slow down. The 0 setting for this parameter is suited for tracking subjects that move at a steady speed. Most of the subjects that I shoot accelerate or decelerate whilst i am tracking them. Also, if I have a subject coming towards me, even if that subject is staying at a steady speed, I have to allow for the relative increase in speed the closer to me that subject gets. Think of trying to track a bird flying towards and right by you…your panning motion has to speed up dramatically as the subject gets closer to you and actually passes by. As I like to try and shoot fast moving subjects whenever possible, I have started leaving this setting on (+1) with good results. According to Canon, setting it to (+2) will make it very responsive but also a bit less stable. At the time of writing I have not found need yet of using this setting on (+2).
AF Point Auto Switching
If you are a photographer that prefers to always use the camera in Single AF point mode, (or Single Spot AF), then you can disregard this parameter. It’s function only applies when shooting with those AF mode options that utilize more than one AF point.
On the 7D Mark 2, these are : Expand AF Area (selected plus 4 surrounding), Expand AF Area Surround (selected plus 8 surrounding), AF Zone, Large Zone AF and Auto Select 65-Point AF.
AF Point auto switching controls how rapidly the AF will switch to a new AF point whenever the initial or primary AF point (again, only when there is more than one AF point) leaves the subject. It will rapidly switch to surrounding AF points to continue to follow the subject.
The (+1 and +2) settings are used when shooting subjects with faster, erratic movement in any direction,whilst the (0) setting provides a more stable switching of AF points. To date, I have not felt the need to change this setting from (0) on either the 7D Mark2. I tend to shoot mostly with a single manually selected AF point, but I also use do sometimes use the AF Zone grouping on both cameras, and have found the point switching to be fast enough to date on the (0) setting.