In our previous post about the Canon 5D Mark IV, we covered the basics of how auto focus works for still photography and the different auto focus modes. If you're wondering what One-Shot AF, AI Focus, or AI Servo means on your camera, that post is for you.
Here, we're looking more in depth at the other important aspect of autofocus systems, how to choose and use AF points. We'll cover what they are and how they can work together as AF areas.
Get yer' AF Points Here!
The AF Point layout for the Canon 5D Mark IV.
The Canon 5D Mark IV has 61 selectable AF points distributed through the central portion of the viewfinder. These are the tiny squares that you see in your viewfinder. The system is designed to work with many different subjects and types of photography. Knowing what your camera has to offer, and how each mode works is the key to selecting the right settings for your shoot.
The first thing you should do with the 5D Mark IV is be familiar with how to select different AF points. The easiest method is to press the "AF point selection button" then use the multi-controller joystick to select the point or zone you want to use.
When looking in the viewfinder, use the AF Point Selection button and Multi-controller to move focus points.
This is what you'll see when you press the AF point selection button in the viewfinder (with grid lines turned on).
Single Point AF Modes
Now that we know how to move and select an AF point, lets cover the different options you have for AF points. Let's talk about at the first two AF point types:
Single Point AF - The selected AF point is the larger empty square.
Spot AF - Half the size of a single AF point and looks like a square within a square when selected.
The single and spot AF points are the ones where you are fully in charge of what your camera is focusing on. If your subject isn't under the selected AF point, you'll be focusing somewhere else.
Obviously the difference between single and spot AF mode is how large of an area the AF point looks at. The Spot AF mode gives you the smallest and most precise area control over what you are focusing on in your frame. This mode is ideal when you have lots of obstructions between you and your subject or you want to focus on a very specific part of your subject.
The downside of Single point selection is that if you or your subject moves, even in AI Servo, the camera will likely lose focus. The AF system does no tracking in these modes so its best suited for static subjects or ones with complex 3d surfaces.
Using the "Q" button and touch screen is a good way to learn the AF point layouts.
Give me some breathing room - Expand AF Modes
If the thought of trying to keep a tiny AF point on your subject at all times gives you anxiety, there's a mode for that! AF Point Expansion Mode maintains some precision but is a bit more forgiving for subject movement relative to the chosen AF point.
AF Point Expansion is designed to acquire focus via any of the selectable AF points but it will also check with the AF points right next door to stay focused on a subject if it happens to move. There are two layouts for the expanded AF coverage.
Expand AF - This has a cross shaped pattern and uses 5 AF points.
Expand AF Surround - This mode is shaped like a square and uses 9 AF points.
It's somewhere over there - Zone AF ModeS
The Zone AF modes are designed to give you a wider AF sensitivity area at the expense of handing over some of the AF point control to the camera. Zone AF looks at several AF points at once and takes data from all of them, averaging the result. This works well if you are shooting with smaller apertures where you have less depth of field concerns.
Again, there are two sizes to choose from in Zone AF.
Zone AF - Comprised of 9-12 AF points, Zone AF uses 15% of available AF points.
Large Zone AF - This mode uses 20-21 AF points and splits the AF area into a left, center, right layout.
Zone AF has two different behaviors based on the AF focus mode. In One-Shot AF it will survey the selected zone and focus on the closest subject. Any AF points that are considered "in-focus" will show up as highlighted squares in the selected zone.
Zone AF will confirm areas of focus by outlining the boxes that have achieved focus.
Here's an example of how the camera tracks moving subjects in the viewfinder with Large Zone AF and AI Servo mode. You can see that the camera does prioritize the area with the greatest contrast, the face and hairline, as the subject gets closer. You can also see the blinking dance of the AF points that the camera considers to be in focus.
Canon 70-200 f/2.8L IS II | Large Zone AF Area (center) in AI Servo Mode
I don't care, you decide - Auto Area AF
The Auto Area AF pattern uses every available AF point in an effort to achieve focus on the closest subject
When you want to leave the autofocus completely up to the camera, the Canon 5D Mark IV has the Automatic AF area mode. There are two ways this this mode works. When the camera is set to One-Shot mode, the camera focuses on what it thinks is the most likely subject and locks focus. When in AI-Servo mode, the camera will let you choose a starting AF point to track a subject with.
Here you can see Automatic Area AF while In AI Servo mode will track subjects while in the AF area.
This mode can be amazing when it works. The downside is that there's a good chance the camera will get confused about your subject at some point and you'll miss your shot. Thankfully there are ways to customize the behavior of the 5D Mark IV's auto focus system but we'll take a look at those in another post.
Hopefully this post gives new and veteran shooters alike further understand about how their cameras work. The more you know, the better you'll be able to choose the right settings for any shooting situation your find yourself in. If you have questions, leave them in the comments below.