Now that you know that not all autofocus systems are made the same, it probably won’t surprise you as much to hear that choosing the correct autofocus mode may also depend on your camera model.
For instance, mirrorless cameras may offer both Phase Detect and Contrast Detect AF modes interchangeably; some even include a Hybrid AF mode, as I mentioned above. DSLRs, by virtue of their mirror box-based design, can only use Contrast Detect autofocus modes when in Live View.
Also, note that for those days when you do feel like switching back to manual mode, mirrorless also possesses a certain edge. Most DSLRs employ something called a digital rangefinder, which measures and notifies you of the perfect manual focusing distance, usually by a blinking light in the viewfinder. Mirrorless cameras are capable of using more advanced technologies, such as focus peaking, to give you a more detailed idea of which parts of your frame are in focus.
Many DSLRs also lag behind their mirrorless brethren a bit when it comes to AF point selection. While many flagship MILCs may boast literal hundreds of autofocus points scattered all over the viewfinder, DSLRs often only make do with a few dozen. On top of that, you can expect most of these to be clustered around the middle of the frame (with manual AF point accuracy generally decreasing a lot on DSLRs the further you go away from the center).
The only major place where camera designs don’t differ so much is in the kind of focusing modes that you can use. Let’s now take a look at each AF mode available on modern digital cameras and discuss their advantages!
Single Autofocus Modes (AF-S) for Stationary Subjects
AF-S, also known as one-shot AF, is the default autofocus mode on many cameras today. The ‘S’ here stands for ‘Single Servo’, which is also another way of referring to this kind of focus mode.
In AF-S mode, your camera autofocus system engages as soon as you half-press the shutter button. Alternatively, you may trigger AF-S via back-button focus as well.
AF-S is mostly used in portraiture, landscape photography, and in other situations where movement and subject tracking are of little relevance to the shot. Because your camera will only try to acquire focus once, it’s a great mode to use when precision is key.
Continuous AF Mode (AF-C)
The total opposite of Single Servo autofocus is AF-C mode, short for Autofocus Continuous.
Continuous AF works just as the name implies: as long as you hold your finger down on the shutter button and until you take the shot, the AF point of your choice will continue to try and acquire focus. This is the main mode to use when you know you’ll be dealing with a quick, hard-to-track subject.
By combining AF-C mode with the right AF area mode (more on that in the next chapter below), you can effortlessly get continuous focus and sharp images even when the shooting rate exceeds your physical reaction speeds. This enables creative possibilities that would seem almost unachievable when limited to AF-S only!
Note that on Canon cameras, this mode is usually labeled AI Servo AF. Apart from the label, it’s the same technology underneath!
Full-Time Servo (AF-F) Focus Mode
AF-F is an alternative continuous AF mode for fast moving subjects. Like AF-C, it engages the AF servo in a continuous fashion, making it more flexible than single-servo AF-S. Though the risk of mutual confusion is pretty great, there are some differences in operation when you compare AF-F and AF-C side-by-side.
Instead of engaging autofocus as soon as you half-press the shutter button and until you release the shutter all the way, AF-F fires up immediately as soon as you select it.
Half-pressing the shutter release is what actually locks focus in place when you’re in AF-F! Some of you may find this ergonomic difference to amount to a significantly improved workflow. Others may be deterred by the constant whirring of the autofocus motor – it’s your choice in the end whether to use AF-F.
Automatic Autofocus Modes (AF-A, AI Focus AF)
These advanced autofocus modes don’t offer any unique features but are there instead to streamline the user experience. They are especially useful for photographers working in challenging environments who find themselves switching modes a lot.
AF-A, or to use Canon’s terminology, AI Focus AF, intelligently chooses between AF-S and AF-C modes depending on the conditions of the scene. Of course, this system isn’t perfect. Oftentimes, it may turn out neither as fast as AF-C nor as sharp as AF-S. However, it offers you one way of dialing in a jack-of-all-trades focus mode that’s good for just about any situation.
AF Area Modes Compared
Just like it’s important to tailor your focus modes to the shot at hand, so is it crucial for you to know your way around your camera’s AF area modes. These determine the behavior of the focus points that we talked about earlier.
The wrong combination of camera autofocus modes and AF Area may result in wasted shots. Even when all your other relevant camera settings are in order, poor AF management can backfire! That’s why I highly recommend getting in some practice with all of the settings covered below.
Single AF Area Modes
This is the most basic AF Area mode of them all and the one that many photographers will find themselves using the most frequently. In Single Point AF Area mode, you manually choose a single focus point which will serve as a baseline for the AF system on where to concentrate focus.
You can freely move this one focus point around whether you’re in AF-S, AF-C, or a different focus mode.
Dynamic AF Area Mode
This is a great mode to use for more unpredictable subjects that move around a lot. In Dynamic AF Area mode, you select one autofocus point just as above.
As soon as you half-press the shutter button, the AF mode will track your subject within the general area surrounding that point. What distinguishes Dynamic AF from all other Area AF modes is its ability to switch to a neighboring focus point area if your subject leaves the one you selected. This allows you to set up a reasonable focus point configuration before your shot and ‘fire and forget’ no matter how your subject moves during composition.
Dynamic AF Area mode is also called ‘single point AF Area mode’, as it combines the benefits of both single point selection and area-wide AF tracking. Paired with a continuous autofocus mode, it can be impressively powerful.
Auto AF Area Mode
As the name implies, Auto AF Area modes arrange and select autofocus point groups for you. Depending on the needs of the shot, Auto AF Area may pick a single point or a large group. These can adaptively change shape and size as the camera tracks the subject.
Generally speaking, this mode is not as fast as the conventional AF Area modes because your camera will try to make use of all the autofocus points it has available instead of basing itself on a user-determined selection. It’s also not the most precise, as you won’t have any manual control over focus acquisition whatsoever. That could lead your camera to automatically focus on something that wasn’t what you had in mind for the shot, for example. However, for sheer flexibility, it’s hard to beat!
Group AF Area Mode
This is the most basic of all the different AF Area modes. In Group AF, you simply draw a selection of any number of focus points to use in your shot. Your camera’s autofocus mode will not try to compensate for or adapt this selection while you’re composing, and the AF area will remain static until and unless you choose to manually edit it.
This mode works great for relatively predictable subject movement, as well as for static subjects spaced far apart, which wouldn’t work well enough in single-point AF mode.
Why Autofocus Modes Matter
No matter what combination you might find most useful to your photography, autofocus modes are crucial for maintaining full control over your gear. Whether homing in on one focus point in AF-S or using AF-C continuous focusing mode to track difficult subjects, AF modes, and their accompanying AF area modes can make or break the shot in almost any situation you might encounter.
That’s partly why today’s lessons are so crucial for success! Remember to thoroughly practice every bit that you have learned. Especially the modes you’re less familiar with should get some shooting time out in the field.
Even if you think you’re unlikely to make much use of, say, AF-C or AF-A, it’s healthy to get some training hours in to be comfortable with their operation, just in case. You never know when it might come in handy!
