|Selecting the right autofocus mode can help ensure photos are sharp and in focus.|
Browsing through the camera menu, it's easy to overlook the AF-S and AF-C options as some sort of confusing alphabet soup, but it's much harder to ignore that photo where everything but the subject is in focus. AF-S, AF-C and AF-A are all autofocus modes and selecting the right one will help produce crisp, focused images. But don't overlook the Dynamic AF and Single Point AF either—these focus area settings can also be particularly useful too, not to mention the possibilities within manual focus equipped cameras. Grab the camera and start getting acquainted with focus modes.
In any newer camera, the autofocus works by pressing down the shutter release halfway. On most cameras, the LCD screen or viewfinder will use boxes or dots to highlight what's in focus so the user can check before pressing the shutter release all the way to take the shot. Simple enough, right?
The challenges come in to play when the subject is moving, when there's something in the foreground (i.e. something in front of the subject), or when only part of an object should be in focus.
Selecting an autofocus mode tells the camera not what to focus on, but how to focus. The basic (and perhaps best) autofocus mode is AF-A, or automatic autofocus. On a good, newer model camera, the user will seldom have to switch the AF settings off of auto. Other models, however, are not as good at reading the situation and selecting the best option and the photographer should switch to a AF-S or AF-C mode as needed.
The S in AF-S stands for Single. Canon models use the term One Shot AF. On the AF-S mode, the focus doesn't change once the shutter release is pressed halfway. The AF-S setting is best for shooting stationary objects. (Stationary is a great mnemonic for AF-S if you have trouble remembering which is which.)
AF-C (or AL Servo AF on Canon cameras) means continuous autofocus. Once the shutter button is pressed halfway, the camera continues to adjust the focus as the subject moves. As the name implies, this mode is best for shooting moving subjects, like in sports. Since the camera is constantly working, however, the AF-C is not as friendly to battery life as the AF-S.
Along with changing if the autofocus works continuously or not, most cameras allow the user to change the focus area, or the portion of the frame that the camera focuses on. Most scenarios do well with the auto area, which can cover a wide portion of the image or a small portion. Refocusing in the auto area mode generally results in a different set of focus points, so changing the focus is an option.
Single Point Autofocus is best for settings where only a portion of one object should be in focus, like in macro photography. Some models allow the user to move the focus point using the arrow keys, others have it fixed in the middle.
Dynamic Autofocus or Subject Tracking is offered on many newer advanced models. This autofocus area stays focused on one object—even when that object moves. Some models also have face recognition, which works similarly. While subject tracking is a great feature, it does have its downfalls. Most cameras won't re-recognize the subject if it leaves the frame momentarily, so dynamic autofocus isn't always best for those scenarios.
DSLRS, advanced compacts, and mirrorless models generally include manual focus, as well as a less advanced models. Short of getting out a tape measure and measuring the distance from the camera to the subject, manual focus is generally set using the viewfinder or LCD screen to determine when the desired portions of the image are in focus.
In DSLRs and in a few cases compacts with a manual ring like the Sony RX100, focus is adjusted through twisting a lens ring. This method is the most accurate and easiest to adjust. Models without a manual ring use the LCD screen and arrow buttons to highlight a portion of the screen to focus on, but don't offer as much control as using a manual ring.
More advanced cameras will have a viewfinder with a diopter adjustment, which allows the user the customize the viewfinder to their particular eyesight—which is particularly helpful for getting manual focus right. The diopter adjustment is generally located by the viewfinder and resembles a dial or switch.
Focus: Tips and Tricks
Many DSLRs have a focus lock button (often denoted by a key symbol or AF-L), which is useful for tricky situations. Even without an AE lock button, however, any autofocus camera can lock focus. Put the desired subject in the center of the frame, then press the shutter button halfway. While keeping the shutter button half pressed, move the camera until you have the desired composition, then press the shutter release all the way. As long as you keep the button pressed, the original focus will remain even as the camera moves.
Once you understand how your digital camera's focus works, get creative with your shots by adding on out-of-focus element to the front of the picture (called the foreground). Try using single point autofocus with some macro shots and test out the dynamic autofocus on some action shots.
Many cameras will function just fine on AF-A mode, but understanding the various autofocus modes and areas can help fix a blurry shot or help get those creative juices flowing with some unusual compositions. Understanding your camera's autofocus mode and autofocus area settings can led to better images with less frustration.