Choosing Autofocus Modes
Back in the good old days, during the infancy of autofocus, you had two options when it came to autofocus: On or Off. Now, with advancements in technology, many cameras, even simple point-and-shoot cameras, have a dizzying array of high-tech autofocus modes to choose from. Honestly, they are intimidating even to experienced shooters.
Before we dive in, be forewarned: almost every manufacturer has proprietary autofocus technology, nomenclature, and features. Even more confusing, the interface to access these modes is often different from model to model. So, know that we will focus on (pun intended) the basics here but as we do, grab your camera, as well as your camera’s operating manual, and get ready to dive into the somewhat confusing world of autofocus modes.
The most basic autofocus controls on your camera may be accessed and changed via a switch or a button on the camera. Most modern cameras have three or four basic autofocus modes to choose from.
The photographer adjusts the focus manually. Yes, this article is about autofocus but, on modern autofocus cameras, the lines between manual and autofocus can become blurred. On some cameras, when you focus manually, you are engaging the lens’s autofocus motors to change the position of the focusing lens or group. Other cameras completely disengage the autofocus system and you turn a helicoid that moves the glass. It is important to know that some autofocus technologies can assist you in your manual focus endeavors. Some cameras will indicate when the image is in focus by showing you a focus confirmation indicator in the viewfinder. Mirrorless cameras, or some DSLR cameras using Live View, may incorporate a feature called “focus peaking” that shows visually what is in focus on the image. Suffice it to say when you engage manual focus on a modern camera, you’ll likely have some electronic assistance.
One Shot / S-AF / Single Servo / AF-S / S, etc., is the simplest form of autofocus. In general, you depress the shutter-release button halfway, or your camera may have a separate AF-ON button, and the camera will lock focus on a subject on which you have placed the active autofocus sensor. Press the shutter button the rest of the way to take the image. The advantage? Simplicity. You aim, the camera focuses, and you shoot. The disadvantage? Did your subject move? Did you move? If the distance between camera and subject changed, that initial focus solution is no longer valid. You will have to go through the process again. If your camera has an “autofocus assist” light on the front, it is likely that you need to be in this mode to get the lamp to illuminate the scene so the camera can focus.
Continuous AF / C-AF / AI Servo / AF-C, etc. is where the camera’s electronic brains start to do some pretty cool things to help you keep your subject in focus. In general, the camera locks onto a designated subject, chosen by you using the autofocus point(s), and then tracks that object as it moves in the frame. If the locked subject moves closer or farther, or if you move, the camera will adjust focus accordingly. The advantage? Taming dynamic situations with sports action, moving kids, or roaming wildlife. The disadvantage? If you must recompose your image after the focus is locked, your camera may get confused into locking onto another part of your frame.
AI-Focus / Auto-Servo AF / AF-A, etc., is where the camera evaluates the scene and decides for the photographer if you want single or continuous autofocus assist. The advantage? You can let the camera decide. The disadvantage? The camera may choose poorly. Many professional cameras do not have this mode, as it is considered more useful for beginner photographers. However, with the computing power of today’s cameras, your results will probably be very good with this mode. Forgoing it or using it depends on how much you want to control the photograph.
AF Area Modes
The modes described above are the basic modes that you will likely encounter on a modern autofocus camera. After the basic modes, depending on the brand and model of your camera, you might be faced with a host of other options—usually giving you some choice over how the camera chooses autofocus points or areas of points. It would be foolhardy to try to cover every mode on every camera, but I will attempt to summarize the different modes you may encounter. Did you get your manual out before you started reading? This would be a good time to dive in. As you are about to see, they are all very similar, but all have particular characteristics that you will need to know in order to utilize them properly.
Single-Point: Many DSLR cameras today will do single-shot or continuous autofocus on any number of individual focus points. Back in the old days of autofocus, the only point was in the center of the frame. Now, DSLR cameras have literally dozens of points you can choose through different interfaces. The number of active points may depend on the lens’s maximum aperture—greater aperture, more light, and more points. Also, not all focus points are made equal. Crosshair-type points look for two-dimensional contrast detection (put simply, both phase detection and contrast detection are measuring contrast) and are more accurate than vertical line points that only “see” in one dimension.
Many new cameras that use contrast detection autofocus allow you to focus almost anywhere in the frame. Focus points can be activated through various controls, including simply touching a point on the rear LCD where you want the camera to focus.
Group: Not much different than the Single-Point Mode, this approach activates several focus points and evaluates the information from that cluster of points. This is especially useful for action shooting. If you are tracking a subject, the group mode will strive to keep tracking the subject even if the point in the center of the group loses track. Several cameras now use this group mode to recognize a face and lock onto the nearest eye, tracking it as it moves.
Dynamic: Similar to Group Mode, the camera locks on a single point and then tracks the object if it moves to surrounding points—even points beyond what the Group Mode would activate. The camera assumes you will try to keep the object in that same spot, but it will adjust the focus points as needed to help you out.
Automatic: The camera uses all of its focusing brain power to do the work for you. Depending on the camera, the mode may search for skin tones and lock onto a person in the frame, or it will evaluate information from multiple points to just lock onto the nearest object. This a good mode if you want to focus on composition or other things around you while photographing.
Video: Not a mode, but new mirrorless and DSLR cameras that are capable of shooting video may likely have specialty focusing modes that function best when shooting video with your camera.
Confused? Intimidated? Me too!
The best way to move toward confidence and knowledge now is to experiment with your camera’s different modes and see how they work for different types of photographs. Still got your manual handy? Good. You will need it. If you are out making images and finding that your camera is behaving erratically when it comes to focusing, switch the basic and/or area modes so that you can tell the camera what you want to focus on. You will find that on many cameras, the control’s interface is designed to allow you to change modes on the fly, instead of diving deep into menus, just for this reason.
Finally, do not be afraid of manual focus. This is the only way that you, and only you, can decide what is in focus in a particular frame. It is challenging, but it can also be fun and it might expand your photography creatively. Use the camera’s technology to help you focus manually and, if you are an eyeglass wearer, either keep your glasses on, or set your viewfinder’s diopter to compensate for your vision before you embark on a manual-focus adventure.
Now get out there, experiment, photograph, and enjoy!