Teachable Moment - Auto Focus Modes in DSLR Photography
Autofocus is a great feature that we all rely on in our photography. When it’s set up correctly, AF will intuitively allow you to just get on with your photography and you’ll barely notice it’s there. If., however, it’s not in the right mode for they kind of photography you’re doing, AF can seem like it’s working against you.
Typically there are 3 AF modes in most cameras - AF-S (Nikon) / One Shot (Canon), AF-C (Nikon) / AI Servo (Canon) and AF-A (Nikon) / AI Focus). I’ll quickly unpack these below:
AF-S / One Shot
This mode is best for stationary subjects as it prioritises focus over shutter release, meaning the system won’t allow you to take a photograph until it has locked focus on something. If your subject isn’t moving this is nom problem and you’ll be able to shoot intuitively, knowing that the camera will have focussed where you’ve set the AF point. If, on the other hand, you’re photographing a moving subject, you will frustratingly not be able to take a photo as the AF system will struggle to lock on to the subject and the camera will refuse to allow the shutter to release.
Subjects for AF-S / One Shot:
AF-C / AI Servo
This mode is best for moving subjects as it prioritises shutter release over focus. In other words, the system will allow the camera to take photographs even though it’s not certain that a focus lock has been achieved. This might sound dodgy but it’d actually a good thing when your subject is moving because as long as you’re activating the AF (half press the shutter release button OR holding the AF-ON back button) then the AF system will continue to hunt for something to focus on which allows you to better track a moving subject - think about a cheetah on the run or a car on a racing track.
Subjects for AF-C / AI Servo
AF-A / AI Focus
This mode is a bit of an inbetweener as it allows the camera to choose which AF mode to use. I seldom, if ever, use this mode but if you’re unsure it’s probably a good place to be.
Different subjects need different approaches and it’s helpful to have things like this in mind before you start shooting. This allows you to get the best setup for your camera and be more efficient when things start happening. With the camera working in the most intuitive way possible then we can do our work and barely notice that the camera is there.
I hope this little nugget helps you in your photography. Let me know if you have any questions or comments.