A focus mode where the camera continually refocuses on a moving subject. The more advanced the AF system, the better it will be at keeping the subject in focus. It’s used mostly in continuous shooting mode for sports and action photography but can also be used for video.
Here, the camera focuses once when you half-press the shutter release then holds that focus point until you press the button the rest of the way to take the picture. This is the usual mode for taking one photograph at a time (as opposed to continuous shooting).
Here, the camera tracks subject in continuous autofocus mode and uses its movement within the frame and any changes in its distance from the camera to work where it’s going to be at the moment the shutter fires.
An autofocus system that checks the position of objects from two angles. If they don’t line up the object is out of focus – and the system can use the difference to work out how far to refocus the lens and in which direction. Phase detection AF sensors are used on DSLRs and now phase detection pixels are built into some mirrorless camera sensors.
Useful when you want to make the most of depth of field – with often means focusing between two objects rather than on one or the other. It’s also handy for ‘zone focusing’ in shoot-from-the-hip style street photography, where you want an instant shutter response.
Autofocus system that combines contrast autofocus and phase detection autofocus. It works using special phase-detection sensors built into the sensor. Contrast AF is typically slow but accurate, while phase detection AF is typically fast if potentially less accurate.
Autofocus systems can focus at different points around the frame – the more advanced the autofocus system, the greater the number of AF points. You can either leave the camera to choose the autofocus point with ‘auto AF’ mode (or ‘auto area AF’) or select it yourself with single-point AF mode. Some cameras offer face-detection or subject-tracking AF options.
A special display mode designed to help with manual focusing when using an LCD display or electronic viewfinder. It exaggerates the edges of objects when they come into focus and can give a much more visible focus ‘snap’ than the regular display.
Camera autofocus systems work in one of three modes: single-shot autofocus (usually abbreviated to ‘S’), continuous autofocus (‘C’) and manual focus (‘M’). If you’re taking one photo at a time, use single-shot autofocus – the camera will focus once and then fire. If you’re using continuous shooting mode, use continuous autofocus – the camera will keep refocusing all the time the shutter button is held down.
A switch found on some telephoto and macro lenses to restrict the autofocus to a specific range. This speeds up the autofocus for situations where you know you won’t need the lens’s full focus range.
Some autofocus systems identify human faces within a scene and then adjust the focus and exposure for that face. It’s popular on compact cameras and is used on some DSLRs and mirrorless cameras too.