Single shot autofocus will lock onto the object in the autofocus area and then keep the camera focus locked even if you or the subject move.
Any situation where your camera AND your subject are stationary like landscapes or still life.
Continuous shot autofocus will continue to refocus on the object in the autofocus area for as long as the focus button is pressed, allowing you to track a moving subject.
Any situation where either you or the subject is moving like sports, handheld shooting, and even portraits (because even people standing still will move slightly).
This mode will automatically choose between single shot and continuous.
This mode is good for beginners who aren't sure which mode to choose, but it can result in missed shots occasionally.
Manual focus will allow you to adjust focus yourself by turning the focus ring on the lens.
Fine tuning focus when the camera and subject are stationary and also can be useful when shooting video.
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