My camera has these settings for autofocus, and I don't know what they mean. I suspect "A" is "Auto", and "C" is "continuous", but I have no idea what "S" is.

  • What is the make and model of your camera? – Matt Grum Jul 28 '11 at 17:58
  • @Matt: It's a Nikon D7000 but I believe I have seen similar markings on a friend's Canon before. – Billy ONeal Jul 28 '11 at 17:59
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    See also: photo.stackexchange.com/q/496/21 – Rowland Shaw Jul 28 '11 at 19:07
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    @Rowland: No, I'm not talking about AF-S lenses, I'm talking about the autofocus mode. (It's unfortunate the names overlap) – Billy ONeal Jul 28 '11 at 19:59
  • It's often best to include enough information in the question to make it unambiguous -- I see Craig has now edited it to include that; it would also be good in the future to give an indication as to what your camera is; many of the abbreviations used are specific to a particular manufacturer (for example, @vlad259 tries to cover both options) – Rowland Shaw Jul 29 '11 at 7:32

This link explains it well. Paraphrasing the article:

  • AF-C (AF-continuous or servo mode) is used for photographing moving subjects.
  • AF-S means single shot and is used for subject that is stationary.
  • AF-A is where the camera decides whether the subject is moving or not and tries to alternate between the servo and single shot mode accordingly.
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There is another important difference between AF-S and AF-C. With AF-S, you cannot take a shot without focus being locked (green light being on). With AF-C you will take a shot anytime the shutter release is pressed. So with AF-C, while it will attempt to track focus on a moving subject, you can take shots at any time whether or not the AF has focus lock.

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  • At least on the D7000, this is configurable. The default behavior of AF-S is to wait for a lock because it is intended to shoot stationary subjects. But you can override this and force the camera to take the shot anyway by holding the AF-LOCK button (or you can change how this works completely). – Billy ONeal Dec 31 '12 at 7:14

Sometimes 'Servo' - continuous autofocus and sometimes 'Single' - one shot.

Try it by focusing on a moving subject and see what it does...

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When AF-S appears on a lens:

AF-S: Autofocus Silent Focusing is driven by a "Silent Wave" motor in the lens instead of the focus drive motor in the camera. AF-S lenses focus faster than standard AF-Nikkors and almost completely silently. AF-S lenses with a "II" designation weigh less and are generally smaller than their equivalent predecessors.

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    The question wasn't about AF-S in a lens's specification; it was about the AF-S autofocus setting in the camera. – scottbb Apr 4 '18 at 7:32

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