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.
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.
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.
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.