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I have seen these autofocus options on all my Nikon DSLR cameras (D50, D80, D90) but I have never really used them. There is the AF button on top.

What are AF-A, AF-C, and AF-S ?

How do I use each mode, and when? I'm interested in which pictures or situations each is appropriate for, not camera specifics.

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The question's a little vague: could you add more detail? For example, what cameras have you seen these abbreviations on, and whereabouts on the camera do they appear (on a dial, in the menus, etc.)? Generally speaking, the more specific you can be in your question the better the answers you'll receive. –  Mark Whitaker Sep 14 '11 at 10:36
    
Added @Mark Whitaker –  denislexic Sep 14 '11 at 12:10
2  
For what it's worth, I thought this was a more useful Q&A without being narrowed to a particular camera brand or model. –  mattdm Sep 14 '11 at 13:09
    
@mattdm: the bits missing were "autofocus" and "Nikon". As a Canon user I had literally no idea what was being asked in the original question. –  Mark Whitaker Sep 14 '11 at 13:14

1 Answer 1

up vote 16 down vote accepted

AF-S is AF 'single'- your camera will focus on a fixed object when you press the AF button and will remain focused on that point for as long as you hold the button down. This is best for static subjects.

AF-C is AF 'continuous' - the camera will focus on whatever is in the relevant AF points (depending on how you have your AF coverage set up) and will attempt to keep the subject in focus wherever it moves, whether that's towards/away from the camera or laterally. This is best for continually-moving subjects, e.g. birds in flight.

AF-A is AF 'auto' and automatically switches between the two AF modes depending on what the subject is doing. This requires less effort on the part of the photographer, but you are relying on the camera guessing correctly what you are focussing on, and may result in unexpected focus.

For completion, on a Canon camera the equivalent modes are, respectively, One-Shot AF, AI Servo AF and AI Focus AF.

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Great answer @Nick Miners –  denislexic Sep 14 '11 at 12:09
    
Is it safe to say that AF-S on a lens description is totally separate from this discussion? Meaning 35 mm f/1.4G AF-S, AF-S means Autofocus-Silent and only that? It is not related to AF 'single' at all. –  Thanh Sep 14 '11 at 21:47
    
@djnotepad : I didn't know that either, but Mister Nick answered exactly what I was hoping for. Might add a question relative to the markings on lenses, cause I never know what they mean appart for macro...ha. –  denislexic Sep 15 '11 at 2:30
    
This question has an answer that lists all the lens terms: photo.stackexchange.com/questions/496/… –  Nick Miners Sep 15 '11 at 5:28

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