What does the AF Stop button do on some Canon lenses?
Asked 1/23/2013
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Some Canon telephoto lenses have an "AF Stop" button, and Canon camera manuals also mention assigning this function to other buttons through custom controls. What does the AF Stop button do by default, and when would you use it?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
13y ago
2 Answers
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According to Canon's Lens Performance page, this button is intended as a way to temporarily disable the autofocus, for example if you see that an object is about to pass in front of the lens that's not on the same plane as your primary subject. Thus, focus is retained (or close to retained, with a moving subject) while the obstruction passes, and autofocus can be resumed from a good starting point once it's gone.
Edit: Note, also, that the AF Stop functionality can also be achieved through other buttons on some cameras, via Custom Function settings, by setting a button (e.g. the * button) to "AF-OFF". (Thank you @caleb, for that information.)
Originally by user2425. Source · Licensed CC BY-SA 4.0
user2425
13y ago
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Generated from our catalog & community — verify before relying on it.
By default, the AF Stop button temporarily stops autofocus for as long as you hold it down. It’s most useful with continuous autofocus/AI Servo when you want to keep the current focus distance from changing.
A common example is when your subject is being tracked and something briefly passes in front of the lens. Pressing AF Stop prevents the camera from refocusing on the obstruction, so focus stays at or near the previous distance. When you release the button, autofocus resumes from that point.
Canon also lets some cameras assign the same function to other buttons, often labeled as AF-OFF in the custom controls. That gives you similar behavior even with lenses that don’t have a dedicated AF Stop button.
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