What is Back Button Focus all about?

Started Mar 25, 2014 | Discussions thread
WilbaW Forum Pro • Posts: 11,562
Re: What is Back Button Focus all about?

BobT wrote:

I see a lot of you use this. So what is it?

Using a button on the back of the camera to trigger autofocus instead of it happening on a half-press of the shutter button.

Why would I ever want it?

When you don't want the system to autofocus every time you press the shutter button. For instance, I used it recently when I was shooting a couple of pelicans on a rock with a long lens on a tripod. I wanted to focus in One-Shot, then reframe, then sit back and wait for an interesting moment. I needed the focus to stay where it was no matter what I did with the shutter button. (I could have switched the lens to MF, but then I'd have to muck about switching it back if I did need to focus again.)

Many like to use it all the time with AI Servo, so they have both continuous or locked focus available, with just one button to press. I think a lot of people like it because it means they don't have to master the fine control of the shutter button half-press that you need to do focus-and-recompose and to hold focus between shots.

And how (step-by-step) would I go about getting it? I shoot with a T2i.

Set custom function IV-9 "Shutter/AE lock button" to 1, and from then on press the "*" button to trigger autofocus.

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