Why use back button focus?

I keep reading people recommending the use of back button focus. What are the advantages of this? I normally use centre point focus using the shutter button and recompose if needed before pressing the shutter all the way.

Vendee wrote in post #14209035
I keep reading people recommending the use of back button focus. What are the advantages of this? I normally use centre point focus using the shutter button and recompose if needed before pressing the shutter all the way.

I use it for sports with AI Servo. That way I can continuosly track my subject and then take the shot(s) when needed. It is much easier to do that than trying to keep the shutter half-pressed when I'm moving the camera around. It took a little while to get used to but it is the only way I shoot now. There is also the added benefit of people not wanting to use my camera either because it won't focus for them with the shutter button!

When shooting action sports, it allows you to track focus of a moving subject prior to locking exposure with the shutter half press. This has two big advantages. In some indoor sports venues, lighting is not even so you don't want to meter until you actually take the shot. Second, tracking AF prior to taking the shot gives the camera time to calculate a focus solution and will get you an almost instant shutter release if you have your custom functions set to give priority to achieving focus versus release shutter. This can mitigate a delay of sometimes half a second or so until the shutter releases if AF is on the shutter button because the camera only begins calculating the AF point when you half press, or fully press the shutter. For shooting indoor sports like swimming, gymnastics, basketball, roller derby, etc, back button focus will get your keeper rate up higher than using shutter button AF. It really comes into it's own on circular or oval track sports where the closing velocity vector of a subject coming at you is constantly changing while the subject is in the curved section of the track. Giving the camera time to calculate an AF solution with back button focus in that situation will always get you a much quicker shutter release than pressing the shutter button to take a shot. Add in spotty overhead lighting where you want exposure metered at the moment of shutter press and not before, and you have the perfect back button AF environment. As stated above, Servo AF is a given for it to make sense.

Vendee wrote in post #14209035
I normally use centre point focus using the shutter button and recompose if needed before pressing the shutter all the way.

That works fine in one-shot AF, but if you use Ai servo the camera will continue to focus while the shutter button's halfway down - making recomposition a PITA. With the two functions on separate buttons, it becomes much easier with continuous AF. That's why sports shooters often use the back button.

Edit: ninja'd twice

I like back button focusing because I set my shutter half-press to lock in an exposure meter, and can then recompose, focus with back-button, and depress the shutter to take a pic. I typically keep my camera on spot metering.

For me, because focusing & metering/exp lock are two seperate functions so have them on two seperate buttons

With the back focus, you can leave it on AI Servo all the time.

Press and release ~ one shot
Press and hold ~ tracking

Vendee wrote in post #14209035
I keep reading people recommending the use of back button focus. What are the advantages of this? I normally use centre point focus using the shutter button and recompose if needed before pressing the shutter all the way.

https://photography-on-the.net/forum/showthre​ad.php?t=46965

http://www.learn.usa.c​anon.com …ckbutton_af_art​icle.shtml

http://www.outbackphot​o.com …hnique/essay06/​essay.html

Vendee wrote in post #14209035
I keep reading people recommending the use of back button focus. What are the advantages of this? I normally use centre point focus using the shutter button and recompose if needed before pressing the shutter all the way.

Another vote for BBF - but then I like to shoot team sports and it is great for that, as explained above.

On a related note you might want to look at customising the mini-joystick to move/select AF points. That can save on having to recompose as you frame the shot and use one of the outer AF points to focus.

Dan Marchant wrote in post #14209251
On a related note you might want to look at customising the mini-joystick to move/select AF points. That can save on having to recompose as you frame the shot and use one of the outer AF points to focus.

I've got this setup as well. pretty quick to change your active AF points, or just press the joystick and select all.

Thanks for the info guys

I like it because that's where my thumb sits and it makes it handy.

What all those other people said

bsmotril wrote in post #14209088
When shooting action sports, it allows you to track focus of a moving subject prior to locking exposure with the shutter half press. This has two big advantages. In some indoor sports venues, lighting is not even so you don't want to meter until you actually take the shot. Second, tracking AF prior to taking the shot gives the camera time to calculate a focus solution and will get you an almost instant shutter release if you have your custom functions set to give priority to achieving focus versus release shutter. This can mitigate a delay of sometimes half a second or so until the shutter releases if AF is on the shutter button because the camera only begins calculating the AF point when you half press, or fully press the shutter. For shooting indoor sports like swimming, gymnastics, basketball, roller derby, etc, back button focus will get your keeper rate up higher than using shutter button AF. It really comes into it's own on circular or oval track sports where the closing velocity vector of a subject coming at you is constantly changing while the subject is in the curved section of the track. Giving the camera time to calculate an AF solution with back button focus in that situation will always get you a much quicker shutter release than pressing the shutter button to take a shot. Add in spotty overhead lighting where you want exposure metered at the moment of shutter press and not before, and you have the perfect back button AF environment. As stated above, Servo AF is a given for it to make sense.

This is one of the best explanations I have ever read of the advantages of back button focus. Thanks for taking the time to write this.

Why? Because it works much more better. If you are advanced photographer