AF button vs BBF

I have the 5D MarkII and thought I was using BBF button when shooting but just found out I was using the AF button. Can someone tell me the difference? Is one better than the other? Is BBF used primarily with moving subjects?

Whatever you are comfortable with using.

When you set BBF don't forget to remove AF from the shutter button also, otherwise it will use both for AF and mess you up. I like to set shutter button to exposure lock (rather than metering start) that way I can pick something to expose for with a half press and recompose, bbf, click.

I like to use AF on the shutter button with One Shot and use BBF with Servo, but sometimes I mix them. All depends on what you're shooting and how you like to do it.

BBF can be better for a few different scenarios .
For focus and recompose : focus centre point on the subjects eye , recompose to centre subject , press shutter release .
For some sports , focus on batsman at cricket (trying to catch the ball hitting the bat or the stumps) focus on batsman once and then free to snap away as the ball comes in .
Used with servo , tack a bird in flight by "tapping" the button to adjust focus when bird flies towards/away from you , or "tapping" it when the bird is under the focus point (only "requesting" a focus when you are sure it is "looking" at the subject (This tapping is called bump focus)

alisaconn wrote in post #14303155
I have the 5D MarkII and thought I was using BBF button when shooting but just found out I was using the AF button. Can someone tell me the difference? Is one better than the other? Is BBF used primarily with moving subjects?

Same thing. AF button is BBF.

Andrew_WOT wrote in post #14304031
Same thing. AF button is BBF.

This is correct.... BBF can be done on 5DII with either the AF-ON button or the * (AE-Lock) button.

So it's not "AF button vs BBF"... It's BBF using AF-On or using * button.

To set it up, go into the menu to Custom Function IV-1 and set it to option 2 "Metering Start/Meter+AF Start". This assigns AF to the AF-ON button only, separating it from the shutter release button. It can be used this way if you wish.

Personally I assign it to the * button instead. It's bigger, more prominent and less of a reach with my thumb. If you want to set it up this way, after doing the above, go to C.Fn IV-2 AF-ON/AE Lock button switch and set to Option 1 "Enable". This simpy swaps the fuctions of those buttons.

BBF is particularly useful with moving subjects and AI Servo shooting, but it's perfectly usable with stationary subjects, too. You can use either AI Servo or One Shot with the latter. One Shot can be a little more accurate.

Foggiest is right, too.... There are several different scenarios where BBF is helpful. You can always focus and recompose in One Shot. AF stops as soon as focus is achieved and so long as you don't release the button fully, you can simply recompose the image as you see fit. If the subject moves or you move and the distance to the subject changes, you have to remember to lift pressure off the button and reapply it, to refocus.

It's with AI Servo you see the biggest gains using BBF. Normally you can't focus and recompose in AI Servo, but you can after setting up BBF. Just lift pressure off the button to stop AF. Otherwise, AF continues working as long as you keep pressure on the button. You do have to concentrate on keeping the AF point on the subject, though.

I've never used "Bump focus" though... That sounds like a technique to use One Shot with a moving subject. I just track continuously and the camera constantly updates the focus in AI Servo.