EOS Bodies - For Stills / Re: Backbutton Focus..do you use it? Pros? Cons? How hard to get used to it?« on: September 27, 2013, 09:00:49 PM »
This might be a stupid question but it functions the same as half press in single shot mode, is it different in other modes?
In AI Servo mode with BBF enabled it allows you more control over focusing. By keeping the button pressed it will continue to focus making it easier for you to take a shot at the decisive moment. Although it functions similar to the half press it is easier to use. Imagine holding the shutter at half press for more than a minute. Also what if you took a break from AF but then suddenly wanted to take a shot? By separating focusing and shutter you can set the focus and it will remain locked at that position allowing you time to recompose before taking a picture.
It's also the ability to not refocus before taking a shot that makes it a useful feature in any mode. Great when there are obstacles moving in front of your subject like cars for example. Let's say you focus on a building with BBF. You can then let go of the button and simply wait until the cars go past or even if you shoot you know it wont refocus on a car because focus is locked. The half press method wouldn't work as everytime you try and take a shot it would autofocus on something, most likely the object in front of you. Sure you could switch to manual focus but for speed and convenience BBF just makes sense.
You have to go out and try it. You also have to remind yourslef once you obtain focus lock you are free to recompose. I sometimes forget and keep pressing the button out of the habbit of needing to hear the "beep"!