Back button focus

[pennypacker]

Have been doing a bit of reading into this, in the hopes of bettering my focus technique, getting sharper pics and more keepers.

I take a lot of pictures of kids and animals at the moment, and they're generally moving targets, so focus can be a bit hit and miss for me.

I am quite a novice, and have a lot to learn, although I think I understand the basic concept of back button focus. Just wanting some input as to whether attempting to use back button focus rather than the shutter button is going to help me. So, will AI mode and back button help me pin down those pesky kids a little better? Will also combine with fast shutter speed wherever possible. I have a couple of pretty fast lenses - one of which was pretty bloody expensive, and I'm not getting the best out of them consistently at this point .

Thanks!

[triptych]

I use back button focus and I would never go back....its good because it locks in focus and you can recompose and it stops it from constantly seeking a focus point, which I found my 7D was constantly doing.

It takes a bit of getting used to, try it and if you like it keep it, if you dont the change it back...I have disabled the focus function on my shutter button so I use back button focus all the time.

[pennypacker]

Thanks triptych, i'm finding the same thing. I read somewhere about the focus and recompose method and was trying that without using back button focus. Needless to say, it was a complete failure, even with static subjects lol.

[James T]

I doubt it will significantly increase your 'keepers'. Your ability to track the subject and time your shots are all that's going to help there.

What it does (almost) do is effectively give you AI servo (continuous) and single shot auto-focus, without having to switch between the two modes. Which of course, can be very handy at times.

[pennypacker]

Well, yes. I realise that, but this, from the Canon article I read (http://www.learn.usa.canon.com/resou...rticle.shtml):

For example, if you were shooting a speaker at a podium, he or she might periodically look up or make a gesture that would be an ideal instant to capture. If you’ve focused with back-button AF, your index finger is free to shoot at the decisive moment. There are no worries about holding your finger half-way down and waiting, waiting, waiting in that position for your subject to do something interesting.

is what I'm thinking is going to help me in tracking and timing shots better with subjects who are decidedly non-static. No?

[James T]

Well, if you were tracking a subject that was moving, like a kid running around.. you would obviously want to focus immediately before/as you pressed the shutter. So in that case, focusing with the shutter release or the back button wouldn't make any difference. Just pick the AF point to suit your composition and fire away.

Using the back button also effectively gives you full time auto and manual focus without having to switch the lens back and forward, again handy in some cases.

FWIW I use back button focus all the time as it suits how I shoot. No harm in trying it out and seeing which you prefer, and when.

[pennypacker]

Thanks James, yeah that makes sense. I think at least some of the trouble I've been having is that I've been attempting to shoot at too low a shutter speed. That, and the fact that I seem to have the reflexes and speed of a sloth .

[Milbs1]

For moving subjects al servo is probably the way to go, choosing your focal point where you want the subject in your frame.
I use back button focussing, takes a little bit of getting used to, but it was the first thing I changed on the settings when I got my 7D...
Switch it on and maybe try practising on subjects that dont move so much!!

[fess67]

I agree AIServo is the way to go. As to front or back button, I agree with James regarding practising the tracking skills. What I found made a massive difference in the number of keepers for me was having all the focus points active rather than trying to get the one point right. Used with AIServo it helped me no end.

[Tannin]

Be sure to also consider reverse back-button focus. This method offers a significantly less radical departure from the habits you already have and (arguably) a more natural mode of operation very similar to standard focus. The basic idea is that you still focus with a half-press but use the back button to hold it if desired. Works very well and easy to get used to.

Try all three before you decide which one is for you.

[pennypacker]

Thanks so much for the replies, really helpful. Once the camera battery's recharged, I'm going to give it a go!