Understanding back button focus

I don't personally use it, I just half press and recompose most of the time.

but my understanding is that it allows you to skip the AF/MF switch. this allows you to determine when to focus. can be useful during landscape shots or in studio when the working distance doesn't change.
 
I use back button focusing, the benefits are as follows -
Instead of having to use your finger on the shutter release to focus and then fire the shutter, you place your thumb on the back button and you can remove your finger from the shutter release button and as long as your thumb keeps the back button pressed, your camera will continue to focus.
It is very useful when shooting wildlife where the subject can be unpredictable.
Just dont forget that if your camera is on M mode, you have to use the back button to focus.
 
It separates your thought process - focus, exposure and taking the shot can now be performed independently.

It's hard to explain why you'd want it, but once you start using it you'll not be able to live without it!
 
Mystery57 said:
Could someone explain in simplistic terms the benefit of setting the camera in this method as opposed to the default method.
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Having focused perfectly on a bird, the wind blows a branch just as I am pressing the shutter, the camera switches focus, the shot of the bird is blurred.

With back button focus this will not happen, as once I have focus I let go of the button.


Just panning a bird in flight, it drops below the distant tree line just as I am pressing the shutter, the camera focuses on the distant trees, not only is the shot of the bird blurred, I struggle to re-establish focus on it, or in most cases even find it again

With back button focus I will have let go of the button, and will only press it again if I need to tweak focus, I will have seen the background change and can wait until the bird is back against open sky before focusing.


I have pre-focussed on a spot I know a bird is landing for a split second, with back button focus I know when I hit the shutter release it will not start searching for a different subject.
 
Probably already covered but what I love about about BBF is that if you're using lenses with full time manual override, you basically have all three focussing modes in one. i.e. your camera is always on AF-C (on Nikon, I forget what Canon call it) which means that you can focus manually or lock focus by simply not pressing the back button, focus continually by holding the back button down or focus and release by holding back button down until you're happy with focus, let go, recompose and shoot. In practice this means that I simply never alter the focus system in any way. It's always AF-C, single point whatever I shoot.

The shutter button will always activate the shutter regardless of focus which somehow makes the camera feel more responsive but has some practical benefits when tracking moving targets as well.

The only downside I can think of is that some cameras aren't really designed to be used in this manner and the back button can be awkward to use. I suppose another disadvantage might be that if somebody else wants to use your camera, they'll likely not have a clue how to auto focus, you might see this is an advantage! Once used to BBF though, you'll find it very hard to return to focusing with the shutter button.
 
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Martyn... said:
Having focused perfectly on a bird, the wind blows a branch just as I am pressing the shutter, the camera switches focus, the shot of the bird is blurred.

With back button focus this will not happen, as once I have focus I let go of the button.


Just panning a bird in flight, it drops below the distant tree line just as I am pressing the shutter, the camera focuses on the distant trees, not only is the shot of the bird blurred, I struggle to re-establish focus on it, or in most cases even find it again

With back button focus I will have let go of the button, and will only press it again if I need to tweak focus, I will have seen the background change and can wait until the bird is back against open sky before focusing.


I have pre-focussed on a spot I know a bird is landing for a split second, with back button focus I know when I hit the shutter release it will not start searching for a different subject.
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This^
It's not justy for birds though. When using AI servo, it's really difficult to stop the camera re-focussing using the shutter button. Using the back button allows you to switch the focussing on and off to suit you without worrying about the camera refocussing when you don't want it to.
Coming from Manual focussing cameras I was frustrated by focussing with the shutter button - discovering BBF is what stopped me going back to MF cameras.
 
Its half way between AF-S and AF-C

AF-S - will focus once when you half push the shutter button and then you choose when to take the photo

AF-C - will constantly focus when the shutter button is pushed down half way.

BBF will focus constantly like AF-C, but when you let go, the focus is fixed like it would be in AF-S.

The added benefit is it won't refocus when you next push the shutter down.
 
Also the camera doesn'tset the exposure until the shutter button is pressed. This allows you to track your subject for some distance through many differently lit areas and it will only lock the exposure on the half press of the shutter button.

In the normal default situation the exposure is decided and lock on the activation of the shutter.
 
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admirable said:
Also the camera doesn'tset the exposure until the shutter button is pressed. This allows you to track your subject for some distance through many differently lit areas and it will not lock the exposure till you decide to click the shutter.

In the normal default situation the exposure is decided on the half press of the shutter button.
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This is switchable on the Canon's I use lock on half press of the shutter button for general shooting, but no exposure lock in challenging lighting.
 
Thank you one and all, I asked what possibly seemed a daft question, but it was something I didnt understand.

I think using BBF is something I will definitely be using a lot from now on - tried it just now and the camera just felt so different and better to use if that were possible, having the focus seem so responsive was good.
 
It also seperates the focusing from the exposure. Most of the time it won't make any difference, but there can be occasions when keeping the two independent can be useful.
 
Try it and if you like it, great :)

But personally I cant understand what it does that other buttons and configurations can't already do on my camera :shrug:

I have an AF lock button if I need to lock focus.

I have an AE lock button if I need to lock exposure

I have a custom setting to alter the delay before the camera re-focuses (bird and twig moment) though all my longer lenses have focus lock buttons on them anyway.
 
treeman said:
Try it and if you like it, great :)

But personally I cant understand what it does that other buttons and configurations can't already do on my camera :shrug:

I have an AF lock button if I need to lock focus.

I have an AE lock button if I need to lock exposure

I have a custom setting to alter the delay before the camera re-focuses (bird and twig moment) though all my longer lenses have focus lock buttons on them anyway.
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So if you're at a horse event and you focus on a horse exiting from a dark wooded area out onto a combo A, B and C jump in in a field with A and B in brilliant sunshine and C in the shade, what do you do about exposure?
 
I thought the exposure is set the instance it takes a photo, not when you half-press the shutter button?

hence Canon menu says "Metering + AF start"
 
treeman said:
Try it and if you like it, great :)

But personally I cant understand what it does that other buttons and configurations can't already do on my camera :shrug:
Click to expand...

short answer is nothing new, but its much easier to do those things,
 
Well...I've just learnt something new, cheers for everyone advice on here :thumbs:
 
treeman said:
I have a custom setting to alter the delay before the camera re-focuses (bird and twig moment) though all my longer lenses have focus lock buttons on them anyway.
Click to expand...

So do I, having tried every combination possible nothing gives me as much control as back button focus ... but there is no right or wrong way, it is just using whichever method feels right for the individual :thumbs:
 
admirable said:
So if you're at a horse event and you focus on a horse exiting from a dark wooded area out onto a combo A, B and C jump in in a field with A and B in brilliant sunshine and C in the shade, what do you do about exposure?
Click to expand...

My camera is set not to lock exposure until the shutter is fired, that way it continually meters, unless I choose to lock it.

wuyanxu said:
I thought the exposure is set the instance it takes a photo, not when you half-press the shutter button?

hence Canon menu says "Metering + AF start"
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Yes.

boyfalldown said:
short answer is nothing new, but its much easier to do those things,
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Debatable, personally I'd rather only press an extra button when I need to, rather than for every shot. :)
 
wuyanxu said:
I thought the exposure is set the instance it takes a photo, not when you half-press the shutter button?

hence Canon menu says "Metering + AF start"
Click to expand...

Sorry You are correct, I had them the wrong way round and have edited my post.

Treeman, didn't notice you were shooting Nikon.
 
Am I the only one who looks through the viewfinder with my left eye? This make BBF bloomin' uncomfortable as I stick my thumb knuckle in my right eye when I've tried it! For this reason alone I gave up with it :)
 
You can't use a remote shutter release, either cable or wireless, with BBF. You have to go back to looking through the viewfinder and pressing the back button to focus, which to a large extent negates the use of a remote.
(Unless there's a setting that I've missed!)
 
I use my left eye no problem.:shrug::lol:
 
I use my left eye and BBF as well, and have never noticed a problem.
 
mickledore said:
You can't use a remote shutter release, either cable or wireless, with BBF. You have to go back to looking through the viewfinder and pressing the back button to focus, which to a large extent negates the use of a remote.
(Unless there's a setting that I've missed!)
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If you are using a remote then presumably the scene ain't moving? Would you not set your exposure values then move to manual focus in that situation anyway? What if focus is lost or incorrect when using one, how would you know unless you went back to check either the VF or LCD?

I don't think I've ever used Autofocus with a remote :thinking:
 
Back-button AF works best when a) you use the centre AF point, b) with focus recompose technique, and c) you're taking several shots of the same subject. That combination fits most most of us, most of the time.

If you're just taking one snap, then there's very little point to BB-AF. You focus with half-pressure on the shutter release, hold that and recompose, then shoot. Done.

But if you're shooting a series, then every time you let go of half-pressure, obviously the AF point is over something else like the background, so when you half-press again the camera refocuses on the wrong thing. It's very irritating and slows you down.

BB-AF means you only halve to focus-recompose once, and it holds good until you're finished.
 
HoppyUK said:
But if you're shooting a series, then every time you let go of half-pressure, obviously the AF point is over something else like the background, so when you half-press again the camera refocuses on the wrong thing. It's very irritating and slows you down.

BB-AF means you only halve to focus-recompose once, and it holds good until you're finished.
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This is the most useful thing to me, not having to focus and recompose for every shot where your main subject is outside your AF point. It's just frustrating wiggling your lens all over the place otherwise.

Focus, let go of back button, recompose, shoot.

Just refocus if you or the subject move and be careful if shooting wide open that the recompose step doesn't push the subject out of focus.

You can still move to a different af point if you are tracking a moving subject composed somewhere else in the frame, and just keep thumb on the back button for instant switch to AF-C.
 
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Phil1974 said:
Am I the only one who looks through the viewfinder with my left eye? This make BBF bloomin' uncomfortable as I stick my thumb knuckle in my right eye when I've tried it! For this reason alone I gave up with it :)
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Should've bought an EU version, as they're designed for left-eye use, just like their cars are designed for left-hand drive.

Simples! :bonk:
 
kestral said:
Are there any instances where back button focus fails?
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No. Only if the back-button is inconveniently placed. If it's right there next to your thumb, it's easy to either press and release on demand, or hold it down for servo tracking etc.
 
DizMatt said:
I knew A lot short of nothing about this. Thanks for the discussion. I'll give this a whirl at the weekend
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Give it a hundred or so shots, it's odd at first but once you're used to it you'll never go back
 
gridlock said:
Yes, when you go to Stockholm, it's -20C, and you forget you've enabled BBF. I thought the lens had frozen :bonk:
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No, you're referring to the common phenomenon that is known as brain freeze - others get it sucking on a slush puppy too quickly.
 
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You can also use the back button as AF-stop, very useful if you're in servo AF with the shutter button and you want the focus to stop tracking momentarily.
 
Can onyone confirm what metering is best to use with back button focus eg..evaluative or spot and to try and get a sharp focus on a moving object am I better using Al servo....thanks
 
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