Understanding back button focus

Something I have never understood, that BBF users always tout as an advantage is the recomposure. If I focus on something, then lock focus, and recomposure, how do you know it is still in focus? Surely recomposing would move the point of focus slightly?

I have tried this method before, and if I am honest I found it a faff as I had never had a problem with focusing.
 
Sectionate said:
Something I have never understood, that BBF users always tout as an advantage is the recomposure. If I focus on something, then lock focus, and recomposure, how do you know it is still in focus? Surely recomposing would move the point of focus slightly?

I have tried this method before, and if I am honest I found it a faff as I had never had a problem with focusing.
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Focus-recompose with the centre AF point is a very fast, easy and accurate method. Millions of photographers can't be wrong, but either way that's got nothing to do with BBAF.

Focus-recompose is only problematic when you're using a very low f/number, like sub-f/2.8 with very shallow depth of field, and also shooting very close, like two or three feet, with the area you want sharp well away from the centre which means a big angle shift.

That can cause problems but it's an unusual situation and in practise the major error there is usually either the subject or camera moving slightly between focusing and shooting.
 
Martyn D said:
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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Metering patterns are subject dependant - to make the most of them you need to understand what your meter is telling you and how it reads a scene. For the most part modern evaluative metering is very good.

Yes you need to use AI servo when focussing on a moving subject. Whether you use BBF or not. The important thing is good technique, picking a focus point that'll cover an area of contrast, getting focussed well before you take any pictures (to allow the camera to 'get it's eye in').
 
Phil V said:
Metering patterns are subject dependant - to make the most of them you need to understand what your meter is telling you and how it reads a scene. For the most part modern evaluative metering is very good.

Yes you need to use AI servo when focussing on a moving subject. Whether you use BBF or not. The important thing is good technique, picking a focus point that'll cover an area of contrast, getting focussed well before you take any pictures (to allow the camera to 'get it's eye in').
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Cheers for the help Phil.
I just can't get to grips with focus on a moving object, and panning. I had a day at silverstone last year, all my "moving" shots were a complete fail and last week took a few as a pheasant took off, looked good in camera but when uploaded were yet another fail and all blurry
 
Martyn D said:
Cheers for the help Phil.
I just can't get to grips with focus on a moving object, and panning. I had a day at silverstone last year, all my "moving" shots were a complete fail and last week took a few as a pheasant took off, looked good in camera but when uploaded were yet another fail and all blurry
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What lens are you using for this? Some will focus better than others, and sharp shots owe as much to shutter speed as they do to focus.
 
Phil V said:
What lens are you using for this? Some will focus better than others, and sharp shots owe as much to shutter speed as they do to focus.
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Not the best of Lenses...55-250...I'll have another go this year, maybe I should have increased the ISO to get a faster shutter speed and will hopefully have something better glass wise. I'm pretty new to this and learning from the mistakes.
Cheers for the help
 
can BBf be re programed to a different button ? say the print / liveview button on the left hand side ?

it's something i have never considered because of the situation with my right hand ( there's not much more than a thumb left ) i'm ok for pressing the shutter but that is pretty much it
 
boyfalldown said:
Give it a hundred or so shots, it's odd at first but once you're used to it you'll never go back
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That's what I did after reading about it on here a couple of years ago, tried it never went back.
 
cosmicma said:
can BBf be re programed to a different button ? say the print / liveview button on the left hand side ?
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Don't know about Nikon but on some Canon's it can be changed to the AE lock button.
 
Sectionate said:
Something I have never understood, that BBF users always tout as an advantage is the recomposure. If I focus on something, then lock focus, and recomposure, how do you know it is still in focus? Surely recomposing would move the point of focus slightly?

I have tried this method before, and if I am honest I found it a faff as I had never had a problem with focusing.
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Quite, I tend to shoot a lot wide open, so the focus recompose simply doesn't work for me.

Selecting another focus point works fine for me. I've had this discussion before and it appears to be Canon users that are the biggest users of BBF, possibly because their focus points are not as good unless the centre one is selected.
 
Martyn D said:
Not the best of Lenses...55-250...I'll have another go this year, maybe I should have increased the ISO to get a faster shutter speed and will hopefully have something better glass wise. I'm pretty new to this and learning from the mistakes.
Cheers for the help
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Martyn, when I first got my camera earlier this year I used this lens a lot, and managed to get some decent moving shots of owls in flight - at the time as a newbie I was using the auto settings for everything !!!

My technique was to have the camera to my eye following the bird in flight and to pivot at the waist to track it
 
treeman said:
I've had this discussion before and it appears to be Canon users that are the biggest users of BBF, possibly because their focus points are not as good unless the centre one is selected.
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I don't think it's got anything to do with whether the points are as good or not as good. I use it so I always have continuos AF available and updated exposure until I press the shutter button.

I don't think the OP wants a Nikon v Canon debate but constructive advice.
 
Gaz J said:
I don't think it's got anything to do with whether the points are as good or not as good. I use it so I always have continuos AF available and updated exposure until I press the shutter button.

I don't think the OP wants a Nikon v Canon debate but constructive advice.
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Yes quite so do I, and my half press of the shutter release does just that, without the need to press a further button.

Its got nothing to do with one make against another, I'm just offering an explanation of why its advocated more by Canon users (though not exclusively) than Nikon users :)
 
treeman said:
Yes quite so do I, and my half press of the shutter release does just that, without the need to press a further button.

Its got nothing to do with one make against another, I'm just offering an explanation of why its advocated more by Canon users (though not exclusively) than Nikon users :)
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So you have a small group of people, You have selected a focus point that's close to, but not on your chosen person (1/3 into group), you recompose, take a shot, zoom out a little as one of the group has moved, take a shot, soom back in, take a shot, alter the composition again, take a shot.

Using the shutter button for the above requires you to keep your shutter button half pressed and hope that your finger doesn't lift too much whilst you're lifting from the shutter.

Using BBF, you focus, let go of the focus button and recompose / zoom at will, the focus will be good until I choose to re-focus.

I always found the shutter button focus would decide to re-focus at a time that was inconvenient to me, it may be 'user error'; but to me it's counter-intuitive to have my focus linked to the shutter button - it was never that way with MF lenses, where the act of focussing was always detached from any other controls. You'll find people who use BBF don't have to bother with focus stop / focus start controls either - just like using a focus ring, it's simple to control when to focus.
 
Do Canons have focus lock buttons on the body? That's what I'd use in the above scenario.
 
Johnd2000 said:
Do Canons have focus lock buttons on the body? That's what I'd use in the above scenario.
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In one shot AF on a Canon the focus is locked on the half press of the shutter button. It also locks in the exposure so that if it changes when you recompose the exposure remains at its previous setting.
 
Gaz J said:
In one shot AF on a Canon the focus is locked on the half press of the shutter button. It also locks in the exposure so that if it changes when you recompose the exposure remains at its previous setting.
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Ahhh, my Nikon doesn't lock the exposure (may have chane mine to do that though) when I do that
 
Last edited:
Should have said that this is the default position on a Canon. There are several options in the menu on certain cameras that give various combinations of metering, AF stop/start,AE lock. But we're back to that devilish BBF again then :)
 
Gaz J said:
In one shot AF on a Canon the focus is locked on the half press of the shutter button. It also locks in the exposure so that if it changes when you recompose the exposure remains at its previous setting.
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Ahh...My Sonys AF is the same but there's also a lock button by my thumb, for then you want to focus once but shoot many times. Exposure doesn't, by default, lock at half-press but the AEL will lock it when needed.
 
Phil V said:
So you have a small group of people, You have selected a focus point that's close to, but not on your chosen person (1/3 into group), you recompose, take a shot, zoom out a little as one of the group has moved, take a shot, soom back in, take a shot, alter the composition again, take a shot.

Using the shutter button for the above requires you to keep your shutter button half pressed and hope that your finger doesn't lift too much whilst you're lifting from the shutter.

Using BBF, you focus, let go of the focus button and recompose / zoom at will, the focus will be good until I choose to re-focus.

I always found the shutter button focus would decide to re-focus at a time that was inconvenient to me, it may be 'user error'; but to me it's counter-intuitive to have my focus linked to the shutter button - it was never that way with MF lenses, where the act of focussing was always detached from any other controls. You'll find people who use BBF don't have to bother with focus stop / focus start controls either - just like using a focus ring, it's simple to control when to focus.
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As I've already said, I don't do focus and recompose, and to have something I wanted in focus not where I could put a focus point, would be very unusual for me.
However in that rare scenario, I'd just use the focus lock button.
 
Johnd2000 said:
Do Canons have focus lock buttons on the body? That's what I'd use in the above scenario.
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So you'd press another button?

A press to start focus, a press to lock focus and then the shutter press. Using BBF I use a button press to focus, then the shutter.

But my way is inelegant?

Change my scenario above to sporadically re-focus and you dance between buttons where i keep a very smooth flow; focus lock shoot shoot focus lock shoot focus lock shoot shoot.
I'd do focus shoot shoot focus shoot focus shoot shoot.
 
treeman said:
As I've already said, I don't do focus and recompose, and to have something I wanted in focus not where I could put a focus point, would be very unusual for me.
However in that rare scenario, I'd just use the focus lock button.
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You'll appreciate that you're either very lucky to always have a focus point exactly where it's needed or composing around your focus points.

Most cameras don't have anywhere near enough focus points to make this a practical alternative.
 
Phil V said:
So you'd press another button?

A press to start focus, a press to lock focus and then the shutter press. Using BBF I use a button press to focus, then the shutter.

But my way is inelegant?
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I wasn't making a judgement just asking a question. Trying to understand, that's all.

The AF lock also activates AF, when in MF mode. My Sony supports BBF but I've never understood the appeal, personally,
 
Johnd2000 said:
I wasn't making a judgement just asking a question. Trying to understand, that's all.

The AF lock also activates AF, when in MF mode. My Sony supports BBF but I've never understood the appeal, personally,
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I guess its what you're used to. To me and many others we wouldn't use anything else. I like the way that I can separate exposure from focusing. Really useful when your subject is passing in front of varied backgrounds. I don't use focus and recompose much but that's down to the subject matter I like to photograph.
 
Phil V said:
So you have a small group of people, You have selected a focus point that's close to, but not on your chosen person (1/3 into group), you recompose, take a shot, zoom out a little as one of the group has moved, take a shot, soom back in, take a shot, alter the composition again, take a shot.

Using the shutter button for the above requires you to keep your shutter button half pressed and hope that your finger doesn't lift too much whilst you're lifting from the shutter.

Using BBF, you focus, let go of the focus button and recompose / zoom at will, the focus will be good until I choose to re-focus.

I always found the shutter button focus would decide to re-focus at a time that was inconvenient to me, it may be 'user error'; but to me it's counter-intuitive to have my focus linked to the shutter button - it was never that way with MF lenses, where the act of focussing was always detached from any other controls. You'll find people who use BBF don't have to bother with focus stop / focus start controls either - just like using a focus ring, it's simple to control when to focus.
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Zooming without refocusing is a dangerous game. It varies by lens, but they all shift focus at least a bit throughout the focal length range, and some a lot.
 
Gaz J said:
I guess its what you're used to. To me and many others we wouldn't use anything else. I like the way that I can separate exposure from focusing. Really useful when your subject is passing in front of varied backgrounds. I don't use focus and recompose much but that's down to the subject matter I like to photograph.
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I think the penny just dropped. The reason I couldn't see the point was because on Sonys the AF/MF button does the same thing. In any AF mode it disengages the AF. In MF mode it engages AF. So AF and exposure can be separated at any point.
 
I'd read a magazine article and had assumed that BBF was only advantageous for photographing fast moving subjects, such as motor sport.

Many thanks everyone for an interesting and informative discussion. I shall have to try taking a 100 shots and see how I get on :)
 
HoppyUK said:
Zooming without refocusing is a dangerous game. It varies by lens, but they all shift focus at least a bit throughout the focal length range, and some a lot.
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I know, and its tried and tested, and to be fair in that scenario the DoF is forgiving too, which is another reason re-focussing is a PITA.
 
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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So you need the camera set in manual focus for this then?
 
WillNicholls said:
So you need the camera set in manual focus for this then?
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I have it set to AF-C, Will ... holding the back button will then activate the auto focus, when I release the back button it will no longer search for focus, if I want to tweak focus I hold down the button again until focus is achieved.

I have been using back button focus for years, it is second nature to me and I am comfortable with it, also allows me to use the shutter release as an exposure lock if needed.
 
Martyn... said:
I have it set to AF-C, Will ... holding the back button will then activate the auto focus, when I release the back button it will no longer search for focus, if I want to tweak focus I hold down the button again until focus is achieved.

I have been using back button focus for years, it is second nature to me and I am comfortable with it, also allows me to use the shutter release as an exposure lock if needed.
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But then when you move to take a photo and press the shutter, why does it not search again?
 
WillNicholls said:
But then when you move to take a photo and press the shutter, why does it not search again?
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There's a custom setting that deactivates the AF from the shutter button, so that it doesn't re focus.

However if you're shooting on a D4 BBF doesn't allow you to do anything that your camera doesn't do already, it'll just be a case of an alternative method of shooting, try it and see if you like it :)
 
WillNicholls said:
But then when you move to take a photo and press the shutter, why does it not search again?
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There is a menu setting to disengage the shutter release from activating focus, item A5 in the settings menu (on my D700)
 
WillNicholls said:
However someone has said that it makes no difference on the d4? How come?
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Because you already have a focus lock and exposure lock as separate buttons on the D4, however as has been said some Nikon users still use BBF, try it and see.

Personally as a left eye shooter, who doesn't use focus and recompose technique and generally shoots everything with shallow DOF, BBF is just a pain :)
 
treeman said:
Because you already have a focus lock and exposure lock as separate buttons on the D4, however as has been said some Nikon users still use BBF, try it and see.

Personally as a left eye shooter, who doesn't use focus and recompose technique and generally shoots everything with shallow DOF, BBF is just a pain :)
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Ok cheers. I will have a play around. It's a new camera so hadn't spotted those yet.
 
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