Back button focus confusion discussion

[Brownbear]

I would like to clarify a few things that have been addressed to ensure that I have a clear understanding of BBF before I try it.

1.
If I'm photographing birds in flight with my camera set to continuous auto focus (set to release on focus) BBF means that once I grab focus on the bird the focus will remain on the bird even if it flies in front of a tree, and even when I'm panning (moving my camera to follow the bird - hand held)? Meaning BBF will allow me to manage more shots in focus?

2.
If I'm photographing a bird sitting relatively still in a tree with my camera set and using manual focus BBF will allow me to hold the focus on the bird even if it is moving a little bit (grooming etc) as long as I keep the bird in the focal point area. (ie; not grabbing focus on the branches instead) Hand held.

3.
If I expect that a bird is going to fly across a certain area, ie; say landing on a tree branch. If I pre-focus on the tree (using continuous auto focus) when the bird lands on the tree and I press the shutter release button the bird should remain in focus during the flutter of landing activity? Would this also work if one was panning horses at the race track at a super low shutter speed? ie; camera moving along with the horse/no tripod and a busy background with lots of other things for the camera to try and grab focus on?

4. If I'm photographing a landscape with my camera set on a tripod (single shot auto focus or manual focus) once I grab focus on the desired portion of the image the use of BBF means that I can move my camera (on its tripod perch) to change the composition as I please as long as I keep the original focus point in the image. And the same would be true if I were using live view? And even if it was a foggy scene (manual focus) with my chosen focal point being a specific tree in the fog?

Thank you.

[Dave Humphries]

Dave - I would change this statement a little in that newer Nikons seem to work this way. I have noticed that the firmware in the D7100 is closer to the D800 than the D7000. As I mentioned above, the D7000 doesn't ignore AF-C or AF-S focus priority like the D7100 and the D800.

I have taken your suggestion John.

Thanks, Dave

[Mike Buckley]

Christina,

With regard to items 2 and 4, BBF has no impact when using manual focus. That's because BBF is a method of using auto focus.

[Dave Humphries]

Hi Christina,

This is how I would (do) configure for these situations:

On a D7100, with the focus mode set to AF-C and AF-ON configured to either the AE-L/AF-L button, or Fn button, hereafter called the BBF button due to its assigned function. The setting of the focus vs release priority mode is then irrelevant - it will be in release priority mode (on D7100 and similar newer Nikons).

Q1.
If I'm photographing birds in flight with my camera set to continuous auto focus (set to release on focus) BBF means that once I grab focus on the bird the focus will remain on the bird even if it flies in front of a tree, and even when I'm panning (moving my camera to follow the bird - hand held)? Meaning BBF will allow me to manage more shots in focus?

You would need to keep the BBF button held down in order for the camera to track changing focus distance AND keep the focus point on the subject*. It is unlikely that BBF will give you more keepers in this instance, since it is not really playing an active role - the same would be achieved if you were in AF-C using the shutter button to focus. It might be argued that you could get less keepers using BBF, because the D7100 camera will shoot regardless whether the subject is AF-locked.

* In the Custom menu; a3 = Focus Tracking with Lock-on - there is a delay setting which determines (after focus is locked on something), how long it waits after (apparently) being presented with a new 'target', before it decides you want it to re-focus on the new target. This is to allow for momentarily 'slipping off' a flying bird, or something coming between the subject and the camera. However, this equally applies to normal focus operation. I currently have mine set to Normal (mid-point of 5 choices), it seems to be the best compromise between waiting too long to acquire focus when you intentionally select a new bird to follow and it losing focus if you pan across say, a lamp stand while following a BIF, or slip off the target to the trees behind.

Q2.
If I'm photographing a bird sitting relatively still in a tree with my camera set and using manual focus BBF will allow me to hold the focus on the bird even if it is moving a little bit (grooming etc) as long as I keep the bird in the focal point area. (ie; not grabbing focus on the branches instead) Hand held.

In this instance, I would focus on the bird by pressing the BBF button, then release it. So long as you and the bird do not move more than the DoF available, the subject should remain sharp, regardless whether the focus point is on the subject or not, because AF is inactive (effectively you are in MF mode). If/when the bird (or you) move, you simply put it under the focus point again and press the BBF button, if the bird is flying, likely resulting in a different distance, keep the BBF button held down, so focus remains active and tracks the subject.

Q3.
If I expect that a bird is going to fly across a certain area, ie; say landing on a tree branch. If I pre-focus on the tree (using continuous auto focus) when the bird lands on the tree and I press the shutter release button the bird should remain in focus during the flutter of landing activity?

As with Q2, I would focus the branch, with a press and release of BBF button, then, as long as the fluttering landing is within the DoF, the bird should be sharp enough, possibly more so than if, in all the fluttering, the focus is driven off when using normal shutter button focus mode. Using BBF, you trust that DoF covers focus, you can then just concentrate on framing to avoid clipping wing tips, without also having to worry about where the focus point is (because AF is not active). In this scenario, BBF is a definite benefit IMHO.

Q3b.
Would this also work if one was panning horses at the race track at a super low shutter speed? ie; camera moving along with the horse/no tripod and a busy background with lots of other things for the camera to try and grab focus on?

No, BBF is not going to make any positive difference to this, much as it didn't in Q1 above. You are arguably better off working in traditional mode. The only thing that will affect things is how accurately you keep the focus point on the subject (bobbing head and all) and possibly that delay setting I mentioned above.

Q4. If I'm photographing a landscape with my camera set on a tripod (single shot auto focus or manual focus) once I grab focus on the desired portion of the image the use of BBF means that I can move my camera (on its tripod perch) to change the composition as I please as long as I keep the original focus point in the image. And the same would be true if I were using live view? And even if it was a foggy scene (manual focus) with my chosen focal point being a specific tree in the fog?

To my mind, it would not matter if you used AF-C with this scenario, because the bottom line is that:
BBF is just way to turn AF on or off instantly AND irrespective of taking pictures.

• If you want to 'spot' focus; press BBF, let it focus, then release.
• If you want MF; just don't press it.

Either way, the camera only focuses (or re-focuses) when you press that BBF button, so if on a tripod, with the focus set for the landscape, take as many shots and re-compose as often as you like when the BBF button is not pressed and they will all retain the original focus, or whatever manual offset you might have made.

The other option, covered in Q1 and Q3b

• If you want to focus track; press and hold BBF, although be aware you might get some not quite properly focussed shots as a D7100 camera is in release priority mode. The sheer convenience of instant AF/MF control, once you have got used to it, often outweighs this though.

The killer benefit of BBF for wildlife shooters is as I outlined in an earlier post; perched subjects partially obscured behind something else (reeds, grass, fence mesh) or surrounded by foliage - I tend to do quite a bit of this.

I can now see that for pure BIF, it may not be the best (on newer Nikons) if you want focus priority mode.
However, if you're waiting for (even an unobstructed view) perched bird to leap in to the air, I suspect you'll get a sharp (pre-focussed) hand held shot off quicker using BBF (i.e. don't initially press the BBF button) than trying to react to it taking flight, getting the focus point on it, not clipping wing tips, waiting for AF, etc.

Cheers,

[Mike Buckley]

Dave,

In your response to Christina's Q2, I believe you accidentally overlooked the assumption that she is using manual focus. That being the case, the BBF will have no impact.

[Brownbear]

Thank you Mike and Dave, and Dave a special thank you to you for your comprehensive explanation.

At this point in time I'm still missing something despite all the wonderful explanations provided. I can see the benefit in Q2 but I was under the impression that one of the prime benefits of using BBF was for birds in flight and panning action shot (as in the sports sequence demonstration in the video on BBF that Richard shared). And this was a prime motivator for me to try BBF, so now I'm not so sure how beneficial it truly is.

It seems that I need more time to wrap my mind around how it works and the benefits.

Thank you.

[Dave Humphries]

Dave,

In your response to Christina's Q2, I believe you accidentally overlooked the assumption that she is using manual focus. That being the case, the BBF will have no impact.

I hate to be pedantic - ok, may be just a bit

I deliberately answered that saying how I would do it, not trying to understand the term "manual focus BBF", as I think when written, perhaps even now, Christina may be thinking BBF does things it does not.

The bottom line big statement is the crux of the matter. I am coming to think that BBF, without the button pushed, is MF.

Our collective understanding is not helped by the fact that it appears to work differently between D7000 and D7100 and arguably, for BIF, the D7000 way, which appears to honour the focus priority setting, would actually be better.

[Mike Buckley]

Understanding is not helped by the fact that it appears to work differently between D7000 and D7100

I'm not convinced that the two cameras work differently. The two manuals have the exact same word-for-word explanation and I would be willing to bet that they really do operate the same.

Despite the best efforts of John, you and me to effectively communicate, it's very difficult to explain things accurately without taking a lot more time than any of us are probably willing to devote. I suspect it's a flaw in our communication that is causing confusion.

[Dave Humphries]

Despite the best efforts of John, you and me to effectively communicate, it's very difficult to explain things accurately without taking a lot more time than any of us are probably willing to devote. I suspect it's a flaw in our communication that is causing confusion.

I expect you're correct Mike, they are complex beasts and what's 'normal' for one of us, clearly isn't for others. e.g. I never use AF-S, if the subject is static enough to use AF-S, rather than change it, I can do it with a quick press of BBF and release. That said, changing between AF-C and AF-S (or AF-A) is very simple to do; hold AF button (to left of lens on front) and rotate rear wheel.

I'm not convinced that the two cameras work differently. The two manuals have the exact same word-for-word explanation and I would be willing to bet that they really do operate the same.

I started off the day thinking one thing, then I discovered that if I use AF-S with BBF, it behaved as your test described.
I also thought you (perhaps John, now I think about it) said that the D7000 wouldn't take a defocussed picture when in Focus priority, but perhaps it was John and perhaps he wasn't using BBF at that moment in time.

[Dave Humphries]

At this point in time I'm still missing something despite all the wonderful explanations provided. I can see the benefit in Q2 but I was under the impression that one of the prime benefits of using BBF was for birds in flight and panning action shot (as in the sports sequence demonstration in the video on BBF that Richard shared). And this was a prime motivator for me to try BBF, so now I'm not so sure how beneficial it truly is.

It seems that I need more time to wrap my mind around how it works and the benefits.

You are not the only one Christina - I have changed my views on its usefulness in some situations a couple of times today.

To clarify; my reply to Mike in post #87 was not intended as a slight on your understanding, we are ALL struggling with it (believe me)

Next fine day I will go find some birds and shoot a lot of 'in flight' frames in both BBF and normal modes - and see if one set or the other has a predominance to produce more 'not quite focussed' shots. From what I have literally discovered/realised today, BBF, in ignoring the Focus priority setting, may be the culprit.

Plus I will try Iso-Auto in 'real life'.

[Mike Buckley]

I also thought you (perhaps John, now I think about it) said that the D7000 wouldn't take a defocussed picture when in Focus priority, but perhaps it was John and perhaps he wasn't using BBF at that moment in time.

Check out Post #80 for my thinking about that.

[Dave Humphries]

Check out Post #80 for my thinking about that.

Yes, that's the one - it does need clarification from John, doesn't it.

[Brownbear]

Thank you Mike and Dave, and to everyone who contributed to this thread.

Indeed I thought that BBF would work in both Manual and Auto focus modes - otherwise it would be called Auto Back Button Focus.

I have a far better understanding of how it works and the benefits, thanks to everyone who contributed to this thread. It is just that this type of thing is not something that comes easily to me.

Dave - I will try it on the first sunny morning (may be a while) on some gulls or pigeons.

[PhotomanJohn]

Yes, that's the one - it does need clarification from John, doesn't it.

I have been out working and come back in to see the thread is still alive and kicking. OK, I will try to be as clear as I can.

D7000 - AE-L/AF-L button programmed to AF-ON, AF-C and AF-S priority set to Focus.

1. Focus mode set to AF-S
a. BB pressed to focus and released, camera panned to an area out of focus, shutter pressed and nothing happens.
b. BB pressed to focus and held, focus is acquired, camera panned to area out of focus, camera does not re-focus, shutter pressed and picture is taken.

2. Focus mode set to AF-C
a. BB pressed to focus and released, camera panned to an area out of focus, shutter pressed and nothing happens.
b. BB pressed to focus and held, camera panned to another area and focus is acquired, shutter pressed and picture is taken.
c. BB pressed to focus and held, camera panned to another area and focus is NOT acquired yet, shutter pressed and nothing happens until focus is acquired.

I never mentioned these other variations because I leave the camera with AF-C and AF-S focus priority in Release, focus mode to AF-C. I release the BB after focus if I want AF-S operation and hold it if I want AF-C operation. Couldn't be easier.

Is this horse dead yet?

John

[Mike Buckley]

Is this horse dead yet?

Yes, but you know what we do to dead horses.

Seriously, that's very precise information that you provided. Until shown otherwise, I'm going to assume the D7100 works the same way.

[Brownbear]

I just tried BBF for the 1st time with my Nikon 7100 on a raindrop hanging off the branch of a fir tree using auto focus.

1. Focus mode set to AF-S/ Center point focus
BB pressed to focus and released, camera panned to recompose so that the water droplet is on the left hand side of the frame.

If I keep my finger on my new focus button I cannot take the picture. If I take my finger off of the new focus button I can take the image and the droplet is in focus. In this mode I also hear the beep to confirm focus.


2. Focus mode set to AF-C/Center point focus

Exactly as I have described above but without the confirmation beep.

I'm not sure if this is helpful or not but sharing because I have the other Nikon.

[Stagecoach]

Hi Christina,

Purely out of interest what exactly are you referring to as "my new focus button"?

Grahame

[Brownbear]

Hi Grahame,

The Auto Exposure/Focus Lock AE-L/AF-L on the back of my camera. I changed this button to BBF to try it out for the learing experience, ie; easier to understand by trying.

Hi Christina,

Purely out of interest what exactly are you referring to as "my new focus button"?

Grahame

[Mike Buckley]

Christina,

In addition to the information Grahame requested, also please provide the priority settings for AF-C and AF-S. Those are menu items a1 and a2, respectively.

Also provide the setting that you applied to the AE-L/AF-L button.

[Stagecoach]

Hi Grahame,

The Auto Exposure/Focus Lock AE-L/AF-L on the back of my camera. I changed this button to BBF to try it out for the learing experience, ie; easier to understand by trying.

Hi again Christina,

Ok, the reason I asked was that I had just read John's excellent post No 94.

What is most noticeable and significant in it is that he has taken great care throughout to use exactly the same terminology each time for the same action. Example, "BB Pressed".

Also an exceedingly well constructed protocol.

Just passing

Grahame