Back button focus confusion discussion

[Brownbear]

In my example I used

AF-S and AF-C with the focus set to release on focus, only.

I just tried it again with the focus set to release whether the image was in focus or not - same results.

Mike... I went into the custom settings section and I changed the function of the AE-L/A-E F button to focus following a procedure I looked up for changing that setting.

If this is not what you are asking me, and if my post has only confused things please let me know right away, and I will delete my post.



Thank you.

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.

[Mike Buckley]

What setting is applied to the AE-L/AF-L button (menu item f4)?

[Dave Humphries]

All,

I will repeat John's post #94 'action for action' tomorrow (Monday) on the D7100.

I'm not sure, but I think Christina's results may have differed from mine (done this morning), so I will also see if using the AE-L/AF-L button performs any differently from (my usual) Fn button (when each configured as AF-ON). I mean, they shouldn't, but who knows?

G'night, Dave

[Mike Buckley]

If assigning the same setting to two different buttons results in different camera operations, I give up.

[Mike Buckley]

Christina,

To be clear, we need the setting applied in menu item f4. Without that information, we can't be of any help. Provide the exact setting displayed in your camera.

[Brownbear]

Hi Grahame,

I can see that it is not readily apparent that I did follow the example of John's excellent post. I tried to the best of my ability to follow his lead. However, I was unable to communicate my findings using the same terminology in a manner that I understood. I was trying to be helpful by sharing. My apologies for confusing the matter further.

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

[Brownbear]

Menu Item under Custom Setting Menu - f controls

f4 Assign AE-L/AF-L button

Press AF-ON

Typed directly as seen on the menu on the back of my camera.

Christina,

To be clear, we need the setting applied in menu item f4. Without that information, we can't be of any help. Provide the exact setting displayed in your camera.

[Mike Buckley]

Thanks, Christina. If you and I are communicating effectively, your D7100 is operating differently than my D7000 using the exact same settings unless there is yet another pertinent setting that none of us have discussed. I look forward to learning Dave's information when he conducts his tests.

To keep things clear, my D7000 is performing exactly as described by John when using his D7000 in post #94.

[Brownbear]

Thank you Mike,

I saw your post so I thought it would be helpful if I shared what I tried. It will likely turn out that in the process I set something incorrectly, somewhere, somehow.

Thanks, Christina. If you and I are communicating effectively, your D7100 is operating differently than my D7000 using the exact same settings unless there is yet another pertinent setting that none of us have discussed. I look forward to learning Dave's information when he conducts his tests.

[PhotomanJohn]

It will likely turn out that in the process I set something incorrectly, somewhere, somehow.

I wouldn't jump to that conclusion yet. As I said much earlier, the firmware in the D7100 is different than that in the D7000 and is more like what is in the D800. I don't have a D7100 so I can't help anymore but I'm sure Dave will sort this all out.

John

[Mike Buckley]

I agree with John, Christina, that you shouldn't assume something is different than what you reported. You were very exact in your reporting, which is quite helpful.

As it stands, John and I concur about how the D7000 operates. If we learn tomorrow that you and Dave concur about how the D7100 operates, that will be very informative on a couple of levels.

[Dave Humphries]

~ but I'm sure Dave will sort this all out.

No pressure then!

I have since had a PM from Christina with another helpful bit of information which I will include in my tests.

I think it is quite likely there may be minor differences between the firmware versions between the D7000 and D7100.

Talking of (exact) firmware versions: on 26 August 2014, Nikon released a new firmware versions for the D7100 - C1.02 (and D7000 - C1.04), I should state now that I have not installed that - I don't believe I have any of the issues it is supposed to fix, so I adopted the "if it ain't broke, don't fix it" rule.
My camera has "C: 1.00" installed (and my 70-300mm lens is "L: 1.008").

More later, Dave

[AB26]

Focus Priority,

I am going to do the dangerous thing now and make an assumption. I will assume that no matter what button you assign the AF-ON function to it will function in exactly the same way a dedicated AF-ON button functions.

The AF-ON button takes over the focusing function from the half press, whenever it is pressed. The AF-ON button overrides the half press shutter release focusing function if the AF-ON only mode is not selected in the menu system.

The half press of the shutter button locks focus in AF-S mode when focus is obtained. In AF-C mode focus is never locked unless the AF-ON button is released or the AF-L button is pressed (depending on how your camera is configured).

The shutter will not release unless that little green light in the viewfinder is on if AF-C and/or AF-S Mode Priority is set to Focus. That is an indication that focus was obtained, no matter on what it is, something will be in focus. As long as the shutter release button is half pressed or the AF-ON button is held down the green light will stay on and the shutter can be released at any time, even if you have re-composed to the extent where nothing is in focus anymore. The system “remembers” that something is in focus as long as you keep the button pressed after obtaining focus. The moment you release the half press on the shutter release button the system is “reset” and focus has to be obtained again before the shutter will release.

With the AF-ON button (or any other button) dedicated to obtain Auto Focus, focus is locked once you release the button and the green light goes out if Mode Priority is set to Focus. Now you can try as hard as you wish, the shutter will not release unless that little green light comes on again. If using BB focus ONLY, with Mode Priority set to Focus, you need to half press the shutter release button before releasing the AF-ON button, to lock focus, keeping it down. Now you can re-compose and shoot even if everything is OOF.
If you do not half press the shutter release button before releasing the AF-ON button the camera “forgets” that something was in focus and the green light will flash once the half press on the shutter is executed. This is an indication that nothing is in focus. You can now swing the camera around, with the shutter button half pressed and as soon as the system finds something that is in focus the green light will stop flickering.
When using BB focus and you do the re-compose thing you can easily get your subject OOF, especially so for close up and macro work. (Do not re-compose when shooting close ups and macro.)

The moment you re-compose you change the focal plane and you need to re-focus.

I hope the above explanation is not to complicated. The best way is to do it in practice.

Now go do your homework!

[AB26]

Mike & Dave

Mike's comment about needing to have focus priority turned off in order to actually do focus and recompose is fundamentally correct.

John

No John, that statement is fundamentally very wrong. I have Focus Priority set to ON and I can use either BB focus or half press focus and re-compose without any problem at all.

If you are using BB focus and re-compose you cannot let go of the buttons before the shot is taken. Holding down the AF-ON button will lock focus in AF-S mode. However it does not lock EXPOSURE.
Exposure has to be locked by using another button. Holding down the AF-ON button only and re-composing you can get incorrect EXPOSURE.
Exposure can be locked once FOCUS has been achieved and the green light is on, in the viewfinder. Half pressing the Shutter Release button will lock exposure and focus and then you can let go of the AF-ON button, hold down the half press, re-compose and shoot. Even with AF-ON set to Shutter and AF-ON.

Now we are back to why not simply use half press if you need to focus and re-compose. How often do you want to focus on one subject but want another object to be correctly exposed at the cost of your main subject. If that is the effect you want – use BB focus but use it correctly and for the right reason.

To me the most important reason to use BB focus is to get better exposed images of moving subjects. The half press can, in many instances, lock exposure prematurely.

[Mike Buckley]

No John, that statement is fundamentally very wrong.

That error that you cite had already been acknowledged and corrected as a courtesy to everyone following the thread. Not so for your inaccurate statement that neither the Nikon D610 nor the Nikon D750 has back button focusing.

[AB26]

I hope everyone by now appreciates that it's nothing less than utter nonsense for anyone to claim that we should always or never do this or that. Such a blanket statement could never come close to covering the various needs and combinations of settings that can completely change the camera's operation. It's far better that we make informed decisions about our settings in accordance with the style of photography and type of subject being considered at the time. Even then, there are often at least two combinations of settings that can result in the exact same capture.

Mike,

I hope you appreciate the utter garbage I am gargling here. At least I know what effect settings will have on any particular style of shooting. (And if for any reason I don’t know I find out!)

But allow me to upset you even more: “You should never need to focus and re-compose” it is something beginners do!

[AB26]

That error that you cite had already been acknowledged and corrected as a courtesy to everyone following the thread. Not so for your inaccurate statement that neither the Nikon D610 nor the Nikon D750 has back button focusing.

Do you understand English Mike? Do you actually read and understand what I write?
When and where did I say the D610 and D750 does not have the BB Focusing function. You think I am an Idiot?
Neither has AN AF-ON BUTTON, it was dropped on the D610 and D750. Do you perhaps know why?

[Mike Buckley]

When and where did I say the D610 and D750 does not have the BB Focusing function.

You wrote that in Post #27 of this thread. Your error was mentioned in Posts #40 and #57, perhaps in others as well.

Do you understand English Mike? Do you actually read and understand what I write?

Comments such as those are insulting, personal attacks. Considering that this is typical of your style of writing, I encourage the moderators to discuss the issue with you. I will not continue this discussion with you.

[Donald]

This thread is now closed.

It's a great pity that, from time-to-time, threads descend into the sort of exchanges in which more heat than light is generated. Continuation of this thread would do nothing to help inform and educate those who seek to understand what back-button focusing is about. Rather all it promotes is dogmatism and all it illustrates that when some of us get something into their head, it gets fixed there and no amount of information to counter it is going to change attitudes. That's when things become totally counter-productive.

[Dave Humphries]

I am saddened that Donald has closed the thread, although I quite understand why.
Fortunately for me I am also a moderator, so I can post this last reply, giving the results of my 5+ hours of work on this, for the benefit of those with open minds that are interested in learning.

My tests today were conducted indoors for the considerable convenience of documenting results immediately on computer. I was focusing (using the single, central, focus point only) obliquely on patterned carpet at distances of 6 or 10 feet (2 or 3m).

My perception of whether focus was achieved was based on two things; whether the centre of the shot looked sharp and also whether the focus point overlay was shown when the shot was subsequently reviewed (signifying the camera thought it was focused).

Camera: Nikon D7100, running firmware V1.00, shooting Aperture Priority with Iso-Auto ON (Max. 6400, Min SS 1/30s)
Lens: Nikon 70-300mm VR, set at 200mm and f/5.3 (wide open at that focal length)

I moved my Conclusions and Suggested Practices to be above the table of results, since the latter are quite 'dry'.

Conclusions:

On the D7100; the AF priority choices (focus vs release) for AF-C and AF-S are only honoured when AF itself is active.
However, this is not the case:
i) when AF is inactive because AF-ON is not being held down at the moment the shutter is pressed
ii) when AF has completed (focus acquired) when you are in AF-S mode (even if AF-ON is being held down)

This appears to be the fundamental difference in AF-ON functionality between D7100 and D7000. Compare my results for Tests 1A and 2A below (which allowed me to capture out of focus images) with those in John's post #94.

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 have proved to myself that the choice of button used for BBF (i.e. set AF-ON in Custom menu) makes no difference; be it AE-L/AF-L or Fn.

However, the choice on the release mode dial may cause issues/confusion to some (e.g. me!).
I always use "CH" (Continuous High) because I mostly shoot wildlife and you often need quick reactions, multiple shots and a high frame rate. In "S" (Single) release mode, it seems to becomes important which order you press and/or release both the shutter and BBF button. If the BBF is held down and shutter button is not released, it does not re-focus (when I think it should, but that may be just me not used to Single shot mode).

AF-S is in itself, a 'single-shot' method, so once focus is acquired, AF is disabled, the same is true if you lift finger/thumb off the BBF button, so the combination of AF-S plus release of BBF button is effectively doing the same thing twice (disabling AF) - which might be confusing if you stop doing one (or the other) and nothing changes.


Suggested Practices to use BBF on Nikon D7100

Set the focus mode to AF-C (the functionality of AF-S is adequately covered by press, focus, release of BBF button)

Set the AF-C AF-priority (a1) to "Focus"

Use the Release mode dial in "CH" or "CL" (Continuous High or Low), not "S" (Single) - because my brain got addled synchronising fingers/thumbs in Single.


The actual tests conducted

Abbreviations used:

BBF = whichever button assigned AF-ON

See test cases; choice of:

AE-L/AF-L (set in Custom: Controls: f4 as Press) or
Fn {Function} (set in Custom: Controls: f2 as Press)

Whichever not used was set to "None"

oof = out of focus

Test methods (same as John's post #94):
A = Press BBF (focus acquired), release BBF, move to frame all out of focus (oof), attempt to take shot
B = Press BBF (focus acquired), continue holding down BBF, move to frame all oof, wait for AF (if active), attempt to take shot
C = Press BBF (focus acquired), continue holding down BBF, move to frame all oof, attempt to take shot before AF re-acquired

Test 1
BBF button used: AE-L/AF-L
Release Mode dial: CH (Continuous High)
Focus Mode: AF-S (AF-S Priority: Focus)
1A: Out of focus shots taken (apparently a different result from John's D7000)
1B: Out of focus shots taken

Test 2
BBF button used: AE-L/AF-L
Release Mode dial: CH (Continuous High)
Focus Mode: AF-C (AF-C Priority: Focus)
2A: Out of focus shots taken (apparently a different result from John's D7000)
2B: In focus shots taken
2C: Shots delayed until focus was achieved

Test 3
BBF button used: AE-L/AF-L
Release Mode dial: S (Single)
Focus Mode: AF-S (AF-S Priority: Focus)
3A: Out of focus shot taken
3B: Out of focus shot taken

Test 4
BBF button used: AE-L/AF-L
Release Mode dial: S (Single)
Focus Mode: AF-C (AF-C Priority: Focus)
4A: Out of focus shot taken
4B: In focus shot taken
4C: Shot delayed until focus was achieved

Test 5
BBF button used: Fn
Release Mode dial: CH (Continuous High)
Focus Mode: AF-S (AF-S Priority: Focus)
5A: Out of focus shots taken (apparently a different result from John's D7000)
5B: Out of focus shots taken

Test 6
BBF button used: Fn
Release Mode dial: CH (Continuous High)
Focus Mode: AF-C (AF-C Priority: Focus)
6A: Out of focus shots taken (apparently a different result from John's D7000)
6B: In focus shots taken
6C: Shots delayed until focus was achieved

Test 7
BBF button used: Fn
Release Mode dial: S (Single)
Focus Mode: AF-S (AF-S Priority: Focus)
7A: Out of focus shot taken
7B: Out of focus shot taken

Test 8
BBF button used: Fn
Release Mode dial: S (Single)
Focus Mode: AF-C (AF-C Priority: Focus)
8A: Out of focus shot taken
8B: In focus shot taken
8C: Shot delayed until focus was achieved


Repeating some with "Release" AF-priority

Test 9
BBF button used: Fn
Release Mode dial: CH (Continuous High)
Focus Mode: AF-S (AF-S Priority: Release)
9A: Out of focus shots taken
9B: Out of focus shots taken

Test 10
BBF button used: Fn
Release Mode dial: CH (Continuous High)
Focus Mode: AF-C (AF-C Priority: Release)
10A: Out of focus shots taken
10B: In focus shots taken
10C: Multiple out of focus shots taken, occasional in focus ones if my continual re-framing was delayed long enough for focus lock

Test 11
BBF button used: Fn
Release Mode dial: S (Single)
Focus Mode: AF-S (AF-S Priority: Release)
11A: Out of focus shot taken
11B: Out of focus shot taken

Test 12
BBF button used: Fn
Release Mode dial: S (Single)
Focus Mode: AF-C (AF-C Priority: Release)
12A: Out of focus shot taken
12B: In focus shot taken
12C: Out of focus shot taken

Some of the combinations of settings and operation above do not make sense for real world use.
However, all are fully documented so we can see which variations made a difference and those which did not.

Best regards, Dave