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AF-C with Back Button Focusing


rwa757

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While shooting objects in motion (BIF), do I need to continually depress the back button to maintain focus tracking? I have the cameras set to AF-C mode.

As Joseph points out above, if you would like to get continuous focus tracking, you need to keep pressing the button. As soon as you let go the button, continuous focus tracking stops.

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While your question has been answered, let me lend my enthusiastic encouragement for use of BBF.

Could you elaborate David?

I've always found a half-press of the shutter button to be reliable and convenient, while poking my thumb up beside my eye is not so comfortable - and I still need to cover the shutter button with my index finger. In short, I really see no advantage to BBF and would rather use that button for AE/AF lock as it's programmed by default.

 

Well, to be honest I'd rather the back-button was moved to a far more ergonomic position altogether, but that's a different story.

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Could you elaborate David?

I've always found a half-press of the shutter button to be reliable and convenient, while poking my thumb up beside my eye is not so comfortable - and I still need to cover the shutter button with my index finger. In short, I really see no advantage to BBF and would rather use that button for AE/AF lock as it's programmed by default.

 

Well, to be honest I'd rather the back-button was moved to a far more ergonomic position altogether, but that's a different story.

We've had this discussion in the past.

About five years back I wrote:-

"For stationary subjects isn't it the easiest to just use AF-S, one point focus, locking focus by pressing the shutter button half way down, re-compose as necessary with shutter half way down and shoot when ready.

I'm sure we had this discussion a couple of years back and yes, the conclusion was that if you are using AF-S then the two methods are equivalent though perhaps different in convenience. For example using the release to lock you have to keep half pressure on the release to maintain focus lock between shots.

In AF-C it is quite different and I think that most of the AF-ON fans above are mostly using that."

 

Anyone know if cameras have changed recently so that things are different now?

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Could you elaborate David?

I've always found a half-press of the shutter button to be reliable and convenient, while poking my thumb up beside my eye is not so comfortable - and I still need to cover the shutter button with my index finger. In short, I really see no advantage to BBF and would rather use that button for AE/AF lock as it's programmed by default.

 

Well, to be honest I'd rather the back-button was moved to a far more ergonomic position altogether, but that's a different story.

 

I'm not David, but I'll tell you why I think it's good to use back button focus and disable focus activation from the shutter release button:

 

1: You never have to switch between AF-S and AF-C, because you get both by leaving the camera on AF-C at all times. If you want to lock focus, you simply release the AF-ON button, and you can recompose at your will, without switching to AF-S.

 

2: If you are using a lens that allows instant manual focus override, you never have to switch between autofocus and manual focus either. You can release the shutter without activating AF. This is useful if you don't want to change focus between two shots. If AF is not removed from the shutter release button, the only way you could deactivate autofocus would be by switching the camera and/or lens to manual focus. I've had situations where it was perhaps difficult to acquire focus, and once I did, I did not want to change it for the next several shots.

 

I personally tried the back button AF once, and never went back to the default setup.

Edited by raczoliver
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It's not quite true that bbf makes AF-S redundant. AF-S will move focus until the camera thinks it achieves focus, then stop. AF-C keeps moving the lens as long as you hold down the focus, so you may never be sure that the camera is locked on. In most situations that's s pedantic distinction - I'm usually more worried about my control over when to focus than the camera's.

 

For example, if I'm trying to capture a bird in a hedge, I often use bbf with AF-C, and leave the focus active because the bird will sway in the wind. The risk is that a twig will swing in front of the bird and the focus will snap away, which wouldn't happen with AF-S - but otherwise you're relying on depth of field to cover the bird's movements. Of course, I also don't have to rely on the lens AF/M override setting if I'm struggling and need to manual focus - I can just take a thumb off the AF-On.

 

In focus and recompose, I'd always rather use 3D tracking in AF-C if possible. Not only does it allow for the subject or photographer moving a bit, the Nikon bodies also don't automatically adjust for how the focal plane moves relative to the subject as you rotate (some Hasselblads actually use the motion sensor for this), so you're actively making the focal plane incorrect as you turn; at large aperture this really matters.

 

On my D850 I can use the button of the joystick to activate AF as I move the AF point around. The D850 also has an oddity that 3D mode will only lock to the nearest of an AF point and its surrounding (non-selectable) helpers, so if there's ground in front of the subject or you're shooting through trees, it won't lock where you ask like the older bodies. Fortunately you can program other buttons to choose group or single focus point and also activate AF - so I often end up with front button focus, using Fn1 or Pv. Coincidentally, this is also what you end up doing on a Coolpix A if you don't want the shutter button to activate AF (and it's slow, so you don't). By the same argument, manually enabling AF on the dSLRs in live view mode is generally better than letting it hunt.

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I prefer BBF for the reasons above, for the most part, but would add that, although the difference is seldom seen, there can be a slight difference in focus accuracy with some cameras. As far as I know this does not occur in any but the lower end ones, but my D3200, for example, which does not have any options for priority, mentions in its instructions that the shutter may fire before AFC has finished and locked. Nikon is not very generous of information, so it's not clear whether AFC will end up as accurate as AFS if you wait long enough, and I never noticed consistent enough differences to judge well, but the possibility remains that BBF with AFC will not always be as accurate as AFS. And as others have noted, since there is no confirmation beep, it's not always easy to tell when and whether it's finished.

 

For some things I like spot metering with BBF and with exposure lock given to the shutter half-press. You can focus on one spot, set exposure on yet another, and still adjust your composition. Being able to separate those things can be very handy if you're looking, for example, at a big scenic shot with very wide dynamic range in large blocks, where recomposition can make changes in the metering as well as the focus.

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WRT Raczoliver's points 1 and 2; surely the AE/AF lock function of the back-button accomplishes those same things, but in a negative fashion? I.e. pressing the button disables focus in the same way that releasing it does with AF-On enabled.

In focus and recompose, I'd always rather use 3D tracking in AF-C if possible. Not only does it allow for the subject or photographer moving a bit, the Nikon bodies also don't automatically adjust for how the focal plane moves relative to the subject as you rotate....

Debatable.

Coincidentally, I was just playing with the D7200 this morning, and noticed that using the centre AF point and then swinging the camera actually gave better focus on the then off-centre subject than composing first and shifting the focus point over it. I know this shouldn't theoretically be the case, but there you are. That's what I found. A curiosity that needs further investigation.

 

However, quite frankly the flakey operation of Nikon's reflected-down-a-well AF sensor system is beginning to exasperate me more than somewhat.

 

So does it really matter which button I push to get rather iffy focus?

Being able to separate those things can be very handy if you're looking, for example, at a big scenic shot with very wide dynamic range in large blocks, where recomposition can make changes in the metering as well as the focus.

That sounds like a prime case for manual control over everything. Not relying on a single spot metering point and AF, but carefully examining the histogram or consulting a handheld incident meter, and setting the focus manually too.

Edited by rodeo_joe|1
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I suppose it's half full vs. half empty. For me personally, it feels more straightforward to push a button when I want to focus and not push it when I don't. The biggest downside of using the BBF is when I want to hand over the camera to someone else to take a picture with me in it once or twice a year. I usually end up giving them my cell phone instead.

 

I have also noticed that the focus and recompose method sometimes gives better results than using a focus point close to the edge of the frame, but I get much better results using the peripheral focus points with the D850 than I did with the D700.

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Could you elaborate David?

Others have already elaborated most of the points I would make. To expand a bit: For me, I generally shoot BBF, AF-C, and a single focus point. This means that for static subjects I can choose a discrete focus point, focus there, release the focus-on button, and then shoot to my heart's content, without worrying that the camera will inadvertently decide to focus on something else in the frame. I also don't have to wait for the camera to re-focus for each shot, with the concomitant risk that it will focus someplace different in multiple shots. When shooting action or moving wildlife, I'll change to more focus points, but keep everything else the same. I haven't found the button position to be an issue, once the muscle memory sets in. I'll acknowledge that BBF is not for everybody, but I like it, and have set up my D810 (with a dedicated focus-on button), my D7100, and even the lowly D5100 for BBF. I continue to use the half-press position on the shutter release to lock exposure, such that I can set the exposure for one point or zone on the image, focus on another, and re-frame, all without changing hand positions or delving into menus. To me, that's the essence of full control over image capture.

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I guess the disabling of SBF is a must too?

Indeed.

I also expect that in general, AF-C priority is set to release rather than focus - at least when a maximum frame rate is to be maintained to catch some action.

The risk is that a twig will swing in front of the bird and the focus will snap away

Isn't that what "focus tracking with lock-on" is for - set appropriately and the focus won't snap away from the subject.

In focus and recompose, I'd always rather use 3D tracking in AF-C if possible.

I guess the performance got better in the D500 (and I assume the D850) - I just can't bring myself to rely on the camera's AF to do what needs to be done in this auto mode. Probably why I have so much trouble adjusting to AF on my mirrorless bodies. Since Nikon refuses to give me d9 on the D500, I mainly use single point or GRP. Occasionally d21 - each mode is mapped to a different button.

 

I switch to BBF a couple of years ago and would never go back to having AF activated via the shutter. Mainly because most of the time I need AF-C anyway and on the occasion where I don't need continuous focus I only have to lift my thumb. Before I started using BBF, I can't count the number of times the camera was in AF-S mode and I forgot to switch to AF-C when I needed to photograph something that moved. I also rather move the focus point where I need it instead of relying on focus and recompose. And I truly have no idea why I would ever need to lock AE or AF via the AE-L/AF-L button.

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Wildlife and BIF is not a big part of what I shoot. Flowers, insects and butterflies are more my thing, where AF-C is pretty essential for overcoming the motion induced by breezes. So keeping my thumb permanently pressed on the back button would be a pretty pointless exercise.

 

Formal portraits, landscape and still-life/product also don't (usually) require anything other than AF-S and a half-press of the shutter button. If I really don't want the focus to move automatically, there are switches on the lens and LH side of the camera body for that. Which, admittedly, don't prevent accidental nudging of the far-too-sloppy focus rings on most AF lenses.

 

(I actually have one AF macro lens that focus-creeps if pointed downwards with the AF/MF switch in manual focus mode, but thankfully that's not the norm.)

 

My medium format and LF cameras had no such back-body switch, in fact no switches at all in the case of the 5x4s. Yet they got the job done. In those days I reserved my right thumb for pushing the plunger of a Bowden-cable shutter release. So sticking it next to my right eye socket is a totally alien position for me.

 

Perhaps if Nikon had placed the button where it doesn't require a contorted camera grip, then I might be more tempted to use it?

Edited by rodeo_joe|1
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...For me personally, it feels more straightforward to push a button when I want to focus and not push it when I don't...
To me, it is merely a question of which button I press to get focus. I have tried BBF many times and my D850 is set up to change af-area modes depending on which button I keep pressed while focusing.

...I get much better results using the peripheral focus points with the D850 than I did with the D700.
Newer cameras have more peripheral cross-type af sensors. Some cameras suffer from poor alignment, others have ”impact damage”. I recall many threads about the D800 having a ”left focus issue” (they had assymetric af problems with the af sensors on their left side).
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I've done a lot of pictures on trips where there was not a lot of time to set up a shot, and where light was pretty quick to change. For that, at least, I have found it more convenient to use back button focus and spot metering, or quick exposure compensation, with A mode. Some of that likely comes down to how comfortable one is with the controls on the camera, or just how used one is to doing it one way or another. Rodeo Joe is, of course, right that one can also go completely manual and take control of everything, but that can be difficult if you're on a Zodiac or a trail and have little time to set up a shot. In addition, for some years I used a D3200, which is not terribly well suited to either manual exposure (with only one control wheel) or manual focus (with a marginal view screen). The D7100 is more suited to manual control and a few other things as well, but habits tend to stick.
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In the past, there had been on argument against BBF - the fact that pressing the AF-ON button did not activate VR; only a half-press of the shutter button did. Thankfully, Nikon saw the error of their ways and took corrective action.

 

I some aspects, I agree with Rodeo Joe - doesn't matter which button to press. In essence, BBF to me is a matter of convenience. I have my D500 set to CH - any accidental full press of the shutter release when only a half-press was intended results in a bunch of images taken that I didn't want and don't need. More importantly though - with AF-ON programmed for single point AF, the joy stick center button for GRP and the PRE button for d21 mode I just have to decouple AF from the shutter release. Switching between these modes (or between AF-S and AF-C) with the - in many instances unreachable - button on the left of the camera (try reaching that one when hand holding a long lens) just isn't an option. I am glad Nikon provides these options and that there are different ways to set up the camera - just pick the ones that suits your needs best. If you don't see the advantage of BBF in what you shoot, then don't use it. For me it is the only way now and I don't see any disadvantage in using it (aside from smudging up the right side of my glasses when getting my thumb to reach the AF-ON and joy stick controller).

 

Over the years and thanks to Nikon providing more options over time, I have resorted to setting my cameras up the same way independent of what the actually shooting scenario is. I am always in M mode (allows me to set shutter speed and aperture the way I like it without having to worry about the limits imposed by using either S or A). I always have AutoISO on - except in the very few instances where I need to go fully manual (panos, for example). Always in matrix mode - only switching to spot in the rare occasion that the lighting situation requires it. WB is always on Auto and I always shoot RAW. So in essence, if A, S, and P modes would be taken away, the AF mode selector vanished, the QUAL and WB buttons disappeared and the exposure mode button failed, I wouldn't notice.

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I believe Nikon changed the VR some time around the time the D3100 was introduced, and cameras since then have activated it with the back button.

 

I actually asked that of Nikon in 2015, and though they were (as usual) vague about it, they responded that VR goes on on "newer cameras." It definitely does so on the D3200 and the D7100.

 

If you have any doubts, it's pretty easy to check, because VR does not depend on AF, so if you have a lens which makes any noise at all in VR, you can just turn off the AF, and if makes any noise you know VR is going on.

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