Back Button Focus

WelliesNBrellas

I've been trying out back button focusing (BBF) for a couple months now and appreciate the advantages. It's particularly handy for stationary objects (which few of mine are!). It's placement for my smaller hands can sometimes put my wrists at wonky angles if I'm shooting from down on the ground, but I can certainly go back to shutter focus lock for those times.

However, I find I'm missing a lot of shots of moving targets trying to re-focus. I'm not sure what I need to do to disengage the focus before I re-engage it. Pressing the AF-On button again is ineffective. It seems like I need to depress the shutter button halfway to be able to reset AF-On, but can't find anything in the reference manual or the Nikon site that tells. With busy moving subjects, the half-press to the shutter AND pressing the AF-On button is fiddly. I also get a frustratingly large number of protected files, although did discover that in ViewNX-i, I can select all and unprotect the whole group.

I'm hoping someone here will be able to tell me more clearly how to use BBF, since the online info is pretty scant.

bruto

It should re-focus each time you press the back button, but if you are on single servo focus, it may have some difficulty. Also, make sure your focus point has not moved by accident, as it's very easy to do. Recenter it with the [OK] button periodically.

If you are going to use back button focus, I suggest you switch your servo to Continuous mode. That way, focus is continuous as long as the button is pressed, following moving objects, and ends when you let go. If you let go it will re-engage when you push the button again. One of the great advantages of BBF is that you can stay in Continuous mode, but still focus and recompose by simply letting go of the button. You get the benefits of both S and C mode at once, and in instances where a subject is moving fast, you can let go of focus and have release priority. That can be very handy for birds in flight, which are easy to lose focus on even when the depth of field is good enough. I use BBF on the D3200 with C and Dynamic Area focus, and it works well. It takes some getting used to, and I missed focus a lot when starting, but now I find it odd to use a camera without it. I have never had great luck with 3D focusing, which supposedly works better in some instances but I find it often loses the subject, especially when hand holding.

To say the online info is scant is like saying the evidence for fairies is scant. Yes indeed, the only real way you'll get ahead of it is to try it all different ways and make up your own instructions.

I don't know if some things have changed between the D3200 and D3300, but if not, one thing you should know is that BBF does not work at all with the infrared remote, though it does with self timer. It also does not work in Live View with AFF mode. If you are doing tripod shots at night with the remote, switch to manual focus or it will try to refocus without telling you.

By the way, also undocumented is a change that was made at some point in the evolution of Nikon DSLR's. Once upon a time, the BBF button did not actuate VR, which was still activated only by the shutter button. At some point before ours were made, this was changed, and VR is now actuated by both BBF and shutter button.

While on the subject of poor instructions, I might mention another one. As you probably know, when in shutter button focus mode, the camera runs in "focus priority," which means that it must find focus before firing. With shutter button focus in viewfinder mode, this is absolute. No focus, no shot. However, in Live View, focus priority is modified, and although it will try to find focus, if it does not, it will fire anyway after a couple of seconds. In LV you can take a picture with the lens cap on. Nowhere will you find this mentioned.

WelliesNBrellas

Thanks Bruto. You always give such thorough answers, which I appreciate.

I've been shooting in Continuous mode, so maybe part of my problem is that I don't really need to be refocusing as often as I do.

Another possibility is that, upon the advice of someone far more advanced than my little newbie self, I moved control of Exposure to the shutter button. For some reason, the AF-On is now behaving as you say it should, refocusing with each press. It's almost like it was toggling between a focus function and a Protect function before. Is that possible? In any case, my camera has behaved much better today.

Thanks for creating a safe place to ask questions!

bruto

It's possible that there's some difference between the D3200 and the D3300. On the D3200, if you turn "AF ON, " it always hands AE lock to the shutter. No other combination is available.

So, if you have back button focus on, AE lock will always occur on a half press of the shutter button. It sounds as if perhaps your advice ended up with the back button returning to AE and AF lock instead of true back button, or maybe the camera just had a momentary cramp. It would not be the first time for that either.

Again, once you're used to it, I think that's a nice arrangement, an easy set of things to remember, and individual control of both.

Anyway, I'm glad it's working better now, because I think once you're used to it, BBF has definite advantages. The main disadvantage is that you can't hand your camera to someone else to take your picture unless you put it back.

WelliesNBrellas

Now that you mention it, it's altogether possible the D3300 hands to AE lock to the shutter. The reference guide never addresses this, but then...say no more.

There was a setting in the menu that I changed that now specifies the assignment of AE lock to the shutter, which is not to say that it didn't have control before. It seems like things are behaving a little friendlier though, so I really couldn't say. "Momentary cramp", I like that!

bruto

Yes, I guess I either forgot or did not think to try it both ways, but you must make sure that AE lock is assigned to the shutter button, because if AF ON is enabled and shutter button AE lock is off, then you get no AE lock at all!

It looks from the D3300 manual as if they might have changed one thing, as the instructions no longer mention Live View AFF and movie recording as exceptions to back button focusing. I wonder if they also changed the behavior with the IR remote.

yobeone

I just discovered BBF, and I am thrilled to learn as much as possible to get the best possible use.

I did my first "panning technique" the other day and started getting a bit confused which focus mode to use. I tried AF-C and AF-A, as well as AF-S.

If I'm doing panning shots, or if the subject is moving and AF-C is engaged, would I still have to hold the BBF down while taking the shot? I would think not if AF-C is engaged.

bruto

Yes, you must hold the back button to keep AFC engaged. When you let go of that button, the camera stops all auto focusing in any mode and stays at the last setting. This is why it is often recommended to stay in AFC mode when using back button focus, since the main reason for AFS, which is the ability to focus and recompose, can be done by simply letting go of the button. In the D3200, AFS may be slightly more precise than AFC, according to the manual, but I have not noticed any significant difference, and keep mine in AFC.

If you're panning birds in flight, etc., you definitely want the AF button down throughout.