trapper1 Loc: Southside Virginia

Why and/or when would this function be selected? If its use is better than the normal focus, why is it not used all the time? Just a newbie looking for insight.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

For me it saves me from having to switch from single shot to continuous and back. When I have focus taken off the shutter button, I am free to acquire focus with the back button and recompose, as well as hold the back button for continuous focus. I never use AF-S, only AF-C.

Bill_de Loc: US

I don't use it. If I did, I would use it all the time. Either BBF or shutter release can work equally as well, provided you set your camera up properly, In AF-C mode you can decide to use the back button to either activate or lock focus. I like having my thumb on the joystick most of the time to move the focus points.

Once you do that you can stick to the method you find works best for you.

BTW - After creating 60+ threads I think you need to drop the newbie label.

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wjones8637 Loc: Burleson, TX

To me it’s a personal choice. I like it others don’t. I can focus on the desired subject then with the focus locked I can recompose if necessary. For moving subjects I can continuously maintain focus without worrying about unwanted exposers from accidentally pressing the shutter button too far down while tracking.

Bill

mmills79 Loc: NJ

Back button focus makes it much easier to recompose a shot without messing up the focus. If you use the shutter button, every time you press the button 1/2 it will refocus. The natural tendency when you use the shutter button is to focus, then let up on the button when you recompose, then when you press the shutter button again, the camera will refocus, which is likely not what you intended. I also find that when taking action shots in continuous mode, like sports, using back button is just easier to maintain focus on a moving object.

srt101fan

Good video:
https://backcountrygallery.com/af-on-and-back-button-autofocus/

Grahame Loc: Fiji

For me, it is used all the time, enabling me to control activation (stop/run) of AF from one button catering for static and moving subjects.

It totally removes any need for me to use and change the AF-S/AF-C function.

frankraney Loc: Clovis, Ca.

It's all I use, 100% of the time. I have bbf (back button focus) and af-c (auto focus continuous) set. Press and release the bbf to focus once and recompose. Press and hold for continuous focus to follow a moving subject and keep it in focus. If not recomposing, I also hold the button down on a supposedly still subject.

larryzplace Loc: Elk Grove Village Illinois

It might be a good idea to watch a youtube video by Steve Perry a member here... It is extremely helpful and he goes thru the why's and what not to do... I had tried before watching his video... was not happy until I watched the video and never looked back...

photoman022 Loc: Manchester CT USA

I love bbf and use it exclusively. I don't know how many times, when I first started out in digital photography, that I tried focusing using the shutter release and wound up focusing on a nearby object and my subject was out of focus. Other times I would depress the shutter release, find focus, try to recompose and depress the shutter release and not have my subject where I wanted it in the photo. With bbf I press the bb, lock in focus, and take the photo. It's made my photographic life simpler and more enjoyable.

wide2tele Loc: Australia

Don't use it and don't think it's good "general" advice to give. I find the AF-ON button is best used for AE lock.

Craigdca Loc: California

I use shutter button focus to change focus for each shot, or back button to focus only occasionally. I look through the viewfinder with my left eye, putting my BBF thumb in my other eye on my T2i. Viewfinder focus seems better than Liveview focus most of the time on this camera, others I might use the BBF a lot more as others are sharing here.

twosummers Loc: Melbourne Australia or Lincolnshire England

It's certainly worth a try (but don't forget to focus). I tried it on real estate work and have never gone back. As others have stated it reserves the shutter button for just that. I often bracket so it's focus once (and it can stay like that for most of the property) and then concentrate on composition and shoot away! Others have said it's great for tracking say a moving person by keeping your finger on the BBF button and firing away. Takes a bit of getting used to but certainly worth giving it a go.

johngault007 Loc: Florida Panhandle

I wouldn't say one is better than the other, it's simply a different method to focus. I find it very easy to use on a 5D and going from primarily landscape photography to transitioning to any composition with movement it works pretty well. But everyone has their own style that fits their needs.

wide2tele Loc: Australia

I don't believe it's down to style, it's down to results. To be honest, I personally can't think of a situation I would use it for. I know it's recommended, we have the linked video etc etc but internet advice you have to take with a grain of salt. People on the internet are searching hits and I found looong ago internet advice is often unreliable.

I'll explain the reasons I don't use it.

First, if you are a AF-S user and are looking for accurate focus with the AF-ON button set in AF-C mode, you won't achieve it. You'll miss critical focus in a massive amount of shots.

If you are a AF-C user predominantly, using AF-C works best for me without needing the AF-ON feature. The only difference is AF-ON will give you that "hit/miss" AF-S lock option if your subject is stationary. The technique to achieve AF-S in AF-C is simply frame more loosely "if" required so you can place a focus point on the required target. The AF system will hold the focus quite well on your subject. You are not always "forced" to fumble around changing AF-S/AF-C modes as they try and tell you. The advantage you get without using AF-ON is once the subject does move, the camera will react far more quickly than you realizing, "Hey, it's moving now, I better press and hold the AF-ON button!"

Then there is VR. From memory it doesn't activate till you press the shutter button and very well may not have time to settle before you trip the shutter. Can't even recall if this is accurate to be honest so people need to check this out for their own camera model.

Then there is the comment made by Bill_de. Thumb available to quickly switch focus points is far more important than wasting it on the AF-ON button.

Finally there is AE lock. The AF-ON buttons are perfectly placed to assign AE lock which is a critical feature. This way even if you have a grip, AE lock is always quickly at hand in both camera orientations.

For speed, ease of use and results, I personally have found it is best to not use the AF-ON button for AF.