Back Button Focus

[Gavjenks]

I don't use it (generally) but I set my release to lock AF/Exposure so that I can recompose. Simply locking focus and recomposing while using BBF will allow exposure to change if using center or spot metering as I do. Or am I missing something?

Also an option. Technically this is not quite as powerful as back button focus, though, because there's no way to ONLY focus without, say, metering or engaging IS if it is available.

Not that I can think of any particular situation where that would be very useful. Other than just saving a small amount of batteries on average.


Additionally, though:
Button 1 = "A and B" Button 2 = "notA"
involves a conditional relationship more logically complex than the additive relationship in:
Button 1 = "A" Button 2 = "B"
Which also means it's easier for me to mess up while under stress.

 

[Trever1t]

Yes Derrell and Gavjenks, many ways to skin a cat, or so they say. I just find it quicker to do it with the shutter release for 95% of what I shoot which are static subjects.

 

[Derrel]

Trev1,

I looked around to find a GOOD article for D800 users. Here's the best article I can find tonight.

Using the AF-ON focussing technique with the Nikon D800 | apple-and-eve.com

Keep in mind, this article presupposes having set the D800 to use AF-C or Continuous autofocus, for almost all situations.

For those who want more understanding, the thread where this article was introduced is well worth a look D800 AF-ON focussing technique - Photo.net Nikon Forum

Back-button focusing is often described as a panacea, some magic form of camera handling knowledge that will magically perform miracles. It's not.

I have to agree...with Nikon's focusing area assignment controls with the big multi-controller on the back of the camera, using the shutter release button to both lock and activate focus is really quite easy for most subjects, especially if you want to go between shooting verticals and horizontals, and use the two shutter release buttons as the focus initiation and lock. But, again, there are literally different "systems"....older Canon consumer bodies used the star button that had to be custom-programmed to take on the AF-ON function; newer Canon models added the dedicated AF-ON button; the pro Nikons have different systems for AE-L and AF-L and AF-ON; the newer bodies D800 and D4 and D7000 series have the "new-style" AF-S and AF-C and Manual focus selector mode switch on the front of the camera...

All of this makes Back Button Focus a potentially VERY complicated or very customizable system, where the user can make a button LOCK focus; or initiate focus until the button is pressed again; or hold focus ONLY while the button is held in; and then there's the Auto-Exposure side of the equation; the pro bodies have one set of options, the consumer bodies have another set. And again, depending on the camera, the AE part of the equation can be set to allow the button to LOCK the autoexposure, or to allow the exposure to run "free", while locking the focusing.

Back button focusing is not just "one,specific thing". It can mean many, many different things, and can control both focus, or exposure, or both, in various ways.

 

[snerd]

Yes, the different ways to set up my 7D BBF:

1: Metering + AF start / AF stop
AF is still at shutter button. Pressing the rear button will actually LOCK the focus; potentially useful if you shoot a lot of moving subjects in AI Servo AF and prefer to activate AF with a conventional half-press of shutter button. Focus is unlocked by removing thumb from back-button.

2: Metering start / Meter + AF start
Back-button AF activation. Shutter button no longer activates AF, but of course fires the shutter. Metering is continuously updated — if you shoot a sequence of pictures, the camera takes a fresh meter reading for each one. There’s no locking of exposure, unless you separately press the AE Lock button (this last item is not possible on some EOS models).

3: AE Lock / Metering + AF start
Back-button AF activation. Difference between this setting and option 2 directly above is that when you press the shutter button half-way, your exposure is locked and won’t change until you pull your finger off the button entirely. Thus, if you shoot a sequence of pictures in any auto exposure mode, the exposure setting used for the first shot is used for each subsequent shot. Can be useful if you were using back-button AF to easily lock focus and shoot a series of portraits, where you wouldn’t expect lighting to change.

4: Metering + AF start / Disable
Similar to setting “0” above, but now, the camera’s rear AF-ON button is disabled. AF activation is at the shutter button. Convenient if you’re worried about accidentally pressing the back-button and don’t want to use back-button AF.

And some reasons listed for doing so:

Easier to lock focus
If you are shooting something like a series of portraits of a person, and you want them composed off-center, back-button AF makes it super-easy to take as many pictures as you want. Focus on your subject by pressing the rear button (more on which button later in this article). Once in-focus, take your thumb off the rear button. Re-compose the shot to move your subject off-center. Shoot as many pictures as you like. With focus activation removed from the shutter button, you now can fire any time you like, and remove your index finger from the shutter button after a shot is taken. No matter what, the camera makes no effort to re-focus when you press the shutter button half-way down again.

Easier timing of shots
Similar to point number one above, but yet another benefit of pulling focus away from the shutter button is that critical timing becomes simpler to manage. For example, if you were shooting a speaker at a podium, he or she might periodically look up or make a gesture that would be an ideal instant to capture. If you’ve focused with back-button AF, your index finger is free to shoot at the decisive moment. There are no worries about holding your finger half-way down and waiting, waiting, waiting in that position for your subject to do something interesting.

Even with a very animated subject that may be moving around, you can have your camera’s focus set to AI Servo AF (to track any movement), and just keep your right thumb on the back button to keep focus active, while your index finger can be ready to shoot with no worries about also preserving focus.

Less risk of focus errors with moving subjects
For sports photographers and others taking action pictures, back-button AF lets you stop focus whenever something might interfere with the moving subject you’re tracking — without requiring you to stop shooting. In sports, for instance, it’s common for a referee or another player to come between the camera and an athlete being photographed. With back-button AF, it’s easy to momentarily pull your thumb off the rear button, and you can still keep shooting by pressing the shutter button fully. The camera instantly stops focusing when your thumb comes off the back button. Once the obstruction is out of your way, you can immediately pick-up your primary subject by pressing your thumb on the back button again.

Easier over-riding of AF with full-time manual focus
More than half of Canon’s lenses have a neat feature called full-time manual focus*. Even if the lens’s AF/MF switch is in the AF position, these lenses allow the shooter to instantly adjust focus manually by simply turning the focus ring on the lens. There’s no need to first move the switch to MF.

With back-button AF, this becomes a nearly foolproof feature. Use the autofocus whenever you like by pressing the rear button with your right thumb. Shoot whenever you like by pressing the shutter button. And if you want to touch-up focus, or totally over-ride what the AF is doing, just pull your thumb off the rear button and turn the ring. No matter how many pictures you shoot, pressing the shutter button will not cause the AF to try to kick-in and re-set the focus you just adjusted manually.

Easier macro and close-up focusing
Many times, you’ll find that it’s actually easier to get consistently sharp close-up pictures of small objects by pre-focusing, and then moving yourself forward or backward until you see the critical sharp focus appear in your viewfinder. Once again, with back-button AF active, you can use the AF to get within general range (press the rear button with your thumb, then take your thumb off the button), and move a little bit to get things critically sharp. Most important, you can then shoot freely, without AF trying to re-focus each time you touch the shutter button. Finally, touching-up focus with the full-time manual focus feature on certain Canon lenses is simple and quick, and the autofocus never fights you by trying to un-do what you just adjusted.