Back-button focus: why?

For those of you who use back-button focus (i.e. changing the behavior of the shutter button half-press to be just 'metering start' instead of 'AF + metering start', then using the AF-ON button to start AF), why do you prefer BBF?

I say this because I considered BBF for a bit, then realized it would completely confuse my wife, and we share cameras a lot. Instead, I change AF-ON to be AF-STOP, leave my cameras in AI SERVO almost 100% of the time, and just hold in the AF-ON button on the rare occasion I want focus lock and/or manual override. This saves my thumb from an endless workout of holding in the button, and saves me from having to make sure I'm always shooting in a position where my thumb can always hold that button in.

I started using it when I got my macro lens and my Kenko 1.4x TC. With both the macro and the TC the focus may not always be right where I want it, so I adjust the focus manually just a bit. If I then press the shutter button, it refocuses back to where it was. I could set the lens to MF, but if my next shot will be AF only, that becomes a pain. By using the BBF, I can get a focus close and then nudge the MF ring and shoot without having to worry about the lens readjusting itself. Try focus stacking with the shutter button set to AF. Doesn't work well.

I think both these ideas are helpful depending on the type of photo you do.

I have been using back button focus exclusively for at least 2 years. It works very well for birds, especially flight shots where you can continuously adjust focus with your thumb and shoot with the index finger. Also, even though I may be in AI Servo, it can mimick One Shot mode in that you can focus using the back button and then re-frame the image before firing the shutter. I was unsure at first but it seems very natural and easy to use.

Peety......I've been using the BBF for about 6 years now. Like Joel, I shoot a lot of birds and was frustrated w/AF (on the shutter release) losing the subject then searching to re-focus. For me personally, the BBF just fits my shooting, of all my subjects, better.

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Originally Posted by Joel Eade

It works very well for birds, especially flight shots where you can continuously adjust focus with your thumb and shoot with the index finger.

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Just playing devil's advocate, you can continuously adjust focus with your index finger and shoot too.

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Originally Posted by Joel Eade

Also, even though I may be in AI Servo, it can mimick One Shot mode in that you can focus using the back button and then re-frame the image before firing the shutter.

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Extending the devil's advocate, this is probably a rare thing, so why "work" for 85-95% of your shots to mimic One Shot when you could instead remap AF-ON to be an AF-OFF button for that 5-15% of your shots to mimic One Shot?

BBF is nice for birds because you can get your focus right and then just wait for the bird to do something... when it moves you're ready to start taking shots. Without it the camera might screw focus up before taking the shots.

Maybe with 1DX, 5D3 etc it isn't an issue, but BBF is worth its weight in gold with the xxD, 6D, and Rebel cameras.

Dave

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Originally Posted by peety3

Just playing devil's advocate, you can continuously adjust focus with your index finger and shoot too.



Extending the devil's advocate, this is probably a rare thing, so why "work" for 85-95% of your shots to mimic One Shot when you could instead remap AF-ON to be an AF-OFF button for that 5-15% of your shots to mimic One Shot?

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It's easier (for me) when I am tracking birds in flight to intermittently "bump" the focus with my thumb or hold the button down with my thumb and shoot when the time is right with my index finger rather than try to constantly re-adjust with a half shutter press. Also it really isn't any extra work to focus on a relatively stationary object, like a perched bird, using your thumb and then re-compose the shot in the frame before firing the shutter. Using the back button focus this way I can stay ready for both stationary and flight shots all the time. I was skeptical too but I suggest you try it for awhile. I was pleasantly surprised how easy it was to get used to and how natural it feels.

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Originally Posted by peety3

Just playing devil's advocate, you can continuously adjust focus with your index finger and shoot too.

Extending the devil's advocate, this is probably a rare thing, so why "work" for 85-95% of your shots to mimic One Shot when you could instead remap AF-ON to be an AF-OFF button for that 5-15% of your shots to mimic One Shot?

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I 'prefocus' a lot. For perched birds, portraits, and other subjects where the distance isn't changing but I want to capture a key moment/expression, traditional BBF works better, IMO. I can relax and wait for the moment, then just press the shutter. I don't want the delay the AF step would impart. With AF-STOP, I'd have to continually hold the button while waiting for the shot (or press it just before the shot, but why?).

I suppose either would work, once one got used to it. But for the reasons above, as well as Joel's statements, I find AF-ON preferable.

Here is an explanation of what "bump focus" means and why it is particularly useful for BIF. Of course it can be done with half shutter press but I like the back button method better. http://www.birdphotographers.net/for...-focus-for-BIF

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Originally Posted by Dave Throgmartin

Maybe with 1DX, 5D3 etc it isn't an issue, but BBF is worth its weight in gold with the xxD, 6D, and Rebel cameras.

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This is what I discovered.

I was very frustrated with the focus, especially in AI Servo, when shooting birds against busy, branch-heavy backgrounds. Focus hunting was awful on my 60D. After switching -- as recently as a few months ago, I woke up -- I'm back to considering a 6D as a viable FF option, though the center point is inferior to my 60D on slower than 2.8 lenses. Depends on how much Santa and my employer's Bonus Fairy brings.