Backbutton focussing

[At The Gates]

Mainly to stop the camera refocusing. If you focus once with AF-ON for example, instead of the shutter then the camera will not refocus until you press it again. Without it with the shutter held all the way down it will continue to refocus which is a nightmare for example if your subject's distance doesn't change but objects before your subject come across the camera. With AF-ON focusing it won't hunt and start refocusing. You will still have a blurry object moving across your focus path but as soon as it's gone your original target is still in focus. It means you'll also get the full FPS out of the camera since the camera is not continually focusing.

 

[Vertigo]

Mainly to stop the camera refocusing. If you focus once with AF-ON for example, instead of the shutter then the camera will not refocus until you press it again. Without it with the shutter held all the way down it will continue to refocus which is a nightmare for example if your subject's distance doesn't change but objects before your subject come across the camera. With AF-ON focusing it won't hunt and start refocusing. You will still have a blurry object moving across your focus path but as soon as it's gone your original target is still in focus. It means you'll also get the full FPS out of the camera since the camera is not continually focusing.

I guess it could be useful in such a situation but frankly I'd just let the camera re-focus for each shot as it hardly takes very long and reconfirms the focus on the off-chance the subject has actually changed distance. If something comes between you at the exact moment you press the shutter button then yes, it'd focus on that instead but you just wait until it's gone then focus again.

If you had a genuinely static subject which you were going to take a lot of shots then I guess it'd make life a bit easier but this so rarely happens in my experience.

Don't get me wrong, I'm not rubbishing BFF at all. I've read enough posts from proponents of the method that it must have real value, I'm just struggling to understand it fully. Whether that's because I've not got my head around the benefits or because its usefulness is limited to situations I rarely find myself in, I don't know

 

[413x]

i have been trying it today and it is awkward, i keep pressing the live view button by mistake
i dont think i really needed it today and meant i needed to hold down two buttons as opposed to 1

 

[Devrij]

This is no different to normal focus and recomposing - just focus on the subject with a half-press of the shutter then recompose and take the shot. The exposure isn't locked until the shutter is released.

I don't doubt that BBF is useful is situations but I still stuggle to understand exactly what they are.

That's not how it works for me. If I were to half-press to focus on a subject, then recompose and fully depress the shutter button I would have an exposure reading weighted to the active focus point as it was when I half-pressed the shutter.

I regularly do this as I described in my post above, so it definitely works. I get my exposure reading from where I want it, and my focus from where I want it, and then I can recompose and shoot independently of both.

I also find it handy when using continuous focus on a moving subject as I can just hold down the focus and let it track my subject while I choose my shots. Granted, this can be done with the default setup, but I find it easier with BBF.

 

[Devrij]

i have been trying it today and it is awkward, i keep pressing the live view button by mistake
i dont think i really needed it today and meant i needed to hold down two buttons as opposed to 1

It takes a bit of getting used to, but it'll soon be second nature.

 

[THC_SsSsSnake]

hmmm.

 

[Vertigo]

That's not how it works for me. If I were to half-press to focus on a subject, then recompose and fully depress the shutter button I would have an exposure reading weighted to the active focus point as it was when I half-pressed the shutter.

I regularly do this as I described in my post above, so it definitely works. I get my exposure reading from where I want it, and my focus from where I want it, and then I can recompose and shoot independently of both.

Ah yes, you're right - if using evaluative metering and one shot AF, then a half-press of the shutter button does lock exposure, my mistake.

 

[englishpremier]

I was looking into this recently and found it useful on lenses and/or camera's that don't have a manual focus switch.

I'd still prefer it if I could focus with the shutter button then press a button to lock or unlock that focus.