Back button focus - what am I doing wrong?

[steveatesh]

I have begun experimenting with BBF to see if it offers any advantages as some say on here and elsewhere.

I have a Nikon D5100 camera and through the menu set the AE/AL button to be used for back button focus. I have read it is a good way of focusing on an object then changing composition to get the shot you want, without having to keep the shutter button half depressed as you move the camera to recompose.

So I focus on a subject, then recompose but occasionally the shutter will not release after re composing. The instructions say that as long as I don't change the distance between the camera and the subject it should fire.

Clearly I'm doing something wrong here, or my expectation is wrong.

What's the trick to using BBF to focus on an object, recompose the shot (I don't change position at all when doing this, just swing the camera around to allow recomposing), in a way that the shutter fires on each occasion rather than when it feels like it?

If I can't sort it I'll have to go back to the half press of the shutter release buttons I'm afraid!

[Mroad]

To get the shutter to fire, assuming you are in AF-C mode, you need to change the AF-C Priority mode to Release which means it will fire without checking if it's in focus.
It's currently thinking when you swing the camera away after pre-focussing that the new object or where you are focussing now is slightly out of focus and won't fire.
If you are in AF-S mode you have to focus with the back focus button (AE-L) and then keep it held down, recompose, fire the shutter when ready then let go the back focus button. There is no option to override the release in AF-S mode so if you let go of the back focus button the shutter won't fire.

Back Button focusing is not for everyone but once I switched it seemed a lot more logical. Some cameras are better set-up for it than others.

Edited by Mroad on Saturday 9th April 02:37

[WWA]

Mroad has answered your question but I will just add that once you get used to BBF you will most likely love it. I find it great for wildlife photography as well as everyday photography. Took a while to get used to at first.

[steveatesh]

Thanks guys, that explains it - I was using the BBF to focus on a point then taking my thumb off it believing the focus would remain locked, then recomposing and using the shutter button to take the photo of course (or try to!) and being frustrated when it would not fire.

So hold the AE/AF to focus and keep it pressed, then recompose and shoot.

And who said men couldn't multi-task!

Cheers, off to experiment

[peter tdci]

Not familiar with the D5100, but on the Nikon DSLRs I've had, the default settings need changing to do what you were trying to do.

If you are in AF-S mode, custom setting A2 (autofocus - AF-S priority selection) needs to be set to 'relase' (the default for AF-C is already 'release', but for AF-S it is 'focus'). This will allow you to use BBF to focus somewhere in your frame, take your thumb off the button, recompose your shot and then press the shutter release button. The camera might 'think' it's out of focus, but the A2 setting will allow the shutter to fire.

There might be some drawbacks to changing the setting and, as Mroad said, keeping the button held down in AF-S mode doens't change the focus point when you recompose and has the same effect.