Shutter release when back button focussing, but 'not focussed'

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 Fraser 01 Nov 2017
I've done something to my D7000 which I usually have set to back button focus, and I can't locate the cause of the rpoblem.

When I focus on a point using the 'back button focus' method, release the back button to lock the focus and recompose, I now can't seem to release the shutter unless the selected auto-focus point is (now accidentally) on a contrasting part of the image. I'm sure that until very recently I'd been able to release the shutter when I've recomposed away from the part of the image I'd focussed on, but this is no longer possible.

I've not been using this camera for 2-3 months and I don't recall changing any settings, but can anyone suggest what I've done or should now do?

Thanks.
 balmybaldwin 01 Nov 2017
In reply to Fraser:

Not sure on a Nikon but on a Canon the function is called Af lock I think. Allows you to do your focusing and exposure control on a particular point, lock the settings and then recompose and take the shot
 The Lemming 01 Nov 2017
In reply to Fraser:

I like to use the nuclear option for problems like this, and return my kit to factory settings.

Maybe you could set your camera back to factory settings and then set up for back button and see if this fixes the problem?
In reply to Fraser:
I have a D7100 and don't use the Back Button however I dug out the manual and had a play. If I use the Custom Setting menu item f4 set to AF ON then the back button does as you say act as autofocus but I can then release the shutter anywhere I choose. I can find no reference in the manual to a restriction. Perhaps if you go back to that menu and choose a different option then return to AF ON it might reset it to what you want.
OP Fraser 01 Nov 2017
In reply to all;

Thanks for the suggestions. I can still AF with the back button, so the AF setting must still be to 'On'. I seem to remember AF-C (for Continuous) being a setting which had maybe been adjusted somehow by accident.

It may yet come to doing a factory reset!
 MrRiley 02 Nov 2017
In reply to Fraser:

Hi Fraser, on my D750 there's an option which allows the shutter to release/not to release depending on whether focus has been acquired or not. Is it possible that somehow during your focus and recompose the camera is actually losing focus and you have the setting on which prevents the shutter firing in this case? The fact it allows you to release the shutter when you point to something contrasty maybe indicates its reacquiring focus and then allowing you to shoot.

Also, when using BBF you can keep the camera in AF-C all the time - hold the back button down for continuous focus, and press it once and release for single focus (effectively AF-S mode). It's super handy never needing to switch between modes.

Hope you get it sorted!
In reply to MrRiley:
That last tip works on the 7100 as well. I habitually use the shutter release to focus and AE/AF lock set to AE which suits my usage. It does mean I have to select the focus area using the selector button on the back. What particular advantages are there for using the back button focus?
Post edited at 16:01
 MrRiley 02 Nov 2017
In reply to keith-ratcliffe:

I quite like having the focus button disassociated from the shutter release so you don't have to keep that half-depression going. Plus if you accidentally lift off its not an issue as you won't have to re-acquire before shooting. The other benefit is for moving subjects where you can just leave your camera in AF-C and holding down the back button gives you continuous focus and pressing it once gives you single focus.

The contentious point is around focusing and recomposing - if you do chose to do this then you don't have to use AF-lock and there's no risk of the camera trying to re-acquire after recomposing if you've accidentally lifted the shutter release button. However, if your camera has a decent focus point spread I would never focus and recompose anyway (potentially dragging the focal plane off your subject). The only caveat is if the subject is outwith the focus point array...
OP Fraser 02 Nov 2017
In reply to keith-ratcliffe:
Pretty much what MrRiley said above.

I find it really useful if I'm hanging on a rope and the climber is coming near and past me relatively quickly. Because I generally shoot with an 11-16mm lens, I'm often within 1-2m of the climber, so large-scale recomposing of the shots is a given. This is exacerbated if I switch between landscape and portrait mode, causing the AF point I'm locking onto to constantly change. (I don't know why, but I always use a single AF point!) Having the ability to refocus or lock the AF with the back button, independent of the shutter release, just seems to save me time and minimises lost shots if the climber is moving relatively quickly and I'm shooting & struggling to recompose and refocus.

It does take a bit of getting used to, but I doubt I'll go back to the 'normal' AF method of using the shutter release button. There are some very good YouTube tutorials on the subject, which convinced me it was worth trying.
Post edited at 17:45
In reply to Fraser:
Thanks Fraser & Mr Riley - I will give it a try - I mainly do scenic work but can see some advantages of the method if I can only handle the new dexterity required!

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