My Nikon D3000 refuses to take a picture if I focus and recompose with the AE-L/AF-L button set to "AF ON". (The focus point is on an out-of-focus part of the image after I recompose, so the shutter doesn't fire. See further info here.)
On my Nikon F80: I select the single focus point I want to use, focus on the subject by pushing/releasing the AE-L/AF-L button, recompose to put the subject where I want it (focus point is now on the out-of-focus background), push the shutter release and the shutter fires.
Reading the manuals for these two cameras, the description is very similar but the behaviour is obviously different. What is the name of this feature? How can I determine if a camera has this ability? Is there a menu setting on the cameras which do have this ability which controls this?
I realise that there are other methods of achieving the same effect: using manual focus entirely, switching to manual focus after autofocusing, setting the button function to AF-L to lock the focus when held down etc. I am more interested in the exact functionality as described for my Nikon F80.