I was trying to take a shot - well lit, not from a weird distance, just a park bench about ten feet away... Nothing weird. But my Nikon D3200 refused to trigger the shutter unless I hit the AE-L or placed the lens to manual focus. My question is... Why? What causes that? What can I do to avoid that? Is it "OK" to just lock the settings and take the shot when that happens? Any information welcomed... Thanks a lot.