I was looking at Area AF focal points using the feature in NX Studio and noticed that some of my NEF images showed them while some did not. I believe that this may be because I hit my back button focus before shot 1, which shows the focus points, and then did not press again before taking shots 2 and 3, which do NOT show focus points. Image 4 again shows them, which matches with probably me feeling that I had focus and didn't need to refocus in the moment. Is this a correct assumption? Do the focus points only show up if you hit bbf prior to each shot? If so....why? Aren't the focus points still there on shots 2 and 3? I don't see any change in the focus, it would simply be nice to be able to pull up the points.
When using Area AF, it appears that the camera is choosing some number of the points that would lie along a plane of focus and discards some number of points that do not. Is this a simplified explanation of the process?