Thank you for the reply. However, the first reason you mention can be done by clicking the focus lock button. (Or doing it "backwards" if the button is set for exposure lock.) For the second, I use the "tracking" setting. To me, these seem simpler than fooling with BBF. But, I guess it's all a matter of what one is used to. Thanks again.
via the lens wrote:
One very basic advantage would be, if you were on a tripod taking a shot of a waterfall, you could first focus where you wanted your focus to be, then roll your focus/exposure point to the brightest part of the waterfall for exposure, right where the sun is hitting it, and then click the shutter button. This way you have exposed on the water which, if not exposed correctly you might blow out, but focused on the overall scene as you wanted. Another advantage is that, while shooting wildlife in flight, you can easily keep clicking the back button as the wildlife moves along if it is moving out of the focused range or just leave it as is if the bird does not move out of the focus range you've set. Once you set the focus it remains at that setting until you hit the button again. If you use the BBF for awhile it becomes very second-nature to use it correctly.
One very basic advantage would be, if you were on ... (
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