This is excellent, thanks so much for posting! I am always looking for the f/4 setting on my 400mm lens, but it just isn't there. Maybe some day!! Thanks Captain.
Cool series; you can see a change in the sharpness in the top of the piece of wood from aperture to aperture. Where was the actual focal point; in the center of the wood measured both ways?
If this doesn't help someone understand better why their background looks the way it does I don't think anything will. It just doesn't get any simpler than that!