With some ultra wide angle lenses, autofocus is next to useless because of the extreme depth of field. It's easier and generally better to leave them on manual focus set to a distance that makes the most use of your extreme depth of field. However, manual focus is not the only way to do it. With some not-so-ultra wide angles I will focus on a spot that is in the middle of the range where I want my depth of field and use the focus lock on the camera when composing the frame. Another thing to consider is that just because the chart says your subject is within the "acceptable" focus range, doesn't mean it's going to be optimally focused.

There's a few smart phone apps that simplify everything for you. The one I use is Photobuddy.

That's the way I use my D7000. AF only turns on when you push the button. It takes a while to get used to it, but it's well worth it once you do. AF only works when you want it to.

then shoot. When I touch the focus ring, focus assist comes on.

My next camera will have focus peaking.

I was always good at math and someday I will learn to use my camera thanks for the link

It ain't art, just a test. Notice the foreground is in focus, and so are the trees in the background. I was shooting into the sun and had some nasty lens flare (cheap lens). Cloned it out in the grass, but the flare on the bottom right path is poorly done.

DOF preview button comes in handy.