Also, the smaller the aperture, the wider the DoF will be, making it more difficult for the camera to decide which of the points in acceptable focus is where you want your focal plane. The focal plane could be moved forward and backward within the wider DoF. You won't know what it's done until you see it in on a monitor or TV. Hence the preference or using Live View for manual focus. In Live View with focus assist you actually watch the DoF shift as you manually focus, as opposed to letting the camera decide where it thinks you should focus.
In images like this...
I use Live View to determine the front and back of the depth of field, because the front and back edges of the DoF is more important than selecting the exact position of the focal plane. This is something that s far as I know, AF cannot be programmed to emulate.
Using an f4 lens stopped down for landscape with everything from 10 feet to infinity in focus, you have a lot of leeway with the exact technical focal plane is. Most of the time, it's not an issue. When your actual focus is 30 feet to infinity, and your lens can do 10 feet to infinity, you really have to mess up to have part of your image out of focus, but it can be done. I've had it happen. If precision is required, AF is always a crap shoot.
Last edited by normhead; 01-15-2021 at 08:53 AM.