f11 is not considered at peak sharpness. Usually f4 to f5.6. Diffraction effects are noticeable at f11. I used to be a resolution freak. Still am. Lens design is a compromise. Also, when stopped down, the depth of field is 1/3 in front and 2/3. So, sometimes it pays to focus slight in front of your subject matter if a large depth of field is important. Back in the day our cameras had depth of field buttons, when depressed stopped the lens down, so you could judge the range of focus. My ultra modern digital doesn't have that feature.

I would love a fully manual digital.