Well,
If I would intend to increase my sharp pics, in a manner to properly pick my aperture for the subject, I would stop down my aperture to 5,6 - 8, sometimes 11-16.
What I found out, is fact that I really don't know where is the exact depth of filed, where my subject is still sharp.
I mean, if you point your camera to the subject and nail focus on it, it would be sharp, but does that "sharp field" covers the space from that point forward or far from you and subject, or the sharpness also exist in the space in a front of you, and in a front of subject?
In other words, WHERE IS NAIL FOCUS POINT IN SHARPNESS FIELD. IN THE MIDDLE OF IT, JUST ON BEGINNING OR IN THE END OF IT.
From what I know, there is no way the nail focus point starts at the end of sharpness, because everything behind will be blurred, in smaller apertures like f8 or f16,
and it's not the case.
But the front field in a front of subject is questionable ... Is the nail focus from your camera on the beginning of sharpness, and everything in a front of is blurred,
or the nail focus is somewhere in maybe middle of that field.
WHY I'M ASK THAT?
because, when I try to catch some moving objects, and when I'm increasing my sharpness dof by stopping down aperture to f8, or f5,6, I want to know WHERE EXACTLY MY SUBJECT CAN MOVE AND STAY SHARP.
If the nail center of camera begin where sharpness begin, that means my subject can not move any closer to me, only away from me.
When I'm shooting some singers on the stage, I like to isolate them with blurred background, and because they constantly move, it's hard to guess where is your sharpness field.
I don't know am I do good explanation here, but I hope you understand... I can bring some graphics later to better visualisation