Make a crib sheet of your own DoF tests.
(Pretty much disregard what's printed on any documentation. Do it yourself.
)
Mount your camera on a tripod.
Pop on lens A.
Set the aperture to as wide open as it goes.
Find a long surface to shoot, like a couter top or fence railing.
Run a METRIC tape measure out, tape head at the tripod's center column support.
Zoom max out - everything should pretty much be in focus.
Roll video for review on a computer later.
Now, zoom max in - very little should be in focus, a narrow DoF.
Roll video.
Repeat at successive stops.
Document precise measurements of what the ACTUAL focal fields are at different f stops and zooms.
Repeat with all your lenses.
Make a crib sheet of what's in focus where, enter this into a spreadsheet program so that you can always print a new one out when the current print out gets lost.
"Lens A @ fX has a Ycm sharp focal field between Zcm and Acm out (from a fixed position, the tripod's central column.)"
Keep this DoF by f stop x zoom crib sheet print out in your camera bag.
Now you can go into a situation, figure out what and where things in motion are going to be, where you and the camera with what lens are going to be OR NEED TO BE to achieve the effect you want, and refer to your crib sheet to KNOW how much focal leeway you can move around in.
“At f2 on my Xmm lens I have a crisp Ycm DoF between Z and A.
I can move within a known range to maintain constant focus.”
Or - you could change the f stop.
Or - you could change lenses.
Or - you could change your movement.
Or - you could change the action's movement.
Or - just redesign the entire shot to accomodate the limitations of the available equipment.
But KNOWING what your euipment can and can't do is a good beginning.
And you can pretty much forget trying to do anything very precise by looking at a camera's cr@ppy little 3" screen.
You gotta learn to trust the numbers. It's just math.
