Quote Originally Posted by Roger Krueger View Post
Sorry, that's clearly incorrect for circumstances where the wider lens is even slightly near (or beyond) hyperfocal. Try it on dofmaster...at f22, 30mm @ 4ft. gives you 36.7 ft. of DoF vs. 300mm @ 40 ft. gives you 7.23 ft. of DoF. But at f2.8 it's only .91 ft. vs .89 ft.

Again, it is just f-stop and magnification, but it's magnification at the point whose focus is being considered, NOT magnification at the plane of best focus. Since you can't keep all of the magnifications the same for different FsoV you get different DoF results.
You are absolutely wrong. Unless you live in a different universe, physics says that you are wrong.

I have posted in the past that while I was studying optics at Kodak, that I raised the question about why when I kept the image size and exposures settings the same, I could not get a better depth of field by changing lenses. The optical engineer started with the depth of field equation and made one substitution. Four lines later the focal length was in every term and then was divided out. The result is exactly as Q.G. stated.

When magnification and f-stop are constant, DOF will be too, no matter how large or small the frame.
Steve