[altarius]

I think you are talking past each other, depth-of-field is dependent on the physical aperture not "F-Stops", which are often also called "aperture". Yes, afaik it's derived from single-element lenses but so are most other measures, and I'd be surprised if a real lens behaved different (at least in the center).

Your 35mm f/1.4 lens has a physical aperture of 35mm/1.4 = 25mm, so the equivalent 70mm lens with a 25mm aperture would have an F-stop of f/2.8. Hmm, can't think of many modern 70mm lenses besides Sigma's 70mm/2.8 macro which should have the same DoF, or if it's a standard zoom they should have equivalent DoF as well (unless it's Canon's f/2 zoom).

The (acceptable) depth-of-field is derived from blur-disk diameter, and the circle-of-confusion, for an object at a certain distance from subject ("point of focus") and relies only on physical aperture and distance to subject as stated (or alternatively, f-stop _and_ focal-length, because "phys. aperture = focal-length / f-stop").