Here is an image that I consider very 3D. It comes, IMO, not from the simple DOF isolation, but from the fact that there are elements in between the focal point and the very out of focus stuff...a gradation of focus. I don't think this is required, but it helps. Sometimes when a subject is
thoroughly isolated focally, it can look a bit like a cardboard cut-out. In those cases the image can have what some would call 3D, because there is an obvious indication of the depth. But to me, they often look like three dimensional separation of a two-dimensional subject, if that makes any sense. It's more likely to happen with longer focal lengths, due to compression. One can still get 3D with a fully isolated subject, and I think Simon's images argue for that. But I think generally, that can only happen with a wider lens. Just my thoughts. I've seen the most impressive 3D from the Zeiss 35/2 Distagon, on full-frame cameras. I have the lens, but only in K-mount. This shot is from the Zeiss 100 Makro-Planar: