I agree completely. 3-dimensionality and depth of field are unrelated.
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How can that be? As I mentioned before, the two most obvious clues that tell the brain it is perceiving a 3-dimensional image when in reality the image is 2-dimensional are (1) distant objects are smaller than near objects, (2) objects that are partially obscured by other objects can only be obscured by objects that are closer. Those are basic concepts we begin to learn as babies.
There is some story I recall related by Michael R, about a remote tribe of natives who had spent all their lives in dense jungle and who had never seen anything further away than a few metres. When they were led out of the jungle by some anthropologist who was studying their culture, and saw for the first time a vast open vista, a plain below the cliff's edge stretching for miles, and what appeared to be in the distance grazing cattle, these natives assumed that the cattle were ants because they were so small. It was difficult to convince them that these tiny creatures were actually huge wildebeeste, presumably because that would have introduced an entirely new concept to their hard-wired brains, namely that there existed vast areas without trees stretching for great distances.
In this sense, great (or extensive) DoF is required for a good 3-D effect. If you can't recognise to some degree those small objects that denote distance, because they are out of focus, then it's difficult to understand how one could get an impression of great 3-dimensionality.
On the other hand, as photographers, we know that those things in that 2-dimensional image that are out of focus are out of focus precisely because they are at a greater or lesser distance than what's in focus.
In the other thread where some photographers posted examples of MFDB images that exhibited, in their opinion, a heightened sense of 3-dimensionality, I recall most of those images had a fairly shallow DoF. For example, a model sitting in the middle of a road with the foregrounf and background clearly OoF, or a close-up of a face with the eyeball and eye lashes razor sharp but the cheek surrounding the eye slightly OoF.
I would suggest what's happening here is, we know from experience that the distance between an eye and the surrounding cheek is very small, in fact so small that it
could be in the same plane depending on the angle of the shot. But we also know that areas that are OoF must be at a different distance. If the surrounding skin were as sharp as the eyeball, it would not be so clear as to whether or not that area of skin was in the same plane as the eyeball. The fact that the surrounding skin is OoF gives the brain the clues it needs for a heightened sense of 3-D.
In the 2 photos of the charcoal drawings in the beginning of this thread, the hands in the foreground are noticeably OoF as well as the back of the head and parts of the clothing, although these differences between what's in focus and what's not in focus have been diminished as a result of downsizing and jpeg compression, which is why these photographic reproductions do not have quite the same feel of heightened 3-D as the original drawings.
You must all be familiar with the phenomenon of a large print that has a discernible shallowness of DoF ceasing to have that same shallowness when reduced to postcard size.
If we get back to this concept of the primitive native who has never witnessed large distances, we might speculate that a similarly remote tribe who was not familiar with the photograph, would not appreciate any heightened sense of 3-D from images with OoF foregrounds and backgrounds.
Hope this is now as clear to you as it is to me .
