Oh, and for the record, there is no 3D effect created or transmitted by a single conventional lens, merely an illusion of the feeling of 3D created...you're not gonna like this---mainly by the lighting of the subject.
I am sorely tempted to write nothing at all. Temptation has passed.
I agree with the first part of that sentence, we are talking about the illusion or feeling of 3D when we talk about a photo taken with one lens. Some also call it the plasticity of the image.
I do not agree that the impression is created mainly by lighting. It is true that lighting can contribute much to the feeling, some lenses seem to create this effect more than others.
Every time this topic comes up we have difficulties discussing it because all the comments made in this thread are made --
a) no two dimensional object (the photograph) can be three dimensional
b) no monocular (taken with one lens) image can create three dimensions
c) the illusion is largely the result of the subject, its placement relative to the other objects in the frame, and the lighting.
IMO:
a) is correct but misses the point
b) is correct and also misses the point
c) is correct in that the aspects mentioned can enhance the effect/feeling/illusion, but incorrect in attributing the whole effect to that.
In addition, our discussions of the topic are hampered because different people have different referents when we talk about the 3D effect. When examples are posted, many involve a foreground subject with san out of focus background which is seen to have "pop". These photos do, indeed, have pop, and that pop is enhanced by the differential focus, but that is not what I understand to be the 3D effect. The 3D effect I understand many, but not all people, to be referring to, manifest in photos where (nearly) everything is in focus.
My belief that some significant part of this effect is generated by the lens itself is supported by several points:
1) we talk about some lenses being "flat" -- that is, again in my understanding, as not producing any 3-dimensionality
2) by the fact that I perceived this illusion with some lenses and subjects when the lighting did not conform to the kind of lighting usually tied to the effect (cross lighting of some sort) but was, rather, uniform top lighting
3) folks more experienced (i.e. with exposure to more photographs and more lenses) than I refer to this property in some lenses and not in others.
I think if we want to break out of this cycle, and we may not, it would be helpful to view a number of photographs and agree on which ones exhibit the effect, and then examine the lenses involved. To gild the lily we could then shoot the same scene (same sensor, same lighting, etc) with the same lens and other lenses commonly taken to be "flat" and do a blind viewing (no pun intended) to see a) if most people discern such an effect and b) consistently attribute it to the "correct" lens.
End of rant, with added apologies for length.
Giorgio
