This is my understanding, but since I do not claim to be experienced this might be right or wrong
:
(1) If you change the camera angle this will change "the angle between the top of the sign and the top of the frame".
This is more or less how I imagine the situation to be, and following from this situation are two puzzling factors in relation to the claim that only distance to subject has any bearing on perspective.
As I've mentioned before, the proof offered so far to demonstrate that focal length of lens used has no bearing on perspective is the situation in the two images I've prsented above. Or to put it another way, the proof offered so far is in this thread, is essentially a very obvious statement to the effect if one takes two shots of identical scenes from the same position using identical lenses, then the resulting images will be identical.
Now I pride myself on having at least a reasonable grasp of logic, and I fail to see how an experiment demonstrating that effectively identical lenses used from the same position produce the same sense of perspective, is proof that non-identical lenses used from the same position also produce the same result.
If we agree that in order to shoot that sign with a different lens, say a 140mm lens, I would have to turn slightly to the left and by doing so would change the perspective of the sign in relation to the sign as cropped from the 24mm shot, then surely that demonstrates that focal length of lens does have a bearing on perspective.
Bear in mind that by turning slightly to the left in order to take the shot of the sign, I have not changed the distance from the camera to the sign and have therefore not stepped outside of that definition that perspective is only affected by distance to subject.
So, if we agree that these points are true, it follows that the statement
"perspective is only affected by distance to the subject and has nothing to do with focal length of lens", cannot be true.
It should be noted that if you point the camera in another direction you take a different photo, NOT a different crop, and it makes no sense comparing.
Good point! If you
don't point the camera in a different direction but use a different focal length of lens instead, have you not also taken a different photo?
Why would it makes sense to compare two photos that are very different in content and composition, as a result of the focal length of lenses used being different, but
not make sense to compare two photos of precisely the same subject taken from the same distance, with the shot using the longer focal length being turned at a slight angle out of necessity?
Perhaps the definition should be changed along the lines, "Perspective in photographic images is affected by both distance to the subject and angle of view."
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