Focal length --> magnification,
sensor dimensions --> field of view,
lens entrance pupil --> perspective,
output viewing distance --> perspective distortion.
That's all there is to it. I'm sorry if the facts confuse you.
Bart, I don't feel at all confused. What I see are confusing statements from people defending the position that focal length of lens or FoV have nothing to do with perspective.
Consider your above statements. They're confused. Admit it. There's certainly no doubt that sensor size can sometimes determine field of view, but sometimes it can't. It depends upon whether one is increasing sensor size or reducing it. As you've admitted in a later post, the diameter of the lens image circle limits the maximum FoV.
It's clear to me that the role of the focal length of a lens is equally important in determining field of view, if not more significant in practice than is sensor size.
Given a specific focal length of lens designed for a specific size of sensor, one can reduce
FoV through cropping but rarely increase
it. However, given a fixed size of sensor, one can either reduce or increase FoV in accordance with the available focal lengths of lenses that fit the camera.
To avoid this confusion and false dichotomy, by ascribing magnification to the role of the lens, and FoV to the role of the sensor, I think it's better to use the 'focal length equivalent' terminology with reference to a standard format such as 35mm format.
I believe also that thousands of people in the photographic industry would agree with me. As I mentioned before, my Panasonic P&S has a marking under the lens, '28mm wide'. This describes the FoV very well in my opinion, and in the opinion of countless others it seems.
Even for many people buying a camera for the first time, who may never have used 35mm format, the equivalent FL in 35mm format terms is still a useful reference, as long as it is understood that 24mm is wider than 28mm and that 40mm is narrower than 28mm.
Below is another confusing statement from you, in reply #138, specifically "relatives sizes result from simple geometry."
It's the same thing, using a few more words to explain. True or actual Perspective is fixed for a given viewpoint (entrance pupil), and all relative sizes result from simple geometry.
Relative sizes do not
result from Geometry, whether simpler or not. Geometry is a passive system of mathematical description
. It doesn't cause anything. Long before the principles of Geometry were formulated, our ancestors were aware that the smaller appearance of the size of familiar objects denoted distance. They would have had to have understood this in order to survive. Geometry merely provides an explanation for this phenomenon.
There is also another aspect of additional confusion that results from attempting to join two experiences of perspective which are clearly separate, viewing the actual and real scene through a camera lens, and viewing a resulting 2-dimensional print of that scene in a completely different environment.
These are two separate activities. Whatever I do when processing an image to make a print, and whatever decisions I make as to paper type, print size, contrast and color saturation etc, etc, etc, and whatever placing of that print on whatever wall and whatever viewing distance is chosen by the viewer, are all factors that are only tenuously
connected with the original experience of perspective in the viewer and the photographer as he took the shot.
Once a print is produced, it becomes a separate 2-dimensional object in a different environment. The same principles of perspective will apply to that object as to any other 2-dimenional object in the same environment, such as a closed window or a stain on the wall.
To argue that by changing viewing distance to the print, in order to correct for an 'unnatural' or 'distorted' perspective in the original image that may have resulted from the choice of a particular focal length of lens, proves that focal length of lens has no bearing on perspective, is ridiculous.
That's pure sophistry, Bart, in the modern sense of the term.
The very fact that one could jump through such hoops when viewing a print, in order to correct for unnatural perspective, rather than just viewing the print from a usual and normal distance equal to, say 1.5x the print diagonal, tends to prove that a change in focal length or FoV without changing position, does indeed have an effect on perspective. If there's no change, there's nothing to correct.