Originally posted by Marc Sabatella You'll have to clarify your usage of the word "perspective" here, then. The usual definition that has been around for several hundred years most definitely is *not* affected by any such thing. The relative positions and sizes of objects don't change, the angles formed by converging parallel lines don't change, the location of the vanishing points don't change, etc.
The relative positions of things appear to change because the relative sizes of their images should change but don't. Perspective is all about appearance. When you have two objects of the same size, and one is further away, it appears smaller. It isn't smaller; it only appears that way. That is perspective. When it doesn't appear enough smaller to account for the actual distance between the objects, then perspective is distorted. The angles formed by converging parallel lines don't change, but distances of points along those lines do change, and not the same way as would be expected with normal perspective.
Quote: You are definitely talking now about something other than perspective. You are referring to the field of view of the print itself and comparing it compares with the field of view of the scene represented. This is a legitimate and interesting comparison to make, but it isn't perspective.
This is quite simply 100% false. I absolutely guarantee you there is no difference whatsoever in the geometry within a picture shot from a given location with one focal length versus another, any more than cropping a picture with a pair of scissors changes its geometry. A square remains square, a rectanlge with dimensions 3:2 remains a rectangle with dimensions 3:2, a right triangle remains a right triangle, etc. Feel free to do the test if you doubt it. But centuries of physics and art instruction are not wrong about this. The above is a myth, pure and simple.
It doesn't skew the geometry from what it is with the other lens; it skews it from what it should be if it were actually closer. This distinction makes the statement 100% true, and it should have been clear by the context. Perspective changes in a certain way with distance. This is normal. Perspective changes in an entirely different way with enlargement or reduction. This is perspective distortion. There is no myth. (Edit: Incidentally, since point of view is part of perspective, the geometry visible on the print is only half the story. The geometry to the point of view is the other half. According to the concept of normal or ordinary viewing distance, doing this most definitely does skew the geometry. Of course, the counter argument would be that the point of view of correct perspective is the one that matters, and it just changes where that is.)
Quote: The only thing that changes is the field of view spanned by the print, and indeed, if you print both pictures at the same size and view them from the same distance, one might appear to match the natural field of view of the scene itself better than the other. Again, that's a legitimate and interesting comparison, but it isn't perspective.
Perspective is about perception. If you change the perception, you change the perspective. So yes, it is perspective. Perspective is about how the apparent relative sizes of things relate to distance. If you change the apparent distance by changing the apparent sizes of things without changing their apparent relative sizes, you change the perspective.
Looking at it the way that you do, you could say that the apparent point of view changes, while the perspective does not, and that is what causes the distortion (distance is still not what causes perspective distortion). However, the definition of perspective is not nearly as specifically and exactly what you are saying as you seem to suppose.