As has been said - lenses don't cause 'compression', distance does in conjunction with our fallible minds. I taught it pretty simply - irrespective of the lens used.. if I am 1 foot from subject A and subject B (same height) is another foot away, B will look half the size of A Stand 100 feet back, subject B is only going to appear 1/100th the height smaller than A.. If i shot this with a long focal length lens other details which could offer hints about the perspective are removed and with example 2, the way our brain processes things is if they look the same size then they must be close to one another - and there's where we get 'compression'* Similarly if we go back to the first example, if one subject looks 1/2 the size then it must be a lot further away.. and so it appears to be expanded. *(another example is the HUGE moon we see when it's on the horizon - we can compare it to things of a known size and our brains go 'OMG, that's HUGE!" .. but when it's high in the sky we loose our frame of reference and go 'meh.. moon')
