Originally posted by Eruditass I'm surprised at that result. Perhaps they meant it doesn't change significantly above a certain camera to subject distance? I can't find the thread if you can help me look.
There are plenty of examples showing very obvious perspective changes. This can be the size of the nose in relation to the face, or the positioning of background elements.
Note that I am not saying focal length changes perspective (it doesn't).
Perspective might not change but a lot of other significant features do change. The depth/compression of the background. the features of your subject with change slightly.
A 50mm lens is always a 50mm lens and will always render that way. Just because the FoV on a APS-C is = a 75mm lens on a FF does not change the optical properties of the lens. It will still have the DoF and optical rendering of a 50mm lens.
To make the comparison obvious... Take a 15mm lens and capture a close head shot. Now take a 150mm, back up and frame it for the same shot. The facial features will be significantly different.
The FoV might not change, but each focal length lens is slightly different in how it renders. Wide angle show barrel distortion and telephoto lens show pin cushioning.