Quote Originally Posted by Michael R 1974 View Post
I'm probably way off here as I don't do any portrait photography, but when taking the portrait isn't it the distance between camera and subject that dictates the perspective rendering, and then the choice of lens is essentially a framing/cropping choice? Ignoring optical aberrations, for a fixed film to subject distance, changing focal lengths does not change perspective, only cropping. If film had infinite resolution and no grain, all you'd need is one short focal length rectilinear lens and you could just crop under the enlarger.
Yes, distance to subject sets up the angular relationships to the camera.

So, if the distance to the subject is the same, say 6', and the subject is printed the same size in separate prints, then both prints should have the same perspective.

The print sizes would be radically different if un-cropped.

If both prints were viewed from 6' then they both would look "normal". If viewed from 3' they both would exhibit "flattening". Viewed from 12' both would bulge in the middle. (Albeit, the small print from the long lens wouldn't normally be viewed at that distance.)