Facial distortion of various focal lengths for headshots: Nikon SLR Lens Talk Forum: Digital Photography Review
About Photography: Knowing your Focal Length. What is it? What does it do? — Steemit
What a Shot - Focal length and Distortion in lenses On most lenses, distortion is minimal. But the more extreme the focal length, the more extreme the distortion photography. A fisheye lens
Does Focal Length Distort Subjects?
Facial distortion of various focal lengths for headshots: Nikon SLR Lens Talk Forum: Digital Photography Review