Focal length is how far you are away from the subject as well as zoomed in. when you are at a small distance from the subject (28mm) the image is warped and the face is thinned, and the background looks closer and sharper. as you get farther away, the image compresses, and rounds out your face, as well as blurs the background. 70mm to 100mm is considered the average human face shape for this example.