This project shows the results of three similar images taken at different focal lengths. They have been cropped slightly to remove extraneous detail. I've done this exercise before, early on in TAOP, I think. With portraits the focal length is even more crucial as an unflattering (or unrealistic) portrait is less than desirable most of the time.
My first two images I consider to be taken at suitable focal lengths. Compression is more pronounced at the longer focal lengths and facial features become less prominent. Unless some sort of quirky effect is required wide angle shots are best left alone.
Image 1 - 200mm.
Image 2 - 65mm.
Image 3 - 18mm.