Focal Length

To show how a focal length can dramatically affect a portrait I have used a range of focal lengths from 24mm to 200mm (the widest at the bottom of my contact sheet below). At 24mm I was lucky to escape the wrath of my model. The face is grossly contorted making her nose leap out at you.  However this is not something that has to avoided at all costs. There could be times when this would really work. What immediately springs to mind is say a photo of a clown. The distortion in this instance might just be what you need to add to the comic sense.
In this situation though only the top three images in the contact sheet are acceptable. That is from 58mm upwards, the models features are more realistic as the focal length increases. I haven't tested this at extreme focal lengths as I don't have lens capability to do this. Looking at sports photos in newspapers though would suggest that the longer the focal length the more flattering the portrait. The first image at 200mm is really the best of them all. Also as the focal length increases it helps you relax your model. For me this focal length means I have to use a tripod as I can't hold such a heavy lens without camera shake, so again I find this useful to be able to engage with the model as I always use a remote trigger when using a tripod.