Even when you want to get a close up of a persons face, you don’t want to actually get close to the persons face. Let me explain The further away you physically are from the person the more flattering and less distorted the picture will be. When you get too close, noses can appear too long, faces can appear disproportionate… think about looking in a spoon… only maybe not quite so extreme. Consequently you want to use a long lens and stay as far away as you can. The ideal focal range for a portrait is 85-135mm. Long enough that the lens will not distort, and close enough that you can communicate freely with your subject.
If you are buying a lens specifically for portraits, you will want to buy a lens which has a wide apature (low f-stop), so that you can blur our the background and make your subject pop in the picture.
My recently acquired 70-200mm f2.8 is definitely going to be my favorite portrait lens, and I am hoping one day to have a 85mm f1.2….honey if your reading….