i do agree, but textbook quotes are 85mm to 135 mm.
Thats wat the threadstarter wanted to know, so i just gave him the textbook answer.
If not, like what you said, the 16mm or 1000mm can also be considered portrait lense.. :bsmilie:
Textbook answer would be:
any lense above 50mm would be useful for beauty shots/facial/closer up shots. They don't distort the faces. As for using 50, 60, 85, 90, 100, 135mm, 200mm, 300mm it depends on the compression of the person/background that you require.
Use lenses below 50mm too close to the subject, when you fill the frame with the subject face, you will notice the big nose effect. 99% of the time it is not nice. However if you were to do full body portraiture/environmental portraiture, the "problems/shortfalls" of wide angle lenses aren't that noticable.
Once again, it depends on what you envision the final image to be. *shrug* there are pros in miami who use 300mm prime lenses to shoot full body/environmental portraiture. I know a pro in sg who does full body group shots of 5 girls standing in a inverted V formation using 200mm prime (in a studio no less).
Best is to know what you want and the lens to give you that result will be the best portrait lens.
On another note. I suppose that's why many portraiture photos in the relevant sub forum are all the same, most photos don't really stand out. That's because they've all been brainwashed to think 85-135mm are the best portraiture lenses. That's why you see many "pros" stagnant at a certain level.