When considering the technique of nude photography vs. portraiture, you won’t get too far by just applying the rules of portraiture to your nude work. Not that there is nothing to be borrowed from portraiture, some of the basics (lighting ratio, etc) share similar concepts, but their application is greatly different.
Nude photography is a discipline in itself. Broaden your approach to more than full-length portrait photography minus the clothes, and you’ll be two steps ahead of most beginners. The lighting and posing concepts for nude photography are different from those of portraiture and fashion photography. I’m not going to tell you to forget everything you know about non-nude photography, because all that knowledge is going to help you. Admittedly, there are similarities between non-nude and nude photography, but you need to know what the differences are, my suggestion is that you neither forget nor rely entirely upon your past experiences, but instead that you learn with an open mind. (from page 10 of my book)
Knowledge of portrait lighting is helpful, but not essential to learning nude lighting. A portrait lighting configuration is not sufficient to light the whole body.
In portrait photography a ratio of 2:1 is traditional; but in nude photos a higher ratio like 3:1 or even 4:1 often yields more dramatic images. It is a matter of taste and style — the more fill light the more detail you will see in the shadows. Higher contrast images are often viewed as more artistic, while lower contrast images (like the 2:1 portrait ratio) can risk looking a little pedestrian.
The techniques around portraiture are distinct from nude photography (at least the kind that I do) in three major ways: 1. they were developed for photographing non-models; 2. they were developed for a subject who is also your customer; and, 3. the rules of portraiture center on the face — a minority in the world of nude photography:
1. Since we’re talking about photographing nude models (not ordinary people) there is little need for all those little tricks for minimizing or hiding flaws. If you do employ those tricks, you’ll likely miss out on some of the more interesting angles for your model.
2. To come up with an interesting image, you needn’t be concerned with the most flattering pose. Granted, you’re not trying to create an unflattering pose, but experimentation is called for. You’re not constrained by your subject being your customer.
3. And finally, the face does not have to be central to a nude. Certainly it can be, and sometimes to great effect. But many if not most interesting nudes are not about a face with the body as an afterthought.
So if you know some techniques from portraiture, begin with a fresh mind as you embark on nude photography.