Ultimately, when working with hard lights to make high-contrast portraits, the key is in the position of the light. Too high, and shadows (and amplified texture) will obscure the face, while a too-low or full-frontal source can eliminate shadows altogether—which will look flat and harsh.
Remember the softbox fill light? It's important because if your main light is too close to the subject and you expose correctly, you could have some really dark shadows devoid of detail. To maintain detail throughout, ensure that you're not blowing out your highlights and add a frontal fill (from a small softbox, a reflector or even a huge octodome placed behind the camera) to bring up detail in the shadows.
When working with a high-contrast lighting scheme like this, losing detail in shadows and highlights can be a big problem. To help prevent this, shoot RAW. Not only can you slightly overexpose to prevent the loss of detail in the shadows, but you'll retain detail in darks and highlights that can be redistributed in RAW postprocessing. When working with a high-contrast lighting ratio, extremes of exposure can look really bad, really fast. With a RAW exposure that doesn't blow out highlights and uses a fill light to maintain detail in shadows, you'll be all set.
The Ring Light
|Perhaps no light source has more dramatic high-contrast potential than a ring light. Originally designed as a way to illuminate macro subjects when the lens and photographer are so close as to cast a shadow on the subject, ring flash systems grew to be larger and more powerful, and gained a "must-have" reputation for fashion photographers.
With a ring flash wrapped around the front of a lens, visible shadows are almost completely eliminated from the subject. The light is coming directly from the lens, after all. But because the light literally wraps around the lens, a halo of shadow is also created that separates subject from background. What the source lacks in directionality and subtlety it makes up for with in-your-face, high-contrast drama.
Working with a ring flash, you have a few options. The first, and perhaps ideal, approach is the use of a specialized ring light designed to work with a studio strobe system. The biggest problem with this approach, aside from bulk, is the cost. The lights are big and powerful, and all but require a fashion photographer's big budget to afford them.
The second option is to adapt a macro photography ring flash for use in portraiture. This approach suffers primarily from a flash that isn't powerful enough for portraits. This is why many photographers have turned to a third option—a light modifier that creates the look of a ring flash by channeling light from a hot-shoe-mounted strobe through a reflector that wraps around the lens. The nice thing about this approach is a TTL flash that still works as it normally would, but with the added benefit of a ring flash's lighting pattern.
Perhaps the most subtle way to use a ring flash (actually, it's the only way to use a ring flash subtly) is to use it as a fill light. When used as a key, the ring light has a harsh, in-your-face look, which can be great in the right circumstance. But dialed way down in relation to another source that's providing the key illumination, a ring flash's subtle fill can add detail to the darkest tones without adding a whole new set of shadows to the scene. Best of all, you never have to worry about positioning of the fill, as it's always right on-axis with the camera.