Upgrade Your Rims
That's because the key light hits your subject and bounces back in a scattered, diffuse way. Not so with a rim light, which typically caroms off of your subject at a very efficient angle. Which means a little bit of light, used as a rim, goes a very, very long way.
Have you every dropped your rim intensity down -- waaaay down -- to see what happens?
You might like the results.
Here is a detail of the relevant area of the photo above, or you can see it larger, here (photo opens in a new window or tab).
See how the rim is not so much blasting off of Monty's (pictured) skin as it is creating cool, three-dimensional detail? That is because it is dialed way down from where we typically set them.
Another example, for this photo of Jordan we left a little more intensity in the rims than we did for Monty, above. Still, check out these numbers for an idea of just how little light is used:
The rims in this case are courtesy two SB-800s in Lumiquest SB-III's, three feet away. The flashes are set to 1/64th power. And we shot at f/10 at ISO 200.
You figure the SB-III eats two stops of light, so that is the equivalent of 1/256th power and still shooting at f/10. That's a teeny weeny amount of light. (Click the pic for bigger.)
To finish off the light, we keyed his face with an SB-800 in a tight grid, with an Orbis for on-axis fill.
If you like this look, there are a couple of things to remember if you are trying to get it. First off, this kind of rim is not a job for a bare speedlight. Those are very small (in area) light sources. And even dialed way down you'll get a very sharp line to the rim light -affected area.
It helps if you have a little transition area in your rim. A little -- but not too much.
A soft box or strip light is probably gonna look a little wishy-washy use it for this. The sweet spot, if you are working in close, is to have something that approximates a normal reflector's size on a big light.
So with a speedlight (that's what we used) you might want to run it through a Lumiquest SB-III, a Honl traveller8 or even an (off-camera) Orbis, as we did here in a pinch.
Anything that softens your light a little bit will work. The particular mod is not so important as increasing the size of the bare light into something in the ~8-10" range. Not too hard, not too soft -- just right.
How Low Can You Go?
And if you do happen to be using a big light, good luck on getting it down low enough. (Well, at least without some serious neutral density stacked onto the head.) This kind of thing takes sooo little light that you may even have trouble coaxing your speedlight down low enough.
So much so, in fact, that you might want to set the rim lights first (with flashes dialed down as much as possible) and adjust your aperture until it looks right. Then build your other lights to hit that exposure. This is bottom-of-the-range stuff.
Rim lights are cool in that they look good at almost any intensity, Different, but good.
I think of rims as being a little like pizza: When they are good, they're good. But when they are bad -- well, they're still pretty good.
And if you like the ultra-low-power rim look -- 3-D and textural and unlike anything else you'll get with a rim in the normal power range -- give it a whirl. This kind of rim is worth a spin.