Q&A: Avoiding Cross Shadows When Rim-Lighting

Strobist reader Ed Roper asks:

I've been using a three-light setup, but running into a pesky shadow problem. Below is an example setup shot with the shadows highlighted. As you can see, I'm already using grids to try to cut down on the spill.

Are these cross shadows just a fact of life when trying to wrap full body like this?

The good news, Ed, is that you have exactly the light mods you need to do this well. And the fix is easy…
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First, a note about Ed's strips. He is using two Paul Buff 10x36" soft boxes with grids. These are great strip lights -- well-built, open like an umbrella and offer a lot of bang for the buck. The mounts are speed rings, which allow interchangeable inserts. I used to use them with AB's and then swapped inserts when I switched to Profoto.

At $119.95, they are reasonable enough to cough up an extra $29.95 for the matching grids, which are very helpful for controlling spill. And that is is exactly what you would want to do here.

Simply put, if you do not want the cross shadows (which Ed has circled for us above) you have to keep the rim light from reaching the ground. There are three ways to do this: feathering, gobo'ing or a combination of the two.

Easiest way is to feather the lights. And in this case you would feather them up. You are gonna have to do this to a greater degree than you think. If you are doing it right, it will look almost comically overdone. The idea is to rim light your subject with the diminishing edge of the beam. By the time it gets down to his feet, it is all petered out.

For even more control I would physically lower those rims a little before feathering them, too.

Most of the time, this will work. But if you need absolute control of weird ground shadows, you'll want to gobo the light off from the bottom. With a bare speedlight, you might use something like a Honl Speed Gobo or even a piece of cardboard on the flash itself. But with a light mod of this size, you'll need something bigger.

In this case the gobos would be large cards, clamped to stands and placed between the rims and the subject. Geometry should tell you exactly how high to place them. The top of the gobo would exactly hit a straight line between the top of the strip box and the bottom of the subject's feet. As you moved up the subject's legs, they would see more and more of the strip box.

Now, no cross shadows on the ground will also mean no light on the ground. Which could be a problem in this case. You'll either have to make that happen with your key light (feather it up for foreground control, too) or scrape another light across the background.