Monday, July 18, 2011
Serious Lighting Control With Just One Light—07/18/11
Turn backgrounds from light to dark in a one-light portrait
|This Article Features Photo Zoom|
When working with a single light source, you actually do retain control over the subject illumination and that of the background. By doing little more than changing the distance between light source, subject and background, you can make the background white or black or practically anything in between. (Lighting-up a black background enough to make it white is really tricky, but with enough distance you can probably get there. In reality, it’s much easier to turn a white background black. The key is distance.)
Keeping a white background white is accomplished by placing the subject close to the background—very close—and illuminating both the subject and the background normally with one light. Whether it’s a softbox or bare bulb doesn’t matter. What really matters is the “depth of light.” That means there’s not enough distance between subject and background for the luminance to fall off noticeably. That means the background (which is immediately behind the subject) will be normally lit; if it’s white it will look white. To do this well, keep the light fairly far from the subject. This will make the light more even across both subject and background.
That seems easy enough, right? But what about creating a dark background? Well, since our goal is normal illumination on the subject and much less or practically zero illumination on the background (to make it look dark gray or even black) you need to move the subject far from the background, and move the light close to the subject. This way the falloff between subject and background will be considerable. To get all the way to a pure black background, you’ll likely put the light very close to the subject—just a foot or two—and you’ll put the subject very far from the background—say, ten feet or so. (The farther the better, just to be safe and allow for some wiggle room.)
For instance, with the light just one foot from the subject, let’s say the correct aperture for a normally exposed subject is ƒ/22. One foot behind the subject (twice the distance from the source) the illumination is two stops darker. That means the correct exposure to keep the background white would be ƒ/11. Since we’re shooting at ƒ/22 to keep the subject correctly exposed, the background will be two stops underexposed—so it will look light gray.
Move the subject farther from the background, let’s say the light is now four feet (twice the distance) from the background. Another quartering of the illumination means the correct exposure on the background would now be ƒ/5.6, so we’re four stops underexposed—and now the background looks dark gray. Double the distance one more time to eight feet and we get another quartering of the illumination, down to ƒ/2.8, so we’re a full six stops underexposed. What was dark gray at four feet is now pure black. And we’re still using just one light.
The legend around my photo school was that a lowly seventh assistant for a famous fashion photographer was catapulted to first assistant when the photographer asked the crew to make the background darker. Every other assistant tried moving the lights farther away, but that just made the background lighter (because the depth of light was greater, and the difference between subject illumination and background illumination was minimized). The well-trained seventh assistant moved the key light closer to the subject, which made the background proportionally darker, and impressed the photographer with this lighting know-how. This skill may not make you famous, but it will definitely improve your understanding of light and your skill in the studio—and that will make you a better photographer.