Diffusion for Contrast Control
Working in direct sunshine means controlling high-contrast lighting. Often you do this by filling shadows with reflectors, but sometimes it’s better to moderate both shadows and highlights together by diffusing the sunlight instead.

Why? Reflectors can look hokey unless deployed with great care. At best, the subject’s fill side may be suspiciously bright for the environment. At worst, the hard light beams give a studio-like “lit” quality that appears fake outdoors. Diffusion can solve these problems, although it brings some of its own, as we’ll see.

In effect, diffusion reduces and/or breaks up direct sunlight by shading the subject with a filter ranging from three to 20 feet square (though the big types are strictly for large production companies with well-stocked grip and juicing trucks). Typically, diffusion material is stretched on frames, suspended with ropes, or simply held by crew members.

Diffusion comes in three flavors: screens, silks, and sunblocks. Screens are simply coarse plastic screening fabric available in the garden department of any home improvement store. Supplied in two or more densities (originally to suit different plant needs, defined by percentage of light blocked), screens are versatile and easy to use.

Silks, by contrast, are not silk. Common ones are simple white bed sheets; professional models are fine, silk-like synthetics that admit more light while still diffusing it. (Historical trivia: in Hollywood’s infancy, studios built interior sets on roof-less stages, lighting them with sunlight filtered through white fabric “ceilings,” to deliver the low contrast required by early film stocks.)

Sunblocks are usually tarpaulins. How can materials that block light completely be “diffusion?” Typically, they’re used where a light ground color (like concrete) delivers the actual diffusion by scattering softened light all over the place.

We’ll cover lighting techniques with each type of diffusion, but first we need to show how to construct and deploy them.

Building Diffusion
You can buy diffusion systems and materials through movie production supply houses; but you can save big bucks by building them yourself.

Smaller units are typically stretched on rigid frames. Four feet square is about the biggest practical size, because bigger frames are tough to support, and because small diameter plastic pipe is too flexible to use in longer lengths.

To build a frame, go through your hardware supplier’s plumbing stock and select the most rigid pipe available (I prefer the thick-walled gray type). Limit the pipe size to 1 1/4-inch inside diameter; bigger pipe requires fabric with very wide hems. Buy 16 running feet (in four-foot increments, of course) and four slip-on 90-degree elbows (figure 1).

If you make your frame four feet square, you’ll need to find fabric (screen or cloth) 56 inches or wider, to accommodate wide hems on each side. If you can’t find this, simply reduce your frame width to a dimension that will fit whatever fabric you can find.

Next, sew hems on all sides, wide enough to take the plastic pipes, leaving the ends open, of course. To assemble a diffusion unit, slip the pipes into the hems and secure them with the four corner elbows. I cement one side of each elbow to one end of each pipe, so I don’t have to keep track of them when I dismantle my rig.

For extra versatility with screens, you may want the option of doubling density by fastening a second screen atop the framed one. I use Velcro-type patches, gluing the loop half on the upper side of each pipe elbow and sewing the hook half at each corner of a second screen. (Yes, you have to buy two different types of Velcro to do this, but we’re talking very short lengths here.)

To make larger diffusion units, old king-size sheets are about as big as you can get with silks, without visible fabric seams. To rig these bigger screens, silks, and tarps, you’ll need to provide grommets for attaching lines. With screens or silks, sew the hems about an inch wider than the grommets you’ll use, to reinforce the edges of the fabric. Then install these grommets at 18- to 24-inch intervals along all four edges. You can buy simple, inexpensive grommet kits at any hardware store.

With tarps, start by finding the type that’s blue plastic on one side and silver on the other (they’re not as common as blue on both sides). Twelve feet square is about as big as you can handle in the field, and 9 x 12 is a useful size. Tarps come with grommets, but they’re usually spaced too widely, so add extras to create tie points every 18 inches or so.

Even with grommets, large diffusion cloths can be clumsy to rig, so carry a supply of tarp grippers, available in camping or automotive departments stores. These plastic gadgets clamp anywhere along the edge of any fabric to provide extra grommet eyes. Add plenty of light nylon line, plus stakes and the plastic doohickeys used to tension tent ropes.

With your fabric framed, and/or prepped for tying, you’re ready to deploy diffusion at outdoor locations. The larger the diffusion screens are, the more they resemble sails ready to fly off to the adjoining county; and even the small ones can cast shadows that hula in the slightest breeze.

Framed screens are fairly easy to manage because they’re light enough for crew members to hold aloft during shots. (A medium stepladder from the Grip Department adds flexibility.) Except near the sunset hour, support stands are not practical because they don’t reach high enough to interpose the diffusion between the subject and the sun. (Production companies use huge, elaborate tinkertoy constructions to secure diffusion.)

Large, frameless diffusion sheets are tougher to rig because they have to be attached on at least two sides to walls, trees, poles, or other tall supports. (TIP: if you regularly need a fairly large silk canopy, buy one of those self-erecting pavilions seen at fairs and farmers’ markets. They set up in minutes and, roofed with white plastic or canvas, supply instant soft, diffused light.)

Using Diffusion
Each type of diffusion creates a distinctly different effect. When the background is in bright sunlight, screens give a realistic look because they reduce the light without scattering it very much. Highlights and shadows remain, but each is less extreme, and so the foreground and background appear similarly lit.

Note that there’s a difference between double-density screening material and two layers of single density. Heavier cloth is still a uniform rectangular grid, while two layers, which are necessarily laid out of registration, interfere more aggressively with the incoming light and diffuse it more strongly. By carrying two layers of single density and one double, I can create a wide variety of screening effects.

Silks are simpler to use because a single layer is almost always sufficient to bathe subjects in a soft, shadowless glow. The result is glamorous lighting — kind to aging and imperfect faces. The problem is that light below a silk doesn’t remotely resemble direct sunlight, so background and foreground won’t match. If you don’t care about realism, fine. If you want to fake a sunlight effect, try using a reflector behind the subject and positioned to clear the rear edge of the silk. You’ll get a hot rim light that makes it look as if the sun is behind the subject.

Another way to use a silk is to place the subject in sunshine, but in front of a shaded background, like a building. Now foreground and background will look alike, but you’ll still get a glamorous glow from the direct sun through the silk.

How about tarps, the kinds with one black side and one silver side? These deliver a somewhat different look because they block nearly all the light from above, creating a deep shadow. The light scattering comes from the ground below and the tarp above, which is rigged silver side down. You need a light ground color to make this work, but the result has a dazzling, sparkly effect that looks great in very bright scenes. As a bonus, blocking the direct sun may reduce the overall light to a level that won’t overwhelm your camcorder chip(s).

No matter what kind of diffusion you choose, you’ll have trouble matching your beautifully modulated closer shots with wider angles, which cover too much area to shade. To minimize the problem, keep those wide shots wide. For example, don’t let a subject enter a sunlit wide shot and walk forward into a medium shot, because the lighting won’t match the diffused closeup that follows.

Another good plan is to use a very distinct change of horizontal angle. That way, it’s difficult to compare facial lighting from wide shot to close shot. It also helps if the close shot background is in shadow.

Good shooting!

Contributing Editor Jim Stinson is the author of the book Video Communication and Production.

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