Diffusion Confusion

by Thomas F. Denove


VIDEO: The power of lighting for video

A picture is defined by light and shadow. The better the light source, the cleaner the shadow. The placement of the light determines the direction, angle and length of the shadow. Shadows reveal dimensional clues about the subject.

Shadows are a beautiful way to create separation. They can also be ugly. The process of shadow-making is a great concern to the videographer-to a point that many of us try to eliminate all shadows created by the lights we use.

In the days of black and white, shadows were essential in the storytelling process. Good camera operators were master shadow-makers. Flat lighting created images of mush.

When red, green and blue entered the picture, a new thought process evolved. Because color creates its own separation and shadows can be ugly, we began playing it safe with softer light. Enter the umbrella-a fascinating instrument used to create shadowless light. The result? Pretty pictures everywhere.

Denove's Law: Shadowless light-a concept lacking in depth.

If you have fallen into the trap of eliminating shadows from your lighting, stop! Nothing is more boring than pictures without texture, definition and soul.

A few years ago, I spent an eternity shooting a lighthearted comedy for a well-known director. Actually, it was only a 24-day shoot, but it felt like forever. In pre-production, he told me, "Tom, there are shadows in real life, but not in my movies." I spent my nights designing new ways to eliminate shadows, while during the day trying to convince him the error of his ways. In the end, the director was a happy camper- he had a shadowless movie. Besides my own sleep deprivation, the eventual loser was the audience.

Denove's Law: If you are asked to shoot for someone who likes flat lighting, run.

Don't hide from shadows; control them. Learn how to manipulate a source light with diffusion. Scrims, nets and diffusion can decrease the light intensity. Diffusion, however, actually affects the quality of the light source-its texture and spread.

Any material that scatters light rays as they pass through it can be considered diffusion. I have focused lights through shower curtains, drapes, acrylic plastic, bed sheets, paper, fabric and even Kleenex (in front of strobes).

Companies such as Rosco, Colortran, The Great American Market, and Cine Mills, make a multitude of plastic diffusion materials that withstand the extreme temperatures of video lights. Each has its unique way in softening shadows.

The farther the diffusion is placed from the light, the more pronounced the effect. Two factors are at play. When the diffusion is moved away from the light, the beam spreads and covers more of the material-more material equals more effect. Also, the illuminated diffusion material becomes the light source, not the light itself. The greater the size of the source, the softer the light.

Diffusion can be cut to fit a gel frame and put directly in front of the light, clipped to the barndoors, or placed on frames of various sizes. Unless you want a softer effect by using a large piece of diffusion away from the light, use the diffusion in a gel frame. Many gaffers attach the sheets to the barndoors to avoid cutting the gel. Don't; you eliminate the control that the barndoors afford and must resort to using cutter and flags to modify the beam. (Remember, diffusion at the end of barndoors becomes the new source of light, and the barndoors are useless.)

For those still using open-faced lights, the farther away the diffusion, the better. The intense heat will quickly destroy even the best gels if placed too close to the source.

Diffusion Confusion

Not all diffusions are created equal. Some work better on open-faced lights, some are kinder to faces, and some can soften without killing the edge. It is important to experiment and learn.

I decided to take a sampling (light to heavy) from a family of gels from Rosco and shoot a test. I chose six (Light Tough Spun, Opal Tough Frost, Tough Frost, Tough White Frost, Grid Cloth and Tough Silk) from their selection of more than 20.

Diffusions soften the edge of a light source by spreading its beam, allowing the light to more effectively wrap around 3-D objects. Usually, the greater the increase in beam width, the softer the shadow. There is also an intensity loss and often a color temperature shift when the light beam is scattered.

I used a doll's face as a controllable 3-D object and a suspended film reel to cast a shadow on a white wall. The light source (a Pepper 650, from LTM, Sun Valley, CA) was placed camera right, about five feet from the doll. The film reel (held by a C-stand) was positioned to throw a distance shadow behind the doll. Another C-stand held an 18" x 24" black flag close to the left of the doll to create a "negative bounce ." This kept unwanted ambient light from illuminating the shadow side of the face. A C-stand with its gobo arm at a 90° angle was positioned 28 inches in front of the Pepper. During the test, this made it very easy to slide different rolls of diffusion on and off the stand.

setupA picture was taken without any diffusion. A Cinemeter was used to measure the intensity of the light at the doll's face (320fc). I measured the color temperature of the lamp with a Minolta Color Meter II-a perfect 3,200°K.

Each diffusion was tested twice to show how distance and surface area affect the softening. A picture was taken with a sheet of diffusion attached directly to the lamp, and then another with a roll of the same diffusion material hung 28 inches in front of the light. (The Pepper's beam covered approximately a 2-foot square area.)

I then completed the test by measuring the beam spread of the Pepper (without diffusion) against a blank wall. A foot-candle reading was taken at the center of the beam. The measurement of beam width was determined at the point where the light fall-off was 50% of the center beam intensity. I then repeated this process, measuring the beam spread, using each diffusion material attached directly to the light. This information was used to compute the percentage increase in beam width.

Light Tough Spun and Opal Tough Frost are light diffusers. Attached to the lamp, they are excellent for cleaning up uneven beam patterns. Light diffusers can take the edge off a light without affecting its directional crispness. Opal Frost has been my favorite diffuser for years.

When Light Tough Spun is held away from the light, a secondary shadow is created (a shadow within a shadow) because much of the light is transmitted "clean" through the open weave of the plastic fibers. This weave can be used to create a subtle cucoloris effect, as if the light is passing through a curtain.


Medium Diffusers

Tough Frost and Tough Silk are considered medium diffusers. Tough Frost is a good, all-around diffusion material either attached to the light or set at a distance in a frame. Even though the light is softened substantially, it still maintains a focusable direction.

Tough Silk retains the same odd diffusion properties of real silk with the advantages of being flameproof and durable. Silks are among the most widely used forms of diffusion-and the most misunderstood.

Upon close examination, you can see parallel; lines running through the plastic. These lines give Tough Silk directional properties. Depending on their orientation to the light source, they spread the beam in one direction - horizontally, vertically or diagonally. Tough Silk can be used to create a slash of light, or you can take advantage of its directional diffusing characteristics to maintain certain shadows while eliminating others. You can subtract or enhance the visual roundness of an object.

Heavy Diffusers

Tough White Diffusion and Grid Cloth are heavy diffusers. Both create near shadowless light when used in large frames away from light. Multiple light sources can be made to appear as one. For example, these diffusers can take five 1,000W lamps grouped together, and the expected multiple shadows will not appear.

Faces love these materials-especially when Tough White Diffusion is placed close to the lamp and when Grid Cloth is mounted far away. Don't believe me, ask the doll in the tests.

Diffusion possibilities are endless. Their use should be based on your own likes and dislikes. Be bold. Experiment. Create. It is important to remember that diffusion is designed to enhance the quality of the light; it is not a cure-all for a badly placed light.