When light from a point source shines on a three dimensional object, shadows are created. Of course, these shadows are the areas where the light does not fall. In nature, the sun on a bright cloudless day is a good example of light from a single point source.
This same basic principle applies to most of the lighting equipment used in film and video production. The reflectors in such fixtures gather the light into a point source and then focus it, usually through a lens. The resulting beam of light is directional, offering a high level of intensity or "punchy but it can also present a number of drawbacks:
On an overcast day, water vapor in the cloud cover alters the harsh directional quality of sunlight by causing it to be spread out or dispersed. The resulting light seems to be coming from the entire sky, producing an illumination that is softly diffuse. Shadows are faint or undefined. Contrast is lowered.
Rosco diffusion material acts in a similar fashion. When placed in the beam path of a lighting fixture, diffusion material modifies the harsh quality of the light by spreading or dispersing the beam. This softens the quality of the illumination by increasing the apparent beam size and thereby altering the beam's "shadow casting properties".
The most important difference between atmospheric diffusion and Rosco's version is that the Rosco diffusion materials can be utilized to produce controllable and predictable results at any time.
Diffusion material can be placed at the source in a gel holder, clipped to barn doors or positioned in front of a fixture in a frame. Each position produces a slightly different effect.
Large diffusion panels can turn multiple lighting fixtures into a single source of soft, low contrast illumination. As overheads, diffusion can be placed above sets to deliver a soft, overcast look or used outdoors to diffuse harsh sunlight. Sets can even be "tented or completely surrounded with diffusion to produce an extremely soft, shadowless quality that is particularly useful for product photography of specular objects like glassware, jewelry and automobiles.
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.
Diffusion Types - "Tough"
The following diffusion groups are designated "Tough". This indicates that the base material is a heat stable polyester that can be used with most high-temperature lighting fixtures.
Feathers the beam edge and softens the overall field, yet beam shape is maintained. Minimal beam spread.
A general purpose group that offers slight to medium diffusion properties. Moderate beam spread, yet still maintains a discernible beam center.
TOUGH WHITE DIFFUSION
A general purpose group that offers medium to dense diffusion properties. Wide beam spread creates an even field of soft, shadowless light that is quite pleasing.
The original dense diffuser. Wide beam spread creates an even field of soft, shadowless light.
A group of reinforced woven materials that offer medium to very dense diffusion properties. Very wide beam spread creates a very soft shadowless quality. Ideal for tenting, overheads, and large area diffusion. Can be sewn or grommetted to fit butterfly and overhead frames.
A unique diffuser with directional properties. Spreads the beam in one direction-horizontally, vertically or diagonally-to create a slash of light. Also useful for spreading out an unwanted beam scallop caused by tight spaces and extreme lighting angles. Good transmission.
Diffusion Types - "Soft"
Soft diffusion materials are quiet when used outdoors in windy conditions. They can also be heat-welded to produce large panels for overhead tenting and large area diffusion. However, these materials are only moderately heat resistant and should not be used directly on high temperature lights.