Sodium screen process
n.phr.
Subject Field: Cinematography

The sodium system is by far the most-used dual film matte system. As originally used in England, it required a backing illuminated by monochromatic sodium light. Didymium glass filters were required on all set lamps to subtract the sodium wavelength from the foreground lighting. These filters caused a light loss of about two stops. An improved sodium system initially introduced in 1959 employed a special beamsplitter and narrow band filter in the camera. It does not require filters on the set lamps and does not significantly affect exposure. The sodium system (or any dual film system) has the basic disadvantage of requiring separation between the backing and the actor. The actor must be kept well away from the backing so as not to be contaminated by sodium illumination. For this reason the actor (and his feet and his shadow) cannot get into and among the elements of the background scene. Ryan			- Hyperonyms - Dual film Bibliography Index Home Conceptual tree
Context: The Sodium Screen process produces the same type composite as the Blue Screen but uses different tools. I believe the system was first introduced by the Rank Organization of England and has ensuingly migrated to the U.S., where it is presently used mainly by the Walt Disney Studios. Abbott Attestation: 3 Metodo della luce al sodio Reliability: 3