Yellow Screen and how Mary Poppins changed film making
Yellow Screen or The Sodium vapour process used by Disney and made famous by Mary Poppins (1964) used a specially coated prism in an old three-strip Technicolor camera. They were able to film technically brilliant mattes even with transparency. There was only one camera with this unique prism. Nobody was able to replicate it, and it was only ever for 35mm film. Blue Screen was developed for larger film formats at the time like 65mm, Ben Hur in particular.