How Disney Made Mary Poppins Without Green Screen

We have gotten used to modern visual effects in movies made with the aid of computers, so much that we only notice them when they are badly done. The most common is the green screen, in which backgrounds can be made by by switching a plain green background for another video. But how did they do this before green screen technology? Oh, we all remember the old projection effects, when people talked in a car with the scenery passing by in the windows as it was on a movie screen. But what about Mary Poppins? She magically entered an animated universe so seamlessly that it was astounding in 1964, and astounding now because the effect is better than most green screen scenes.

Disney used the sodium vapor process, which is not easy, but paid off for Mary Poppins. It was also used in 1990 for Dick Tracy. But it required a custom-made prism, which Disney lost along the way. The Corrider Crew managed to get hold of a prism like it and recreates this abandoned filmmaking technique for our edification and entertainment. There's a skippable ad from 4:25 to 5:21. (via Metafilter)