Corridor Crew
2 HN recommenders · recommended in 5 months, 2025–2026
12:25 · 7.3M views · Apr 7, 2024
Corridor Crew tracks down Disney's lost sodium vapor prism process, used for Mary Poppins-era transparency mattes. They explain how a narrow sodium wavelength and a beam splitter enabled better compositing than green screen.
Recommended as a fun, informative rediscovery of a lost film-effects technique.
6 comments from Hacker News
To add to that (extremely thought-provoking) video, I do think that the Marvel model of "pre-viz everything to death, the edit's already done before filming begins" - [LINK] - can lose a lot of spontaneity. Perhaps the fading luster to Marvel films overall will bring us back from this place. On a more tangential note around green screens and their limitations when used ubiquitously, Corridor Digital's quasi-rediscovery of the Sodium Vapor process used by Disney through the early '80s, but lost to history ever since, is a fantastic watch. this video
Some technologies have been lost, even though they were superior to what is available today. Take, for example, the old “green/blue screen” technique using sodium vapor lamps, used by Walt Disney in film production in the pre-digital era: this video (12 minutes long, but totally worth it).
At the end of this video they link to another video from a year ago [1], where they recreate the sodium vapor process with a rig with a beam splitter, one side had a filter to reject sodium vapor light and the other has one to reject everything but sodium vapor light, and then a camera on each side. The Disney process had the filter essentially built into the beam splitter, but afaik, nobody knows how to make that happen again (or nobody who knows how, knows it's a desirable thing). Seems like the optics might be cumbersome, but the results seem wortwhile. Also, you need still need careful lighting, you don't want your foreground illuminated by sodium vapor, but I wonder if you could light the background screen from behind (like a rear projection setup) to reduce the amount of sodium vapor light that reflects from the foreground to the camera. [1] this video
Half silvered would work too. I was using the 3CCD prism as an example of splitting an image into multiple parts and avoiding issues with parallax. If you stacked cameras on top of each other with their own lenses, you'd inevitably get slightly different focal lengths, focal distances, and camera positions. Aside with the dichotic filter... there was a neat trick that was lost (and refound) with a sodium 589nm dichromic (notch) prism. this video
The lights are relatively easy to get. iirc (it's been a bit since I watched their full video on the subject[1]) the hard part to find was the splitter that sends the sodium-vapor light to one camera and everything else to another camera. 1. this video