Compositing with the sodium vapour process .... Better than green screen!

[Brumby]

In Dave's live stream (just finished) mention was made of a process used in the production of the film Mary Poppins that provided a method of compositing far superior to the well known green screen method.

I remember recently watching a video on precisely this process - and managed to find it:

[ebastler]

Thank you, that is a cool video. I did not know that this approach was used for keying movie images.

But I object the implied claim that making dichroic mirrors (i.e. wavelength-selective beam splitters) is a lost art. They are commonly used e.g. in fluorescence microscopy, and made to very tight spectral specifications, using multi-layer coatings.