For those who’ve not seen this before, Enjoy. It is genuinely breathtaking.
Using a large concave mirror, like one found at the bottom of a telescope, small LED light source, razor blade and imaging device Brusspup reveals differences in air density by placing a variety of objects in front of the mirror. Even subtle changes in ambient air temperature from the palms of hands are visible.
Here’s the rudimentary setup. Note the light source is placed next to the camera lens and not directly in front of it as it may appear:
So how does it work? By reflecting the light source back into the camera and through a filter (in this instance a sharp blade) some of the photons are blocked. The refracted photons that have interacted with the heat source that do return then act as a shadow to reveal the illusion.
Interested in giving it a go yourself and learning more? JoshTheEngineer has put together this incredibly informative and in depth video on how to create your own Schileren video.