Schlieren photography

Schlieren photography

Schlieren photography was invented in 1864 to detect flaws in glass

‘schliere’ being German for ‘streak’. It is familiar today as a way of visualising shock waves in wind tunnels. The technique relies on the change of refractive index (ability to ‘bend’ light) with density. At its simplest, a parallel beam of light passes through the test area and is focussed onto a knife edge. Any change in air density causes part of the beam to be refracted and to fall above or below the knife edge. This makes that part of the image to appear brighter or darker than the background. Modern systems may use filters in place of the knife edge to make a coloured image.

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