We are surrounded by events that we cannot see. Maybe they happen too quickly for our eyes to catch them or too slowly for us to notice. Or maybe they are normally transparent, like the vortices produced by a rotating fan blade or the heat rising from a candle flame. With mirrors or lenses and a camera, schlieren photography lets us see these things.
In zigzag fashion, a beam of light is reflected form a mirror, past the subject – for instance, a burning candle – to another mirror and then into the camera’s lens. But as the light passes through the hot air above the flames, it is bent, or refracted, slightly. The camera is set up to block out the light that is not refracted and to receive the light that is, giving us an image of the candle and its plume of hot air.
Learn more about how to do schlieren from Professor Vandiver’s site.
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WATCH THIS VIDEO! Professor Kim Vandiver demonstrates the schlieren technique.