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Seeing the Unseen - Schlieren Photography



Many things cause changes in the density of the air around us. We don't normally notice because these changes are mostly invisible to our eyes. A technique called Schlieren Photography makes these subtle differences visible. The heat rising from a candle flame, a hair dryer, even the heat from a soldering iron can been seen billowing upward thru the less dense colder air around it.

What am I seeing?
You are seeing the differences in air density. Heated air is less dense than cold air (which is why it rises like in a hot air balloon). Light is bent when it passes thru materials (like air) of different densities. This is called refraction. You have probably seen long road on a sunny day shimmering like a lake. What you are seeing is the light being bent thru the heated air rising from the road.

How does Schlieren Photography work?
Schlieren Photography uses uses light from a single collimated source (all the light waves are parallel). Any differences in the density of the material (air) the light passes through will bend some of the light rays. At the camera, a knife edge blocks some of the bent light creating darker area in the image when the light was refracted by a change in density.



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