Schlieren optik, meaning streaks optics in German, is a method of viewing differences between temperatures and densities in gases and liquids.

I made the simplest schlieren apparatus.

It involves a parabolic mirror, a very small and powerful light source, a camera and either a multicolour filter or a sharp edge such as that of a razor blade.

The idea is that light will refract at different angles depending on what it is shined through. So, say a candle was placed in front of the mirror, the movement of hot air above the camera would be visible as light refracts through it and hits a different part of the mirror to where the light would usually reflect.

The light then bounces towards the camera sensor at different angles. The knife edge is placed in front of half of the camera lens and blocks off part of the light refracted so only part of the light hits the sensor. Or a tricolour filter can be used with one colour in the middle and two different colours either side with the light focused on the central colour so any refracted light would appear a different colour.

It results in a surprisingly sensitive image that can show the convection currents from the heat of my hand.

knife blocking light

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 whole setup

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