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What is Schlieren photography:

Schlieren photography is an optical set-up that allows for the visualization of variations in the refractive index of air and other liquids. These variations are normally caused by density changes due to heat, compression or change in medium.

Schlieren photography is normally used to capture:

  • pressure waves (Mach cones) in air

  • shimmers caused by varying temperatures of air

  • gas leaks or mixing of different fluids

Normal vs Background Oriented Schlieren:

Normal Schlieren set-up consists of a point light source (often a laser), a parabolic mirror, razor edge and a camera. Such a set-up is limited in size by the span of the parabolic mirror. If one wanted to capture a person with such a set-up, he would require a large and absurdly expansive parabolic mirror, let alone capturing an airplane!

BOSchlieren is a Background Oriented Schlieren technique (BOS) sometimes also referred to as Synthetic Schlieren. BOS doesn't use a parabolic mirror and has no such size limitations!

The results of BOS are produced from digital processing of videos, meaning that the results can be filtered and displayed in a variety of ways post capture!

How does Background Oriented Schlieren work:

Background Oriented Schlieren (BOS), as the name implies, uses a contrasting pattern as a background and advanced software that analyses and measures the minute changes caused by air shimmers. This way there is no need for a parabolic mirror, point light source and a razor edge. One simply needs to position the subject between a speckled pattern and a camera, capture the video and analyse it using our "tracker" software (DISPLACEMENTS / Tracker (software)).

Both small and very large objects (such as planes) can be studied this way!

Background Oriented Schlieren
Schlieren examples:

A color coded visualization is used to show the effect. The visualization is superimposed to the video, therefore the magnitude can be altered to show a large dynamic range of the effect.

Check GALLERY / BOSchlieren examples for example videos captured with our systems.

If you are looking for more information about the technology or are interested in using it, contact us at

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