Schlieren optics and the very similar shadowgraph are density-gradient visualization techniques that have been widely used in education and research for a very long time.1,2 There are numerous videos and images of their use on the internet and many articles and websites available.
Numerous configurations for educational applications have been developed. Veith and Friege were able to visualize sound waves using a classical digital camera.3 Gearhart and MacIsaac created shadowgraphs using an iPad.4 With the spread of mobile phones, their use has come to the foreground,5 but the setup is still not simple as the light source, aperture, mirror, and camera require careful adjustment.
In the present article, it will be shown how to achieve good-quality schlieren photography with only a mobile phone and a mirror, which is most likely a setup that cannot be simplified any further. The theoretical background of the method is well...
