effect is often used in video projector technologies. The basic idea is some device, such as a liquid crystal light valve, is used to produce schlieren distortions in a controlled manner and these are projected on a screen to produce the desired image. Projection display systems such as the now-obsolete Eidophor and Talaria have used variations of this approach as far back as the year 1940. See also Background-oriented schlieren technique Laser schlieren deflectometry Mach–Zehnder interferometer Moire deflectometry Schlieren imaging Schlieren photography Shadowgraph Synthetic schlieren References External links Background oriented schlieren for flow visualisation in hypersonic impulse facilities Visualisation of supersonic flows in shock tunnels using Background Oriented Schlieren (BOS) technique Video on Schlieren photographs Schlieren on YouTube Optics German words and phrases Articles containing video clips ja:シュリーレン現象