Schlieren photography

The Schlieren photography is a photographic technique that was developed in 1864 by the German chemist and physicist August Toepler.

The phenomenon that rising air currents maintain on a Sunlit reason their shape and position to change irregular and distorted considered by this air flow objects and appear flickering can be more generally used for identification of variations in the optical density ( gradient of the refractive index) in liquids and gases.

This may be. Around the currently running mixing or solution of various substances with each other to act or thermal convection, for example, air shock waves to flying projectiles or profiles in the wind tunnel

Applies this method accordingly streaks in fluid mechanics, ballistics, the study of propagation and mixing of gases and solutions, and the investigation of heat transfer by convection.

Generating a schlieren receiving the volume to be examined region ( layer) is imaged by an objective, wherein the light of the image is partially intercepted by a shutter in the form of an edge. This is accomplished by the serving for the illumination light source is point-like as possible, and the wedge diaphragm is located exactly at the image plane of the light source.

Density fluctuations of an inhomogeneous medium, in which layer a part of the light rays guided past the edge and create brightness fluctuations in the image ( for example on a ground glass screen ), whereby an image of the local gradient of the refractive index arises.

A similar process is used in the Eidophor video projection - in this case, however, the non-homogeneous layer is an oil film, which is structured by an electron beam.