Schlieren Optical System
Schlieren optics show changes in the condition of a test area of space in the optical path, even when it remains fully transparent. A simplified outline of the arrangement is shown in the scheme at left. A source sends out a beam of light through the apparatus to a film.
Half the field is cut off by a knife-edged screen, K1, which is imaged by a lens, L1, to a position, K1′, in the same plane as a matching screen, K2. The knife-edges of image and screen exactly coincide. A test position, T, is sharply focused on the film. Thus the light flow past K1 to K2 is all cut off from the film if the space at T is completely uniform. Any nonuniformity, such as caused by a wave front in the air at T, causes a scattered light beam to evade the screen, K2 (path a), and reach the film.
Read more about this topic: August Toepler
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