Abstract
In this chapter let us examine how the schlieren and shadowgraph techniques work in principle. The details of how they work in practice will come later.
The basic principle of the schlieren technique is the combination of the optical projection of an object with an indication of its light deflection. Hubert Schardin [2]
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For non-parallel-light illumination, z is measured along radii from a point light source at a finite distance.
A quantitative schlieren method [118] has been used to estimate the effective focal length of a candle plume: −20 to −25 m.
Long before video and computers, evening entertainment was provided by casting candlelight shadow-plays on a wall. Artful shadowcasters used their hands to portray characters: a duck, a dog, Sherlock Holmes. This was called shadowgraphy well before the present connotation arose. An example is seen in the famous Orson Welles movie Citizen Kane.
No focusing lens was in Fig. 2.3 because, in principle, a point-source optical system has an infinitesimal aperture — like a pinhole camera— and thus infinite depth-of-field. In this case disturbances anywhere along the optical path are automatically in focus.
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© 2001 Springer-Verlag Berlin Heidelberg
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Settles, G.S. (2001). Basic Concepts. In: Schlieren and Shadowgraph Techniques. Experimental Fluid Mechanics. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-56640-0_2
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DOI: https://doi.org/10.1007/978-3-642-56640-0_2
Publisher Name: Springer, Berlin, Heidelberg
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