Abstract
The users of schlieren techniques since Toepler’s time have been a prolific group. Eager to add their own touch, they have invented, published, and re-invented dozens of adaptations and changes, grouped here into a few general categories. This diversity may be due in part to the lack of standardized commercial schlieren instruments; users having to build their own naturally add improvements and variations along the way. In any case the trend continues right up to the present, revealing that schlieren techniques still constitute a healthy theme of optics and experimental physics. A few specialized techniques not covered in this Chapter are instead included in Chap. 10 on Quantitative Evaluation.
Genius is nothing more than knowing the use of tools, but there must be tools for it to use.
Samuel Johnson
The result of the experiment depends on the nature and the quality of the tools, not on the ideology of the experimenter.
Freeman Dyson, in ‘The Sun, the Genome, and the Internet’
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Linearity is shown in Fig. 5.1 and is assumed here for convenience. But in fact, nonlinear graded filters can be made and used, and even an honest attempt to fabricate a linear graded filter can result in partial nonlinearity [283].
It was noted by some [130, 146, 154] that the knife-edge schlieren system is not strictly linearly-sensitive to phase gradients from the Fourier-optics standpoint (see App. B), as it is when based purely on geometric optics (see Chap. 3). Zakarin and Stricker [1013] found geometric-optical behaviour with incoherent light but not with coherent light.
See Eqn. 4.7. A method is also given by Hosch and Walters [171] to estimate the size of a slit or other limiting aperture in the cutoff plane for a certain image resolution.
All the dissection techniques, Figs. 5.8j-l, are characterized by relatively-large apertures in the schlieren cutoff plane to avoid image resolution loss due to slit diffraction.
In fact, Nomarski Differential Interference Contrast, which yields colored microscope images, is credited [296] with replacing Rheinberg illumination for that purpose. The opposite holds t rue in schlieren imaging, however: Rheinberg-type color schlieren methods (Sect. 5.2) are dominant and differential interferometry is seldom-used in comparison.
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© 2001 Springer-Verlag Berlin Heidelberg
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Settles, G.S. (2001). Specialized Schlieren Techniques. In: Schlieren and Shadowgraph Techniques. Experimental Fluid Mechanics. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-56640-0_5
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DOI: https://doi.org/10.1007/978-3-642-56640-0_5
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