Abstract
The history of shadowgraphy was covered in Chap. 1, with more depth given below. The theory of light refraction by a schlieren object, underlying both schlieren and shadowgraphy, is given in Chap. 2 and Sect. A.6. In Sect. 2.3 a distinction was drawn between schlieren and the more-rudimentary approach of shadowgraphy, while in Sect. 2.4 the simple “direct” shadowgraph principle was stated. Here the various shadowgraph methods are covered in detail, naturally dividing them into “direct” and “focused” methods and a collection of lesser miscellany.
Shadow is the means by which bodies display their form.
Leonardo da Vinci, Notebooks
This method of observation is absolutely new, and I invite all physicists to try it. I believe it will lead to new discoveries in certain branches of physics
J. P. Marat [28]
In many cases where this method is employed there is a certain element of risk for the film, if not for the photographer1
W. F. Hilton [122]
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This comment by aerodynamicist William F. Hilton (1912–1997) refers to traditional “direct” shadowgraphy’s need for close proximity of the film to the test subject in the dark, which can sometimes be dangerous (e.g. explosions, propellers, and bullets in flight).
Schardin [2] erroneously showed this peak at g/h=0.25, not 0.5. The mistake was later corrected by Weinberg [66] and Kessler and Hebenstreit [498].
Recall from Chap. 2 that a light ray passing through the forward focal plane of a lens — regardless of the ray angle — is returned to its same relative location at the back focus.
Occasionally, in thousands of references, schlierenis promised but a shadowgram is actually delivered. Aside from ignorance and the discrepancy in translating “shadow methods” from the Russian (noted earlier), the only other explanation is that the schlieren cutoff is either ineffectual or missing altogether. What then remains is the superimposed “focused” shadowgram, e.g. [1016].
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© 2001 Springer-Verlag Berlin Heidelberg
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Settles, G.S. (2001). Shadowgraph Techniques. In: Schlieren and Shadowgraph Techniques. Experimental Fluid Mechanics. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-56640-0_6
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DOI: https://doi.org/10.1007/978-3-642-56640-0_6
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