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Über dieses Buch

Schlieren and shadowgraph techniques are basic and valuable tools in various scientific and engineering disciplines. They allow us to see the invisible: the optical inhomogeneities in transparent media like air, water, and glass that otherwise cause only ghostly distortions of our normal vision.

These techniques are discussed briefly in many books and papers, but there is no up-to-date complete treatment of the subject before now. The book is intended as a practical guide for those who want to use these methods, as well as a resource for a broad range of disciplines where scientific visualization is important. The colorful 400-year history of these methods is covered in an extensive introductory chapter accessible to all readers.

Inhaltsverzeichnis

Frontmatter

1. Historical Background

Abstract
It has been on my mind for years to tell the history of schlieren and shadowgraph techniques in detail and proper chronological order. This story reveals a connection generally unappreciated amongst the works of several well-known fathers of technology and others not so well-known, at least not in this context. It is the story of a way of seeing the invisible, and of discoveries centuries before their time; discoveries that nonetheless eventually played an important role in far-flung branches of science and technology. Other elements of this history touch on the key role of direct observation and the almost-lost art of ingenious bench-top experiments in physics. Despite beginnings centuries ago, only now can a complete history be written — thanks in large part to the scholarship of several colleagues who have a fine appreciation of history [11–13].
G. S. Settles

2. Basic Concepts

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.
G. S. Settles

3. Toepler’s Schlieren Technique

Abstract
Why do we call it Toepler’s technique? Recalling Chap. 1, although Toepler was not the strict originator of schlieren imaging, he made it what it is today. Here, Toepler’s schlieren technique distinguishes the basic (lens or mirror) schlieren system with slit-source and knife-edge from all the other adaptations that have arisen since his time.
G. S. Settles

4. Large-Field and Focusing Schlieren Methods

Abstract
Schardin essentially overlooked the large-scale possibilities of the lens-and-grid schlieren technique which he and H. Maecker pioneered [2]. Sixty years later, this and other opportunities have emerged to free the schlieren technique from its traditional bonds of small scale. Concurrently some of these approaches allow narrow depth-of-field as well, hence the ability to focus upon a “plane” in a 3-D schlieren field. Both possibilities are crucial to the renewed vitality of schlieren imaging.
G. S. Settles

5. Specialized Schlieren Techniques

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.
G. S. Settles

6. Shadowgraph Techniques

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.
G. S. Settles

7. Practical Issues

Abstract
Of course nowadays all respectable experiments must employ a laser; you can hardly walk down the street without one.
Sir Brian Flowers, in Proc. 11th Intl. Congr. on High-Speed Photography
Light sources have improved tremendously since Hooke’s first candle-illuminated schlieren system. Combustion lamps eventually gave way to electric sparks, arcs, and filaments, which were then supplemented by coherent and solid-state devices. There is now an expansive literature on the topic that needs no thorough review here. Instead some key references are cited, followed by a brief treatment of the important lamp types for schlieren and shadowgraphy.
G. S. Settles

8. Setting Up Your Own Simple Schlieren and Shadowgraph System

Abstract
In some sense this is a stand-alone Chapter. It describes a modest schlieren system that should be within the financial and technical means of just about anyone who has read this far. Variations of this optical system were built as science-fair projects by several generations (see Stong [344,385,386,532]), and that is, in fact, how your author got his humble start in schlieren imaging at age 16 [385,532]. The optical setup suffices for both schlieren and shadowgraphy, the latter by either direct parallel-light or in the “focused” shadowgraph mode. It deliberately evokes Scientific American magazine's Amateur Scientist section in its heyday, when C. L. Stong’s text and Roger Hayward's splendid artwork helped convince amateurs that it was both fascinating and fun to build the simple — and sometimes not-so-simple — apparatus described there. The same schlieren system is now used as a learning tool by students of the Penn State Gas Dynamics Laboratory. So, despite the science-fair flavor, professionals who are new to schlieren and shadowgraph techniques can equally benefit from this exercise.
G. S. Settles

9. Applications

Abstract
Schlieren and shadowgraphy are paradigms of scientific visualization that permeated the fabric of science and technology during the 20th Century. Both Schardin [2] and Holder and North [98] surveyed this broad range of applications thoroughly. Though technical journals have mushroomed since then, computerized databases and the Internet allow me to continue that tradition here. I make no attempt to cite every reference, but give special attention to the several new and unusual applications that turned up. Of many possible classification schemes, grouping schlieren that occur in solid, liquid, and gaseous states seems the most natural.
G. S. Settles

10. Quantitative Evaluation

Abstract
When the schlieren publication rate ballooned to hundreds of papers per year after World War II, about 10% of them involved quantitative evaluations: This fell dramatically in the 1970's when laser interferometry, a more-directly-quantitative optical tool, took precedence. Still, a few percent of present-day schlieren publications remain quantitative and some interesting possibilities still exist, especially now that digital image processing eases much of the drudgery [357].
G. S. Settles

11. Summary and Outlook

Abstract
Throughout the writing of this book I expected to gain a new perspective on the time-honored techniques considered here: approaches not tried before, clues to important new applications, and a broader appreciation of the role schlieren and shadowgraphy-the optics of inhomogeneous media-play in science and technology. Now comes the moment of truth.
G. S. Settles

Backmatter

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