We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
Fig. 22. Cranz-Schardin optical setup.
Fig. 23. Thirty-objective camera for use with the Cranz-Schardin optical setup.
rate range can easily be obtained by changing a few condensers and resistors. The light sources are krypton tubes of the type shown in Fig. 7C. They may be oriented either horizontally or vertically by rotating the plastic tube mount (Figure 26). The 30 pictures are formed on a standard 24 X 30 cm plate. The 30 objectives are merely achromatic lenses with a focal length of 345 mm and an //number of 1/14. The 30-objectives camera is shown in Fig. 23. Adjustable schlieren knife-edges may be placed in front of the objectives.
For silhouette photography, the optical system consists of an ordinary condenser
with a diameter of 40 cm and a focal length of 1.8 m. The distance between the light sources and the objectives is thus 7.2 m. For schlieren work, we use a single concave mirror accurate to one wavelength, with a diameter of 50 cm and a focal length of 3 m, but it should be noticed that, with the V setup using a mirror, the field common to all frames is much smaller than the mirror diameter (Fig. 24). This is due to the dimensions of the source and objective assemblies, which introduce a noticeable parallax, and to the fact that the subject should be placed sufficiently ahead of the mirror to be crossed only once by the light rays. These facts make the use of the Z setup with two mirrors almost impossible for multiple-frame schlieren photography.
As early as 1929, Cranz and Schardin used this optical setup, with spark-gaps instead of gas tubes, in conjunction with a purely electrical method of control. The Cranz-Schardin circuit essentially consists of a number of Mach LC delay networks connected in cascade. Up to 24 frames at rates ranging from a few thousands to one million frames/sec were successfully obtained. This instrument was further improved by Vollrath at the Ballistics Research Laboratory at St. Louis, France, where several units are in current use. The chief disadvantage of such purely electrical devices is their bulkiness.
618
May 1953 Journal of the SMPTE Vol. 60