An Inexpensive Stroboscope for High Speed Photography

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An Inexpensive Stroboscope for High Speed PhotographyShirleigh Silverman and Wm. H. Warhus Citation: Review of Scientific Instruments 14, 273 (1943); doi: 10.1063/1.1770186 View online: View Table of Contents: Published by the AIP Publishing Articles you may be interested in Off the shelf inexpensive digital highspeed photography from CASIO Phys. Teach. 48, 559 (2010); 10.1119/1.3502522 High Speed Inexpensive Photodiode Assembly Rev. Sci. Instrum. 43, 865 (1972); 10.1063/1.1685791 HighSpeed Photography Phys. Today 9, 32 (1956); 10.1063/1.3059894 HighSpeed Stroboscope for Accelerometer Calibration Rev. Sci. Instrum. 25, 837 (1954); 10.1063/1.1771189 High Speed Photography Phys. Today 4, 32 (1951); 10.1063/1.3067307 This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: to IP: On: Fri, 19 Dec 2014 21:16:18 STROBOSCOPE 273 collected enough zinc oxide smoke directly onto the gold specimen to give a sufficient number of zinc oxide rings of suitable relative intensities concentric with those of gold. Photographs were also taken in shorter cameras. The rings on these photographs were just as well-defined and well-resolved as the others, and the measure-ments led to the same results to within 0.2 percent. From the ZnO photographs, on which at least twenty-five 'rings can be easily measured, we obtained by the method of least squares the following values for the axial ratio colao: 1.6019, 1.6015, 1.6028 (March); 1.6017, 1.6023 (June). The mean value is co/ao=1.60200.0005,8 in excellent agreement with Bunn's x-ray value 1.6020op=0.0001 and our own 1.60320.0010. Hence Finch and Wilman's electron diffraction value 1.607 0.002 is not confirmed by our work and Bunn's explanation of the "difference" in terms of the surface vs. the internal structure does not appear to be necessary. Fro'11 the ZnO+Au photographs we should be 8 This probable error is an estimated measure of the limits of fluctuation from one photograph to another. For measurements on individual photographs, the probable error (in the usual sense) for the axial ratio is ca. 0.0002. THE REVIEW OF SCIENTIFIC INSTRUMENTS able to determine the lattice constants for gold if we assume the lattice constants for zinc oxide, or vice versa. The first procedure was adopted, because our x-ray value for gold had not been made to the desired reliability. Thus we. found for gold ao = 4.05400.0015A (March); 4.0560 0.0015A (June). The mean value, 4.0550 0.0015A, is again in good agreement with Our own x-ray value 4.05490.0015A. Although we have not been able to understand the surprisingly low lattice constant for our gold specimen, we believe that part of the discrepancy in Finch and Wilman's lattice constants for zinc oxide might be attributable to the same source. At any rate, our work indicates that the wave-length calibra-tions obtainable with zinc oxide smoke and with gold foil are in satisfactory agreement. Table I shows the values of sin (J/X for the first fifty-four allowed reflections (for which 2h+4k+3lrf6n+3, n an integer) of zinc oxide calculated from Bunn's lattice constants. The corresponding values of 2 sin 8 calculated for X = 0.0610A are also tabulated in order to provide for easy indexing of the reflections. We wish to thank Dr. Verner Schomaker for the suggestion of this problem. VOLUME 14. ~UMBER 9 SEPTEMBER. 1943 An Inexpensive Stroboscope for High Speed Photography SHIRLEIGH SILVERMAN AND WM. H. WARHUS Pioneering Research Section, Rayon Department, Technical Division, E. I. duPont deNemours & Co., Inc., Buffalo, New York (Received June 18, 1943) A relatively inexpensive stroboscope of tbe Edgerton type for high speed photography has been built. A simple lamp of high light efficiency has been developed. Power requirements are of the order of 1 kva, and the parts are of the type found in most laboratories. Satisfactory photographs have been taken at rates up to 300 per second. INTRODUCTION DURING the past few years, Edgerton! and his collaborators have developed very ele-gant methods of high speed photography. Ex-1 Edgerton, Germeshausen, and Grier, J. App. Phys. 1, 8 (1937). This article contains an excellent bibliography on the subject of high speed photography. cellent photographs have been taken of ballistic phenomena, motions of textile machinery, and other transitory movements of short duration. The General Radio Company has pioneered in the commercial production of equipment for taking such photographs, and at the present time lists an apparatus capable of taking pictures This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: to IP: On: Fri, 19 Dec 2014 21:16:18274 S. SILVERMAN AND W. H. WARHUS FIG. 1. at rates as high as 1500 per second, with an average exposure time of several microseconds per frame. The equipment described in this paper was developed for the study of problems of rather modest proportions: problems in which speeds of approximately 300 frames per second are adequate. The power requirements are reduced accordingly, and are simplified, too, by the use of simple flash-lamps containing new inert-gas mixtures. The latest commercially available mix-ture of 80 percent Xe-20 percent Kr was found to be approximately SO percent brighter for a given power input than any previously avail-able gas. APPARATUS The general hook-up (Figs. 1 and 2) is similar to that described by Edgerton, Germeshausen, and Grier,! and differs principally in simplifica-tion of the power supply and lamps, and the in-clusion of a simple timing axis on the film. c;:----,-... + r~'~~ OUTP~ ~ PelCO SPARK COIL (IRON CORE RrnovEq FIG. 2. POWR St;PPLY FLA..sH LAMPS The camera used is a General Radio 6S1AG, equipped with a S.O-cm, f : 1.5 lens. A small i-watt neon bulb is mounted in a brass tube with a pinhole allowing light to fall on the perforated edge of the film. The usual 1S00-ohm resistor found in the base is remov~d and replaced with a SOO-ohm resistor to increase the brilliance of the bulb. The lamp, operating on 60 cycles, gives a good readable trace at intervals of 1/120 sec. on the perforated edge of the film. This trace can be read without difficulty to 1/1000 sec. The camera actuates a spark by the usual con-tactor on the drive drum, through the thyratron circuit shown in Fig. 3. This circuit fires through the primary of an ordinary automobile spark coil from which the iron core has been removed. The secondary of the spark coil triggers a mercury rectifying tube from an external electrode placed opposite the mercury meniscus. The mercury tube was made by a commercial sign company; it consists of 14-mm Pyrex tubing FIG. 3. Thyratron circuit. with two iron shell electrodes spaced 10 cm apart. The tube is held in a vertical position and sufficient mercury added barely to cover one electrode. The tube is evacuated and the mercury boiled gently to remove trapped vapors before seal-off. Ordinary laboratory shelf-supply mer-cury was found to be quite clean enough for the purpose. The flash-lamps themselves were also made by a commercial sign company. They are straight tubes of 18-mm Pyrex tubing, with cylindrical iron electrodes common to the neon sign trade. Electrode separation was fixed at 75 mm, and the tubes were filled with an 80 percent xenon-20 percent krypton mixture furnished by the Air Reduction Company. Optimum gas pressure was found to be about 14 mm. Some care is necessary This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: to IP: On: Fri, 19 Dec 2014 21:16:18INEXPENSIVE STROBOSCOPE 275 SAFETY DOOR nov ,-________ ~~SW~'~~~CH~------_mmr~~w,--,_.__,~+ FIG. 4. High voltage supply. T I , filament transformer; T2, variac; Ta, power transformer-2000 v, 1 kva; Sit filament switch; S2, double pole voltage switch; Sa, capacity switch; R, 45-sec. delay relay; Pit green pilot lamp; P2, red pilot lamp; Mit 0-1.0 amp.; M 2, 0-2.5 kv; CHI, input choke; CH2, filter choke. to get the tubes into a stable condition, and the following outgassing procedure was adopted: The tube is pumped to a residual air pressure of about 10 mm and a heavy discharge from a 10,000-volt transformer is passed until the electrodes are red hot. The tube is then pumped out untir the pressure is too low to support discharge. The tube is then filled to about 20 mm with Xe-Kr mixture and the process repeated. The tube is then filled with the inert gas mixture to about 14 mm and sealed off. Tubes prepared in this manner proved to be about 90 percent satisfactory. The condensed spark discharge through these tubes is an intense blue white, and the photo-graphic efficiency of this illuminant was found to be as much as 200 percent that of similar tubes filled with earlier gases such as argon or 90 per-cent Kr-l0 percent Xe. The power supply, operating at 2000 v and discharging through 2 /If as shown in Fig. 4, was ample for firing two of these tubes in series with the mercury diode. To improve illumination the discharge tubes are mounted in individual parabolic reflectors with their long direction along the axis of the shield. The lifetime of the mercury rectifier is indefinite, and the discharge tubes themselves will withstand many thousands of flashes before failing. The power pack circui t is shown in Fig. 4. The filter chokes are unnecessary for this type of work, but they were put in as a matter of choice to allow for the possibility of using the power pack for other purposes. The capacity is kept at 2 /If and although the transformer is rated at 2000 v, the voltage falls below this level when the exposure rate runs over 100 frames per second~ There is no tendency toward unequal drain in successive exposures, however, and a complete roll of 100 ft. of film will be uniformly exposed. A lens aperture of f : 3 is adequate for sub-jects of normal contrast for pictures taken at 100 frames per second or less, with a lamp-object distance of three to four feet. At 300 frames per second, an aperture of f : 2 is found desirable at similar lamp-object distance, as the briliiance per flash is reduced by the failure of the condenser to reach full voltage. The authors have felt it worth while to prepare this communication since the apparatus de-scribed herein may prove useful to persons whose needs for stroboscopic photography are limited to exposure rates of several hundred frames per second, and whose budgets restrict them largely to apparatus that may be assembled in the laboratory. In conclusion, the authors are much indebted to the Claude-Neon-Russell Company of Rochester, New York for their care and consideration in preparing the lamps for this camera, and to the Air Reduction Company of New York for co-operation in supplying the inert gas combinations which were used in this research. This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: to IP: On: Fri, 19 Dec 2014 21:16:18