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A TECHNIQUE FOR MULT I FLASH PHOTOGRAPHY OF UNDERWATER 

 EXPLOSION PHENOMENA 



A. R. Bryant and K. J. Bobin 



August 1945 



Summary . 



A iTiethod is described which enables a number o^ photographs to be taken at one rniU isecond 

 intervals of explosion bubbles produced by the detonation underwater of charges weighing about i 02. 

 A total of forty to fifty pictures in two groups nay be taken, the two groups being usually timed to 

 cover the, period when the bubble is near its first and second minima respectively. 



Light from an Arditron discharge lamp is focused by a large metal reflector placed underwater 

 on to the lenses of a twin drum camera housed in a watertight casing situated at the same level as the 

 charge, thus producing a bright field of light against which the bubble appears silhouetted. 



The electrical gear producing the discharges in the Arditron is housed in a laboratory near 

 the experimental tank and connected by ao feet of cable to the Arditron which is situated just above 

 the water. 



A description of the electrical circuits and the underwater camera is given together with a 

 set of photographs frcm a typical shct. 



Introduction. 



In two previous papers (1) a method has been described for obtaining single flash photographs 

 of an underwater explosion bubble produced by small charges. In order to determine the behaviour of 

 the bubble in the neighbourhood of targets such as the box-model, however, it was necessary to devise 

 some method of taking a succession of pictures during the course of a single explosion. This note 

 describes apparatus developed for this purpose. 



Gene ral Arrangemen t . 



Figure 1 shows diagranmat ically the experimental arrangements. A rptating twin-drum camera 

 housed in a watertight casing, and with all controls electrically operated, is bolted on to a rigid 

 steel framework which is lowered by crane on to the sloping side of the experimental tank and clamped 

 in position with the camera at the required depth..- Light from an Arditron discharge lamp in a housifig 

 just above the water's surface, illuminates a large curved metal reflector and is focused on to the 

 camera lens as shown, so that the reflector appears in the photograph as a bright ground more than 

 filling the field of view. The charge and the target are suitably placed to appear silhouetted 

 against this reflector. 



The Arditron lamp is operated stroboscopically by electrical equipment housed in a nearby 

 laboratory, the lamp teing connected to the equipment by high voltage concentric cable. since most 

 of the bubble shape changes and displacements occur when the bubble is small, and since these are the 

 times when the bubble causes damage, it was decided to restrict photographs to two periods near the 

 first and second minima respectively. The apparatus has therefore been arranged to take a total 

 of forty to fifty pictures in two groups, one on each camera drum, the pictures in each group being 

 spread at 1 millisecond intervals. 



Mult if lashing 



