PHOTOGRAPHY OF UNDERWATER EXPLOSIONS 



217 



can be used at even higher frame speeds but the duration of exposure is 

 greater (e.g., 80 microseconds for the Eastman High-Speed running at 

 3,000 frames per second). 



A number of varieties of continuous high intensity sources have 

 been used, among which may be mentioned capillary high-pressure 

 mercury arcs and underwater flares. For the relatively short times of 

 1 or 2 seconds at most, photoflash bulbs with durations of from 6 to 100 



— DETONATOR 

 -TETRYL 



SHOCK 

 FRONT 



GLASS WALLED TANK 



LIGHT SOURCE 



ONE FOOT 



50 MICROSECO^CS 



(a) (b) 



Fig. 6.2 Shock wave velocity measurements for small charges. 



milliseconds can be simply employed, several bulbs being fired in se- 

 quence by mechanical or electrical means if it is necessary to prolong 

 the illumination. A difficulty common to many such sources is their 

 relative fragility, as a result of which they must be suitably protected 

 from shock wave pressures if they are not to be extinguished or dam- 

 aged. This consideration evidently also applies to cameras, which 

 must be housed in cases strong enough to withstand hydrostatic and 

 explosion pressures. In extremely clear open water natural sunlight 

 may be adequate for photography of relatively slow motions. As an 

 example, motion pictures of the bubble pulsation from 50 and 300 pound 

 charges have been taken from 60 feet with natural sunlight in water off 

 the Bahamas. 



E. Lighting and synchronization. The most effective lighting ar- 

 rangements evidently depend on the end to be achieved, and so many 

 variations are possible that it would be futile to attempt any very gen- 

 eral rules. Such things as suitable arrangements of source and camera 



