976 
(c) 
(a) 
For most single flash photographs, Zastman Contrast Process Ortho film was used 
and developed in D-11. Typical lens openings with a 250 gm explosive flash charge 
at 8 ft. from the camera varied from f/3.5 to f/8 depending on water conditions. 
Cameras for flash photography. -- A variety of cameras were used for flash 
photography with approximately equal success. In order to keep the size of the 
equipment at a minimum, 35 mm still cameras were used. 
(4) Argus C-3. Figure 1 shows the Argus C-3 camera and its water and explosion- 
proof case. This camera has an internal synchronizer which was sometimes 
used to set off explosions when the shutter was at its maximum opening, The 
case was constructed from 6 1/2 in. 0.D. by 3/4 in. thick steel pipe and the 
window is of 1 in, thick "tempered" glass having a 2 1/8 in. diameter for the 
unsupported area. The case and window have successfully withstood the 
explosion of a 300 pound charge 50 ft. away, both charge and camera case being 
at a depth of 40 ft. 
(11) Kodak "35". Figures 2 and 3 show a Kcdak "35" and case. This case which was 
made from a pipe coupling, has also survived the explosion of a 300 pound 
charge at 50 ft. The camera was later modified as shown in Figure 4 which 
shows a much smaller homemade camera using the lens and shutter of the Kodak 
35. A smaller case would obviously have been built for this camera. 
(iii) UERL camera. In the early stages of this work it was considered that com- 
mercial cameras might not be rugged enough for the work we were doing, and 
a camera with laboratory designation "Brute" was constructed. The "Brute" 
camera consisted merely of a solid brass cylinder with a heavy spring-driven 
rotary shutter, a hole for the lens, and another for the film. The camera 
also contained a "foolproof" synchronizer for firing the charge which con- 
sisted of a contact made by the shutter at any desired time in its travel. 
By using an SSS seismographic cap (No. 8) which explodes within a millisecond 
of the time the circuit is closed, the synchronizer could be set to close the 
circuit when the shutter was barely opened and the timing would then auto- 
matically be right. 
Subsequent experience showed that the commercial shutters were sufficiently rugged 
so long as they were not immersed in sea water, and the "Brute" camera was rarely 
used, 
The cameras were all mounted on rubber as a matter of principle. 
(iv) Automatic photography. One photograph was obtained by means of an automatic 
rig. A charge was detonated which activated a pressure switch. The pressure 
switch closed a solenoid circuit which tripped the camera shutter. As the 
shutter opened, a synchronizing switch fired a cap in the flash charge, The 
battery required was enclosed in the camera case. The resulting photographic 
image is not reproduced. This method can be used in experiments in which 
external connections with the camera are undesirable or impossible. 
Light sources. -- Still close-up photography of explosion phenomena requires 
exposures of the order of a (sec and a light source of about a million candle- 
power. A satisfactory source “of light was developed by the Explosives Research 
Laboratory at Bruceton, Pennsylvania 2/ utilizing a spherical cast explosive 
charge of pentolite mounted concentrically in a round bottom glass flask; the 
space between the charge and flask being filled with argon at atmospheric pressure. 
Duration and intensity of the light increased respectively with the thickness and 
area of the argon layer. 
2/ The Flash Photography of Detonating Explosives to May 1, 1943, Explosives Research 
Laboratory, Bruceton, OSRD Report 1488. 
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