989 
on the ends of the case prevent camera motion along the axis of the cylinder. 
The case for this camera is made of standard 16 in. 0.D. by 3/8 in. wall 
thickness steel tubing, and the ends are hot rolled steel 1 in. thick. We 
have never tested this case near its ee strength, but it was calculated 
that it would stand over 1000 lbs./in.* static pressure and considerably more 
dynamic pressure of low time constant, 
The high speed camera can be used at speeds up to 3000 frames per second. 
Due to the rotating four-sided prism that is interposed between the lens and 
the film, the ratio between exposure time and the time between frames is fixed 
at 1/4 and the minimum exposure time is 80 microseconds. Another effect of 
the optical system is that it requires long focal length lenses (63 mm mini- 
mum) with the result that the field of view is small (angle of view ca. 5°) at 
reasonable object distances. This feature is a drawback in underwater photog- 
raphy due to the further restrictiond the field which results from the high 
index of refraction of water, and the severe limitations on object distances 
due to water turbidity. 
(14) Jerome camera. Figure 14 shows the Jerome 35 mm camera. This camera is of 
a conventional type, electrically driven, and is limited to speeds slower 
than 100 frames per second. The angular opening in the shutter is variable, 
-go that exposures as short as one millisecond can be made. A 1 in. focal 
length lens was used to obtain the widest possible angle of view. The shock 
mounts shown in the figure engage tracks in the case. 
(411) Victor camera. Our first underwater movies were taken with an ordinary 
spring-wound 16 mm camera running at 64 frames per second, with an exposure 
time of approximately 1/130 second. 
(b) Associated equipment for underwater photography. 
(4) Underwater gear, One of the rigs used for photographing damage to cylindrical 
targets is shown in Figures 15 and 16. The photograph (Figure 15) shows the 
rig arranged for photographing by reflected light while the drawing (Figure 
16) shows the set-up for silhouette. The parallel beams in this frame can 
be extended to obtein greater object distances. Figure 17 shows the firing 
circuit diagram. 
(ec) ht_s es. 
(4) Photoflash lamps. In order to increase the duration of the illumination used 
in these photographs, several photoflash lamps may be set off in sequence by 
means of the rotating commutator switch shown in Figure 18. The proper time 
interval to use between #31 photoflash lamps is 80-100 milliseconds. In the 
clear waters around the Bahamas, it was found that a good silhouette of a 
cylinder could be obtained at 2500 frames per second with the lens at f/11 
using two #31 photoflashes 9 ft. from the camera. 
(41) Mergury Arc. The light source used with the Victor camera was a G. E. high 
pressure H-6 mercury arc. This proved satisfactory except that in a fair 
fraction of the experiments the light was extinguished by the shock wave. 
Furthermore the intensity is too low for high speed work, and 60 cycle fluctu- 
ation would be undesirable in short exposure pictures. 
(4) ipers. -- Each camera is equipped with a small neon flasher which provides timing 
by marking the edge of the film at a frequency determined by tuning forks - 1000 
cycles for the High Speed and 50 cycles for the Jerome. Circuit diagrams for the 
power supplies that operate these lamps are given in Appendix III. 
(e) Power supply for cameras. -- The cameras must be brought up to speed gradually. 
The High Speed is equipped with an internal mechanism which cuts out a resistor 
and provides for gradual acceleration. The Jerome is accelerated by hand with a 
Melia: ae Speed requires about 1.5 kw (2 at starting) and the Jerome 
ss than ° 
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