CHAPTER N 



UNDERWATER PHOTOGRAPHY 



N-1 General Remarks. — Recent years have 

 seen a marked increase in the development and 

 use of imderwater photography. Location and 

 identification of sunken ships and other sub- 

 merged objects, studies of bottom topography, 

 studies of fish and other biological life, studies 

 of reefs and coral growth, and studies of the 

 ocean bottom in relation to its sediment struc- 

 tures are a few of the many applications of un- 

 dei'water photography. 



N-2 Underwater Cameras. — Underwater 

 cameras may be classified under two categories : 

 Those operated in shallow water by divers, and 

 those automatic deep sea systems that are low- 

 ered from ships. Both gi-oups use either color 

 or black and white film. The deep sea under- 

 water camera systems are automatic systems 

 that are lowered from ships or installed on deep 

 sea submersible vehicles. The Edgerton, Ger- 

 meshausen, and Grier (EG&G) deep sea under- 

 water camera systems (fig. N-1) used by the 

 Oceanographic Office to produce stereo, double- 

 camera, or single-camera photography make 

 use of the following components: (1) Camera, 

 35 mm., Still, Electrically-driven; (2) Light 

 Sources; (3) Battery Pack; (4) Mountmg 

 Rack; and (5) Sonar Pinger. 



N-3 Camera (EG&G Model 204).— This cam- 

 era (fig. N-2) is an electrically-driven, 35-mm., 

 still camera encased in a watertight steel hous- 

 ing tube. The housing tube is designed to oper- 

 ate to a maximum pressure depth of 17,500 psi. 

 The camera takes about 500 separate exposures 

 on a standard 100-foot roll of film. The lens, an 

 f/4.5 Hopkins, is specially designed to correct 

 for the distortion introduced when light passes 

 from the water through the housing window to 

 the air inside the camera housing. The lens is 

 prefocused to give a depth of field in water of 

 about 314 to 20 feet. The maximum distance 

 above bottom at which photographs of the bot- 

 tom are possible is determined by the film 

 speed, light intensity, and lens aperture. 



N-4 Light Source (EG&G Model 214).— II 



lumination for underwater photography is pro- 



vided each camera by an accompanying 200 

 watt-second, electronic flash (strobe) unit (fig. 

 N-3) . The unit is enclosed in a water-tight steel 

 housing tube and utilizes a Xenon flashtube 

 which is fired by a bank of capacitors. These 

 strobe units are designed to work in synchroni- 

 zation with the camera advance motor. Ap- 

 proximately each 15 seconds, the capacitors dis- 

 charge and fire the strobe light; then, during 

 tlie next 6 seconds, the film advance motor 

 moves the film to the next frame; meanwhile, 

 the capacitors are being charged to repeat the 

 cycle. 



N-5 Battery Pack (EG&G Models 280 and 

 281). — Power for the light source and the cam- 

 era motor is supplied by two battery packs (fig. 

 N-4). Tliey are contained in steel tubes similar 

 to those of the camera and the light source. Each 

 battery pac-k contains two series connected six- 

 volt, silver zinc wet cell batteries (fig. N-5). 

 Model 280 contams a clock-driven mechanical 

 time delay switch, and Model 281 contains a 15- 

 second cycling device. Batteries usually must be 

 recharged after each lowering. 



N-6 Mounting Rack. — U.S. Naval Oceano- 

 graphic Office survey ships use 6-, 8-, and 12- 

 foot long Unistrut (a registered trade name) 

 mounting racks for miderwater photograpliy. 

 The racks are designed to accommodate a vari- 

 ety of camera arrangements. The rack is con- 

 structed of galvanized or stainless steel channel 

 members, brackets, spring-loaded nuts, bolts, 

 and instrument holders. The spring-loaded nuts 

 slide to any position in the channel members so 

 that cameras, light sources, battery packs, and 

 pinger can be mounted to suit the project at 

 hand. 



N-7 Sonar Pinger. — The Sonar pinger is a 

 battei-;y' powered, automatic-cycling, submersi- 

 ble, sound-generator unit for positioning ocean- 

 ographic equipment within measured distances 

 of the ocean floor. Chapter R gives a complete 

 description of the Sonar pinger. This unit oper- 

 ates independently of the camera components. 



N-1 



