19. UNDERWATER PHOTOGRAPHY 



H. E. Edgerton 



1. Introduction 



Next best to active personal observation or remote television viewing is the 

 photographic camera record with its tremendous ability to memorize a scene 

 for later and repeated study. Even when a person does descend into the sea to 

 observe, he also greatly needs a camera: (1) to help him remember exactly 

 what he saw ; (2) to enable him to show the original subject or view to others ; 

 and (3) to record rapid events which he might not notice. 



There are many technical difficulties to be solved when a vehicle is designed 

 to transport a human observer to depths in the sea. The vessel must be capable 

 of navigation in three dimensions under control of the crew. Safety is an im- 

 portant requirement. Support of auxiliary vessels is necessary. As a result, 

 very few devices have been built for exploration in the sea because of the 

 complications of construction and operation. 



The camera itself can go into the sea without human accompaniment to 

 record original information, which is then studied later by scientists. In this 

 way, a relatively simple device, which can be considered expendable, goes into 

 the deep inaccessible parts of the oceans with ease. Dm^ing the wave of explora- 

 tion of the oceans that is scheduled for the next decade, the camera, of both 

 still and motion-picture type, will be exploited fully because of its ease of 

 operation compared with other systems involving people or electrical 

 connections. 



It is fortunate that most of the sea is clear of light-diffusing or scattering 

 material so that an optical camera can function. Only near the coast is the 

 water full of sediment which makes it impossible to take photographs unless 

 tlie dirty w^ater in the optical path is displaced. 



Since light from the sun is absorbed by water almost completely at shallow 

 depths, the cameras require artificial light for photography. Flash seems the 

 most advantageous since the light is only on when the photograph is being 

 taken. The expendable flash bulb has been and still is greatly used for single 

 exposures per camera lowering. The electronic-flash system is in very common 

 use for camera systems involving more than one photograph. 



Advantages of the electronic flash (strobe system) are : (1) many flashes can 

 be obtained efficiently from a small battery ; (2) the instant of flash can be 

 electrically controlled: (3) the color is daylight in quality; and (4) the flash 

 duration is short, producing clear photographs of rapidly moving objects. 



Strobes with 20 W-sec input at 24 flashes per second have been used with 

 motion picture cameras at depths of 3000 m. The camera-lamp assembly 

 mounted on a rugged sled can be dragged across the bottom, obtaining a 

 dynamic view of the scene that exists there. Single-flash still cameras with 

 100 W-sec of energy in the flash have been used in many ways to make both 

 mid-Mater and bottom photos. The electronic-flash equipment used under 



[MS received January, I960] 473 



