320 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1960 



of the visual range. In the deep sea we find that water has great 

 clarity owing to the absence of suspended matter and that for ranges 

 up to 20 feet or so no loss of definition of the image occurs. Thus a 

 conventional camera viewing through a plain glass window with suit- 

 able illumination will give a good picture. There is, however, one 

 optical problem that arises if high-resolution, wide-angle photographs 

 are required. The path of light from water into air is refracted at 

 an oblique interface, the refraction being a function of the wave- 

 length. Hence, the angular field of view of the lens is reduced and, 

 unless monochromatic light is used, the image off the axis is not sharp. 

 The first effect is not important unless maximum coverage is required. 

 The second effect can be corrected by placing in front of the camera a 

 suitable lens that will introduce an equal amount of chromatic aber- 

 ration in the opposite sense. 



In the shallow water around tlie coasts and on the continental slope, 

 the turbidity of the water is an important limiting factor. In many 

 places, especially in harbors and river mouths where photography 

 has important practical applications, the visibility is reduced to a 

 foot or less, and if photographs are required, a means has to be found 

 of displacing the turbid water in the object field with clear water. 

 This is a difficult practical problem, and photography in shallow water 

 is, therefore, of only limited use. 



The practical design of a deep-sea camera can best be illustrated 

 with reference to the one designed and built at the National Institute 

 of Oceanography (England) [2]. Tlie camera consists of three basic 

 units, the photographic unit, the flashlight unit, and the acoustic trans- 

 mitter or "pinger" unit. Each of these has its own watertight casing 

 and its own power supplies. The watertight cases are required to with- 

 stand external pressures up to 10,000 Ib./in.^ The simplest cases for 

 the purpose are cylindrical, and, in order to keep the overall weight 

 to a minimum, an internal diameter of 3 inches was chosen. The cases 

 are of light alloy having a wall thickness of three-fourths of an inch 

 and being sealed throughout by 0-ring seals. The window for the 

 camera is made of Perspex in the form of a truncated cone 11^4 inches 

 thick, in a conical seating. 



The photographic unit comprises a lens and shutter, 15 feet of 35- 

 mm. film enabling a series of up to 100 pictures to be taken, and a 

 motor and gearbox, driven by torch batteries, to move the film auto- 

 matically after each exposure. This unit is shown in plate 1, figure 1. 

 The electronic flasli unit is of conventional design working from dry 

 batteries and generates 100-joule flashes. The pinger unit, which is 

 triggered when a photograph is taken, transmits signals through the 

 water to the operator on the surface telling him that the camera has 

 reached the bottom. It is housed in one of the tubes forming the 



