474 EDGERTON [CHAI". 1 !♦ 



water is composed oi" the same circuit elements as used in commercial 

 equipment. 



'I'hc i)ressure of the water on camera and lamp housings gives the designers 

 of equipment some problems with strength of containers, optical windows, and 

 electrical connections. At the maximum known dej^th of 36,000 ft the i)ressure 

 is about 18.0(K) ])si. Several authors (Ewing et al., 1946 ; Edgerton and Hoadiey, 

 1955: Thorndike. 1959; 81ii])ek, 1957) give practical housing designs that have 

 been found useful in oceanographic research. 



From a strength-to-weight standpoint, the hollow sphere offers the most to 

 a designer. However, the long cylinder is widely used although the wall thick- 

 ness is about double that of the sphere for the same crushing strength. Various 

 materials, such as aluminum and steel, are used. Tempered stainless steel, 

 such as 17-4-PH, is excellent for long-time exposure to sea-water without rust. 

 This steel can be machined before it is tempered. The tempering does not 

 change the dimensions or cause surface scale. 



The "O" ring has been almost universally adopted in all deep-sea housings 

 in place of the gaskets of earlier designs. With the "O"' ring, the seal consists 

 of metal against metal with a rubber "O" ring filling the joint to seal against 

 leakage at low pressure. 



Windows of glass are best from optical considerations but, for various 

 reasons, Plexiglas is often used. Glass is very strong in compression but very 

 weak in tension, esj^eciall}^ if there are any cracks or scratches. A window with 

 a small scratch on the inner surface is, therefore, liable to develop cracks and 

 it may even fracture. However, if the window inner surface is highly polished, 

 the window will resist very high pressures and produce excellent photographs. 



A standard lens behind a glass or Plexiglas window will show a restricted 

 angular field which has serious chromatic aberrations at the edge of the field. 

 Thorndike (1959) and A. IvanofF, J. Baker and R. E. Hopkins have suggested 

 several solutions to the aberration problem. A Hopkins lens of 35-mm focal length 

 and / 1 1 aperture was used to take several of the examjales that accompany 

 this article. Hopkins and Edgerton, in 1961. described an/ 4.5, .35 mm lens. 



Stereophotography is made jiossible by the use of two cameras mounted to- 

 gether. The visual results are very revealing to the observer in giving details 

 that nuiy be missed in a single photograph. Color photographs also assist 

 the observer greatly. 



2. Camera Details 



A. Data C/untiber 



A photogra])hic record of i)ressure (de])th), time, ])ositional data (long, and 

 lat.), date, vessel, lens, film, crew, etc. on the actual film with the ])hotogra])hs is 

 a most desirable feature for a deep-sea camera. One advantage of such a 

 marking system is the certainty that the data and the ])hotographs are not 

 separated. At sea and in processing, it is easy to get data and films marked 



