Successive photographs taken at regular intervals along the bottom provide field 

 coverage over an area determined by the set and drift of the lowering vessel. Features 

 made visible by the development of the photographs obtained are then studied to help 

 reveal the nature of environments. The most efficient use of the deep-sea camera is 

 obtained by proper planning of ship time in selected areas of study. Depth is still 

 the primary factor in determining where photographs can be taken, how long it will 

 take to get them, and how many can be obtained on a single lowering of the camera. 



Camera Settings, Film and Optics 



Camera settings are made in advance before each lowering when corrections for 

 water refraction, turbidity, depth, picture size, and subject distance can be taken into 

 consideration. A fast lens of short focol length has been used extensively In the 35-mm 

 robot camera and has given highly satisfactory results."* A shutter setting of 1/25 second 

 permits easy synchronization with the short (1/1500 second) duration of the flash 

 and exposes the film properly for clear, sharp negatives. 



Tri-X film has been found most suitable for underwater use and is now employed 

 almost exclusively for black-and-white bottom studies. It is a very fast panchromatic 

 film of moderate groin, with wide exposure and development latitude, and provides 

 maximum detail and depth of focus in the field of photographic coverage." 



To correct for the higher index of refraction introduced by the air-to-quartz-to- 

 water interfaces it is necessary to correct the true camera-to-subject distance for work 

 under water. A standard rule for corrections is: set the lens for a distance equal to three- 

 fourths the actual distance.* For normal use, at depths where no extraneous light is 

 present, the lens is set at f8 for an apparent camera-to-subject distance of 6 feet; for 

 more light the lens is opened to 6.3 and for less light stopped down to 11 or 16. 



High-speed Ektachrome film. Daylight, has worked well for color. For best 

 results the camera lens is opened to f2.8 and the subject distance adjusted to insure 

 adequate lighting on the subject. Field testing is recommended to determine the best 

 camera settings to use at specific preset subject distances. 



Figure 7 illustrates the optical relationships between air, quartz, and water 

 interfaces inherent in the design of the camera unit. The lens of 30-mm focal length 

 has an angular field coverage of 57.6° in air. The net refractive effect of the clear 

 quartz window (index of refraction 1.54) and salt water (index of refraction 1.33) 

 narrows this angular field coverage to 42.4° which results in a loss of 15.2° field 

 angularity.** 



Filters are not employed on NEL deep-sea cameras at the present time because 

 of their absorption throughout the spectrum.^ Also, a large part of the photography 

 being done with the Type III Camera is in deep water where turbidity is low. To place 

 the camera closer to the subject in areas where the turbidity is high a wide-angle lens 

 system can be employed."* 



Field Illumination 



A 2000-volt Heiland-Wilcox P-2 Flash unit and a Kemlite V4X flash tube provides 

 flash illumination." Figure 5 shows the basic electrical circuits employed. The flash 

 tube is enclosed in a clear plastic envelope capable of withstanding hydrostatic 

 water pressures in excess of 10,000 Ib/sq. in. The water-flooded aluminum reflector in 

 which the tube is mounted is designed to provide illumination with a minimum of back 

 scattering (see fig. 6). 



* See ref. 6, pp. 3-4. 



