54 UNDERWATER GUIDE TO MARINE LIFE 



a distance lack contrast and three-dimensional effect. This is similar to shooting 

 pictures in a fog. Because of scattering, the camera should be as close to the 

 subject as possible in order to obtain sharp contrast. 



Sea water also has the effect of absorbing colors differentially, the red end 

 of the spectrum suffering the greatest loss. The deeper sunlight penetrates, the 

 greater the loss of colors. The deterioration of color from the surface to the depths 

 in clear water is as follows (for photographic purposes): At about 3 to 4 feet 

 from the surface, red begins to disappear noticeably; at 15 feet so little remains 

 that photographs taken without filters show no red. Orange goes out at about 

 30 feet, yellow at about 65 feet. Below 65 feet only green and blue remain, until 

 at approximately 1,800 feet all light visible to the human eye disappears. These 

 figures are approximate and dependent upon water conditions. (Chapter 1.) 



Exposure Under Water 



Exposures under water depend upon surface conditions, the type of bottom, 

 and the turbidity of the water. Because of turbidity, light-meter readings are 

 more accurate the closer the subject is to the meter; the greater the distance, 

 the less reliable the reading. In shallow water with only one kind of bottom 

 (e.g., sand) generally one reading is sufficient for all exposures as long as the 

 surface conditions remain the same. Clouds and water currents that stir up 

 particles are factors that change lighting conditions. 



In calm water only about 3 to 4 per cent of the incident light is lost because 

 of reflection, but choppy water results in a 20 to 30 per cent loss in intensity 

 at 2 or 3 feet below surface. On bright calm days in clear waters, exposures at 

 about 5 feet below surface are almost the same as above the surface. To 30 feet, 

 use a meter or increase the lens opening one more stop. A direct-reading light 

 meter (Weston) can be mounted in an underwater housing in line with the 

 lens for constant readings. 



Shutter speeds under water are generally the same as above water. A general 

 working shutter speed is 1/50 to 1/100; for static subjects (e.g., coral) 1/25 may 

 be used for increased depth of field, provided the camera is not in motion. The 

 success of increased shutter speeds for taking fast-moving objects is somewhat 

 limited by the low light-level conditions. 



Camera 



Under certain conditions any type of camera can be used to take underwater 

 pictures, but the most successful underwater pictures are taken with the 

 camera arrangement which reduces mechanical handling to a minimum. This 

 allows the photographer to take advantage of opportunities and to concentrate 

 on safety and subject. These are important considerations when one remembers 

 the equipment the swimmer has to carry, the constant motion, the attention that 

 must be paid to safety, and the time element involved in use of the aqua-lung. 

 Also, if an exciting specimen swims by, the swimmer with an ordinary camera 

 could not take more than one picture if he had to struggle with setting the 

 shutter speed and lens opening, cocking the shutter, and advancing the film. 

 Another factor operating to complicate picture taking is that the reaction time 



