MAN AND THE SEA, I 57 



wide apertures— resulting in lower depth of field. It is important when selecting 

 a wide-angle lens for scientific work that there be no distortion at the edges 

 and corners— the type of distortion found with some extreme wide-angle lenses. 

 This distortion is acceptable for amateur work. 



The Normal Lens and Underwater Close-up Photography 



There are all forms of interesting life— coral, crabs, small reef fishes, plandike 

 animals, etc.— that require close-up photography. Most camera range finders 

 are useless under water, but single-lens reflex viewers for critical focus give a 

 large enough image to be useful. 



The depth of field at short camera-to-subject distances is slight (even with 

 small apertures) and a miscalculation of only an inch or two is enough to cause 

 out-of -focus pictures. (A workable rule for determining depth of field for any 

 aperture is one third the distance in front of the subject facing the camera and 

 two thirds behind.) The wide-angle lens is desirable for photographing large 

 marine subjects, but it necessitates that one get close to the subject in order 

 to fill the negative. This lens is not effective when working close to small 

 moving subjects; small reef fishes are generally -skitterish when approached 

 closely, within a few feet, and swim off or become hyperactive. The use of a 

 reflex camera equipped with a normal lens set for distances of 18 inches to 3 

 feet gives a slight telephoto effect allowing the photographer to back off so as 

 not to disturb the subject yet fill the negative. This is contrary to the general 

 belief that only wide-angle lenses are suitable for underwater work. 



With nonreflex cameras a measured stick is useful to determine distances 

 when photographing static life, but drives off the active life. Since most small 

 fishes are constandy moving about a small area around the reef, a ruled stick 

 can be used to determine probable distances where the subjects have a good 

 possibility of appearing. This involves studying subject behavior before shooting, 

 but it can be very rewarding. Keep in mind that the yardstick appears one third 

 longer under water. 



Color-Correcting Filters 



Color correction filters will function to a depth of approximately 50 feet. 

 Beyond this depth in most waters not enough of the remaining red, orange, and 

 yellow light is left (because of the effect of selective absorption, scattering of 

 light, and lack of intensity) to make filtering practical. Some source of arti- 

 ficial light is necessary to restore color below this depth. There are shallow-water 

 photographers who feel that filters are unnecessary and that the blue-green effect 

 is desirable and truly representative. This is a matter of individual preference. 

 The authors feel that the complete elimination of the blue-green effect results 

 in the loss of the unique color tones of the underwater world and prefer the use 

 of filters which do not completely eliminate this effect. 



For waters that tend toward blue with litde green use a CCR series (color- 

 correcting red) filter. If the water tends toward yellow, that is, has a definite 

 green tinge, use a CCM series (color- correcting magenta) filter. For a clear tropical 



