Page 251 - Green - Maritime Archaeology: A Technical Handbook. 2nd ed

230 Maritime Archaeology: A Technical Handbook, Second Edition
discovery. It is impractical to have a photographer on all dives to cover every possible eventuality. An alternative is to halt the operations and get the photographer down to cover the situation when a “find” is made, but in many cases this is difficult. By selecting the time and place to take a general photograph, a number of objects can be covered in one operation. However, such photographs, can have a staged look and care is required to make them look as natural as possible. If the results then provide a photograph that enables the archaeologist to illustrate the type of work being carried out, or to promote the project through sponsorship or fundraising, then, pro- vided the artifact does not suffer, the process is more than justified.
A. LOW LIGHT LEVELS
Poor underwater visibility can be caused by two separate effects: the water clarity, which can range from clear to pea soup; and the light levels, which can range from brightly lit to dark. With turbid water and high light levels (at the surface) it is like swimming in brightly lit soup. The deeper the water the more the turbidity filters out the light, thus reducing its level until it is totally dark. On the other hand, the water may be clear and the light level low, and one is similarly in the dark at depth. However, in the latter case, the introduction of supplementary lighting can make a con- siderable improvement in the photographic image, particularly with color photography, and a flash or lamps can be used without much difficulty to illuminate the subject. Naturally, the composition needs to be considered, because it is impossible to illuminate level subjects that are in the fore- ground and subjects that are in the background at the same intensity. Either one can get flat-on to the subject by swimming over the seabed and illumi- nating and photographing downward, or choose to illuminate the subject in the foreground, leaving the background dark.
At low light levels in turbid water conditions, the problem is much more difficult and it is debatable if supplementary lighting is worth the trouble. If the lighting is placed too close to the lens, the suspended matter in the water is illuminated, causing strong backscatter. To avoid this, the lens- lighting separation has to be as great as possible. Archaeological site record photographs are often vertical and these are difficult to take with the flash or lights far enough away from the camera lens to prevent backscatter, but, at the same time, not creating uneven light levels across the subject. Because it is usually more practical to work with a flash, it is usually not possible to check if the arrangement is working until one sees the results. Some flash units now have a tungsten lamp that can be used to illuminate the subject so that the photographer can get some idea of what the effect of the flash