Page 253 - Green - Maritime Archaeology: A Technical Handbook. 2nd ed

232 Maritime Archaeology: A Technical Handbook, Second Edition
One effective solution to the backscatter problem is to create an artifi- cial sun with a flash unit. By using a very powerful flash unit mounted on a pole several meters above the camera, the flash acts as a diffuse light source. This technique has proven to be very effective and for any flash work, other than close up (300–500mm), it has proven to be the only viable method although exposure tests are essential. Certainly, the flash unit should never be used close to the camera in turbid water.
As a general rule, provided the light meter registers and one can see about a meter or so, it is probably better not to use supplementary lighting. The quality in these conditions may not be particularly impressive, but con- sistent results can usually be obtained. If one wants any color at all in a pho- tograph, irrespective of turbidity, then the use of a flash or lights is essential.
If there is only one camera available, it may be preferable to use color film rather than black and white, because color film can be copied in black and white and the results are reasonably effective, although having rather high contrast. Ideally it is better to use two cameras and to get color and black and white coverage. Usually, the kind of photographs that one wants to take in color are different from those in black and white, so two cameras are an advantage, although one often ends up with the perfect photograph on the wrong type of film. Color photographs are mainly used to illustrate talks and for glossy format publications, whereas black and white pho- tographs are usually used in reports and for recording purposes. This should be considered carefully in planning any underwater photographic coverage.
Once again, the digital camera has real advantages in low light condi- tions and in turbid water. Certainly both digital still cameras and video cameras can actually see more than the human eye in turbid conditions. As a rule of thumb, the camera seems to be able to resolve objects at almost twice the distance that the human eye can see, with obvious advantages.
VI. TECHNICAL FIELD PHOTOGRAPHY
Photography plays another important role in maritime archaeology, i.e., as a means of surveying a site, recording the technical progress of an exca- vation, and recording artifacts in situ. The restrictions on the time a person can spend under water make the camera an excellent tool for simple site documentation. A maritime archaeologist does not have the easy access to the dig that a land archaeologist has, to be able to return at any point during the excavation, and make additional recordings in a reasonably relaxed environment. Methods of recording under water have been developed to get the maximum information under constraining conditions in the fastest