Page 348 - Green - Maritime Archaeology: A Technical Handbook. 2nd ed

Chapter 12: Artifact Photography 327
Nikon, Canon, Olympus, Pentax, and Minolta, all of which produce a number of different camera types with different features, but each doing basically the same things. The SLR camera has a variety of interchangeable lenses ranging from ultra wide-angle (focal length 10–24 mm), wide-angle (24–35 mm), normal (35–80 mm), or telephoto (80–300 mm). There are also zoom lenses which have variable focal lengths, most commonly 28–55 mm, 40–80mm, and 80–200mm, and macro lenses which are close-up lenses capable of focusing from infinity down to object-to-image ratios of 1:2 or 1 : 1. There are also fast lenses with f-stop numbers down to f 1.2.
The use of many of these lenses lies beyond the scope of this book and readers are referred to standard textbooks and manuals of photography (Hedgecoe, 1977). For general archaeological photography, the standard lens used is the 55-mm macro lens. The 24-mm wide-angle lens is a useful additional lens for general expedition photography. It is very effective for close quarters, for example, on a boat or for landscapes and used with color film and a polarizing filter, dramatic effects can be achieved. However, care must be taken to avoid perspective distortion in architectural work (Figure 12.2).
Another useful lens is the macro telephoto of either 100- or 200-mm focal length for accurate, detailed object photography. This lens reduces per- spective effects in object photographs, but as it typically has a narrow depth of field, great care is required to ensure all of the object is in focus. A good general purpose lens is a 35- to 105-mm macro zoom lens. This covers the basic requirements of general artifact and expedition photography, although it does not coverthe useful 24-mm wide-angle range.
Most 35-mm SLR cameras have a through-the-lens metering system, which measures the light arriving at the photographic surface. The meter reading can usually be observed in the viewfinder, so the operator adjusts the speed and aperture without needing to remove the eye from the viewfinder. Many cameras are now fully or semi-automatic, so the operator has merely to press the shutter release without worrying about the light reading or setting the controls. Some automatic cameras allow the through- the-lens metering system to be coupled to a flash system, so that the flash duration can be controlled automatically to give the correct lighting. This, too, is very useful in a variety of applications.
One of the main disadvantages with the 35-mm format is its small size. Because photographic film has a finite grain size, there is a limit to the amount the negative can be enlarged. This is usually not a problem because the selection of a suitable lens will give the optimum use of the format (i.e., full frame). However, where a very big enlargement of the frame is re- quired, grain can pose a problem. Another drawback is that manufacturers of photographic paper do not produce photographic paper in the same format ratio as the 35-mm negative (paper ratio is 1 : 1.25 whereas film ratio