Page 207 - Green - Maritime Archaeology: A Technical Handbook. 2nd ed

186 Maritime Archaeology: A Technical Handbook, Second Edition
Figure 6.10 Small tripod used to steady camera in low-light conditions. (Courtesy of Brian Richards, Department of Maritime Archaeology, Western Australian Maritime Museum.)
nonstereophotogrammetry is currently available for archaeologists or archaeological surveyors who are prepared to learn some simple tech- niques. In this situation, routine archaeological surveying work can be con- ducted in the field by people who are directly involved in the work, rather than by technical experts remote and unconnected with the project, as was previously the case.
A. OPTICAL ALIGNMENT
At times it is extremely useful to be able to align cameras on a stereo- bar so that their optical axes are parallel. One simple and effective method to do this utilizes mirrors and optics. The cameras are mounted on the stereo- bar with the normal lenses either replaced with mirrors set flat against the lens mount or with the plane port 35-mm lens (the glass acting as a plane mirror). The camera separation is accurately measured. A second bar is constructed with round targets set at exactly the same separation as the cameras. This target bar is set on a tripod several meters away from the camera bar. The targets have small viewing holes drilled in their centers so that one can look through the targets and observe the mirrors on the cameras. The first operation is to set both bars level and parallel. Leveling can be done with a spirit level. The bars are set parallel using a plane mirror