Some Underwater Hints 
  
As the result of several years of stereophotography in a beautiful but 
often frustrating environment, some simple techniques and precautions have 
evolved that help to ensure the success of a photographic mission. 
(1) Always rigorously check the flash units and take a complete set of spares. 
The rubber seals on the flash units or the wiring from them to the camera 
seem to be the items of equipment most prone to water leakage and failure. 
(2) To rapidly relocate the transects to be rephotographed, the divers 
should carry a mosaic of the photographs taken on the previous occasion, 
waterproofed with clear contact adhesive sheeting. This allows them to re- 
photograph close to the previous position. 
(3) A fibreglass surveying tape stretched along the transect between the 
terminal pegs serves a dual purpose. It can assist the photographer to 
orient the camera rig prior to exposure every l to 1.5 metres (say) and 
provides some ground control for later analysis. 
(4) The camera rig should have at least two spirit level bubbles affixed at 
right angles where vertical photographs are required. Circular (or bull's 
eye) bubbles have proved much more difficult for divers to level than two 
straight vials. 
(5) Always photograph a calibration frame at the beginning of each transect 
or roll of film. This frame should also carry information on the date, 
locality, etc. and can be used to work out the relative orientations of the 
cameras for that transect. Unless the camera rig has been very carefully 
made, the cameras will not fit exactly back into the same relative orient- 
ation after changing films. Their lens centre to image plane distances will 
also vary as a result of removing the lens during reloading. 
(6) Avoid altering the aperture or the focussing settings underwater as this 
will necessitate a re-calibration photograph. 
(7) Always have an assistant in the diving boat who is "dry" and is adept at 
changing films and flash batteries. 
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