Dave Bunnell wrote:...They sell this fiber optic cable for the slave, which I gather lets you move the sensor off the body of the flash (I think that's the function) but obviously it would be a more robust package for caving without the extra cord hanging off....
That cord is meant to cover the on-camera flash, and send a portion of the light to an off-camera strobe. The problem in the water, is light bouncing back from particles in the water, near the lens. The same problem exists in "dry" caves when there is fog near the camera.
The cable could be used to route a flash to the sensor, when a slave flash is pointed away from the camera, but I don't know if enough light would get to the sensor. I will drag mine outside tonight, and experiment.
Any opinions are personal.