Techniques for Deeper Underwater Photography
In Kyle's e-mail he further explained that the problem with his Blue Hole images was that while the stalactites looked great, the water in the background of his shots was so under exposed that it was almost black. As a result, the darkly hued divers all but disappeared into the near-black background.
The answer to this dilemma requires using an advanced wide-angle shooting technique for working in deeper, darker waters, in or near the openings to caves or when shooting in the early morning or late afternoon.
Kyle was diving under a huge overhang, early in the morning, in relatively deep water, on an overcast day. He was using a strobe to light the stalactites in the foreground, and he set his shutter speed at 1/125th of a second. (This shutter speed is the synchronization speed of his camera, the fastest possible speed that allows his strobe to fire at the same time that the shutter is wide open.) When using a shutter speed of 1/125th of a second, and with a 100 speed film, even with a wide-open f/stop of f/2 or f/2.8, there was not enough available light to expose the background water.
Kyle wanted the water in the background to look blue, which would have helped both the stalactites and the divers stand out in his photographs. To accomplish this, he could have (1) dived at noon on a clear day, (2) used a faster film or (3) used a slower shutter speed. Kyle could not control the weather or the trip itinerary, so option number one was impractical. Perhaps he should have used a faster film, but 100 speed film is commonly used in wide-angle work in clear water, so it is hard to fault Kyle's film choice, especially when he had not previously dived the site.
Given the situation, Kyle could have tried using a shutter speed of 1/60th, 1/30th or 1/15th of a second, depending upon the choices available for his camera. A strobe will fire when the shutter is wide open as long as you select a shutter speed that is the synchronization (sync) speed or one that is slower. A slower shutter speed would allow more ambient light to reach the film, adding exposure to the background water, but the foreground would not be affected because there is not enough ambient light available to add exposure un-der an overhang in dimly lit deep water. As long as he was able to hold his camera steady, the slower shutter speed would not have impacted the appearance of a stationary foreground subject, and those stalactites haven't moved in eons.
Kyle's fear was that the strobe lit stalactites would not be sharply focused because his hands would shake too much while the shutter was open. On land, when fighting the weight of a camera, that would probably be true, and he would need a tripod to create a similar image. But underwater it is much easier to hold a camera steady when using shutter speeds as slow as 1/15th of a second because you don't have to fight gravity. Also remember that it's a good idea to exhale before tripping the shutter, and to try to gently squeeze the shutter to the point of release.
In the final analysis, Kyle's pals were correct in suggesting that, had he used a slower shutter speed and made no other changes, he might have been much happier with his results. The background water would have appeared blue, adding impact to his images.