Something really important to think about is the position of the light source in relation to the lens. If you have c it too close to the lens you can get a thing called backscatter. Here is the dictionary definition of backscatter.
So in other words, backscatter is an underwater version of cats eyes. Muck and dead skin is lit up by the light from the strobe. If the lights are pointing straight forward they are more likely to bounce light back inside the lens and show up add ghost spots. One way to avoid this is the angle your lights forward but slightly off to one side. I will add an example slide to the next post.
My first commercial underwater shoot was with Sandstorm Luxury Swimwear at a pool in Skipton (Rendezvous Hotel). It was also the largest shoot as far as logistics were concerned (up to 20 models / beauty pageant nominees in total).
It was also my first shoot using an underwater strobe (flash gun). Before this shoot I only used either available light or constant underwater video lights. There are advantages and disadvantages to both lighting systems.
Available light means you do not use any sort of added light and often required a lot of light to make the image use able and not overly grainy.
Video lights are great for showing and lighting the scene which allows you to frame and image in low light, how ever the burn time (run time) of these sort of lights can be very short. I averaged 10-20 mins burn per light. So when shooting for several hours (in total we shot for 5 hours on this occasion).
Flash lighting (strobe) was a massive step up for me. It allowed much better shooting duration (around 1000 shots per set of AA batteries) and meant I could shoot at much higher F – stops and lower ISO’s (f11 and 400 ISO average).