I started taking these shots with the idea that it could transport the non-diver into the underwater realm, giving them a chance to experience what we as divers see and experience on any given day. I have subsequently found that they have become one of my many cinematography addictions. If you are trying to create a shot like this one of the keys is knowing the topography of the dive site and the direction of your main light source. Of course being on a quiet dive site and having good visibility also help.
Knowing the depth at which you are as well as where natural features are on the Y-axis and when they are going to provide shade or exposure helps to smooth the shots overall exposure. With this shot taken at White Rock I white balanced and exposed along the naturally occurring sand bar and ensured I was maintaining a constant depth. Using the natural topography to provide shade from the majority of light as I move towards the light source, preventing over exposure before I move to travel south when the light is on my left side.
Other key tips for this kind of shot are to use your breath to smooth between fin kicks, regulate your breathing and choosing the right speed. You also need to maintain the cameras frame to prevent wobbles and jolts from your fin strokes. You'll know if you are doing a shot like this right as at the end your wrists will feel like they're ready to drop off!!