Close Focus Wide Angle is probably the oldest and most described of all underwater photography techniques. This is because of the huge impact it will make on your images when you employ this old secret.. Let's talk first about why this is, and then how we do it.
The why is pretty simple.. we are cheating the visibility. Most of us consider 100' of visibility to be crystal clear, and many will refer to 100' viz when it's closer to 60 feet. Just because you can see something 100' away doesn't mean that it is sharp, or that you can capture intricate details when you photograph it. This may be obvious for subjects that are a good distance away, but what about shooting at three feet from the dome vs 6 inches?? There is a difference, and it is huge. This is the reason so many photographers shoot super wide lenses.
The wide lens (Fisheye or Rectilinear) allows you to shoot an image from inches away while using the forced perspective to make it look a comfortable distance from you.. so 5 inches looks like 5 feet to the eye. This means that all of the water between you and your subject (and the cloudiness it carries) is reduced. It also means your light travels a shorter distance as it reflects off of the subject and on to your sensor.
The "How" is more complicated, and there are no hard rules- as this is art and different techniques come into play. The method described here is only one of these choices, but is time proven -particularly with the Ikelite TTL System, and has yielded many cover shots from many photographers over the years.
The two things to keep in mind first are that you want an upward camera angle, and that you want to carefully maneuver your dome port to be as close as is practical to your subject without touching it.
The exposure you select can vary depending on the effect you like, but for tropical diving fixing your ISO low (200 or so) and setting your shutter to a standard flash synch speed (around 125th-160th second) and leaving them both there will allow you to vary the Aperture for the effect you want. In this situation, the Aperture will determine the brightness of your background- which will usually be the water column, and the sun ball; perhaps a silhouetted diver, boat, shark etc.
A Pro trick is to simply waste a frame and look with a trained eye at the water column. If it is black or super dark green or blue, open the lens a stop or two and try again. If the water column is bright and milky, close down the Aperture. You will find the sun shows up in a lot of your images because the lens is so wide, and you are shooting upwards.. the Aperture will also control the size of this sun ball.. closing it down makes the ball shrink, opening the Aperture up will make the sun ball grow.
Once you have determined the settings you like you can concentrate on the one important thing- Composition! The wide lens will make anything around the edges into a "frame" for your subject- use these shapes to draw the eye to the subject. As you shoot different subjects the detail will be sharp and crisp, and your background the shade of blue that you like- so the final step is to swim the reef and begin to develop your eye to anticipate the distortion that all wide lenses provide- this curvature varies lens to lens, but is always a compositional tool- and one that you will get better with the longer you use it. Photographers go through cameras like candy, but there are plenty of Pro's shooting the same lens over a decade.
Depending on which wide lens you choose, two strobes will be helpful to cover the foreground, but one strobe can suffice.. (and a dome diffuser will help here!) Be aware of letting the light be seen in the side or corner of your frame. With Fisheye lenses like the 8-15mm it's easy to accidentally light the water column since your lights will be so close. This won't be as obvious in your preview screen as it will be once you download your images. Typical flash position would be 10:00 and 2:00 on the clock face, but feel free to move your strobes around to use side lighting and control and create shadows. Just be aware that they will need to be behind your dome to not show up as a flare.
Big domes and small domes will both produce CFWA images well. Big domes have better optical characteristics typically, and many contend that smaller domes are an advantage because you can get closer. The most important thing is to have a close focusing super wide lens (our favorites are the Tokina 10-17mm Fisheye and either the Nikon or Canon 8-15mm Fisheye) -and the correct port assembly. These lenses have an incredible depth of field, even at close distances.
But we haven't talked about flash settings!! This part is easy, we shoot our cameras on manual, but set the strobes to TTL.. when an Ikelite flash goes off, the camera sees it, understands it, and quenches it for the perfect exposure. Certainly manual power settings are available and will work, they just take time to determine.. our most precious resource underwater.