Wide angle photography has the benifit of enabling the photographer to get closer to their work, there by reducing the water column between them and their subject. A typical "standard" lense is usually between 28 and 35 mm. Wide angle lenses vary from 15 to 20 mm. The field of view for a 20mm lense (Motormarine) is 80 degrees, a 15mm will cover over 90 degrees. A standard lense covers approx. 46 degrees.
When "upgrading" to a wide angle lense a photographer must also consider their strobe. Most underwater flashes have a coverage of 90 degrees. This means that if you go for the 15 or 16mm lense then you must also add a second flash for even lighting. (Nikonis makes a strobe that will cover the wider lenses, though it is fairly pricey) The main uses for this type of photography is in capturing large marine life, shipwrecks, and divers. These types of lenses do not work well for smaller reef life as the subject gets lost in the background. These photographs are best shot with a Standard or Macro setup
Underwater Photography Basics
Underwater Photography Terms
Adventurers Dive Club
Adventurers Dive Log
Wolfe Islander II prop. image by Doug Amos