I've been looking around for info on strobes as well. I came across this on a website and found it to be very informative.
Accessory Lighting for Digital Cameras
When you use an external light source instead of the camera's built-in flash you can improve the underwater image quality by reducing back scatter (light reflected from suspended particles between the subject and the lens. It looks like a snow storm.). In some underwater cases, the flash built-in to the camera is obscured by the housing, or wide angle lenses that have been added to the camera housing, but can still be used to trigger a slave flash.
External lighting can be provided either by flash or by video lights, but flash usually gives the best results by freezing action provided that the triggering and exposure control systems operate correctly. The video light has a different (warm) light color than flash and the camera will have to use internal auto color balance to correct for this or you can, on some cameras, control the white balance with the control menu in the camera.
Pre-flash Cameras: Many digital cameras use a pre-flash system, whereby the cameras flash fires twice. The first flash is for the camera to adjust the exposure and set the focus distance and second to make the final exposure. This action will pre-trigger a conventional slave strobe (cause it to fire at full power during the pre-flash, and fail to fire during the main flash which occurs a 200 milli-seconds later). If your digital camera does not use pre-flash, you may be able to use conventional non-digital slave-flash strobes. To get the best results, a TTL slave system or varying the flash output manually will be required to make the correct exposure. You can see the results played back on the camera's LCD and make further adjustments to get the correct exposure.
If you are not sure about your equipment, or want to have the option to upgrade to a pre-flash camera, use only pre-flash compatible strobes such as the Ikelite digital series or the Epoque 150D Full-flash Cameras: Some cameras fire the internal flash at full output and control exposure by adjusting the sensitivity of the imaging device (CCD). Such cameras should be used with a variable-output manual slave-flash such as the Epoque ES-150DS or Sea & Sea YS25DX or YS90DX, or with a video light. Note that the Ikelite TTL DS-125 also has a manual variable-output mode, but it will not be possible to use the TTL function with a full-flash camera.
Metered-flash cameras: A more sophisticated digital camera uses a built-in light-metering sensor to control the output of the cameras built-in flash. This includes the Olympus 3040 and 4040 cameras. This may be either a TTL sensor, or a sensor on the body of the camera. Control is achieved by switching-off (quenching) the flash when sufficient exposure has been achieved. In this case, the Ikelite 50D with the Remote TTL sensor (cut-off detecting) slave flash system will provide best results by making full use of the camera exposure control system.
Cameras with flash connector: Nikon Coolpix 950, 990, and 995 cameras are provided with a sync connector. Ikelite housings for these cameras bring the sync connector out to a bulkhead socket, and may be used, via a conventional sync cord, with any Ikelite TTL Substrobe (i.e. DS-series strobes and conventional Substrobes from the film-camera equipment. The Tetra and Subal housings also have this ability for the Nikon 5000 system Flash
Trays and brackets.
Once you know what lighting system you will use with your camera then you need to find the proper way to attach it to the housing. Some lights come with an arm or bracket suitable to connect to several housings, as is the case with most Ikelite systems. Others require a bracket (arm and tray) to be purchased separately. Some housings (e.g., Ikelite) are supplied with a tray, most others have a 1/4" tripod socket on the bottom and will attach to a standard tray.
Marc
