One of my hobbies, when I get the time and the weather is good, is scuba diving and there's nothing more pleasurable than sharing this experience with non divers. Being under water is like being in a different world. You have to experience it to really understand this. But the time came when I wanted to use more than just a water proof camera, so I needed to rethink and invest in some kind of light to help bring out the colour and details of what lies beneath our oceans. I purchased the Digital Intova external flash a few years back and its worth its weight in gold. Most importantly it is robust and kicks out a lot of light with just using 4 x AA batteries. It operates by sensor recognition so there are no pesky wires to plug into your underwater camera. The unit can be attached to the top of your camera on the hot shoe, but if needs be, then you can use/fire it independantly as it has a slave feature. You simply turn it on by the big silver knob on the top right of the unit and the battery compartment is at the rear. It chucks out enough light to take good pictures that are approx 6 meters away from you. If you're shooting close ups of sea life you'll have to change your camera F stop accordingly as you'll risk nasty over exposure of your subject. Not only can you use this flash under water you can use it for normal flash work out of the sea too. Works a treat for fill in flash work. Paired with a quality underwater camera this external flash unit is the bees knees and will even knock spots off of the more expensive models that my diving partner has used in the past. Purchased for £120 from Ebay nearly 2 years ago.
Intova External Flash Model 2011. - Slave flash- Operates with sensor recognition- Batteries 4xAA (not included)