I've read some about the internal flash causing problems for underwater pictures. Do you guys usually use the internal flash, an external flash, or no flash at all when picture taking there?

The internal flash can cause back scatter but it can used to good effect on things like Sea Horses and Frog Fish if you get very close i.e. less than 12 inches away. Other than that I would use an external strobe or colour filter and or software to add the colours back.

Agree with Brian, use the internal within a foot or two and turn off outside of that. This leads to the biggest rule of UW photography, get close then closer, if it's outside of a foot away then the picture will probably suck anyway.

Shawn,

Brian and Cecil have already explained and offered solutions. Hope this expansion of their thoughts helps........

The proximity of the internal (or onboard) flash to the lens is the problem. The light emitted from the onboard flash illuminates the water column directly between the lens and the subject. Within the water column there exists suspended, floating, tiny particles. Because these tiny particles are captured out of focus, they appear to increase in size (google the term Bokeh for expanded explanations) . When these particles are unintentionally illuminated, the result is what we refer to as backscatter. As Brian and Cecil have already stated, one solution is to remove as much water between the lens and subject as possible to minimize the effect.

Once an understanding as to how backscatter is created, it becomes easier to understand why an external strobe at the end of a strobe arm is desirable, especially for situations other than close macro work.

Many photographers rely on a strobe aiming technique described as "painting with the edges of light". If you'd like to read more on the topic, follow this link for a basic explanation:

http://www.scubahound.com/index.php?page=strobes

hth,
b

Thanks, Robert, that was very good information.