Hi Bruce,
as you already guessed it, a remote strobe should always be prefered. If you get a strobe arm, you can position it slightly above your object (usually in a 45° angle) and far away from the camera, so that the flash will not be “directly” reflected into the lense. If you have even two strobes you can place them left and right to get full coverage.
The internal flash is usually fired directly from the camera, so reflection/backscatter is maximized if you do not have ultra-clean water conditions or if you can put the camera macro-close to the object. However I have seen many beautiful macros in our gallery which went fine using the internal strobe and sometimes a diffuser.
The Problem concerning your camera is that I do not know any external strobes which can directly sync with a cord to control the intensity. There are some solutions which make use of fibre optics from Ikelite and Sea&Sea which you may try.
An alternative might be to buy a set of videolights. But a normal torch will do fine as well if you buy it with a flood spot option… This will usually result in very warm ambient lighted photos, which I personally prefer. But you will not be able to capture fast moving objects like for example a “dancing” spanish dancer… (this occured once to me on a night dive, where I used a kowalski torch to illuminate the scene). The Edges will turn unsharp as you can only “freeze” fast moving actors with a strobe.
Hope this helped a little,… :wink: Maybe someone else can provide infos about the focus problem.
Andi