Aloha Abril,
I consider digital zoom to be worthless, especially underwater. Yes, it is grainy. I have resolved myself to not getting a strobe for this camera/housing. Therefore, all my photos have to be closeup, either with macro or optical zoom. Not too far on the optical zoom, as distance will defeat the built in flash. I have more success using the manual settings than the auto ones. I haven't yet mastered using manual white balance from my dive slate while at depth for the "no flash" photos. The photos are not that good. Bottom line is: no strobe = stay real close to the subject. Try setting your internal flash on the max setting (+2.0) for zoom shots and the 0.0 or less setting for macro shots. I shoot mostly between F5.6 and F8 in the A mode of the A/S/M dial. I also + and - the exposure value between shots of the same subject. I think your waters and those here on Maui are clear enough to get by w/o a strobe except if you want more distance and/or want to use a wide angle lens. Of course, if you have the money the strobe is a definite plus.
:shades: