You don't need/want a wide angle to shoot macro. Rather just the opposite.
--The wide angle lenses you are asking about give you a wider perspective which allows you to get closer to large objects and scenes and still get them in the frame. Getting closer is important underwater because it puts less light absorbing, backscatter creating water between the camera and the subject.
Macro Lenses:
--On a G11 camera, you can gain magnification of a subject by either getting really close or by zooming in. But you cannot do both simultaneously. If you try to do both the camera won't focus and your pics will be blurry. A macro lens will allow you to both get close and zoom. This means you will be able to fill the frame with a subject otherwise too small. I use Reefnet.ca Subsee adapters for my DSLR and my wife uses them for her G10. We prefer SubSees to others we have tried.
F-stops for macro:
--Usually to learn you want to shoot with the smallest (highest) f-stops that you have enough light for. If you have an external strobe that means you will mostly use f7.1 and f8.0 for macro. As you gain experience you may find situations where you want only a narrow slice of the photo to be in focus. In this case you will use larger f-stops (smaller numbers) like f4.5 or f2.8, but will need to adjust downward the power of any lighting to compensate.
