After considering it for five years, I have decided to invest in a housing and underwater strobes.
I like wide-angle and I'm also planning to play with filters in the green waters here in the Netherlands. However, in a couple of months I will need to take close-ups of phylidiid nudibranchs in Indonesia for research. I'll be there as part of an expedition and I would also like to cover the bigger picture for several publications when I get back.
Above the surface I mostly use a Canon EOS 5D with 24-70mm f/2.8L lens. I also have a 20mm f/2.8 lying around. I guess these will probably not cut to the chase for both the wide-angle and the close-ups?
So I'm thinking I may be better off with the housed 5D with e.g. a 15mm fisheye, and bring another compact for the nudibranchs.
I would very much appreciate to hear your thoughts on this.
I have used the 24-70mm f/2.8 lens UW. With a 1Ds MkII in a Subal housing, I got my best results with the recommended 100mm ext tube, FE2 and a 500D diopter and an f stop > 9. With this setup you can shoot WA with a touch of softness in the extreme corners and "not too shy" creatures down to about 2" on the same dive. One has to recognized the tradeoffs when using this type of lens as it is a good lens, but not the best for either extreme WA nor extreme macro. I like it for bigger creatures or when I want a lens that covers most of the bases.
For straight WA work, I like using either the 15FE with a 1.4 teleconverter, or for rectilinear WA the new 24mm f/1.4 II with a 500D diopter. Either of these two setups will provide extremely sharp centers and especially with the 24mm very sharp corners. I do not like the canon 14mm II. The 16-35mm II is OK.
For straight Macro work, as others have stated the 100mm macro is very good! I especially like it with a 1.4 tele and a wet diopter when I want to shoot something really small-----think dwarf seahorses. Canon has a new version of the 100mm coming out with IS so this might be something you may wish to explore. For Nudis, this is what I would use. Have you considered getting a rental?
FWIW I also use a G9 UW. And while it is a nice camera, and I like it for what it is. It's not as good as the above setups.
imasleeper