Supermacro

[Mariozi]

You are absolutely right, it is very hard and requires training.
Normally when I dive with such a SM setup I lock the focus at the max magnification and hunt for subjects.
Well good luck, just be careful with the wet diopters, as I said they don't add a multiplier to the amplification factor, and it is very hard to get a 2x effect out of one.
If you are looking for one I suggest the ReefNet Inc. SubSee Adapter, I think it is the most powerful an versatile one in the market. I was never a big-fan of these adapters, but I will get one SubSee to try. Just remember that the only way to properly check the amplification that they give is to do the check yourself by shooting a ruler on a big bowl of water or in a pool.

Good luck.

 

[Mariozi]

Just one thing, the shutter speed is the least of your worries... I normally set it to the sync speed (1/250s in my case) and shoot away. In reality your subject will be frozen by the flash which lasts anywhere from 1/1.000s to 1/10.000s depending on the power setting.

 

[TTA]

Wow lots of very informative replies.

In the end this is what I've gone with.

Equipment: Canon 40D (cropped sensor), 100mm, Kenko 1.4 TC, Subsea Adaptor
Ports:Extension Ring 40 (56111), NX Compact Macro Port Base (56201), Compact Macro Port S (35) (56211).

The port combination is a bit odd as they are basically a reconfiguration of my existing ports (for my 60mm and my 10-22mm wide angle) so I don't have to buy a new port for the 100mm. It fits, but no manual focus - but the subsea guys were explaining that they basically do their photography on auto anyway. Plus I can always fix the focus if I want. This may not be ideal if you want to buy a port especially for the 100mm, but it works for me. Anyway I'm just listing them here if any one is interested.

Can't believe that Sea&sea actually figured out a combination with my existing ports and didn't try to get me to buy a whole range of new ports! Nice.

About to go on a macro focused dive trip next week. Will report back.