i understand the diver who started this thread has had their trip, but wanted to add my 2 cents for anyone else planning a trip in the future. Just back from 10 days, including 4 at Wolf and Darwin. I use a 7d (crop sensor) in a Nauticam housing with a Tokina 10-17 on all wide shoots, and brought a 60mm macro lens and port that I used on a few dives (bat fish). While there are other good choices, I felt happy with what I had. I also shot a GoPro, and was surprised when I got home to see how much more interesting the GoPro footage was than what I shot with the big camera. Now some of this is a reflection of my poor wide angle technique, but still when I go back I will do a few things different when shooting the big fish.
1. Shoot more often with available light with the 7d.
We had a lot of sunny days with milky visibility of 35-45 feet. The sharks usually stayed about 20-30 feet away, where strobes did no good and caused moderate to severe backscatter. The GoPro did admirably in those situations. Limiting strobe use also put less stress on the animals, who would approach a bit closer.
2. If the dive plan calls for less than 60 ft, it's bright and the sun behind me, use a magic filter and manual white balance and leave the strobes on the boat.
We had exceptionally strong currents, which often moved strobes out of position (causing backscatter) and made the camera physically hard to handle, especially if you needed to use one hand to hold on. Using strobes also negated the fast firing modes of the camera. Hiding behind rocks to avoid current lost shooting angles. When I go back, I will dive at least some dives with no strobes and look for a rock I can ride like a saddle. That way I can use my legs to hold on, use both hands to control the camera and have an unobstructed field of view.
The last is more important than you might think, I have several videos of divers struggling to shoot pictures of animals in the middle difference while other sharks were immediately behind or overhead. Often the best shot is behind you.
3. Use a strap to stabilize the camera for video.
I use the luggage strap from my carry on as a aid to stabilizing my housing. I hook each end to the housing and shorten it until when I have the strap around my neck and extend my arms the housing is held taut.
4. Stay close to the guides.
They know where the animals most closely approach the reef.
Tom