Just thought I would throw this out. I'm sure its been discussed before. I'm shooting with a OM-D EM5. I have the panni 8mm and don't get me wrong the panni is a wonderful lens for getting up close and personal with your subjects. I also have the oly 60mm. I would like to add another lens. A wide angle lens would be my next choice to shoot bigger and faster subjects.
Does anyone have any thoughts on this advantages and disadvantages with the sort of lenses you might be using out there. Be happy to hear some thoughts.
Marko
You could do a Panasonic 7-14mm. Gives you a bit of zoom range while still being wide enough for sharks/dolphins. There's also the cheaper Olympus 9-18mm which I have, but it's not as sharp. I took the 9-18mm to the Galapagos back in October in the standard Olympus flat port and it was wide enough for the hammerheads, but not the whale shark. If you are using a non-Olympus housing, I think you can use the 12-40 pro lens. I have no experience with it, however.