firstly, the aperture isn't great, which may affect depth of field if you shoot balanced (blue-water) macro; second, there's not the wealth of underwater experience and third, the difference in "stand-off" distance. It's going to be more difficult than the traditional 60mm, but without the advantages of the 105mm, I would guess.
Diopters are a nightmare: I certainly wouldn't try one before being really experienced with the unadulterated lens, and with lighting macro images. I have found it really hard to locate wildlife that would let me get as close as a diopter needs, and still yield an image that works with the minimal depth of field.
Tim
Thanks for the input.
i am not sure i understand what you mean by "may affect my depth of field if i shoot balanced macro?" i have spent a lot of time looking at photos that people shot and also shooting with this lens, i have found that i prefer the picture around f/stop 14, so how would that effect if i can not have down to 2.8? Can you go into a bit more depth for me, again i am not knowledgeable in this realm of underwater. If for focus, not enough light, ill use a focus light. I see no real use for an f/stop under 8 for underwater, if you feel otherwise please let me know.
Next the underwater experience, well at some point someone has got to try the new things, i am sure a lot of people said that things about dSLR when they came out...I found another post on here where someone seems to like the 85mm under water?
85mm like 
As for "stand-off" distance it is really similar to the 105mm but allows just a bit closer, not to mention about half the price, which was a big factor for me because i am new to this world, and i want to see if it something i am going to like before getting the best equipment.
-K
