Ok, here's where I get a bit lost. and please don't slam me for being novice, because I am and just trying to research to make the best decision.
But, I just researched the Tamron Lens, it is 70-300mm, again, new here, but that seems like a huge range, also, the canon 70-300 goes for close to $500, the Tamron70-300mm is selling on Amazon for $164.95,
Also, why the 70-300 instead of the 60mm?
Thanks again appreciate the information
b
Anybody that slam's you for being a novice has a short memory span, we where all novice at one point and all of us had our "questions" about the gears! the reference to the 70-300mm has more to do with being satisfied with the Tamron brand (rightly so BTW) than an actual recommendations of lens choice for underwater. I know of no manufacturer who actively support this kind of very long focal lenght lenses for underwater photography, it is just not a partical lens for this type of photography. The typical lens kit for a APS sensor camera is something like this:
Tokina 10-17mm fisheye for wide angle
A 60mm Macro lens (Canon or Tamron being the likely candidate here)
to expend, most often the choice will be among the following
Canon 10-22mm or Sigma 10-20 (these being rectilinear and not fisheye)
and the Sigma 17-70mm HSM OS which has a very decent close up capabillity along with a nice zoom range (very good scouting lenses BTW and I would recommend this lens in lieu of the kit lens from Canon).
If you get into tiny wheeny stuff, the the 100 macro will be a welcome addition, the 100mm does not make for a "bigger" picture than the 60mm, but it gives more working distance and when coupled with diopter or other close up attachements, that extra distance will make the difference between crunching stuff or not.
I am sure that they are more lens combination, but with the selections above, there is no reason why your shots would not be great apart from the human factor, (this later can be upgraded/updated on a daily basis, so no big problem here

) just soak in the info and apply it. We all screw up once in a (frequent) while, and I for one, need one or two dive to dial myself in (not the equipment) whenever I go on a trip. (and I work in this field every day)