Hello all. I am hoping to tap into the vast knowledge here on this board. I am getting ready to go on a cruise through the Eastern Caribbean and am looking to get a new lens to take along. First of all, my set up is a Canon T1i and I have the standard two lenses that came with a kit (18-55mm f/3.5-5.6 and a 55-250mm f/4.5-5.6). I am thinking about getting another wide angle or super wide angle lens. I have looked online at a Tamron 17-50mm f5.8; Tamron 10-24mm f/3.5-4.5; and the Canon 20mm f/2.8. The first thing I am unsure of is just exactly how much difference each of these would be from my "stock" 18-55mm I already have? Also, are these the lenses I should be looking at to expand my options? I am still fairly new at the digital SLR photography and appreciate any help I can get. Thank you!!