I have owned a Canon Rebel XT since 2006, as well as a Canon 70-300 IS lens. My Sigma wide-angle F3.5, 18-55mm lens recently broke and I need another wide-angle lens. I would like to go down to an F2.8 because we may be moving to Germany and I want to be able to shoot in lower light such as inside castles and cathedrals or in dusk to capture lighted buildings. I would need as wide as possible to capture large rooms and buildings. My budget is roughly $400. What do you suggest? Thanks!