I'm heading to Seoul National Museum in a few weeks and just wondering if the 17-55mm is good in very low light situations. I read in one of Scott Kelby's books that buying a cheapish 50mm lens with 1.4 or 1.8 aperture is great for low light situations such as church weddings but of course SNU is darker than any church I have been to. So is the 17-55mm great for museums or is the cheap 50mm the way to go?