Hi. I'm going to New York City during the week of Easter and I'm hoping to be able to take take some very nice shots of the city and other things on my trip. I'm scarred that when I try to take photos at night of the city, they're going to be too dark. Would an external flash make much of a difference in a big lighted city like NYC? Eventually, I'm going to want an external flash, but since I'm going to NYC, I'd like one sooner. Should I buy one if it will be useful at night when taking pics of NYC at night?