I need to shoot some photos for a friend's marriage ceremony whicj will take place in a medium sized hall with large windows and tungsten lighting-what's the best(cheapest) way to go about it? will i need to buy a flash light of some sort or will i be o.k with 400 asa film-how will slide film holdout there? i'm using a Sigma SLR cam-please advise as it takes place on sunday and i'd hate it if the photos didn't come out, thanks all