tonight ill be shooting in a very low light environment (a bar). last time i shot it, i was shooting digital so i could adjust my settings as i saw fit, but this time id like to shoot film. the settings i had it on was iso 1600, f/3.5-5.6 18-55mm (kit lens) and i set the shutter for 1/30. this time, im going to be using film. iso 400 and a 50mm f/1.7. what should my shutter be to keep that same exposure? what about if i shot at f/2.8?