Hey everyone. I have a quick question about the apperture of lenses in general. I understand that the lower the f-stop the wider the apperture, but why do I hear some photographers call lenses with lower f/#'s "fast" or "faster". I thought that the lower the f/# the shallower the depth of field. Personally when I shoot I try to get the higher f/# so that I get a less shallow depth of field. Am I thinking incorrectly? Why are the prime and low f/# lenses usually more expensive? Thanks for your help in advance.