Okay, so school's asked me to cover the Easter production of The Wizard of Oz and I figure I'm going to need a decent long range lens. After checking out what kind of lighting I'll be dealing with (typical stage lights) I'm sure I could get away with an f/4 lens however, I'm curious as to what sort of DOF effects could be achieved with an f/2.8. Has anyone got experience with either of these lenses and is willing to advise? Bear in mind, there's £500 difference between the two and I'm not but a lowly student. Thanks in advance.