The latest information issued by NASA's Jet Propulsion Laboratory suggests that this comet could get as bright as magnitude -11.6 on the astronomers' brightness scale; that's as bright as nearly full moon! That would also be bright enough for Comet ISON to be visible during the daytime.
What mountain do you plan to put in the shot? If it stays in the sky for as long as historical mega comet have, we may be able to get a lot of view time out of this one. I hope it does indeed prove to be a bright as they are saying it could.
I have a year to buy a good camera!