Reply #8: You should try it with the clouds out sometime [View All]

you can get some wild effects. If you get serious about it, I'd highly suggest looking into "image stacking" (basically taking a ton of shorter exposures on a tripod) or dark frame subtraction (this involves a second photo of the same length with the lens cap on, and is available as "long exposure noise reduction" on most DSLRs), as you can start to get a ton of ugly noise from the sensor at those kinds of exposure times.

If you can get away with it - I'd prefer f/8, unless you're using an old manual focus lens with a hard infinity stop, you're going to need some tolerance in your DOF. Photo below was wide open at 2.8, 60s before I got a remote for bulb mode. I wish I could have stopped down, but then I'd have been looking at very high ISO or a shutter speed I couldn't do without a remote.

Also - look into a battery grip. I got a genuine Canon one, used, without the useless AA battery adapter for $30. Then you can have 2 batteries powering the camera.