Just a couple of quick tips relating to long exposures….
When using an ND filter, paired with a low ISO value, it’s often difficult to get a meter reading. A standard solution is to crank up the ISO, take a meter reading, and then count stops back to the desired ISO. For example, suppose you want to shoot at ISO 100. Change the ISO temporarily to 6400: 1 second @ ISO 6400 = 2 seconds @ ISO 3200 = 4 seconds @ ISO 1600 = 8 seconds @ ISO 800 = 16 seconds @ ISO 400 = 1/2 minute @ ISO 200 = 1 minute @ ISO 100.
A shortcut I’ve used for a long time is to think of this in a slightly different way. The time in seconds at ISO 6400 is the same numerical value in minutes at ISO 100. 1 second @ ISO 6400 = 1 minute @ ISO 100. 10 seconds @ ISO 6400 = 10 minutes @ ISO 100. 1/4 second @ ISO 6400 = 1/4 minute @ ISO 100.
Most cameras offer 30 seconds as the longest timed shutter speed. After that you have to use an intervalometer shutter release such as the Nikon MC-36. These things have long cords, so how do you keep one from blowing around in any breeze while it’s dangling from your camera running a long timed exposure? For that matter, what’s a good way to control that cord in a camera bag? My solution is this: http://www.thinktankphoto.com/products/redwhips.aspx, basically a thin bungee cord and a cord lock. You can easily make these yourself, but I admit being partial to ThinkTank’s red ones (easier to find when dropped). Here’s a composited illustration, showing the MC-36 ready to pack, and attached to a tripod leg.