I thought I’d write a note about how I go about taking these long exposure shots, what gear I use etc.
The main piece of kit you need is a neutral density filter. I have a 10 stop filter, or ND1000 as it is. That means it blocks out 10 stops of light, which quickly means you need to start taking very long exposures. I have a B+W 77mm filter and a step up filter so I can use it on a couple of lenses.
I also use a tripod (a Manfrotto x055 Pro) with ball head and a cheap ebay remote trigger to avoid any unwanted shakes.
Because the filter is so dark when it is on the camera it’s impossible to see anything though the viewfinder and the camera will notbe able to meter or auto focus. So you have to setup the shot with the camera on the tripod and the camera in manual focus (or use AF then switch to M).
Once the shot is composed and focused you need to take a meter reading of a properly exposed shot without the filter so that you can use this to determine the exposure 10 stops lower. You will need to keep the aperture the same between the normal shot and the long exposure shot with the ND filter and only vary the shutter speed so as to maintain your desired depth of field and focusing. I do this by taking a reading in Aperture priority mode and then switch to Manual mode for the long exposure.
Once you know the shutter speed you need for a normal exposure you’ll have to work out what 10 stops (or whatever filter strength you’re using) less than that reading is. I use a printout of this chart for looking up the exposures. Simply look up the reading you’ve taken across the top and then read the shutter speed off in the 10 stops row. So a reading of 1/60th becomes 15s and 1/8th becomes 1 minute (as you can see it very quickly can get into exposures of minutes in length).
Once you’ve worked out the exposure you’re going to need, carefully screw the ND filter onto the lens making sure not to move the camera setup or adjust the focusing on the lens.
For shutter speeds up to 30s I can use the normal manual settings on my D300. For anything longer I have to put the camera into “Bulb” mode and then use the remote release. You can do this by pressing the button once to open the shutter then counting using a watch before pressing the button again to close the shutter. My trigger allows me to input in the exposure time I want and let it do the counting and releasing the shutter leaving me free to keep my hands warm in my pockets.
The camera settings I use are 14 bit lossless compressed RAW recording with a neutral picture profile. I leave long exposure noise reduction on. I can then make best use of the files back home on the PC.
On my D300 the camera will do its own long exposure noise reduction in camera and I reccomend that you use it. It gets rid of a lof of sensor gain noise that you’ll otherwise spend ages removing with a clone tool in post production. The only problem with it on the D300 is that it takes as long to do this step as it does to take the picture. So if you take a 15 minute picture it’ll take 15 minutes to perform the NR, which is a bit annoying, I think that the D3 and D700 are faster in this regard.
The long time that it takes to take just one long exposure shot means you end up spending a lot more time setting up a shot and making sure that it’s composed well and it just so before you take it. Because if you didn’t you’ve just wasted a good 5 minutes.