I haven’t been shooting long exposure images for a long time yet but I have always loved them. Even then when I hadn’t known how the are done. I figured it out quite quickly when I started learning the subject though. How smart I am ).
The trick is to cut the light substantially with a filter in front of the lens and keep shutter open until you get a desirable exposure. That’s where a 10 stops ND coms handy. Let’s say your exposure without the filter at a certain f stop is 1/100th of a second and with the filter it becomes about 5.5 seconds. Well 5.5 seconds is not that long actually to get nice milky effect when you’re shooting water, and especially if you want to get a motion blur in the clouds . I prefer to keep the shutter open between 1 and 5 minutes depending on the scenery.
The best time to shoot is around sunset or sunrise. Unfortunately sunrises are better here in Sydney so I’m forced to get up at 4 to get the shot. With such a long shutter speed and the best lighting lasting about an hour and a half it’s impossible to take a lot of images and fiddle with the settings. There is not much room for mistake – you have only a few tries and “the golden” or “the blue” hour will be gone, so you need to get to the location beforehand, unpack the gear, choose the spot, put the filter on the lens, calculate the right exposure and be absolutely ready by the right time comes.
At the moment I can’t tell much about the filters as I’ve used only Formatt HiTech Pro Stop 10. It’s made of resin and gives blue colour shift. The colour shift is not huge and fixable in post. I would prefer not to have it at all but for the price I paid for the filter having a slight colour shift is forgivable. I’ve heard and read about Lee’s “Big Stopper” but haven’t touched it yet.