You saw that wonderful long exposure image on the internet, with a smooth water surface and moving clouds in the sky, and you thought; I want to shoot images like that. So you invested in a dark neutral density filter that makes it possible to shoot with shutter times that are 1000x longer. Now you can start making those long exposure images.
Shooting long exposures is very popular. Many photographers have a filter system for square filters, or they use the round filters that are placed directly on the lens. I too have started with those dark neutral density filters because I liked those photos a lot. I bought a Lee Big Stopper and used it for many years. Recently I changed these filters for the much better Kase Wolverine filters, for which I wrote an article about. But no matter what brand of filters you use, it basically comes down on extending the shutter time long enough to smoothen out the water.
Creating these smooth water surfaces can divide the photo community in two groups. Or you hate it, or you love it. I often get the feeling there is no in-between. And indeed, it is a kind of photography that must suit you, otherwise you are better off without the use of these filters.
It is not only large water surfaces that can be smoothed, also mountain streams and waterfalls can be photographed with these dark filters. During my workshops participants often reach for their ND64 or ND1000 filter without hesitation, or without thinking about the effect these filters will produce. They seem to be eager to use their expensive filter, because they bought it to shoot moving water.
During one of my presentations someone mentioned about smooth water surfaces, that it doesn’t show the reality. And perhaps that is true. But when I showed a picture with a waterfall that was frozen still by a fast shutter time, some other person in the group made the remark that this wasn’t reality also. This simple conversation during that presentation strengthened my believes, that the truth is somewhere in-between and it eventually lead to this article. I want to give the advice to think carefully what it is you want to show in your image. If you have made a decision on how the water must appear, than it is time to think which filter you will need to achieve that goal. So don’t grab for that 10 stop neutral density filter because you own it, but because you need it to end up with the photo you want to have.
If you want an image of a sea surface that has been smoothened out, it is quite simple. Use a 10 stop neutral density filter, or even an extreme 15 stop filter to reach shutter times that are between two and five, ten, or fifteen minutes. Be careful though; don’t make the shutter time longer than necessary. If the water is already smooth in two minutes, it is not necessary to make the exposure time much longer. So don’t use a 15 stop ND filter because you have it in your bag, if a 10 stop ND filter can do the trick also.
If you still want some movement visible in the water, an extreme ND filter is not necessary. That is why it could be wise to have a set of ND filters available, like a 3 stop, 6 stop and a 10 stop, so you can extend your shutter time exactly to the length you need.
The way to work is quite simple. Look at the water, the way it is moving, and the speed in which it is moving. Take the focal length into account and the distance, because that also has its effect on how the movement will show up in the image. If you have done this, try to anticipate the shutter time you need to get the effect you want to achieve. By looking at the exposure without a filter, you can calculate how much stops light you need to block, and you know which filter you must use.
If you are searching for complete smooth water, you just have to make the exposure very long. But if you want to catch the strength of the water, the movement and dynamics of the scene, you need to set the shutter speed exactly right.
Most of the times the surf will take between 4 seconds and ¼ of a second, depending if you catch the incoming wave, or the outgoing water flow. Choose the right ND filter to get the shutter time you want, and perhaps you don’t need a filter at all. So don't use it because you have one, but only when you need it to get the image you want.
When photographing waterfalls you can also choose to smooth out the water, or to keep details in the falling water. Shutter times between 15 seconds and 1/15 of a second can do the trick, depending on the length of the waterfall, and the effect you want to have. This also applies with mountain streams, which can have a lot of speed variations.
So next time you stand next to a waterfall, mountain stream or on a beach, don’t grab for the darkest filter because you have one in your bag, but think of the effect you want to capture and use the filter that can help you reach that goal. But making that choice can be difficult, I found that out from my own experiences. That is why I would advise to make both shots, one with a long exposure and one with a faster slow shutter speed. This way you have both and you can make that decision later. I have collected a couple of images from my archives with an explanation what kind of filter I used and why. Just for inspiration purposes.
I would like to hear what kind of affects you like the most. Is it smooth water or do you prefer to see the movement and strength of the water, and what kind of ND filters do you use to achieve that goal? I love to read about your preference in the comment below.