Neutral density filters are what dreams are made of. Okay, maybe that’s pushing it, but they are often what long, flowing dreamy waterfall photos are made of. To get that soft water effect on your photos, you need to get the shutter to stay open for a while. At least a second. Sometimes up to 10 seconds, depending on the speed of the water and the effect you’re going for. Waterfalls are far from the only use for this technique, but it’s what many people think of when they think of long exposure photography.
The problem with simply programming your camera to leave the shutter speed open longer is that, on bright days, you let too much light in and your pictures come out overexposed. Enter the neutral density filter, which (in simple terms) is just a dark piece of glass that screws onto the end of your lens, making the scene darker so you can leave your camera’s shutter open longer.
The problem with using standard ND filters is that they come in fixed degrees of darkness. So you either need to buy (and probably carry) several different filters of different degrees of darkness. That’s why I’ve always preferred variable neutral density filters. These are dual-glass filters that you can rotate to gain access various degrees of darkness, even hitting all the points in between full stops.
The problem with variable neutral density filters is that they’re still somewhat of a novelty, therefore tend to be very expensive and difficult to find in less common sizes. For example, I searched and searched for one that would fit my little Olympus lenses and could only find one… And it got bad reviews. So what did I do? I made my own!
All you need is 2 circular polarizing filters and a small screwdriver. Take the glass out of one and flip it over, then screw the two together, putting the flipped one furthest from the camera body. Travis L. Patterson has an excellent video on his Vimeo channel of how this is done: