The only way to soften and blur water in motion is to lengthen your exposure, normally a second or more. But what if you’re in bright, mid-afternoon light that calls for exposure times closer to 1/100 of a second? Time for an ND filter…
“Sunny 16” Rule
This photo of Berry Falls in Big Basin Redwoods State park was created on a sunny afternoon. Even before getting my camera out of the bag, I knew that a regular exposure would be too fast to blur the water. The “Sunny 16 rule” calculates this well, calling for an exposure at f/16 as the reciprocal of the ISO. In other words, if it’s sunny outside and you shoot at f/16, your exposure will likely be close to 1/100 for ISO 100, 1/200 for ISO 200, and so on.
When I did get my camera out and into aperture priority mode at f/16 and ISO 100, it called for an exposure of 1/250. Slightly faster than the Sunny 16 rule predicted, likely because of all the white (water) in the scene that the camera didn’t want to blow out. So how did I end up with a 5 second exposure at f/11?
Out came the Lee Big Stopper ND filter for a 10-stop light loss. This turned an f/16, ISO 100, 1/250 second scene into 2.0 seconds at f/11 and ISO 100.
If you don’t have an extremely dark ND filter like the Big Stopper, perhaps you have two Graduated Neutral Density (GND) filters you can stack together and align such that the neutral density section completely covers the frame.
Circular Polarizer Filter
I also used a B+W Circular Polarizer filter. These are well known for making blue skies bluer, but they can be even more useful for cutting reflection off rocks and foliage. The image above shows the difference between having and not having a circular polarizer in use for this scene. I almost always use them for photographing waterfalls and fall foliage.
Remember that circular polarizers also account for some light loss. My B+W filter experiences about 1.3 stops, which is why the photo below ended up at 5.0 seconds at f/11 and ISO 100 instead of 2.0 seconds had I only used the Lee Big Stopper ND filter.