Benefits of using a variable neutral density (ND) filter on your DSLR camera.
What is a variable neutral density filter?
These filters reduce the amount of light entering your camera, so think of the filter like a pair of sunglasses. There are many different models and manufacturers to choose from, but the most popular reduce light from 1-5 stops or 2-8 stops. These filters won't affect the color, contrast or sharpness of your photos. By having multiple stops, you can effectively choose the setting to achieve your desired result. You can also purchase a fixed ND filter, ie. 4 stops, but you won't be able to vary the exposure like you can with a variable filter.
When, or why would you want to use a ND filter?
These filters are most commonly used to blur the movement of water, especially when photographing lakes, oceans, risers and waterfalls. For example, let's say you want to photograph a lake scene, where the water is totally calm and tranquil. You will probably want to shoot at a slow exposure of 10-30 seconds. The challenge is that even choosing the lowest ISO of 100 and the smallest aperture (f22 - f32), your camera won't allow you to shoot any longer than 1/15 second, or you will overexpose the photo. By adding the variable ND filter (2-8 stops), to your lens, you can effect effectively shoot the same scene at an exposure of 16 seconds. Another example might be a waterfall you are wanting to photograph at a slow exposure of 1 second, but your camera won't allow an exposure of longer than 1/15 seconds due to the time of day. Again, by adding the ND filter, you can easily shoot at 1 second by reducing the light by 4 stops.
How do you use the filter?
These filters simply screw onto the front of your camera lens, so make sure you order the right size, ie. 55mm, 72 mm etc. Once it's treaded to your lens, you can monitor the effect by rotating the filter, which is similar to using a polarizer.
Tip: It's entirely possible that when you dial the filter to it's darkest setting, it reduces so much light that your camera won't be able to auto focus or correctly meter the scene. To overcome this, dial the filter to its lightest setting (where it lets in the most light) and depress the shutter half way to lock in the focus and meter setting. Now that the camera has locked in the autofocus, while continuing to hold down the shutter half way, dial the filter back to it's darkest setting, then depress the shutter all the way. It goes without saying that your camera will need to be mounted on a tripod and you might also find it easier to use an electronic shutter release.
I'm attaching 2 examples of photos where I used the ND filter. The fist one of the Weirs Beach Pier, was shot at 8 seconds and f22. The second photo of Meredith Bay was shot at 10 seconds and f32. Notice how the lake is calm and tranquil? Good luck and don't hesitate to contact me, Ron Bowman, with any questions: [email protected]