An introduction to ND filters and graduated ND filters -- and what's the difference?

Since we work with filters every day, and deal with so many experienced photographers, we sometimes forget that not all of our readers and customers are familiar with the basics of Solid ND (neutral density) and Graduated ND filters.

Apart from being a noted outdoor photographer and author, Rod Barbee is also a workshop instructor and is aware of the confusion some photographers experience when it comes to selecting and using Solid ND and Graduated ND filters, so we asked Rod to review the basics.

"At one of last year’s workshops," says Rod, "a client wanted to learn to use her new 'ND' filter. She'd been told that she needed a 'neutral density filter' to control the contrast in her landscape pictures. When asked which filter she had, she pulled out her brand new 'solid' neutral density filter. Oops. What she really needed to get was a graduated neutral density filter.

"If this sounds like it could happen to you, don’t feel bad. Confusing the terms solid ND filter and graduated ND filter actually happens with some regularity -- even among experienced photographers. Many people, workshop instructors included, refer to graduated ND filters simply as 'ND filters.' So when someone relatively new to outdoor photography is told they need to get a “2-stop neutral density filter” to control bright skies, they dutifully order a 2-stop solid neutral density filter. Ouch.

"OK, what is the big difference, you ask? Read on….

"Many solid neutral density (ND) filters are mounted in threaded rings just like many other optical filters so they can be quickly and easily mounted on the front of our lenses. They are dark grey in appearance and come in several different 'densities' that reduce the amount of light passing through the lens by a specific amount (from 1-stop up to 5-stops or more). The word 'neutral' in neutral density is important because it indicates the filter is completely neutral in terms of its color -- meaning it won’t affect the natural color of anything in your scene. . .so the blue sky stays blue, the grass stays green, and the yellow roses stay yellow."

Editor's Note: Singh-Ray offers the 5-stop Mor-Slo Neutral Density Filter in a ring mount (above), as well as our rectangular George Lepp Solid ND Filters in 1, 2, 3, 4 or 5-stop density to fit the Cokin P-size or Z-Pro filter holders.

"Now let's discuss what you can do with solid ND filters. Their purpose is to cut down the amount of light reaching your film or digital sensor -- which lets you keep your shutter open for as long as 30 seconds or more in broad daylight. Some uses for longer shutter speeds include blurring water in streams, waterfalls, and various moving subjects. You may also want to slow your shutter speed in order to stretch moving clouds across a sky, creating various zoom effects, and blurring the action of objects moving around a still object. In the photo of the seagull (above), I used an ND filter to achieve a one-second exposure which added some motion blur to the water.

"You can also use neutral density filters to control the amount of light needed to shoot at a specific aperture and shutter speed, as I did for this tulips-in-the-rain image (actually, tulips with a watering can). First decide on the aperture you need to get the pleasing blurred background you want and then choose a specific shutter speed that will show some motion in your moving subject. When the existing light level is too much to give you exactly that exposure, you can place an ND filter on the lens that will reduce the amount of light to a level that lets you use your predetermined exposure settings. Let's say you want f/4 at 1/8th second but at f/4, your camera gives you a shutter speed of 1/125th. Since you’re probably using your lowest ISO setting already, the only solution is to cut the amount of light entering the camera. A neutral density filter can do this (in this case, 4 stops of ND are needed).

"There are many creative things you can do with a set of neutral density filters. The photograph of a fishing boat in Newport Harbor on the Oregon coast was made by zooming the lens during a long exposure achieved by adding a neutral density filter. But you don’t need to buy a whole array of ND filters with various densities since Singh-Ray developed the variable ND filter that offers any density you need from 2-2/3 to 8 additional f-stops of density. Singh-Ray’s Vari-ND is my go-to filter whenever I want to get creative with my shutter speeds.

"Now let's briefly talk about the purpose of graduated neutral density filters (also often called 'ND Grads'). These are the contrast controlling filters used to reduce the transmission of light in only a part of an image -- such as the bright sky in a landscape. Professional quality graduated ND filters are flat, rectangular filters that are half clear and half dark. When properly positioned in front of your lens, the gradient area blocks just enough light from the overly bright areas in the scene to bring the light levels in the scene into a range our film or digital sensor can record. Many of the most dramatic scenes in nature involve a bright, beautiful dramatic sky at sunrise or sunset coupled with a compelling foreground. Often the range of light in a scene like this is beyond the ability of the film or sensor to capture all by itself. That’s where a Graduated ND filter comes in.

"This pair of photos of Lake McDonald in Glacier National Park shows the subtle but important difference an ND grad can make. The shot at left was made without any filter, and the shot at right was made with a Singh-Ray 3-stop soft-edge Graduated ND filter. As you can see, my Graduated ND filter allowed my camera to capture the full tonal range in the scene that would otherwise not be possible. (Click the image to enlarge the comparison.)

"Both Solid ND filters and Graduated ND filters from Singh-Ray may take a little practice to use, but once you start using them, you’ll never leave them out of your camera bag. In my book, they're essential to every landscape photographer's success."

To check out what else Rod has to teach you, visit his website at www.rodbarbee.com to learn more about his upcoming workshops and ongoing writings.