When I was a photography student shooting a sunset 20 years ago, I encountered a vexing problem. When I metered for the sky glowing above Death Valley's mountains in California, I got a wildly different reading than I did when I metered off the dunes below the horizon. Because I knew my slide film couldn't handle more than a three- or four-stop exposure range, I realized I couldn't get detail in both the sunset and the landscape beneath it. Sure enough, the shots exposed for the sky showed a silhouetted landform, and the shots exposed for the dunes blew out the bright sky completely.
The challenge still exists today, but there's an effective solution: graduated neutral-density filters. Also known as grad NDs, split NDs or just plain grads, these filters have a neutral-density coating over half of their area and are clear on the other half. The graduated boundary between light and dark helps make the transition between the two areas indistinct so that your image will look natural.
Placed in front of your lens, they hold back exposure from lighter areas, like the sky in my sunset, and allow you to increase exposure in the image's darker areas. The result is an image with midtones and plenty of detail in what would have been a dark foreground, and sky tones that also are correctly exposed.
Like polarizing filters, grad NDs have an important place in digital photography. Although a lot of people think that Photoshop can fix everything, or that shooting RAW gives you limitless dynamic range, it's simply not true. Like film, most imaging sensors can't capture clean detail in both the highlights and deep shadow areas when contrast is high. If you try to push the limits, you'll either blow out your highlights (they can't be put back) or get a lot of noise in your shadows. Ultimately, even a RAW file won't provide image detail that your camera's sensor is unable to capture in the first place.
You also can use a grad ND when an extreme range of light and dark tones isn't a problem. Say you've got a nice shot set up, but the sky is a bit pale or bland. A one-stop grad ND filter artfully placed over a part of that sky can deepen the color and make your photo look more dramatic. If you want to add a splash of color, graduated filters are available in a variety of hues. They can turn a gray sky into something more interesting or help make up for a lackluster sunset.
Grad NDs are commonly available in densities from one to three stops, and some manufacturers offer as much as a five-stop filter. (Some companies label the filters by density, with 0.3 equaling a stop, 0.6 equal to two stops, 0.9 equal to three stops and so forth.) The common wisdom is that if you have to pick just one filter, then a two-stop grad ND is a good all-around choice for slides. For print film or digital, a three-stop filter probably is better.
Sometimes, the one-stop filter works for subtle changes, but other times, you'll need three or more stops. (Imagine equalizing a row of trees in the shadow of a mountain with the blue sky above them.) Pros often carry several grad NDs to make sure they have just what they need for a range of circumstances and to stack them together for more strength.
Many filter manufacturers offer a choice between hard-edged and soft-edged filters. Use the hard-edged filters when you have a straight, clearly delineated horizon. Since the world isn't always that neat and tidy, soft-edged NDs offer a more gradual change between light and dark. The subtle transition avoids a telltale edge where the boundary area crosses your image.
You also can choose between convenient screw-in grad NDs and square or rectangular ones. The square and rectangular filters take a little longer to set up, but they let you position the light-dark boundary precisely where you need it. These filters fit into special holders by Lee, Cokin and other manufacturers that keep the filters properly placed.
B+W offers one- and two-stop screw-in graduated NDs in filter threads from 49mm to 82mm, as well as graduated color filters in a wide variety of hues. List Price: From $88.
|B+W (Schneider Optics)
Cokin Filters (OmegaSatter)
Heliopan (HP Marketing Corp.)
Hoya (THK Photo Products)
LEE Filters USA(Panavision)
Sunpak (ToCAD America)
Cokin's well-known system of square filters includes graduated neutral-density and colored filters in sizes from 36mm up to 112mm. Special filter holders let you stack the filters in place over your lenses. List Price: From $21.
Heliopan's screw-in grad ND filters are available in strengths from one to three stops, and filter sizes from 49mm to 77mm. List Price: $102 to $187.
Hoya makes a two-stop ND with a sharp edge between light and dark in screw-in sizes from 49 to 58mm. Graduated color filters of the same size also are available. List Price: From $60.
Lee Filters offers rectangular grads with a broad range of colors and in NDs, with densities from one to three stops in half-stop increments. The 100x150mm filters are available in both hard and soft versions, and work with Lee's filter holder system. "P" size filters fit Cokin filter holders. List Price: From $79.
Schneider Optics' graduated filters come with either a hard or soft edge in a wide variety of colors, as well as neutral densities from one to four stops. The company offers both 4x4-inch and 4x5.650-inch sizes that fit a Lee holder with the available 4mm spacers. List Price: From $228.
Singh-Ray's grad NDs are available in densities from one to five stops, with either a hard or soft edge. The rectangular filters can be ordered in either a 120mm length for Cokin "P" filter holders or a 150mm length for Lee holders, and the company will custom-make a filter if you can't find what you need. List Price: From $99.
Sunpak makes screw-in graduated filters in sizes from 49mm to 77mm, and they include gray, sepia and wine colors. List Price: From $39.
Tiffen Color Grad filters come in one-, two- and three-stop strengths of neutral gray, as well as shades of blue and orange. The filters are available in both screw-in (ND is two stops) and square versions, and with soft- or hard-edged transitions. List Price: From $53.