How to Shoot With a Split Neutral Density Filter
By Josh Anon
26 February 2007
Recently, I was shooting in Yosemite and drove past Gates of the Valley, a wonderful spot where you can see the valley reflected in the Merced river. It's actually a tricky shot, though, to meter right, but there's a secret to make this shot (and shots like it) work. However, not one single person seemed to know the secret of the split neutral density (ND) filter, and I can guarantee that not one person had a properly-exposed shot from that spot.
When we look at a scene, our eye's pupil adapts its size (aka its exposure) as it moves from the bright parts to the dark parts, enabling us to see detail everywhere we look. Unfortunately, an image we take with a camera is just a static capture of light--there's no adjusting the image's exposure as our eyes gaze over the image. The ratio between the brightest part and darkest parts of a scene is called dynamic range, and film/average digital cameras can capture about five stops of dynamic range. As long as we're not shooting in harsh light, our cameras are usually able to capture both shadow detail and highlight detail.
Unfortunately, for landscape photographers, even when there's no harsh light in a scene, landscapes often have a greater dynamic range difference between the ground and sky than a camera can capture. For example, imagine a mountain at sunrise reflecting in a lake. Here, if you meter so that the reflection's properly exposed, the sky will be too bright and vice versa. As another example, when the sun's setting and there are clouds with color in the sky, if you meter for the sky, the ground will be black (or close to it). Metering for the ground will cause the sky to be blown out.
Enter the split ND filter. Typically, this is a rectangular filter that's darker on one end and clear on the other. A soft-step filter will have a smooth gradient from dark to clear (taking about 1/2 - 2/3 of the filter), and a hard-step split ND is literally darker on one half and clear on the other. They're available in different brightnesses, typically ranging from 1-3 stops (I highly recommend purchasing a 2-stop soft-step filter. The Singh Ray Galen Rowell 2-stop soft-step filter is my most-used one because it doesn't have any color tint and is very high-quality glass). With the right split ND filter, both the ground and sky in a landscape will have detail and be more appealing.
Shooting with a split ND is easy and involves two parts, attaching and metering. Filter companies often sell special holders to attach the filter to the lens, but they often cause vignetting and, with hard-step filters, can make the gradient line very apparent. Therefore, especially if you're using a hard-step filter, I recommend the hand-held shooting method to make the split line less visible:
1. Compose your scene
2. Hold the filter in your left (non-shutter) hand
3. While looking through the viewfinder, extend your arm in front of you and bring the filter up to the viewfinder
4. Take the shot, holding the filter in front of the lens. Be careful not to push against the lens, as you might defocus it or add shake.
If you prefer not to hand-hold it, use tape to attach the filter to the lens. Using tape instead of filter holders also let you stack multiple split ND filters at different angles.
Metering is similarly easy. If you're using evaluative metering, simply put the split ND filter on the lens, meter as normal, and shoot. If you're using spot (or other) metering, meter for the foreground subject and then slide the filter into place.
I promise you that, if you like shooting landscapes, a split ND filter will become as essential as your tripod.
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