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Using Split Neutral Density Filters
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We’ve all seen, and taken, pictures of a mountain reflected in a lake with the reflection beautifully exposed and full of detail, and the mountain and sky washed out and pale. Slide film has a typical latitude range of about 5 stops of light. That means if you meter on a shaded foreground there’s a good chance that the sunlit mountain in your background is going to be brighter than the film can record. Or if you meter on the sunlit mountain, your foreground will go very dark, or even black, on film. One thing that can greatly improve your photography is taking control of the exposure process. One way of doing this is by using split neutral density filters to control contrast in your landscape images. Split neutral density filters can’t create great light, but they can help you record it on film. Split neutral density (ND) filters (also called graduated neutral density filters) are filters that are clear in one half and dark in the other. As the name implies, they are color neutral filters. This means that when you place them in front of your lens colors are not changed, only the amount of light passing through the lens. Split ND filters come in a variety of densities. Most common are the 1,2 and 3 stop split ND’s (sometimes designated as 0.3, 0.6, and 0.9 respectively). They are available in soft and hard-edged transitions. They also come in a variety of sizes. Don’t bother with the screw in split ND filters as they force you to place the horizon line in the middle of the frame. Choose a brand that offers a size that will cover your largest lens. Cokin “A” types are not large enough. Filters by Tiffen, Singh-Ray, Lee, and Hi-Tech are long enough. There are two types of materials that split ND’s are made of, an optical resin material and glass. Resins scratch easier than glass but glass will break easier than resins. Some split neutral density filters, most notoriously the Cokin graduated gray filters, are not truly neutral; compare them before you buy one. Singh-Ray, Tiffen, Lee and Hi-Tech are more expensive but are also more consistently neutral. Singh-Ray, Tiffen, Hi-Tech and Cokin make filters that will fit the Cokin P holders. Lee filters use their own holders. Using split ND filters: First thing to do is to determine which filter you’ll need to use, or even if you will need one. The best way I’ve found to go about this is to use your camera in the manual exposure mode with spot metering. Set your lens to the aperture appropriate to what you’re trying to accomplish. For a wide-angle landscape with close foreground you’ll probably want f/16 or f/22. Spot meter an important element in your foreground, like a reflection in a lake or a flower, and change your shutter speed so that your subject will be the tonality that you want it to be. This will be the exposure setting that you use to make the image. Next, point your spot meter to the brightest part of your background in which you want to preserve the detail and while changing your shutter speed, count the number of whole stops it takes to set that background object to the tonality you want it to be. The number of stops you counted determines which split ND filter you’ll need to use. Many newer cameras have shutter speed increments of ⅓ or ½ stop. You’ll need to be aware of this while counting; one click may not mean one stop, it may only be a third of a stop. After you’ve determined which filter you need to use, change your shutter speed back to the original setting used to determine the foreground exposure. This is very important to remember. It often happens that you’ll figure out which filter is needed, put it on the lens and fire away and then wonder later what went wrong when you see your image 2 or 3 stops under exposed. Once you’ve determined which filter you need and have returned your camera settings to the foreground exposure, you’ll need to place the filter in front of the lens and take the photograph. You can either use an appropriate filter holder or hand-hold the filter. Both methods work, but hand holding has the advantage of allowing you to work fast in quickly changing light. This takes a little practice and you’ll need to beware of possible camera movement while handholding a filter. Also, if you’re using a push-pull zoom lens, make sure you’re not changing your focal length while holding the filter to the lens. Hold the filter in front of the lens and move it up and down so you can see the transition. The depth of field preview button can be a considerable aid in this, especially when using a 1-stop split ND. If you’re using a filter holder, press the DOF preview button and slowly move the filter into place, you can also rotate the filter to better see the transition. Once you have the filter where you want it, making
sure it’s flat against the front of your lens (if you’re
hand-holding it), take the picture. One method I’ve developed for
myself involves using one hand to hold the filter, while the other is
used to press the DOF preview button so I can place the filter where it’s
needed. I’ll put the remote cable release in my mouth and use my
tongue to fire the shutter. Not too dignified but it works remarkably
well.
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Here’s a real world example. In this image of Mt. Rainier, I spot metered on the foreground grasses using an aperture of f/22. I changed the shutter speed setting until the meter read “0” to make the grass a medium tone. I then pointed the spot meter at the brightest part of the mountain and started changing the shutter speed setting until the meter read about +1 2/3, which is where I like to expose white when using Fuji Velvia slide film. I had to change the shutter speed by three stops to achieve this so I then knew I needed to use my 3-stop split ND filter. Next I changed my shutter speed back to the first setting I made while spot metering the foreground, placed the filter over the lens using my depth-of-field preview button to help place the transition and took the shot.
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Mt.
Rainier from the Bench Lake trail autumn, Mt. Rainier National Park, WA.
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Mt.
Rainier from the Bench Lake trail, autumn, Mt. Rainier National Park,
WA.
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In the image of the East Temple in Zion National Park, the important elements were the face of the Temple and the reflection in the stream. After finding my composition, I took the camera off the tripod and spot metered first the reflection and then the sunlit cliff face. I wanted to be sure that the reflection was about one stop darker than the cliff and I also knew that I wanted to make the tonality of the rock on the cliff one stop brighter than medium. So I set the reflection as a medium tone and spot metering the cliff, changed the shutter speed until the meter read +1 stop. In this case, I also needed a 3-stop split ND. |
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For the sunset on Hurricane ridge I wanted the sky to come out on film just like it was to my eye. In this case it was a bright sky with some color. I also wanted to make sure that the distant ridges were slightly dark. In this case I again started with the foreground and setting the sunlit lupine flowers so that they would come out a little bit brighter than medium, maybe +1/3 stop. I then moved to spot meter the sky just above the mountain. I wanted the sky to be light so I changed shutter speed until the meter read about +1 1/3. This required 2 stops of change. Just to make sure every thing in the image would fall where I wanted it to, I moved the spot meter to the distant ridges and saw that the meter read about –2/3, which is right where I wanted the ridges to be. Good news, everything would fall in right where I wanted it by using a 2-stop filter. Since the mountain itself was mostly showing its shaded side, I wasn’t worried about the whites blowing out; that is, being way too bright on the film. Again, I used the DOF preview button to place the filter on a diagonal at the edge of the lupine field. |
 Lupine field at sunset, Hurricane Ridge, Olympic National Park, WA. Nikon F5, 35-70 f/2.8 lens, Fuji Velvia. 2-stop split ND filter. |
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Alternative metering method: Determine the filter needed as above, change over to your matrix or evaluative metering and place the filter where you need it. Let your meter determine the exposure. The most accurate metering method, though, is by just using your spot meter and following the steps above. The real key to using split neutral density filters, or any exposure modifying technique, lies in knowing what your film is capable of and in interpreting what your meter is telling you. If you know that your film can only record a narrow range of tonalities, and if you use your spot meter to meter a scene and determine if your film will be able to record what’s in your viewfinder, you’ll be well on your way to taking total control of your exposures.
Tips: · The best images taken with split ND’s are those where the viewer cannot tell that the filter has been used in the first place. Some scenes can really lend themselves to this while others are more difficult. · Remember that reflections look more natural if they are slightly darker than the object being reflected. · Split ND filters can be combined if necessary. · A 2-stop soft edged filter is probably the most often used. If you can only afford one, that’s the one to get. · Be sure to take pictures with and without the filter; it’s very educational. · For Velvia film, I’ve found that treating it as if it had a latitude of plus or minus 1 2/3 stops instead of plus or minus 2 stops has given me better results. Velvia seems to have a bit more contrast than other films with the whites losing detail at +2 stops and the blacks losing detail at –2 stops. · Split ND filters with a soft-edged transition are good for hiding the transition line in trees or other jagged lines. Hard edged filters are good for shots where there is a definite, straight transition, like sunsets or sunrises over water, where you have a distant, straight line horizon.
Sources
Singh-Ray Filters2721 SE Highway 31 High quality, large variety. Split ND’s are made of resin material. Also offered are reverse split neutral density filters, strip filters, intensifiers, polarizers, high quality UV filters and plain neutral density filters, including the new Vari-ND filter, which allows you to dial in the amount of neutral density you need. Very cool.. B&HThe Filter Connection1-800-882-2832 A variety of filters available including Tiffen, Hitech, Schneider.
Singh-Ray filters are $100 each for the standard split ND’s and are made of an optical resin. Available in hard and soft edged. Used by many professionals. Tiffen’s filters are made of glass and are a bit shorter than the Singh-Ray filters. They are approximately $95. Hitech filters are made from an optical resin, like the Singh-Ray filters, and are about $35-40 each. A great price for a quality filter. The also come in soft and hard edges though their hard edge is equivalent to the Tiffen or Singh-Ray soft edge. The Schneider multi-coated filters are very, very expensive (over $400 each) ©Rod Barbee, 2001 [a version of this article appeared in the Sept. 2001 issue of Outdoor Photographer Magazine]
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