Graduated NeutralDensity Filters
No film can record the contrast range that our eyes can see. If you are standing in a location with contrasty lighting—for example, a forest on a bright, sunny day—you can see detail in both the darkest shadow areas and the brightest highlight spots simultaneously. Our eyes are very accommodating; most people's vision can handle a contrast range of about 12 to 14 stops. This is not true of film, which at best can only deal with about a 5-stop range in any one scene. Most beginning photographers ignore this limitation, only to be sadly disappointed in their photographs. Recognizing this compressed contrast range and learning to view subjects the same way that film records contrast, are vitally important to your photographic growth.
The newest cameras, the most expensive lenses, the latest films . . . all these won't change this most basic photographic fact. If you must photograph in a high-contrast situation, a scene that goes beyond those 5 stops from light to dark, you can't record all the detail on film. If you make an exposure favoring the dark area, the highlights will blow out, turning into detailless, washed-out areas. Expose for the brightest areas and the shadows block up, resulting in a solid, featureless black blob. Split the difference, and nothing looks good.
If you're not sure you can recognize this situation, it's fairly easy to use your camera meter for a precise answer. Meter both the brightest area of your scene and the darkest area, placing them tonally where you want them to be. Now compare the two meter readings. If they are beyond five stops, you've got a problem.
for example, suppose you want to photograph snow-capped Mt. Rainier. It's a beautiful morning of a blue-sky day, with puffy white clouds slowly drifting past. You're standing in a meadow filled with wildflowers that is still shadowed at this time of day. The mountain is bathed in fantastic sunlight, and you can easily envision a great picture. But :an film record the scene?
Take a meter reading of the snow on the mountaintop. Remember to use a narrow-angle meter, such as your spot meter, as you want to meter the snow and only the snow. Your meter gives you the direct values of 1/125 sec. at //16, but you know that this will render the snow as a medium tone. To make the snow a pure white, you must open up 2 stops to 1/125 sec. at //8. Now meter the foreground—the shadowed meadow. It's basically a medium-toned area. There are some slightly lighter flowers and a few dark er leaves, but it averages out to a medium value. Take a meter reading here, using an overall metering pattern. The values read out as 1/60 sec. at //2.8. Now, count how many stops difference there are between these two readings. Well, you slowed the shutter speed by I stop, and you opened the aperture by 3 stops, for a total of 4. If you expose the film so that the white snow is indeed rendered as a white, the meadow will be recorded four stops darker. Refer back to my exposure chart (page 25) and you'll discover that 4 slops below while will yield an "extremely dark" tonality. The meadow will become on film 2 stops darker in tonality than it appears to your eyes. Not good; it's a great meadow and you want all the flowers to be visible. But if you expose it properly, as a medium-toned subject, what happens to VIt. Rainier? You still have that 4-stop difference, so if you set your camera to record the meadow as a medium the snow on Mt. Rainier will be 4 stops lighter. Four stops lighter than medium is so light that nothing will record on the film, so there will be a blank section of film base where the snowy top of Rainier should appear.
At this point you have several choices. You could give up in frustration and not take any pictures at all. Or you could take a photo of only the meadow and a second photograph of only the mountain. But if you want both in the same frame, there's only one possible answer: you need to somehow cut the light on the sunny portion of your frame by 2 stops, or add 2 stops of light to the foreground meadow area. You need a 2-stop graduated neutral-density filter.
Neutral-density (ND) filters are simply dark filters that cut the amount of light coming through your lens. True ND filters are indeed neutral; they add no color of their own to the photo and do nothing but reduce the light. Quality ND filters are available in distinct increments of density—I stop, 2 stops, 3 stops, and so on. Graduated neutral density filters are part dark and part clear. Half of the filter has the dark density, which then fades to a totally clear area on the other side of the filter. The graduation itself can occur over some distance—a so-called "soft" graduation—or it can shift abruptly—a "hard" graduation. If you add such a filter over your lens, you can reduce the light falling on one portion of your film, effectively compressing the contrast range of a scene. Exactly where this occurs within your photo depends on how you orient the dark area of the filter, lust be aware that the shift from dark density to clear filter
SINGH-RAY GRADUATED ND FILTER IN C0KIN FILTER HOLDER MOUNTED ON LENS.
This is how rectangular graduated NI) filters are supposed to be used. The holder can be rotated, and the filter slides back and forth into any position.
occurs in a straight line across the filter, so it helps greatly if the contrast problem in your scene is also delineated by a straight line. In that Mt. Rainier scene, suppose a tree was coming out of the shaded foreground so that its top was protruding into the sunlit half of the frame. Add density to this portion of the picture, and you'll end up with a tree that is half light and half dark.
I should mention here that graduated filters are available with colored densities as well as neutral density. My advice is to stay far away from these half-colored filters.
Photographs made with them are almost always easy to spot. I've seen too many photos where a scene with even light suddenly turns tobacco-colored in the sky. Yuck.
Graduated ND filters are sold as standard round screw-in glass filters in the usual filter sizes, or in rectangular shapes designed to be inserted into filler holders that, in turn, screw onto your lens. The standard round filters have one major drawback which in my opinion renders them useless: the graduation from clear to dark falls exactly through the center of the filter. Since a screw-in filter cannot be repositioned, this shift of densities will always occur right through the middle of your picture. I don't think I've ever had reason to use a graduated ND filter with this placement. You want a system where the density can be positioned wherever you desire.
The rectangular filters are the answer.
These are usually made from an acrylic-
resin, and are designed lo be used in special filter holders. The holder allows the filter to slide from end to end, and also to rotate. Consequently, you can position the graduation exactly in the location where you want it to fall. For years I did not use a filter holder
howse peak and reflections in This photo is over-filtered. I used a 2-stop graduated ND where I should have
LOWER WATERFOWL LAKE, BANFF . . J , vr . . . n . . . ,•»,»,•,.
national park c anada " a ' Notice that the reflection of the mountain is slightly lighter
Nikon U, Nikon 28-7omm lens. Fuj; Velvia. than the mountain itself, a physical impossibility.
howse peak and reflections in This photo is over-filtered. I used a 2-stop graduated ND where I should have
LOWER WATERFOWL LAKE, BANFF . . J , vr . . . n . . . ,•»,»,•,.
national park c anada " a ' Notice that the reflection of the mountain is slightly lighter
Nikon U, Nikon 28-7omm lens. Fuj; Velvia. than the mountain itself, a physical impossibility.
at all, but just held the filter up to the front of my lens during my exposure. This method worked okay, but I've gotten frustrated with trying to do several things at once. Mold the filter with one hand, take a meter reading, hold the remote release with the other hand, reposition the camera.... Good grief, John, use a filter holder.
Good-quality graduated NDs arc available from a number of manufacturers including Tilïen, B+W, and Lee. In my opinion the best are made by Singh-Ray and can be had in 1-, 2-, and 3-stop densities in both hard and soft graduations. These are expensive acrylic-resin filters (they run about $100 each) and you probably won't need all six versions. I would suggest starting with a two-stop soft edge, then letting your field needs dictate any future purchases. For information, contact:
Singh-Ray Corporal ion 153 Progress Circle Venice, FL 34292 Phone: (800) 486-5501 Fax: (863) 993-4100 w ww. s i ngh - r ay. co m
These filters slide into a Cokin "P" series filter holder, which is available at almost any camera store. The holder uses different adapter rings which slide into the back, so with the proper ring you can use it on any lens. The Cokin holder is designed to hold several different filters at once, which creates a problem if you add it to a lens wider than about 24mm: the holder's thickness creates a vignette effect on the corners of the frame. 1 don't like to stack filters, so I modified my Cokin filter holder. I took a hacksaw, laid the blade in the outermost filter slot, and cut the holder down to a one-filter size. Not a very high-tech solution, but it worked perfectly. I don't like to use more than one graduated NL) at a time because you can almost always spot a picture taken in this manner. It's too much filtration. We all know, from looking at thousands of photos, there should be some apparent contrast. The sign of good filter usage, in my opinion, is that the casual observer does not realize a filter has been used. If I'm ever really desperate and have no choice but to use two graduated filters, I'll just hold the second one in front. So far it's never happened.
All acrylic-resin filters scratch fairly easily if mishandled, plus they tend to hold a charge and attract dust. While Singh-Ray ters are color neutral, this is not true of graduated filters. If you are purchasing locally, try to shoot a lew test frames various filters to find the most neutral ones. At the minimum, lav several out on a
box or over a piece of white paper. You be astonished at the color casts. ('okin filters are by far the least costly way to start working with graduated filters, but you must beware of color casts. Cokin doesn't actually
any graduated neutral-density filters, hut does have two strengths of "graduated gray."
After all this discussion, the question how to actually use these graduated NI)
ters in the field remains. I.et me refer to mv
earlier Ml. Rainier example, in which you counted the number of stops you needed to compress the tonal range. In that case you needed lo reduce the contrast by 2 stops, since you wanted the correct 2-stop difference to remain between white and middle tone. You needed a 2-stop graduated Nl) filler oriented so that the dark half covered the brightest part of the scene.
6o Kqi ipmknt ani> Film
The best, most precise way to meter with a graduated ND is to mount the filter over your lens so that the dark part is entirely in front of the lens. Now meter the bright area and place it at its correct tonal value. So for Mt. Rainier, meter the snowy area through the dark side of the I]Iter, then open up the exposure by 2 stops to make the white snow record white. Metering through the dark side takes care of any possible discrepancies in the tonality of the filter. Is your filter exactly 2 stops neutral density? 2 1/3 stops? I 7/8 stops? It doesn't matter, since you've just metered right through the dark portion. This works for all brands of graduated filters, but I will say that working with the Singh-Rays is particularly easy because the stop ratings are correct.
Now that you've placed the bright area, recompose the scene as you want it to appear, then reposition the filter. This is not always easy to do. When you're viewing through a lens, the graduation line is very difficult to see, especially when the lens is wide open. Stop down your lens with the depth-of-ficld preview, and slightly jiggle the filter. Doing this permits you to see exactly where the graduation occurs so that you can precisely align the filter as you desire. Be careful that you line the graduation up exactly with the shift of contrast in the scene itself. Position the density so that it overlaps into the foreground area, and you create a dark band running across the area where the highlights and shadows meet. Position it so that the graduation stops while still over the highlight area, and you get a bright highlight streak. Be exacting and precise in aligning the filter. When you look at a graduated ND filter, the greatest change from dark to clear seems to occur in the lighter area. I lowever, what shows up on your film relates more to the dark side of the graduation.
By the way, the more you stop down for your final exposure, the greater the filter's effect. This is particularly true with wide-angle lenses, which are the lenses you'll use most with these fillers. If you work with your lens set wide open, the filter will have little effect, since it lies far outside the depth of field of the wide-open aperture. Stick with apertures around //16 for the best results.
One last hint: Don't try to position the filter by looking at where the graduation occurs in front of your lens. Doing so will give you a false impression of the final results. How much density covers the front element does not directly equate with how much of the film image is affected. There is absolutely no substitute for looking through your lens at your shooting aperture.
COW-PARSNIP BELOW SLATE MOUNTAIN. EAGLES NEST WILDERNESS. COLORADO.
COW-PARSNIP BELOW SLATE MOUNTAIN. EAGLES NEST WILDERNESS. COLORADO.
In this photography I placed a 2-stop ND across the very top of the frame.
Graduated Neutral-Density Filters 6i
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