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Over the past few years with the advent of simplified, robust and speedier high dynamic range (HDR) software, not to mention the implementation of graduated neutral-density filters (also known as graduated filters or grad NDs) in Photoshop's Adobe Camera Raw (the converter used for RAW image processing), Lightroom and other plug-ins and software, I've found myself using the grad NDs in my camera bag less and less. I wondered if I was getting lazy in the field, or if these new digital options were providing more control and better results. So, I decided to put it to the test to see if there was still a need for on-lens, in-camera grad NDs.
Understanding Grad ND Filters
Clear on the bottom and dark on the top, graduated or split neutral-density filters were originally designed for a specific purpose, a critical task physically impossible to recreate by any photographer no matter how amazingly talented he or she was. To stretch the ability of film or the digital image sensor to handle the dynamic range, the contrast from highlights to shadows is measured in stops of light in a given setting (as seen in Fig. 1, using a two-stop grad ND). The difference between grad and split NDs is the line of delineation from neutral density to clear, the grad ND changing smoothly over a longer section of the filter whereas the split ND transitions immediately.
Grad or split NDs can be used in a variety of situations, in color or black-and-white scenes, even upside down, yet their main design is to darken a bright sky, preventing overexposure while maintaining detail in the lower half of the frame, often a less illuminated landscape or cityscape area. A specific dodging (with the clear section of the filter) and burning (with the neutral-density section) is what's effectively happening when the filter is applied. They're mostly used with wide-angle lenses roughly no wider than 18mm and no longer than 35mm for two reasons: 1) the top and bottom of the filter needs to be seen to be effective, and a wide-angle's coverage provides this (as seen in Fig. 2, using a 24mm lens); 2) any wider than a 18mm lens and you risk vignetting from the filter or filter holder. As you stretch past a 35mm lens, maybe from 50mm to 80mm, a split ND can be used since the line of delineation is blurred by the longer lens, but after 80mm, only part of the filter is seen, and it becomes less, if at all, effective.
Digital Grad ND
The ability to recreate a grad ND layer in previous versions of Photoshop was possible by applying a gradient, but it was less effective, time-consuming and a bit more complicated. When Adobe introduced the Graduated Filter tool in CS4, located in Adobe Camera Raw, also included in Lightroom 2, it was a wonderful addition for outdoor photographers. Two Photoshop versions later up to CS6, and the filter has improved. When used in combination with the Highlight, Shadows, Whites and Blacks sliders in ACR, the results are incredibly accurate and the tones are recovered well, giving the photographer great control over the final detail and look. Working with digital images in ACR and Lightroom, nondestructive workflow is also applied, so if you review the image a day, month or year later and want to change it, the unaltered RAW file is still available with the changes embedded, but reversible. With an on-camera filter, that just isn't possible.
One of the digital benefits with ACR are the sliders that control contrast, highlights, shadows, clarity and saturation, as well as sharpness and even color. Similar to colored grad ND filters, you can apply any hue to your filter in ACR—to any degree of saturation and intensity. I'm not much for enhanced color since I prefer more realism, but the option is nice to have when you may have lost some of the original color in the exposure. In Figs. 3a, 3b, 3c, 3d and 3e, a scene captured no less with a 200mm lens, you can see the options—3a, with no applied ACR grad ND; 3b, with a two-stop ACR grad ND; 3c, also with a two-stop ACR grad ND-compacted ND gradation and 3d, with a colored ACR grad ND. Fig. 3e is the final two-stop ACR grad ND version.
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Similar to on-lens grad NDs, you can also rotate ACR's filter, tilting the line of ND delineation. But digital takes it farther with the precise exposure control up to 5/100th of a stop, from 0, where no change is applied, to -4 or +4 stops, if necessary—rarely used to those degrees, but nice to have the existing option.
Also resembling on-lens grad ND filters, you can determine where you start and stop the line of ND delineation by dragging the start-stop lines in ACR. However, in ACR, you also can expand or compact the length of the ND gradation and that, too, offers the precise control a physical filter can't provide.
Other software manufacturers also have implemented grad filters into their programs. Nik Software's HDR Efex Pro 2 has full 32-bit depth with its built-in Graduated Neutral Density control, applying it to the merged HDR image, providing detailed control for a natural effect, especially on images with a strong horizon line. The other Nik plug-ins such as Color Efex Pro 4 and Silver Efex Pro 2 also have versions of grad NDs, yet as good as any digital grad ND may be, recovering detail from an overexposed area is limited. Apple's Aperture 3 doesn't offer a graduated filter, and some prefer the dodge and burn tools to "paint" areas needing lightening or darkening, but third-party plug-ins like Nik Software's products easily can be imported into Aperture. In fact, when I loaded Nik Software's suite of plug-ins, a menu option allowed me to import them into Photoshop, Lightroom and Aperture during the installation.
In HDR Efex Pro 2, in a section entitled "Finishing," the Graduated Neutral Density sliders offer Upper Tonality (the upper areas of the composition), Lower Tonality (the lower section in the image), plus Blend, Vertical Shift and Rotation, once again giving you ultimate grad ND tweak control of your photograph.
When Should You Use Your On-Lens Grad ND Filters?
Some new to outdoor photography falsely assume techniques like grad ND filters or HDR imagery can be used virtually anytime. That's just not true. The goal is to choose the appropriate tool for the given situation. Light and contrast play critical roles in the decision to add a filter or create an HDR; so does exposure. Without the proper knowledge of utilizing the right light or metering the scene well, you can blow both processes.
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The general rule always has been that it's best to use any filter on your camera to attempt to get as much as you can in your original RAW image file rather than add or create something in post-capture editing. On some occasions, if you don't capture certain highlights or details in your original file, it may take quite a bit of time to pull them back using Photoshop or other software methods—and on many occasions, the final file may not look optimal or as realistic as if you caught it in-camera. So, for fast-moving subjects where other techniques like HDR may create issues, an on-lens grad ND could be applied.
Landscapes with high contrast are impossible to capture in one single image without losing some detail. As most nature photographers can attest to, when it comes to metering, skies often need less exposure than the land below them—anywhere from one to three stops of light depending on the circumstances, time of day and weather conditions. These filters "fix" that inability through a one-, two-, or three-stop grad ND adjustment. The best ones are square with a filter holder to slide up and down depending on where you want the ND to start because you don't always want the ND line to start exactly in the center of the frame.
Put one of these filters to use in the right situation, and it's the difference between a lousy-looking exposure without the filter and an amazing landscape image when the filter is applied (Fig. 5a without a filter, Fig. 5b with a 3-stop grad ND, both exposed at 1⁄4 sec. at ƒ/22 using ISO 100). Many workshop students, when viewing my images, would comment on how they could never get a shot like that—yet it was mostly due to the application of my grad ND filter.
HDR Vs. Grad NDs
An advanced technique of combining multiple-bracketed exposures to retain all detail in a high-contrast scene (15 to 20 stops of light), HDR imagery changed the landscape of exposure, never seen with such accuracy in the nearly 200 years of photography. HDR Efex Pro 2, HDRsoft Photomatix, Photoshop's HDR Pro and other programs have given fans of HDR imagery tools that are easier to use to produce these amazing feats of exposure "stretchability."
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The beauty of HDR imagery when compared to an on-lens grad ND is the incredibly specific spots HDR covers without altering other higher-contrast areas nearby in the shot, including shadow regions in the lower half of the frame where the gradation of an on-lens grad ND wears off. Figs. 4a, 4b, 4c and 4d show this contrast in techniques.
Figure 4a was shot with no on-lens filter; 4b, with an on-lens, two-stop grad ND; 4c, with an on-lens, three-stop grad ND and 4d was an HDR combining five exposures. You can see in the details of these shots—Fig. 4d, the HDR composite, and Fig. 4c, the 3-stop, on-lens grad ND filter—that there's better color and detail in the HDR version, created with little post work, especially when you expose the bracketed series correctly. Regardless, the learning curve for HDR isn't as small as most think and takes an understanding of exposure, lighting, contrast and proper tonality. The reason why many overdone HDRs look fake, weird or simply unrealistic is that they're oversaturated and overcooked with too much detail in too many areas. There has to be a realistic feeling maintained in the image when it comes to contrast, light and saturation of color. Most viewers aren't used to seeing these exposure miracles, so a landscape including very bright and very dark areas adds a sense of realism. It's not about obtaining all detail in every tiny nook and cranny, yet more so the overall feeling—fine-tuning areas and maintaining details even though they're far apart in measured stops of light.
When Not To Use An On-Lens Grad ND Filter
|If a grad ND is applied for the wrong scene, it can be obvious and distracting; when applied well, it's hardly noticeable. Here are a few scenarios where a grad ND might hurt your final photograph:
1 When the light matches fairly well in exposure from sky to ground, and the contrast isn't large enough to warrant a filter, a grad ND most likely isn't needed, and the filter's effects end up creating an odd-looking surreal image. Possibly a subtle one-stop grad ND can be applied for some drama in the sky, but not much more than that.
It's also good to note that not all scenes work well as HDRs, whether or not allowed by the subject matter or not extreme enough in contrast to warrant the merged exposures. You have to shoot fast to avoid ghosting (image artifacts created by merging digital files together where objects moved between exposures) with any moving subjects—clouds, water, people, vehicles and so on. Yes, the effects of movement can be interesting, but it also can look strange depending on your subject. Think of a view of a moving boat; even a speedy bracketed motordrive couldn't stop that vessel in a number of exposures.
HDRs also used to take quite a bit of time to produce—the "hit the OK button and go grab a cup of coffee" amount of time, maybe even a 30-minute cup of joe. But today, my screaming-fast MacBook Pro with Retina Display can build it in less than five minutes. Simply put, HDR is reaching levels of precision no on-lens grad ND could ever match, and that's good for all outdoor shooters.
The Final Word
Although camera manufacturers and digital technology seem to be leading us toward the day where we'll be able to execute all our exposure difficulties in-camera or through post-capture software, I also believe the need for physical on-lens grad ND filters is still great in outdoor photography. They're a quick fix to an exposure problem not easily solvable, provide contrast and drama to landscapes, and bring back strong detail otherwise lost in a high-contrast scene. I'll continue to recommend on-lens filters in my articles, books, lectures and workshops for two reasons: 1) they're effective in helping to cut contrast and bring back detail; and 2) many photographers may not have the resources—computers, software, time or know-how—to create an HDR, whether through exposure or software knowledge or budget limitations.
Sean Arbabi is a commercial photographer and author of The Complete Guide to Nature Photography and The BetterPhoto Guide to Exposure (Amphoto Books/ Random House). Published worldwide the past 20 years, Arbabi also teaches workshops live and online. You can see more of his photography by visiting his website at seanarbabi.com.