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:
1When 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. 2When the lens you're using is longer than 100mm, a grad ND or even a split ND will have little positive effect on the final scene since the line of delineation is blurred too much. 3 When working with the disadvantage of a bright sky, it helps to produce a dreamy or heavenly mood, such as a foggy situation. Sure, to technical photographers those bright areas could be detail-less and overexposed, but the art of photography isn't always about perfect technical shots. It's just as much about telling a story and conveying a message. 4Sometimes creating an HDR gives you a better final photograph. You have to be careful in situations where the grad ND can be seen, such as in overcast conditions or low-contrast scenes where a one- or two-stop change can appear unrealistic. Another situation is when your subject begins at the bottom and continues to the top of your composition, such as a tree, rock wall, building or person. Adding a grad ND can alter the exposure so your subject starts with exposure detail at the bottom and ends up virtually black at the top. Here, the filter becomes very limited and, again, odd-looking. Yes, the filter can be rotated to tilt the line of ND delineation, but your options are limited.
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.