One of the great things about the advent of digital photography is that it has greatly reduced the number of filters I need to carry. Many of the functions we used to carry out with filters (warming/cooling, color filtering for B&W, soft-focus effects) are now much more easily and more accurately controlled in post-processing. But a few filters are still impossible for me to replace, particularly my polarizers and my set of neutral density gradient filters (ND grads).
ND grads were designed to address one of the fundamental challenges of photography, the challenge that light has too much dynamic range. We see the world with image sensors of seeing detail in a range of 13-14 stops in the same scene, our cameras tend to top out (even if we nail our exposures perfectly, which we don’t always do) at a few usable stops fewer than that. This means that we often see scenes in the world where we can make out detail and color in the shadows and in the highlights, scenes that our cameras cannot capture entirely. Because we often have the situation where the highlights are on on side of an image (e.g., the sky) and the shadows are on the other (e.g., the land), ND grads are an attempt to address this by darkening the lighter part of the image to bring it closer in exposure to the darker part. They’re grey (neutral) on one side, clear on the other, and there’s usually some sort of transition zone between the transparent grey area and the clear area to possibly make the effect less overt.
(HDR imaging can sometimes be used as an alternative to ND grads–however, it will be much harder to get a good result from HDR imaging if you’ve got moving subjects in your images.)
Some manufacturers make both “soft” and “hard” ND grads. These terms describe whether that transition zone is broad and gentle (“soft”) or narrow and abrupt (“hard”). Certainly, in the same situation the “hard” grads will produce much more abrupt transitions than the “soft” grads. Yet, just how ‘soft” the transition appears in the image is not only a function of the filter itself, but also the aperture, focal length and focus distance. With respect to focal length, the longer the focal length, the more gradual the effect of an ND grad will appear. As for the other parameters, if you think of the filter itself as an object you’re photographing, the more “out of focus” it is (wider aperture, focus farther from the camera), the softer the effect of the filter.
I work primarily with two- and three-stop filters. It’s rare that I need a one-stop filter; the scenes that could use just a little darker sky are easily adjusted later. For scenes with even greater contrast ranges I’ll sometimes use multiple filters, as I did in Mt. Oberlin Alpenglow.
Because you’ll want to adjust the placement and orientation of the transition when you shoot, I recommend the use of ::amazon(“B001RRSDJU”, “rectangular-style filters”):: and ::amazon(“B0010841A6”, “filter holders”)::, avoid screw-in ND grads at all cost. Adjusting the placement of these filters is made more difficult by the fact that the effect varies with aperture, just looking through your viewfinder won’t show you the right effect unless you use your depth-of-field preview button, and using it (which I recommend) will make it difficult to see what you’re shooting. LiveView is an workable alternative on some cameras.
With practice and care, you’ll find that these filters can allow you to capture single images of scenes with enormous contrast, even with moving subjects. That unique ability is what earns these little gems a place in my gear bag.