Why I Don't Use Graduated Neutral Density (GND) Filters — The Loche, RMNP

A June sunrise image of The Loche in Rocky Mountain National Park requires a 2.7 mi, 1,056 ft elevation gain hike in the middle of the night. Getting location information on a relatively remote lake early in the season is challenging, but there was a report of open water, so my daughter and I set off for an adventure.

Upon arrival, the report proved technically correct. However, ice prevailed in the target location. While the ice would have been an OK foreground (these mountains can make nearly any foreground work), a reflection was the big benefit of hiking to a lake.

Moving to a nearby small area of open water accomplished the reflection goal. Here, a twisted tree and its roots, along with rocks flowing into the scene, provided additional foreground entertainment at this location.

Back to the leading question: Why don't I use graduated neutral density (GND) filters?

I'll start with the answer to a more basic question, what is a graduated neutral density (GND) filter?

Since Wikipedia already created this answer, I'll share it here:

"A graduated neutral-density filter, also known as a graduated ND filter, split neutral-density filter, or just a graduated filter, is an optical filter that has a variable light transmission. Typically half of the filter is of neutral density which transitions, either abruptly or gradually, into the other half which is clear. It is used to bring an overly-bright part of a scene into the dynamic range of film or sensor. For example, it can be used to darken a bright sky so that both the sky and subject can be properly exposed. ND filters can come in a variety of shapes and sizes and densities and can be used in all types of photographic applications from still photography, motion photography and scientific applications."

Here is the big problem. In general, graduated ND filters have straight lines of transition. However, these filters are primarily needed outdoors, and the outdoor landscape transition from dark to bright is seldom a straight line — unless a large body of water or a great plain fills the background. It is unrealistic to create filters for every horizon shape, and especially wide-angle zoom lenses usually have focal lengths with geometric distortion that further complicates the needed transition shape.

While soft transition GND filters better hide the dark to light transition, the final image seldom hides the unnatural brightness change.

Round threaded GND filters are available, and logically using one requires the brightness transition to be placed in the middle of the frame — another big limitation. To vary the location of the brightness change requires rectangular filters sized much larger than the front of the lens. While the density transition is still in the center of these filters, the larger size means they can be positioned off-center, placing the brightness transition anywhere desired.

Rectangular GND filters can be handheld during the shot, though avoiding movement against the lens requires a steady hand, and holding the filter slightly off of the lens permits light leaks (that may or may not matter). A filter holder provides a better solution optically, but the large rectangular filters require even larger filter holders.

Purchasing the complete set of transition types (hard to soft) and densities required to ideally mix the various lighting levels encountered, along with a filter holder, is expensive. In addition, the functional set is somewhat burdensome to carry and time-consuming to set up.

What is the alternative? Capture the scene in two or more exposures (if necessary, as processing a single image to differing brightness may be adequate), and blend the results using an HDR technique. A straight transition line is no longer important, and the adjusted areas do not need to be contiguous. Any brightness transition rate can be used (hard to soft), and the rate can vary in a single image.

Additionally, all focal lengths and lens sizes are supported, from a circular fisheye to the longest telephoto lens available.

I can often tell when a GND filter was used for an image, and usually, the result is not my favorite. Not everyone shares my view, and that is OK.

There are a lot of graduated ND filters sold, and sometimes only a graduated ND filter can get the job done properly. A primary advantage of graduated neutral density filters is that action transcending the density change (waves on an ocean, for example) remains perfectly aligned. Another big filter advantage is that post-processing is greatly reduced or eliminated, and those recording video or JPG format still images need to capture the final brightness.

Circling back to the image shared here. There are no graduated neutral density filters in the shape of the shadow line. Also, the perfect filter to match the digital graduated neutral density processing needed to darken the sky, excluding the tree. That filter, of course, does not exist. Thus, I don't carry it — or any other variant.


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