At a time when photography software can do almost anything, is there any reason to use physical glass filters in front of your lens? Absolutely! Some problems are still best solved with filters. Today, I’ll introduce one of my favorite types: the graduated neutral density (GND) filter.
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What Are Graduated Neutral Density Filters?
Graduated neutral density filters, or GND filters, are clear on one side and darker on the other, with a transition zone in the middle. They look like this:
The word “graduated” in the name refers to the soft transition zone in the middle of the filter. The words “neutral density” indicate that the darker portion of the filter is neutral in color. (You may find some color graduated filters available, too, but these are unusual and very specialized.)
If you put a GND filter on your lens and take a photo of a featureless subject, the photo will look like this:
In short, a graduated neutral density filter darkens part of the photo. With most filter holding systems, you’ll have full control over the height and rotation of the GND filter, allowing you more control over which portion of the image to darken.
The most common purpose of GND filters is to darken the bright sky in a landscape photo while leaving the foreground untouched.
Types of GND Filters
Graduated neutral density filters come in many varieties. One question is how the graduated portion looks – including whether the transition zone is soft, hard, or a more unusual shape. Another question is how dark the darkest portion of the filter gets. I’ll dive into those two considerations here.
1. Shape of the Filter’s Transition Area
Graduated neutral density filters come in two main varieties: hard and soft. This refers to how sharp the gradient of the transition zone is. A hard neutral density filter transitions very quickly from dark to clear, while a soft neutral density filter is much more gradual. (Some companies also offer medium neutral density filters that are somewhere in between.)
You may also come across more unusual GND filters, such as a reverse GND, where the transition zone itself is sharp, but the filter gradually becomes brighter again toward the top of the filter. Meanwhile, some GND filters are totally atypical and may have a round or triangular shape. Below is an example of each.
In a minute, I’ll discuss which graduated neutral density filter might be right for you. For now, a rule of thumb is that hard GND filters are best when the horizon is flat and well-defined, while soft GNDs are good for irregular horizons. Those are the two main types of graduated filters and are the most useful 95% of the time.
Any other style of GND is more specialized, but can still be useful. For example, a reverse GND is ideal when the brightest portion of the sky is directly on the horizon, such as the sun dipping below the horizon at sunset.
2. Density of the Filter
Neutral density filters come in a variety of densities, usually ranging from 1 stop to 4 stops. If you need a quick refresher, reducing the light by one stop is the same as cutting it in half. So, the scale works like this:
- 1 stop GND: 1/2 as much light
- 2 stop GND: 1/4 as much light
- 3 stop GND: 1/8 as much light
- 4 stop GND: 1/16 as much light
Generally speaking, the most useful graduated neutral density filters are in the range from 2 to 3 stops. Anything less than that and the filter is hard to notice; anything more, and the filter is too strong.
Most companies that make graduated neutral density filters label them with a decimal system as follows:
- 0.3: 1 stop filter
- 0.6: 2 stop filter
- 0.9: 3 stop filter
- 1.2: 4 stop filter
You’ll also find some filters that are partway in between these whole values, such as a 2.5 stop filter (or 0.75 in the decimal system).
What GND Filter(s) Should You Get?
The right graduated neutral density filter depends upon the subject.
I already mentioned that a hard GND filter is good for sharp horizons, while a soft GND filter is good for irregular horizons where there may be hills or mountains in your photo. However, that’s a bit of a simplification, because it also depends upon the focal length of the lens you’re using!
With a wide-angle lens, any graduated filter will appear have a harder transition. Take a look at the comparison below between using the same filter on a 24mm lens and a 200mm lens:
This is a pretty dramatic difference, and it goes to show that the right filter really depends on your lens. For an ultra-wide lens, I will generally use a soft GND except when the horizon is totally flat. Meanwhile, with a telephoto lens, I use a hard GND filter 100% of the time, since the effect of soft GNDs is almost invisible.
Along similar lines, using a narrower aperture value will also make the transition line appear harder. This is not as major of an effect, but it’s still interesting that you can change the apparent softness of your filter (at least slightly) just by adjusting your aperture.
If you plan to get any graduated filters, my recommendation is to get at least two of them: a soft filter for your wide lenses, and a hard filter for telephotos and flat horizons. I think that specialized GND filters with different shapes are not necessary for most photographers, including reverse GND filters and especially any rounded or triangular GNDs.
I also strongly recommend avoiding GND filters that are circular and screw into your lens. These filters are pretty useless because you can’t raise or lower the position of the filter. Instead, go with a rectangular GND that works in conjunction with a proper filter holder system like those from Lee, NiSi, or Cokin.
That leaves me with my overall recommendation: Get two GND filters, one soft-edge and one hard-edge. Personally, I find that 2-stop GNDs are a bit too weak much of the time – I would recommend either a 2.5 stop or a 3 stop filter instead. In my opinion, an ideal kit would be a 2.5-stop hard GND and a 3-stop soft GND.
Also, I tend to recommend glass filters rather than resin as a general rule. This actually rules out some popular GND filters on the market, but I find that glass has less flare and better colors/contrast than resin, most of the time.
Is Any of This Even Necessary?
The main purpose of graduated neutral density filters is to capture high-contrast scenes more easily, especially when the sky is much brighter than the foreground. However, today’s cameras have very impressive dynamic range, and you can always take HDR or AHDR images to extend things even further.
For that reason, I would say that graduated neutral density filters are a bit of a luxury these days – not just in price, but also in the space they take up in a bag (especially in combination with a full filter holding system) and the time they take to set up. Many photographers will find it more practical to take a few photos to merge later as an HDR.
Even so, GNDs are still useful. Maybe your multi-image HDR doesn’t blend properly because of some unexpected movement in the frame. Plus, high-quality GND filters can even reduce flare if they help darken the bright sun in your photo. (Although low-quality GND filters will add flare if the sun is in your frame.)
Most of all, I’m a big proponent of “getting it right in-camera.” There’s something to be said for the thoughtful nature of using a GND filter and taking the time to ensure that your raw file is as good as possible – that it won’t require doing backflips in post-production in order to look right.
A well-filtered image is a joy to work with in Lightroom. You won’t run into any of the color shifts, weird contrast, or haloing artifacts that you might find in an HDR, not to mention that HDRs can be difficult to blend properly if there’s significant movement in your frame.
While there are other pieces of camera equipment that I would prioritize first, I do think that a graduated neutral density filter (or two) belongs in the bag of most landscape photographers. This article should have given you a good idea of how GND filters work and which ones are right for you! Let me know in the comments if you have any questions, and I’ll do my best to answer.