Balancing Exposure: Using Graduated ND filters
By Geoff Harris •
Why balancing exposure is so important and why using graduated ND filters will improve your landscape photography.
So what is a graduated ND filter? It’s not easy being a landscape photographer. You often have to walk miles to reach your subject. Then, as have no control over the weather, you may find that capturing what you see is suddenly very difficult indeed.
Soft graduated ND filters (left) have a far more attenuated transition zone between the semi-opaque and transparent areas than hard (right) or very hard.
You can either sulkily give up for the day or try to make the best of the situation. I’m not asking for sympathy (though it’s always appreciated). as the times when everything goes right more than makes up for the times when it doesn’t.
One of the problems regularly faced by landscape photographers is contrast. Cameras can’t record the vast range of tones that is often seen in a typical landscape. The poor landscape photographer is often forced to compromise exposure, typically sacrificing shadow detail in order to avoid losing the highlights.
The commonest example of this is when the sky is bright but the landscape itself is in shadow. Expose for the sky and the landscape is dark and muddy. However, expose for the ground and the sky burns out. Fortunately, we landscape photographers have a secret weapon: the graduated ND filter.
Graduated ND filters can be stacked. The difference between the sky and foreground in this scene was 4-stops - too high to record detail in both (left). By stacking a 1- and 3-stop graduated filter I was able to make the correct exposure in-camera (right).
The graduated ND filter is related to the ND filter described previously (if you’ve not seen this article go and read it right now. I’m happy to wait). The difference is that the bottom half of a graduated ND filter is transparent and only the top half is semi-opaque.
Just like an ND filter the opaqueness of the top half is measured in stops: the higher the value, the more opaque the top half. Typically graduated ND filters are sold in strengths of 1-stop, 2-stop and 3-stop.
The transition zone between the two halves is described as being soft, hard or very hard. The transition between clear and semi-opaque in a soft graduated ND filter is very gradual, more abrupt in a hard graduated ND filter and even more abrupt in a very hard graduated ND filter.
Soft graduated ND filters work well when the difference between the light and dark areas of a scene is uneven - when you have a line of mountains or city skyline for instance. Harder graduated ND filters are more useful when the horizon is straighter - such as a seascape.
That said, harder graduated ND filters are easier to place where needed. Soft graduated ND filters can be frustrating to use because the transition zone is more ambiguous.
Avoid the temptation to use too strong a graduated ND filter when shooting reflections. Reflections should always be darker than the reflected subject. For this scene a 1-stop graduated ND filter was sufficient.
Let’s go back to the example above with the bright sky and unlit landscape. The reason this is a problem is that the sky and landscape essentially need two different exposure settings. Usually this would be an impossible situation (you could of course make two images using different exposure settings and blend the results later in postproduction).
What the graduate ND filter allows you to do is expose for the darkest part of the scene. Then, by covering the brightest part of the image with the semi-opaque half of the filter, the exposure can be made to match across the entire image. The greater the difference in exposure, the stronger the graduated ND filter you’d use.
Graduated ND filters slot into filter holders fitted to the front of a lens. This means that they can be moved up and down for precise positioning. You don’t even need to use them vertically.
Used horizontally they are excellent for balancing exposure when shooting window-lit portraits. Personally I never leave home without mine, even if sometimes I’m not out long because it’s just started raining. Again.
If you would like to learn more about how to control light, why not consider taking Nigel Hicks’s 4 week online course, Understanding light & Exposure.
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