Neutral density graduated filters (usually shortened to ND grads) are one of the most important little add-ons for landscape photography. Anyone shooting in this genre will need to have a couple in their kit bag. This article describes what they are, what they do and how you can use them.
So what are ND grad filters?
ND grad filters are a rectangular sheet of optical quality plastic, with one half darkened and the other half completely clear. There are essentially two types: hard and soft, terms that describe the type of transition from clear to dark in the filter’s central area. Not surprisingly, hard filters have a sharp transition between the two zones, whereas soft filters have a gradual transition. Recently, leading filter manufacturer, Lee Filters, have introduced medium and extra hard filter types.
In addition, the filters come in a range of darkening grades, usually termed 0.3, 0.6, 0.9 and 1.2. These equate, for the 0.3 filter, to a one-stop reduction (ie a halving) of the amount of light passing through the dark part of the filter. For the 0.6 it is a two-stop (four-fold) reduction; for the 0.9 it is a three-stop (eight-fold) reduction; and for the 1.2 it is a four-stop (16-fold) reduction.
What are ND grad filters used for?
Everyone who has taken a landscape photograph has had the experience where in the final photos either the land is well exposed but the sky is burned-out, with all cloud details lost, or the sky looks great but the land is lost in a dark, almost featureless zone. This can happen even though the view looks just fine to the eye.
The explanation is that, although the eye can handle a huge contrast range between, say, a bright sky and a darker landscape just fine, the digital sensor is just not up to that. As a result, it can correctly expose either the land or the sky, but not both.
What ND grad filters do is, by putting the dark part of the filter over the bright part of the view, they greatly reduce that contrast range. This brings it down to something the digital sensor can cope with, enabling it to capture all the detail in both the bright sky and the darker landscape. The result will be a photo more closely resembling what you saw with your eyes. Essentially, ND grad filters are an important technical fix for a major failing in the digital sensor.
They can also be used to exaggerate the real situation, for example increasing the apparent storminess of a cloudy sky, helping to increase the sense of drama and/or mood in the photos.
How do you use them?
You fit these rectangular filters to the front of your lens, using a special holder, which itself needs to be fixed to the lens using a threaded adaptor ring. When first kitting up, these will need to be bought in addition to the filter(s). Make sure to buy adaptor ring(s) of the right thread size(s) for your lenses.
When mounting the ring and holder onto the lens, you should first remove any circular filters you may already have on your lens (eg a UV filter). If such filters are left in place, there is the danger of vignetting – ie having dark corners – in your photos, especially if shooting with a wide-angle lens.
After sliding the ND grad filter into the holder, look through the camera’s eyepiece or at the live screen view, and slide the filter up and down until its light/dark transition zone matches up with the landscape’s horizon. Of course, this is much easier if the camera is rock steady on a tripod with the image view already composed, but you can also do it with the camera hand-held if done carefully.
Once everything is lined up, you can shoot normally. The in-camera exposure meter works perfectly well with the ND grad filter in front of the lens.
The choice of ND grad filter to use becomes easier with experience. Generally, a hard grad is the one to use when you have a distinct horizon (such as the sea against sky), whereas you would use a soft ND grad when it is not clear where the horizon is, such as in woodland or in misty/foggy weather. In terms of what grade to use, of course this depends on how big the view’s contrast range is. However, generally, the 0.6 grade is the most useful.
The types of cameras ND grads can be used with
ND grads have, in general, been developed with DSLRs in mind. For use with these, although filters can come in a number of different sizes, it is best to use filters that are 100mm wide and 150mm long. This size covers use with just about any lens available on the market, including those with very wide-angle views. Smaller filters (often called A and P sizes) can be useable with smaller lenses, but can be problematic with a very wide-angle lens, oftern causing vignetting (darkened corners) in the photos. Larger filters are also available for those using medium format cameras, such as Mamiya, Hasselblad or Phase One cameras.
Recently, Lee Filters has also started to produce smaller filters specifically tailored for use with the more compact mirrorless cameras, though these cameras can also take the standard 100mm filters just fine, provided the right thread size adaptor ring is used.
Unfortunately, it is very difficult to use ND grads with compact cameras. For one thing there is no lens-front thread that can take an adaptor ring and holder, and secondly the lens can quite radically change length when zooming and/or focussing, making it almost impossible even to hold the filter in front of the lens.
Equipping yourself with ND grad filters
Several manufacturers produce ND grad filters, principally Lee Filters, Cokin and Hi-tech. The first of these produce what are generally considered to be the top-of-the-line, industry standard filters, whereas those by Cokin and Hi-tech are rather more budget products. That said, all ND grad filters can be quite expensive, so if your budget is limited there is no need to splash out on a full set right away. Just invest in the holder, adaptor rings and one, or maybe two filters initially – the 0.6 hard and 0.6 soft are probably the most useful filters in the range.
Caring for your ND grad filters
These filters are quite fragile and can be easily scratched. Handle them carefully, by the edges, and always keep them in the pouches provided. They also readily attract dirt, particularly if you’re shooting by the sea. Finger prints and salt spray can be remarkably difficult to remove. A good quality fibre-free lens cloth can help remove the former, but generally just smears the latter. To remove salt spray rinse the filter in warm soapy water and then dry with a very soft towel. Don’t use hot water as this can warp the filter. If this happens then put the filter under some heavy books for a couple of days. Don’t try to bend the filter back into shape by hand.
Learning more about ND grads with Nigel
To find out more about ND grads with me, you could sign up for any of my 2019 one-day photography workshops.
To find out about the workshops, click here…>
Hopefully, these notes will help get you up and working with ND grad filters. Don’t be shy to get in touch if you have any queries.
A future article will cover the related subject of neutral density filters (ie all-over ND, not graduated).