A neutral density (ND) filter is a type of grey filter that easily attaches to a camera lens, to control how much light enters the camera’s sensor. Since a neutral density filter is neutral, it doesn’t have any impact on image colour, contrast or sharpness.
By reducing or blocking out light to your camera lens, a neutral density filter lets you manipulate your photos to achieve really creative results.
ND filters are available according to how much light they restrict from your camera. This is measured by f-stops. The smaller the f-stop number, such as f-2, the more light the filter lets in and the larger the aperture.
The most common f-stop densities are those with two, three or four stops. If you want to block out more light and slow things down, choose a darker f-stop with a higher number.
You can also combine ND filters to achieve a larger f-stop and boost the density strength, but be careful not to end up with an undesirable vignetting effect. If you use a high density filter to get long exposures, consider using a tripod with your camera.
Some photographers use individual ND filters with different f-stops to influence light exposure, but you can also get variable ND filters which are a single filter that can be rotated to cover a number of f-stops. This offers great flexibility. It also means you don’t need to keep changing filters every time you want to alter light levels.
Why would a photographer want to control light exposure by using ND filters? By reducing light entering the lens, a photographer can use a higher aperture for a longer period of time. This can create a number of desirable image effects, many of which wouldn’t be possible in bright conditions.
In particular, a neutral density filter can add movement or blur to objects.
You can capture blurry, smooth, misty or silky images of water, using a longer exposure time with an ND filter. This effect is especially awesome when shooting moving water, such as waterfalls or choppy waves. It adds huge drama and visual appeal to an image. But, it can also let you introduce movement in one scene, whilst keeping the rest of the scene static.
Clouds and foliage also make great subjects for shooting with a neutral density filter. Moving objects, such as people or vehicles, can also be blurred or distorted to great effect with this lens filter.
When the sun is very bright, it’s hard to capture the perfect shot. This is where a neutral density filter comes to the rescue. It lets you use a wide aperture to achieve a shallow depth of field, without causing any overexposure.
Without a neutral density filter, a camera would struggle to achieve a small enough aperture to capture these same effects.
If you lean towards landscape or outdoor photography, you’ll find that a neutral density filter comes in handy many times. By adding motion or blur to images, you can bring static scenes to life. This introduces a more interesting dimension to what might otherwise be a rather dull subject. What also makes this filter so useful is that many of its effects can’t be replicated by post-production software editing.
As well as the standard ND filters, you might also come across graduated ND filters at some point. These differ in that the filter glass doesn’t have an even ND distribution effect, so only part of an image will be affected. You might choose to use this filter if you want to darken the background of a scene, usually the sky, but leave the foreground untouched.
Depending on the fade effect you want to achieve, you can also find soft-edge and hard-edge graduated ND filters. The soft-edge type produces a smooth, quick fade and is perfect for using with uneven horizons or when objects, such as mountains, cover part of the sky. On the other hand, hard-edge filters create a large fading distance without any unnatural-looking or noticeable hard lines running through a scene.
If you’re new to using ND filters, there’s a lot to get your head around at the offset. But, the best advice is just to stick one (preferably a good quality make) on your lens and experiment. These are probably one of the most exciting filters to play around with, allowing you to create interesting and unique photographic effects.