Learn how to harness one of the most useful filters for photographers: the neutral density filter.
Words and Photography by Urth HQ
Neutral density (ND) filters are essential for capturing high-quality photos with effects that can’t be replicated in post-production editing. But what does an ND filter actually do and when should you use one? Here’s what you need to know.
What does an ND filter do?
A neutral density (ND) filter is a type of dark filter that easily attaches to the front of a camera lens, to control how much light enters the camera’s sensor. Since a neutral density filter only affects light levels, it doesn’t have any impact on image colour, contrast or sharpness.
Essentially, it’s like a volume control for light. By reducing the amount of light that comes through your camera lens, a neutral density filter lets you shoot in harsh lighting conditions and manipulate your photos to achieve really creative results.
Why do photographers use ND filters?
By reducing light entering the lens, a photographer can create a number of desirable image effects, many of which wouldn’t be possible in bright conditions. With an ND filter you can do one of two things:
1. Use a wider aperture to capture beautifully shallow depth of field
2. Use a slower shutter speed to capture long exposures and motion blur for a longer period of time.
Wider apertures are great for portraits, when you want the person in the photo to be the sole focus of the image, and the background to be soft and not in focus.
With slower shutter speeds, you can add movement or blur to objects that are moving, while keeping the rest of the scene static. This effect is especially awesome when shooting moving water, such as waterfalls or choppy waves. It adds drama and visual appeal to an image.
Do ND filters affect image quality?
Whether lens filters affect image quality or not is one of the most debated topics in photography. But in short, the answer is no. Most ‘before’ and ‘after’ filter shots used for comparison testing show that lens filters, including ND filters, don’t adversely affect image quality. As long as you use high quality lens filters, you won’t see a noticeable difference in image quality.
When should you use an ND filter?
An ND filter has uses in almost any type of photography. But it really comes into its own when used for outdoor or landscape scenes, when it’s important to be able to adapt to changing light. By adding motion or shallow depth of field to images, you can bring otherwise dull scenes to life.
Some great uses for ND filters include:
SUNNY AND HARSHLY LIT SETTINGS
When the sun is very bright or you’re shooting in harsh lighting conditions, 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.
Cutting back light reaching your camera reduces depth of field and isolates an image from its background. This makes it appear sharper, without causing overexposure. Animal or bird images can be brought to the fore without any background interference when using this filter, for instance.
CLOUDS AND FOG
ND lens filters also earn their worth when used to capture clouds and sky scenes. This clever filter can blur the motion of clouds making them appear more dramatic, streaky and magical, giving your scene an extra helping of visual intrigue.
FOLIAGE AND FIELDS
Many landscape photographers shoot images of foliage and fields, and capturing the perfect scene can often prove tricky. With an ND lens filter helping to block out light, it’s easier to add visual intrigue by capturing a shallow depth of field.
WATER AND MOTION
By using longer exposure times, this filter can capture silky, softened, smooth, foggy, dreamy or blurred effects from water. This adds drama and atmosphere to a scene, bringing it to life. It also helps to draw the viewer in, without any distracting overexposure. It’s perfect when introducing movement to a single part of your image, whilst keeping the rest of a scene static.
It’s often assumed that an ND lens filter only has a place for shooting sky, water or foliage. But, if you’re a cityscape photographer, you’ll also find this filter earns its place on your camera lens.
In particular, scenes of moving vehicles, sports matches or crowds of people can be blurred or distorted to great effect. This helps to add atmosphere to images that may otherwise appear flat or static.
VIDEO AND FILM
The beauty of using ND filters for video and film is that you can shoot a shallow depth of field and achieve a dramatic effect. Especially when shooting in harsh light, and when the sun is intense, an ND filter can reduce the lighting right back while capturing a really cinematic feel.
Portraits can be beautifully enhanced by ND filters for the same reasons they make landscapes so interesting. You can play around with depth of field in bright conditions, use motion blur to powerful effect and bring your subject to the foreground with exceptional clarity.
How do I know which ND filter to use?
ND filters come in a lot of different shapes and sizes. Just like a camera, the best way to figure out which one you prefer is to experiment. There are a few different types available on the market:
FIXED ND FILTERS
Fixed ND filters block a fixed f-stop of light from entering your camera. The lower the ND number, the less light it blocks from entering your camera. For example, an ND4 filter blocks out 4 f-stop of light, and an ND1000 blocks 10 f-stops of light.
Fixed ND filters are usually preferable for photographers who tend to stick to the same level of light exposure or shoot in conditions where you can take your time to set up a shot or change filters if you need to. They’re also stackable, meaning you can use multiple filters at the same time.
ND FILTER CHART
Use the chart below to understand the light reduction and transmission that results from each type of ND filter.
|ND Filter||Light Reduction||Light Transmission||Best Light Conditions|
|ND2||1 f-stop||50%||Low light|
|ND4||2 f-stop||25%||Low light|
|ND8||3 f-stop||12.5%||Low light|
|ND16||4 f-stop||6.25%||Low light|
|ND32||5 f-stop||3.12%||Bright light|
|ND64||6 f-stop||1.56%||Bright light|
|ND128||7 f-stop||0.78%||Bright light|
|ND256||8 f-stop||0.39%||Harsh light|
|ND512||9 f-stop||0.19%||Harsh light|
|ND1000||10 f-stop||0.10%||Harsh light|
|ND10000||13 f-stop||0.01%||Harsh light|
VARIABLE ND FILTERS
As the name suggests, variable ND filters can be rotated to cover a number of f-stops. This offers great flexibility – it means you don’t need to keep changing filters every time you want to alter light levels.
Variable ND filters are great for photographers who work with changing light conditions, when you need to shoot fast. They’re also great for photographers who are new to ND filters and want to experiment with different options. More on variable ND filters here.
GRADUATED ND FILTERS
You might also come across graduated ND filters. These differ in that they reduce light across only half your image. 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 fade and is perfect for use with uneven horizons or when objects, such as mountains, cover part of the sky. On the other hand, hard-edge filters transition from light to dark quickly, so they’re perfect for even horizon shots like the ocean at sunset.
An ND CPL filter is an ND filter combined with a circular polarising/linear (CPL) filter. Essentially, these filters cut polarised light from a scene to reduce glare and enhance both contrast and colours.
Multifunctional ND CPL filters are useful for when you want to control both glare and light, without having to stack multiple filters to achieve the desired effect.
Understanding ND filters and f-stops
An f-stop specifies the aperture of a lens. It’s determined by the focal length of the lens divided by the diameter of the aperture.
The smaller the f-stop number, the wider the aperture, and the shallower the depth of field. But usually if you try to use a small f-stop number in a brightly lit setting, the wide aperture means you’re letting a lot of light into your lens, resulting in an overexposed image.
This is where ND filters come in to block a certain number of f-stops of light, so you can use those smaller f-stops and wider apertures in any setting.
The most common f-stop densities for ND filters are those with two, three or four stops. If you want to block out even more light to capture extra long exposures or balance light in harshly lit scenes, choose a stronger ND filter with a higher number, like an ND1000.
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 to stop movement.
Visit our quick guide to aperture to get a better understanding of f-stops.
Which ND filter is best?
If you’re new to using ND filters, there’s a lot to get your head around. The best advice is just to put one (preferably a good quality make) on your lens and experiment with what it can do. Not sure which one to start with? Check out our buyer’s guide to ND filters to help you choose the right one.
ND filters are some of the coolest camera accessories to play around with, allowing you to create unique photographic effects and unlock new creative possibilities. Discover Urth’s collection of ND filters online.