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How to Use a Neutral Density Filter to Control Depth of Field

If your photography isn’t focused around landscapes, there’s a fair chance you don’t have a set of neutral density filters. These accessories are mainly for landscape photographers as their use in long exposure photography is invaluable. Because they are most associated with slow shutter speeds, their application in other genres, like portrait photography, isn’t immediately apparent. A neutral density filter can, however, be vital to gain control over your depth of field in some situations.

This tutorial will show a quick and dirty tip for two scenarios in which to use ND filters to control the depth of field in your photography; one outdoors in natural light and the other in a studio environment.

What is a Neutral Density filter?

At its most basic, a neutral density filter is a piece of material (usually plastic, resin, or glass depending on the quality) you place between your lens and subject to reduce the amount of light entering your camera. This will result in a slower shutter speed being required, a larger aperture, or a higher ISO in order to achieve the correct exposure. The filters come in different strengths, usually ranging from a loss of one stop to three stops of light. For example; if you are metering an exposure of f/8 at 1/250th and you place a 1-stop ND filter on your lens, to compensate you will need to change either your shutter speed to 1/125th or your aperture to f/5.6.

How to Use a Neutral Density Filter to Control Depth of Field

Neutral density filters are a valuable tool in landscape photography, but they are also useful in other genres.

In terms of photographing landscapes in low light, you can probably see how they are useful. A 2-stop ND filter turns a 2-second exposure into an 8-second exposure. Alternatively, it turns an 8-second exposure into a 32-second exposure. If you’re trying to smooth out water or clouds on a windy day, an ND filter makes it a breeze.

For portraits, however, you will almost never want to reduce the shutter speed. If anything, you will often want to increase it. Why, then, would you want to put something on your lens that reduces the amount of light coming in? The answer is simple – when you have too much light in the first place.

Outdoors

If you’re taking photographs outdoors on a bright sunny day, you may find yourself limited to smaller apertures like f/11 and f/16. This is great for capturing a high amount of detail, not so much if you would like a shallow depth of field.

This is where a neutral density filter comes in. A 2-stop ND filter will turn an aperture of f/8 into f/4. A 3-stop ND filter will make it f/2.8, making it far easier to obscure a cluttered background with a shallow depth of field.

How to Use a Neutral Density Filter to Control Depth of Field

Both of these images were taken moments apart. Left: Shot at f/8 without an ND filter. Right: Shot at f/4 with a 2-stop ND filter.

In the studio

The idea behind using the ND filter in a studio environment is the same as it is outdoors. The main difference is that with natural light, you can always wait until later in the day. With high powered studio lights, that’s not always the case. If you’re aiming for soft light , you need to get your light source in close to your subject. If you have high-powered studio strobes, you may not be able to turn the power down low enough to use large apertures.

Again, a quick solution is to pop a neutral density filter on your lens. By doing so, you don’t have to sacrifice the softness of your light and you gain the benefit of complete control over depth of field.

How to Use a Neutral Density Filter to Control Depth of Field

Taken in a studio environment at f/8

How to Use a Neutral Density Filter to Control Depth of Field

Adding a neutral density filter reduced the aperture to f/4 without changing anything else in the scene.

Bonus round

Chances are that throughout this tutorial, the problem-solving side of your brain has figured out that all of these scenarios have a multitude of other methods to solve them. Outdoors, you could use a diffuser that cuts down exposure, or you could move to an area of open shade where the intensity of the light is reduced. In a studio, it’s often easy enough to move a light backward or to move your subject. Using an ND filter just adds another potential tool, and like most techniques, it is neither a be all or end all, nor is it required. It’s just another option.

That said, what do you do in a situation where you can’t control the intensity of your light and if you were to move it even an inch further away from the subject, everything in the frame would completely change? Same with diffusing it? I ran across this exact situation recently, as illustrated below, and it was a 2-stop ND filter that solved the problem.

How to Use a Neutral Density Filter to Control Depth of Field

Moving the light source in this instance, would have ruined the effect of the lighting. A neutral density filter allowed for a larger aperture while still allowing the camera to be handheld.

That’s it

In the end, if you want to have full control over your camera and the depth of field in your images, then neutral density filters deserve a place in your kit bag even if you never set eyes on a landscape.

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John McIntire
John McIntire

is a portrait photographer currently living in the UK. He studied commercial photography and is always looking to improve. Admittedly a lighting nerd through and through, John offers lighting workshops and one-to-one tuition to photographers of all skill levels in Yorkshire.