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How a Neutral Density Filter Works

September 11, 2023 by

In this guide, I’ll be covering everything you need to know about neutral density (ND) filters.

I’ll be covering what they are, how they work, the different types, when to use them, and lots more.

Let’s dive in!

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Henry Turner
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How Does A Neutral Density Filter Work?

A neutral density (ND) filter is an optical filter that goes on your camera lens and reduces the amount of light entering your camera lens uniformly across the spectrum, allowing for controlled exposure adjustments and creative effects without introducing color shifts.

An ND filter differs from a CPL filter, which minimizes reflections and enhances color saturation by blocking certain light waves.

Imagine you’re trying to look at a beautiful, sunny day through a window. But it’s just too bright to see anything. You pull the blinds, reducing the light’s intensity and making it possible for you to appreciate the scene.

That’s essentially what a neutral density filter, or ND filter, does for your camera.

It’s like sunglasses for your lens, reducing the amount of light reaching your camera’s sensor.

Let’s say you’re at the beach and it’s the middle of the day.

You want to capture the beauty of the waves coming in, but even with your camera’s smallest aperture and fastest shutter speed, it’s just too bright – your photos are coming out overexposed.

This is where an ND filter comes in handy. It can knock down the intensity of the light, allowing you to slow your shutter and capture a gorgeous, silky shot of the ocean waves.

nd filter on beach
ND filter on beach

Different Types of ND Filters

There are different types of ND filters.

Fixed ND Filters

Some are like a one-size-fits-all dress with predetermined densities – these are your fixed ND filters.

These neat gadgets play around with shutter speeds; with lighter filters extending your shutter’s leisurely stroll, and denser filters bringing it almost to a standstill.

This gives you more control over your image’s motion blur.

Variable ND Filters

Then you have your tailor-made suit: the variable ND filter.

This bad boy is made up of a duo of polarizers that spin around to give you control over the quantity of light that waltzes into your camera.

Think about opening or closing the blinds – that’s your variable ND filter altering the light.

Consider also that despite their advantages, ND filters can have some drawbacks that I’ll touch a bit more on later.

For instance, they can sometimes result in color shifts and vignetting. No need to panic, though, as quality manufacturing and design minimize these issues. Just remember to choose your ND filter wisely.

But you could look at this from a glass-half-full perspective. ND filters are essentially your passport to controlling light in a way that ordinarily wouldn’t be possible.

They offer you the power to manipulate exposure, focus, and blur at will, and in a sense, make the laws of photography more malleable. Enjoy the journey!

Understanding the Different ND Filter Stops

Understanding ND (Neutral Density) filter stops involves grasping the concept of light reduction and its impact on your photography.

The “stops” in ND filters refer to the different levels of light reduction they provide.

Each stop represents a doubling or halving of the amount of light passing through the filter.

Here’s how to understand ND filter stops:

1. Stops and Light Reduction

Each stop corresponds to a factor of 2 in terms of light reduction.

For example, going from ND2 to ND4 reduces the amount of light by 2 stops, which means only 25% of the original light passes through.

Similarly, going from ND8 to ND16 reduces the light by 2 stops again, allowing only 25% of the already reduced light to pass through (0.25 x 0.25 = 0.0625 or 6.25%).

2. Exposure Adjustment

ND filters allow you to use slower shutter speeds, larger apertures, or both, without overexposing your image.

This is particularly useful in situations of bright light, where you want to control the amount of light entering the camera.

For instance, if you’re shooting a waterfall in bright sunlight and want to create a smooth, milky effect of the water, you can use a higher-stop ND filter to achieve a longer exposure.

3. Creative Effects

ND filters can also be used for creative purposes.

By using a stronger ND filter, you can intentionally underexpose your image to capture motion blur in busy scenes, like crowded city streets.

Lower-stop ND filters might be used to capture a wider aperture for shallower depth of field in bright conditions, creating a pleasing bokeh effect.

4. ND Filter Rating

ND filters are often rated by their optical density or f-stop reduction.

Common ND filter ratings include ND2 (1 stop), ND4 (2 stops), ND8 (3 stops), ND16 (4 stops), ND32 (5 stops), and so on.

5. Stacking Filters

You can stack multiple ND filters to achieve greater light reduction.

However, be cautious about image quality degradation, vignetting, and color shifts that may occur with excessive filter stacking.

What Is The Purpose Of A Neutral Density Filter?

What is the purpose of a neutral density filter?

You may find yourself in a situation, when you want to take a photo, where the scene is just too dazzlingly bright for your camera to handle.

That’s when ND filters come to the rescue.

These helpers work by reducing the intensity of all wavelengths of light equally – kind of like turning down the overall brightness dial.

They don’t discriminate between colors or details, they just lower the whole light level down a notch or several.

ND filters are used primarily to control levels of exposure. Whether you’re shooting landscapes with blindingly bright skies or you’re trying your hand at long exposure photography, ND filters are your go-to solution.

For example, they allow you to slow down the shutter speed, producing dreamy, blurred motions of a waterfall or clouds.

But don’t forget, as you play around with ND filters, you’ll also need to adjust other camera settings, such as the exposure time, to compensate for the reduced light.

At this stage, knowing the three elements of the exposure triangle (aperture, shutter speed, and ISO) is crucial.

exposure triangle cheat sheet
exposure triangle cheat sheet

This helps maintain a proper balance and avoid unnecessarily dark images.

As you embark on your photography journey, ND filters will become an indispensable part of your toolkit. They offer a world of creativity, from stunningly ethereal long exposures to perfectly balanced portraits and landscapes. It’s an investment you won’t regret making.

Advantages of a Neutral Density Filter

Here are the advantage of a neutral density filter:

1. Control Over Exposure

The first advantage of using neutral density filters is that you gain better control over your exposures.

Since ND filters reduce the amount of light entering the lens, this is particularly useful, especially if you photograph during bright conditions.

2. Creative Long Exposures

The second advantage of ND filters is that they enable you to capture long exposure shots more easily.

Examples of creative long-exposure shots include silky smooth waterfalls and streaking clouds during the day.

This would be hard to do without the use of the filter (during daylight).

3. Motion Blur and Movement Effects

The third advantage of ND filters is their ability to allow you to create motion blur and movement effects more easily.

These types of effects are captured using slower shutter speeds.

But when you use a slower shutter speed, it will allow more light to enter the camera sensor, which can result in an overexposed image.

But since you will be using an ND filter, it will reduce this chance.

motion blur in image
motion blur in image

4. Wide Aperture in Bright Light

The fourth advantage of ND filters is their ability to let you use a wide aperture in bright light.

Imagine you’re in a situation where you want a creative effect with a shallow depth of field.

You want your subject to be in sharp focus while the background is beautifully blurred (bokeh). To achieve this, you would typically need to open your aperture wide (use a lower f-number like f/1.8).

However, opening your aperture wide in bright conditions would lead to overexposure, as too much light would hit the camera sensor.

This is where a Neutral Density (ND) filter comes in. By placing an ND filter on your lens, you can reduce the amount of light entering the camera while keeping your desired wide aperture setting.

This allows you to achieve a shallow depth of field and separate your subject from the background even in bright lighting conditions.

The ND filter essentially ‘neutralizes’ the excess light, allowing you to use your desired aperture without overexposing the image.

5. Balanced Exposures

The fifth advantage of ND filters is that they allow you to have more balanced exposures.

Sometimes we end up in situations where our scene has both bright and dark elements such as during sunset or sunrise.

If this is the case, an ND filter can help better balance the exposure between the two, preventing overexposure of the background.

Disadvantages of ND Filters

Now that we’ve covered the advantages of ND filters, let’s take a look at some of the disadvantages.

1. Color Cast and Quality Loss

The first disadvantage of ND filters is the chance of color cast and quality loss.

If you purchase an ND filter that may be on the cheaper end, it can introduce a color cast or reduce image quality due to optical imperfections.

Moral of the story — purchase a high-quality ND filter.

2. Bulk and Storage

The second disadvantage of ND filters is their bulk and storage.

ND filters come in various densities and sizes and can make your bag a bit bulkier in terms of storage, especially if you buy multiple filters.

A small price to pay but one to remember.

3. Cost

The third disadvantage of ND filters is the cost.

If you opt for a high-quality ND filter, then it can become a bit costly, with some filters ranging in the $100 or more range.

This cost can be a barrier for some, especially if you have already spent money on a camera, bag, lighting, lenses, etc.

4. Vignetting and Lens Flare

The fourth disadvantage of ND filters is the vignetting and lens flare.

Higher-density ND filters can lead to slight vignetting or increased susceptibility, which is just something to be aware of.

5. Increased Complexity in Use

The fifth disadvantage of ND filters is their increased complexity in use.

When working with ND filters, it requires a basic understanding of exposure settings, exposure times, and sometimes bracketing in order to achieve your desired effect.

This prerequisite can add complexity to the photography process, especially for beginners.

Who Would Benefit From Using A Neutral Density Filter?

Who would benefit from using a neutral density filter?

The answer lies not only in the hands of professional photographers but also in those of budding beginners, hobbyist snappers and even cinematic creators who seek to capture perfectly exposed, creatively controlled shots.

Landscape Photographers

To truly grasp this, picture yourself as an outdoor landscape photographer for a moment.

The sky is taking on those gorgeous hues of sunset, but your camera just can’t get the sky exposure and the richness of the landscape right simultaneously.

Enter, the neutral density (ND) filter, particularly the graduated kind, which can darken the sky (that’s too bright) without affecting the exposure of the landscape.

Portrait Photographers

Or, imagine you are trying your hand at portraiture.

Maybe you’re shooting in broad daylight and you wish to use a wide-open aperture to blur the background, but the excess light is causing overexposure.

An ND filter could be your artistic ally here, reducing the intensity of light hitting the camera sensor, and allowing for that perfect balance you crave – sharp, well-exposed subject against a buttery smooth backdrop.

Architecture Photographers

Are you an architect or real estate aficionado, capturing buildings in their prime daylight?

You’re battling harsh shadows and bright reflections. A polarizing ND filter would serve you well, managing those contrasts and rendering a scheme you and your clients can admire.

Long Exposure Photographers

Moreover, for those adventurous souls who dabble in the world of long-exposure photography, creating dreamy seascapes, star-streaked skies or surreal cityscapes, ND filters become your essential partner.

Much like a dimmer switch lets you control the brightness in your room to create a mood, a variable ND filter would let you manipulate time itself, slowing down shutter speeds to blur motion.

So, the ND filter is not just a piece of gear, it’s a versatile tool sculpting light to suit your photographic canvas.

It provides you, and everyone passionate about photography, with the flexibility and control to achieve the image you envision, regardless of lighting conditions.

long exposure image using ND filter
long exposure image using ND filter

When Should A Photographer Use A Neutral Density Filter?

In short, a photographer should use a neutral density filter when the scene is just too dazzling for your camera to handle.

You wouldn’t stare into sunlight without protection, right? Give your camera the same courtesy!

ND filters are an indispensable friend to the mindful photographer.

They allow you to control exposure, experiment with motion blur, and handle tricky light situations, such as during a bright, sunny day.

They may require a little bit of an investment, and you might need to make a few adjustments to other camera settings, but the benefits they provide make them more than worth their price.

Ultimately, photography is all about capturing the world as you see it, and ND filters help your camera see it just right.

Where Can One Purchase A Neutral Density Filter?

ND filters are available in a variety of places. The most common place to start would be your local photography stores.

Entering one of these stores is like walking into an Aladdin’s den for a photography enthusiast. Shelves after shelves of equipment, gear, and yes, a multitude of camera filters.

You can walk straight up to the desk and ask for ND filters. Remember to check the filter size matches your lens!

However, sometimes you may find that physical stores might not fully satisfy your needs, due to limited stock or accessibility issues.

This is where online marketplaces step in. Websites like Amazon, B&H or Adorama have a vast array of ND filters, right from your budget-friendly options to your more premium ones.

Remember that purchasing filters online allows you to read customer reviews and see ratings.

It’s like having a friend, who’s already tried that particular filter, sharing their first-hand experience with you!

Now, if you’re looking for a more professional-grade ND filter, often the camera manufacturer’s websites carry professional-grade filters.

Canon, Nikon, Sony, or whatever brand your camera is, you can look directly on their websites.

Purchasing a filter isn’t just about clicking ‘Buy Now’. It’s a quest! It’s about researching, understanding your requirements, and getting satisfactory results.

While you can start this quest either in a physical store or an online platform, either way, your images are about to take a real step up in quality.

So, go ahead, get your ND filter and step into the fascinating world of controlled shutter speeds, aperture combinations, and oh-so-dreamy motion blurs.

Frequently Asked Questions

How many stops is 1.2 neutral density filter?

A 1.2 neutral density filter reduces the amount of light entering the lens by 4 stops.

Is a 3-stop ND filter enough?

A 3-stop ND filter is often sufficient for achieving moderate light reduction, allowing creative control over exposures in various lighting conditions.