ND filters can be confusing, whether it be figuring out how to size them, when to use them, or even how to decipher what the varying numbers printed on them mean. Luckily, it is fairly easy to learn how to use ND filters and open a whole new world of photographic opportunities for you. They come in all shapes and sizes, so when it comes to selecting what will work best for you it is best to keep a few things in mind:

How do you size a ND filter? To learn what size ND filter to use, find your lens’s diameter by one of these methods:

  • Look inside the lens cap.
  • Inspect the filter thread; diameter is designated by the symbol ø.
  • Some models print the diameter on the side of the lens.
  • Use a ruler to measure between filter threads as accurately as possible.

Some lenses won’t have a filter thread, such as compact cameras or ultra-wide-angle lenses. These cameras will often require specialized set-ups in order to use filters, and as they are exceptions to the rule I won’t cover them in this article. Instead, we will focus on the most common filter sizes used with cameras that have either screw-on or filter-holder capabilities.

If you’ve never heard of an ND filter and don’t know why you would need them, you’re not alone. A lot of photographers run into confusion when it comes to using an ND filter, but once you know the basics they are a breeze to use and can help you elevate your photographs to the next level. To find out more about ND filters including how to select a size, choosing the right density, and deciding when to use them, read on below.

Understanding an ND Filter

An ND filter, also known as a Neutral Density Filter, is a piece of photography equipment that can affect the amount and quality of light that reaches your camera’s sensor. A neutral density filter isn’t a necessary accessory when taking photos, but it can help you achieve better photographs and so many photographers will have one in his or her gear bag.

ND filters are usually made of glass and can either be placed in front of the lens or dropped into a filter slot. Some people like to compare ND filters to a pair of sunglasses, but while the ND filter will reduce the amount of light entering the camera, it will not change the color of the light entering as a pair of sunglasses would.

Filters come in a variety of sizes, all designated by millimeters. While the choice of size will ultimately depend upon the diameter of your lens, some of the most common sizes for DSLR lenses are 43mm, 49mm, 52mm, 54mm, 58mm, 62mm, 68mm, 72mm, and 77mm. You will want to select the ND filter that corresponds to the diameter of your lens.

While photographers are often striving to let more light reach the camera’s sensors, there are certain situations where too much light will be entering the camera and the image will be overexposed. In order to avoid this, ND filters can be employed. Read on below to find out more about how and when to use an ND filter.

Reasons to Use an ND Filter

There are several reasons why a photographer may grab for a neutral density filter when trying to capture a particular shot. Chief among these are:

  • To permit shallow depth of field in bright settings.
  • To emphasize a sense of movement in a photograph.
  • To shoot a long exposure photograph in bright light.

To achieve a shallow depth of field, most photographers will set their aperture quite wide. With this wide aperture, more light will reach the sensor. While this is often a good thing, if you are already shooting in a very bright environment, like a sunny day, it could result in an overexposed image. An ND filter will reduce the light reaching the sensors, so the aperture can remain wide but there will be less risk of overexposure.

ND filters are also frequently used to capture a sense of movement. When less light is entering the camera due to an ND filter, the shutter speed often needs to be slower than usual for a given aperture setting. This slower shutter speed will result in anything moving to appear blurred in your photograph.

This blur effect can offer a great stylistic element to your photographs. It will require a tripod or a very steady hand, as even a little movement when taking the photo will result in the entire frame being blurred, rather than just the elements in motion. This technique works great with subjects like waterfalls, rivers, traffic, and clouds.

For any photograph where you are wanting to be able to keep your shutter speed slow but shoot in broad daylight, you will need an ND filter. The longer exposure will give beautiful, smooth landscapes and city scenes, but without the ND filter you risk having a horribly washed out, overexposed image. An ND filter permits long exposure even in a brightly lit setting.

Do ND Filters Fit All Lenses?

When it comes to ND filters, they are not one-size-fits-all. First of all, not all camera lenses are even capable of attaching an ND filter. Compact cameras such as point and shoot models usually do not have a way to attach a filter and some very wide-angle lenses can’t attach a filter because the angle of the lens is so wide that it will actually show the edges (video below) of the filter if it is attempted or the lens is so curved the flat filter cannot fit over it.

YouTube video

That being said, camera lenses that can utilize filters still come in different diameters and thus need filters of a matching size in order to have the best results. If the camera lens has a filter thread, then the size of the screw-on filter needed is usually given on the lens. It is designated by a ø followed by a number, such as ø77. This lens would require a 77mm filter.

What to Do if Your Lens Doesn’t Have a Filter Thread

If you find your camera’s lens doesn’t have a filter thread, it doesn’t mean that you can’t use an ND filter. While many DSLR lenses have a filter thread, there are still plenty that do not. If your lens happens to not have a filter thread, you can use a filter holder system such as one of these.

Some of these filter holder systems still require a filter thread, so be careful to look for versions that can be mounted outside of the lens. These mounted filter holders tend to be designed to hold larger filters, which will often come in rectangular or square shapes.

Using a mounted filter holder system can be a bit more bulky and cumbersome to use than screw-in varieties, but it can also allow you to stack filters more easily if desired. If you don’t have the option to screw-in your filter, a filter holder system will allow you to still achieve the sought after result of an ND filter.

One of the main downsides to using a filter holder, however, is the cost. These mounted holders tend to be much more expensive and can scare away anyone who isn’t sure if they really will get a lot of use out of a filter or who just want to play around with the idea of filters.

However, these filter holder systems can be well worth the expense considering their improved quality. They can also fit a number of lenses and so you might have more versatility in using them.

Understanding the Numbers on ND Filters

Another confusing element of ND filters beyond what size to use is how to decipher the grading system used to differentiate between lenses. ND filters are typically graded in stops, meaning they are designated by the amount of light they block from entering the camera.

A stop is either the “doubling or halving of the amount of light let in” when you are capturing a photograph. When considering ND filters, we are specifically talking about the halving of light let in. For example, a 1 stop ND filter will reduce the light by 50% from a standard exposure. The higher the stop number, the more the light is reduced. As the stop number gets higher, you will need to slow your shutter speed accordingly in order to ensure the photo is not too dark.

For each increase in stop value, you can set your shutter speed to a correspondingly slower value. For example, a 6 stop neutral density filter will permit you to slow your shutter speed six times slower than what you would use without the filter.

To make things more confusing, some ND filter manufacturers will use different numbers when describing the stops of a filter. These manufacturers may list the optical density of the filter, such as 0.9, or an ND factor. These numbers mean the same thing as the stops, but are simply a different way of presenting the information. They can be correlated to a corresponding stop value.

For a helpful chart that gives the value of the equivalent stops for various optical densities and ND factors, check out this one available here.

Helpful Equipment to Consider When Using ND Filters

If you are planning to use ND filters frequently, it can be useful to acquire additional equipment to make capturing images easier.

Many times, ND filters are used by those seeking to use a longer exposure time. The higher the stop for the filter, the longer the permitted exposure length. However, when you start to have longer exposure times it becomes critical to keep the camera as steady as possible. The slightest tremor during the period of time the aperture is open will result in the entire image being blurred, which is usually not the desired effect.

To avoid a completely blurry photo, utilize a tripod. When you have an ND filter in place, the longer exposure will allow elements in motion to appear smooth and blurred while stationary elements will still be crisp and sharp. A tripod will allow you to ensure that the stationary elements will remain detailed and in focus. For example, when photographing a rocky shoreline with an ND filter, the waves will be smooth and blurred but the rocks crisp and sharp.

Along this same line of thought, it can also be helpful to have a cable release or a remote trigger. This allows you to trigger your shutter using a remote button rather than having to depress the shutter button on the camera. The physical action of pressing the shutter button can sometimes shake the camera enough to induce blur in long exposure shots, so using a remote triggering system can be very convenient and help avoid this.

What to Look for When Buying ND Filters

When it comes to selecting an ND filter, you have a lot of options available today on the market. However, there are a couple of factors that can be helpful to keep in mind when making your selection.

Think first about what you wish to accomplish with the ND filter. If you want very smooth, minimalist landscape shots, then you will want a very dense ND filter with a high stop value. If you’re just looking to be able to slow down your shutter speed a little or have a shallower depth of field, you won’t need as high of a density.

Round ND filters are best for those cameras using a filter thread attachment method. They are convenient and reliable, but if you have cameras with varying lens diameters you won’t be able to interchange ND filters between them. Square ND filters are meant to be used with filter holding systems, so this is often a better choice if you plan to use filters between a number of lens sizes.

Filter holding systems also allow for the option of stacking ND filters as well as other filters. This means you have the option to use an ND filter and a polarizing filter at the same time, or other combinations that allow for the desired final result and extra effects.

Variable ND filters are more expensive, but they allow you to adjust the density of the filter. This means you can use a single filter to achieve more nuanced control over the exposure of your image. However, keep in mind these filters tend to have a slight color tint, and so aren’t considered as “neutral” as a fixed ND lens and often aren’t as accurate as fixed varieties.

Best ND Filters

Once you’ve determined what size of ND filter you need, you may be wondering what the best option is for your lens. Generally, you will want to look for good quality materials that will not cast any color onto the image, i.e., be truly neutral, and keep the image sharp.

One top pick is the Cokin Nuances Extreme ND filters. These glass ND filters are impact-resistant and deliver truly neutral images. They are available in 6-stop and 10-stop densities and three separate sizes. These filters are meant to be used with Cokin’s EVO filter holder, which is an impressively sturdy and lightweight accessory but like most filter holders it runs on the pricier side.

Hoya also produces a wonderful line of ND filters under their PROND range. They have a wide variety of densities available and are catered to fit the most common sizes of filter threads. The Hoya PROND filters feature a special ACCU-ND coating on both sides of the glass lens that helps keep exposure levels accurate and eliminate potential color shifts that you can find in inferior quality ND filters.

If price is no concern, the ProGlass IRND filters by Lee Filters are a fantastic option for photographers. These filters not only maintain neutrality and avoid color shifts, but they also block infrared and ultraviolet light that can compromise image quality. This means your photos remain crisp and vibrant. These filters were originally designed for cinematography and have very precise optical density across the entire visible spectrum of light.

The Formatt-Hitech Firecrest ND offers a lot to be desired. It gives photographers the option of either circular or square formats, with a wide variety of sizes and densities offered. The square filter sizes are designed to fit nearly any filter holder, so it is a great option if you already have a particular holder you are fond of. The round frames also come in super-slim varieties that allow them to be stacked more easily than most.

Final Thoughts

Though many beginning photographers may be intimidated by the world of neutral density filters, there really is no reason to not use them once you understand the basics. Finding out what size ND filter to purchase simply requires you to determine the diameter of your lens or to purchase a filter holder system if your lens does not have a way to readily mount filters.

ND filters can help you achieve a shallow depth of field in brightly lit settings by limiting the amount of light that enters through a wide aperture setting. This can be especially helpful in outdoor portrait photography. For landscape or urban photography, ND filters allow for longer shutter speeds that can smooth out motion and give a beautiful, dream-like beauty to scenes.

With a little knowledge and a good quality ND filter, you’ll soon be on your way to capturing breathtaking photos in a whole new light.