The neutral-density filter, or ND filter, is a powerful tool photographers use to reduce the amount of light entering a camera lens in order to select exposure combinations that would otherwise result in overexposed images. This guide will explain the basics of ND filters as well as how to use them.
Light and its effects on the scene are fundamental principles of photography. Photography is a term that derives its name from the Greek words “phos”, (light), and “graphe,” (draw).
Light can change the mood and scene in a photograph. It is crucial for photographers to be able to adjust the light to suit his own needs. But how a photographer can control the available light in the scene?
This is the reason that photographic filters were invented along with the first cameras and lenses, as they provide the ability to control the available light based on the needs of the shooting.
What is an ND Filter?
A neutral-density (ND) filter is a colorless piece of glass that decreases the intensity of the incoming light evenly in all wavelengths — meaning it aims to not affect the colors in a scene — allowing us to have precise control over the amount of light that will enter the camera sensor.
ND filters are available in circular and square types, and they are produced in all sizes so it is certain that you will find one suitable for your lens(es).
How Do Neutral-Density Filters Work?
The ND filter blocks some of the light entering the lens.
A good example would be the sunglasses that we use on bright sunny days. They allow our eyes to see clearly in the bright sunlight.
If you wanted to look at the world with your eyes wide open (like using a larger aperture) in strong sunlight, you could wear some sunglasses to block some of that sunlight from reaching your eyes. Otherwise, you would need to squint (reducing the size of your aperture) in order to not hurt your eyes (like overexposing a photo).
ND filters can be separated according to their blocking power. This means there are filters that block more light and others that block less light.
When Would You Need an ND Filter?
The most frequent use of an ND filter in daytime is to extend the shutter speed to [******************************************************************************************************************************************************] because there is still a lot of light available.
Even if a narrow aperture is used, such as f/11 or f/16, there is still a lot of light available and it is not possible to extend the shutter speed to more than 1 second.
An ND filter, depending on its blocking strength will allow us to extend the shutter speed to several seconds, as was done in the example below.
Another situation when an ND filter is useful is when a wide-open aperture (f/1. 4, f/2) must be used under daylight but the shutter speed must remain constant; for example, for video shooting or when the light meter warns us of overexposure even if we reached the fastest shutter speed (i.e. 1/8000). We can get beautiful depth-of-field shots by using ND blocking. The filter reduces light levels.
Do Neutral-Density Filters Degrade Image Quality?
No matter how good and capable your camera sensor might be in retaining all details and having high resolution, you must keep in mind that light enters the camera through the lens as well as the filter, which is most often attached to its front.
Depending on what filter elements are used, your final image may have less sharpness, or other optical aberrations. This can be caused by flaring, color shift, or color cast. It is often very difficult to correct in post.
This is a problem that affects all filters, not just ND. However, ND filters have a tendency to experience color shift. You should not have your ND filters negatively affect your image quality.
How to Know What Kind of ND Filter to Buy
As we mentioned earlier, ND filters are available in both circular and square versions and in all sizes, so it is easy to find one for your lens. However, they are also separated based on their light-blocking strength, which is the most important factor when you are searching for an ND filter to buy.
Other than its brand name, (i.e.
Other than its brand name (i.e. Cokin, Hoya or Tiffen), ND filters often have text and numbers printed on their product cases that tell us about its strength. This text might be something like “ND1000” or “ND3.0” or just “10-stop ND.”
All these three names indeed refer to a 10-stop ND filter, but each of them refers to something specific.
ND1000 refers to the Filter Factor Number, which translates to how much light is reduced. In this case, it’s 1/1024.
ND3.0 refers to Optical Density Number, which is the amount of energy blocked by the filter.
Below is a list of common ND filters.
But how can this be translated to real-life shooting scenarios so that we can better understand what ND we should choose?
Here is another table containing some practical data, with shutter speed examples.
There is of course the option of stacking two separate ND filters together — a 5-stop ND and a 10-stop ND to have a 15-stop ND filter, for example — but keep in mind that in most cases and no matter the quality of the filters, many optical aberrations might be visible, as also there is a big possibility of vignetting being introduced into your photo.
How to Use a Neutral-Density Filter
After we reach our shooting location, we start by fixing and finalizing our composition, and then we take some test shots to check the light levels and if the image is exposed properly according to our creative vision.
We also check if the image is focused properly as even with the most recent cameras, it can be very difficult to achieve proper autofocus with a 10-stop ND in front of the lens.
After everything is checked and finalized, we attach the filter.
Note: Before we attach the ND filter to the lens, we must be sure it is clean with no visible dust or oil spots that might be visible on the final image.
Depending on the blocking strength of the ND filter we selected, we have to make the necessary changes to the exposure settings based on our initial tests.
So for example, if our initial base exposure test (without a filter) was aperture: f/8, shutter speed: 1/400, and ISO: 64 and we selected a 10-stop ND, then the exposure settings should be aperture: f/8, shutter speed: 2. 5sec, and ISO: 64 so to have the same amount of light as the initial shot.
To avoid micro-movements from ruining your shot, make sure the camera has a stable tripod.
Are There Other Types Of ND Filters Available?
There are other types of ND filters available.
Variable ND Filters
This is an ND filter that has adjustable variable density strength, such as ND3-400, which means that the blocking strength is not constant, but it can be adjusted by the user depending on the shooting needs.
These filters are very handy when you don’t want to carry many different ND filters in your camera bag and are extremely helpful for video shooting as the user can adjust the density on the fly. For example, they can be used when filming for a wedding and there is a scene in which the couple is outside in daylight and then they walk into a much darker building.
Graduated ND Filters
The graduated neutral density (GND) filter is a type of ND filter that’s a must-have for landscape photographers as they can balance the exposure between the bright sky and the foreground, providing a smooth transition of the light of the scene. These filters are mostly available in rectangular form, although there is a blender type (circular) available as well.
These filters have a clear bottom part which is designed to allow foreground light to pass unimpeded, while the ND part is located on the upper portion to block some of the light from the brighter sky.
Recommended ND Filter Strengths
If you are in landscape photography, then a 10-stop ND as also a Graduated ND are must-haves to cover most shooting scenarios out in the field.
If you are into urban photography (travel, portrait, architectural) then a 5-stop ND is probably more suitable for your needs. Or you may want to consider a combination of 3-stop and 6-stop ND filters that can also be stacked.
If you are a video shooter, then a Variable ND is probably ideal, giving the ability to easily and quickly change the blocking strength on-the-fly.
Conclusion
We hope this introductory guide on neutral-density filters was helpful to you in your journey as a photographer.
Conclusion
We hope this introductory guide on neutral-density filters was helpful to you in your journey as a photographer.
Image credits: Header photo from Depositphotos. All other photos, unless otherwise noted, by Christophe Anagnostopoulos
