If you’re a beginner photographer who is interested in long-exposure photography, you’ll quickly learn about an invaluable tool that will help you get the soft, smooth, and silky look you can only achieve with extremely long shutter speeds.

That tool is called a neutral density filter. It allows you to keep your shutter open longer to achieve long exposures. It’s so useful, in fact, that any landscape photographers consider it an essential part of their kit.

This article will explain what a neutral density filter is, and why & when you might want to use one. We’ll go over the different kinds of neutral density filters. Then, we’ll explain how to use one.

Neutral Density Filters
Photo by Mathieu Perrier on Unsplash

What is a neutral density filter?

Neutral density filters, commonly called ND filters, are dark pieces of glass that attach to the front of your camera lens. Their purpose is to block a certain amount of light from entering your lens. They are called “neutral density” because they block the light in a neutral way — meaning, they shouldn’t change the color of the light that passes through the filter.

Why use an ND filter?

It seems counterintuitive to block the light that enters your camera. After all, light and exposure are good things, right? However, when you’re trying to take a long exposure photograph – sometimes too much light can be a bad thing. 

That’s when ND filters are invaluable. They give you the means to control the amount of light that enters your lens. That way, you can keep your shutter open for many seconds at a time or using a very wide aperture without letting in too much light, even in situations that would normally drastically overexpose an image.

For example, if you want to photograph a popular long-exposure waterfall photo in bright daylight, an ND filter is extremely useful if not absolutely necessary.

long exposure waterfall
Photo by Jeffrey Workman on Unsplash

Different types of neutral density filters

Neutral density filters come in all shapes and sizes, from many different brands and in a wide range of prices. It can be confusing to know what to get if you haven’t done the research. First, it’s important to know there are two main types of filters, with pros and cons of each — screw-on and square filters:

Screw-on filters

These, like the name implies, screw on to the front of your lens. They tend to be a good value, are easy to find for most lenses, and they’re lightweight. They’re a great option for photographers who don’t want to carry a lot of gear.

However, screw-on filters make it difficult to use more than one filter, because they can cause obvious vignetting when you stack them. Also, if you use more than one size lens, you’ll need to purchase a new filter for each lens.

Square filters

Square filters are more advanced than the screw-on type, but the payoff is that they are higher quality filters. With square filters, a filter holder is attached to the lens. Then, square filters, such as ND filters or polarizing filters, are then inserted into the filter holder.

The main advantage with this type of filter is that they are higher quality. Also, they can be stacked without causing vignetting. However, they are much bulkier and much more expensive than their screw-on counterparts. Also, some of the less expensive brands have a tendency to leak light.

long exposure
Photo by Arnaud Mesureur on Unsplash

Understanding the different strengths of ND filters

ND filters are offered in different strengths, depending on the amount of light you want to block. Most commonly, they’re referred to by the number of “stops” of light they block. You’ve probably already heard the terms 3 Stop, 6 Stop, and 10 Stop when referring to ND filters — these are the most common.

Sometimes, ND filters aren’t labeled by the amount of stops they block. Instead, they are given an optical density number such as ND1.8 or ND3.0. The following chart will help you decipher how many stops each ND filter blocks:

ND filters stops
ND filter chart

Graduated neutral density filters

Graduated neutral density filters, otherwise known as ND grads, are ND filters that have a gradient from light to dark. You would use one if you have a lot of contrast in your scene, for example, a very bright sky and a dark foreground, to even out the light and balance your exposure.

Tips for using a neutral density filter

Just how you use an ND filter will vary depending on what you’re shooting, the lighting conditions, and your personal style.

  • To get the smooth, glass effect on water, look for water that is already somewhat calm.
neutral density filters
Photo by asoggetti on Unsplash
  • For smooth clouds in the sky, look for a sky that has just a few clouds so you keep the texture. A full, overcast sky will just look gray after an ultra-long exposure.
  • Try to shoot in the morning or evening.
  • If you’re shooting long exposures, use a tripod.
  • Figuring out the math for long exposures with an ND filter can be tricky. An ND calculator app takes the guesswork out of it.
  • When it comes to filters, most of the time you get what you pay for. Cheap filters will affect the color. Don’t invest in good lenses and then slap a cheap filter on the front of it.

Final thoughts

If you’re a photographer who shoots long exposures, there’s no doubt that a neutral density filter belongs in your gear bag. The best advice now is to stick one on your lens and experiment!