What’s a ND Filter? Neutral Density Filters Explained

A Guide To Neutral Density Filters

Have you ever wondered how professionals get those great shots so the clouds looked amazing and the water looks like silk running over rocks?  Or what about those wonderful hazy photos where the movement is really blurred even though the scene was photographed in broad daylight? How do you do that, I hear you ask?

Well it’s really simple all you need is a Neutral Density filter!

Image Courtesy of Paul Pichugin

The Problem

Normally, as photographers we seek the perfect sharp shots, especially in landscapes. It’s a given that landscape photographers like to choose a small aperture, which always results in fairly long exposures. The problem is the exposure times aren’t normally never long enough to blur clouds or water movement, especially during the brights times of day.

In order to get exposure times ranging from several seconds to minutes, you need to cut out of a lot of light, and to do this you will need a neutral density filter.

The Neutral Density Filter

A Neutral Density filter (ND in short) is nothing more than a special semi-transparent piece of glass that blocks out light from reaching the sensor thereby pushing the exposure time to seconds or minutes, depending on the strength of the ND filter.

ND filters are classed by their optical density or equivalent f-stop reduction (number of stops).

Most manufactures use one of these previously described numbers (optical density and f-stop reduction) to describe their filters. The result of a larger f-stop reduction is a longer exposure.

Brands like Hoya, B+W, Cokin use code ND2 (1-stop reduction) or ND2x, etc, whereas Lee Filters and Tiffen all use codes like 0.3ND (1-stop reduction).  Lastly Leica uses the following 1x (1-stop reduction), 4x, 8x, etc.

To explain how it works further we’ve constructed a helpful table:

 Notation depends on manufacturer:
 ND .Number Notation   NDNumber Notation Optical Density   f- stop reduction    % Transmittance
ND 0.3
ND 0.6
0.6225 %
ND 0.9
ND 1.2
1.246.25 %
ND 1.5
ND 1.8
1.861.563 %
ND 2.1
ND 2.4
2.480.391 %
ND 2.6
2.68 2/30.25%
ND 2.7
2.790.195 %
ND 3.0
ND1024 (also called ND1000)  
ND 3.3
3.3110.049 %
ND 3.6
ND 3.9

So basically, a ND 0.3 filter (ND2) will block 50% of the light, thereby resulting in a one f-stop reduction. This means you will need twice the exposure time if you stay at the same aperture setting for a correct exposed image. A ND 0.9 (or so called ND 8) filter will result in a 3 f-stop reduction, thereby leading to a 8 times longer exposure.

Choosing A Good Neutral Density Filter

Good ND filters are constantly grey and won’t produce a color cast on your images. They will only reduce the amount of light, not decreasing contrast or saturation. We highly recommend you to stay away from the no-name or cheap filters!

Here’s some ND filters we would recommend:

Tiffen 77mm Digital Neutral Density Filter Kit (ND 0.6, 0.9, 1.2 + Wallet)

B&W B+W 77mm ND Neutral Density Filter

Lee Foundation Kit

Lee Graduated Neutral Density Resin Filter Set

What Should You Expect the Results to be Like?

Here some more stunning images from a couple of F Stop Lounge contributors…

Image Courtesy of André Appel

Image Courtesy of Paul Pichugin

Andy Gray

Image Courtesy of Andy Gray

If you would like the most versatile system available, which will most probably achieve the greatest results (due to the glass quality), I would recommend:

  • Lee Foundation Kit / Filter Holder
  • Lee 4×6 Graduated Neutral Density Resin Filter Set

I hope you found this article informative, and I look forward to seeing your long exposure images on our Google+ Photography Community.

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I'm a professional photographer from Central Germany where I run a photo studio. I love to shoot portraits and I always like to push the limits. Whenever I'm not in the studio I'm outside chasing the light. I'm totally addicted to photography!

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