A beginner's guide to ND filters

A beginner's guide to ND filters

ND filter is an abbreviation of the term Neutral-Density, also known as a neutral gray filter. They are an indispensable tool for photographers who want to control exposure and achieve creative effects in their photography. For beginners, the world of ND filters may seem a bit mysterious, but in this detailed guide, we will provide you with all the necessary information to understand and effectively use these filters.

What are ND filters and how do they work?

They are optical filters that reduce the amount of light passing through the lens into the camera. Simply put, they function like sunglasses, as they block or darken the image to eliminate the effects of excessive light. Their main purpose is to reduce exposure, allowing photographers to work with longer exposure times or wider apertures in bright conditions. This effect is useful for capturing motion, achieving blurry effects, or using wide apertures in bright situations.

ND filters enable:

  • Motion blur: Water in a stream becomes silky, clouds dissolve into abstract patterns, and cars on highways transform into light trails.
  • Increased depth of field: When shooting in bright light, you can achieve greater depth of field, capturing more details in the frame.
  • Shooting with an open aperture: Even in sunny conditions, you can shoot with a beautiful bokeh effect.

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Types of ND filters

Fixed ND filters

They have a specific light reduction value (e.g., ND2, ND4, ND8) and their intensity cannot be changed. Fixed ND filters are ideal for specific scenarios where changing the intensity is not necessary.

Variable ND filters

These filters allow you to adjust the intensity of light reduction. They are practical in situations where lighting conditions change, but they may cause unwanted vignetting or other unnatural phenomena in the image.

Graduated ND filters

They have a gradient effect that allows for gradual reduction of light intensity from one side of the filter to the other. They are suitable for photographing horizontal scenes where light is divided. They create captivating transitions, such as from a darkened sky to a bright one, but have very narrow usage.

Overview of common types of ND filters and their impact on light:

  • ND1: Allows 50% of light transmission (1-stop reduction)
  • ND2: Allows 25% of light transmission (2-stop reduction)
  • ND3: Allows 12.5% of light transmission (3-stop reduction)
  • ND4: Allows 6.25% of light transmission (4-stop reduction)
  • ND8: Allows 3.125% of light transmission (5-stop reduction)

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How to choose an ND filter based on usage?

The main parameter for selection is the so-called ND factor. It indicates how much light passes through the filter to the lens. By knowing this factor, you can adjust the exposure time to your goal. This parameter can also be found under designations such as EV reduction, optical density, or transmittance.

  • Filters with lower ND factors are suitable for photographing portraits or filming. These are filters with factors up to 64, as they are transparent enough to allow comfortable focusing and work in illuminated spaces.
  • A filter with a stronger ND factor of 64 and above (up to several thousand) is suitable for photographing landscapes, clouds, sky, and other types of photos requiring very long exposure. 

For example, for ND1000, it means extending the exposure time by 1000 times. This means that if you normally use an exposure of 1/60, with an ND1000 filter, the exposure time would extend to 1000/60 = 16.67 seconds.

For example:
This shot was captured using a Hoya ND64 filter, shutter speed 120s, aperture f/13, and ISO100.

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How to use ND filters?

ND filters are useful for capturing images that require long exposure times. For example, when photographing water surfaces, setting a long exposure time creates a smooth effect, making the water calm and resembling glass. Leaving the shutter open for seconds, instead of fractions of a second, is the only way to achieve this type of shot, as longer exposure times lead to smoother images. Photographing with long exposure times is difficult to master, but the resulting images are undoubtedly beautiful.

However, during long exposures, the shutter remains open for so long that too much light hits the sensor, causing overexposure of the image. And this is where ND filters come into play. By using an ND filter, you limit the amount of light hitting the sensor, so you can leave the shutter open as long as you want (assuming you have the right ND filter) without worrying about overexposing the image.

ND filters are created in stops. For example, darkening or brightening the image by 1 stop. In the case of ND filters, you always multiply the exposure time. So, a 1-stop ND filter stops light by 50% or half.

Remember that for long exposure shots, you only want to change the shutter speed. If you have an exposure of 2 seconds without a filter and then add a 1-stop ND filter, you effectively halve the amount of light entering the camera. To balance this, you need to increase the time during which light enters the camera, in this case, doubling it. See the table below.

This is the basic principle of ND filters, stopping light entering your camera, which forces you to compensate by allowing light to enter for a longer time. The table below shows this with a 1-second exposure and adding various strong ND filters. Notice how the new exposure times double gradually. For example, when you add a 4-stop ND filter, you need to double the original exposure time 4 times.

Original closing time

ND filter

New closing time

1s

1

2s

2

4s

3

8s

4

16s

5

32s

6

64s

7

128s

ND filters are also popular among portrait photographers. To achieve a beautiful creamy bokeh and very shallow depth of field, you need to have the aperture fully open. Some lenses can open up to f/0.95. Even at the lowest ISO setting and the fastest shutter speed, there may still be too much light to achieve the correct exposure. An ND filter can help mitigate this issue.

Tips for using ND filters:

  • Use a tripod: Stability is important for long exposures.
  • Experiment with different shutter speeds: Discover which effects you like the most.
  • Follow composition: Long exposure highlights even the smallest details in the scene.
  • Watch out for overexposure: When using ND filters, it's easy to overexpose images.

ND filters are a powerful tool that allows you to capture light in a new light. With a bit of experimentation and practice, you'll be able to create stunning long exposure photos that will awe your surroundings.