ND Filter Tips - How to use ND filters

Tips for using ND filters (howto):

Unsure about which ND filters to buy, and want a guided recommendation? Use the ND Filter Chooser → Right Here

Using an ND filter can lead to some really nice, natural and smooth movement. To get the most out of your ND filter and pick the best ND filter for your video, we first need to be thoughtful and careful about how the camera is set up.

What do ND filters do?

Besides offering some physical protection for the lens, ND filters are especially useful for two things when filming action-camera video:

  1. Making the jello effect caused by vibration and a rolling shutter less visible
  2. Giving video a more cinematic and natural look that is similar to how our eyes see while in motion

This video shows what those effects actually look like in real footage:

(You can read a more in-depth description of what ND filters do and how they work right here - it's worth a read!). 

Both effects come from using a slower shutter speed. The ND filter cuts the light, so the shutter can stay open longer without overexposing the image. If the camera or subject moves while each frame is being captured, that movement is recorded as a small amount of blur. This is what we call motion blur. The faster something moves across the frame, the more blur you will see.

  • An ND4 filter lets through 1/4 of the light
  • An ND8 filter lets through 1/8 of the light
  • An ND16 filter lets through 1/16 of the light
  • An ND32 filter lets through 1/32 of the light
  • An ND64 filter lets through 1/64 of the light

Those numbers only help if the filter actually matches its rated density. See how we test ND accuracy and colour neutrality.

 The Easy way to use ND filters (“Set and forget”)

Get the app!  We now have a free iPhone/Android app that helps you pick exactly the right ND filter and camera settings in seconds!  You can download it here: CameraButter.com/ndmeter.

You can leave your camera in auto mode with very good results.  Just put an ND filter on your camera based on the chart below, and leave it.   You would only need to remove it if you are filming video in low light (e.g. sunset) or dark conditions.  This can give motion a smoother look and make jello less visible.

The drawback of this easy way is that the amount of motion blur may change during the shoot if the light changes and your camera has to adjust the shutter speed. This happens regardless of having an ND filter or not, it is just less pronounced without one.  

The “Expert” way to use ND filters

The shutter speed is indicated in 1/seconds.  A shutter speed of 60 means that the shutter is open for one 60th of a second.  A shutter speed of 120 means that the shutter is open for one 120th of a second.  So, because 1/60th of a second is twice as long as 1/120th of a second, twice as much light gets in.

Traditionally, to get a “cinematic feel”, a good starting point is a shutter speed of one over 2x the frame rate.  So, with a frame rate of 30fps, that would be 1/60th of a second. This is a starting point, not a rule. With heavy movement or electronic stabilization, a somewhat faster shutter can work better because too much motion blur can make stabilized footage look smeary or jittery. You can read more about that in Why is my Footage Choppy or Jittery? and ND Filters and HyperSmooth/Stabilization: The Real Story.

We can’t just set the fps to 30 and the shutter speed to 1/60 on a sunny day, because the camera would let in too much light and the footage would be much too bright and overexposed.  We might need to use a shutter speed of 1/120, 1/240 or faster, but that would also reduce the motion blur.  An ND filter blocks some of the light so we can use a slower shutter speed without overexposing the image.

To best control shutter speed on a GoPro, use Pro Controls on newer cameras or enable Protune on older models.  The exact menu names vary by model, but these are reasonable starting points: 

  • Color: Doesn’t matter for this, your preference
  • White balance: Doesn’t matter for this, your preference
  • ISO Min: 100
  • ISO Max: 400 is a good starting point. Higher values can help if the light changes a lot, but they also add image noise.
  • Shutter Speed: Set this for the amount of motion blur you want, then choose an ND filter that gives you the correct exposure. At 30fps, 1/60 is the traditional starting point; at 60fps, use 1/120.

To choose the best ND filter for video, use the following ND filter based on the light available:

  • Cloudy/low light: ND4
  • Partially cloudy: ND8
  • Sun: ND16
  • Very bright sun: ND32
  • Extremely bright sun, snow or water: ND64

Preview the image on the camera or in its companion app. Does it look properly exposed?  If it’s too bright, use a stronger ND filter.  If it’s too dark, use a lower-value ND filter.  If you don’t want to change the filter, you can try changing the shutter speed up or down to the next setting. This will also change the amount of motion blur, but getting the exposure right is more important.

Regularly check the exposure.  If the light level changes, for example as it gets darker at the end of the day, you may need to change the ND filter or use a slower shutter speed or your footage will be too dark.  Eventually, you will get a good feel for the settings and this will become second nature.

Find filters for your camera

 

Not sure which one you need? Use the ND Filter Chooser.

More info: