All About Neutral Density Filters
Several months back, I received this question on Twitter from @HusbandInTow:
Would love to see basic stuff for photo novices, like how to use a filter, how to slow shutter speed, etc
Thanks for the question @HusbandInTow. The best way to slow your shutter speed is by using Neutral Density Filters. To make the most of these, you should first have a good grasp on the basics of exposure. You should know what a stop is, and you should be able to use the manual functions on your camera including setting the aperture, ISO, and shutter speed.
For more on understanding these things, see my 7 part guide to Shooting and Editing Photos, available for free here at The Polar Route.
Let’s get to your answer.
I’m all about adding interest to photos, and one of the most reliable ways to do that is by using a neutral density filter, or ND filter. ND filters are like sunglasses for your camera. They decrease the amount of light going in, thereby forcing your camera to compensate to great photographic effect. There are three reasons you might want to use a neutral density filter:
- Ability to use a more open aperture, allowing blurred backgrounds in bright daylight
- Ability to capture motion through long exposures, day or night
- Ability to remove motion from a scene by shooting really long exposures
A Little Background on Neutral Density Filters
ND filters are categorized based on the number of stops by which they cut the light. Cutting light by a stop is the same thing as cutting the light in half. Obviously, there’s a little bit of math involved in figuring this out, but it needn’t be difficult:
A 1 stop ND filter allows 1/2th the light through, necessitating an exposure that’s 2x longer.
A 3 stop ND filter allows 1/8th the light through, necessitating an exposure that’s 8x longer.
A 10 stop ND filter lets just 1/1024th the light through. This requires an exposure that’s 1024x longer.
ND filters are for some reason labeled in a series of 0.3 increments. A 1 stop ND filter is sold as 0.3, a 3 stop ND filter is sold as 0.9, and a 10 stop filter is sold as 3. To me, that does nothing but add to the complication. Go figure.
When to use each filter
I own a 3 stop, a 4 stop, and a 10 stop ND filter. Which one I choose depends entirely on the scene and on the kind of effect I want to create. The more frequently you use ND filters, the less you’ll have to rely on trial and error and the more comfortable you’ll become in deciding which one to use. You can also buy variable ND filters. These offer a one size fits all solution, but they’re very expensive. In general:
- Blurred backgrounds for portraits: 3 or 4 stop ND filter + large aperture (f/2.8 and below)
- Capture motion: 4 or 10 stop ND filter + small aperture (f/16 or so)
- Remove motion: 10+4 stop ND filter combined + small aperture (f/16 or so)
Evening / blue hour shooting
- Blurred background: no filter + large aperture (f/2.8 and below)
- Capture motion: no filter + small aperture (f/16 or so)
- Remove motion: 4 stop ND filter + moderate aperture (f/11 or so)
How to use an ND filter
How you use the filter depends on what effect you’re going for.
For daytime portraits with blurred backgrounds, just throw the filter on and start shooting with an open aperture! The camera will compensate for the reduced light automatically.
To capture motion, put your filter on and set your shutter speed somewhere in the range of 1/10 sec. You’ll need a tripod to do this.
Removing motion requires extremely long exposures in excess of 30 seconds. This calls for a slightly different technique. I’ve put together a short and sweet PDF guide on how to do this here: Sunset on Koh Samui. You might also want to watch the accompanying video here: Introducing the Visual Guide to Travel Photography.
Long exposures are a great way to add interest to your photography. With the right ND filter, you’ll be able to capture a different side of the world that’s completely invisible to our eyes. You never quite no what you’re going to get from long exposures until you take the picture, and that’s part of the fun.