What you'll learn
1. What an ND filter is.
2. When to use ND filters
3. How to use ND filters
ND (or Neutral Density) filters are a really useful bit of kit to have in your bag. They offer up a solution to a few problems which you can run into. But what exactly are ND filters and what do they do?
What you'll need
- ND Filter
- Cable Release
A bit of theory
An ND (Neutral Density) filter is a totally neutral filter – meaning that it does not affect the colour of your photos – that cuts down on the amount of light entering the lens, not unlike a pair of darkened sunglasses. This allows you to slow your shutter speed down slightly, or use a wider aperture than you would be able to usually.
There are 3 main kinds of ND filters. The most commonly used is a standard ND filter. These come in different grades or densities, which are defined by how much light they block from entering the camera. The naming convention on ND filters can be a little confusing because they can be labelled with either the ND number or by how many stops of light the filter cuts out. A one stop filter will block one full stop of light from entering the camera, but this is also known as an ND2 or an 0.3ND. The different numbers do all have meanings. For example the 0.3ND represents the optical density of the glass, whilst the ND2 represents how much light enters the lens in terms of a fraction. So an ND2 lets ½ of the amount of light in, whilst an ND4 lets in ¼ of the amount of light through.
ND filters come in a range of grades, from one stop all the way to 12 stop filters. The higher grade filters can be much more expensive and much more difficult to come by.
This can all be rather confusing, so here’s a handy table to refer to.
There is also a kind of ND filter called variable ND filters. These allow you to change how much light is stopped by simply turning the front of the filter.
Finally, there is graduated ND filters or ND Grads. An ND Grad is a pretty neat filter which starts at the maximum density it is rated for and then becomes less dense across the frame, usually until about halfway down where the ND effect stops. This allows you to selectively darken bits of the frame, such as the sky, making it really useful for people interested in landscape photography.
ND filters have a huge range of uses. For example, if you’re shooting a timelapse and want to get a specific aperture and shutter speed but are unable to get the correct exposure even with the lowest ISO, add an ND filter which gives you enough of a reduction to get the exposure settings you want. Another common use for an ND filter is to shoot longer exposures during the day. If you use a 10 stop filter you can get some really interesting effects, especially with landscapes and seascapes as it smoothes out any motion of water or the clouds. Another great example of when to use an ND filter is if you want to shoot with your lens wide open, on a sunny day. Often this results in over exposed photos, but an ND can help bring the overall exposure down allowing you to correctly expose your photos.
If you’re using an ND filter to allow you to shoot with your aperture wide open in the middle of the day, just use the camera normally and let the exposure metering do the work for you.
Capturing the photos
Press the button!
Take your photo! If your exposure is really long, use a cable release to help reduce any movement on the tripod.