You may have heard the phrase ‘ND grad filters’ without knowing what it means, particularly if you’re new to photography. Graduated neutral density filters – or ND grad filters – are used for controlling light levels and balancing the tones of a photograph to give a result far closer to how it appears to the eye.
Many professional landscape photographers use these filters, but how exactly do they work and when should they be used?
Imagine staring at a gorgeous sunset, with a sky full of burning oranges and yellows. The light levels in scenes such as these are extreme, but as you look around, it’s very easy to see detail in both the bright sky and the deep shadows. In the landscape, you’ll notice that most of the light is actually separated into two areas, above and below the horizon.
Unfortunately, unless you use something to reduce the light levels in the bright sky, camera technology still can’t capture this huge range of light in one image, so detail gets lost and the resulting image looks radically different from the real thing.
By positioning an ND grad in front of the lens so that the dark part of the filter covers the brightest part of the sky, this difference can be significantly reduced. The image can now be captured in one frame.
How to use an ND grad filter in 3 simple steps
Step 1: Shoot in manual mode
Use manual mode for the best control over exposure. With the filter applied, the camera may struggle to assess the correct exposure. If you’re shooting a landscape, set an aperture of f/11 or f/16, and focus a third of the way into the scene.
Step 2: Take a reading
Set your camera to evaluative metering so the camera can measure the light levels across the entire frame. Spot or centre-weighted metering may be far too biased to the most intense areas of light (see our guide to How to use a hand-held light meter for perfect exposures).
Step 3: Check the histogram
Take a test shot and check the histogram to make sure the filter is reducing the light levels significantly without blowing out highlights or losing shadow information.
If the histogram doesn’t reach the far right, the filter is too dark for the scene (see our guide to What your histogram says about your landscapes).