How a Neutral Density Filter Works
Top Reasons to Own a Neutral Density Filter
- More control over shutter speed and aperture in full sun conditions
- Create motion blur in water, clouds and busy city streets
- Shoot wide-open at F1.4 in direct sunlight
- Create dramatic long exposures in any lighting condition
How it Works
Neutral Density (ND) filters reduce the amount of light entering the camera. Often times when shooting a scene, the dynamic range of light supersedes what a camera can capture. In other words, the shadows are too dark or the highlights are too bright for the camera to record all of the information of a scene in a single exposure. A ND filter is essentially a piece of dark glass placed over the lens to “block” or “darken” the brightest areas of a particular scene.
ND filters are manufactured in a variety of ways, all designed to filter light reaching the camera sensor. A quality ND filter allows the photographer more control in selecting shutter speed and aperture combinations that will record a sufficient amount of data to the camera’s sensor.
The two types of neutral density filters are variable and fixed. Below is a list of pros and cons of each type of filter:
Fixed neutral density filters have coating(s) evenly distributed across the frame of the filter.
Variable neutral density filters can be used in place of several fixed filters and have a double ring design that allows the photographer to rotate the outer ring to allow different grades, or amounts, of darkening.
The downsides to most ND filters are unpredictable “color shift” and/or vignetting.
Almost all ND filters have some sort of color shift. When an image is produced that has a green color cast, it is often the result of a poorly designed filter. On the other hand, when infrared (IR) light penetrates the camera sensor, the resulting image can have a magenta cast.
Color shift is amplified by low-quality materials, poor manufacturing, and ignoring the infrared band of the light spectrum.
Quality manufacturing and design resolves these issues.
Vignetting is determined by the amount of light fall off toward the outer edges of your lens. The wider the lens you choose and the longer the exposure time you have, the more vignetting can occur. Poorly designed and manufactured filters will increase the amount of unwanted vignetting. A quality filter will either have no color shift at all, or, at the very least, have predictable results.
Here are features to look for in deciding which ND filter is best for you:
- Color Shift: Should be non-existent or at minimum predictable results
- Vignetting: A quality filter does not amplify vignetting from a lens.
- Durability: Filter is resistant to inevitable dings and knocks
- Simplicity: The system is easy and quick to set up and use on location and/or during a shoot.
Neutral Density filters are popular because of their versatility. Almost any situation can necessitate the use of a ND filter. Often times, ND filters are the difference between a good photo and a great one. Below are examples of common subjects where a ND filter can be used:
CLOUDS: A neutral density filter darkens the scene, and allows a longer shutter speed. Because clouds are moving, the result is blurred clouds that often look smoother and “cleaner.” Karl the Fog over the Golden Gate Bridge, steam from trains, city buildings, and early morning mist across lakes are all places that ND filters can work in a photographers favor.
WATER: Moving water can be blurred through a longer shutter speed. It can be helpful to also use a polarizing filter with water to minimize glare and reflection off the surface.
MOTION: Any scene that contains movement: cars, trains, buses, boats, bicycles, and people can often create a “busier” scene than the photographer would like. A neutral density filter can help by allowing the photographer to choose a shutter speed slow enough to blur out movement as if it isn’t there or to creatively capture the movement to add something special to the final image. This is especially useful in crowded tourist spots where people can become more of a distraction than an addition to an otherwise beautiful image.