How a Neutral Density Filter Works
Top Reasons to Own a Neutral Density Filter
What is a neutral density filter?
Neutral Density (ND) filters reduce the intensity of all wavelengths, or colors, of light equally from entering the camera, in measured amounts. This allows the photographer more control in selecting shutter speed and aperture combinations in a variety of conditions.
Fixed ND filters, also referred to as solid ND filters, have coating(s) evenly distributed across the frame of the filter. The density of the filter is predetermined.
Fixed ND filters come in a range of densities to meet the needs of the photographer and the conditions they might be shooting in. A lighter density filter, like a 3-stop, will allow the photographer to select a shutter speed 3 stops slower:
A denser filter, like a 6-stop or 10-stop will allow the photographer to select even slower shutter speeds for increased motion blur:
There are several variables including weather, time of day, ambient light, etc... that will determine which neutral density filter is appropriate for the occasion. It is up to the photographer to select the right shutter speed and corresponding filter to make an otherwise ordinary shot something more powerful.
Variable ND filters
Variable ND filters are essentially two polarizers placed together with one plane preventing a fixed amount of light and the other rotating to prevent incremental amounts of light from entering the camera.
Variable ND filters can be advantageous to the photographer on the go. Carrying a set of fixed ND filters and constantly changing fixed filters can be cumbersome and time-consuming. With a variable ND, the photographer can just rotate the filter like a polarizer to get the desired effect.
Troubleshooting
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.
Features to look for
- 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.
Popular Hoya ND Filters
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Hoya Solas IRND
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Hoya Solas Variable NDX
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