A neutral density filter is the rarest thing in a photographer’s bag: a piece of glass that lets the camera record something it could not record without the filter. Every other accessory either replicates an effect you could do in post (warming filter, polarizer to some extent) or simply protects the lens. An ND lets you capture motion blur in daylight, shoot wide-open portraits in bright sun, and time-collapse moving water and clouds. This article explains how ND filters work, what each strength is best for, and how to pick a quality filter that does not turn your sky purple.
How neutral density actually works
An ND filter is a piece of optical glass that absorbs or reflects a specific percentage of light across the entire visible spectrum. “Neutral” means the absorption is roughly equal at all wavelengths, so colors come through unchanged. “Density” refers to how much light is blocked.
The standard measurement is stops. Each stop halves the light. A 1-stop ND lets through 50 percent. A 3-stop ND lets through 12.5 percent. A 6-stop lets through 1.6 percent. A 10-stop lets through 0.1 percent. Filter manufacturers use three different naming conventions, so the same 6-stop filter might be labeled ND64, ND 1.8, or 6-stop depending on the brand.
| Stops | Light reduction | Manufacturer codes |
|---|---|---|
| 3 | 1/8 | ND8, ND 0.9 |
| 6 | 1/64 | ND64, ND 1.8 |
| 10 | 1/1024 | ND1000, ND 3.0 |
| 15 | 1/32768 | ND32000, ND 4.5 |
The four main use cases
Motion blur in moving water
Waterfalls and streams are the classic ND application. Without a filter, daylight shutter speeds run 1/250 to 1/1000 second, freezing every droplet. The water looks crisp but visually noisy. A 6-stop ND at f/8 ISO 100 in shaded shooting conditions pushes the shutter to 1 to 4 seconds. The water blurs into silk threads and the surrounding rocks and foliage stay sharp.
For ocean shots, the math gets bigger. Bright daylight at f/11 ISO 100 wants 1/250 second. To get 30-second exposures that turn waves into mist, you need a 13-stop reduction. A 6-stop alone is not enough. Stack a 6-stop and a 10-stop, or buy a single 13-stop filter.
Cloud streaks and time-collapsed skies
Moving clouds in a 30 to 120 second exposure produce streaks that emphasize wind direction and add a surreal quality to landscape work. In bright daylight at f/11 ISO 100, a 10-stop filter gets you to about 30 seconds. A 15-stop gets you to 4 to 8 minutes for extreme streaking effects.
This is the kind of shot that defines the long-exposure landscape genre. It cannot be replicated in post because the original frame is a single instant. Sky compositing in software can approximate the look but never the actual recorded data.
Empty streets and removed crowds
In a city scene at golden hour, a 4 to 8 minute exposure (requires 15-stop ND in bright light, 10-stop in shade) makes any pedestrian who keeps walking disappear from the frame. Only stationary people and objects record. The effect is dramatic for tourist locations like the Trevi Fountain or Times Square shot just before or after dawn.
Wide aperture in bright sun
A different use case entirely: shallow depth of field portraits at noon. A 50mm f/1.4 lens at f/1.4 and ISO 100 in bright sun wants 1/8000 second. Most cameras max out at 1/8000 or 1/4000 mechanical shutter, and even at 1/8000, some cameras meter overexposure in extreme conditions. A 3-stop or 6-stop ND brings the shutter back into a workable range and lets you keep the shallow depth of field.
Video shooters use NDs almost constantly for the same reason. The “180-degree shutter rule” says shutter speed should be roughly twice the frame rate (1/50 second at 24 fps). In daylight, that requires f/11 and ISO 100, which is too narrow for most cinematic looks. A 6-stop variable ND brings the aperture back to f/2.8 or f/4 for proper subject separation.
Variable ND filters
A variable ND uses two stacked polarizing filters on a rotating outer ring. Turn the ring, the polarizers cross more, less light passes. Range is typically 2 to 8 stops in a single filter.
The advantage: one filter covers most use cases. You can dial the strength to match the scene without swapping filters. For video, this is essential because you change shooting conditions constantly.
The disadvantage: a cross-polarization X pattern appears at the strongest settings on cheap filters. The pattern looks like a dark X across the frame. Quality variable NDs (Polar Pro Quartzline, Nisi True Color, Breakthrough Photography X4 ND VND) eliminate the X by limiting the maximum range or by using more careful polarizer alignment. Expect to pay 200 to 400 dollars for a good variable ND.
Color casts and quality differences
Cheap ND filters introduce visible color shifts that are hard to correct in post. The most common cast is a magenta-to-red bias above 6 stops and a warm yellow tint at lower strengths. The shift comes from imperfect spectral absorption: the filter blocks slightly more blue than red.
Quality filters use either dyed glass with carefully matched absorption curves or vapor-deposited metal coatings that block more evenly. Brands with good color neutrality in 2026 include Nisi, Breakthrough Photography, Lee, Haida, and Kase. Expect 80 to 250 dollars per filter depending on size and quality.
For variable NDs specifically, color shift gets worse as you turn the ring further. The best variable NDs maintain color neutrality through their full range. The cheap ones turn skies green at maximum strength.
What to buy first
Start with a 6-stop fixed ND in your most-used filter size (usually 77mm, 82mm, or 67mm). One filter handles 80 percent of landscape long-exposure work and runs 80 to 150 dollars from a quality brand. Use a step-up ring to fit it to smaller lenses.
Add a 10-stop ND second. The big-stop filter unlocks daytime cloud-streak photography and 30-second ocean shots. Budget 100 to 180 dollars.
Add a variable ND third, only if you shoot video or you change shooting conditions often. Variable NDs for stills are a luxury, not a necessity.
For more on filters that affect color and reflection rather than just light volume, read our polarizer use guide. And for the broader question of whether a UV filter belongs on your lens at all, see our UV filter debate breakdown.
Frequently asked questions
What does an ND filter actually do?+
It reduces the amount of light reaching the sensor without changing color or contrast. Think of it as sunglasses for your lens. The reduction is measured in stops. A 3-stop ND cuts light by a factor of 8. A 6-stop cuts by 64. A 10-stop cuts by 1024. The lower light level lets you use slower shutter speeds or wider apertures than the scene would otherwise allow.
Why would I want a slower shutter speed?+
Motion blur. Waterfalls turn to silk at 1 to 4 seconds. Ocean waves blur to mist at 30 seconds. Moving clouds streak across the sky at 60 seconds. Crowds disappear from busy streets at 2 minutes. None of these effects are reproducible in post-processing because the camera never captured the motion. An ND filter is the only way to record those looks.
What is a variable ND filter and is it worth it?+
A variable ND is two polarizing filters stacked on a rotating ring. As you turn the outer ring, the polarizers cross more and reduce more light. Cheap variable NDs introduce a dark X pattern across the frame at strong settings and cause color shifts. Good ones (Polar Pro Quartzline, Nisi True Color, Breakthrough X4 ND) handle 2 to 6 stops cleanly and are excellent for video where you change settings often.
Do I need a tripod for long exposures?+
Almost always. Any exposure longer than 1/60 second with a heavy lens, or 1/15 second with a light setup, will show camera shake when handheld. ND filter work usually means exposures of 1/2 second to 2 minutes, which require a sturdy tripod, a remote release or 2-second self-timer, and ideally mirror lockup or electronic shutter to eliminate vibration.
What stop strength should my first ND filter be?+
A 6-stop ND is the most versatile single filter. It handles waterfall blur in bright daylight, smooths fast-moving water in shade, and gives you 30 to 60 second exposures during golden hour. Add a 10-stop later for daytime long exposures of clouds and waves. A 3-stop is too weak for serious daytime work and only earns its slot in your kit for video shooting.
Jamie Rodriguez
Jamie Rodriguez writes for The Tested Hub.