ND filters neutrally reduce the amount of light and enable longer exposure times in bright light to create effects such as motion blur or bokeh. They are specified by ND factor, stops, and optical density. Variable ND filters offer flexibility, while fixed-value filters provide better quality. Screw-in and drop-in systems are common mounting methods. Practical tip: Set focus before attaching the filter, and calculate the exposure time using a formula or app.
Category: Photography – Advanced Topics > 12. Camera & Technology – In-Depth Article ID: 12.6 Created: May 2026
Key Takeaways
- ND filters (Neutral Density) reduce the amount of incoming light without changing the colors, enabling longer exposure times in bright light
- Density is specified as an ND factor (ND2, ND8, ND1000), stops, or optical density—three different scales for the same thing
- Typical applications: silky water, light trails during the day, and wide apertures in bright light
Explanation
What Does an ND Filter Do?
An ND filter is gray-tinted glass that evenly reduces light across all wavelengths—hence “neutral” (no color shift). This allows:
- Longer exposure times in bright daylight → create motion blur when no other option is available
- Wide apertures in very bright light → achieve bokeh even in midday sun
- Creative long exposures during the day: clouds become streaks, water becomes silky, and people disappear from city scenes
The Naming Systems—Confusing but Solvable
ND filters are designated using three different systems. They all mean the same thing:
| ND Factor | Stops | Optical Density (OD) | Light Reduction |
|---|---|---|---|
| ND2 | 1 Stop | OD 0.3 | 50% |
| ND4 | 2 Stops | OD 0.6 | 75% |
| ND8 | 3 Stops | OD 0.9 | 87.5% |
| ND16 | 4 Stops | OD 1.2 | ~94% |
| ND64 | 6 Stops | OD 1.8 | ~98% |
| ND400 | ~8–9 Stops | OD 2.7 | ~99.8% |
| ND1000 | 10 Stops | OD 3.0 | 99.9% |
| ND100000 | 16–17 Stops | OD 5.0 | ~99.999% |
ND1000 (10 Stops) is the most commonly recommended all-purpose filter: In sunlight, it enables exposure times ranging from several seconds to minutes.
Which ND Filter for Which Application?
| Application | Recommended Strength | Reason |
|---|---|---|
| Wide aperture in sunlight | ND8–ND64 (3–6 Stops) | Sufficient to expose correctly at f/1.8 |
| Soften a waterfall (1–2 s) | ND8–ND64 | Short to medium exposure time |
| Remove people from a city scene (30 s+) | ND400–ND1000 | Very long exposure time required |
| Clouds as streaks during the day | ND1000 | Exposure lasting several minutes |
| Video (wide aperture, cinematic look) | ND4–ND32 | Maintain 1/50 s at 25 fps |
Calculating the New Exposure Time
Formula: New exposure time = Original exposure time × ND factor
Example: Without a filter: 1/500 s at f/8, ISO 100 With ND1000: 1/500 × 1000 = 2 seconds
Free apps are available for quick calculations in practice (e.g., “ND Timer” and “Long Exposure Calculator”).
Variable ND Filters vs. Fixed-Value Filters
Variable ND filters: Two rotating polarizing filters—the density is continuously adjusted by rotating them. Practical, but:
- At extreme settings, often color casts or an X pattern (cross-polarization)
- Significant quality differences between manufacturers
Fixed-value filters: A fixed density. More neutral color reproduction, but you need several for different situations. Better for critical quality.
Recommendation for beginners: A mid-range variable ND for flexibility; for serious work: fixed-value ND filters from quality manufacturers (B+W, Hoya, NiSi, LEE).
Filter Systems: Screw-In vs. Drop-In
Screw-in filters: Screwed directly onto the lens. Affordable and compact. Disadvantage: Each lens diameter requires its own filter or step-up ring.
Drop-in system (square filters): A holder is mounted on the lens, and filters are inserted into it. One filter set for all lenses. Better for professional use (NiSi, LEE, Cokin).
Practical Tip
Long-Exposure Checklist with an ND Filter:
- Set up the tripod and connect the remote shutter release
- Set the composition and focus without the ND filter (then lock focus/set it manually)
- Attach the ND filter
- Take the shot in Bulb mode or using a timer
- Calculate or test the exposure time using an app
Always set focus before attaching the filter—autofocus is not possible through dark ND1000 filters.