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Filmmaking Dictionary: Number 0 / 0.9 ND
Definition
0.9 ND is a neutral-density filter strength that reduces exposure by approximately three stops. It transmits about one eighth of the incoming light. The equivalent filter-factor designation is commonly ND8.
In camera-department conversation, a request for “an ND nine” may refer to 0.9 optical density. Confirm the intended strength when the wording is unclear: density, filter factor and stops are different numbering systems.
Understanding the Numbers
| Optical density | Nominal reduction | Approximate transmission |
|---|---|---|
| 0.3 ND | 1 stop | 1/2 |
| 0.6 ND | 2 stops | 1/4 |
| 0.9 ND | 3 stops | 1/8 |
The 0.9 value does not mean 90% of the light is removed. Three stops leaves roughly 12.5% and removes roughly 87.5%. These are practical rounded values; actual transmission depends on the filter and wavelength.
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Exposure Example
An exterior shot is correctly exposed at f/8 without ND. The cinematographer wants f/2.8. Opening from f/8 to f/5.6, then f/4 and finally f/2.8 adds three stops. Inserting 0.9 ND offsets that change while allowing the wider aperture.
If the aperture stays at f/8 instead, the filter simply makes the image three stops darker. ND only maintains the original exposure when something else compensates for its light loss.
Uses in Film and Video
- Controlling depth of field: Makes a wider aperture possible at the selected exposure.
- Keeping a consistent shutter: Avoids using a faster shutter merely to reduce brightness.
- Managing changing daylight: Provides a predictable density step when the scene becomes brighter.
- Working at a selected camera sensitivity: Reduces incoming light without requiring an ISO change.
Three stops is not automatically enough for a sunny exterior. A camera at a high base ISO, a wide-open lens and a conventional motion-picture shutter may need considerably more density. Determine the required reduction from the actual exposure.
Checks After a Filter Change
Look for colour shifts, flare, internal reflections and vignetting. A filter described as neutral is intended to reduce visible light evenly, but real products and camera systems differ. Stronger combined filtration can also make infrared contamination more apparent on susceptible cameras; use the filtration specified for the camera and job.
Keep track of the full filter stack. A 0.9 ND combined with a 0.3 ND gives a nominal 1.2 density, or four stops. A diffusion filter or polarizer may add exposure loss that is not expressed on the same density scale.
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Frequently Asked Questions
Are ND8 and 0.9 ND the same strength?
Usually, when ND8 is a filter-factor label. Both indicate approximately three stops. Confirm the product’s stated stop rating.
Does 0.9 ND make the lighting softer?
No. A solid camera ND reduces exposure. Diffusion and the size and placement of the light source control softness.
Related Terms
Browse all terms starting with 0 or return to the filmmaking dictionary.