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Filmmaking Dictionary: Number 0 / 0.3 ND
Definition
0.3 ND is a neutral-density filter strength that reduces the light reaching the camera by approximately one stop. It transmits about half the incoming light. With the lighting and camera settings unchanged, adding it makes the recorded image one stop darker.
The number 0.3 describes optical density. It does not mean 0.3 stops, a 30% reduction or the filter’s physical thickness. On a filter that uses the filter-factor scale, the equivalent strength is commonly labelled ND2.
What Changes When You Add 0.3 ND?
A one-stop ND gives the camera department a small exposure adjustment without having to change the lighting, shutter setting or chosen ISO. To keep the same exposure after inserting it, open the lens by one stop. For example, an exposure of f/4 without ND becomes approximately f/2.8 with 0.3 ND.
- Optical density: 0.3.
- Nominal reduction: one stop.
- Approximate transmission: 50%.
- Common filter-factor label: ND2.
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Example on Set
A close-up is correctly exposed at T4, but the cinematographer wants T2.8 to reduce depth of field. Inserting 0.3 ND and opening to T2.8 keeps the subject at roughly the same recorded brightness while changing the lens aperture. The shutter angle and frame rate can stay where they were.
The filter has not softened the light or changed the lighting ratio. It has reduced the exposure of the whole image. A bright window remains brighter than a face by approximately the same amount, unless another part of the setup changes.
When One Stop Is Useful
- Fine exposure adjustments: Moving between light levels that do not require a large density change.
- Matching an aperture: Keeping coverage near a chosen working stop as daylight changes.
- Preserving motion blur: Reducing exposure while retaining the selected shutter setting.
- Combining densities: Adding a nominal one stop to another compatible fixed ND filter.
Stacked optical densities add. A 0.3 and a 0.6 ND together give a nominal 0.9 density, or three stops. Extra glass can introduce reflections, flare or vignetting, so a single suitable filter is often the cleaner practical choice.
Common Mistakes
Do not confuse 0.3 ND with an ND3 filter-factor label, or assume that a variable ND’s markings use the same scale. Read the manufacturer’s stated stop reduction. Also check the image after a filter change: real filters can produce small exposure or colour differences.
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Frequently Asked Questions
Will 0.3 ND create shallow depth of field?
The filter itself does not change depth of field. It lets you open the aperture while maintaining exposure, and that aperture change affects depth of field.
Is 0.3 ND enough for bright sunlight?
Only if the required correction is about one stop. The necessary density depends on the light, lens aperture, shutter and camera sensitivity.
Related Terms
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