Every ND Filter Combination You Will Ever Need: A Reference Guide by Stop

The Set That Had Every Filter Except the Right One

A gaffer on a bright exterior commercial had a full set of Tiffen IRND filters: ND 0.3, ND 0.6, ND 0.9, ND 1.2, and ND 1.8. The DP needed 5 stops of ND to shoot at T1.8 in full sun at 24fps with a 180-degree shutter. The 1.8 is 6 stops. The 1.2 is 4 stops. There was nothing rated at exactly 5 stops.

The solution was to stack the ND 0.9 (3 stops) and ND 0.6 (2 stops): 3 + 2 = 5 stops. But the gaffer was not sure whether stacking added stops arithmetically, and the director was waiting. The DP confirmed the math, the stack went on, the shot was made. But the 90-second delay came from a gap in nomenclature literacy, not from a lack of equipment.

This post is the reference guide that covers all three ND labelling systems, converts between them, and gives you every stacking combination you are likely to need on set.

The Three Labelling Systems

System 1: Optical Density (OD) Notation

The most mathematically consistent system. Optical density is a base-10 logarithm of the opacity factor. ND 0.3 means the filter transmits 10^-0.3 = 50% of incident light. ND 0.6 = 10^-0.6 = 25%. ND 0.9 = 10^-0.9 = 12.5%.

To convert OD to stops: stops = OD / 0.3 (because each stop halves the light, and log10(2) = 0.301).

This system is used by Tiffen, Schneider, and most professional filter manufacturers. It is the standard on matte box filters and on cinema camera built-in ND systems (ARRI, RED, Sony FX3 IRND selections).

System 2: Multiplier Notation (ND2, ND4, ND8...)

Older notation common on consumer and prosumer circular filters and some camera spec sheets. The number indicates how many times darker the filter makes the exposure. ND2 = 1 stop (2x darker), ND4 = 2 stops (4x darker), ND8 = 3 stops, ND64 = 6 stops.

To convert multiplier to stops: stops = log2(multiplier) = 3.321928 x log10(multiplier).

This system is common on Hoya, Kenko, and budget circular filters, as well as on older Cokin filter designations.

System 3: Stops Notation (colloquial)

Simply calling the filter by its stop count: "a 3-stop ND," "a 6-stop ND," "a 10-stop." Common in on-set verbal communication and in product marketing (especially for screw-in variable NDs). No conversion needed -- it is already in stops.

The Master Reference Table

The table below converts between all three systems for every common ND value. Use this to cross-check what filter you actually have and what it does.

Note: ND1000 is sometimes sold as a 10-stop filter and sometimes as a 9.97-stop filter (because ND 3.0 = 1,000 exactly, and 2^10 = 1,024, not 1,000). The difference is 0.03 stops, which is not meaningful in practice.

Stacking Combinations: 1 to 16 Stops

When you need a stop count not available as a single filter, stack two filters whose optical densities (or stop counts) add up to your target. With optical density notation, stacking is additive: ND 0.9 + ND 0.6 = ND 1.5 = 5 stops. With stop counts, they add directly: 3 stops + 2 stops = 5 stops.

The table below shows the minimum-filter-count combinations from a standard pro kit (ND 0.3, ND 0.6, ND 0.9, ND 1.2, ND 1.8, ND 2.1) to achieve every stop count from 1 to 16.

Stacking more than two filters introduces image quality concerns (internal reflections between filter surfaces, slight colour cast accumulation, and increased flare). For practical production, stacking is acceptable for 1 to 2 additional filters. For 10 or more stops in a matte box system, a single ND 3.0 is preferable to a stack.

How Many Stops Do You Actually Need?

The Sunny 16 rule gives a starting point for outdoor daylight. At 24fps with a 180-degree shutter: the correct shutter speed is approximately 1/48s. At ISO 100 in direct sunlight, correct exposure is approximately f/16 at 1/100s (or f/11 at 1/48s for cinema). To open up to a wide aperture for shallow DoF, calculate the stop difference:

In overcast daylight, available light is typically 1 to 2 stops lower than direct sun. In open shade, 2 to 3 stops lower. Adjust the table by reducing the required ND density accordingly.

The ND Filter Calculator computes the required ND for any combination of ambient EV, target aperture, shutter speed, and ISO. For on-set use, running the calculation before each exterior setup confirms exactly which filter combination to reach for.

Variable ND Filters: Pros, Cons, and the X-Pattern

Variable ND filters (sometimes called VND filters) use two polarising elements that rotate relative to each other to produce a continuously adjustable density from approximately 2 stops to 10 stops in a single filter. Popular products include the Tiffen Variable ND, the Syrp Variable ND, the Schneider True-ND, and built-in variable ND on cameras like the Sony FX series.

Advantages: One filter replaces 4 to 6 individual filters. Quick adjustment in changing light conditions. Minimal matte box space required.

Disadvantages: Colour cast, particularly in the magenta shift direction, is common at high density settings on lower-cost variable NDs. The "X-pattern" or "cross-polarisation" effect appears as an X-shaped darkening across the frame at maximum density settings, caused by over-rotation of the polarising elements. All variable NDs have a minimum density -- they cannot be fully removed without taking the filter off -- and at their minimum setting (often ND 0.6 to ND 0.9), they still remove 2 to 3 stops of light even when you want none.

For high-quality variable ND, the Tiffen Nat'l Density, Schneider True-ND, and ARRI's built-in NDs minimise colour cast and cross-polarisation. For matte box applications, individual fixed NDs remain the benchmark for colour neutrality and image quality.

IRND vs. Standard ND: Does It Matter?

Standard ND filters block visible light but may pass near-infrared radiation, which digital sensors are sensitive to. In strong sunlight, IR contamination from a standard ND can produce a pinkish colour cast in dark areas of the image (particularly in foliage) -- the so-called "IR pollution" effect.

IRND (Infrared Neutral Density) filters block both visible and near-IR radiation. For digital cinema cameras without strong internal IR-cut filters, IRND is the correct choice for outdoor use. Most professional cinema matte box filters from Tiffen, Schneider, and Lee are now manufactured as IRND as standard. When purchasing used filters or working with older filter sets, confirm whether the filters are ND or IRND. For interior work where IR pollution is not an issue, standard ND is sufficient.

Pro Tips and Common Mistakes

Pro Tip: Label every filter in your kit with its stop count in addition to its optical density marking. Write "3 stops / ND 0.9" in white paint marker on the filter frame. On a fast-moving set, a gaffer or AC reaching for a specific filter in dim conditions will grab the right one in one motion if the stop count is clearly visible.

Pro Tip: Test your ND filter stack for colour cast before any critical exterior shoot by shooting a grey card or colour chart at each density combination you plan to use. If a warm or cool shift appears, note the amount (in Kelvin) and correct it in the camera's white balance offset or in colour grading. Knowing the cast before the shoot eliminates surprises on set.

Pro Tip: For cameras with electronic variable ND built in (Sony FX3, FX6, FX9, VENICE 2), the internal ND system is designed to produce minimal colour shift and avoids the IR contamination issue. On these cameras, external ND is only needed when the internal range is insufficient. Sony's internal IRND on the FX9 covers ND 0.3 to ND 1.8 (1 to 6 stops), which covers most practical outdoor cinematography scenarios without a matte box.

Common Mistake: Using ND filter density numbers from two different systems as if they are comparable. ND 0.9 and ND9 look similar but are very different: ND 0.9 is 3 stops; ND9 does not exist as a standard optical density value and is likely a mis-labelling. When a filter is labelled with a single digit under 10 without a decimal point (ND3, ND6, ND9), it is the multiplier system -- ND3 is less than 2 stops, ND6 is approximately 2.5 stops. Confirm which system the label uses before calculating.

Common Mistake: Stacking filters without checking for vignetting. On ultra-wide lenses (16mm and shorter on Super 35), the filter holder and stacked filter frames may vignette the corners of the frame at some apertures. Test for vignetting by shooting wide open at the widest lens in the kit with the full filter stack before the shoot begins.

Frequently Asked Questions

Do ND filters affect depth of field?

No, not directly. ND filters reduce the amount of light reaching the sensor without changing the aperture. If you add an ND filter and then open the aperture to maintain exposure, the wider aperture changes the DoF. But the filter itself has no optical effect on the image geometry -- only the aperture does.

What does the 1/3-stop ND 0.1 filter do?

ND 0.1 reduces light by approximately 1/3 stop, transmitting approximately 79% of incident light. It is used for minor exposure fine-tuning rather than large density changes. Few productions carry ND 0.1 as a standalone filter, but some graduated ND sets include it. For cinematography, 1/3-stop corrections are more commonly made with ISO adjustment or minor aperture moves.

Can I use a circular polariser as an ND substitute?

A circular polariser reduces light by approximately 1.5 to 2 stops (it removes light from certain polarisation angles). It is not a neutral density filter -- it also changes the colour of specular reflections and the saturation of blue skies. On a bright exterior where you need 2 stops of reduction and are also managing reflections on water or glass, a polariser works for both simultaneously. As a pure ND substitute, the colour and reflection effects make it unsuitable.

How should I store ND filters to prevent coating damage?

Store each filter in its individual case or pouch, not stacked against other glass without protection. Matte box filters with soft coatings can scratch if stored in contact with other filters or if cleaned with abrasive materials. Use a lens pen or microfibre cloth designed for coated optics. Avoid storing IRND filters in direct sunlight for extended periods, as UV exposure can degrade some coatings over time.

Related Tools

The ND Filter Calculator computes the required ND density from ambient EV, target aperture, shutter speed, and ISO -- giving you the specific filter combination to pull from the case rather than doing the arithmetic on set. For the full exposure calculation that puts the ND requirement in context, the Exposure Triangle Calculator shows how aperture, shutter, and ISO interact with each other and with your available light.

For the full workflow of setting exposure before and after ND is applied, Understanding Exposure for Cinematographers covers the triangle and ND in an integrated system. For situations where you need wide aperture in bright light but also want zone focus coverage, Zone Focusing for Filmmakers covers how aperture choice interacts with the DoF zone you have available.

Bookmark This Page Before Your Next Exterior Shoot

ND filter nomenclature is unnecessarily fragmented across three labelling systems because different manufacturers adopted different conventions at different times. The table in this post is the Rosetta Stone: enter with the label printed on your filter and exit with the stop count, no calculation required. The stacking table gives you every combination achievable with a standard pro kit. The exposure scenario table tells you which filter to reach for in direct sun. The only thing left is to test your specific filters for colour cast before any production you plan to use them on.

This post covers still neutral density filters for production cinematography. Graduated ND (GND) filters and special-effect graduated filters involve additional positioning and alignment considerations not covered here. Which filter combination have you most often had to improvise on location, and how did the stacking work out?