ND 3.6

Overview

"ND 3.6" is not a device or manufacturer designation, but an indication of Neutral Density. The number 3.6 is the value of optical density. Neutral density filters and ND gels reduce the amount of light uniformly across the visible spectrum without changing the color temperature – they act like "gray sunglasses" for the camera or light source.

With a density of 3.6, ND 3.6 is at the very strong end of the scale. More common in sets are graduated values of 0.3 / 0.6 / 0.9 / 1.2 (1 to 4 stops). A value of 3.6 is significantly denser and is usually achieved – if needed at all – by stacking multiple filters or gels.

Technical Classification

There is a fixed mathematical relationship between optical density, stops, and transmission:

• Stops ≈ Density ÷ 0.3 (more precisely ÷ 0.301)
• Transmission = 10^−Density

For ND 3.6, this results in:

Each additional density of 0.3 halves the light (one stop). Therefore, ND 3.6 allows only a minuscule fraction of the incident light to pass through.

On-Set Usage

Such extremely high ND values are used to control very bright lighting situations – such as direct sun or glaring windows – in order to still be able to shoot with an open aperture (for shallow depth of field) or with a specific shutter speed. Two typical applications are distinguished:

• In front of the lens: as an ND or IRND glass filter (e.g., in matte box format like 4x5.65"). With digital sensors, IRND filters are usually used at high densities to avoid infrared contamination and thus color casts.
• In front of the light source or at the window: as an ND gel from manufacturers like Rosco or Lee, to reduce daylight coming through windows to the interior level.

A density of 3.6 is an extreme value: single filters of this strength are rare; in practice, the value is often achieved by combining multiple ND grades. When stacking, the densities add up (e.g., 1.2 + 1.2 + 1.2 = 3.6).