ND filters work by attenuating the light passing through them. They are usually made of optical glass or plastic, coated with a neutral density material that absorbs a specific percentage of light. The degree of attenuation is measured in optical density (OD), with higher OD values indicating greater light reduction. For example, an ND filter with OD 1 reduces the light intensity by 90%, while OD 2 reduces it by 99%.
