Neutral-density optical filter
CVI Melles Griot
Light is absorbed rather than reflected.
No back reflections or scattering occur.
These filters are recommended for low-power applications because of their absorbing properties.
Absorptive ND filters provide an alternative to metallic ND filters. The neutrality of the filter is a function of material and thickness. Since there can be large variations between glass melts, actual thickness and glass material may vary in order to guarantee optical density.