Features
An ND (neutral density) filter attenuates the amount of incident light by a certain amount and is used to compensate for camera and sensor sensitivity. It can obtain a flat transmittance spectrum in the desired wavelength band. We can manufacture this filter for each wavelength band from ultraviolet to infrared.
ND filters come in two types, reflective and absorbent. The reflective-type has a multilayer dielectric film coated on a glass substrate. The absorbent-type has a metal film with light absorbing characteristics coated on a glass substrate.
We can also make a non-reflective ND filter that suppresses the reflection of incident light on the substrate surface.
ND filter characteristics are indicated by transmittance or optical density (OD).
The relationship between transmittance (T%) and OD is as follows.
Applications
Dimming light source, sensor sensitivity correction, cameras
Example characteristics
These are the characteristics of standard absorbent ND filters.
Flat and with transmittance in the visible light range of 10%, 30% or 50%.