Filter coating

 Band Pass (narrow) and Band Pass (wide) coatings are used to create a type of wavelength selection filter operational over a specified wavelength band from the UV to the far IR. A Band Pass Filter allows only the wavelengths in the specified range to pass through the filter, while blocking wavelengths outside of the transmission region with high rejection ratio. A Band Reject Filter blocks a specific wavelength range with high rejection ratio, while transmitting wavelength regions on either side of the rejection region.Attenuating Filter Coatings, at the most basic level, are thin film coatings, which reduce the amount of light energy transmission in an optical system. For static applications, a fixed ND (neutral density) filter provides a constant level of transmission over a wide wavelength band. A more complex variable (or gradient) filter provides a density change over a custom defined region. The variable function can be defined as linear, circular, or radial and in either in a continuous or step pattern.

Coating curve