The angle of incidence (θ) in the image is the angle between the incoming collimated light and the normal to the surface of the filter.
How the angle of incidence affects filter performance:
Transmission: The amount of light that passes through the filter (transmission) can be affected by the angle of incidence. Generally, filters are designed to have maximum transmission when the light is incident perpendicularly (θ = 0 degrees). As the angle of incidence increases, the transmission may decrease, especially for filters with high optical densities or complex coatings.
Polarization: The polarization of the transmitted light can also be influenced by the angle of incidence. Some filters, such as polarizing filters, are designed to selectively transmit light based on its polarization. The polarization properties of these filters can vary with the angle of incidence.
Angular dependence of filter properties: Certain filter properties, such as spectral transmission or optical density, may vary with the angle of incidence. This is particularly true for filters with complex coatings or structures.
Scattering and reflection: As the angle of incidence increases, the amount of light that is scattered or reflected by the filter's surface may also increase. This can reduce the overall efficiency of the filter and introduce unwanted background noise.
