Filters

Absorption Filters (Colour Filters)

Absorption filters (colour filters) function on the basis of choosing a glass recipe with chromophoric constituents which absorb a specific range of wavelengths. Typically these are long pass edge filters, but some bandpass types with limited functionality are available. Note that this filter type may fluoresce when used for blocking UV light.

Dielectric Filters (Interference Filters)

Dielectric filters (Interference Filters) absorb very little light. The functionality is based on reflection of the unwanted spectral regions based on optical interference within the layer structure of the filter coating. These filters can be manufactured for use in the UV, visible and IR. In order to reduce the number of coating layers – and thus the cost – a combination may be made by dielectric coating a colour (absorption type) glass substrate. This is common for some bandpass filters. The following table gives an overview of the main criteria for deciding between these two physical principles of filters. In addition, there are four basic functional types of filters. These are represented below as symbolic transmission curves as a function of wavelength:

Functional types:

We offer filters cut to any shape. Black anodized aluminium rings may be provided for ease of mounting.