What is a bandpass filter?


A bandpass filter is an optical filter that is only permeable to light within a certain wavelength band. Outside this transmission band, it blocks the incident light. The width of the passband is typically in the order of one to several hundred nanometers. Bandpass filters are available both as interference filters and as coloured glass filters.

In addition to the appropriate transmission band, attention must also be paid to the actual blocking band in which the filter allows small fractions of light to pass. The degree of blocking is usually given as optical density (OD); the higher the optical density, the higher the quality of the bandpass filter. Fluorescence microscopy, for example, requires bandpass filters with very good blocking in the blocking band.

How does a bandpass filter work?

A bandpass filter only allows incident light to pass in a certain wavelength band and blocks the light outside this band.

What are bandpass filters used for?

Bandpass filters are required, for example, for fluorescence microscopy.

How is a band pass filter specified?

In the case of a bandpass filter, important specifications are the transmission band (i.e. the wavelength range within which the filter is permeable to light), the actual blocking band and the optical density.