Bandpass
Bandpass filters only transmit a certain wavelength band, and block others. The width of such a filter is expressed in the wavelength range it lets through and can be anything from much less than an Ångström to a few hundred nanometers. Such a filter can be made by combining an LP- and an SP filter.
Examples of bandpass filters are the Lyot filter and the Fabry-Pérot interferometer. Both of these filters can also be made tunable, such that the central wavelength can be chosen by the user. Bandpass filters are often used in astronomy when one wants to observe a certain process with specific associated spectral lines. The Dutch Open Telescope and Swedish Solar Telescope are examples where Lyot and Fabry-Pérot filters are being used.
Read more about this topic: Filter (optics)