Know All About Longpass, Shortpass & Bandpass Filters!
Longpass filter is an optical filter or coloured glass that passes every wavelength from a given wavelength to the red of the wavelength. Emission filters are generally longpass filters. Usually, these filters transmit long wavelengths and block the short wavelengths. It can have a very sharp slope, normally referred to as edge filters, described by the cut-on wavelength at 50% of the absolute transmission.
You can see typical applications of longpass filters in fluorescence microscopy, cell biology microscopes and emission filters. In fluorescence microscopy, these filters are often used in dichroic mirrors and barrier filters. The term used to denote the wavelength location of the longpass filter is ‘cut-on’. It has brighter backgrounds as compared to bandpass filters.
Shortpass filters are specially designed to transmit shorter wavelengths than the longpass wavelength while rejecting longer wavelengths. It passes short wavelengths and blocks longer ones. They are also grouped as edge filters as it brings up to the steep cut-on and cut-off amid transmission and rejection. Also referred to as barrier filters as it rejects greater sections of long or short wavelengths. Applications of shortpass filters can be seen in longpass filters for custom bandpass filtering. Shortpass are often employed in fluorescence microscopy in dichromatic mirrors and excitation filters.
As in applications, both longpass and shortpass filters are used in precision spectroscopy as band separators. While in photometry these filters are applied as order sorting or blocking filters, which in course are used to a detector’s window to reject any further distortion. They are also used requently used in Raman spectroscopy.
Bandpass filters are an electronic circuit that allows only signals between specific frequencies to pass through and attenuates/rejects frequencies which are outside the range. These filters simply transmit a definite wavelength band and block remainders. The wavelength range is the calculation of the width of such a filter that lets through. The range can be anything from much less than an Ångström to a few hundred nanometers. Such a filter can be prepared by combining longpass and shortpass filters. Bandpass filters are created when there are applications wherever a particular band, or spread, or frequencies is required to be filtered from a wider range of mixed signals.
Bandpass filters are chiefly applied in wireless receivers and transmitters, and also in areas related to electronics. It is also frequently used in astronomy when there is a need to observe a certain process with specific associated spectral lines.
