Filters are frequently utilized in optical microscopy, both for visualization of specimens and for photomicrography. This interactive Java tutorial explores the visible light spectral characteristics of the major types of filters used in microscopy.
To operate the tutorial, use the Choose A Filter pull-down menu to select a filter type, and a typical visible light absorption spectrum for that type of filter will be displayed in the applet window. After the filter has been selected, use the Wavelengths Passed slider to move the absorption spectrum back and forth in the visible region to view the range of spectral characteristics available for that type of filter. The wavelengths passed by the filter are listed below the slider.
The following filters are described in this tutorial:
Short Wavelength Pass - Filters in this class are almost exclusively interference filters. They transmit visible light of lower wavelengths and block light with higher wavelengths.
Long Wavelength Pass - This class of filters allows light of longer wavelengths to pass through the filter. Long wavelength pass filters effectively block shorter wavelengths, and are used primarily as barrier filters in fluorescence microscopy. Together with short wavelength pass filters, these filters can be combined to pass defined bands of wavelengths.
Band Pass Filters - Able to transmit one particular region (or band) of the visible or ultraviolet light spectrum, these filters usually have rather broad transmission characteristics (they pass a significant number of wavelengths). Band pass filters are used extensively in fluorescence microscopy.
Sharp Cutting - Similar to short and long wavelength pass filters, sharp cutoff filters have a very short transition region of wavelengths that are blocked and passed. These filters can be used to eliminate specific spectral regions with great accuracy when compared to short and long wavelength pass filters.
Broad Band Filters - Broad band filters have spectral characteristics that are essentially reversed from those of band pass filters. They pass only a very narrow region of wavelengths and block a majority of visible light incident upon the filter surface.