Barrier Filter (Ba Filter) - Nikon ECLIPSE MA200 Instructions Manual

Chapter 3 Operation Details
3.19.3

Barrier filter (BA filter)

A barrier filter transmits only fluorescent lights emitted by the sample but blocks the excitation lights. This filter
makes it possible to observe the fluorescent image without unnecessary light (that is, on a dark background).
There are two types of barrier filters: LP filters (long-pass filters), which block all lights that are shorter than a
certain boundary wavelength and allow all lights to pass that are longer than the boundary wavelength, and
BP filters (band-pass filters), which allow only lights in a certain bandwidth to pass. The LP filter is a barrier
filter that is provided on the MA200.
The boundary to block or transmit lights using an LP filter is called the cut-on wavelength.
An excitation light is a light that is irradiated to the sample. The fluorophore in the sample absorbs the
excitation light energy. As a result, fluorescent lights are emitted from the fluorophore instead. When a sample
is labeled with a fluorophore that emits fluorescent lights of very close wavelengths to the excitation light,
select a barrier filter with the shortest cut-on wavelength permitted by performance requirements for efficient
fluorescent microscopy.
A longer cut-on wavelength tends to result in a more complete separation between an excitation light and
fluorescent lights, rendering a darker background of the fluorescent image. With the recent advancement in
filter performance, however, filters with shorter cut-on wavelengths can be used for this purpose and they are
used more often than before.
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Light source for the epi-fl microscopy
To perform the epi-fl microscopy, the standard light source (a halogen lamp) may not be able to provide the
sufficient brightness. In such case, attach an HG Precentered Fiber Illuminator (C-HGFI/ C-HGFIE) that uses
a mercury lamp as a light source to perform the episcopic illumination (refer to 3.22).
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