128 BD LSR II User’s Guide
Even though an optical filter is rated at its 50% transmission point, the filter
passes—or lets through—a minimal amount of light outside of this indicated
rating.
The slope of an optical filter transmission curve indicates filter performance. A
relatively steep slope indicates a high-performance, high-quality optical filter that
provides deep attenuation of out-of-band wavelengths. A less steep slope
indicates that more light outside the rated bandwidth is being transmitted.
Two kinds of filters are used on the BD LSR II flow cytometer:
• longpass (LP)
• bandpass (BP), including discriminating filters (DF) and ALPHA filters
(AF)
A third filter type, the shortpass (SP), is not recommended, but can be used in
some custom configurations. See Shortpass Filter on page 129.
LP, BP, and SP filters are referred to as dichroic filters. See Dichroic Mirrors on
page 131.
Longpass Filter
LP filters pass wavelengths longer than the filter rating. For example, a 500-LP
filter permits wavelengths longer than 500 nm to pass through it and either
absorbs or reflects wavelengths shorter than 500 nm.
wavelength (nm)
% transmission
longpass
LSR2.book Page 128 Tuesday, April 25, 2006 3:34 PM
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