Appendix A: Technical Overview 113
Optical Filters
Optical filters modify the spectral distribution of light scatter and fluorescence
directed to the detectors. When photons encounter an optical filter, they are
either transmitted, absorbed, or reflected.
Figure A-6 Effect of an optical filter on incident photons
Two kinds of filters are used on the BD FACSCanto flow cytometer (default
configuration):
• longpass (LP)
• bandpass (BP)
Longpass Filter
In general, 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 (Figure A-7 on
page 114).
photons
transmitted
photons
reflected
photons
absorbed
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