Phil Marder writes: >Speaking of fiber optics.... > I seem to remember about 20 yrs ago that some Ortho instruments used >fiber optic collection schemes. Howard, or anyone else, please >refresh our memories on how these worked and why they were dropped by >the manufacturers. > The Ortho System 30 and System 50 instruments, which appeared in 1978, had provision for more PMT's than most contemporary commercial flow cytometers. They didn't use fiber optics to collect light; short lengths of fiber were, instead, used as relays, allowing the PMT's to be placed farther away from the flow cell and other optics than they might have otherwise and reducing crowding of components. A metal plate with a small hole in it was located in the plane at which an image of the observation point was formed; the bandpass filter was placed in front of the plate, and the light in the wavelength region selected by the filter was collected by a Crofon plastic (N. A. 0.54) fiber optic and relayed to the PMT. Light loss was low, although polarization was not preserved. If you tried to put the filters behind the fiber, it wouldn't work because stray excitation light would induce fluorescence in the plastic fiber. The fibers didn't gain anything optically; as I said, they would prevent doing polarization measurements, in which some folks were interested back then. So, manufacturers don't see much reason to use them. Fibers have been advocated as collection and relay elements for miniaturized (not-quite-cytometer-on-a-chip) systems, but, in my experience, systems without fibers work at least as well as systems with them. -Howard
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