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>Dear Guy,
>
>Just to make it more precise: You can do APD-imaging also with a 
>Zeiss-confocal if you have the ConfoCor3 FCS/FCCS setup. IT works 
>very nicely and gives you indeed a huge signal increase.
>
>Cheers    Gabor
>
>--
>Gabor Csucs Light Microscopy Centre, ETH Zurich
>Schafmattstrasse 18, HPM F16 CH-8093, Zurich, Switzerland
>
>Web: www.lmc.ethz.ch
>Phone: +41 44 633 6221
>Fax: +41 44 632 1298
>e-mail: [log in to unmask]

I agree that ConFoCOr seems an appropriate use: the signal level is 
very low indeed. And the contrast is basically the presence or 
absence of a single fluorophor in the spot.

The STED also is noted for low signal levels as most of the 
excitations are "entrained" by stimulated emission to go away from 
the detector.  On the other hand, even with a 30MHz counter you can 
conceivably count up to about 20 pulses in a microsecond, before the 
pileup losses become too obvious to the eye, while a faster circuit 
or a longer pixel-dwell time allow you to count proportionally more.

Cheers,

Jim P.
-- 
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3D Microscopy of Living Cells Course, June 14-26, 2008, UBC, Vancouver Canada
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	       "If it ain't diffraction, it must be statistics." Anon.