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I think I may have stated our situation unclearly.  Our PMT 1 is 70%
less sensitive than PMT 3 when viewing reflected laser light from a
front face mirror regardless of the wavelength of detection.  In other
words, our PMT 1 is ~70% less sensitive than PMT 3 at 488nm as well as
633nm.  PMT 2 is about 35% less sensitive than PMT 2 at both ends of the
detection spectrum.
    Has anyone recorded signal intensity values for new/working PMTs at
particular gain/offset settings for reflected laser light of known power
output at the objective?  I would like to determine if PMT 3 (our best
PMT) is performing up to par or if it is performing poorly and happens
to be the best of our PMT's at the moment.
    I might be able to understand a 7% discrepancy between PMT signal
values, but  70% makes me wonder.
    Thanks to all for your constructive input.
Best Regards,
Karl

Karl Garsha wrote:

> Search the CONFOCAL archive at
> http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>
> Greetings,
> Has anybody determined a benchmark for evaluating PMT sensitivity on the
> SP-2 platform?  I've recently discovered that our PMT 1 is showing
> roughly 30% of the sensitivity of PMT 3 and PMT 2 is showing 65% of the
> sensitivity of PMT 3 (at either end of the spectrum).  This is a little
> alarming and I would like to determine whether PMT 3 is in fact
> performing well or if the sensitivity is down for it as well.  Thanks in
> advance for any suggestions.
> Cheers,
> Karl G.