On Wed, 12 Feb 1997, Rui Malho wrote:
>escence. You need an optical section so you're not going to open the
>pinhole.
> So ideally what you want is a detector which allows you to pick up a
>similar signal (with a better signal-to-noise ratio) but with a lower
>laser power. In this case, you have to depend on your gain (or voltage
> applied to the PMT) to adjust the intensity of the signal. Shouldn't
>then the sensitivity of the PMT be related with the gain settings ?
Following the discussion, I've noticed that the term PMT gain and
PMT voltage are somewhat interchanged. My understanding was that the
parameters that can be controlled are PMT voltage and amplifier gain.

What is meant by PMT gain?

I don't know what the "gain" knob actually controls in the MRC 600.

However, in the Zeiss LSM 410, PMT voltage and amplifier gain can be
controlled separately (both from software). With a constant PMT voltage,
(and a properly adjusted dark current, called "brightness") image
intensity varies linearly with the gain. By collecting images at different
amplifier gains, one can thus virtually expand the 0-255 integer range
just by correcting for the change in gain.

Image intensity vs. PMT voltage not only is not linear but also changes
the noise characteristics (from gaussian at low voltages to Poisson at
high voltages).

Regards,

Carlos