Yes, Christian Lohr makes an extremely important point here regarding
comparisons involving the Leica SP.  The slit diameter in front of the
detectors (NOT to be confused with the pre-detector pinholes in other
systems) is variable - a blessing (very selective in terms of wavelengths
that are allowed to reach the detector) and a bane (cuts down on total
photon flux when set at a narrow, selective setting).


>In addition, I find at difficult to compare the sensitivity of the two
>systems. Especially in the SP system, the laser power you need to obtain
>a certain fluorescence intensity depends much on how narrow you set the
>spectrometer slits in front of the PMTs, i.e. how much of the tails of
>the emission spectra you cut off (to avoid background, cross talk etc.).
>Differences between the sensitivities of a filter system (Zeiss) and the
>filterless SP system (Leica) may also depend on the prep and the dye
>combination (does the filter system match the spectra of the dyes, does
>cross talk occur?) or the lenses (NA).
>From what I have in mind, when we were in the same situation as you and
>had to choose between Leica and Zeiss last year, we did not notice a
>significant difference in the sensitivity using our preps
>(Alexa-488-filled neurons in leech ganglia).
>