Bang Labs sells beads that are coupled with dye to various
extents.  I got three bead types that had an intensity range of about
50 fold.  Then I made up slides with a  mixture of beads dried onto
the slide and a coverslip and mounted one on the other with a spacer
in between.  With this slide, I then did a number of tests.  First, I
measured the power level at the stage with a laser power meter with
no lens in the turret of the microscope at a laser/AOTF setting where
I could just image the brightest or dimmest beads.  With this measure
I was able to get an idea of the relative sensitivity of two
different confocal systems.  This is not terribly accurate, but the
three I compared were in the same ballpark of sensitivity.  As a
rough idea of dynamic range, I determined whether I could measure the
different intensity beads at the same time.  The brighter bead was
imaged so it was just under saturation and the ability to image
dimmer beads at the same time was determined.  Another test I did not
have time to do extensively, but should be informative is to look at
the Z profile of the beads on the coverlip surface as opposed to
those at the slide surface.  This should give a good indication of
how well the optics are dealing with the refractive index mismatch
between mounting media and immersion oil.  You can compare water
lenses to oil lenses and the effect of different mounting media with
this approach.
        I have harped on this issue before, but I will restate, since
it was the critical test I did not do, and bought the wrong system as
a result.  Most confocal systems allow adjustment of the Z section
depth by adjusting the pinhole diameter.  This is not true of the
Leica systems.  You can only change the Z depth by about 30% as
opposed to 300% for others.  For live cell imaging I find it critical
to be able to trade off confocality against more photons (and happier
cells) by playing with the pinhole size.  You simply cannot do this
with the Leica making it a poorer choice for live cell imaging IMHO.
--
Permanent Address
Dr. David Knecht
Department of Molecular and Cell Biology
University of Connecticut
75 N. Eagleville Rd.   U-125
Storrs, CT 06269-3125
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home page: http://www.sp.uconn.edu/~mcbstaff/knecht/knecht.html

Current Address 9/01-8/02
Dr. David Knecht
School of Biosciences
The University of Birmingham,
Edgbaston,   Birmingham,
B15 2TT,    U.K.
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