I know that this response is a bit slow but Eric Hines said:
 
>  Guy Cox is correct re single mirror and when we tested all
>available brands we found the Leica to be the most sensitive on our
>samples. Note that BioRad only had the MRC500 available at the time.
>
>Cheers, Eric Hines
 
and I just wanted to point out that this wasn't a very fair comparison.
The MRC-500 had 11 metal mirrors and the signal was not properly integrated
over the full  pixel time.  the MRC-600 had dielectric mirrors that
conveyed about 3x more signal from the eyepiece to the PMT and the
full-integration digitizer that was incorporated sampled the signal for
about 4x longer (16x longer on slow scan) than the earlier capacitive
integrator.  Together these two improvements made the MRC-600 at least 12x
more sensitive than the MRC-500.
 
Jim Pawley
1675 Observatory Drive,
Madison, Wisconsin, 53706.
Ph.  608-263-3147,  FAX 608-262-7420
Prof. James B Pawley, [log in to unmask]