Hi David
I have the Canon (for about 2.5 years) and I have been happy with it for
my purposes, however, both Minolta and Nikon have continued to develop
their scanner lines and have produced newer models.
If you absolutely need multisampling (without multipass) then you can't
look at the Canon (or the Minolta?).
Some people say Nikon is not noted for edge to edge sharpness as focus is
a bit more critical due to a wide aperture lens used to gain scan speed
and to compensate for the lowish effective intensity of the LED light
source (each colour turned on in turn which slows things by a factor of
3).
I wonder if you will do much better than your Polaroid, but I have no
direct experience of them, just from what I have read here. Can you just
clean the mirrors and keep going? There is a detailed explanation on
the web for DIY cleaning the SS4000 mirrors.
Are you confusing overexposure halos with dust?
Have you tried the long exposure option in Vuescan? - that usually (but
not always) works for me in reducing slide shadow noise.
Have a look at the scanner bake off below.
http://www.jamesphotography.ca/bakeoff2004/scanner_test_results.html
the SS4000 performs at the upper end of scanners tested. It is sharp,
has competitive chromatic aberration and has a good to excellent
signal/noise ratio (better than the Canon and I think the Minolta,
similar to the Nikon from a quick look).
I'm sure the test has its limits, but I think it shows that the SS4000 is
a competitive scanner in basic scanning performance terms.
I have not tried Silverfast, that may be another way to spend money if
you keep the SS4000! (free demo download to try).
Also, if you are scanning old Kodachromes, you can't really use ICE and
if you are scanning new E6 slides, you probably keep them clean anyway,
so no need to waste time with a second IR pass (I know it happens on the
first pass with the Nikons).
Just some thoughts.