<<<Supposedly, according to the literature of my service bureau, the
ProPhotoCD scan is "sufficient for prepress color separations, image
retouching and digital archiving". >>>
Take this with a grain of salt, or maybe a bag of it. "Sufficient"
should be a red flag--we're not talking about a flat-out quest for
quality here, but about an adequate commercial product. The higher
levels of PhotoCD scan are quite sufficient for 133 line web-press
magazine reproduction at up to full page repro, but would look quite
disappointing when reproduced on a 300 line sheet-fed press like those
used for a high-end annual report or fine art monograph. On resolution
alone, that thousand-dpi 4x5 scan could only be scaled up about 150% at
the 600 final dpi required for first-rate 300 _line screen_ offset
litho. But there's more to the data than simple resolution or
"sharpness", as David's article explains very clearly: tonal scale is
the more difficult thing to capture.
If you are doing experimental work these scans are a great way to get
your feet wet, but don't expect to produce anything that equals a
genuine in-camera negative or properly-made chemical enlarged neg. The
"data density" required to make a satisfying silver or platinum print
far exceeds that needed for offset lithographic reproduction, partly
because the 4/C press "fakes" convincing color and tone by the
interaction of the four printing plates. You don't get to do that in
standard monochrome printmaking in either silver or platinum. And if you
want to enlarge the negative, then of course it has to have enough
data-density to retain the target point after enlargement. For an 11x14
from a 4x5, that would be roughly 3x600 or 2400 dpi. Drum scan territory
for now.---Carl
---Carl