From: Tod Gangler (artandsoul@mindspring.com)
Date: 02/24/01-06:01:31 PM Z
On Friday, Feb 23, 2001, Judy Seigel wrote:
>Does that mean digital negatives are fraught?
Hi, Judy,
I would say , rather, that digital is fraught.
But regarding the contact printing of digital negatives, I undertook a
survey of graphic arts shops using stochastic screening before ever trying
it myself. Many shops, all making negs for offset printing, told me that
proofing and plating stochastic negs was very difficult. Apparently, the
stochastic negative's small spot size and its tendancy to produce greater
dot gain means that very good contact in proofing and plate-making is
required in order to assure accurate tone control. When contact wasn't
perfect, tones didn't reproduce accurately or smoothly. I heard a lot of
stories about shops running the vacuum for 30 to 45 minutes before making a
single exposure. Many shops told me that they had abandoned stochastic
screening due to these problems. (I learned only later how hard it was to
get repeatable results off of an imagesetter when making these kinds of
negatives with the teeny spot sizes. Hard to quantify error, when all is
so fraught.)
Stochastically screened negatives are still a kind of line negative. Negs
made with very small spot sizes will do a great job of reproducing fine
detail, and can simulate the sharpness of a traditional continuous-tone neg
very well, if the spots are small enough and the negatives are made with
skill. What is still difficult for any digital negative, and especially
any digital stochastic negative, is to reproduce well the subtle tonal
graduations that continuous tone negs do so well. Jeffrey Mathias' recent
posts addressing digital negatives, bit depth, etc. define this problem
pretty well. In stochastic screening, while the word stochastic itself
means something like "random" in Greek, graduated tones are made of very
carefully mapped hard-edged spots which are not random at all in their
placement. When the spots are small, like 14 to 20 microns, and the
contact is not perfect, these graduated tones can look even less smooth.
If this problem is compounded on several successive pieces of film which
will combine later in the printing process to make duo-tone, tri-tone or 4
color work, the effect can be magnified, and not so nice. The "spot-size"
of a neg made an Epson printer is much larger, and the spots themselves
have softer edges. Don't know how well all this relates to that kind of
negative making. I think that once the spots are bigger than 20 microns,
it may not be such a problem.
For alt-photo, I've been using stochastic negatives made on an imagesetter
for 4 color carbon printing. When the digital negative's spots are so
small and the contact isn't perfect, I've had problems holding those spots
of gelatin in printing. Either they print too light in the area of poor
contact, or they (more usually) wash away entirely, leaving blotchy holes
where one has wished to see silky smooth graduated tones. Fraught indeed.
The NuArc NuVac vacuum easel, combined with a fancy Stoesser Spring-Vac pin
register board that inserts into the vacuum frame, has solved these
problems for me. Previously, I used a NuArc platemaker just like yours
(but I never paid much attention to draw down time or pressure, back then,
either.)
Love that Post-Factory Journal,
Tod G
Art & Soul
Seattle, WA.
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