From: David J. Romano (romano@agfa.com)
Date: 02/26/01-07:39:30 AM Z
Judy,
One problem with stochastic screening is that the contact between film
and paper is much more critical than with regular screening. Naturally,
the smaller the dot, be it a 400 lpi highlight dot or a stochastic dot,
the more critical the contact. Without perfect contact, light will
undercut the dots and ruin the print. Since most photographic processes
are negative working, the result of poor contact will be a darkening of
the afflicted areas. One problem with this is that it never happens
evenly, darnit all!
This has been one of the major reasons why stochastic screening has not
been embraced by the printing industry until the advent of computer to
plate systems where the imaging laser exposes the plate directly,
skipping the film step. I work for Agfa and we make alot of these
machines, like the Avantra. In fact I am currently doing alot of testing
of stochastic screening on our laser platemakers. I could get into a
huge discussion on causes of banding, exposure variations, dot loss,
etc, but it's probably a bit off topic. If anyone is interested, write
me off-line.
One other thing, there is another stochastic screening program available
from UGRA of Switzerland called Velvet Screen. I used to work there and
have used the program alot. It's not too expensive and works right on
your own computer. Never tried it with alt process though.
http://www.ugra.ch/ugra_e/products/velvet/index.html
Dave
Judy Seigel wrote:
>
> On Thu, 22 Feb 2001, Tod Gangler wrote:
> >
> > I purchased a NuArc NuVac vacuum easel because of its superior ability to
> > contact negatives made with stochastic screening with very small dots. It
> > can be difficult to get good contact when printing this kind of neg with
> > some brands of vacuum easels. The NuVac unit uses a different kind of
> > bladder design, and it has a second pressure pump in addition to the vacuum
> > pump. This easel makes great contact on negatives made with 14 micron
> > stochastic spots.
>
> Tod, could you explain why contact is more of a problem with stochastic
> screening? Does that mean digital negatives are fraught?
>
> Judy
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