We generally want our B/W negatives to have the "full" tonal range, 256 shades
of "gray" in PostScript, aka 8 bit, which is what our graphic programs and
imagsetters are geared to. I have compared gray scale negatives output at 133
lpi 150, lpi, and 200 lpi. I have prepared these negatives for contact printing
with silver (silver chloride - Kodak's "AZO" paper) and other negatives prepared
for platinum/palladium, Van Dyke and cyanotype. Granted that the density of the
two types of negatives are different, the 200 lpi is as fine as one ever needs
to go and so minimally better than 150 that it's not worth aiming for 200 for
alternative processes. For the alterrnative processes even 133 lpi is so close
to the 200 ideal that I do not think one needs to go above 150 - 175 for most
purposes.
I have been immensely pleased with these negatives but I have been disappointed
with the bitmap negatives as suggested by Dan Burkholder. The problem may well
be mine and not the methods, as I know Dan to be an immaculate technician as
well as a most superior artist, but my bitmapped negatives were always blocked
up in the lower values. (Dan, where are you? Can you comment?).
I hope I am not oversimplifying, but I think I am not: Scan in at 2200 -2400 dpi
for an output at 150 lpi. The negative will be more than satisfactory if
you've done your curves properly. Leave the ratio of dpi over lpi squared to
those working in four colors who need to work out the shades, it's really not
for us B/W negative makers to worry about.
Two final comments: As many of us have learned working with litho film, and I
have to relearn the hard way all the time, it attracts fingerprints like iron
filing to a magnet. Second, it is not easy to find a good service bureau; if
you find one, stick with it and don't argue price.
Dan, if you can, we would appreciate your criticism of my comments.
Joachim Oppenheimer