To sum up my results thus far for those of you not in personal e-mail
correspondance with me...
Our story thus far:
1. Using an elliptical-dot linescreen (300 lpi) seems to yield smoother
tones than the diffusion dither bitmap advocated by Dan Burkholder in his
book.
2. 300 lpi should be satisfactory for high quality prints. I would not
go lower than that however.
3. The negs (or the paper actually) doesn't "hold the dot" above 90%.
This means that your positive image file should not have any areas darker
than 90%. 90% and above will print black. If you measure the film with
a densitometer, the differences are there, however, because of the
paper's characteristic curve everything above 90% prints the same.
4. I am using 1% as my lightest highlight to avoid any possible
posterization. Just print so 1% comes out white.
5. My standard paper developed in my standard potassium oxalate
developer can accept a negative with a density range of about 2.4.
My #5 developer (with 4 drops/100ml. of a sodium dichromate solution --
25g. sodium dichromate, 50ml. water -- added) can accept anegative with a
density range of about 1.9. I am hopeful that I can get by using a #2
solution (1 drop/200ml.).
6. Scan resolution should be such that you get 600 dpi or better in the
final print.
Latest news:
I was staring to get slightly more grain when I used the #5 developer so I
was hoping that I could change the contrast of my *sensitizer* with the
addition of more hydrogen peroxide thus allowing me to use my standard
developer. Well, this didn't work. There was absolutely *no difference*
between adding 1, 2, 3, or 4 drops of hydrogen peroxide to each of my
sensitizer coatings (total number of drops in each coating = 31-34
depending upon how much H2O2 was added). In this regard, the negative
seems to be printing as a true halftone. Therefore, it seems that, in my
case at least, that the only way to alter contrast is with the developer.
I printed a "perfect" digital step tablet and then made some measurements
with a densitometer. My 10% step printed as 56% so it seems that all the
action is happening down in the highlight region of the curve. In the
future I will be printing a complete tablet and posting the measurements.
I have found that sharpening of the digital file (using unsharp masking)
was responsible for a *lot* of the posterization/grit/grain I was getting
in the smooth high tone areas. While I now think you could get decent
prints from a diffusion dithered bitmap neg, I still think that the
linescreen neg looks slightly smoother and avoids problems in the 50%
areas. Without sharpening the grain looks more like mild "mottling". With
sharpening it looks more like posterization. I hope to do some more
experiments on sharpening to see just how much the negative can take
without going Grit City. I was using the sharpening recommended by Dan
Burkholder in his book.
Well that's all for now...
Best regards,
David Fokos