From: Liam Lawless (liam.lawless@blueyonder.co.uk)
Date: 09/20/02-01:03:06 AM Z
Judy,
Perhaps because the Stouffer has logarithmic opacity increments (density is
the log of opacity)whereas they're linear in the dig. neg (aren't they?)
Your Stouffer covers a range of 10-1/2 stops but it's under 7 stops on the
dig. neg, which could account for the smaller number of steps.
FWIW, I compared silver and ink densities (grey image printed with colour
inks), finding the closest ink % to match each of the Stouffer steps that
had separated in a VDB print. (Stouffer & dig. neg both printed with same
exposure!) Results were:
Ink % Print density Stouffer step Print density
10 .26 17 (2.45) .25
16 .29 16 (2.3) .29
18 .31 15 (2.15) .31
22 .40 14 (2) .42
30 .58 13 (1.85) .54
34 .68 12 (1.7) .67
38 .79 11 (1.55) .80
42 .90 10 (1.4) .91
46 1.06 9 (1.25) 1.04
50 1.19 8 (1.1) 1.19
56 1.29 7 (.95) 1.30
72 1.36 6 (.8) 1.36
96 1.41 5 (.65) 1.41
100 1.45 4 (.5) 1.44
Stouffer steps 1, 2 & 3 were all joined together. If there's no clear
correlation between ink and silver densities, maybe it's that ink and silver
produce different characteristic curves. If you're wondering why I'm still
not in bed at 08.00, it's the toothache.
Liam
riginal Message-----
From: Judy Seigel [mailto:jseigel@panix.com]
Sent: 20 September 2002 06:34
To: alt-photo-process-l@sask.usask.ca
Subject: digital question (flaunt expertise, please...)
To all digital "experts" or wannabes:
I have, between catastrophes, been trying to generate enough info on
digital negatives (the first cause of the most hellacious upgrade in the
history of ones & 0s) for an article slated for the vaunted P-F #8. I
seem to be moving backwards, however, stumbling in well-covered ground.
For instance, here's how I made a 21-step for digital tests:
I made a ramp from zero to 100% in Photoshop, then posterized it into 21
steps.
(Even if you did this at 5% and 95% I doubt results would be much
different.)
So here's my question:
Why does it print fewer steps -- on each of 5 substrates I'm testing --
than the Stouffer 21-step I'm printing next to it.
And I mean by about a third.
And here's my other question -- the Stouffer 21-step shows lovely even
steps -- about 6, 7 or even 8, in various gum emulsions, depending on
length of the soak. My digital 21-steps from hell are, except for the ones
on mere vellum (feh!, kid stuff) wildly uneven -- sort of grand canyon
leaps at top, then squished at the bottom. (The vellum "curve" is quite
straight... but the material is otherwise problematic and I'm trying to
find something better.)
Sneers OK if info is good.
Judy
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