Hi Susan,
I know what you mean. We all just want it to work, unless you've got
exactly the same hardware as I do and are creating and processing
plates in exactly the same manner, using my curve without any adjusting
of your own will almost certainly not be as good. Consider any curve
supplied to you from someone else a starting point - you'll need to
learn to tweak it to get the results you want, I'm afraid. I think I
mentioned before, I wouldn't use the curve posted on my website when
using a coarser scree or plates other than the KM73. This is because
the curve was designed specifically with a KM73 plate and finer
stochastic screen in mind. There are other variables that require you
to tweak the curve: Your inkjet printer may output transparencies with
more or less density than mine as well -- you'll want to adjust your
curve or exposure times as a result of your testing.
A curve compensates for the fact that we're transferring an image from
one medium to another. Images generally gain contrast, as they "lose
data" -- Much like when you copy 3rd and 4th generations of audio tapes
... the fidelity of copies of copies start to become less defined.
Compensation curves adjust for a known and expected loss in certain
areas of density. When I said 100% maps to 82%, I mean the 100% blacks
are adjusted to actually be 82% when output on the inkjet printer.
That's what Chris meant by Input 100/Output 80 as well. We do this
because if we didn't, all the shadows from 100-82% black would all look
the same -- we wouldn't have as much shadow detail. How do we know?
Because we've done tests and tweaked our process, exposure times, and
curve with each successive test (though usually one thing at a time is
best of course :-)). Curves are one of the best control tools we've
got to make images look like we think they should when using digital
images for alt processes.
Dan Burkholder has an excellent "Tiny Tutorial" on creating curves, why
and how to do it here:
http://www.danburkholder.com/Pages/right_frame_pages/turtorial-right-frame.html#
Click on Adjusting Digital
Negative Curves.
Dan makes it more fun than it would be otherwise. His book is also a
great resource if you don't already have it. If you don't, buy it and
if you do, read it! :-)
Cheers,
Jon
SusanV wrote:
Jon and Chris..
Great work on all this screen information. Another reason this list
and the people on it are such treasures!
As for the curves discussions, I must admit that when I start reading
about those things, my hair hurts. I'm just not up to speed when it
comes to curves (as relating to digital positive/negatives for alt
process output). I don't even understand a lot of the terms you all
use ( "100% mapped to about 82%", "moving the point top right down to
Input
100/Output80" ....SAY WHAT????? ). I'm just late to this digital
neg/pos party you've all been doing for a while now. I'm not at all a
technophobe... but in this particular instance, I just want a simple
solution to get me making my images. I'm using Jon's curves at this
point, but I do wish I understood how to tweak them to get the best
result for my own workflow with the 1280 printer and Nuarc and km73
plates, etc...
ok, i'll stop whining, haha... it's just been a killer week here and
I'm wiped out. I'll go take a nap and come back later :o)
susan
www.susanvossgravures.blogspot.com
www.dalyvoss.com
On 2/24/07, Jon Lybrook <jon@terabear.com> wrote:
Small world. That's neat Chris.
Elizabeth Dove's page is very informative, but she doesn't list the
specs of her screen (dpi, density, etc.) and only says that it works
for
Photopolymer and ImagOn. I'm sure it does work, but filtering through
the specific imagesetter screens I know David Hoptman has tried and the
some dozen screens I've tried, I've come to want a more info. Is it
any
different from the standard aquatint screens one can buy from Graphic
and Chemical or Dan Welden? Too coarse and the dots become apparent,
too fine and the plate breaks down too easily when cleaning... I
believe I've found the happy medium for the way I work in choosing the
1800 dpi screen, but I'll be interested to see how other approaches
work
out for people and learning more details about them.
I too got wildly diverging exposure times for image/screen early on. I
think it has to do with the relationship between the screen and the
image I described in a posting a last week where the image actually
contributes to the "aquatint" in a somewhat unpredictable way. I'd get
an image that looked ok, but it wasn't quite "right" and with not much
latitude for tweaking. Ultimately I went with the relationship closer
to, but not exactly 50/50 image/screen time.
Super-damp paper (glistening) might lead to patches like what you
showed, but unless that's the case, it sure looks like general contact
issues and/or the weird problems I've described related to UVBL
bulbs...
Regarding curves...when using solarplate and coarser screens I do start
out with 100% mapped to about 82%. With the KM73 curve I developed
along with the 1800 dpi screens -- I don't - I start with 100% being
100%, but drop off drastically from there. This is because I believe
the finer screen can represent more shades of grey without needing to
compress the curve as drastically as one does with solarplate or
imageon
and the coarser screens.
Again, I'll post when I know more about this source I found for the
1800
dpi screens. I'll need to update the sources list on my website in any
case if Copygraphics isn't going to be able to deliver the goods from
now on... :-\
Jon
Christina Z. Anderson wrote:
> Well, Jon, I have a funny--last night I checked out Keith Taylor's
> aquatint screen source, Elizabeth Dove. Come to find out she
lives in
> MT! And teaches at U of M! Our rival :)
>
> So I ordered one last night, and even funnier, she emailed back
and
> said, "This is weird, on a friday night I get two orders for these
> screens, which I don't get much, wonder what is going on?" The
other
> order was from a guy in TX.
>
> I told her there was a post to the alt list about her and that
Keith
> was a blabbermouth, heheheh. So there's one happy woman and
another
> reason this alt list is so wonderful.
>
> I've been rereading every text I have on solarplate--Keith Howard,
> Eskola, Boegh, Welden/Muir (ordered the Ponsaing book Keith
> recommended, have had the others quite a while), and the more I do
it
> and read the greater my understanding is growing. For instance,
silly
> me--I thought Boegh had a particular image backwards in his
book--it
> was of a test strip of aquatint exposures ranging from 15 sec to
90
> sec, but the lighter exposure was 15 sec. This flew in the face of
> reason that the greater the exposure on solarplate the lighter the
> print, so I just assumed he did it wrong. BUT what I have since
> realized from rereading all books and looking at Jon's little dot
> diagram, is that the exposure of the screen starts OUT washed out,
> then gets blacker. No WONDER I had a calibrated exposure of
screen to
> be 1mn 15 sec and couldn't figure out why I needed longer. I was
> looking only for where open bite disappeared, but I should have
been
> really looking for when first max black occurs. AND when doing
this
> with a UVBL unit, the exposures should NOT be in steps of 15
sec--too
> short--but in 1 minute steps up to maybe 10 minutes!! I found
this in
> another little part in Boegh's book, a caption to a photo where it
> talks about relative exposures of metal halide to UVBL.
>
> Little things like this make more sense.
>
> When Keith mentioned wetness of the paper a culprit, I again found
ref
> to the fact that blotches/uneven tones can be a result of the
> wetness/dryness of the paper, lack of evenness, etc., so again, no
> WONDER it is good to soak a long time but to let paper sit in
bags.
>
> So every little bit helps on my way to perfection, short of
ordering a
> vacuum frame. Pray for a tax refund. At least all these failures
will
> benefit the alt process manual chapter; no better way to learn a
> process than to fail at it over and over again.
> Chris
> PS one last thing--when doing the Boegh and others method of
clipping
> tones in a curve dialog box to 80%, this only works on grayscale
the
> way he suggests--moving the point top right down to Input
> 100/Output80. If in RGB mode you have to move the bottom LEFT UP
to
> Input 0/Output 50--dif numbers and dif directions. But you all
> already know that. I am not using this method of curving,
preferring
> instead to build a PDN curve with no tonal clipping, but for those
who
> want a low tech way of adjusting the image to suit a plate, this
is it.
> ----- Original Message ----- From: "Jon Lybrook"
<jon@terabear.com>
> To: <alt-photo-process-l@usask.ca>
> Sent: Saturday, February 24, 2007 10:43 AM
> Subject: Sources for stochastic screens
>
>
>> I called around and found a guy here in Boulder who seems to
know
>> what he's talking about in terms of outputting an 1800 dpi 80%
>> density stochastic screen on him imagesetter. I'm meeting
with him
>> next week to show him the screen I'm using to see if he can
>> accurately reproduce it. He said typically they output at
much
>> higher rez natively, but can make it output at 1800.
>>
>> I actually called a company that sells imagesetters in New
Jersey
>> first and asked them if they could recommend any of their
clients.
>> They just said, look under 'typesetting' in the phone book. I
was
>> dubious, but looked and there was one entry, for this one
company.
>> Might try it in your own town...and help keep those
imagesetters in
>> business! In the meantime I plan to work with this guy a
little to
>> get at least one screen made, and if he proves reliable, and
can give
>> me the screen I've been using without issues, I'll post their
contact
>> info later in the week.
>>
>> Hooray!
>>
>> Jon
>>
>>
>>
>
>
>
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