From: Judy Seigel (firstname.lastname@example.org)
Date: 11/12/01-09:57:38 PM Z
On Mon, 12 Nov 2001, Ed Stander wrote:
> There are a lot of processes out there, and each sensitizer appears to
> be sensitive to different parts of the spectrum. Further, each binding
> agent seems to absorb different parts of the spectrum.
Ed, My IMPRESSION (after at least an hour spent contemplating the
point over 10 years) is that those "different parts of the spectrum"
for our processes are basically within 50 nm of each other.
So can you really proceed on the principle that you'll get a better print
if you use the bulb that most closely matches sensitivity of a given
emulsion? I believe there is some testimony to that effect, but remain
skeptical. I get the sense (judging anyway by gum) that even if so,
sensitivity changes with any change of materials. Also, that it would be
stultifying to lock oneself into one process and/or set of ingredients.
In any event, I've taught classes covering 4 processes (pt-pd, gum, cyano,
VDB) by at least 4 different lighting systems, & never noticed difference
in effect. True, these were beginners, not maestros, but surely we'd have
noticed something. I'll add that my impression from the diagrams of holes
& spikes in the mfr's lit is that there's plenty energy at other nms
> If we knew the ins and outs of each process, we could design a light
> source that would direct those watts precisely to the task at hand.
As noted, I doubt the task-target is constant. ... and if it is, for all
practical purposes one rich-in-UV-light source is much like another. I've
also heard, for instance, one cyano printer say the sun gave best most
delicate print of all, another says s/he didn't like it as well.
> Unfortunately, we don't have any such understanding, as may be shown by
> even a cursory reading of the list's archives.
I think what the archives show is dream of the perfect light source, no
evidence that it exists. The super actinics were reportedly faster, but
now there seems some disagreement on their divinity.
> Fluorescent lights (at least those commercially available) give all of
> their light in a very narrow wedge of the spectrum. If this happens to be
> the right part of the spectrum, all's well and good. Your observations on
> cyanotype are right on here.... why use 5000 watts, when you can get away
> with 400?
Ed, you're the maven in that department, so I shouldn't argue with you,
but .... you're suggesting that the metal halide is broader than the
fluorescent? Than which fluorescent?
> On the other hand, what good are those 400 watts, if they fall outside
> of the active zone of the sensitizer? The beauty of the hallies is their
> broad spectrum in the UV.
As noted above, I haven't seen any of the major processes that don't work
without complaint in BL, AQA, & BLB fluorescents, also sodium mercury.
What "active zone" do you have in mind that my BLs (for instance) don't
> I found this out firsthand when I replaced a narrow spectrum halide
> lamp with a wide spectrum one. Times immediately decreased by 500%. The
> reason: more light where it counted.
How narrow is narrow? Is "wide" halide as wide as regular BL??? From what
you say here, you didn't compare with BL at all....?????
> Electricity costs around 12 cents per kilowatt hour. If I used my
> light for one hour it would cost me 60 cents. That's 1 cent per kilowatt
> minute, or 1/2 a cent per exposure. I can deal with that.
You omit the cost of removing the excess heat in summer, but I'll give you
that. And I note that my electricity costs nearly 17 cents per KWH. No
matter, it's the principle, not the absolute amount. If we all saved 50%
of all our energy use, the Saudis, for instance, would have had much less
wealth to share with "evil doers," we'd have had half the global warming,
half the loss of ozone layer, and twice as much remaining for future
generations. Or think in terms of saving across the board 50%, or 20% or
even 10 % of everything we spend.
> and one of these days I'll get that 24 dollars off
> to you (even though that comes to nearly 40 hours of exposure time.... )
But you didn't say what the MH setup costs... probably 1000 hrs exposure
time ! You could endow an entire library for that. Meanwhile, how far
upstate are you? Husband just heard on TV it's 25 degrees F in Kingston.
It's about 50% warmer here. If you heat your house with that halide bulb
you might save about 12% on fuel...??? (Apologies to metric friends --
that's so cold it's off my photo temp chart & it never gets that cold in
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