Keith Schreiber (jkschreiber@worldnet.att.net)
Wed, 16 Jun 1999 01:12:58 -0700
> If you already mentioned this,
> please forgive me -- I'm still a bit foggy & could be repeating what you
> just said ... Voltarc told me that the AQA in the name stands for
> Aquarium; these are made as bulbs to light aquaria, ie., fish tanks.
Judy - OK you are forgiven. In fact there is a little logo printed on the
bulbs with the word "AQUA" right next to the F40T12/AQA ... and I'm sure the
definition of "case" is highly variable. :}
> Finally I decided to go with the BL bulbs, because I already had some, and
> they are *nominally* closer to the sensitivity of gum -- 360 nm, while the
> AQA is 413, supposedly the sensitivity of platinum. But I taught a couple
> of gum workshops at ICP with their AQA bulbs, and there was no difference
> in effect that I could detect. If I'd known all about the numbers at the
> time, I'd have made some comparison tests, but I didn't, and I didn't.
> I think, though, that for gum printing, other variables -- such as mix,
> pigment, thickness, color, etc. -- will lead to "spikes" of sensitivity at
> wavelengths all the way up into the visible zone, so the 360 number is
> more theoretical than real. (We talked about this on the list several
> times in the long ago, or the almost long ago.)
> But speaking of spectra and spikes, if you can get one of the fluorescent
> bulb catalogs from, say, GE, they have a "profile" of light output of
> their various bulb types, from the low UV through the visible spectrum.
> It's very interesting to see the range -- looks like a bunch of really
> tall thin mountains in the diagram. (Hmmmm, that might be good to
> reproduce one day, if I can ever squeeze out an extra 2 inches.)
Regarding peak sensitivity, I may be wrong, but I think output range is at
least as important for our purposes as output peaks. Supposedly, one of the
benefits of the new Metal Halide systems being offered by nuArc and others
over the Mercury Vapor (which is probably what you have in your 26-1K), is
that its output is much more even, i.e. less spiky, over its range. Indeed,
just because a particular bulb peaks at 360 or 420 or whatever doesn't mean
that is the only wavelength at work.
> However, it may not work the other way around -- it's entirely possible
> that the spectral sensitivity of platinum is much more constant. Certainly
> Bill Laven has found with HIS materials that the super-actinic 420 nm
> bulbs are consistently "better" & faster [have I got that right Bill?] as
> described page 42 of current Post-Factory, by the way.... though I gather
> not YET in California, which is a place apart.
No disrespect towards Bill, but faster by itself is not necessarily better
(though I doubt that is what he means). One qualitative observation I have
made regarding the 2 types of fluorescent bulbs that I have used, BL and
AQA, is that with Pt/Pd - especially straight Pd though I've seen it with
50/50 as well - the AQAs were much less likely to cause solarization with
long exposures. As I said in another message, I decided not to go with SAs
so that I'd have consistency between my 2 lightboxes. I think I've done
enough testing for a while. Now I have a lot of prints to make.
> My tests with Daylight fluorescents, incidentally, showed that they were
> slower and MUCH more contrasty than the BL for gum. So it's entirely
> possible that those 420nm Super Actinics, or the AQA, would be an
> excellent happy medium for gum. However, truth to tell, I myself am hooked
> TOTALLY on the vacuum frame, so I mostly use the NuArc with its sodium
> quartz whatever bulb. I confess.
>
> It's noisy & hot in summer, but... addicts are not creatures of reason. I
> keep the BL's handy for certain tests and for emergencies, like when you
> live in the country you keep flashlights & candles in case of power
> outages.
>
> > When I built my smaller unit about 6 years ago, the 24 inch F20T12/AQA
bulbs
> > cost $17.50 each. The 48 inch F40T12/AQA bulbs that I bought a month ago
> > cost $15 each. That is about the same as the BLs that I got at Home
Depot
> > about 4 years ago (which they no longer stock BTW).
>
> Keith, are you printing that large, or running several prints at a time???
Not so much large as long as in 10x24 (and eventually 8x30, 10x32, etc.) You
can see some examples in the next issue of View Camera. I know my subject
matter ain't your cuppa tea but I won't hold it against you. <g>
I have the light suspended from the ceiling with pulleys over a vacuum frame
salvaged from an old copy camera. It does also allow 2 or 3 contact frames
to be used simultaneously which is nice at workshops. Now if I could only
find a 40 inch wide vacuum frame ....
- Keith
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