From: Richard Sullivan (richsul@earthlink.net)
Date: 04/25/00-09:40:00 AM Z
Ed makes some good points. When one looks at all the different processes
and the variables involved, testing in any real sense becomes a nightmare.
One can "test" for gum or platinum or silver and come up with some highly
subjective judgements, but beyond that, the data doesn't mean too much.
Even "printing speed" can vary from one process to another. I see
differences between Ziatype and DOP.
I think the best analogy as to judging the "quality" of the light might be
in loudspeaker evaluation. You can look at the plots produced by
loudspeakers but the quality of the sound can vary enormously and have no
seeming relationship with the plot. Surprisingly some speakers that have
very flat highly faithful reproduction plots sound very "unmusical."
I am somewhat skeptical of the idea that some lights actually produce
better looking prints than others. I have just heard this so many times
over the past years that I feel there is something to it.
The bottom line is that testing exposure units can give us some general
guidelines but beyond that it can become a frivolous obsession. I think we
all probably know a "zoney" who obsessively tests, films, developers,
lenses, and heaven only knows, probably film holders too, and yet never
produces an image worth looking at. Then there is the photographer who uses
the sheet packed with the film and determines it is "cloudy bright" and
does knockout pictures. Go figure.
As for the pizza oven box we are aware of that problem. There are other
products to come form B+S both in the exposure unit area and others. We are
working on a combo vacuum-inspection frame that will fit the LumenAria
desktop models at this very moment. The engineering is complete however
there is no ETA on it yet.
Gordon is cranking out Hobos like popcorn right now and we have to gear our
up manufacturing up to handle the increased load. There should be a very
positive review of the Hobo coming out in a major photo magazine in the
next month so keep an eye out for that. (No it is not Sputterbug.)
--Dick
At 09:18 AM 4/25/2000 -0400, you wrote:
>Jeff:
>
> I've run tests on several light sources using gum as the medium, and have
>found the following:
>
> Gum appears to respond best to frequencies 365 nm and below. Energy
>above 385 nm is pretty well lost on the process. Thus, one can have a
>wonderful bank of BL bulbs giving enormous amounts of UV in the 420 nm
>range, and yet require long exposure times with gum.
>
> Mercury metal halogen bulbs provide strong spikes in their output, one of
>which is in the important 320-380 nm range. However, here we run into
>problems with pigment absorption. Some pigments strongly absorb light at
>the spike, making (once again) long exposures a necessity.
>
> The best light source out there is the Sun - no question - although the
>source does have a habit of not being user friendly. The Sun provides a
>very wide band of UV light without major spikes, allowing the light to
>effectively "get around" the pigment blockage.
>
> The second best source is the mercury-iron metal halide bulb. The
>addition of iron iodide in the bulb widens the UV output, and produces a
>spectra similar to the Sun's. For an example of this - see www.olec.com,
>and check out the spectra of their L-902 (mercury-iron) and L-900
>(mercury) bulbs.
>
> The L-902 type bulb requires a high energy input to get it going, and is
>usually reserved for high end graphic arts lamps - such as the Violux and
>Olec AL-913. The mercury bulb in the B&S oven is fine for Platinum, but
>would suffer by comparison in gum applications. In other words - 400 watts
>is nothing if it all goes to the wrong place!
>
> A side issue with the Pizza Oven light box is the difficulty of using
>same with a vacuum frame. These simply don't fit. Hope this helps! Ed.
>
> P.S. - I still have one Violux unit to get rid of, as well as some 20x24
>sheets of direct positive LPD4 film should anyone be interested (contact
>me offline)..... E.
Note address change!
Please change your address book to richard@bostick-sullivan.com
505-474-0890 FAX 505-474-2857
<http://www.bostick-sullivan.com>http://www.bostick-sullivan.com
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