From: Judy Seigel (jseigel@panix.com)
Date: 09/28/01-12:46:17 AM Z
On Thu, 27 Sep 2001, Sandy King wrote:
> 1. With the end of the bulb fixed at 20" from the exposing plane the
> metal halide unit is 3.5 stops faster than my BL unit, with the
> processes I tested: carbon, Vandyke and traditional Kallitype.
Since my fluorescent blacklight bulbs expose gum from a digital negative
in 40 to 45 seconds and from a silver gelatin negative in 1-1/2 minutes,
and I assume others have similar times, I'd say it sounds like the metal
halide bulb simply introduces more complications -- the on-off wait, the
light falloff, AND greater heat & eye exposure. Seems to me Sandy you've
done a public service with this info (especially about the contrast being
the same -- scotch one more rumor) but, well --- what are your usual
exposure times?????? Where's the fire ????
PS. If you gave the wattage of the metal halide, I missed it -- but total
watts of 8 fluorescents (24") is 160... The halide is probably 1000???
Even with the shorter time, still takes more electricity.
PS. Is it politically OK to say "scotch" a rumor?
Judy
>
> 2. Light fall off at the corners of a 16X20 print is about 1/2 of a
> stop with the bulb at 20" from the exposing plane. Light fall off at
> the extreme corner of the 23X29 frame is about 1.5 stops. Keeping the
> lamp fixed at 20" from the exposing plane it is possible to even out
> the illumination completely over the 23X29" area of the vacuum frame
> by placing a round, black center filter of about 6" diameter directly
> under the center of the lamp at about 12 inches from it. This
> reduces illumination at the center but the unit is still 2 full
> stops faster than the BL unit. Some would find it more convenient to
> simply increase the distance from the lamp to the exposing plane to
> three or four feet, with about 1-2 stops loss in light compared to
> the 20' distance.
>
> 3. The metal halide lamp takes about 2 minutes to reach full output,
> and if you switch it if off it is necessary to wait about 5 minutes
> before turning it back on.
>
> 4. The metal halide unit produces a lot of heat, and I mean *mucho*.
> Use of a cooling fan is necessary.
>
> 4. Image contrast is approximately the same with BL tubes and the
> metal halide unit, with the processes I tested.
>
> I think this kind of exposing unit deserves some consideration by
> anyone looking for a good UV exposing unit. It is quite a bit faster
> than a bank of BL tubes, costs about the same (or perhaps less) than
> to assemble a bank of BL lights, and comes basically ready to go in
> that all you need to do to use the unit is connect the wires to an
> extension cord and either hang it or place it on some solid support.
>
> Sandy King
>
>
>
>
>
>
>
>
>
> >I forgot to say yesterday that P-F #6 has an article on "Light Carpentry"
> >(& I admit to some pride in the title): four UV light systems with
> >instructions to build, most requiring only light carpentry skills (such as
> >mine own).
> >
> >Jarek Mirkowicz gets the romance prize: "My first experience with the
> >beauty parlor lamp was preparing gelatin matrixes for underground
> >bulletins against the communist regime in my country" (Poland). His
> >current design folds up compactly for storage.
> >
> >Nick Makris made his from off-the-shelf parts, except for the bulbs,
> >which he jiggered for stronger light for platinum.
> >
> >I show my first REALLY basic system as a thumbnail & the new improved
> >"reversible" version in photographs with glass in "open" and "closed"
> >position.
> >
> >Bob Schramm's brainstorm is a set of mercury vapor arc lights hung high
> >enough on the garage ceiling to cover an area 6 feet square (tho exposure
> >is hours). Bob, nuclear physicist, explains difference bet. sodium &
> >mercury vapor bulbs -- both are yard lights, but one works for our
> >purposes, the other doesn't.
> >
> >And, speaking of CONTACT FRAMES: last year I sold my supersized $224
> >custom built contact frame -- on this list as a matter of fact. It was a
> >thing of beauty (Great Basin) but NOT as practical & easy to use (at least
> >for a weak woman) as a simple plate glass sandwich, which lets really
> >large paper stick out the ends, and doesn't require the MUSCLE those
> >heavy-duty springs do. Contact, especially with a weight on top, is at
> >least as good, maybe better.
> >
> >Don Bryant's customized version of the Edwards construction plans
> >(he improved design of ventilation slots, etc.) is in Issue #5. He also
> >covered it with formica, if you could believe.
> >
> >cheers,
> >
> >Judy
> >
> >.................................................................
> >| Judy Seigel, Editor >
> >| World Journal of Post-Factory Photography > "HOW-TO and WHY"
> >| info@post-factory.org >
> >| <http://rmp.opusis.com/postfactory/postfactory.html>
> >.................................................................
>
>
> --
>
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