From: Sandy King (sanking@CLEMSON.EDU)
Date: 09/27/01-06:26:32 AM Z
I have used a UV light source consisting of a bank of Sylvania 350nm
BL tubes for many years. The unit has served me well. It is
reasonably fast, provide a large area of even illumination, does not
produce a lot of heat, and can be switched on and off with no delay.
Recently, however, I set up a second UV exposing unit consisting of
a 1000 watt 5K metal halide unit. With ballast, fixture and 23"
diameter reflector this is a rather large and heavy (35lbs or so)
unit. However, I managed to hang it from a 2X4 in the ceiling with a
very large eye bolt. My fixture, and many on the market, come with a
3/4 thread at the top by which it hangs. Wiring was easy, as you just
connect the black, white and green cord to an extension. The only
complication is that the unit is multi-voltage so you have to choose
a black wire that corresponds to your socket, that is, 120 volts,
220, 240 and 270. The cost of the unit, retail, was $232, complete
with ballast, fixture and lamp.
After running some comparison tests between the BL unit and the metal
halide unit I can report the following.
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.
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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