From: Judy Seigel (jseigel@panix.com)
Date: 09/29/01-01:03:15 AM Z
On Fri, 28 Sep 2001, Sandy King wrote:
> Judy,
>
> From similar data we have reached some very different conclusions. In
> my estimation the two-to-three and one-half stop increase in speed
> offered by the metal halide unit over the bank of BL tubes is a huge
> improvement in performance, even though some persons might consider
> the operational trade-offs (extra wattage, heat) as significant.
> However, since your opinion as stated is based primarily on the speed
> comparison I think we should explore a bit more that aspect of the
> problem.
Sandy, I defer to you instantly in the matter of the *math* involved, but
still suppose the tradeoffs for the halide bulb would be a matter of
personal preference... I don't think an 8 minute exposure is a big deal
(that's what my denser negs took in cyano & VDB is similar) but certainly
an hour-long exposure would be a drag.
As I recall, my bulbs are about 2-3 inches from the paper stage, that
extra inch does I think make a difference. They're also ranked as closely
together as the double-bulb fixtures permit, which also adds speed. The
only other thing I can think of is that sometimes the bulbs get a coating
of dust/grime, whatever-- perhaps mine moreso since they face up, but I'd
suspect that even in your clean-air zone, there's stuff in the air which
does deposit on glass from year to year.
But I'm curious on one point -- which you may have mentioned, if so,
please excuse: how big a print can you make in the cone of even light at
20 inches?
Judy
> First, my comments about relative speed of the two units were based
> on testing Stouffer TP 4X5 step wedges, with the speed point
> determined, by convention, as the step wedge that gives the first
> maximum black. In those circumstances, with the BL tubes set at 4"
> above the printing frame and the metal halide unit at 20" and
> printing with Vandyke, the first maximum black was obtained with the
> BL unit at 8 minutes, the first maximum black with the metal halide
> unit at 45 seconds. Tests with carbon and traditional kallitype show
> a similar gain in speed for the metal halide unit, though these
> processes are about twice as fast as Vandyke.
>
> Now, unless something is wrong with my BL bulbs , which I doubt, the
> absolute minimum exposure time to reach the first maximum black of
> the process is 8 minutes for Vandyke and 4 minutes for carbon and
> traditional kallitype, with the BL exposing unit. This observation
> is not based on a comparison of *my* negatives to *your* negatives,
> but on printing with a step wedge the qualities of which are known
> within fairly narrow parameters.
>
> The assumption that your typical printing times are consistent with
> those of others (45 seconds for digital negatives, 1.5 minutes for
> silver gelatin negatives) may or may not be generally true. Maybe we
> will hear from others on what are typical exposure times.
>
> In my case it is definitely at odds with reality as my typical
> exposure times (with carbon printing) range from a minimum of about
> 15 minutes (for negatives with a Dmin of about .20) to an hour or
> more for negatives with a Dmin of .45-60. The two stop increase in
> speed provided by the metal halide unit effectively allows me to
> complete exposures in the 4-15 minute range as opposed to the 15-60
> minutes with the BL unit.
>
> Sandy King
>
>
>
>
>
>
>
>
>
>
> >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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