Re: light table

Judy Seigel (jseigel@panix.com)
Wed, 27 Nov 1996 19:45:27 -0500 (EST)

On Wed, 27 Nov 1996, Sandy King wrote:
> A "drop in unit" in my terminology is a self-contained fixture in which one
> can place one or two tubes. Ballast is included.
> >
> >> Unfortuantley, spacing is much greater than possible with single bulb
> >> fixtures, which means that the unit must be used farther from the printing
>
> >How far apart is "much greater" (approximately)? The 4-bulb units I've
> >seen were all four feet long, but the bulbs were very close together.
>
> Now excuse me, Judy, but what do you mean by "very close together"?
>
> In my units, spacing between the tubes on the drop in units was about 3/4".
> With bi-pole holders spacing can be less than 1/8".

I have 9 two-foot fluorescents in a light table, some of them on single-
bulb self-contained fixtures (ballast & plug included), some on double
fixtures. The distances between the bulbs range from just under 3/4 inch
to one and 1/4 inch. The bulbs in the 2-bulb fixture are about 3/4
inch apart. I don't know how you get them 1/8th inch apart, unless you're
wiring the whole business yourself, with ballasts on the side, etc. and
god bless you.

However let me make certain observations:

1. I have *NEVER* been able to get a noticeably uneven print, even at 1
1/2 inches from the bulbs, at least by the method I devised to test,
which was to coat a very large sheet of paper with cyanotype, sloshing it
on so there was full saturation over the whole paper, then *underexposing*
the print by about 60%. The rationale for that was that when you fully
expose you tend to get d-max which could mask uneven exposure. Perhaps
there is a flaw in my reasoning, or a better way, but I was satisfied.
Then I moved the paper stage up 1 1/2 inches, for a paper-to-bulb distance
of 3 inches, so evenness should be even evener.

2. Since my times were so fast with the bulbs spaced at average 1 inch
(that was the reason I moved up), I saw no point in trying to get the
bulbs closer.

3. It's almost as cheap, or even cheaper, to use prefab fixtures as to
assemble, at least if you buy ballasts at standard suppliers, at least
judging by the prices I found when I thought I might have to take the
plunge.

4. In my experience cyanotype exposures have averaged maybe 3/4 of
platinum exposures, and I would *guess* are about the same as carbon
exposures (judging by the times Klaus used at school, which as I recall
were 10 minutes, under lights that average 8 to 12 minutes for cyanotype).
Which is to say, why do you need distances between bulbs of 1/8th inch --
unless your negatives are terrifically dense, of course, or perhaps you're
turning out great volume.?

5. I said all this a couple of times (in the a-------). If my surmises are
wrong, I wish someone would say.

Cheers,

Judy