From: Joe Smigiel (jsmigiel@kvcc.edu)
Date: 07/14/03-08:00:43 PM Z
Sandy,
I think the FEL might be more even in another housing. (I haven't investigated that possibility since the exposure times work OK for my setup.) The DP unit has more of a dark spot than a hotspot which is what I focus to eliminate. It has been a few years since I tested it, but I seem to recall I got the illumination to within 1/10 of a stop over a ~14"-16" circle at 6 feet. I'll pull it out again next time I'm at work and measure it for you.
Joe
>>> sanking@clemson.edu 07/14/03 20:06 PM >>>
Joe,
I am glad that the Quartz halogen lamp is working better for you than
the UV tubes. Today I have an opportunity to look at a spectral
distribution power chart of several FEL Quartz Halogen lamps and they
do indeed put out quite a bit of light in the 400-500 nanometer range
to which gum has fair sensitivity.
I have a few questions about how you use the lamp. You mentioned that
you expose with the lamp at about six feet from the sensitized
material, and that you are making 8X10 prints. Is this the maximum
area of even illumination you can get at that distance, or is it
possible to spread out the focus of the lens over a wider area at the
expense of printing speed? I am trying to get some idea how this lamp
would compare to a 1000 watt metal halide or mercury vapor HID lamp.
I use a lamp of this type for some of my printing and with the pod of
the lamp at 36" from the printing material the area covered evenly
has a diameter of around 30 inches, with about a 1/3 stop fall-off in
light at the far edges of the circle. How would the 1000 watt Quartz
halogen lamp compare to this?
Sandy
>Sandy,
>
>I think a lot of folks have trouble printing gum and the fogging
>problem with UV tubes may not be restricted to just my experience.
>But, instead of advising people to change the UV source, people are
>usually directed to alter the size or paper or sensitizer ratio,
>etc., when maybe, just maybe, the UV tubes are not the best choice
>for gum printing. I've made good prints with the UV tubes, but in
>my experience the exposures are not consistent print to print and
>this weird fogging problem crops up once in awhile.
>
>The standard advice in most books on gum printing is to use Knox
>gelatin for size, Rives BFK paper, Winsor & Newton Alizarin Crimson,
>Cad. Yellow, Winsor Blue (pthalocyanine blue) and Lampblack pigment
>with 14B gum and to measure tube pigments by the inch and expose
>using UV tubes. Well, I have never been able to make a print with
>Winsor Blue that didn't stain. (Others apparently have.) Winsor
>Blue is a beautiful transparent blue but one of the most staining
>pigments you can buy. I've made some good prints on Rives BFK, but
>find other papers are better for my methods. Cad. Yellow is opaque
>and to me, a poor choice for gum printing. Alizarin is another
>stainer and apparently a bit fugitive. Knox is soft and higher
>bloom ossein works better for me. I also think ammonium dichromate
>is more prone to fogging than potassium. And the Andersen pigment
>stain test...well just check the archives for that one.
>
>My point is that the light source has never been considered as a
>potential problem in gum printing. I don't know why the UV tubes
>give me a problem once in awhile, but I've pinned down my fogging
>problems with gum printing to the light source and made an
>adjustment which has eliminated the fogging. I'd suggest that
>others might try the same if fogging problems occur.
>
>Several years ago on the Bostick & Sullivan bulletin board the issue
>of light sources for printing gum did come up. Several people
>reported much improved results simply from switching from UV tubes.
>Several people switched to quartz lamps at that time, including
>myself. We just didn't hear much about it on this list.
>
>Joe
>
>>>> sanking@clemson.edu 07/13/03 22:14 PM >>>
>Joe,
>
>If the quartz halogen lamp works better for you than UV tubes, great.
>Other folks on the list may want to experiment with this lamp since
>it is really dirt cheap compared to virtually all other UV light
>sources.
>
>As for the consistency of UV tubes your experience is just vastly
>different form mine. However, I have to belive that if there really
>were a generic problem of consistency with UV tubes in printing gum
>(as opposed to your particular problem) a bunch of other people would
>have noticed and commented on it since the tubes are so widely used.
>
>Sandy
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