From: Richard Sullivan (richsul@earthlink.net)
Date: 04/25/00-02:23:25 PM Z
>Here's a visual:
>http://members.aol.com/kallitype/UV_Q.jpg
>This is the first test of a quartz halogen FEL lamp vs. UV flurescents
>that I ran a few months ago. The gum emulsion appears fogged, not
>overexposed, or longer scale, etc. It is just plain fogged. This is only
>a preliminary test, but it sure surprised me. Obviously much more testing
>is needed but the results here would indicate that the UV tubes are not an
>ideal source for gum printing. Halogen lamps appear to print cleaner,
>with better separation and contrast with respect to the gum
>emulsion. I'll be testing more now that the current school semester is
>ending.
Joe,
Looks like some good testing!
Intuitively I have noticed the same thing printing Ziatypes. I plan to run
more tests soon as well. My thoughts are that the Zias print cleaner due to
the faster exposure and the cooling system in the box and the light being
collimated.
We've put one hell of a fan in there. It is rated at 520 cubic foot per
minute which is a complete change of air in the box every second, of course
theoretical, and also supposing a perfect flow. It is impressive flow
through it. In an early prototype we used a 1100 CFM fan and it was a
little ridiculous. I think the unit could double as a hover craft it had
such a flow of air through it.
>Before someone asks about controlling an infinity of variables in the
>test, let me say it is impossible to hold everything constant in a test of
>this nature. So the uncontrolled variable I chose was the time between
>exposures using the same negative. It was either that or introduce
>something else (e.g., paper coated at a different time, slightly different
>emulsion mixed at different times or the same emulsion sitting around and
>thus aged before the second exposure, different test negatives, etc.) I
>tried to match the maximum print density on the exposures and adjusted the
>distance/time of the FEL exposure to match the UV printer bank. I think
>the fogging is due to some elusive quality of the light source rather than
>the 7 minute lag between exposures. It might be due to some temperature
>effect caused by the sources heating the contact frame to different
>degrees, but I didn't notice any large difference (and also didn't measure
>for it either...next time).
One might expect heat to cause the fogging but since you get less fog with
the Halogens that is a puzzle as well.
The other issue is diffused (fluorescent) vs point-source (in our case
collimated since we use a 16 and 24 inch aconic reflectors.) I even suspect
that we have lost a little of the point-sourcedness due to our positioning
the bulb for a wide angle dispersion. This we have done to get an very even
distribution of light. I think it is an established fact that enlarger
diffusion heads give the least contrast, point-source the most, and
collimated in the middle and I suspect similar principles apply here as well.
We also need to explore mercury vapor further. It is a little known fact
that standard metal halide ballasts over 250 watts can interchange mercury
vapor bulbs with metal halide. My wholesale supplier had a hemorrhage when
they found out that I was going to try them out in the ballasts I bought.
The sales person questioned me when I bought the ballast and both types of
bulbs. I got a call later from the sales manager telling me my warrantee
was void if I used the mercuries in the ballasts. I explained that this
could be done and he said absolutely not, under no circumstances would it
work, and the unit would likely go into a China Syndrome meltdown or some
such catastrophe. Needless to say I had found out about the switchability
bit from the manufacturer and it was also clearly stated in the catalog as
safe and ok to do. The same unit is sold under two catalog numbers.
The biggest problem with MV over MH is the warm up period. MV takes about 8
minutes vs 5 minutes for MH. Strangely enough, MV produces a lot more heat
too.
Just a thought. Assume a layer of particles. Light striking straight down
would expose less just beneath the particle than a diffused source which
could angle around and expose under it.
--Dick
>Joe
Note address change!
Please change your address book to richard@bostick-sullivan.com
505-474-0890 FAX 505-474-2857
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