_______________________________________
February 21, 2015
Since my normal workflow uses RPX 16x20 uv unit (the one with tube lights and not CFLs) and a Takach10” x 12” stochastic screen for 5 minute screen exposure and 5 minute
image/transparency exposure, I placed the PPM-1 over the RXP unit to measure
the dose of a 5 minute exposure.
Dose 1: 5466 cold unit, first firing
Dose 2: 5978 lowered PPM-1 unit
closer to lamps
Dose 3: 5683 careful to place PPM-1
unit at exact same distance from UV tubes as the outer face of the contact
frame class is from the UV tubes.
Average dose: 5709
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February 25, 2015
Testing outside with PPM-1 to see how long it takes to get a
dose of 5700
Direct sunlight
12:23 pm 169
seconds dose = 5706 last intensity reading = 333
12:29 pm 157
seconds dose
= 5735 last intensity reading = 365
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March 2, 2015
Direct sunlight 3:10
pm
Expose KM73 polymer plate to the “Gamelights…” transparency
using same contact frame and screen as normal workflow, to make a new plate for
comparision
Target dose = 5700 for each exposure (screen & image)
Actual:
Screen dose:
5761 time:
279 seconds last intensity reading: 92
Image dose: 5813 time:
354 seconds last intensity reading: 157
Notes:
Using a plastic bag to cover contact frame from exposure is
awkward. Perhaps light leaks?
The current clamp system made holding the contact frame
difficult and impossible to put down so I had to hold it (had to keep adjusting
attitude of frame).
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March 4, 2015
Printed new plate (outside exposure with PPM-1) and old
plate (exposed with RXP 16x20 uv tube unit) using same ink and paper.
(Note: image resolution degraded/grainy to protect copyright)
 |
| Old Plate |
 |
| New Plate |
Conclusion:
PPM-1 is a good device that makes exposing any plate size
possible. Needs a new curve, probably a
less aggressive curve, probably making the transparency more closely resemble
that of a film inter-negative. This
first experiment was overexposed a little bit because I was not able to
accurately control the exposure with just a plastic bag. A good light-proof cover needs to be designed
to control the exposure. It might be
worth making an entirely new contact frame that has edges that can rest
squarely on the ground without the clamps getting in the way, so the exposure
process can happen at the same attitude (angle facing the sun) throughout both
the screen and image exposures.
Speculation:
Since the sun is a single point source of UV, undercutting
does not happen to the same degree as with fluorescent tubes. This might explain the darker tone above 30%
density (undercutting/scattering of UV with tubes over cures these sensitive
tones, thus making them lighter). Also,
the darker areas (above 85%) are lighter, probably because the UV intensity is
higher so they are a bit over cured.
