From: Sandy King (sanking@clemson.edu)
Date: 11/11/01-09:06:42 AM Z
Ed,
Thanks for the information from your cyanotype tests. Perhaps you can
correlate what you did to the tests I also ran last night with this
paper. I got the following result from my tests with the commercial
metal halide unit that I use, and the Stouffer TEP 4X5. I also tested
the BL bank at the same time.
If you will recall from a previous message I can use the MH unit at
20" from the exposing plane, in one of two modes: A) without a center
filter, which gives even light for up to about 11X14" size prints,
and B) with a center filter that evens the light out over a 23X29"
area.
I do not have a spectral distribution chart for the Venture 5K 1000
watt metal halide bulb that was used for the exposure but I know that
it is rated at 5200 Kelvin.
Test Data-- 20 minute exposure
Mode A -- First maximum black at step #8, last visible step above
paper white at step #16. This indicates an exposure scale of about
1.35, or nine steps. Since this step tablet is over-exposed by four
full stops, the actual printing speed to get maximum black on step
#2 would be about 75 seconds.
Mode B -- First maximum black at step #6, last visible step above
paper white at step #13. Exposure scale is still 9 steps. This test
being overexposed by two and one-half stops, the actual printing
speed to get maximum black on step #2 would be just under two minutes.
By comparison, my bank of BL tubes printed as follows. First maximum
black at step #6, with last visible step above paper white at step
#16. Speed was therefore virtually identical to that of the MH unit
in Mode B, but the exposure scale was 11 steps, or about 1.65. In
other words, the MH unit gives more contrast by about two steps.
I am of course calculating actual printing speed based on the time
needed to get a maximum density at step #2.
Sandy King
>Dear all:
>
>Sandy kindly sent me two sheets of his cyanotype paper, allowing me to test
>my olec graphic arts lamps against his. I used a 1000-2000-5000 watt
>system set up 24 inches above a nuarc vacuum table. I also used two
>different bulbs - a L-1250 and an L-1252, both of which are brand spanking
>new. The L-1250 provides strong peaks at 400 and 420 nm, and a weaker
>bump at 365nm (similar to a typical metal halide bulb, and not far from a
>fluorescent). The L-1252 provides a stronger across-the board flat
>spectrum. Both spectrums can be viewed at www.olec.com for comparison
>(look under spectromatch).
>
> The L-1250 bulb set to 1000 watts gave a good exposure after 20
>minutes, as Sandy suggested it would. Step 1 and 2 of the Stouffer tablet
>are dark, and 8 distinct steps are present. A reading on my Blak-Ray
>Ultraviolet meter (recently calibrated at 365 nm) provided a value of 1000
>microwatts/square cm during the exposure.
>
> This is all as it should be.
>
> The neat thing came when I replaced the L-1250 with the L-1252 wide
>spectrum bulb, again used at 1000 watts. This bulb pegged my poor UV
>meter at 6000 microwatts/square cm. Further, an exposure time to four
>minutes gave a result identical to the L-1250 at 20 minutes (ie: 8
>distinct steps commensing from max blue at step 2). This suggests that I
>should be able to make a cyanotype in 30 seconds with the system running at
>full brightness. Pretty neat.
>
> So you see - metal halides are not all the same. Some are a little
>more so.
>
> Cheers, Ed Stander.
--
This archive was generated by hypermail 2b30 : 12/10/01-11:12:21 AM Z CST