From: Sandy King (sanking@clemson.edu)
Date: 12/07/01-10:46:00 PM Z
Neal,
I did not find that the sharpness decreased at all in Mode B with the
center filter with the pod of the light at 20" from the exposing
plane. It seems excellent as is and I can not imagine that elevating
it to 30-40" would add any appreciable sharpness, but this is only an
opinion as I have not actually make any tests to compare the two
conditions.
It sounds to me like your use of the 575 watt HMI light source is
quite a bit different from what I am doing with the HID lamp because
you appear to be really using it as a point-source light, whereas my
use is as a semi-collimated light.
As for exposure time I would think that either the metal halide or
mercury vapor HID lamp described in the article would provide much
faster printing times with VDB when used at 40" than the 45-70
minutes you got from the HMI lamp. If you look at the chart in the
article of vandyke with the metal halide unit you will see that there
is already maximum density at step #4 with a five minute exposure
when using the unit in Mode B, indicating over-exposure of from 1-2
stops depending on where on the step wedge you want the first maximum
density. The actual correct exposure to get a maximum density at step
#2 would have been 2.5 minutes. Remove the center filter and elevate
the unit to 40" and there is about a 1 1/2 to 2 stops loss in
printing speed, which puts you in the 5-10 minute range.
Sandy King
>Sandy,
>Congratulations, that's a very interesting and thorough article on UV
>sources. Did you find that the sharpness decreased at all in the mode B,
>with the disk, or increased when the HID light source was elevated to
>30-40"?
>The reason I ask is that I have spent the past few years printing a series
>of cyanotype and VDB photograms exposed through diaphanous textiles. The
>prints were large, about 50" on the long side and I ended up using a 575
>watt HMI light source (used in cinema lighting), bare bulb at about 40".
>This gave me better sharpness than the FL bank, acting as a point light
>source and covered the print evenly. One problem was that exposures were
>quite long (45-70 minutes for VDB). From your research it sounds like the
>HID will provide a similar quality of light, with faster exposures and
>cheaper.
>Thanks, Neal
>
>> From: Sandy King <sanking@CLEMSON.EDU>
>> Reply-To: alt-photo-process-l@skyway.usask.ca
>> Date: Thu, 06 Dec 2001 14:44:55 -0500
>> To: alt-photo-process-l@skyway.usask.ca
>> Subject: UV Article
>>
>> I finally finished the article on UV light sources. If anyone is
>> interested you can see it at http://unblinkingeye.com/
>>
>> Sandy King
>>
>>
>>
>> --
>>
--
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