From: Sandy King (sanking@clemson.edu)
Date: 11/12/02-10:47:50 PM Z
Jeff wrote:
I am not saying that the variations in temperature and humidity are
not an issue. However, I will say with absolute certainty that 2-3
minute warm up time is not sufficient for most commercial metal
halide lamps to reach full output. With an integrator you calibrate
the unit to reach a certain output, which in my case I have set to
100 when the the unit of operation is approximately one second. At
2-3 minutes my unit, as measured by the integrator, has only reached
a reading of 20-30 units, that is, less than 25% of full output.
Obviously if your exposures are in the 10 minute range and you begin
them at 2-3 minutes of turning on the light, you should be seeing
significant variations in printing density, irrespective of any other
factors.
Sandy King
>Clay & Sandy: Thanks for the suggestions. As you know, I have a
>metal halide HID. I don't worry much about timing the exposure,
>because they run 6-8 minutes typically and I don't see how the 2-3
>second fudge in my crude timing system can make any difference. The
>intensity of the lamp is another matter. When I got the thing last
>spring, I followed leads to get an integrator, but pretty much
>crapped out when the glass-virtuoso guy proved no help. On the
>other hand, looks like I should be doing a longer warm-up. I've
>been doing 4 minutes because the electrician said 2-3 minutes would
>be plenty. As for the quiet time around the house, I can manage
>that sometimes and I try to.... Say, are you guys saying that the
>variations in temp and humidity I noted are probably not at issue?
>-JB
>
>At 11:04 PM 11/12/2002 -0500, you wrote:
>
>>Clay wrote:
>>
>>>Jeff:
>>>
>>>What are you using for your light source? And how are you timing
>>>it or measuring it. I find I get pretty consistent results with
>>>the same materials and ambient conditions... But I'm using a Nuarc
>>>most of the time.
>>
>>
>>When using any UV light source without an integrator one is almost
>>certain to observe some small differences in print density, even
>>when all other things are held to absolute consistency. I find this
>>to be true with both my bank of BL tubes and with the HID lamp when
>>used without the integrator.
>>
>>If one must work without the integrator it is best to do so when
>>the house is relatively quite and there are no large and sudden
>>current drains. Also, for maximum consistency all light sources
>>should be allowed to warm up for a few minutes before exposing. Two
>>to three minutes is enough for fluorescent tubes, while HID mercury
>>vapor and metal halide lamps need from 5-8 minutes to reach maximum
>>output.
>>
>>Sandy King
>>
>>
>>>
>>>Clay
>>>On Tuesday, November 12, 2002, at 08:58 PM, Jeff Buck wrote:
>>>
>>>>Actually, it's the tendency of a phenomenon to recur in the same
>>>>form.... Anyway, after doing platinum/palladium for about
>>>>fifteen months now, I find if very difficult to achieve. I
>>>>arrive at a print that is satisfying. I want to repeat it. So,
>>>>I use the same paper, the same chemicals (plain FO, pure
>>>>palladium, PO w/ sodium dicromate mostly), the same exposure, and
>>>>the same developer. As for ambient temperature and humidity, I
>>>>can get pretty close to repeating, especially this time of year
>>>>when I'm producing both artificially (by and large). Like the
>>>>last couple days, I'm printing this negative, and the temp is
>>>>between 65F and 70F, the humidity is in the range of 60% to 70%.
>>>>In each instance, the paper has been laying out in the area of
>>>>that temp and humidity for a few hours; it's a little "heavy" and
>>>>tacky to the touch. I guess I made four prints in these
>>>>conditions (I was double-coating Platine, if that makes any
>>>>difference). There were notable differences in the overall
>>>>darkness of the prints and in degree of contrast. Would you
>>>>expect discernible differences working within these variations in
>>>>temp and humidity? How do you measure the temperature of the FO
>>>>and platinum or palladium? I'm squeamish, maybe for no reason,
>>>>about putting a thermometer into a bottle of precious metal....
>>
>>
>>--
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