[pure-silver] Re: Same Exposure Different Prints?
----- Original Message ----- From: "Nicholas O. Lindan" <nolindan@xxxxxxxxxxxxx> 
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Sunday, July 06, 2008 4:37 PM
Subject: [pure-silver] Re: Same Exposure Different Prints?



<eroustom@xxxxxxxxxxx>
The Darkroom Automation meter reads 4.60 with a 0.01 or 0.02 fluctuation. At other times in the day I've seen the reading 
dip down to 4.51.
A difference of 0.09 stops in light intensity (4.60 to 4.51) isn't going to be a very noticeable change in the print density unless you are using a #5 contrast filter. For normal paper it 
is about 1/5th of a zone.
A difference of 0.01 or 0.02 can be ignored. Moving around the darkroom with the enlarger on should produce about the same 
change.
It doesn't sound, from the numbers above, that voltage fluctuations 
are the cause of print variation.
Will a voltage regulator like the one in the link solve that problem? 
http://www.pcconnection.com/IPA/Shop/Product/Detail.htm?sku=459725&oext=1038A&ci_src=14110944&ci_sku=459725
No, it will make things worse. These things have a multi-tap transformer and when they sense the voltage sagging they switch to a higher voltage tap. If you are sitting on the edge of one of the trigger points they can turn a 1 volt sag into a 14 volt boost. They only regulate so the power stays between 110 and 125V. You need to be able to regulate to 
117V +/- 1volt or so.

The best solution is
http://www.sola-hevi-duty.com/products/powerconditioning/cvs.htm,
rather horribly expensive when new, but available on ebay in large numbers. They are very reliable and long-lived. Don't get one any larger than you need - they draw full power all the time, doesn't matter what the load is. But, from the meter figures you gave above, unless you want to do sensitometery, you won't notice any difference. 

==
Nicholas O. Lindan
http://www.darkroomautomation.com/index2.htm
Darkroom Automation
Cleveland, Ohio 44121
The thing above is the Sola tranformer. They have been around for years and are very effective in leveling out line voltage variations and are also much more effective in filtering out line transients than the things sold as computer filters. Be careful of used Sola transformers. The operation depends on a non-polarized capacitor. If the cap is defective the transformer won't work right. Usually bad ones are easy to replace but may be difficult to find the special cap of the right value. Also, I have a couple of Solas that do not work right even though I have good capacitors in them. I have not figured out what is causing this. I suppose I could write to Sola but I think they are more interested in selling new transformers than in fixing ancient ones. Also, the Sola will shut down if the output is shorted so its a good safety device. 

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 
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