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Subject: Re: Calibrated Thermometers

Hi to all,

As an old time photographic scientist, I would say NEVER, NEVER, NEVER use a
mercury thermometer in a darkroom. When I was at RIT in the 70's , a
mercury thermometer in the graduate darkrooms was grounds for expulsion. The
Kodak thermometers of the day were all alcohol based. If you break the
mercury thermometer in your darkroom, you might as well move out. It has a
terrible potential to fog the film and it is very bad for your long term
health. I use a Weston Bi-metallic thermometer. I also use a digital unit
that attaches to one of my voltmeters. It is more precise than the Weston,
but I use the Weston to calibrate the digital meter. It is easier to read
small differences on the Digital meter. Over the years, I have found that it
is more important to be consistent than accurate. I'm not sure how accurate
the Weston is, but it has been a long time friend and I have based all my
personal timing work on it.

Tom Lianza
Director of Display and Capture Technologies
GretagMacbeth LLC
3 Industrial Drive
Unit 7&8
Windham, NH 03087
603.681.0315 x232 Tel
603.681.0316 Fax

"Richard Knoppow" wrote in message
> "Nicholas O. Lindan" wrote in message
> news:Rt58g.508$x4.183@newsread3.news.pas.earthlink.net...
>> On Mon, 08 May 2006 19:11:05 -0400, "Greg "_""
>> posited:
>>>? Thoughts [calibrating/ed thermometers ????]
>> You can always stick it up your a---. Should
>> be 98.6 +-.
>> Fever thermometers are accurate to +- .2 degrees
>> and make good calibration standards: put both
>> thermomters in hot water in a styrofoam cup -
>> keep the water gently stirred.
>> Only color photography is sensitive to
>> temperature, and that gets processed at 100
>> same as body temperature: they are both organic
>> chemistry.
>> B&W is a +-2 F game, and you only need
>> to have a repeatable temperature and the ability
>> to read the deviation to +-10%. A grossly
>> inaccurate thermometer will do as long as
>> it is linear.
>> Temperature calibration is tough to do with
>> great accuracy. A triple-point ice cell is
>> the only common temperature reference.
>> http://www.its-90.com/wtpguide.html
>> http://www.omega.com/ppt/pptsc.asp?ref=TRCIII&Nav=temk03
>> If you would rather have someone else calibrate your
>> thermometer:
>> http://www.omega.com/toc_asp/frameset.html?book=Temperature&file=INTRO_GLASS_THERM
>> Or buy a 'Kodak Color Thermometer' or 'Kodak Process Thermometer' on
>> ebay and be as Alfred E. Neumann: "What, me worry?"
>> --
>> Nicholas O. Lindan, Cleveland, Ohio
>> Consulting Engineer: Electronics, Photonics, Informatics.
>> Remove blanks to reply: n o lindan at ix . netcom . com
>> f-Stop enlarging timers: http://www.nolindan.com/da/fstop/
> B&W needs better than +/- 2F for good control. Look at the temperature
> increments on the Kodak developing charts, they are 2F and the time
> difference is significant.
> For B&W time can be adjusted to comensate for temperature to a greater
> extent than in color. One reason that color is so sensitive is the
> difference in induction time of the various layers. At a fixed temperature
> a particular developer affects all the layers in a predictable way. Color
> can be done at lower than 100F but usually the developer needs some
> change. 100F was chosen mostly for speed of processing since most color
> film is processed in automatic machines.
> Last time I looked body temp was 98.6F.
> I agree entirely about accurate calibration of thermometers, its not a
> trivial process. I did this as a project in a physics lab at college back
> when the dinosaures roamed.
> --
> ---
> Richard Knoppow
> Los Angeles, CA, USA
> dickburk@ix.netcom.com


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