Time Temperature compensation factors

greenspun.com : LUSENET : B&W Photo - Film & Processing : One Thread

Recently on one of the lists someone posted a simple chart for calculating times and temperatures using easy to understand maths. It was something like time * or / by [factor] for a temperature decrease or increase. I had the chart but stored it somewhere safe. Tragic isn't it getting old. If anyone has a copy of this could they re-post it or send it direct to me

Thanks Steve.

-- Steve Nicholls (gl1500@chariot.net.au), May 11, 2001

Answers

Can you run a DOS application? If so, I have a spiffy little program that can do what you want and even spit out a time/temp chart to the printer. Let me know and I'll send it to you.

-- John Hicks (jbh@magicnet.net), May 12, 2001.

Go two thirds down this page http://www.ilford.com/html/us_english/bw.html for Ilfords PDF Temperature Conversion Chart jim

-- Jim Vanson (p645n@hotmail.com), May 12, 2001.

I've looked at charts and times over the years and it seems that there is not a universal set of multipliers for all developer + film combinations. You can see this on, say, the Agfa data sheets where the graphs of dev times for various films show different gradients as a function of temperature, even for the same developer. I have an equation that I worked out from Kodak charts for HC-110. My dev time at 20C was 6 minutes for Tri-X, and the time d for different temperatures t (deg C) is: 59.4*e^(-.1146t) This can be programmed into a spreadsheet or a sci calculator. Unfortunately you need to make an equation for each film + dev combo, based on the published charts for the exponent AND your individual time at a known temperature for the multiplier (59.4 in my case). But I only used one film + one developer in those days. Hope this is helpful

-- John Stockdale (jjss@bigpond.net.au), May 15, 2001.

Did you mean this"

"I never claimed to be the cripiest fry in the basket, but I could NEVER understand why Ilford instructions packaged with developer and tech sheets have the same goofy TIME/TEMP conversion chart/graph.

Blamed thing is useless IMHO - too small and vague - leaves you guessing. Why can't they just publish T&T like Kodak does in their B&W Darkroom Dataguide - i.e. Tri-X Pro at iso 320 in D-76 1:1 @ 65 68 70 72 & 75 degrees or whatever?

Then I came across a conversion method in Aaron Sussmans book from the late 60's "Amatuer Photographers Handbook".

You take the given time at ANY given temperature for whatever combination you've got and can calculate the given time at any other given temperature fairly quickly and certainly with a finer degree of precision than with the aformentioned graph.

I know this may seem hypocritcal coming from a guy who develops by inspection and "eyeballs" exposures with an incident meter but I find it re-assuring to have something that seems at least a bit less of a SWAG than the chart.

It goes like this:

"Given the developing time at 68 degrees, you convert to the time at any other temperature by multiplying the given time by the desired temperature factor T. To convert from the time at any temperature other than 68 degrees, to any other temperature, you divide the time of the given temperature by its own factor and then multiply by the factor of the desired temperature."

Here's the chart:

Temp in Farenheit followed by factor

64 deg factor 1.23 65 1.16 66 1.10 67 1.05 68 1.00 69 .95 70 .90 71 .85 72 .81 73 .78 74 .75 75 .72 76 .69 77 .66

This is on page 382 of the edition I have. Hopefully the times and factors will line up when I "send" this to the forum. FWIW Sussman has all kinds of neat info in his book. It would definatley behoove us to look over old photo manuals at yardsales, library used book sales, etc. etc. etc. My copy came with an enlarger my wife bought me a while back."

-- Sean yates (yatescats@yahoo.com), May 20, 2001.


Just to make it international and line up... (hope this works!!)

Fahrenheit 64.00 65.00 66.00 67.00 68.00 69.00 70.00 71.00 72.00 73.00 74.00 75.00 76.00 77.00
Celsius 17.78 18.33 18.89 19.44 20.00 20.56 21.11 21.67 22.22 22.78 23.33 23.89 24.44 25.00
Factor 1.23 1.16 1.10 1.05 1.00 0.95 0.90 0.85 0.81 0.78 0.75 0.72 0.69 0.66


-- Nigel Smith (nlandgl@unite.com.au), May 20, 2001.



and 2 seconds after posting that I thought of a slight alteration...

Fahrenheit 64.00 65.00 66.00 67.00 68.00 69.00 70.00 71.00 72.00 73.00 74.00 75.00 76.00 77.00
Celsius 17.78 18.33 18.89 19.44 20.00 20.56 21.11 21.67 22.22 22.78 23.33 23.89 24.44 25.00
Factor 1.23 1.16 1.10 1.05 1.00 0.95 0.90 0.85 0.81 0.78 0.75 0.72 0.69 0.66


-- Nigel Smith (nlandgl@unite.com.au), May 20, 2001.


Moderation questions? read the FAQ