How accurate is using time to compensate for temp?

I forgot to answer your question. The Darkroom Cookbook has a time-temperature scale that works pretty well if you know one successful time. Mark that time and temperature and go parallel to the nearest constant CI line to find the time. This scale is a log scale, you may notice.

The attached .pdf file shows the Kodak recommendations for 12 films in D-76 at full strength, roll film, small tank, intermittent agitation at 65, 68, 70, 72, and 75 Fahrenheit. Data points are Kodak's, which are rounded to 15 second intervals according to long established practice. Smoothed lines are done in the spreadsheet. X is temp in Centigrade and Y is recommended development time in minutes.

Sometimes I learn more quickly from a graphic representation rather than a table of data. I'm reminded of Yogi Berra's admonition, reported as variations on some form of "you can learn a lot by watching".

Ilford's ID-11 (equivalent to D-76) information sheet is at: http://www.ilfordphoto.com/Webfiles/20062161159472874.pdf

Lee

The Kodak Master Darkroom Dataguide has what they call a developing computer. You come up with a number for your film/developer combination. Either use the Kodak number or find your own. Then you line up the temperature with the number and read the time for that temp. I'm usually within a few degrees and just adjust time using the wheel. For example with number 39 68 deg gives 9m, 75 deg gives 6.5m, 65 deg gives 11.3 min. Seems to work for me over the years.

Doremus Scudder said:

This discussion has aroused my curiosity about a couple of things. Sorry if this is a "quasi-hijack" to some degree, but I think it belongs here instead of in another thread.

First questions to Tom Hoskinson: Could you give some instruction to a non-mathematician about how to use the Arrhenius equation in this context? What is the difference between Kelvin and Celsius, how can I derive a new time for a different temperature from a known one?

And now to Frotog. I would be interested in hearing what evidence you have to support your statements that image color and contrast are also affected by time/temperature changes. Could you elaborate a bit please?

Thanks in advance to both of you for enlightening me.

Best,

Doremus Scudder

www.DoremusScudder.com

Click to expand...

Here are a couple of Hewlett Packard calculator KEYSTROKE Programs that I generated a long time ago to make the subject Arrhennius calculations.

ARRHENNIUS FUNCTION 1
(calculates time at a new temperature, given an activation energy and time at temperature) ARRHENNIUS FUNCTION 2
(calculates activation energy from Development times at 2 different temperatures)

00 ( 86 BYTE PROGRAM ) 00 ( 136 BYTE PROGRAM )
01 >LBL “NUTIME” 01 >LBL “ARHEN”
02 INPUT “EA” 02 INPUT “TMM”
03 STOP 03 INPUT “TMN”
04 INPUT “TA” 04 INPUT “TA”
05 INPUT “TMN” 05 INPUT “TB”
06 INPUT “TB” 06 8.6170881E-5
07 RCL+ “TK” 07 ENTER
08 RCLx “K” 08 STO “K”
09 STO “TO” 09 273.15
10 RCL “EA” 10 STO “TK”
11 RCL “TO” 11 RCL “TMM”
12 E^X 12 LN
13 RCL “TMN” 13 RCL “TMN”
14 XY 14 LN
15  15 -
16 STO “TO” 16 STO “T”
17 RCL “EA” 17 RCL “TA”
18 RCL “TA” 18 RCL “TK”
19 RCL+ “TK” 19 +
20 RCLx “K” 20 RCL “K”
21 RCL “EA” 21 x
22 XY 22 1/X
23  23 ENTER
24 E^X 24 RCL “TB”
25 RCL “TO” 25 RCL “TK”
26 x 26 +
27 END 27 RCL “K”
28 x
29 1/X
30 STO “ZX”
31 -
32 RCL “T”
33 XY
34 
35 STO “EA”
36 RCL “ZX”
37 x
38 E^X
39 RCL “TMN”
40 XY
41 
42 STO “ZX”
43 RCL “EA”
44 END

ARRHENNIUS FUNCTION 2
(calculates activation energy from Development times at 2 different temperatures)

00 ( 136 BYTE PROGRAM )
01 >LBL “ARHEN”
02 INPUT “TMM”
03 INPUT “TMN”
04 INPUT “TA”
05 INPUT “TB”
06 8.6170881E-5
07 ENTER
08 STO “K”
09 273.15
10 STO “TK”
11 RCL “TMM”
12 LN
13 RCL “TMN”
14 LN
15 -
16 STO “T”
17 RCL “TA”
18 RCL “TK”
19 +
20 RCL “K”
21 x
22 1/X
23 ENTER
24 RCL “TB”
25 RCL “TK”
26 +
27 RCL “K”
28 x
29 1/X
30 STO “ZX”
31 -
32 RCL “T”
33 XY
34 
35 STO “EA”
36 RCL “ZX”
37 x
38 E^X
39 RCL “TMN”
40 XY
41 
42 STO “ZX”
43 RCL “EA”
44 END

Thanks Tom!

Doremus Scudder

www.DoremusScudder.com