influence of temperature, agitation and dilution on the film

bonk

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The Kodak Basic Photographic Sensitometry Workbook states that a film's "Contrast Index is affected by four variables: time, temperature, agitation, and developer activity". (I suppose with developer activity they mean dilution.)

How the contrast index changes based on development time is shown in a graph ("characteristics curve" or "D-Log E curve") in that workbook and that is also what I have seen beeing provided by the film makers for their films.


But why are those graphs only ever shown (as far as I can tell) for one of the four variables, the development time, but never for the other three variables, temperature, agitation, and developer activity. Shouldn't that be of interest to?

I have always wondered if and how modifying temperature, agitation, and developer activity modifies the contrast and overall appearance of the final negative. Would the characteristics curves (or D-Log E curves) look much differently when changing temperature, agiatation or dillution (but compensated with development time to get a proprerly development film)?
 

ic-racer

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There is no good way to quantify or measure 'agitation' . Those examples by Kodak are just 'examples' of what you might come up with in your darkroom. One take home message is to only change one variable at a time.

BTW: There is a time-temp chart in the Ilford literature. Kodak had one incorporated into a wheel in the old Darkroom Databook.
 

Sirius Glass

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I used the 10 second agitation & inversion with tank thumps and then agitation & inversion for 5 seconds every 30 seconds. The I started using the Jobo processor with its constant agitation and I have stuck with that ever since. Agitation in photography discussions quickly move to the cult religion level very quickly.
 
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bonk

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BrianShaw said:
For example...
https://imaging.kodakalaris.com/sites/prod/files/files/resources/f4017_TriX.pdf

the assumption for agitation is provided
compensation for temperature is provided

more homework required!
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Sorry for the late reply, I am aware of those adaptation tables for some temperatures, but my question was why is the change of the CI characteristics based on temperature never shown in a graph, why do film vendors only show graphs for the CI based on time but not based on temperature (or developer activity)?
 

Sirius Glass

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One scales time up or down from 20 degrees C and the characteristics do not change.
 
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bonk

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michael_r said:
The curves would look similar or the same if you adjusted the other variables by the appropriate amounts (barring extremes). ...
Click to expand...
Thank you for the detailed answer. This makes perfect sense to me! I have a little follow up question:

In what other ways other than the contrast index does dilution, temperature and time affect the final outcome of the image? Can I use dilution, temperature or time to control different aspects of the appearance of the image (other than CI)? For example, do all three things affect the “graininess” of the image in a similar way?
 
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bonk

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Sirius Glass said:
One scales time up or down from 20 degrees C and the characteristics do not change.
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The example characteristics graph from the sensitometry workbook I posted initially says otherwise. If I scale time up from 8min to 13min but keep it at 20°C, the characteristics curve totally changes.
 

Sirius Glass

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bonk said:
The example characteristics graph from the sensitometry workbook I posted initially says otherwise. If I scale time up from 8min to 13min but keep it at 20°C, the characteristics curve totally changes.
Click to expand...

I have never had a problem with that other than when the time gets less than five minutes and then I either wait for another day or chill the chemicals.
 

Adrian Bacon

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same here. Jobo all the way. I also remove temperature and developer activity as variables and control contrast solely through development time. I very much doubt changing the other variables will significantly change the shape of the curve outside or more or less contrast, so there’s not much reason to make it any more complicated than it needs to be.
 

Adrian Bacon

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bonk said:
The example characteristics graph from the sensitometry workbook I posted initially says otherwise. If I scale time up from 8min to 13min but keep it at 20°C, the characteristics curve totally changes.
Click to expand...

the contrast changes. The general shape of the curve, not so much. You would be hard pressed to see a difference between equivalent prints made with them outside of the higher contrast negative having different looking grain, assuming you’re enlarging enough to actually see the grain. A lot of this boils down to: you have 4 variables. Each one doesn’t significantly change the overall shape of the curve, but can effect contrast. Development time is the easiest to change, so that is what is presented.
 
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