relation between dilution and time?

I found this thread while searching to answer a different question about why it is necessary to dilute developer when push processing, but now have many more. Part of which are my difficulty with math and the other with terminology.

brianmquinn said:

In theory if you dilute a developer to
2x it’s original volume you need 1.4x the time.
4x it’s original volume you need 2.0x the time.
8x it’s original volume you need 2.8x the time.
16x it’s original volume you need 4.0x the time.
32x it’s original volume you need 5.6x the time.
64x it’s original volume you need 8.0x the time.
If those numbers look like f stops that is because the same kind of math applies.
Also remember that theory and the real world aren’t in exact agreement.

Published times are sometimes more than 1.4X time for a 2x (1+1) dilution but when in doubt develop LESS. A flat negative is easier to print or scan then an overdeveloped and contrasty negative.

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Q#1. When you state "x it's original volume" do you mean

4x = 1 developer + 4 water
8x = 1+8
16x = 1+16

RalphLambrecht said:

Is this similar to the assumption that 10 degrees of temperature half or double the chemical activity during development?

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Q#2. Never heard this before either and didn't feel it was addressed. And do you mean "time", "Agitation", or "dilution" when you say "Chemical activity" ?

Thomas Bertilsson said:

Agitation is in fact the primary contrast control in film developing. I judge how the contrast in the scene I photographed needs to be processed. If high contrast, I let the agitation intervals become longer in duration, and the opposite if the contrast was low.
Then, the total duration of development is a side effect of the changed agitation and must be altered as agitation intervals are changed.
In summary it's agitation that is the primary contrast control, not the duration of the whole development cycle.

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Q#3. "Agitation intervals" can you explain your meaning? The duration of time in between agitating? Or, the duration of time you are actually agitating? Or, both and how do you make these decisions? Personal testing?

Q#4. More agitation creates more contrast or flattens contrast out?

Q#5. Is my original question of why do you change dilution of developer when push processing rather than using the same dilution for a longer period of time? Is this another contrast control as you would loose some contrast shooting a 400 film at 800 and then further loose contrast with the longer development time?

Thank You

#3 - intervals = how long of a time duration I allow between agitating the film. So an interval of 3 minutes means that I agitate at the 3min, 6min, 9min, etc marks.

#4 - More agitation creates more contrast. The part of the film that 'consumes' most developer activity is the highlights, as this is where the most density in the film is built. When you agitate, fresh developer contacts the highlight areas, and they will develop more rapidly and build density faster. So if developing time is constant, and you take one film and agitate it every 30s, and another film you agitate every 3m, you will have a significant difference in highlight density between the two while the shadow density remains the same. That = more total contrast.

#5 - I don't change dilution when I push process. But if you use Rodinal, for example, you could go from 1:25 to 1:50, which will make the total development time longer, and this will help your shadow values, because development time somewhat determines your shadow detail (shadow detail = film speed).

- Thomas

jerk151 said:

Q#2. Never heard this before either and didn't feel it was addressed. And do you mean "time", "Agitation", or "dilution" when you say "Chemical activity" ?

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Look up "Arrhenius Equation" - it's the scientific basis for Ralph's statement:

http://en.wikipedia.org/wiki/Arrhenius_equation

Thomas, are you developing sheet film in a tray or roll film in a tank.Right now I'm using a tray for my sheet film and have been doing 1 minute agitation with xtol stock and replenished when needed.I'm pretty satisfied with the way the open sky area is coming out,at 30 sec agitation there was streaking of the sky.Have not tried longer agitation intervals as was afraid of mottling of sky areas.Have you done this with sheet film yet

Mike

Thank you for your time, patience and explanation TB, it is greatly appreciated. I think I now have a weekend project as to what you suggested. Maybe a ½ cilp roll and agitate differently and maybe extremely as to get a better feeling for it.

Kirk, Thank you, I am now sitting in a corner, wrapped in a sheet, thumb in mouth and drooling a little bit. I do think I get the overall point, but I will have to check that once I wake from my nap.

Mike, I don't use sheet film. It's all roll film. 120 and 135. Sorry.

I get such quality from Tmax 400 and either Xtol or Edwal 12, that I don't feel I need sheet film.

Re: Streaking. If you get streaking with Xtol, you are not agitating properly most likely. You have to agitate enough so that the chemistry that touches the film surface is fresh and completely replacing the old. So you have to find a way of getting the chemistry in good movement.

- Thomas

mike c said:

Thomas, are you developing sheet film in a tray or roll film in a tank.Right now I'm using a tray for my sheet film and have been doing 1 minute agitation with xtol stock and replenished when needed.I'm pretty satisfied with the way the open sky area is coming out,at 30 sec agitation there was streaking of the sky.Have not tried longer agitation intervals as was afraid of mottling of sky areas.Have you done this with sheet film yet

Mike

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Posted by titrisol, comments from Dickerson and Zawadzki, creators of Xtol, on dilution and development times:

(there was a url link here which no longer exists)

Lee

Yes! Learning by doing is always best.

And, remember to print your negs often, as this is the only way you will really learn what effect your negative tweaks will give in the print.

It will soon be intuitive to you what you have to do to your film to get the most out of it, every single time.

jerk151 said:

Thank you for your time, patience and explanation TB, it is greatly appreciated. I think I now have a weekend project as to what you suggested. Maybe a ½ cilp roll and agitate differently and maybe extremely as to get a better feeling for it.

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Thanks Thomas,I use 120 also but got the large format bug lately and was experimenting with contrast controls by agitation and water bath .The open sky's are giving me a run for my money now.

jerk151 said:

Kirk, Thank you, I am now sitting in a corner, wrapped in a sheet, thumb in mouth and drooling a little bit. I do think I get the overall point, but I will have to check that once I wake from my nap.

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I understand. I think the really important info on that link is in the first couple paragraphs. Don't worry about the fancy equations further down...

Is there a relation between the dilution of a developer and developing time like the proportionality between time and temperature?

Yes. But the relationship alters with different films and different developers.

While it would be nice to be able to push a couple buttons and never have to get our hands wet,
a quick survey of manufacturers' data shows that testing outruns any attempt to predict what will happen.

.