Agitation and contrast?
I was reading a Kodak publication on XTOL and saw this line in the instructions:
"Agitation should consist of 2 to
5 cycles, depending on the contrast you need and the
type of tank."
There was no further explanation. Could someone please explain to me the relationship of agitation to contrast as well as what the type of tank has to do with it?
More agitation, more exchange of fresh developer to the film.
This results in more contrast due to more fresh developer getting to the film and doing a better job.
Less agitation lets the developer that has soaked into the emulsion do it's thing.
Highlight areas with lots of exposure will eat up the available developer. With no exchange of fresh developer this tends to keep highlights under control to a degree.
This is known as semi-stand and gives a compensating effect in high dynamic range (contrasty) scenes.
Note this an increase in amount of agitation, not intensity. I would say two would be a standard agitation regimen. Up to five would provide increased contrast.
Increase intensity and you could produce faults in your negatives. Example, with 35mm film, you could get dense streaks stretching out from the sprocket holes with overly vigorous agitation.
What publication were you reading? Their current document on Xtol, J-109, recommends "...initial agitation up to 5 cycles, depending on your results. For KODAK PROFESSIONAL T-MAX Films, provide initial agitation of 5-7 cycles in 5 seconds." The publication for T-MAX 400, F-4043, states the same. This assumes a small tank.
And to answer your question, the more agitation, the more contrast attained due to increasing the amount of time fresh developer is in contact with the film. If you want to see the results, shoot three rolls exactly the same, then develop one like the instructions say, develop the second with no agitation at all, and develop the third with constant agitation. Develop all three for the same amount of time. I have my students do this to see the effects.
Last edited by Greg Davis; 02-26-2011 at 08:46 PM. Click to view previous post history.
As you develop your film in the tank, your film uses up developer chemical components that is TOUCHING the film emulsion first. If you don't agitate, that portion of the chemical gets used up and loses power to develop the film. Slow diffusion takes place so it never completely loses it, but it slows down. When you agitate, you move the chemical around so fresh chemical will be in contact with the emulsion. The developing process speeds up again until the next agitation cycle.
More you agitate and more frequent you agitate, faster developing action takes place because of this.
Now, when you develop film, shadow portion gets done first but highlight portion keeps going longer you process your film. That means, more you agitate and speed up the process, your highlight gets brighter and brighter, thus increasing contrast.
That's the simplest I can make it to explain this.
Now with that said, it is VERY important to keep your process the same every time you process your film. You control your development by adjusting and keeping constant, development time and agitation schedule. If you don't at least keep one the same, keeping consistent result will become very difficult.
Why the tank matter? The amount of chemical is different and how the fluid mix together is different. So Kodak specifies which kind of tank they are talking about when they mention what/how to process.
Develop, stop, fix.... wait.... where's my film?
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On page 3 of that J109 document, center left column, step 6 in the "developing in Small Tanks" section.
Originally Posted by Greg Davis
Thanks everyone, that explains everything clearly.
Yeah, reading that I would definitely hit it at two agitation cycles.
For more contrast, you might try adjusting time rather that augmenting agitation as this a more readily repeatable process.
Different agitation can always be compensated by shorter or longer deveolpment time. So you can start with any way of agitation, if you try to find a devolopment time suitable for your image copnception. But is is important to keep this agtitation method.