kaiyen
local man of mystery
naw, no need to fill in the closed parenthesis. I goofed, let's let it live for posterity 
.
As you develop film, it's not entirely, 100% true that you develop for the highlights. That implies, after all, that development affects only the highlights. In reality, it pulls the whole curve up, though it certain pulls the highlights up faster than it does the lower end of the curve. So yes, increased agitation, or increased time, should pull the toe up a bit. I think the reason why increased agitation in particular would make a difference is because you'd be constantly putting fresh developer over the shadow areas, rather than ever-so-slightly exhausted developer. Just more time in developer in general would not do that.
In fact, the real reason for intermittent agitation is really increased sharpness, which is important in 135 and 120 formats, but not really in sheet film. That's why many people develop sheet film in continuous agitation.
.As you develop film, it's not entirely, 100% true that you develop for the highlights. That implies, after all, that development affects only the highlights. In reality, it pulls the whole curve up, though it certain pulls the highlights up faster than it does the lower end of the curve. So yes, increased agitation, or increased time, should pull the toe up a bit. I think the reason why increased agitation in particular would make a difference is because you'd be constantly putting fresh developer over the shadow areas, rather than ever-so-slightly exhausted developer. Just more time in developer in general would not do that.
In fact, the real reason for intermittent agitation is really increased sharpness, which is important in 135 and 120 formats, but not really in sheet film. That's why many people develop sheet film in continuous agitation.
Roger Hicks
Mentor
The way to get maximum toe speed, for given contrast (i.e. a given highlight density), is constant agitation. Compared with normal intermittent agitation, this reduces sharpness slightly and increases grain slightly. Again we're into 'slightly' and a lot of people exaggerate the effect. Severely reduced agitation (the minimum required to get even development) gives a more significant increase in sharpness, a modest reduction in grain, and a small loss of speed.
Cheers,
Roger
charjohncarter
Mentor
So Kaiyen and Roger, the increase in shadow detail is so slight with increased agitation that it is probably best (considering grain, sharpness) to do what most of us have always done: expose (maybe a little more) for the shadows and develop for the highlights. And then maybe, if we expose a little more, have to print on a little harder paper. Perhaps, I shouldn't bring up the C word.
Thanks, to both of you.
Carter
Thanks, to both of you.
Carter
Chris101
summicronia
I'm confused on this concept of shadow enhancement with increased agitation. I believe you, you have empirical evidence, but I don't understand it conceptually: When film is placed into the developer it begins to develop. Without agitation, the parts that develop the fastest, the highlights, will deplete the developer in contact with that part of the film. By agitating, the developer is refreshed, and highlight development continues at the same rate throughout the time in the developer.
With shadows, the developer is depleted at a much slower rate, possibly not at all for pure black (clear negative.) Logically, considering this, I would predict that there would be little or no effect on the shadows from increased agitation, as the developer does not deplete as much in the shadow regions.
Now as I said, I completely believe your statement of the facts. Can you explain why my hypothesis does not fit the facts? Thanks!
With shadows, the developer is depleted at a much slower rate, possibly not at all for pure black (clear negative.) Logically, considering this, I would predict that there would be little or no effect on the shadows from increased agitation, as the developer does not deplete as much in the shadow regions.
Now as I said, I completely believe your statement of the facts. Can you explain why my hypothesis does not fit the facts? Thanks!
kaiyen
local man of mystery
I think the keys are that 1) the distinction between the developer being just slightly more used up in the shadows vs. completely fresh and 2) that overall increase in developer activity (be it via time or agitation) does pull up the curve even in the shadows.
You're confusion is exactly what the reality is that the difference is so, so slight. It's barely worth noting...
You're confusion is exactly what the reality is that the difference is so, so slight. It's barely worth noting...
Roger Hicks
Mentor
As far as I know, Kaiyen has it. It's the small difference between partially exhausted developer (which is, remember, partly in the gelatine) and fresh developer. Constant agitation gives fresh, active developer all the time. Diffusion into the gelatine is important, and the concentration gradient is almost certainly steeper than we think.
Your reasoning is impeccable, and as far as I am aware, no-one has done enough research to find out the differences between agitation for 10 seconds/minute, 20/minute, 30/minute, 40/minute, 50/minute and 100%.
It may be something to do with induction times, or with diffusion rates into gelatine, or maximum possible dev rates. In other words, I dunno, and I'm not sure anyone else does, but that is the way that it is. Part of the classic 'science of colour, alchemy of black and white'.
Cheers,
R.
charjohncarter
Mentor
I'd still like to know, Roger, if when you did your shadow density test and noticed a rise in shadow density from increased agitation, if you compared it to the rise in highlight density. You may have stated this in a previous post with this thread, but I didn't catch (understand) it. I think Chris101 would like to know the answer too. It may be very pertinent to his (and my) use with the grunge genre.
Chris101
summicronia
Oh man! You remembered! I have a roll of trix sitting right here, ready for development. I know there are some exposure errors on the roll, because I noticed the filter on the lens AFTER I made my exposures. So now I'm thinking "which would be grungier: no agitation, or continuous?"
Roger, thank you for spending time with this. Even though I will probably never have 1/3 stop of precision, it's good to have another tool to use to correct things after the fact. And the knowledge of the process is invaluable!
Roger Hicks
Mentor
Dear John,
The clue is in the phrase 'for a given contrast', i.e. you adjust time downwards to compensate for the added agitation so that the slope of the Dlog E curve is constant.
In other words, if the highlight density remained constant, the contrast would decrease (the 0,10 density speed point would rise while the point 1.50 log units to the right remained constant). The highlight density (or at least, the density at 1.50 units to the right, which is good enough) does rise, but so does the speed point, so the slope remains constant.
With less agitation and more time, the speed point rises more slowly than the highlight density, so the contrast increases, i.e. you are no longer meeting ISO conditions, but 'pushing'.
Sorry this is so complicated, but that's the way it is. My own results merely indicated that this might happen, so I talked to Ilford about it, and they confirmed (from their own considerably more rigorous knowledge) that it does.
Once again, I'd emphasize that this is SLIGHT. The maximum 1/3 stop speed gain was a guess, based on what might be possible with the ideal film and developer at the optimum concentration, pH and temperature. Kaiyen's statement that 1/6 stop is far more likely is absolutely correct. I strongly suspect that what I noticed in my own films was down to experimental error and wishful thinking, or I wouldn't have noticed it at all.
Edit: for pushing, extra agitation will also give you more shadow detail at a given contrast.
Cheers,
R.
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kaiyen
local man of mystery
Again, note that Roger is saying "at a given contrast" in his post script. Many people push in order to achieve proper midtones while sacrificing highlights. People don't push to maintain a given contrast that is close to normal, non-pushed contrast. That's why we don't usually use extra agitation, much less continuous. Sometimes the exact opposite is used - stand development.
charjohncarter
Mentor
Roger, as Chris101 says, it is nice of you spend the time with us on this. I'm sure you feel like you are teaching a remedial photography class, anyway thank you.
Chris101
summicronia
As I was developing my film yesterday, I was thinking about this (although I didn't change my normal agitation routine one lick.) It seems that the key is the diffusion into the emulsion. As the rate of diffusion is held constant, the concentration on one end of the 'membrane' will determine how close to equilibrium the interior developer concentration is. Thus the shadows will maintain a higher developer concentration inside the gelatin. Thanks for a great physical chemistry problem to think about.
Carter: yep. Second semester gen-chem.
charjohncarter
Mentor
Chris101, I think maybe it is better if I don't think (just do as I am told). But I do like your theory/analysis (even though I don't want to think about it).
Chris101
summicronia
I'm a chemistry teacher, what can I say?