another way to ponder 'intermittent' agitation

Discussion in 'B&W: Film, Paper, Chemistry' started by David Lyga, Apr 12, 2013.

  1. David Lyga

    David Lyga Subscriber

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    Although some of us agitate film continuously, most of us do so intermittently in the developer. We are told to agitate 'every 30 seconds', 'every 60 seconds', or other inventive ways. Maybe a better, more rational approach would be to space agitations according to how long development time is.

    My theory is this: with long development times it takes a proportionally longer time to exhaust developer at the specific location it is on the film. This local exhaustion necessitates refreshing that developer with 'new' developer, and that is done through agitation. If development time is really short that means that the developer is working very quickly and, thus, exhausts rapidly.

    Why not, instead of 'standardized' agitation intervals, simply divide the TOTAL development time by a factor of, say, 10, and base those agitation intervals upon that? For a 10 minute development time that would mean we agitate every minute. For a five minute development time that means that we would agitate every 30 seconds, and so forth.

    At least to me, this would seem to result in a negative process that more closely conforms to the ACTUAL capacity of the developer and respects that developer's ability to reduce silver in a standardized way, regardless of the speed (and inherent contrast) of the negative material it processes. And it simplifies much: from now on ALL films get 'ten agitations'. - David Lyga
     
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  2. Laurent

    Laurent Subscriber

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    Others, more expert than me, will react to this, but the first thought this brings to my mind is that, when times are longer it is -usually, at least for me- because dilution is higher, therefore exhaustion would be faster and the timed agitation could make sense.
     
  3. michael_r

    michael_r Subscriber

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    David - it also depends on the film and developer. Remember that the purpose of agitation is not only to replenish exhausted developer, but also to remove development by-products that can lead to streaking and other problems depending on the developing agents present, pH, film type.
     
  4. Richard S. (rich815)

    Richard S. (rich815) Subscriber

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    I just do it one way, and stick to it for consistency, then adjust my other variables as needed. There's enough other stuff to over-think. I think.
     
  5. Kevin Kehler

    Kevin Kehler Member

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    A film/developer combination which needs 20 minutes of time does not exhaust 1/20 of it's power every minute. Rather than being a linear relationship, I would think it is a sliding scale, where 40% of the development occurs in the first 5 minutes, 20% in the next 5 minutes, etc., etc. which is why reducing or increasing developing times has a strong influence on highlights and contrast as these are the areas that need the most development time. So, while I understand what you are trying to do, I suspect you would have incomplete highlight/contrast development under your theory.

    Just my opinion, I am sure there are more scientific answers.
     
  6. kintatsu

    kintatsu Member

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    Rather than rely on some formulaic method of agitation, one should probably rely on the actual contents of the negative to determine agitation. With decreased agitation, separation between high and low values is decreased. The opposite is true for increased agitation. With higher values, the developer exhausts quicker than with lower values, therefore your development and agitation should be matched to some context of the individual scenes. By altering your agitation, as with altering your times, you change the range of values. The greater the alteration, the greater the change. As agitation is only part of it, I should think there is no magic one size fits all.

    I have found that changing agitation to match my scenes gives me better pictures than using a solid set in stone standard.
     
  7. cliveh

    cliveh Subscriber

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    I don’t follow this theory at all. Some of us want complete consistency of method. There are enough variables within photographic capture and processing without increasing them.
     
  8. kintatsu

    kintatsu Member

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    Generally speaking, standard agitation, tested for each film, is correct. Consistency is the key, but to achieve results consistently may require trading consistent methodology for something more likely to produce the consistent results we desire. That's why we have expansion and contraction, and other methods of obtaining the final print we want.

    Decreasing, or increasing, agitation just to have some mathematical formula seems to defeat the purpose of controlling the values we wish to present in our print. It can't work if it's based only on some formula, as each scene with values that deviate from the photographer's mathematical norm will likely be a disappointment. That's why we test and create a system that works for us.

    The point I was trying to make was that using just mathematical numbers and formulas without consideration of values and subject just doesn't seem a good idea.

    These comments are only based upon my own experience and study, which is limited, so please don't think I'm trying to offend anyone, and if I did, I apologize.
     
  9. David Lyga

    David Lyga Subscriber

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    Maybe I will learn something new here.

    I honestly thought that all chemical reactions slowed down with a developer/film combination that required long development. Take, for example, D-23 with Tri-X at 68F: it takes 'forever' to achieve adequate contrast. So, I thought logically, that agitation with that combination should be about every two or three minutes, with a total development time of 20 to 30 minutes. Or take HC-110 using a rather active dilution of 'B', with Pan F: Maybe less than five minutes, total, would be adequate for such development (achieving same gamma), and, with that combination, agitation at least every 30 seconds would become mandatory for complete freedom from possible inconsistency.

    kintatsu posits that separation between high and low values is decreased with less agitation. That is true in an absolute sense, of course, but not necessarily true in the two relative senses I pose above. With long, long development times I don't think that 'every 30 seconds' achieves any greater separation than with 'every two or three minutes'. Why? Because with slow development the developer reducing the highlight area remains just as strong as the developer reducing the less taxing shadow areas for a lot longer time. Thus, there is no exhausted developer to replace (yet). But with the fast development for Pan F and HC-110, the exhaustion takes place far more rapidly, thus agitaion must be far more frequent.

    Regardless, maybe I am incorrect; your diverging viewpoints are certainly welcomed. Sometimes that which seems logical proves to be misguided when others offer better reasons. - David Lyga
     
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  10. cliveh

    cliveh Subscriber

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    I don't see this as a trade off. Please explain.
     
  11. David Lyga

    David Lyga Subscriber

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    cliveh: I think that kintatsu is defining 'consistency' literally.

    Consistent agitation is not necessarily going to result in consistent results, as I said, previously. When you agitate every three minutes for the Tri-X/D-23 combination that does not translate into the same results for agitation every three minutes with the Pan F/HC-110 combination. 'Consistenty' there yields wholly inconsistent results. It's a matter of semantics: true consistency would mandate using different (ie, 'inconsistent') agitation methods. - David Lyga
     
  12. cliveh

    cliveh Subscriber

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    No David, this has nothing to do with it. It is the trade off I don't understand.
     
  13. MattKing

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    I depend on my routine to help me keep from screwing up, so David's suggestion definitely wouldn't work for me :wink:.

    With a lot of free time and a bunch of extra film and developer, I could see there might be some benefit in designing a customized agitation routine for each different film/developer combination.
     
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  15. pentaxuser

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  16. kintatsu

    kintatsu Member

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    First, I didn't mean to imply that there is a trade-off. There are just different ways to skin a cat. My stating that way was a mistake, I should have said something else. Just to clarify my thought pattern in this matter, on this subject we are looking at 1 process, or element, out of several. If 3 identical exposures are made of the same normal scene, the effects of agitation can be easily seen. With your normal agitation the scene appears correct. With a decrease, the contrast is decreased, and the opposite holds true with an increase. When all 3 are printed, the results are visible, and to get the same print from each, printing controls are used. In most cases, we determine our own normals based on our work and vision. Your normal may not for someone like me, without the experience to make it work.

    At each step, deviations can be, and are, made to compensate for what we desire in our print. These deviations are based on the scene and our tools, which includes our knowledge. A scene with a longer or shorter scale, one that exceeds our vision, we resort to controls at every stage. Dodging, burning, and grades of printing can be used, expansion and contraction in the negative when developing, and even filters during exposure are tools that deviate from consistent methods.

    I was just positing that this is another tool in our box, basing our choice where we are inconsistent, or vary our approach. Based on David's question, I would assume that there are too many factors for a one for all approach, that's just my thought. Of course, it's easier in sheet film when developing only 1 shot, as my values are often outside the ranges for that method.

    And, cliveh, your photos are magnificent, so whatever is working for you, don't change!
     
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  17. kintatsu

    kintatsu Member

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    That pretty much sums it up. I've seen it on my own work. Trying to make every action the same, instead of making the results the same caliber, just got me more confused. I agree with cliveh that consistency in our processes is important, but only in-so-far as it supports our desired results.
     
  18. Doremus Scudder

    Doremus Scudder Member

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    Some thoughts:

    Developers that take longer to develop are less active but do not need less-frequent agitation. Just the opposite in many cases.

    Initial agitation is to ensure even absorption of the developer by the negative and to get rid of the initially high amount of by-products. I agitate more at the beginning of development than after the halfway point.

    The amount of agitation (if one can even quantify that...) plus the development time = the total amount of development for a given developer. Increasing agitation while leaving time the same is the same as increasing time but not changing the agitation: the overall contrast of the negative is increased. Most of us like to increase time for expansions since it is more controllable and repeatable.

    After 50% of the development, most of the shadow areas and mid-tones are developed almost to where they will be at the end of the developing time. It's the highlights and more dense areas that continue to increase in density. The amount of increase with time is proportional to the amount of exposure with more exposure areas developing more than the lower. This means that agitation in the first part of development is what affects the lower-exposure areas more. If one wants evenness in the shadows and lower mid-tones, then a fairly regular agitation early on seems to be logical.

    Agitation schemes that use reduced agitation do so for particular reasons. Compared to continuous agitation, reducing agitation to a certain point, say, every 15-30 seconds, has little more effect than extending the development time a bit since the developer is not exhausted in any of the negative areas and the by-product build up is not significant.

    Extending the time further (and the exact point this happens is different for different developers, etc.) results in the developer running out of activity in the denser areas of the negative while remaining fully active in the less dense areas (BTW this would happen more quickly in weaker developers, i.e., developers that needed longer developing times...). This results in the compensating effect, which reduces the development of the highlights proportional to density and allows squeezing a bit more information onto the negative. This is the primary reason for most reduced agitation schemes. The more one reduces the frequency of agitation, the more pronounced the compensating effect. The risk is getting uneven development and mottling/streaking.

    Another reason for reducing agitation frequency is to get edge effects. On a micro scale, the same mechanism that causes the compensation effect will cause developer in denser areas adjacent to less dense areas to exhaust. However, there is a bit of diffusion of developer across the border between the two areas of differing density. This results in the edge of the dense area being infused with a bit of more active developer, creating a thin line of greater density along its edge. The opposite happens to the edge of the lower-density area, it gets some of the less-active developer which results in a thin line of reduced density along its edge. These lines are adjacent to each other and lend the prints made from these negatives a more contrasty line of definition between areas of different densities creating the illusion of more sharpness or even outlining of forms. These are called Mackie lines and are clearly visible in my grain focuser (I use PMK with a reduced agitation scheme for the last half of developing just to get more of these edge effects. Reducing the agitation in the first half of developing results in uneven development).

    So, I would think that an agitation scheme should be chosen on the basis of 1) getting even development, 2) getting the compensating effect one wants (or none at all), and 3) encouraging formation of or preventing edge effects.

    If one wants no compensation and no edge effects, then continuous agitation will work just fine, just with a shorter development time than, say, agitation every 30 seconds.

    Best,

    Doremus


    www.DoremusScudder.com
     
  19. markbarendt

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    Good thoughts Doremus.

    One thought/question though here;

    Isn't compensation more about fitting the scene to the paper by encouraging the film curve to shoulder off by discouraging highlight development?

    Seems to me that compensation is actually "designed" to get to more print detail by actually reducing the negative's highlight detail.

    Put another way, isn't compensation simply trying to create more of an S-curve than a linear curve?
     
  20. cliveh

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    kintatsu, thank you for the clarification and the compliment.
     
  21. kintatsu

    kintatsu Member

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    No problem. Your work is great stuff, and several of your posts have been quite helpful to me.

    Have a great rest of the weekend!
     
  22. michael_r

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    Correct, Mark. The total "information" that can be in the negative is limited by the film's inherent exposure scale, and exposure. Development can either maintain that information, or reduce it. It can not increase it. Compensating development preferentially reduces highlight contrast. Highlight information is "expensed" for easier printing.
     
  23. kintatsu

    kintatsu Member

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    I remember reading somewhere that with proper exposure, compensation can also be used to improve local contrast in the mid-tones, especially for portraits.
     
  24. markbarendt

    markbarendt Subscriber

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    Compensation reduces contrast so...
     
  25. albada

    albada Member

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    The OP is proposing using a fixed number of agitations instead of a fixed time-interval.
    My knowledge of chemistry is rudimentary, but this makes perfect sense to me.
    If a chemical reaction only proceeds half as fast and thus takes twice as long, then doubling the time-interval (giving the same number of agitations) will produce the same result as double-speed and half-interval.

    However, the rate of diffusion through gelatin does not depend on dev-rate, so that complicates things.

    Anyway, I have created a concentrate giving XTOL-quality, and I designed it to have twice the dev-time as XTOL. And I recommend agitating every 60 seconds instead of Kodak's recommendation of every 30 seconds. It's worked fine in my experiments.

    Mark Overton
     
  26. Kirk Keyes

    Kirk Keyes Member

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    Has anyone mentioned "diffusion" yet? (Doremus used "infuse"...)

    The reason for agitation has little to do with chemical "reactions" but a lot to do with helping the chemicals diffuse into the gelatin matrix of the film. The agitation ensures that fresh developer solution is brought into physical contact with the surface of the gelatin so that fresh developer gets into the gelatin and it helps remove development byproducts from the gelatin faster than if there was no agitation.