Agitation

Discussion in 'The Darkroom' started by Actor, Aug 5, 2009.

  1. Actor

    Actor TPF Noob!

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    One of my photography books shows three different prints made from different negatives, but of the same subject. In producing the prints the only variable was the agitation of the film during processing: the first received "normal agitation", the second received no agitation and the third received constant agitation. The normally agitated negative is advocated as the best.

    But I wonder. The problem with "normal agitation" is the difficulty in achieving consistency. The book suggests "...inverting and righting the tank with a twisting motion of your wrist. Turn the tank completely upside down, then reverse the process..." Something of a mouthful and not completely clear at first reading.

    The purpose of agitation is to keep fresh developer in contact with the film. Continuous agitation would seem to be a better approach. Placing the tank on a motorized set of rollers, similar to a rock tumbler, comes to mind.

    Of the three prints, the no-agitation one seems dark, the continuously agitated one seems light, implying that the negatives were too light and too dark respectively. In other words, it appears that the continuously agitated negative is over developed. I.e., the processing time needs to be shortened. How much shorter probably can only be determined by experimentation.
     
  2. CSR Studio

    CSR Studio TPF Noob!

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    There are problems with continuous agitation. First off, overdevelopment as you stated and what it does to highlights and shadows. Also, you oxidize the developer. Shadows are really affected by over agitation. "Normal" agitation isn't hard to achieve. Continuous for the first minute then 15 seconds every 3 minutes. That is what I do for HC-110.
     
  3. djacobox372

    djacobox372 No longer a newbie, moving up!

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    Less agitation = less contrast... however, the darkest exposed (non-black) parts of an image will always be the same value regardless of agitation. This means that if you ONLY decrease agitation you will get a dark low contrast image--the trick is to increase development time to push the image back up to the brightness you want. The longer development times will increase the brightness of dark areas of the image, while less agitation will have a counteracting effect on the highlights.

    The process behind it is this:

    * The less exposed areas of an image deplete developer very slowly, so replenishing the developer via agitation has little impact on development. The only way to increase their development is by a longer dev time or stronger developer.

    * The more exposed areas of the photo deplete developer quickly, agitation replenishes the developer around the exposed areas increasing the strength of the development.

    You can exaggerate this effect by using a dilute developer that is exhausted more quickly by highly exposed areas of the film.
     
  4. Torus34

    Torus34 No longer a newbie, moving up!

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    Agitation, as with any other part of chemical processing, is something that you learn to standardize roll to roll. The main thing you're after is to visualize the final print at the moment of exposure. This just isn't possible if you don't have a stable, reproducable chemical process.

    Agitation affects contrast. More agitation = greater contrast. In modern B&W you control contrast through VC filtration. So if you aren't happy with the specific filter you usually use for 'normal' prints, you can change the film development agitation to increase or decrease the contrast of the negative and, as a result, change the filter.

    But once you're satisfied, lock in on the agitation and don't vary it.
     
  5. christopher walrath

    christopher walrath No longer a newbie, moving up!

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    I agree with the above poster that consitant agitation is both simple to acheive and easy to maintain. Close with HC 110 I agitate the first 30 sec and then 5 sec at the top and bottom of each minute thereafter.
     
  6. madrid01

    madrid01 TPF Noob!

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    Hello everybody,
    You are saying that all three negatives are in different quality?


     
  7. Torus34

    Torus34 No longer a newbie, moving up!

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    A 'no agitation' negative will be 'flatter' in contrast and lighter overall than a normally-agitated one. A 'continuous agitation' negative will be darker overall and more contrasty than a normally-agitated one.

    Again, the key to film processing is to provide sufficient agitation [usually as per the instructions of the developer or tank manufacturer] and then do it in the same way each time. You'll find more information on this in the series of articles on b&w photography on this site. Parts III and VI in particular cover the importance of standardized film development and how to go about achieving it. If you've any questions about the information in them, please do PM me. [I know the author personally.]
     
    Last edited: May 25, 2010

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