Bellows Extension, Reciprocity Failure and Development Compensation

Discussion in 'Macro Photography' started by 36cm2, Apr 26, 2011.

  1. 36cm2

    36cm2 Member

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    Am I correct that, when one extends exposure time due to bellows extension and then extends exposure time again due to film reciprocity failure, the recommended reduction of development time is intended to offset increased contrast arising from reciprocity failure (and not from bellows extension). I ask because this morning I extended an exposure to 2 minutes due to bellows extension, but did not compensate for reciprocity failure (as I was using Acros film). I would like to confirm that I don't need to reduce development time in this case, as I believe that bellows extension alone should not increase contrast.

    Also, what are the general guidelines for how much to reduce development time to compensate for reciprocity failure?

    Many thanks for your help,
    Leo
     
  2. 36cm2

    36cm2 Member

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    Just to clarify, I understand how to compensate for bellows extension and how to compensate for reciprocity failure. I'm seeking guidance on how development time needs to be adjusted, if at all, where either or both of these occur. My understanding is that (i) increasing exposure time to counteract reciprocity failure will result in increased image contrast and (ii) reducing development time will offset that increased contrast. I'm trying to understand that relationship.

    Ian, thanks for the PM, it was very helpful.

    Leo
     
  3. RalphLambrecht

    RalphLambrecht Subscriber

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    You are correct.

    See attached, but these are theoretical values. In practice, the contrast increase is not as high as exposure differences would indicate. I've never figured out why that is.
     

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  4. 36cm2

    36cm2 Member

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    Ralph, you are THE MAN! Greatly appreciated.

    Leo