Characteristic Curve

Discussion in 'Talk About Developing Film' started by Ian-Barber, Jun 28, 2017.

  1. Ian-Barber

    Ian-Barber Administrator Staff Member

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    For those with experience reading characteristic curves, can someone tell me what this curve tells them


    Screen Shot 2017-06-28 at 22.18.19.jpg
     
  2. Bill Martindale

    Bill Martindale Member

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    It tells me you need to get out more Ian. :)

    My interpretation is that for various developing times (bottom set of figures) the film can be rated as shown on the S curve, the contrast slope is on the G bar curve and the D min is on the bottom curve which I think may be the Film Base plus Fog figure. In the absence of dilution information I assume this is for stock developer.
    So if you develop for 8 minutes you can rate the film at 125 ISO, the contrast slope will be about 0.77 and the D min just above 0.1. That is their prediction, your actual numbers may vary due to equipment differences and your developing technique.
    Working the other way if you know what G bar you want you can read off the development time to use, the speed to set and the expected D min. As you scan your negatives I am not sure what G bar you need to get a good scan but for darkroom it would be about 0.57.
    No doubt other will have their own interpretations.
     
  3. Ian-Barber

    Ian-Barber Administrator Staff Member

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    Excellent Bill, many thanks for that. I had most og it right just needed confirmation on the G bar. As for the G Bar and scanning, this is something I am trying to figure out
     
  4. mpirie

    mpirie New Member

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    I agree with Bill........especially the first comment ;)

    You would also need to know which light source you have in the enlarger since you would want a higher contrast negative for a diffusion light source as opposed to a lower contrast for a condenser light source.

    It's a shame they cram 3 graphs onto one table as (to me) it makes it much more confusing.

    For scanning, i'd assume you would want the lowest contrast possible since you can add it digitally.....but that's where the two processes diverge.....too low a contrast is very hard to compensate for in the enlarger.
     

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