Film ISO rating temperature

Discussion in 'B&W: Film, Paper, Chemistry' started by edebill, Aug 26, 2007.

  1. edebill

    edebill Member

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    Can anyone explain what the temperature measurement frequently paired with an ISO rating means? For instance, I have a box of HP-5+ here that says it's "ISO 400/27 degrees". Some Fuji Pro 160S says ISO 160/23 degrees.

    Should I be altering my film speed for ambient temperature?

    Temperature is on my mind since getting a Jobo - I have to use ice baths to get the water bath (filled with cold tap water) down to 75F for b+w developing.
     
  2. Nick Zentena

    Nick Zentena Member

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    No. It's the older DIN system. Just ignore it. Unless you've got a meter that lets you set to European DIN instead of ASA. I think ISO is supposed to be a bit of a cross between ASA and DIN so they show both numbers.
     
  3. Markus B

    Markus B Member

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    It is the sensitivity of the film in the older DIN*-scale values.

    33 DIN = 1600 ASA = 1600/33 ISO
    30 DIN = 800 ASA = 800/30 ISO
    27 DIN = 400 ASA = 400/27 ISO
    24 DIN = 200 ASA = 200/24 ISO
    21 DIN = 100 ASA 100/21 ISO
    18 DIN = 50 ASA 50/18 ISO
    15 DIN = 25 ASA 25/15 ISO

    *Deutsche industrie norm = German industry standard
     
  4. edebill

    edebill Member

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    Thank you! I hadn't noticed that they were all the same for a given ISO.
     
  5. Roger Hicks

    Roger Hicks Member

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    It's not older: it's still current, though less popular. 3 degrees = doubling, because it's logarithmic.

    Most people find arithmetic (the first number) easier. Once you're used to DIN, there's nothing in it.