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Thread: ASA developer

  1. #31

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    The sensitometry chapter in Haist includes a good summary of ANSI formulas and procedures for determining the speeds of various photographic materials. Interestingly, the developer composition specified in PH2.5-1972 is identical to the one in PH2.5-1979 except for a weaker carbonate alkali system: 1.5g Sodium carbonate (anhydrous) and 1.0g Sodium bicarbonate, with a specified pH of 9.4 +/- 0.2. I wonder why the change was made in 1979 and how the composition was determined.

  2. #32

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    It should be noted that the ISO standard which is used currently does not specify a special developer. It is left to the manufacturer to select one.
    A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.

    ~Antoine de Saint-Exupery

  3. #33

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    Quote Originally Posted by Michael R 1974 View Post
    (...) the developer composition specified in PH2.5-1972 is identical to the one in PH2.5-1979 except for a weaker carbonate alkali system: 1.5g Sodium carbonate (anhydrous) and 1.0g Sodium bicarbonate, with a specified pH of 9.4 +/- 0.2 (...)
    Thanks for this observation. In order to avoid mistakes, could you give the full formula ?

  4. #34

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    Harold, see post #20. The rest of the ANSI PH2.5-1972 formula is identical to the formula Stephen posted from ANSI PH2.5-1979. The only differences are in the concentrations of Carbonate/bicarbonate. Also see the second part of post #20 for the 1943 formula used in the fractional gradient method.

  5. #35

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    Quote Originally Posted by Gerald C Koch View Post
    It should be noted that the ISO standard which is used currently does not specify a special developer. It is left to the manufacturer to select one.
    Indeed Ilford for example are explicit in this:- EXPOSURE RATING HP5 Plus has a speed rating of ISO 400/27 (400ASA, 27DIN, EI 400/27) to daylight. The ISO speed rating was measured using ILFORD ID-11 developer at 20oC/68oF with intermittent agitation in a spiral tank."

    http://www.ilfordphoto.com/Webfiles/...1054152313.pdf
    http://www.flickr.com/photos/red_eyes_man/

    Photographer not a job description - a diagnosis.

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