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ASA developer

The origins of the 1/3 stop meme may have come from the Forward of the standard. It's in the 1979 version and may be in the earlier versions. "(3) For any specific developer, the sensitometric speed rating method of this standard includes a 1/3 stop underexposure safety factor." This refers to where the average shadow exposure falls in relation to the fractional gradient point and is explained in the paper Safety Factors in Camera Exposure.
 
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.
 
Michael R 1974 said:
(...) 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 (...)
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Thanks for this observation. In order to avoid mistakes, could you give the full formula ?
 
Gerald C Koch said:
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.
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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/20106281054152313.pdf
 
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