Doug Kerr
Well-known member
A number of years ago, during one of my recurring "waves" of interest in the matter of photographic exposure metering (an incredibly rich area), I came upon a curiosity in the ISO standard for (free-standing) photographic exposure meters, ISO 2720-1974.
It turned out that the authors of the standard had committed a serious mathematical "gaffe", which then precipitated the invention of a bizarre (and wholly fruitless, and meaningless) arrangement with regard to the matter of the exposure metering constants, K and C.
In any case, I shortly wrote an elaborate technical article discussing this matter. But somehow I never "published" it on The Pumpkin.
I bumped into it recently while dealing with a related topic, and recognized its "stalled" state. I decided that I should in fact publish it.
It was way too elaborate in some of the background areas, so I pruned it a bit, refined some of the mathematical presentations, and added a photograph to illustrate one of the practical aspects of the matter (regarding the design of exposure meter calculators).
The article, entitled "A Gaffe in the ISO Standard for Photographic Exposure Meters ", is indexed here:
http://dougkerr.net/Pumpkin/index.htm#ISO_gaffe
Best regards,
Doug
It turned out that the authors of the standard had committed a serious mathematical "gaffe", which then precipitated the invention of a bizarre (and wholly fruitless, and meaningless) arrangement with regard to the matter of the exposure metering constants, K and C.
It was as if an author, showing how to determine the area of a circular pond in acres, gave equations with the diameter in both feet and meters, but had misunderstood the relationship between feet and meters.
Finding that the results for the two cases did not agree, he fixed it by prescribing the use of a different value of pi for the two cases.
I published the story of this either here or on dpr (I can't remember now which). This elicited a response from a member to the effect that how dare I think that these learned fellows had made a serious error in this auspicious document, and presented a harebrained theory of why the scheme in the document actually was perfectly sensible. (So this probably did happen on dpr!)Finding that the results for the two cases did not agree, he fixed it by prescribing the use of a different value of pi for the two cases.
In any case, I shortly wrote an elaborate technical article discussing this matter. But somehow I never "published" it on The Pumpkin.
I bumped into it recently while dealing with a related topic, and recognized its "stalled" state. I decided that I should in fact publish it.
It was way too elaborate in some of the background areas, so I pruned it a bit, refined some of the mathematical presentations, and added a photograph to illustrate one of the practical aspects of the matter (regarding the design of exposure meter calculators).
The article, entitled "A Gaffe in the ISO Standard for Photographic Exposure Meters ", is indexed here:
http://dougkerr.net/Pumpkin/index.htm#ISO_gaffe
Best regards,
Doug