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Old 19th March 2019
Petrochemist Petrochemist is offline
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Re: ISO is Fake - Seriously

Originally Posted by Naughty Nigel View Post
Surely the ISO sensitivity of a film or digital camera is a logarithmic function, so it is simply calculated from a standard of (say) 100?
The DIN part of the scale which is the bit after the slash & frequently left off is actually the logarithmic part, while the ASA portion is Linear. The speed you referred to is officially ISO 100/21

Ignoring that (as everyone now ignore the DIN bit),If it's as simple as that why has ISO produced so many methods for doing it?

ISO 6:1993 for Black & white film
ISO 2240:2003 for colour slide film
ISO 5880:2001 for colour negative film
& ISO 12236:2019 for digital cameras
I've not heard of the revisions to the 2006 version of ISO12236, but that had FIVE different procedures, that didn't give the same results.

The Wikipedia page ( is quite interesting if you want more technical details. gives a preview of the new version of the standard. Possibly only FOUR procedures with the deletion of Annex E.

Less relevant perhaps we also have:
ISO 2720 for exposure meters
ISO 2721 for camera auto metering
ISO 5763 for flash
ISO 7187 for direct positive colour film
ISO 10157 for flash meters
Compulsive photographic Dabbler.

Last edited by Petrochemist; 19th March 2019 at 11:57 AM.
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