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Old 15th March 2019
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Re: ISO is Fake - Seriously

Originally Posted by Bassman51 View Post
ISO is indeed a standard for digital camera jpgs, just as it was for negative and positive film. And just as happened in film days, different manufacturers’ ISO assignments for their products is a matter of judgement that is and was open to dispute by users.

Back in the day, some serious photogs would buy a brick of film (a bunch of rolls from one manufacturing lot) and use the first roll to carefully test and determine what the “real” ISO they would use for the rest of the brick.

Today, many digital cameras give us the opportunity to tune our view of their ISO to our liking by setting a permanent offset in the menu.
You are correct that the ISO standard applies to digital cameras (and not just Jpeg images) just as it does to film. However, the difference is that digital cameras often deviate wildly from that standard whereas better quality film cameras and light meters had to be within half a stop or so; especially if transparency films were being used.

In my experience any deviation in film cameras was fairly linear, so setting the film speed a third of a stop faster than rated was all that was needed to ensure perfect exposure and saturation when using transparencies. Even using consumer films I didn't find much variation from the clamed speed. (Negatives have massive exposure latitude so a stop either way didn't matter too much.)

However, in my experience once again, the true ISO sensitivity of digital cameras tends to be fairly close to the ISO standard at lower speeds, but falls a long way short at higher speeds; therefore providing much cleaner images than would be possible if ISO sensitivity was somewhere near what is should have been. That fact that current digital cameras provide a much wider range of ISO sensitivities only exacerbates this effect.

In my view this is little different to motor manufacturers who make false claims about fuel consumption or CO2/NOX emissions. In every case the deviation benefits the manufacturer more than the consumer, and is used as a selling tool.

Naughty Nigel

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