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Olympus E-PM2 Actual ISO vs IS0 set in camera?

Started Aug 17, 2014 | Discussions thread
OP Leo Veteran Member • Posts: 6,445
Re: Misinterpretation by DXO of the definition of ISO speed

BJL wrote:

What DXO insists on referring to as "ISO" is what the actual ISO standard 12232 describes as the lower limit of the exposure latitude of the camera at a given "ISO speed" setting: basically a measure of how much exposure you can give the camera at that setting without saturating the sensor and blowing the highlights: "SSAT" in the jargon of that ISO standard.

ISO standard 12232 actually recommends a different measure of sense speed or sensitivity, "SSNR40", which is basically about getting a SNR of at least 40:1 in the mid-tones; this measured shadow handling, and is much closer to what the ISO film speed refers to.

BJL,

Thank you for the clear and easy to understand comment!

Now I low were the number 40 came from

Leo

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