DxOMark's measured ISOs vs. manufacturer ISOs

Started Mar 13, 2013 | Discussions thread
John Sheehy Forum Pro • Posts: 21,617
Re: DxOMark's measured ISOs vs. manufacturer ISOs

cptobvious wrote:

It's been stated numerous times in this forum that certain manufacturers overstate their ISOs in order to make their cameras seem to have better noise performance than they actually do. Out of curiosity, I took a sample (non-scientific) of 22 tested cameras from 8 manufacturers on DxOMark, divided their measured ISO by the manufacturer ISO, and took the average of the results across the tested ISO range.

The number reflects what percentage the measured ISO is to the manufacturer ISO. In the one case (GH-1) where the percentage exceeds 100%, the measured ISO was higher than the manufacturer ISO. In all other cases it was lower. The two worst offenders were the Olympus OM-D E-M5 and the Fuji X100.

DxO's ISO ratings have nothing whatsoever to do with the issues of manufacturers mis-stating ISOs.  DxO is concerned with rating the ISOs to meet a standard amount of RAW headroom; the issue with manufacturers has to do with metering, as cameras will vary in the real exposure the metering gives when set to an ISO.  The two are completely independent of each other, other than the fact that there is a practical limit to how little headroom you could have above metered middle gray.

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