DxOMark's measured ISOs vs. manufacturer ISOs

Started Mar 13, 2013 | Discussions thread
OP cptobvious Contributing Member • Posts: 811
Re: DxOMark's measured ISOs vs. manufacturer ISOs

GordonBGood wrote:

cptobvious wrote:

Yes, the ISO standard is silly, that's why comparisons based on a single testing methodology is needed.

Yes, the as the ISO standard only applies to output formats and isn't all that exact even at that, DxOMark had to come up with their own sensitivity "standard: for the purposes of comparing linear raw sensor outputs, and there is nothing wrong with their "standard" for its intended purpose.

However, your concern about the comparison between the raw sensitivity and the camera ISO isn't really a concern as DxOMark shows that the actual Olympus OM-D E-M5 sensor performs normally for the size of the sensor as to performance so that after making whatever post processing adjustments are necessary for the actual raw sensitivity, the image quality is in line with a rating based on sensor size, while the Fuji X100 does have a slight amount more noise in the bright tones than other APS-C sensors; the overall DxOMark sensor scores for these cameras are mostly down graded because the sensors do not use as low a real sensitivity as some other camera sensors do and that the digital data acquisition circuits put a cap on Dynamic Range (DR) at about the camera measured ISO 400 sensitivity for the Olympus.

In short, for real equivalent use, although the Olympus E-M5 does have about a stop less high ISO sensitivity usability due to its smaller sensor, it's real limit is more due a limited DR as compared to the best sensors for low ISO sensitivity use (but not everyone needs or uses this) and the Fuji X100 has this same limit with in a additional slightly less efficiency in photon gathering efficiency per unit area than the best sensors; other than the difference in maximum DR, there is only about a half a stop in difference in high ISO use between these cameras and the best sensors, which won't be a major factor in choice of cameras - other factors such as user interface and usability or lens selection will weigh much more.

Regards, GordonBGood

Your points are well taken. But my concern with the E-M5's ISO calculation methodology is that it has misled reviewers to claim that it has the same noise performance as larger sensors that obviously perform better but had their ISOs calculated more conservatively. Some examples:

http://www.imaging-resource.com/PRODS/omd-em5/omd-em5RAW.HTM (scroll down for D7000 comparison)

http://www.stevehuffphoto.com/2012/05/31/crazy-comparison-the-olympus-om-d-e-m5-vs-nikon-d800-for-high-iso/ (claiming the E-M5 holds its own in ISO performance against the D800)


http://dslr-check.at.webry.info/201204/article_10.html (Japanese site)

http://www.pcmag.com/article2/0,2817,2403444,00.asp (claims better noise performance than the NEX-7)

Even DPReview's studio shot comparison tool uses different aperture settings:


I have seen posted on reviews and on forums numerous times that the E-M5's sensor is as good or even better than the Sony Exmor APS-C equivalents at noise performance. The links I just pulled up are from just one search on Google in 10 minutes. To me this is just dishonest on the part of Olympus, and is inevitably going to lead to a 'race to the bottom' in future generation of cameras by manufacturers playing looser with their reported ISOs.

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