DxOMark's measured ISOs vs. manufacturer ISOs

Started Mar 13, 2013 | Discussions thread
texinwien Veteran Member • Posts: 3,326
What we can compare? Image Quality

olliess wrote:

texinwien wrote:

olliess wrote:

...From the EXIF data it looks as if both shots were taken with the same 50 mm Olympus lens at f/6.3, but the OM-D shot was exposed at 1/800 while the G3 shot was exposed at 1/1300, which is about +2/3 stops more exposure for the OM-D. This would agree with the subjective differences in brightness (and suggest that you would need to dial in +2/3 stop on the G3 to make the shutter speeds match). But what good is this as a "comparison" of images at fixed ISO, e.g., 3200?

Although you would think that to be the case, DPReview has addressed this in great detail and with absolute certainty - the EXIFs on these shots cannot be used to determine relative exposure levels, due to DPReview's testing regime.

So what can we determine from this comparison, if anything?

The correct question is, I believe, what can we reliably compare between two such images taken with two separate cameras at the same ISO?"

The answer to that question is, "everything." We can compare noise, color depth and fidelity, contrast, ddetail. Everything you'd normally want to compare between two cameras at the same ISO.

Here a couple of excerpts from one of Andy Westlake's posts on how to use the comparison tool to compare noise (between the E-M5 and G3):

At the same shutter speed and aperture, the E-M5 appears to be giving an image 1/3 stop darker than the G3, according to our initial testing. That's what the ISO tests in our reviews are there for. You shouldn't rely on the EXIF data from studio samples (because we've recently changed the lighting), and you certainly shouldn't pay any attention to DxOMark's 'measured ISO', which measures something completely different and therefore won't necessarily give the same answer (although with some cameras it might).

...

[(1. load up the ISO6400 RAW conversions from both cameras. (2. Stop there - then mentally factor in the apparent 1/3 stop difference in ISO sensitivity. That really is all you need to do.

...

And there you have it. Again, there's a LOT of highly detailed discussion of this and related topics that you should familiarize yourself with before trying to wade in too deep. Many of these questions have been answered over and over and over again.

tex

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