OMD now on DPreview's studio scene comparison

Started Apr 25, 2012 | Discussions thread
Anders W
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Re: OMD now on DPreview's studio scene comparison
In reply to Timur Born, Apr 25, 2012

Timur Born wrote:

Anders W wrote:

...shutter speeds used by DPR for the two cameras. First, these speeds are clearly irrelevant if we talk simply about the signal levels in the two files, as Detail Man does in the passage quoted above. They are also irrelevant for the purpose of indirectly trying to determine how much light the two cameras were effectively given since, as reported by Andy Westlake, the lighting conditions for the studio samples are not strictly controlled and may vary from one camera to another.

As far as I can tell the difference in shutter speed corresponds more or less to the difference in gain/amplification (reported to be equivalent to ISO 120 at ISO 200 setting, shutter difference correspond to ca. ISO 130). So any difference on top of that is very likely different light levels in the studio setup (using the new dimmer).

DPR does not even try to take into account the "ISO" differences you refer to (which do not really have anything to do with the ISO standard as defined by ISO itself). Based on Andy Westlake's description of DPR procedures, two different cameras should be given the same effective exposure (same amount of light on the sensor) when shooting the studio scene if they both conform to the ISO standard (as defined by ISO). This is tested by DPR in a prior step, before shooting the studio samples. The ISO standard in question says nothing about the behavior of RAW files at all. It only refer to jpegs. Consequently, one producer, such as Olympus, can choose to saturate the sensor to a relatively small extent and apply a greater scaling factor when converting to OOC jpegs. Another producer, such as Panasonic, can choose to saturate the sensor to a greater extent and apply a smaller scaling factor when converting to OOC jpegs. If both deliver jpegs with the correct brightness when given a certain amount of light, all is well as far as the ISO standard is concerned.

Second, what I have said above should not be taken to mean that I am out to defend DPR or that I am personally convinced that the studio samples for the two cameras at issue are indeed fully comparable. Rather, what I have said should only be taken to mean that my factual basis for considering the comparability issue differs from that of Detail Man.

I'm cool with that. Both you and Detail Man pointed out a likely "disadvantage" of the E-M5 studio samples and since I am the one who keeps using those as a basis for comparison (or rather corrects the worse basis coming straight from the comparison tool) I thought that I should take DM's last quote from the other thread (hit 150) and put it in context.

My lack of experience with the number crunching doesn't allow me to judge who got the right number, but what's important to know is that even when exposure seems to be equal in DPR/my comparison the E-M5 may do better when its given the same light as the other cameras got. In practice the RickAstro comparison suggest not more than 1 stop difference to the GH2, but also not much less.

When it comes to DPR, the problem is that we are not really sure that the two cameras got the same amount of light on the sensor. Consequently, it is a bit hard to tell if the comparison between them is entirely fair. When it comes to RicksAstro's comparison, we can be sure. And I agree with you about the outcome in that case.

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