OMD now on DPreview's studio scene comparison

Started Apr 25, 2012 | Discussions thread
Timur Born
Senior MemberPosts: 3,843
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Re: OMD now on DPreview's studio scene comparison
In reply to Anders W, Apr 27, 2012

Anders W wrote:

Timur Born wrote:

I just gave this another thought. DPR exposed the E-M5 2/3 longer vs. the GH2 while light level of the studio seemed to be about 0.8x EV lower for the E-M5.

Not sure how you arrive at the difference in studio light level. I have my own about how that might perhaps be deduced but let me hear what you say first so I don't need to take the trouble explaining things you have already realized.

Based on RickAstros' ISO 200 raw files of the GH2 vs. E-M5 I derived a difference of about 0.6 EV for their full scale histogram (also fits visually). This means that the E-M5 needs to be pushed by roughly +0.6 EV in order for the histograms to be matched. We know that according to DxO the GH2 uses a gain factor corresponding to its reports JPG ISO (209 vs. 200). My interpretation is that the difference of roughly 0.6 EV corresponds to the difference in analog gain between the cameras (aka E-M5 uses a gain corresponding to about ISO 130).

DPR exposed the E-M5 2/3 stops longer than the GH2, so at same aperture the E-M5 should have received more light/photons than the GH2, that is unless the studio light levels were lower on the E-M5. Since the 2/3 stops longer exposure compensates close to +-0 EV for the difference in analog gain any remaining difference between their exposures should be the difference in studio light levels.

And indeed, one has to push the E-M5 raw file by your calculated 0.85 EV in order to match their histograms (also visually). So the final calculation goes:

+0.66 EV (time) - 0.6 EV (gain) + 0.85 EV (manual compensation) = about 0.8 EV difference in studio light levels

Now the important part:

Does this not mean that the E-M5 did not get that much of a disadvantage as far as light exposure is concerned, but rather mostly suffered from the analog gain difference which had to be compensated digitally?

In what sense do you think the E-M5 "suffered" from the analog gain difference? If two cameras are shot so as to be given the same amount of light at the same ISO setting, in what way would the comparison be unfair or the one camera "suffer"?

I didn't mean that it would "suffer", but replied to DM's suggestion that the E-M5 had a disadvantage versus the GH2 in DPR's studio shots, because the E-M5 received less light. My argument is that the E-M5 did not suffer a 0.85 EV light disadvantage, because it received 0.66 EV longer exposure time. So the remaining difference would result in only about a 0.2 EV light disadvantage for the E-M5.

The note about possible a possible analog vs. digital gain disadvantage points to the analog gain difference that needs to be compensated digitally. How much of a visual difference that 0.6 EV analog vs. digital gain make, is another question.

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