What I learned from Gollywop -- and what I wonder

Started Mar 26, 2013 | Discussions thread
Detail Man
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Re: GH2 Information
In reply to Anders W, Mar 27, 2013

Anders W wrote:

Detail Man wrote:

Anders W wrote:

Detail Man wrote:

Anders W wrote:

Detail Man wrote:

Anders W wrote:

You are largely (though not exactly) right about the GH2 whose only "real" ISOs are 160, 320, 640, and 800.

I don't think that it is clear that ISO=800 on the GH2 is unmanipulated. See bg2b's OP here:

Could be that you are right about that. Logically, it seems that the series of "real" ISOs should end at 640 rather than 800.  But if so there appear to be some unresolved mysteries here. I remember asking Ken W about this in a prior thread and he found the ISO 800 distribution to be perfectly continuous, without the gaps we would expect as a result of digital scaling. On the other hand, he didn't find that going from 640 to 800 had any tangible benefits in terms of reduced read noise. See here:

http://forums.dpreview.com/forums/post/40403509

Less than 0.1 EV (net) difference. Here are some RawDigger histograms of GH2 dark-shots that I recorded. The vertical Y-axis display scaling was adjusted to be in direct proportion to the (rated) ISO value for viewing. Though they appear a bit "rough" to the eye, it seems possible to get something of a feel from observing them about how much digital processing manipulation(s) may be going on. ISO=800 does perhaps appear as being the closest to the ISO=640, ISO=320, and ISO=160 series:

I don't think those (partial) distributions do much to resolve the issue of what goes on at ISO 800 relative to ISO 160, 320, and 640. When the expected number of hits in each bin is very low, as it is here towards the right edge of the distribution, you should expect gaps as a result of mere chance. You need to look at a distribution such that you'd normally expect plenty of hits in each bin. If, under such circumstances, you nevertheless find some bins empty, that's a sign of digital scaling.

I am sure that's what Ken did at ISO 800 and didn't find any empty bins where they would have been expected if digital scaling were involved.

Really ? Do you have a link to that information from Ken ? I recall asking him at one point whether he had done that, mentioning bg2b's statement about ISO=800 (quoted below), and my recollection is that Ken communicated to me that he had not done that. After that, he sold his GH2 and switched to a E-M5.

Yes. In the first paragraph of the link I already gave you above, he says he did that.

Discrepancy explained. I see that my recollection is from what kenw posted 15 days prior to the date of the post that you referenced, where he stated (regarding bg2b's observations):

... so far I've only done dark exposures so my conclusions are drawn from just the lowest ADC count values and read noise. He also uses relatively dark exposures but it is possible some of the artifacts he's seeing appear further up the histogram where I don't really have good data.

http://forums.dpreview.com/forums/post/40274527

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