What I learned from Gollywop -- and what I wonder

Started Mar 26, 2013 | Discussions thread
Anders W
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Re: What I learned from Gollywop -- and what I wonder
In reply to bowportes, Mar 27, 2013

bowportes wrote:

Michael Meissner wrote:

richarddd wrote:

Another good source of information is this thread http://forums.dpreview.com/forums/post/42595072

See the links in the first post. You may have to click on the camera name in the right pane. The linked chart clearly shows the noise issue on the E-M5 between ISO 200 and 400.

Various posts over the years have said that the Panasonic sensor used by the earlier Pens tends to have less noise when you use the full stop ISO's (200, 400, 800, 1600, 3200) rather than the intermediate versions. There is an option to only use whole stops in auto ISO. It sounds like the same is probably true of the Sony sensor used in the E-M5, E-PL5, and E-PM2.

I may remember poorly, but I think I read once (somewhere in the forum) that 160, 320, 640, 1280, etc. Were the appropriate full stops on the GH2. And I had inferred from that that those were the ones to focus upon on the G5. If this is wrong, I'd like clear word on that

You are largely (though not exactly) right about the GH2 whose only "real" ISOs are 160, 320, 640, and 800. The intermediate ISOs between these are accomplished by means of digitally scaling the RAW values upwards rather than by analog amplification. The same is true about any ISO above 800. It follows that using any ISOs other than those I listed will not bring you any benefits above using the next lower ISO among those listed. They will be the same for read noise but worse for the risk of highlight clipping.

Whether the G5 behaves the same way, I don't know. And I am not sure anyone else here does either at this point. You can find out for yourself by using RawDigger and inspect the histogram for different ISOs. If digital scaling is employed, there will be gaps in the histogram (i.e., certain specific ADU values will not occur). See here for example:

http://forums.dpreview.com/forums/post/37798663

Another interesting case here is the GH3, which uses analog amplification all the way up to ISO 6400 but neither analog amplification nor digital scaling from that point on. The RAW values recorded will be the same at 6400 as at 25600. The only thing that happens on the camera when you crank up ISO from 6400 is that the metering changes, that the scaling factor used in the OOC jpeg conversion changes, and that the instruction to the RAW converter embedded in the RAWs changes to tell it to change the scaling factor in the same way as the in-camera jpeg engine.

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