Where does the OMD EM1II's "ISOless" range start?

Started 6 months ago | Discussions
Architeuthis Regular Member • Posts: 197
Where does the OMD EM1II's "ISOless" range start?

Stimulated by a very interesting discussion, that we had over the last few days (https://www.dpreview.com/forums/thread/4404316) about the low extended ISO range of the EM1II, I was interested to find out where the "ISOless" range starts in this camera, i.e. the ISO setting where a further increase in ISO brings reduced dynamic range, but now more benefit for S/N ratio (see http://www.clarkvision.com/articles/iso/, Figure 2 for the meaning of "ISOless" range).

Settings were: Noise filter off, noise reduction off, Auto WB, raw files.

First series (high ISO), I exposed to the right (ETTR; center spot) at extended ISO16000 and then made test shots at lower ISOs at identical aperture/shutter settings. I corrected exposre in LR ( shown here are images that were corrected in +1 eV increments) to produce similar brightness so that differences in S/N ratio can be compared:

extended ISO16000, no compensation

Extended ISO8000, +1 eV

ISO4000, +2 eV

ISO2000, +3 eV; a minimal increase in S/N in the shadows is observed...

ISO1000, +4 eV; clear increase of S/N in shadows

ISO500, +5 eV; S/N ratio worst, even WB is harmed...

Since my LR versions allows only for compensation of max. 5 eVs, I made another series for comparison of the lower ISO settings:

ISO3200, no compensation

ISO1600, + 1 eV

ISO800, + 2 eV; small increase in S/N ratio in shadows

ISO400, + 3 eV; S/N ratio rises clearly

Base ISO200; + 4 eV; worst S/N ratio in series

Extended ISO100; +5 eV; S/N ratio improves a little compared to ISO200 (is this real !??)

I conclude that, apart from sampling as much light as circumstances allow (exposure, aperture), increase of up to ISO400-800 helps to reduce S/N ratio after post-processing. In exceptoinal curcumstances, when the dynamic range of the motiv allows, ISO up to 2000 brings a little further improvements. Extended high ISO above ISO4000 is unimportant, when working with raws and postprocessing...


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