Is the EM5’s Miss-Stated ISO concerning to you?

ISO calibration makes ABSOLUTELY NO difference for Astrophotography.   90% of the quality of the shot is the amount of light you are capturing (duration and aperture).  ISO plays a very minor role.

For serious astrophotography, you must use RAW images.   If you've done any amount of experimenting,  you'd have seen that a shot taken at ISO400 pushed 2 stops in PP and a shot taken at ISO 1600 with the mostly ISOless cameras like the GH3 or EM5 show virtually identical sky background noise levels for the same duration of exposure and aperture.  The only difference would be that the one at 1600 would have clipped more of the brightest star's cores so their profile is no longer gaussian, making them white blobs rather than the awesome color stars can exhibit.

Even for cameras aren't ISOless where read noise/signal is lower for the higher ISOs (like Canons), how they are calibrated makes no difference.    You select the ISO that allows the sky background to be well above the read noise floor for the conditions at hand and use it.   It doesn't matter one bit what that actual number is.

You already have the GH3 and DXO shows  regardless of how they chose to calibrate ISO, the EM5 performs virtucally identically with the GH3.     So why would you want the EM5?    IBIS does absolutely no good for minute+ shots.  The flip screen is more convenient with the GH3 for odd angles.   What is causing this keen interest?

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Rick Krejci
http://www.ricksastro.com