Thanks Michael, got it. Neat undocumented feature. Though in the best case there would have been a setting for the step size. I believe there is a half-step option for time and aperture, but not for ISO.
So now I need a button set free for ISO. Currently I have the down-button-on-wheel, but that is too far away from the thumb if you want to use the rear dial (not rear wheel) when in VF mode. C1 is magnifying and very handy for me so I cant replace that.
A prospect is the AEL button. I've changed so AEL is also achieved with half press shutter button. This makes no sense for AF users, but I am manual only person so it is perfect (I hope).
However, when you press the AEL button there's the industry standard asterisk (*) shown in VF and that is al well. But oddly, when half pressing the shutter the asterisk is NOT shown. But AEL is locked. Can anyone find a reason for that?
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As a Canon (5D2) user and used to super swift change of ISO this seem to be a drag on the Sony. Love the customization possibilities (which is far beyond Canon) but this one seem unnecessarily quirky.