Yesterday I posted about the Nikon Z6 and Z7 fake ISOs. This is a post for those who are skeptical that the camera really works that way.
Here’s how to demonstrate that the ISO’s below base ISO are fake for raw files.
Put your camera on a tripod.
Point it at something that isn’t going to move much.
Set the camera to manual.
Pick an exposure that’s not going to clip highlights.
Make four shots at that exposure, at base ISO and the next three ISOs down from that.
Look at the statistics in the raw file inspector of your choice. I used RawDigger for the screen shots below. Ignore the max and min, since they are not repeatable from shot to shot. Just look at the averages and the standard deviations.
They are virtually the same.
QED.
That test showed that the camera doesn’t change sensitivity when the ISO setting is dropped below base ISO. This next one will show that the camera meters as if the camera became less sensitive.
Put your camera on a tripod.
Point it at something that isn’t going to move much.
Set the camera to aperture priority.
Pick an exposure compensation that’s at least one stop under one that will just barely not clip highlights.
Make four shots at that setting, at base ISO and the next three ISOs down from that.
Look at the statistics in the raw file inspector of your choice as before.
Note how the average counts increase with each step down in ISO setting, and that the ISO 50 counts are about double those at ISO 100. The meter operates as if the camera sensitivity does change. Since it doesn’t really change, the ISO portion of exposure reciprocity fails.
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