Quote Originally Posted by Kayaker72 View Post
First off, understanding all this does help. Right now, I think the
astrophotographers
have it figured out, likely because it helps that type of photography the most. At least three astrophotography blogs I found focused on where a camera becomes ISO invariant. They have focused on the ISO where upstream noise (generated by increasing ISO) is greater than downstream noise. Looking at charts, I would agree with you/dpreview concluded, for the 5DIV, it is about ISO400.

But, dpreview bases all their "ISO invariance" tests on ISO 100, ignoring the fact that different cameras become invariant at different ISOs. Maybe they get it and are only concerned about base ISO. Then, some of the tests TN/Fstoppers did could be explained by a dual gain sensor (TN figured it out in the second video).

Sounds familiar to the old DR discussions. Sony is obviously better.

Most of the discussion is centered around camera bodies. Really that may only be half of the equation in the discussion. Don't you think it would be just as important to understand what is happening with your PP software? Or are we assuming all PP programs are equal and as such invariant? Do all the PP programs simulate the gain boost just like the camera?