Hi Afre,
Random but unlikely guess: Could it have something to do with how the light is penetrating the sensor? Like X-Trans rectangles and related topics?
I’m not sure I understand the X-Trans explanation, so I don’t know if that could relate to this thread. I do think I’ve been chasing a ghost or my tail, just because I didn’t take the admonitions given by others in other forums to run the camera at ISO 100.
I mean, the thing takes such darned good pictures at ISO 100. So, for my “dark room” tests, I thought I’d push it up (but only a little, to ISO-200). I didn’t really believe the admonitions about ISO, I guess. But, I believe them now. The Foveon loves the low end of the ISO scale. When it’s down there, it does great in this camera. Lesson learned. The fact that it has ISO-50 I suppose is a hint.
As mentioned a couple messages prior to this one - the spots/artifacts are gone when I use ISO-100, with near-darkness or with the lights turned on - either one.